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This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html.
This Internet-Draft will expire on March 4, 2005.
Copyright (C) The Internet Society (2004).
The Network News Transfer Protocol (NNTP) has been in use in the Internet for a decade and remains one of the most popular protocols (by volume) in use today. This document is a replacement for RFC 977 and officially updates the protocol specification. It clarifies some vagueness in RFC 977, includes some new base functionality, and provides a specific mechanism to add standardized extensions to NNTP.
This document is a product of the NNTP Working Group, chaired by Russ Allbery and Ned Freed.
This document is written in XML using an NNTP-specific DTD. Custom software is used to convert this to RFC 2629Rose, M., Writing I-Ds and RFCs using XML, June 1999.[RFC2629] format, and then the public "xml2rfc" package to further reduce this to text, nroff source, and HTML.
No perl was used in producing this document.
UNIX is a registered trademark of The Open Group.
1.
Introduction
2.
Notation
3.
Basic Concepts
3.1
Commands and Responses
3.2
Response Codes
3.2.1
Generic Response Codes
3.2.1.1
Examples
3.3
Pipelining
3.3.1
Examples
3.4
Articles
4.
The WILDMAT format
4.1
Wildmat syntax
4.2
Wildmat semantics
4.3
Extensions
4.4
Examples
5.
Session administration commands
5.1
Initial Connection
5.2
MODE READER
5.3
LIST EXTENSIONS
5.4
QUIT
6.
Article posting and retrieval
6.1
Group and article selection
6.1.1
GROUP
6.1.2
LAST
6.1.3
NEXT
6.2
Retrieval of articles and article sections
6.2.1
ARTICLE
6.2.2
HEAD
6.2.3
BODY
6.2.4
STAT
6.3
Article posting
6.3.1
POST
6.3.2
IHAVE
7.
Information commands
7.1
DATE
7.2
HELP
7.3
NEWGROUPS
7.4
NEWNEWS
7.5
Time
7.5.1
Examples
7.6
The LIST commands
7.6.1
LIST ACTIVE
7.6.2
LIST ACTIVE.TIMES
7.6.3
LIST DISTRIBUTIONS
7.6.4
LIST DISTRIB.PATS
7.6.5
LIST NEWSGROUPS
8.
Framework for NNTP extensions
8.1
Initial IANA registry
8.2
Standard extensions
8.3
The LISTGROUP extension
8.3.1
LISTGROUP
8.4
Article metadata
8.4.1
The :bytes metadata item
8.4.2
The :lines metadata item
8.5
The OVER extension
8.5.1
OVER
8.5.2
LIST OVERVIEW.FMT
8.6
The HDR extension
8.6.1
HDR
8.6.2
LIST HEADERS
9.
Augmented BNF Syntax for NNTP
9.1
Commands
9.2
Command continuation
9.3
Responses
9.3.1
Generic responses
9.3.2
Initial response line contents
9.3.3
Multi-line response contents
9.4
LIST EXTENSIONS responses
9.5
Articles
9.6
General non-terminals
10.
IANA Considerations
11.
Security Considerations
11.1
Personal and Proprietary Information
11.2
Abuse of Server Log Information
11.3
Weak Authentication and Access Control
11.4
DNS Spoofing
11.5
UTF-8 issues
11.6
Caching of LIST EXTENSIONS results
12.
Acknowledgements
13.
References
13.1
Normative References
13.2
Informative References
§
Author's Address
A.
Future Directions
B.
Interaction with other specifications
B.1
Header folding
B.2
Message-IDs
B.3
Article posting
C.
Summary of Response Codes
D.
Formal specification of the standard extensions
D.1
The LISTGROUP extension
D.2
The OVER extension
D.3
The HDR extension
§
Intellectual Property and Copyright Statements
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This document specifies the Network News Transfer Protocol (NNTP), which is used for the distribution, inquiry, retrieval, and posting of Netnews articles using a reliable stream-based mechanism. For news reading clients, NNTP enables retrieval of news articles that are stored in a central database, giving subscribers the ability to select only those articles they wish to read.
The Netnews model provides for indexing, cross-referencing, and expiration of aged messages. For server-to-server interaction, NNTP is designed for efficient transmission of Netnews articles over a reliable full duplex communication channel.
Every attempt is made to ensure that the protocol specification in this document is compatible with the version specified in RFC 977Kantor, B. and P. Lapsley, Network News Transfer Protocol, February 1986.[RFC977]. However, this version does not support the ill-defined SLAVE command and permits four digit years to be specified in the NEWNEWS and NEWGROUPS commands. It changes the default character set to UTF-8Yergeau, F., UTF-8, a transformation format of ISO 10646, November 2003.[RFC3629] instead of US-ASCIIAmerican National Standards Institute, Coded Character Set - 7-bit American Standard Code for Information Interchange, 1986.[ANSI1986] (note that US-ASCII is a subset of UTF-8). It now requires all articles to have a message-id, eliminating the "<0>" placeholder used in RFC 977 in some responses. It also extends the newsgroup name matching capabilities already documented in RFC 977.
Generally, new functionality is made available using new commands. A number of such commands (including some commands taken from RFC 2980Barber, S., Common NNTP Extensions, October 2000.[RFC2980]) are now mandatory. Part of the new functionality involves a mechanism to discover what new functionality is available to clients from a server. This mechanism can also be used to add more functionality as needs merit such additions.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119Bradner, S., Key words for use in RFCs to Indicate Requirement Levels, March 1997.[RFC2119].
An implementation is not compliant if it fails to satisfy one or more of the MUST requirements for this protocol. An implementation that satisfies all the MUST and all the SHOULD requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the MUST requirements but not all the SHOULD requirements for NNTP is said to be "conditionally compliant".
For the remainder of this document, the term "client" or "client host" refers to a host making use of the NNTP service, while the term "server" or "server host" refers to a host that offers the NNTP service.
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The following notational conventions are used in this document.
UPPERCASE indicates literal text to be included in the
command;
lowercase indicates a token described elsewhere;
[brackets] indicate that the argument is optional;
ellipsis... indicates that the argument may be repeated any
number of times (it must occur at least once);
vertical|bar indicates a choice of two mutually exclusive
arguments (exactly one must be provided).
The name "message-id" for a command or response argument indicates that it is the message-id of an article as described in Section 3.4Articles, including the angle brackets.
The name "wildmat" for an argument indicates that it is a wildmat as defined in Section 4The WILDMAT format. If the argument does not meet the requirements of that section (for example, if it does not fit the grammar of Section 4.1Wildmat syntax) the NNTP server MAY place some interpretation on it (not specified by this document) or otherwise MUST treat it as a syntax error.
Responses for each command will be described in tables listing the required format of a response followed by the meaning that should be ascribed to that response.
The terms "NUL", "TAB", "LF", "CR, and "space" refer to the octets %x00, %x09, %x0A, %x0D, and %x20 respectively (that is, the octets with those codes in US-ASCIIAmerican National Standards Institute, Coded Character Set - 7-bit American Standard Code for Information Interchange, 1986.[ANSI1986] and thus UTF-8Yergeau, F., UTF-8, a transformation format of ISO 10646, November 2003.[RFC3629]). The term "CRLF" or "CRLF pair" means the sequence CR immediately followed by LF (that is, %x0D.0A). A "printable US-ASCII character" is an octet in the range %x21-7E. Quoted characters refer to the octets with those codes in US-ASCII (so "." and "<" refer to %x2E and %x3C) and will always be printable US-ASCII characters; similarly, "digit" refers to the octets %x30-39.
Examples in this document are not normative but serve to illustrate usages, arguments, and responses. In the examples, a "[C]" will be used to represent the client host and a "[S]" will be used to represent the server host. Most of the examples do not rely on a particular server state. In some cases, however, they do assume that the current selected newsgroup (see the GROUP commandGROUP) is invalid; when so, this is indicated at the start of the example. Examples may use commands (or other names) not defined in this specification (such as an XENCRYPT command). These will be used to illustrate some point and do not imply that any such command is defined elsewhere or needs to exist in any particular implementation.
Terms which might be read as specifying details of a client or server implementation, such as "database", are used simply to ease description. Providing that implementations conform to the protocol and format specifications in this document, no specific technique is mandated.
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NNTP operates over any reliable data stream 8-bit-wide channel. Initially, the server host starts the NNTP service by listening on a TCP port; when running over TCP/IP, the official port for the NNTP service is 119. When a client host wishes to make use of the service, it MUST establish a TCP connection with the server host by connecting to that host on the same port on which the server is listening. When the connection is established, the NNTP server host MUST send a greeting. The client host and server host then exchange commands and responses (respectively) until the connection is closed or aborted.
The character set for all NNTP commands is UTF-8Yergeau, F., UTF-8, a transformation format of ISO 10646, November 2003.[RFC3629]. Commands in NNTP MUST consist of a keyword, which MAY be followed by one or more arguments. A CRLF pair MUST terminate all commands. Multiple commands MUST NOT be on the same line. Keywords MUST consist of printable US-ASCII characters. Unless otherwise noted elsewhere in this document, arguments SHOULD consist of printable US-ASCII characters. Keywords and arguments MUST be each separated by one or more space or TAB characters. Keywords MUST be at least three characters and MUST NOT exceed 12 characters. Command lines MUST NOT exceed 512 octets, which includes the terminating CRLF pair. The arguments MUST NOT exceed 497 octets. A server MAY relax these limits for commands defined in an extension.
Where this specification permits UTF-8 characters outside the range U+0000 to U+007F, implementations MUST NOT use the Byte Order Mark (U+FEFF, encoding %xEF.BB.BF), and MUST use the Word Joiner (U+2060, encoding %xE2.91.A0) for the meaning Zero Width No-Break Space, in command lines and the initial lines of responses, and SHOULD apply these same principles throughout.
The term "character" means a single Unicode code point and implementations are not required to carry out normalisation. Thus U+0084 (A-dieresis) is one character while U+0041 U+0308 (A composed with dieresis) is two; the two need not be treated as equivalent.
Commands may have variants, using a second keyword immediately after the first to indicate which variant is required. The only such commands in this specification are LIST and MODE. Note that such variants are sometimes referred to as if they were commands in their own right: "the LIST ACTIVE" command should be read as shorthand for "the ACTIVE variant of the LIST command".
Keywords are case-insensitive; the case of keywords for commands MUST be ignored by the server. Command and response arguments are case- or language-specific only when stated, either in this document or in other relevant specifications.
An NNTP server MUST implement all the commands in this specification except for those marked as optional and those in extensions.
Each response MUST start with a three-digit response code that is sufficient to distinguish all responses. Certain valid responses are defined to be multi-line; for all others, the response is contained in a single line. The first or only line of the response MUST NOT exceed 512 octets, which includes the response code and the terminating CRLF pair; an extension MAY specify a greater maximum for commands that it defines, but not for any other command.
All multi-line responses MUST adhere to the following format:
Note that texts using an encoding (such as UTF-16 or UTF-32) that may contain the octets NUL, LF, or CR other than a CRLF pair cannot be reliably conveyed in the above format (that is, they violate the MUST requirement above). However, except when stated otherwise, this specification does not require the content to be UTF-8 and therefore it MAY include octets above and below 128 mixed arbitrarily.
This document does not place any limit on the length of a subsequent line in a multi-line response. However, the standards that define the format of articles may do so.
An NNTP server MAY have an inactivity autologout timer. Such a timer SHOULD be of at least three minutes duration, with the exception that there MAY be a shorter limit on how long the server is willing to wait for the first command from the client. The receipt of any command from the client during the timer interval SHOULD suffice to reset the autologout timer. Similarly, the receipt of any significant amount of data from the client while in the midst of sending a multi-line message to the server (such as during a POST or IHAVE command) SHOULD suffice to reset the autologout timer. When the timer expires, the server SHOULD close the TCP connection without sending any response to the client.
Each response MUST begin with a three-digit status indicator. These are status reports from the server and indicate the response to the last command received from the client.
The first digit of the response broadly indicates the success, failure, or progress of the previous command:
1xx - Informative message.
2xx - Command completed OK.
3xx - Command OK so far; send the rest of it.
4xx - Command was syntactically correct but failed for some reason.
5xx - Command unknown, unsupported, unavailable, or syntax error.
The next digit in the code indicates the function response category:
x0x - Connection, set-up, and miscellaneous messages
x1x - Newsgroup selection
x2x - Article selection
x3x - Distribution functions
x4x - Posting
x8x - Reserved for authentication and privacy extensions
x9x - Reserved for private use (non-standard extensions)
Certain responses contain arguments such as numbers and names in addition to the status indicator. In those cases, to simplify interpretation by the client the number and type of such arguments is fixed for each response code, as is whether or not the code introduces a multi-line response. Any extension MUST follow this principle as well, but note that, for historical reasons, the 211 response code is an exception to this in that the response may be multi-line or not depending on the command (GROUPGROUP or LISTGROUPLISTGROUP) that generated it. In all other cases, the client MUST only use the status indicator itself to determine the nature of the response. The exact response codes that can be returned by any given command are detailed in the description of that command.
Arguments MUST be separated from the numeric status indicator and from each other by a single space. All numeric arguments MUST be in base 10 (decimal) format, and MAY have leading zeros. String arguments MUST contain at least one character and MUST NOT contain TAB, LF, CR, or space. The server MAY add any text after the response code or last argument as appropriate, and the client MUST NOT make decisions based on this text. Such text MUST be separated from the numeric status indicator or the last argument by at least one space.
The server MUST respond to any command with the appropriate generic response (given in Section 3.2.1Generic Response Codes) if it represents the situation. Otherwise, each recognized command MUST return one of the response codes specifically listed in its description or in an extension. A server MAY provide extensions to this specification, including new commands, new variants or features of existing commands, and other ways of changing the internal state of the server. However, the server MUST NOT produce any other responses to a client that does not invoke any of the additional features. (Therefore a client that restricts itself to this specification will only receive the responses that are listed.)
If a client receives an unexpected response, it SHOULD use the first digit of the response to determine the result. For example, an unexpected 2xx should be taken as success and an unexpected 4xx or 5xx as failure.
Response codes not specified in this document MAY be used for any installation-specific additional commands also not specified. These SHOULD be chosen to fit the pattern of x9x specified above.
Neither this document nor any registered extension (see Section 8Framework for NNTP extensions) will specify any response codes of the x9x pattern. (Implementers of extensions are accordingly cautioned not to use such responses for extensions that may subsequently be submitted for registration.)
The server MUST respond to any command with the appropriate one of the following generic responses if it represents the situation.
If the command is not recognized, or it is an optional command or extension that is not implemented by the server, the response code 500 MUST be returned.
If there is a syntax error in the arguments of a recognized command, including the case where more arguments are provided than the command specifies or the command line is longer than the server accepts, the response code 501 MUST be returned. The line MUST NOT be truncated or split and then interpreted. Note that where a command has variants depending on a second keyword (e.g. LIST ACTIVE and LIST NEWSGROUPS), then 501 MUST be used when the base command is implemented but the requested variant is not, and 500 MUST be used only when the base command itself is not implemented.
As a special case, if an argument is required to be a base64-encoded string [RFC3548]Josefsson, S., The Base16, Base32, and Base64 Data Encodings, July 2003. (there are no such arguments in this specification, but there may be in extensions) and is not validly encoded, the response code 504 MUST be returned.
If the server experiences an internal fault or problem that means it is unable to carry out the command (for example, a necessary file is missing or a necessary service could not be contacted), the response code 403 MUST be returned. If the server recognizes the command but does not provide an optional feature (for example because it does not store the required information), or only handles a subset of legitimate cases (see the HDR commandHDR for an example), the response code 503 MUST be returned. Note that where a command is optional (e.g. LIST ACTIVE.TIMES) and is not provided by a server, this MAY be treated as an unimplemented command (response code 500 or 501 as appropriate) or as a working command where the information is not available (response code 503).
If the client is not authorized to use the specified facility when the server is in its current state, then the appropriate one of the following response codes MUST be used.
- 502:
- it is necessary to terminate the connection and start a new one with the appropriate authority before the command can be used. Note that the server MUST NOT close the TCP connection immediately after a 502 response except at the initial connectionInitial Connection and with the MODE READERMODE READER command. See also the latter command for historical usage of this response.
- 480:
- the client must authenticate itself to the server (that is, provide information as to the identity of the client) before the facility can be used on this connection. This will involve the use of an authentication extension such as [NNTP-AUTH]Vinocur, J., Newman, C. and K. Murchinson, NNTP Authentication, July 2004..
- 483:
- the client must negotiate appropriate privacy protection on the connection. This will involve the use of a privacy extension such as [NNTP-TLS]Vinocur, J. and C. Newman, Using TLS with NNTP, October 2003..
- 401:
- the client must change the state of the connection in some other manner. The first argument of the response MUST be the extension-label (see Section 8Framework for NNTP extensions) of the extension (which may be a private extension) that provides the necessary mechanism, or "MODE-READER" if it is necessary to use the MODE READERMODE READER command.
If the server has to terminate the connection for some reason, it MUST give a 400 response code to the next command and then immediately close the TCP connection.
The client MUST be prepared to receive any of these responses for any command (except, of course, that the server MUST NOT generate a 500 response code for mandatory commands).
Example of an unknown command:
[C] MAIL
[S] 500 Unknown command
Example of an unsupported extension:
[C] LIST EXTENSIONS
[S] 202 Extensions supported:
[S] LISTGROUP
[S] .
[C] OVER
[S] 500 Unknown command
Example of an unsupported variant:
[C] MODE POSTER
[S] 501 Unknown MODE option
Example of a syntax error:
[C] ARTICLE a.message.id@no.angle.brackets
[S] 501 Syntax error
Example of an overlong command line:
[C] HEAD 53 54 55
[S] 501 Too many arguments
Example of a bad wildmat:
[C] LIST ACTIVE u[ks].*
[S] 501 Syntax error
Example of a base64-encoding error (the second argument is meant to be base64-encoded):
[C] XENCRYPT RSA abcd=efg
[S] 504 Base64 encoding error
Example of an attempt to access a facility not available to this connection:
[C] MODE READER
[S] 200 Reader mode, posting permitted
[C] IHAVE <i.am.an.article.you.will.want@example.com>
[S] 502 Permission denied
Example of an attempt to access a facility requiring authentication:
[C] GROUP secret.group
[S] 480 Permission denied
followed by a successful attempt following such authentication:
[C] XSECRET fred flintstone
[S] 290 Password for fred accepted
[C] GROUP secret.group
[S] 211 5 1 20 secret.group selected
Example of an attempt to access a facility requiring privacy:
[C] GROUP secret.group
[S] 483 Secure connection required
[C] XENCRYPT
[Client and server negotiate encryption on the link]
[S] 283 Encrypted link established
[C] GROUP secret.group
[S] 211 5 1 20 secret.group selected
Example of a need to change mode before using a facility:
[C] GROUP binary.group
[S] 401 XHOST Not on this virtual host
[C] XHOST binary.news.example.org
[S] 290 binary.news.example.org virtual host selected
[C] GROUP binary.group
[S] 211 5 1 77 binary.group selected
Example of a temporary failure:
[C] GROUP archive.local
[S] 403 Archive server temporarily offline
Example of the server needing to close down immediately:
[C] ARTICLE 123
[S] 400 Power supply failed, running on UPS
[Server closes connection.]
NNTP is designed to operate over a reliable bi-directional connection such as TCP. Therefore, if a command does not depend on the response to the previous one, it should not matter if it is sent before that response is received. Doing this is called "pipelining". However, certain server implementations throw away all text received from the client following certain commands before sending their response. If this happens, pipelining will be affected because one or more commands will have been ignored or misinterpreted, and the client will be matching the wrong responses to each command. Since there are significant benefits to pipelining, but also circumstances where it is reasonable or common for servers to behave in the above manner, this document puts certain requirements on both clients and servers.
Except where stated otherwise, a client MAY use pipelining. That is, it may send a command before receiving the response for the previous command. The server MUST allow pipelining and MUST NOT throw away any text received after a command. Irrespective of whether or not pipelining is used, the server MUST process commands in the order they are sent.
If the specific description of a command says it "MUST NOT be pipelined", that command MUST end any pipeline of commands. That is, the client MUST NOT send any following command until receiving the CRLF at the end of the response from the command. The server MAY ignore any data received after the command and before the CRLF at the end of the response is sent to the client.
The initial connection must not be part of a pipeline; that is, the client MUST NOT send any command until receiving the CRLF at the end of the greeting.
If the client uses blocking system calls to send commands, it MUST ensure that the amount of text sent in pipelining does not cause a deadlock between transmission and reception. The amount of text involved will depend on window sizes in the transmission layer, and is typically 4k octets for TCP. (Since the server only sends data in response to commands from the client, the converse problem does not occur.)
Example of correct use of pipelining:
[C] GROUP misc.test
[C] STAT
[C] NEXT
[S] 211 1234 3000234 3002322 misc.test
[S] 223 3000234 <45223423@example.com> retrieved
[S] 223 3000237 <668929@example.org> retrieved
Example of incorrect use of pipelining (the MODE READER command may not be pipelined):
[C] GROUP misc.test
[C] MODE READER
[C] DATE
[C] NEXT
[S] 211 1234 3000234 3002322 misc.test
[S] 200 Server ready, posting allowed
[S] 223 3000237 <668929@example.org> retrieved
The DATE command has been thrown away by the server and so there is no 111 response to match it.
NNTP is intended to transfer articles between clients and servers. For the purposes of this specification, articles are required to conform to the rules in this section and clients and servers MUST correctly process any article received from the other that does so. Note that this requirement applies only to the contents of communications over NNTP; it does not prevent the client or server from subsequently rejecting an article for reasons of local policy. Also see Appendix BInteraction with other specifications for further restrictions on the format of articles in some uses of NNTP.
An article consists of two parts: the headers and the body. They are separated by a single empty line, or in other words by two consecutive CRLF pairs (if there is more than one empty line, the second and subsequent ones are part of the body). In order to meet the general requirements of NNTP, an article MUST NOT include the octet NUL, MUST NOT contain the octets LF and CR other than as part of a CRLF pair, and MUST end with a CRLF pair. This specification puts no further restrictions on the body; in particular, it MAY be empty.
The headers of an article consist of one or more header lines. Each header line consists of a header name, a colon, a space, the header content, and a CRLF in that order. The name consists of one or more printable US-ASCII characters other than colon and, for the purposes of this specification, is not case-sensitive. There MAY be more than one header line with the same name. The content MUST NOT contain CRLF; it MAY be empty. A header may be "folded"; that is, a CRLF pair may be placed before any TAB or space in the line; there MUST still be some other octet between any two CRLF pairs in a header line. (Note that folding means that the header line occupies more than one line when displayed or transmitted; nevertheless it is still referred to as "a" header line.) The presence or absence of folding does not affect the meaning of the header line; that is, the CRLF pairs introduced by folding are not considered part of the header content. Header lines SHOULD NOT be folded before the space after the colon that follows the header name, and SHOULD include at least one octet other than %x09 or %x20 between CRLF pairs. However, if an article has been received from elsewhere with one of these, clients and servers MAY transfer it to the other without re-folding it.
The content of a header SHOULD be in UTF-8. However, if a server receives an article from elsewhere that uses octets in the range 128 to 255 in some other manner, it MAY pass it to a client without modification. Therefore clients MUST be prepared to receive such headers and also data derived from them (e.g. in the responses from the OVER extensionThe OVER extension) and MUST NOT assume that they are always UTF-8. How the client will then process those headers, including identifying the encoding used, is outside the scope of this document.
Each article MUST have a unique message-id; two articles offered by an NNTP server MUST NOT have the same message-id. For the purposes of this specification, message-ids are opaque strings that MUST meet the following requirements:
Two message-ids are the same if and only if they consist of the same sequence of octets.
This specification does not describe how the message-id of an article is determined. If the server does not have any way to determine a message-id from the article itself, it MUST synthesize one (this specification does not require the article to be changed as a result). See also Appendix B.2Message-IDs.
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The WILDMAT format described here is based on the version first developed by Rich Salz [SALZ1992]Salz, R., Manual Page for wildmat(3) from the INN 1.4 distribution, Revision 1.10, April 1992., which in turn was derived from the format used in the UNIX "find" command to articulate file names. It was developed to provide a uniform mechanism for matching patterns in the same manner that the UNIX shell matches filenames.
A wildmat is described by the following ABNFCrocker, D. and P. Overell, Augmented BNF for Syntax Specifications: ABNF, November 1997.[RFC2234] syntax (note that this syntax contains ambiguities and special cases described at the end):
- wildmat =
- wildmat-pattern *("," ["!"] wildmat-pattern)
- wildmat-pattern =
- 1*wildmat-item
- wildmat-item =
- wildmat-exact / wildmat-wild
- wildmat-exact =
- %x21-29 / %x2B / %x2D-3E / %x40-5A / %x5E-7E / UTF8-non-ascii ; exclude * , ? [ \ ]
- wildmat-wild =
- "*" / "?"
UTF8-non-ascii is defined in Section 9Augmented BNF Syntax for NNTP.
This syntax must be interpreted subject to the following rule:
Where a wildmat-pattern is not immediately preceded by "!", it shall not begin with a "!".
Note: the characters \ , [ and ] are not allowed in wildmats, while * and ? are always wildcards. This should not be a problem since these characters cannot occur in newsgroup names, which is the only current use of wildmats. Backslash is commonly used to suppress the special meaning of characters while brackets are used to introduce sets. However, these usages are not universal and interpretation of these characters in the context of UTF-8 strings is both potentially complex and differs from existing practice, so they were omitted from this specification. A future extension to this specification may provide semantics for these characters.
A wildmat is tested against a string, and either matches or does not match. To do this, each constituent wildmat-pattern is matched against the string and the rightmost pattern that matches is identified. If that wildmat-pattern is not preceded with "!", the whole wildmat matches. If it is preceded by "!", or if no wildmat-pattern matches, the whole wildmat does not match.
For example, consider the wildmat "a*,!*b,*c*":
the string "aaa" matches because the rightmost match is with "a*"
the string "abb" does not match because the rightmost match is with "*b"
the string "ccb" matches because the rightmost match is with "*c*"
the string "xxx" does not match because no wildmat-pattern matches
A wildmat-pattern matches a string if the string can be broken into components, each of which matches the corresponding wildmat-item in the pattern; the matches must be in the same order, and the whole string must be used in the match. The pattern is "anchored"; that is, the first and last characters in the string must match the first and last item respectively (unless that item is an asterisk matching zero characters).
A wildmat-exact matches the same character (which may be more than one octet in UTF-8).
"?" matches exactly one character (which may be more than one octet).
"*" matches zero or more characters. It can match an empty string, but it cannot match a subsequence of a UTF-8 sequence that is not aligned to the character boundaries.
An NNTP server or extension MAY extend the syntax or semantics of wildmats provided that all wildmats that meet the requirements of Section 4.1Wildmat syntax have the meaning ascribed to them by Section 4.2Wildmat semantics. Future editions of this document may also extend wildmats.
In these examples, $ and @ are used to represent the two octets %xC2 and %xA3 respectively; $@ is thus the UTF-8 encoding for the pound sterling symbol, shown as # in the descriptions.
Wildmat Description of strings that match
abc the one string "abc"
abc,def the two strings "abc" and "def"
$@ the one character string "#"
a* any string that begins with "a"
a*b any string that begins with "a" and ends with "b"
a*,*b any string that begins with "a" or ends with "b"
a*,!*b any string that begins with "a" and does not end with
"b"
a*,!*b,c* any string that begins with "a" and does not end with
"b", and any string that begins with "c" no matter
what it ends with
a*,c*,!*b any string that begins with "a" or "c" and does not
end with "b"
?a* any string with "a" as its second character
??a* any string with "a" as its third character
*a? any string with "a" as its penultimate character
*a?? any string with "a" as its antepenultimate character
| TOC |
- Responses
- 200 Service available, posting allowed [1]
201 Service available, posting prohibited [1]
400 Service temporarily unavailable [1][2]
502 Service permanently unavailable [1][2]- [1]
- These are the only valid response codes for the initial greeting; the server MUST not return any other generic response code.
- [2]
- Following a 400 or 502 response the server MUST immediately close the connection.
There is no command presented by the client upon initial connection to the server. The server MUST present an appropriate response code as a greeting to the client. This response informs the client whether service is available and whether the client is permitted to post.
If the server will accept further commands from the client including POST, the server MUST present a 200 greeting code. If the server will accept further commands from the client, but it is not authorized to post articles using the POST command, the server MUST present a 201 greeting code.
Otherwise the server MUST present a 400 or 502 greeting code and then immediately close the connection. 400 SHOULD be used if the issue is only temporary (for example, because of load) and the client can expect to be able to connect successfully at some point in the future without making any changes. 502 MUST be used if the client is not permitted under any circumstances to interact with the server, and MAY be used if the server has insufficient information to determine whether the issue is temporary or permanent.
Example of a normal connection from an authorized client which then terminates the session (see Section 5.4QUIT):
[Initial TCP connection set-up completed.]
[S] 200 NNTP Service Ready, posting permitted
[C] QUIT
[S] 205 NNTP Service exits normally
[Server closes connection.]
Example of a normal connection from an authorized client that is not permitted to post; it also immediately terminates the session:
[Initial TCP connection set-up completed.]
[S] 201 NNTP Service Ready, posting prohibited
[C] QUIT
[S] 205 NNTP Service exits normally
[Server closes connection.]
Example of a normal connection from an unauthorized client:
[Initial TCP connection set-up completed.]
[S] 502 NNTP Service permanently unavailable
[Server closes connection.]
Example of a connection from a client where the server is unable to provide service:
[Initial TCP connection set-up completed.]
[S] 400 NNTP Service temporarily unavailable
[Server closes connection.]
- This command MUST NOT be pipelined.
- Syntax
- MODE READER
- Responses
- 200 Posting allowed
201 Posting prohibited
400 Service temporarily unavailable [1]
502 Service permanently unavailable [1]- [1]
- Following a 400 or 502 response the server MUST immediately close the connection.
MODE READER SHOULD be sent by any client that intends to use any command in this specification (including Section 8Framework for NNTP extensions) other than IHAVE, HEAD, STAT, LIST ACTIVE, or LIST EXTENSIONS; other extensions MAY also require MODE READER to be used. Servers MAY require that this command be issued before any commands other than the above are sent and MAY reject such commands until after a MODE READER command has been sent. Such rejections SHOULD use response code 401 with argument "MODE-READER", but for historical reasons response code 502 MAY be used, even though this situation does not meet the conditions for that response.
Once MODE READER is sent, IHAVE (and any related extensions) MAY no longer be permitted, even if it were permitted before the MODE READER command. The results of LIST EXTENSIONS MAY be different following a MODE READER command than prior to the issuing of that command.
The server MUST return a response using the same codes as the initial greeting (as described in Section 5.1.1Usage) to indicate its ability to provide reading service to the client. Note that the response need not be the same as the one presented during the initial greeting.
Servers are encouraged to not require this command even though clients SHOULD send it when appropriate. It is present to support some news architectures that switch between modes based on whether a given connection is a peer-to-peer connection with another server or a news reading client.
Example of use of the MODE READER command by an authorized client which then terminates the session (see Section 5.4QUIT):
[C] MODE READER
[S] 200 NNTP Service Ready, posting permitted
[C] QUIT
[S] 205 NNTP Service exits normally
[Server closes connection.]
Example of use of the MODE READER command by an authorized client that is not permitted to post; it also immediately terminates the session:
[C] MODE READER
[S] 201 NNTP Service Ready, posting prohibited
[C] QUIT
[S] 205 NNTP Service exits normally
[Server closes connection.]
Example of use of MODE READER by a client not authorized to receive service from the server as a news reader:
[C] MODE READER
[S] 502 NNTP Service permanently unavailable
[Server closes connection.]
Example of a connection from any client where the server is temporarily unable to provide news reader service:
[C] MODE READER
[S] 400 NNTP Service temporarily unavailable
[Server closes connection.]
Example of a facility that requires MODE READER before use, using the preferred response:
[C] GROUP misc.test
[S] 401 MODE-READER currently in peering mode
[C] MODE READER
[S] 200 NNTP Service Ready, posting permitted
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
Example of a facility that requires MODE READER before use, using the historical but deprecated response:
[C] GROUP misc.test
[S] 502 Not available in peering mode
[C] MODE READER
[S] 200 NNTP Service Ready, posting permitted
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
Example of a facility that cannot be used after MODE READER:
[C] IHAVE <i.am.an.article.you.have@example.com>
[S] 435 Duplicate
[C] MODE READER
[S] 200 Reader mode, posting permitted
[C] IHAVE <i.am.an.article.you.have@example.com>
[S] 502 Permission denied
- This command is optional.
- Syntax
- LIST EXTENSIONS
- Responses
- 202 Extension list follows (multiline)
402 Server has no extensions
The LIST EXTENSIONS command allows a client to determine which extensions are supported by the server at any given time. See Section 8Framework for NNTP extensions for further discussion of extensions.
This command MUST be implemented by any server that implements any registered extension, and is optional otherwise. A server MUST NOT generate the generic response 401, 480, 483, or 502 (all of which indicate "not permitted") to this command.
This command MAY be issued at anytime during a session. It is not required that the client issues this command before attempting to make use of any extension. The response generated by this command MAY change during a session because of other state information (which in turn may be changed by the effects of other commands). An NNTP client is only able to get the current and correct information concerning available extensions at any point during a session by issuing a LIST EXTENSIONS command at that point of that session and processing the response, and the server MUST ensure that those extensions currently listed in the returned information are available. Therefore, if an extension (including those in Section 8Framework for NNTP extensions) is only available before or after a MODE READER command, the LIST EXTENSIONS command MUST only include the extension in that situation. Similarly, if only some of the commands in an extension will be available, or if the behaviour of the extension will change in some other manner, before or after a MODE READER command, this MUST be indicated by different arguments to the extension-label in the results of LIST EXTENSIONS in each situation.
While some extensions are likely to be always available or never available, others will "appear" and "disappear" depending on server state changes within the session or external events between sessions. An NNTP client MAY cache the results of this command, but MUST NOT rely on the correctness of any cached results, whether from earlier in this session or from a previous session, MUST cope gracefully with the cached status being out of date, and SHOULD (if caching results) provide a way to force the cached information to be refreshed. Furthermore, a client MUST NOT use cached results in relation to security, privacy, and authentication extensions. See Section 11.6Caching of LIST EXTENSIONS results for further discussion of this topic.
The list of extensions is returned as a multi-line response following the 202 response code. Each extension is listed on a separate line; the line MUST begin with an extension-label and optionally one or more arguments (separated by one or more spaces). The extension-label and the meaning of the arguments are specified as part of the definition of the extension. The extension-label is a string of 1 to 12 US-ASCII letters and MUST be in uppercase (that is, %x41-5A). Arguments are strings of 1 or more printable UTF-8 characters (that is, either printable US-ASCII characters or any UTF-8 sequence outside the US-ASCII range, but not space or TAB).
The server MUST NOT list the same extension twice in the response, MUST list all supported registered extensions, and SHOULD list all supported private extensions. The order in which the extensions are listed is not significant. The server need not even consistently return the same order. If the server does not support any extensions, it MUST return an empty list. The 402 response code is documented for historic reasons only; clients SHOULD handle it gracefully, but servers MUST NOT generate it.
Following a generic failure response, such as 403, an extension might still be available, and the client MAY attempt to use it.
Example of a successful response:
[C] LIST EXTENSIONS
[S] 202 Extensions supported:
[S] OVER MSGID
[S] HDR
[S] LISTGROUP
[S] .
The particular extensions shown here are simply examples of what might be defined in other places, and no particular meaning should be attributed to them.
Example where no extensions are available:
[C] LIST EXTENSIONS
[S] 202 Extensions supported:
[S] .
Example from a non-conforming server which indicates "no extensions available" using the 402 response code:
[C] LIST EXTENSIONS
[S] 402 Server has no extensions
- Syntax
- QUIT
- Responses
- 205 Connection closing
The client uses the QUIT command to terminate the session. The server MUST acknowledge the QUIT command and then close the connection to the client. This is the preferred method for a client to indicate that it has finished all its transactions with the NNTP server.
If a client simply disconnects (or the connection times out or some other fault occurs), the server MUST gracefully cease its attempts to service the client, disconnecting from its end if necessary.
The server MUST NOT generate any response code to the QUIT command other than 205 or, if any arguments are provided, 501.
[C] QUIT
[S] 205 closing connection
[Server closes connection.]
| TOC |
News reading clients have available a variety of mechanisms to retrieve articles via NNTP. The news articles are stored and indexed using three types of keys. One key is the message-id of an article. Another key is composed of the newsgroup name and the article number within that newsgroup. That key MUST be unique to a particular server (there will be only one article with that number within a particular newsgroup), but is not required to be globally unique. Additionally, because the same article can be cross-posted to multiple newsgroups, there may be multiple keys that point to the same article on the same server. The final key is the arrival timestamp, giving the time that the article arrived at the server.
The server MUST ensure that article numbers are issued in order of arrival timestamp; that is, articles arriving later MUST have higher numbers than those that arrive earlier. The server SHOULD allocate the next sequential unused number to each new article.
Article numbers MUST lie between 1 and 4,294,967,295 inclusive. The client and server MAY use leading zeroes in specifying article numbers, but MUST NOT use more than 16 digits. In some situations, the value zero replaces an article number to show some special situation.
The following commands are used to set the "current selected newsgroup" and the "current article number", which are used by various commands. At the start of an NNTP session, both of these values are set to the special value "invalid".
- Syntax
- GROUP group
- Responses
- 211 number low high group Group successfully selected
411 No such newsgroup- Parameters
- group = name of newsgroup
number = estimated number of articles in the group
low = reported low water mark
high = reported high water mark
The required argument is the name of the newsgroup to be selected (e.g. "news.software.b"). A list of valid newsgroups may be obtained by using the LIST ACTIVE command (see Section 7.6.1LIST ACTIVE).
The successful selection response will return the article numbers of the first and last articles in the group at the moment of selection (these numbers are referred to as the "reported low water mark" and the "reported high water mark"), and an estimate of the number of articles in the group currently available.
If the group is not empty, the estimate MUST be at least the actual number of articles available, and MUST be no greater than one more than the difference between the reported low and high water marks. (Some implementations will actually count the number of articles currently stored. Others will just subtract the low water mark from the high water mark and add one to get an estimate.)
If the group is empty, one of the following three situations will occur. Clients MUST accept all three cases; servers MUST NOT represent an empty group in any other way.
The set of articles in a group may change after the GROUP command is carried out. That is:
Except when the group is empty and all three numbers are zero, whenever a subsequent GROUP command for the same newsgroup is issued, either by the same client or a different client, the reported low water mark in the response MUST be no less than that in any previous response for that newsgroup in any session, and SHOULD be no less than that in any previous response for that newsgroup ever sent to any client. Any failure to meet the latter condition SHOULD be transient only. The client may make use of the low water mark to remove all remembered information about articles with lower numbers, as these will never recur. This includes the situation when the high water mark is one less than the low water mark. No similar assumption can be made about the high water mark, as this can decrease if an article is removed, and then increase again if it is reinstated or if new articles arrive.
When a valid group is selected by means of this command, the current selected newsgroup MUST be set to that group and the current article number MUST be set to the first article in the group. If an empty newsgroup is selected, the current article pointer is made invalid. If an invalid group is specified, the current selected newsgroup and current article number MUST NOT be changed.
The GROUP command (or the LISTGROUP command, if implemented) MUST be used by a client and a successful response received before any other command is used that depends on the value of the current selected newsgroup or current article number.
If the group specified is not available on the server, a 411 response MUST be returned.
Example for a group known to the server:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
Example for a group unknown to the server:
[C] GROUP example.is.sob.bradner.or.barber
[S] 411 example.is.sob.bradner.or.barber is unknown
Example of an empty group using the preferred response:
[C] GROUP example.currently.empty.newsgroup
[S] 211 0 4000 3999 example.currently.empty.newsgroup
Example of an empty group using an alternative response:
[C] GROUP example.currently.empty.newsgroup
[S] 211 0 0 0 example.currently.empty.newsgroup
Example of an empty group using a different alternative response:
[C] GROUP example.currently.empty.newsgroup
[S] 211 0 4000 4321 example.currently.empty.newsgroup
- Syntax
- LAST
- Responses
- 223 n message-id Article found
412 No newsgroup selected
420 Current article number is invalid
422 No previous article in this group- Parameters
- n = article number
message-id = article message-id
If the current selected newsgroup is valid, the current article number MUST be set to the previous article in that newsgroup (that is, the highest existing article number less than the current article number). If successful, a response indicating the new current article number and the message-id of that article MUST be returned. No article text is sent in response to this command.
There MAY be no previous article in the group, although the current article number is not the reported low water mark. There MUST NOT be a previous article when the current article number is the reported low water mark.
Because articles can be removed and added, the results of multiple LAST and NEXT commands MAY not be consistent over the life of a particular NNTP session.
If the current article number is already the first article of the newsgroup, a 422 response MUST be returned. If the current article number is invalid, a 420 response MUST be returned. If the current selected newsgroup is invalid, a 412 response MUST be returned. In all three cases the current selected newsgroup and current article number MUST NOT be altered.
Example of a successful article retrieval using LAST:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] NEXT
[S] 223 3000237 <668929@example.org> retrieved
[C] LAST
[S] 223 3000234 <45223423@example.com> retrieved
Example of an attempt to retrieve an article without having selected a group (via the GROUP command) first:
[Assumes current selected newsgroup is invalid.]
[C] LAST
[S] 412 no newsgroup selected
Example of an attempt to retrieve an article using the LAST command when the current article number is that of the first article in the group:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] LAST
[S] 422 No previous article to retrieve
Example of an attempt to retrieve an article using the LAST command when the current selected newsgroup is empty:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] LAST
[S] 420 No current article selected
- Syntax
- NEXT
- Responses
- 223 n message-id Article found
412 No newsgroup selected
420 Current article number is invalid
421 No next article in this group- Parameters
- n = article number
message-id = article message-id
If the current selected newsgroup is valid, the current article number MUST be set to the next article in that newsgroup (that is, the lowest existing article number greater than the current article number). If successful, a response indicating the new current article number and the message-id of that article MUST be returned. No article text is sent in response to this command.
If the current article number is already the last article of the newsgroup, a 421 response MUST be returned. In all other aspects (apart, of course, from the lack of 422 response) this command is identical to the LAST commandLAST.
Example of a successful article retrieval using NEXT:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] NEXT
[S] 223 3000237 <668929@example.org> retrieved
Example of an attempt to retrieve an article without having selected a group (via the GROUP command) first:
[Assumes current selected newsgroup is invalid.]
[C] NEXT
[S] 412 no newsgroup selected
Example of an attempt to retrieve an article using the NEXT command when the current article number is that of the last article in the group:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] STAT 3002322
[S] 223 3002322 <411@example.net> retrieved
[C] NEXT
[S] 421 No next article to retrieve
Example of an attempt to retrieve an article using the NEXT command when the current selected newsgroup is empty:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] NEXT
[S] 420 No current article selected
The ARTICLE, BODY, HEAD, and STAT commands are very similar. They differ only in the parts of the article that are presented to the client and in the successful response code. The ARTICLE command is described here in full, while the other commands are described in terms of the differences. As specified in Section 3.4Articles, an article consists of two parts: the article headers and the article body. When responding to one of these commands, the server MUST present the entire article or appropriate part and MUST NOT attempt to alter or translate it in any way.
- Syntax
- ARTICLE message-id
ARTICLE number
ARTICLE- Responses
- First form (message-id specified)
- 220 0|n message-id Article follows (multiline)
430 No article with that message-id- Second form (article number specified)
- 220 n message-id Article follows (multiline)
412 No newsgroup selected
423 No article with that number- Third form (current article number used)
- 220 n message-id Article follows (multiline)
412 No newsgroup selected
420 Current article number is invalid- Parameters
- number = Requested article number
n = Returned article number
message-id = Article message-id
The ARTICLE command selects an article based on the arguments and presents the entire article (that is, the headers, an empty line, and the body in that order). The command has three forms.
In the first form, a message-id is specified and the server presents the article with that message-id. In this case, the server MUST NOT alter the current selected newsgroup or current article number. This is both to facilitate the presentation of articles that may be referenced within another article being read, and because of the semantic difficulties of determining the proper sequence and membership of an article that may have been cross-posted to more than one newsgroup.
In the response, the article number MUST be replaced with zero, except that if there is a current selected group and the article is present in that group, the server MAY use that article number. (The server is not required to determine whether the article is in the current selected newsgroup or, if so, what article number it has; the client MUST always be prepared for zero to be specified.) The server MUST NOT provide an article number unless use of that number in a second ARTICLE command immediately following this one would return the same article. Even if the server chooses to return article numbers in these circumstances, it need not do so consistently; it MAY return zero to any such command (also see the STAT examplesExamples).
In the second form, an article number is specified. If there is an article with that number in the current selected newsgroup, the server MUST set the current article number to that number.
In the third form, the article indicated by the current article number in the current selected newsgroup is used.
Note that a previously valid article number MAY become invalid if the article has been removed. A previously invalid article number MAY become valid if the article has been reinstated, but such an article number MUST be no less than the reported low water mark for that group.
The server MUST NOT change the current selected newsgroup as a result of this command. The server MUST NOT change the current article number except when an article number argument was provided and the article exists; in particular, it MUST NOT change it following an unsuccessful response.
Since the message-id is unique for each article, it may be used by a client to skip duplicate displays of articles that have been posted more than once, or to more than one newsgroup.
The article is returned as a multi-line response following the 220 response code.
If the argument is a message-id and no such article exists, a 430 response MUST be returned. If the argument is a number or is omitted and the current selected newsgroup is invalid, a 412 response MUST be returned. If the argument is a number and that article does not exist in the current selected newsgroup, a 423 response MUST be returned. If the argument is omitted and the current article number is invalid, a 420 response MUST be returned.
Example of a successful retrieval of an article (using no article number):
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] ARTICLE
[S] 220 3000234 <45223423@example.com>
[S] Path: pathost!demo!whitehouse!not-for-mail
[S] From: "Demo User" <nobody@example.net>
[S] Newsgroups: misc.test
[S] Subject: I am just a test article
[S] Date: 6 Oct 1998 04:38:40 -0500
[S] Organization: An Example Net, Uncertain, Texas
[S] Message-ID: <411@example.net>
[S]
[S] This is just a test article.
[S] .
Example of a successful retrieval of an article by message-id:
[C] ARTICLE <45223423@example.com>
[S] 220 0 <45223423@example.com>
[S] Path: pathost!demo!whitehouse!not-for-mail
[S] From: "Demo User" <nobody@example.net>
[S] Newsgroups: misc.test
[S] Subject: I am just a test article
[S] Date: 6 Oct 1998 04:38:40 -0500
[S] Organization: An Example Net, Uncertain, Texas
[S] Message-ID: <411@example.net>
[S]
[S] This is just a test article.
[S] .
Example of an unsuccessful retrieval of an article by message-id:
[C] ARTICLE <i.am.not.there@example.com>
[S] 430 No Such Article Found
Example of an unsuccessful retrieval of an article by number:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 news.groups
[C] ARTICLE 300256
[S] 423 No article with that number
Example of an unsuccessful retrieval of an article by number because no newsgroup was selected first:
[Assumes current selected newsgroup is invalid.]
[C] ARTICLE 300256
[S] 412 No newsgroup selected
Example of an attempt to retrieve an article when the current selected newsgroup is empty:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] ARTICLE
[S] 420 No current article selected
- Syntax
- HEAD message-id
HEAD number
HEAD- Responses
- First form (message-id specified)
- 221 0|n message-id Headers follow (multiline)
430 No article with that message-id- Second form (article number specified)
- 221 n message-id Headers follow (multiline)
412 No newsgroup selected
423 No article with that number- Third form (current article number used)
- 221 n message-id Headers follow (multiline)
412 No newsgroup selected
420 Current article number is invalid- Parameters
- number = Requested article number
n = Returned article number
message-id = Article message-id
The HEAD command behaves identically to the ARTICLE command except that, if the article exists, the response code is 221 instead of 220 and only the headers are presented (the empty line separating the headers and body MUST NOT be included).
Example of a successful retrieval of the headers of an article (using no article number):
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HEAD
[S] 221 3000234 <45223423@example.com>
[S] Path: pathost!demo!whitehouse!not-for-mail
[S] From: "Demo User" <nobody@example.net>
[S] Newsgroups: misc.test
[S] Subject: I am just a test article
[S] Date: 6 Oct 1998 04:38:40 -0500
[S] Organization: An Example Net, Uncertain, Texas
[S] Message-ID: <411@example.net>
[S] .
Example of a successful retrieval of the headers of an article by message-id:
[C] HEAD <45223423@example.com>
[S] 221 0 <45223423@example.com>
[S] Path: pathost!demo!whitehouse!not-for-mail
[S] From: "Demo User" <nobody@example.net>
[S] Newsgroups: misc.test
[S] Subject: I am just a test article
[S] Date: 6 Oct 1998 04:38:40 -0500
[S] Organization: An Example Net, Uncertain, Texas
[S] Message-ID: <411@example.net>
[S] .
Example of an unsuccessful retrieval of the headers of an article by message-id:
[C] HEAD <i.am.not.there@example.com>
[S] 430 No Such Article Found
Example of an unsuccessful retrieval of the headers of an article by number:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HEAD 300256
[S] 423 No article with that number
Example of an unsuccessful retrieval of the headers of an article by number because no newsgroup was selected first:
[Assumes current selected newsgroup is invalid.]
[C] HEAD 300256
[S] 412 No newsgroup selected
Example of an attempt to retrieve the headers of an article when the current selected newsgroup is empty:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] HEAD
[S] 420 No current article selected
- Syntax
- BODY message-id
BODY number
BODY- Responses
- First form (message-id specified)
- 222 0|n message-id Body follows (multiline)
430 No article with that message-id- Second form (article number specified)
- 222 n message-id Body follows (multiline)
412 No newsgroup selected
423 No article with that number- Third form (current article number used)
- 222 n message-id Body follows (multiline)
412 No newsgroup selected
420 Current article number is invalid- Parameters
- number = Requested article number
n = Returned article number
message-id = Article message-id
The BODY command behaves identically to the ARTICLE command except that, if the article exists, the response code is 222 instead of 220 and only the body is presented (the empty line separating the headers and body MUST NOT be included).
Example of a successful retrieval of the body of an article (using no article number):
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] BODY
[S] 222 3000234 <45223423@example.com>
[S] This is just a test article.
[S] .
Example of a successful retrieval of the body of an article by message-id:
[C] BODY <45223423@example.com>
[S] 222 0 <45223423@example.com>
[S] This is just a test article.
[S] .
Example of an unsuccessful retrieval of the body of an article by message-id:
[C] BODY <i.am.not.there@example.com>
[S] 430 No Such Article Found
Example of an unsuccessful retrieval of the body of an article by number:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] BODY 300256
[S] 423 No article with that number
Example of an unsuccessful retrieval of the body of an article by number because no newsgroup was selected first:
[Assumes current selected newsgroup is invalid.]
[C] BODY 300256
[S] 412 No newsgroup selected
Example of an attempt to retrieve the body of an article when the current selected newsgroup is empty:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] BODY
[S] 420 No current article selected
- Syntax
- STAT message-id
STAT number
STAT- Responses
- First form (message-id specified)
- 223 0|n message-id Article exists
430 No article with that message-id- Second form (article number specified)
- 223 n message-id Article exists
412 No newsgroup selected
423 No article with that number- Third form (current article number used)
- 223 n message-id Article exists
412 No newsgroup selected
420 Current article number is invalid- Parameters
- number = Requested article number
n = Returned article number
message-id = Article message-id
The STAT command behaves identically to the ARTICLE command except that, if the article exists, it is NOT presented to the client and the response code is 223 instead of 220. Note that the response is NOT multi-line.
This command allows the client to determine whether an article exists, and in the second and third forms what its message-id is, without having to process an arbitrary amount of text.
Example of STAT on an existing article (using no article number):
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] STAT
[S] 223 3000234 <45223423@example.com>
Example of STAT on an existing article by message-id:
[C] STAT <45223423@example.com>
[S] 223 0 <45223423@example.com>
Example of STAT on an article not on the server by message-id:
[C] STAT <i.am.not.there@example.com>
[S] 430 No Such Article Found
Example of STAT on an article not in the server by number:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] STAT 300256
[S] 423 No article with that number
Example of STAT on an article by number when no newsgroup was selected first:
[Assumes current selected newsgroup is invalid.]
[C] STAT 300256
[S] 412 No newsgroup selected
Example of STAT on an article when the current selected newsgroup is empty:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] STAT
[S] 420 No current article selected
Example of STAT by message-id on a server which sometimes reports the actual article number:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] STAT
[S] 223 3000234 <45223423@example.com>
[C] STAT <45223423@example.com>
[S] 223 0 <45223423@example.com>
[C] STAT <45223423@example.com>
[S] 223 3000234 <45223423@example.com>
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] STAT <45223423@example.com>
[S] 223 0 <45223423@example.com>
[C] GROUP alt.crossposts
[S] 211 9999 111111 222222 alt.crossposts
[C] STAT <45223423@example.com>
[S] 223 123456 <45223423@example.com>
[C] STAT
[S] 223 111111 <23894720@example.com>
The first STAT command establishes the identity of an article in the group. The second and third show that the server may, but need not, give the article number when the message-id is specified. The fourth STAT command shows that zero must be specified if the article isn't in the current selected group, the fifth shows that the number, if provided, must be that relating to the current selected group, and the last one shows that the current selected article is still not changed by the use of STAT with a message-id even if it returns an article number.
Article posting is done in one of two modes: individual article posting from news reading clients using POST, and article transfer from other news servers using IHAVE.
- This command MUST NOT be pipelined.
- Syntax
- POST
- Responses
- Initial responses
- 340 Send article to be posted
440 Posting not permitted- Subsequent responses
- 240 Article received OK
441 Posting failed
If posting is allowed, a 340 response MUST be returned to indicate that the article to be posted should be sent. If posting is prohibited for some installation-dependent reason, a 440 response MUST be returned.
If posting is permitted, the article MUST be in the format specified in Section 3.4Articles and MUST be sent by the client to the server in the manner specified (in Section 3.1Commands and Responses) for multi-line responses (except that there is no initial line containing a response code). Thus a single dot (".") on a line indicates the end of the text, and lines starting with a dot in the original text have that dot doubled during transmission.
Following the presentation of the termination sequence by the client, the server MUST return a response indicating success or failure of the article transfer. Note that response codes 340 and 440 are used in direct response to the POST command. Others are returned following the sending of the article.
A response of 240 SHOULD indicate that, barring unforeseen server errors, the posted article will be made available on the server and/or transferred to other servers as appropriate, possibly following further processing. In other words, articles not wanted by the server SHOULD be rejected with a 441 response and not accepted and silently discarded. However, the client SHOULD NOT assume that the article has been successfully transferred unless it receives an affirmative response from the server, and SHOULD NOT assume that it is being made available to other clients without explicitly checking (for example using the STAT command).
If the session is interrupted before the response is received, it is possible that an affirmative response was sent but has been lost. Therefore, in any subsequent session, the client SHOULD either check whether the article was successfully posted before resending or ensure that the server will allocate the same message-id to the new attempt (see Appendix B.2Message-IDs) - the latter approach is preferred since the article might not have been made available for reading yet (for example, it may have to go through a moderation process).
Example of a successful posting:
[C] POST
[S] 340 Input article; end with <CR-LF>.<CR-LF>
[C] From: "Demo User" <nobody@example.net>
[C] Newsgroups: misc.test
[C] Subject: I am just a test article
[C] Organization: An Example Net
[C]
[C] This is just a test article.
[C] .
[S] 240 Article received OK
Example of an unsuccessful posting:
[C] POST
[S] 340 Input article; end with <CR-LF>.<CR-LF>
[C] From: "Demo User" <nobody@example.net>
[C] Newsgroups: misc.test
[C] Subject: I am just a test article
[C] Organization: An Example Net
[C]
[C] This is just a test article.
[C] .
[S] 441 Posting failed
Example of an attempt to post when posting is not allowed:
[C] MODE READER
[S] 201 NNTP Service Ready, posting prohibited
[C] POST
[S] 440 Posting not permitted
- This command MUST NOT be pipelined.
- Syntax
- IHAVE message-id
- Responses
- Initial responses
- 335 Send article to be transferred
435 Article not wanted
436 Transfer not possible; try again later- Subsequent responses
- 235 Article transferred OK
436 Transfer failed; try again later
437 Transfer rejected; do not retry- Parameters
- message-id = Article message-id
The IHAVE command informs the server that the client has an article with the specified message-id. If the server desires a copy of that article a 335 response MUST be returned, instructing the client to send the entire article. If the server does not want the article (if, for example, the server already has a copy of it), a 435 response MUST be returned, indicating that the article is not wanted. Finally, if the article isn't wanted immediately but the client should retry later if possible (if, for example, another client is in the process of sending the same article to the server), a 436 response MUST be returned.
If transmission of the article is requested, the client MUST send the entire article, including headers and body, in the format defined above (Section 3.1Commands and Responses) for multi-line responses (except that there is no initial line containing a response code). Thus a single dot (".") on a line indicates the end of the text, and lines starting with a dot in the original text have that dot doubled during transmission. The server MUST return either a 235 response, indicating that the article was successfully transferred, a 436 response, indicating that the transfer failed but should be tried again later, or a 437 response, indicating that the article was rejected.
This function differs from the POST command in that it is intended for use in transferring already-posted articles between hosts. It SHOULD NOT be used when the client is a personal news reading program, since use of this command indicates that the article has already been posted at another site and is simply being forwarded from another host. However, despite this, the server MAY elect not to post or forward the article if, after further examination of the article, it deems it inappropriate to do so. Reasons for such subsequent rejection of an article may include such problems as inappropriate newsgroups or distributions, disc space limitations, article lengths, garbled headers, and the like. These are typically restrictions enforced by the server host's news software and not necessarily the NNTP server itself.
The client SHOULD NOT assume that the article has been successfully transferred unless it receives an affirmative response from the server. A lack of response (such as a dropped network connection or a network timeout) SHOULD be treated the same as a 436 response.
Because some news server software may not be able immediately to determine whether or not an article is suitable for posting or forwarding, an NNTP server MAY acknowledge the successful transfer of the article (with a 235 response) but later silently discard it.
Example of successfully sending an article to another site:
[C] IHAVE <i.am.an.article.you.will.want@example.com>
[S] 335 Send it; end with <CR-LF>.<CR-LF>
[C] Path: pathost!demo!somewhere!not-for-mail
[C] From: "Demo User" <nobody@example.com>
[C] Newsgroups: misc.test
[C] Subject: I am just a test article
[C] Date: 6 Oct 1998 04:38:40 -0500
[C] Organization: An Example Com, San Jose, CA
[C] Message-ID: <i.am.an.article.you.will.want@example.com>
[C]
[C] This is just a test article.
[C] .
[S] 235 Article transferred OK
Example of sending an article to another site that rejects it. Note that the message-id in the IHAVE command is not the same as the one in the article headers; while this is bad practice and SHOULD NOT be done, it is not forbidden.
[C] IHAVE <i.am.an.article.you.will.want@example.com>
[S] 335 Send it; end with <CR-LF>.<CR-LF>
[C] Path: pathost!demo!somewhere!not-for-mail
[C] From: "Demo User" <nobody@example.com>
[C] Newsgroups: misc.test
[C] Subject: I am just a test article
[C] Date: 6 Oct 1998 04:38:40 -0500
[C] Organization: An Example Com, San Jose, CA
[C] Message-ID: <i.am.an.article.you.have@example.com>
[C]
[C] This is just a test article.
[C] .
[S] 437 Article rejected; don't send again
Example of sending an article to another site where the transfer fails:
[C] IHAVE <i.am.an.article.you.will.want@example.com>
[S] 335 Send it; end with <CR-LF>.<CR-LF>
[C] Path: pathost!demo!somewhere!not-for-mail
[C] From: "Demo User" <nobody@example.com>
[C] Newsgroups: misc.test
[C] Subject: I am just a test article
[C] Date: 6 Oct 1998 04:38:40 -0500
[C] Organization: An Example Com, San Jose, CA
[C] Message-ID: <i.am.an.article.you.will.want@example.com>
[C]
[C] This is just a test article.
[C] .
[S] 436 Transfer failed
Example of sending an article to a site that already has it:
[C] IHAVE <i.am.an.article.you.have@example.com>
[S] 435 Duplicate
Example of sending an article to a site that requests the article be tried again later:
[C] IHAVE <i.am.an.article.you.defer@example.com>
[S] 436 Retry later
| TOC |
This section lists other commands that may be used at any time between the beginning of a session and its termination. Using these commands does not alter any state information, but the response generated from their use may provide useful information to clients.
- Syntax
- DATE
- Responses
- 111 yyyymmddhhmmss server date and time
- Parameters
- yyyymmddHHmmss = Current UTC date and time on server
This command exists to help clients find out the current Coordinated Universal TimeInternational Telecommunications Union - Radio, Glossary, ITU-R Recommendation TF.686-1, October 1997.[TF.686-1] from the server's perspective. This command SHOULD NOT be used as a substitute for NTPMills, D., Network Time Protocol (Version 3) Specification, Implementation, March 1992.[RFC1305] but to provide information that might be useful when using the NEWNEWS command (see Section 7.4NEWNEWS). A system providing NNTP service SHOULD keep the system clock as accurate as possible, either with NTP or by some other method.
The server MUST return a 111 response specifying the date and time on the server in the form yyyymmddhhmmss. This date and time is in Coordinated Universal Time.
[C] DATE
[S] 111 19990623135624
- Syntax
- HELP
- Responses
- 100 Help text follows (multiline)
This command provides a short summary of commands that are understood by this implementation of the server. The help text will be presented as a multiline response following the 100 response code.
This text is not guaranteed to be in any particular format and MUST NOT be used by clients as a replacement for the LIST EXTENSIONS command described in Section 5.3LIST EXTENSIONS
[C] HELP
[S] 100 Help text follows
[S] This is some help text. There is no specific
[S] formatting requirement for this test, though
[S] it is customary for it to list the valid commands
[S] and give a brief definition of what they do
[S] .
- Syntax
- NEWGROUPS date time [GMT]
- Responses
- 231 List of new newsgroups follows (multiline)
- Parameters
- date = Date in yymmdd or yyyymmdd format
time = Time in hhmmss format
This command returns a list of newsgroups created on the server since the specified date and time. The results are in the same format as the LIST ACTIVE command (see Section 7.6.1LIST ACTIVE). However, they MAY include groups not available on the server (and so not returned by LIST ACTIVE) and MAY omit groups for which the creation date is not available. The results SHOULD be consistent with those of the LIST ACTIVE.TIMES commandLIST ACTIVE.TIMES, except that if the specified date and time is earlier than the oldest entry in the latter then the results of this command may include extra groups.
The date is specified as 6 or 8 digits in the format [xx]yymmdd, where xx is the first two digits of the year (19-99), yy is the last two digits of the year (00-99), mm is the month (01-12), and dd is the day of the month (01-31). Clients SHOULD specify all four digits of the year. If the first two digits of the year are not specified (this is supported only for backwards compatibility), the year is to be taken from the current century if yy is smaller than or equal to the current year, otherwise the year is from the previous century.
The time is specified as 6 digits in the format hhmmss, where hh is the hours in the 24-hour clock (00-23), mm is the minutes (00-59), and ss is the seconds (00-60, to allow for leap seconds). The token "GMT" specifies that the date and time are given in Coordinated Universal TimeInternational Telecommunications Union - Radio, Glossary, ITU-R Recommendation TF.686-1, October 1997.[TF.686-1]; if it is omitted then the date and time are specified in the server's local timezone. Note that there is no way using the protocol specified in this document to establish the server's local timezone.
Note that an empty list is a possible valid response and indicates that there are no new newsgroups since that date-time.
Clients SHOULD make all queries using Coordinated Universal Time (i.e. by including the "GMT" argument) when possible.
Example where there are new groups:
[C] NEWGROUPS 19990624 000000 GMT
[S] 231 list of new newsgroups follows
[S] alt.rfc-writers.recovery 4 1 y
[S] tx.natives.recovery 89 56 y
[S] .
Example where there are no new groups:
[C] NEWGROUPS 19990624 000000 GMT
[S] 231 list of new newsgroups follows
[S] .
- Syntax
- NEWNEWS wildmat date time [GMT]
- Responses
- 230 List of new articles follows (multiline)
- Parameters
- wildmat = Newsgroups of interest
date = Date in yymmdd or yyyymmdd format
time = Time in hhmmss format
This command returns a list of message-ids of articles posted or received on the server, in the newsgroups whose names match the wildmat, since the specified date and time. One message-id is sent on each line; the order of the response has no specific significance and may vary from response to response in the same session. A message-id MAY appear more than once; if it does so, it has the same meaning as if it appeared only once.
Date and time are in the same format as the NEWGROUPS command (see Section 7.3NEWGROUPS).
Note that an empty list is a possible valid response and indicates that there is currently no new news in the relevant groups.
Clients SHOULD make all queries in Coordinated Universal Time (i.e. by using the "GMT" argument) when possible.
Example where there are new articles:
[C] NEWNEWS news.*,sci.* 19990624 000000 GMT
[S] 230 list of new articles by message-id follows
[S] <i.am.a.new.article@example.com>
[S] <i.am.another.new.article@example.com>
[S] .
Example where there are no new articles:
[C] NEWNEWS alt.* 19990624 000000 GMT
[S] 230 list of new articles by message-id follows
[S] .
As described in Section 6Article posting and retrieval, each article has an arrival timestamp. Each newsgroup also has a creation timestamp. These timestamps are used by the NEWNEWS and NEWGROUP commands to construct their responses.
The DATE command MUST return a timestamp from the same clock as is used for determining article arrival and group creation times. This clock SHOULD be monotonic, and adjustments SHOULD be made by running it fast or slow compared to "real" time rather than by making sudden jumps.
Clients can ensure that they do not have gaps in lists of articles or groups by using the DATE command in the following manner:
- First session:
- Issue DATE command and record result
Issue NEWNEWS command using a previously chosen timestamp- Subsequent sessions:
- Issue DATE command and hold result in temporary storage
Issue NEWNEWS command using timestamp saved from previous session
Overwrite saved timestamp with that currently in temporary storage
In order to allow for minor errors, clients MAY want to adjust the timestamp back by two or three minutes before using it in NEWNEWS.
First session:
[C] DATE
[S] 111 20010203112233
[C] NEWNEWS local.chat 20001231 235959 GMT
[S] 230 list follows
[S] <article.1@local.service>
[S] <article.2@local.service>
[S] <article.3@local.service>
[S] .
Second session (the client has subtracted 3 minutes from the timestamp returned previously):
[C] DATE
[S] 111 20010204003344
[C] NEWNEWS local.chat 20010203 111933 GMT
[S] 230 list follows
[S] <article.3@local.service>
[S] <article.4@local.service>
[S] <article.5@local.service>
[S] .
Note how <article.3@local.service> arrived in the 3 minute gap and so is listed in both responses.
- Syntax
- LIST ACTIVE [wildmat]
- Responses
- 215 Information follows (multiline)
- Parameters
- wildmat = groups of interest
The LIST ACTIVE command with no arguments returns a list of valid newsgroups and associated information. The server MUST include every group that the client is permitted to select with the GROUPGROUP command. Each newsgroup is sent as a line of text in the following format:
- group high low status
where:
- "group"
- is the name of the newsgroup;
- "high"
- is the reported high water mark for the group;
- "low"
- is the reported low water mark for the group;
- "status"
- is the current status of the group on this server.
Each field in the line is separated from its neighbouring fields by one or more spaces.
Note that an empty list is a possible valid response, and indicates that there are currently no valid newsgroups.
The reported high and low water marks are as described in the GROUP command (see Section 6.1.1GROUP).
The status field is typically one of:
- "y"
- posting is permitted
- "n"
- posting is not permitted
- "m"
- postings will be forwarded to the newsgroup moderator
The server SHOULD use these values when these meanings are required and MUST NOT use them with any other meaning. Other values for the status may exist; the definition of these other values and the circumstances under which they are returned may be specified in an extension or may be private to the server. A client SHOULD treat an unrecognized status as giving no information.
The status of a newsgroup only indicates how posts to that newsgroup are normally processed and is not necessarily customised to the specific client. For example, if the current client is forbidden from posting, then this will apply equally to groups with status "y". Conversely, a client with special privileges (not defined by this specification) might be able to post to a group with status "n".
If the optional wildmat argument is specified, the response is limited to only the groups (if any) whose names match the wildmat. If no wildmat is specified, the keyword ACTIVE MAY be omitted without altering the effect of the command.
Example of LIST ACTIVE returning a list of newsgroups:
[C] LIST ACTIVE
[S] 215 list of newsgroups follows
[S] misc.test 3002322 3000234 y
[S] comp.risks 442001 441099 m
[S] alt.rfc-writers.recovery 4 1 y
[S] tx.natives.recovery 89 56 y
[S] tx.natives.recovery.d 11 9 n
[S] .
The same output on an implementation that includes leading zeroes:
[C] LIST ACTIVE
[S] 215 list of newsgroups follows
[S] misc.test 0003002322 0003000234 y
[S] comp.risks 0000442001 0000441099 m
[S] alt.rfc-writers.recovery 0000000004 0000000001 y
[S] tx.natives.recovery 0000000089 0000000056 y
[S] tx.natives.recovery.d 0000000011 0000000009 n
[S] .
Example of LIST ACTIVE omitting the second keyword and returning no newsgroups:
[C] LIST
[S] 215 list of newsgroups follows
[S] .
Example of LIST ACTIVE with a wildmat:
[C] LIST ACTIVE *.recovery
[S] 215 list of newsgroups follows
[S] alt.rfc-writers.recovery 4 1 y
[S] tx.natives.recovery 89 56 y
[S] .
- This command is optional.
- Syntax
- LIST ACTIVE.TIMES [wildmat]
- Responses
- 215 Information follows (multiline)
- Parameters
- wildmat = groups of interest
The active.times list is maintained by some news transfer systems to contain information about who created a particular newsgroup and when. Each line of this list consists of three fields separated from each other by one or more spaces. The first field is the name of the newsgroup. The second is the time when this group was created on this news server, measured in seconds since the start of January 1, 1970. The third is plain text intended to describe the entity that created the newsgroup; it is often a mailbox as defined in RFC 2822Resnick, P., Internet Message Format, April 2001.[RFC2822].
The list MAY omit newsgroups for which the information is unavailable and MAY include groups not available on the server; in particular, it MAY omit all groups created before the date and time of the oldest entry. The client MUST NOT assume that the list is complete or that it matches the list returned by LIST ACTIVE. The NEWGROUPS commandNEWGROUPS may provide a better way to access this information and the results of the two commands SHOULD be consistent (subject to the caveats in the description of that command).
If the information is available, it is returned as a multi-line response following the 215 response code. If the optional wildmat argument is specified, the response is limited to only the groups (if any) whose names match the wildmat and for which the information is available.
Note that an empty list is a possible valid response (whether or not a wildmat is specified) and indicates that there are no groups meeting the above criteria.
Example of LIST ACTIVE.TIMES returning a list of newsgroups:
[C] LIST ACTIVE.TIMES
[S] 215 information follows
[S] misc.test 930445408 <creatme@isc.org>
[S] alt.rfc-writers.recovery 930562309 <m@example.com>
[S] tx.natives.recovery 930678923 <sob@academ.com>
[S] .
Example of LIST ACTIVE.TIMES returning an error where the command is recognized but the software does not maintain this information:
[C] LIST ACTIVE.TIMES
[S] 503 program error, function not performed
Example of LIST ACTIVE.TIMES sent to a server that does not recognize this command:
[C] LIST ACTIVE.TIMES
[S] 501 Syntax Error
- This command is optional.
- Syntax
- LIST DISTRIBUTIONS
- Responses
- 215 Information follows (multiline)
The distributions list is maintained by some news transfer systems to contain information about valid values for the content of the Distribution header in a news article and about what the various values mean. Each line of this list consists of two fields separated from each other by one or more spaces. The first field is a value and the second is a short explanation of the meaning of that value.
If the information is available, it is returned as a multi-line response following the 215 response code.
Example of LIST DISTRIBUTIONS returning a list of distributions:
[C] LIST DISTRIBUTIONS
[S] 215 information follows
[S] usa United States of America
[S] na North America
[S] world All over the World
[S] .
Example of LIST DISTRIBUTIONS returning an error where the command is recognized but the software does not maintain this information:
[C] LIST DISTRIBUTIONS
[S] 503 program error, function not performed
Example of LIST DISTRIBUTIONS sent to a server that does not recognize this command:
[C] LIST DISTRIBUTIONS
[S] 501 Syntax Error
- This command is optional.
- Syntax
- LIST DISTRIB.PATS
- Responses
- 215 Information follows (multiline)
The distrib.pats list is maintained by some news transfer systems to choose a value for the content of the Distribution header of a news article being posted. Each line of this list consists of three fields separated from each other by a colon (":"). The first field is a weight, the second field is a wildmat (which may be a simple group name), and the third field is a value for the Distribution header content.
The client MAY use this information to construct an appropriate Distribution header given the name of a newsgroup. To do so, it should determine the lines whose second field matches the newsgroup name, select from among them the line with the highest weight (with 0 being the lowest), and use the value of the third field to construct the Distribution header.
If the information is available, it is returned as a multi-line response following the 215 response code.
Example of LIST DISTRIB.PATS returning a list of newsgroups:
[C] LIST DISTRIB.PATS
[S] 215 information follows
[S] 10:local.*:local
[S] 5:*:world
[S] 20:local.here.*:thissite
[S] .
Example of LIST DISTRIB.PATS returning an error where the command is recognized but the software does not maintain this information:
[C] LIST DISTRIB.PATS
[S] 503 program error, function not performed
Example of LIST DISTRIB.PATS sent to a server that does not recognize this command:
[C] LIST DISTRIB.PATS
[S] 501 Syntax Error
- This command is optional.
- Syntax
- LIST NEWSGROUPS [wildmat]
- Responses
- 215 Information follows (multiline)
- Parameters
- wildmat = groups of interest
The newsgroups list is maintained by some news transfer systems to contain the name of each newsgroup that is available on the server and a short description about the purpose of the group. Each line of this list consists of two fields separated from each other by one or more space or TAB characters (usual practice is a single TAB). The first field is the name of the newsgroup and the second is a short description of the group.
The list MAY omit newsgroups for which the information is unavailable and MAY include groups not available on the server. The client MUST NOT assume that the list is complete or that it matches the list returned by LIST ACTIVE.
If the information is available, it is returned as a multi-line response following the 215 response code. If the optional wildmat argument is specified, the response is limited to only the groups (if any) whose names match the wildmat and for which the information is available.
Note that an empty list is a possible valid response (whether or not a wildmat is specified) and indicates that there are no groups meeting the above criteria.
Example of LIST NEWSGROUPS returning a list of newsgroups:
[C] LIST NEWSGROUPS
[S] 215 information follows
[S] misc.test General Usenet testing
[S] alt.rfc-writers.recovery RFC Writers Recovery
[S] tx.natives.recovery Texas Natives Recovery
[S] .
Example of LIST NEWSGROUPS returning an error where the command is recognized but the software does not maintain this information:
[C] LIST NEWSGROUPS
[S] 503 program error, function not performed
Example of LIST NEWSGROUPS sent to a server that does not recognize this command:
[C] LIST NEWSGROUPS
[S] 501 Syntax error
| TOC |
Although NNTP is widely and robustly deployed, some parts of the Internet community might wish to extend the NNTP service. This document defines a means whereby an extended NNTP client can query the server to determine the service extensions that it supports.
It must be emphasized that any extension to the NNTP service should not be considered lightly. NNTP's strength comes primarily from its simplicity. Experience with many protocols has shown that:
Protocols with few options tend towards ubiquity, whilst protocols with many options tend towards obscurity.
This means that each and every extension, regardless of its benefits, must be carefully scrutinized with respect to its implementation, deployment, and interoperability costs. In many cases, the cost of extending the NNTP service will likely outweigh the benefit.
Given this environment, the framework for extensions described in this document consists of:
The LIST EXTENSIONS command is described in this document (see Section 5.3LIST EXTENSIONS) and is the mechanism for clients to use to determine what extensions are available. Except where stated otherwise, the commands in this document are understood (even if not supported) by all servers and are not described in the list of features returned by the LIST EXTENSIONS command.
The IANA shall maintain a registry of NNTP service extensions.
An extension is identified by a unique extension-label, which is a string of 1 to 12 uppercase US-ASCII letters. The extension-label will often be the name of a new command that the extension adds. However this is not a requirement: an extension might not add any new commands or keywords.
An extension is either a private extension or else it is included in the IANA registry and is defined in an RFC (in which case it is a "standard extension" or "registered extension"). Such RFCs either must be on the standards track or must define an IESG-approved experimental protocol.
The definition of an extension must include:
A private extension need not be included in the output of LIST EXTENSIONS. A server MAY provide additional keywords - for new commands and also for new variants of existing commands - as part of a private extension. To avoid the risk of a clash with a future registered extension, the names of private extensions and commands defined by them SHOULD begin with "X" and MUST NOT be the same as the name of a registered extension.
If the server provides a registered extension (indicated by listing it in the output of LIST EXTENSIONS), it MUST implement all of the commands in the specification of the extension except for those marked as optional. If it does not implement the extension as specified, it MUST NOT list the extension in the output of LIST EXTENSIONS under its registered name; in this case it MAY, but SHOULD NOT, provide a private extension (not listed, or listed with a different name) that implements part of the extension or implements the commands of the extension with a different meaning.
A server MUST NOT send different response codes to basic NNTP commands documented here or commands documented in registered extensions in response to the availability or use of a private extension.
The IANA's initial registry of NNTP service extensions consists of these entries:
| Extension | Label | Added behaviour |
|---|---|---|
| Specific article numbers | LISTGROUP | Defined in this document |
| Overview support | OVER | Defined in this document |
| Batched header retrieval | HDR | Defined in this document |
N.B. while these extensions are standard extensions, the term includes all extensions in the IANA registry, not just these three.
Each of the following sections describes an extension that a server MAY provide. If the server provides the extension, it MUST include the appropriate extension label in the response to LIST EXTENSIONS. If it does not provide it, it MUST NOT include the appropriate extension label. The descriptions of facilities in each section are written as if the extension is provided. If it is not provided, the entire section should be ignored.
The formal definitions of these extensions are provided in Appendix DFormal specification of the standard extensions.
This extension provides one command and has the extension label LISTGROUP.
- Syntax
- LISTGROUP [group]
- Responses
- 211 number low high group Article numbers follow (multiline)
411 No such newsgroup
412 No newsgroup selected [1]- Parameters
- group = name of newsgroup
number = estimated number of articles in the group
low = reported low water mark
high = reported high water mark- [1]
- The 412 response can only occur if no group has been specified.
The LISTGROUP command is used to get a listing of all the article numbers in a particular newsgroup. As a side effect, it also selects the group in the same way as the GROUP command (see Section 6.1.1GROUP).
The optional argument is the name of the newsgroup to be selected (e.g. "news.software.misc"). A list of valid newsgroups may be obtained from the LIST ACTIVE command. If no group is specified, the current selected newsgroup is used.
On success, the list of article numbers is returned as a multi-line response following the 211 response code (the arguments on the initial response line are the same as for the GROUP command. The list contains one number per line, is in numerical order, and lists precisely those articles that exist in the group.
When a valid group is selected by means of this command, the current selected newsgroup MUST be set to that group and the current article number MUST be set to the first article in the group. If an empty newsgroup is selected, the current article pointer is made invalid. If an invalid group is specified, the current selected newsgroup and current article number MUST NOT be changed.
The LISTGROUP command MAY be used by a client as a replacement for the GROUP command in establishing a valid current selected newsgroup and current article number.
If the group specified is not available on the server, a 411 response MUST be returned. If no group is specified and the current selected newsgroup is invalid, a 412 response MUST be returned.
Example of LISTGROUP on an empty group:
[C] LISTGROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup list follows
[S] .
Example of LISTGROUP on a valid current selected newsgroup:
[C] GROUP misc.test
[S] 211 2000 3000234 3002322 misc.test
[C] LISTGROUP
[S] 211 2000 3000234 3002322 misc.test list follows
[S] 3000234
[S] 3000237
[S] 3000238
[S] 3000239
[S] 3002322
[S] .
Example of LISTGROUP failing because no group has been selected:
[Assumes current selected newsgroup is invalid.]
[C] LISTGROUP
[S] 412 no current group
[C] GROUP example.is.sob.bradner.or.barber
[S] 411 no such group
[C] LISTGROUP
[S] 412 no current group
The OVER and HDR extensions refer to the concept of "article metadata". This is data about articles that does not occur within the article itself. Each metadata item has a name which MUST begin with a colon (and which MUST NOT contain a colon elsewhere within it). As with header names, metadata item names are not case-sensitive.
When generating a metadata item, the server MUST compute it for itself and MUST NOT trust any related value provided in the article. (In particular, a Lines or Bytes header in the article MUST NOT be assumed to specify the correct number of lines or bytes in the article.) If the server has access to several non-identical copies of an article, the value returned MUST be correct for any copy of that article retrieved during the same session.
This specification defines two metadata items: ":bytes" and ":lines". Other metadata items may be defined by extensions. The names of metadata items defined by registered extensions MUST NOT begin with ":x-". To avoid the risk of a clash with a future registered extension, the names of metadata items defined by private extensions SHOULD begin with ":x-".
The :bytes metadata item for an article is a decimal integer. It SHOULD equal the number of octets in the entire article - headers, body, and separating empty line (counting a CRLF pair as two octets, and excluding both the "." CRLF terminating the response and any "." added for "byte-stuffing" purposes).
Note to client implementers: some existing servers return a value different to that above. The commonest reasons for this are:
Implementations should be prepared for such variation and MUST NOT rely on the value being accurate.
The :lines metadata item for an article is a decimal integer. It MUST equal the number of lines in the article body (excluding the empty line separating headers and body); equivalently, it is two less than the number of CRLF pairs that the BODY command would return for that article (the extra two are those following the response code and the termination octet).
This extension provides two commands, OVER and LIST OVERVIEW.FMT. The label for this extension is OVER.
The OVER extension provides access to the "overview database", which is a database of headers extracted from incoming articles. Only certain headers are included in the database. The database also includes some article metadata.
The information stored in the database may change over time. If the database records the content or absence of a given field (that is, a header or metadata item) for all articles, it is said to be "consistent" for that field. If it records the content of a header for some articles but not for others that nevertheless included that header, or records a metadata item for some articles but not others to which that item applies, it is said to be "inconsistent" for that field.
The LIST OVERVIEW.FMT command SHOULD list all the fields for which the database is consistent at that moment. It MAY omit such fields (for example if it is not known whether the database is consistent or inconsistent). It MUST NOT include fields for which the database is inconsistent or which are not stored in the database. Therefore if a header appears in the LIST OVERVIEW.FMT output but not the OVER output for a given article, that header does not appear in the article, and similarly for metadata items.
These rules assume the fields being stored in the database remain constant for long periods of time, with the database therefore being consistent. When the set of fields to be stored is changed, it will be inconsistent until either the database is rebuilt or the only articles remaining are those received since the change. Therefore the output from LIST OVERVIEW.FMT needs to be altered twice: before any fields stop being stored, they MUST be removed from the output, then when the database is once more known to be consistent, the new fields SHOULD be added to the output.
Support for the message-id form of the OVER command is optional. If an implementation supports this form, it MUST use the argument "MSGID" following the extension label in the output of LIST EXTENSIONS; if not, it MUST NOT use any argument.
This extension is based on the Overview/NOV databaseRobertson, R., FAQ: Overview database / NOV General Information, January 1995.[ROBE1995] developed by Geoff Collyer.
- Syntax
- OVER message-id
OVER range
OVER- Responses
- First form (message-id specified)
- 224 Overview information follows (multiline)
430 No article with that message-id- Second form (range specified)
- 224 Overview information follows (multiline)
412 No newsgroup selected
423 No articles in that range- Third form (current article number used)
- 224 Overview information follows (multiline)
412 No newsgroup selected
420 Current article number is invalid- Parameters
- range = number(s) of articles
message-id = message-id of article
The OVER command returns the contents of the headers and metadata in the database for an article specified by message-id, or from a specified article or range of articles in the current selected newsgroup.
The message-id argument indicates a specific article. The range argument may be any of the following:
If neither is specified, the current article number is used. Support for the first (message-id) form is optional. If it is not supported, the generic response code 503 MUST be returned.
If the information is available, it is returned as a multi-line response following the 224 response code and contains one line per article, sorted in numerical order of article number (note that unless the argument is a range including a dash, there will only be one line but it will still be in multi-line format). Each line consists of a number of fields separated by a TAB. A field may be empty (in which case there will be two adjacent TABs), and a sequence of trailing TABs may be omitted.
The first 8 fields MUST be the following, in order:
"0" or article number (see below)
Subject header content
From header content
Date header content
Message-ID header content
References header content
:bytes metadata item
:lines metadata item
If the article is specified by message-id (the first form of the command), the article number MUST be replaced with zero, except that if there is a current selected group and the article is present in that group, the server MAY use that article number (see the ARTICLE commandARTICLE and STAT examplesExamples for more details). In the other two forms of the command, the article number MUST be returned.
Any subsequent fields are the contents of the other headers and metadata held in the database.
For the five mandatory headers, the content of each field MUST be based on the content of the header (that is, with the header name and following colon and space removed). If the article does not contain that header, or if the content is empty, the field MUST be empty. For the two mandatory metadata items, the content of the field MUST be just the value, with no other text.
For all subsequent fields that contain headers, the content MUST be the entire header line other than the trailing CRLF. For all subsequent fields that contain metadata, the field consists of the metadata name, a single space, and then the value.
For all fields, the value is processed by first removing all CRLF pairs (that is, undoing any folding and removing the terminating CRLF) and then replacing each TAB with a single space. If there is no such header in the article, or no such metadata item, or no header or item stored in the database for that article, the corresponding field MUST be empty.
Note that, after unfolding, the characters NUL, LF, and CR cannot occur in the header of an article offered by a conformant server. Nevertheless, servers SHOULD check for these characters and replace each one by a single space (so that, for example, CR LF LF TAB will become two spaces, since the CR and first LF will be removed by the unfolding process). This will encourage robustness in the face of non-conforming data; it is also possible that future versions of this specification could permit these characters to appear in articles.
The server SHOULD NOT produce output for articles that no longer exist.
If the argument is a message-id and no such article exists, a 430 response MUST be returned. If the argument is a range or is omitted and the current selected newsgroup is invalid, a 412 response MUST be returned. If the argument is a range and no articles in that number range exist in the current selected newsgroup, a 423 response MUST be returned. If the argument is omitted and the current article number is invalid, a 420 response MUST be returned.
In the first three examples, TAB has been replaced by vertical bar and some lines have been folded for readability.
Example of a successful retrieval of overview information for an article (using no article number):
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] OVER
[S] 224 Overview information follows
[S] 300234|I am just a test article|"Demo User"
<nobody@example.com>|6 Oct 1998 04:38:40 -0500|
<45223423@example.com>|<45454@example.net>|1234|
17|Xref: news.example.com misc.test:3000363
[S] .
Example of a successful retrieval of overview information for an article by message-id:
[C] LIST EXTENSIONS
[S] 202 extensions supported:
[S] OVER MSGID
[S] .
[C] OVER <45223423@example.com>
[S] 224 Overview information follows
[S] 0|I am just a test article|"Demo User"
<nobody@example.com>|6 Oct 1998 04:38:40 -0500|
<45223423@example.com>|<45454@example.net>|1234|
17|Xref: news.example.com misc.test:3000363
[S] .
Note that the article number has been replaced by "0".
Example of the same commands on a system that does not implement retrieval by message-id:
[C] LIST EXTENSIONS
[S] 202 extensions supported:
[S] OVER
[S] .
[C] OVER <45223423@example.com>
[S] 503 Overview by message-id unsupported
Example of a successful retrieval of overview information for a range of articles:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] OVER 3000234-3000240
[S] 224 Overview information follows
[S] 300234|I am just a test article|"Demo User"
<nobody@example.com>|6 Oct 1998 04:38:40 -0500|
<45223423@example.com>|<45454@example.net>|1234|
17|Xref: news.example.com misc.test:3000363
[S] 3000235|Another test article|nobody@nowhere.to
(Demo User)|6 Oct 1998 04:38:45 -0500|<45223425@to.to>||
4818|37||Distribution: fi
[S] 3000238|Re: I am just a test article|somebody@elsewhere.to|
7 Oct 1998 11:38:40 +1200|<kfwer3v@elsewhere.to>|
<45223423@to.to>|9234|51
[S] .
Note the missing "References" and Xref headers in the second line, the missing trailing field(s) in the first and last lines, and that there are only results for those articles that still exist.
Example of an unsuccessful retrieval of overview information on an article by number:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] OVER 300256
[S] 423 No such article in this group
Example of an unsuccessful retrieval of overview information by number because no newsgroup was selected first:
[Assumes current selected newsgroup is invalid.]
[C] OVER
[S] 412 No newsgroup selected
Example of an attempt to retrieve information when the current selected newsgroup is empty:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] OVER
[S] 420 No current article selected
- This command is optional.
- Syntax
- LIST OVERVIEW.FMT
- Responses
- 215 Information follows (multiline)
The LIST OVERVIEW.FMT command returns a description of the fields in the database for which it is consistent (as described above).
If the information is available, it is returned as a multi-line response following the 215 response code. The information contains one line per field in the order they are returned by the OVER command; the first 7 lines MUST (except for the case of letters) be exactly:
Subject:
From:
Date:
Message-ID:
References:
:bytes
:lines
except that, for compatibility with existing implementations, the last two lines MAY instead be:
Bytes:
Lines:
even though they refer to metadata, not headers.
All subsequent lines MUST consist of either a header name followed by ":full", or the name of a piece of metadata.
There are no leading or trailing spaces in the output.
Note that the 7 fixed lines describe the 2nd to 8th fields of the OVER output. The "full" suffix (which may use either uppercase, lowercase, or a mix) is a reminder that the corresponding fields include the header name.
This command MAY generate different results if used more than once in a session.
Example of LIST OVERVIEW.FMT output corresponding to the example OVER output above, using the preferred format:
[C] LIST OVERVIEW.FMT
[S] 215 Order of fields in overview database.
[S] Subject:
[S] From:
[S] Date:
[S] Message-ID:
[S] References:
[S] :bytes
[S] :lines
[S] Xref:full
[S] Distribution:full
[S] .
Example of LIST OVERVIEW.FMT output corresponding to the example OVER output above, using the alternative format:
[C] LIST OVERVIEW.FMT
[S] 215 Order of fields in overview database.
[S] Subject:
[S] From:
[S] Date:
[S] Message-ID:
[S] References:
[S] Bytes:
[S] Lines:
[S] Xref:FULL
[S] Distribution:FULL
[S] .
Example of LIST OVERVIEW.FMT returning an error where the command is recognized but the software does not maintain this information:
[C] LIST OVERVIEW.FMT
[S] 503 overview.fmt not available
This extension provides two new commands: HDR and LIST HEADERS. The label for this extension is HDR.
The HDR extension provides access to specific headers and metadata items (collectively "fields") of articles or groups of articles. In the case of headers, an implementation MAY restrict the use of this extension to a specific list of headers or MAY allow it to be used with any header; it may behave differently when the HDR command is used with a message-id argument and when it is used with a range or no argument.
The HDR command may take information from a database rather than directly from the articles. If so, the same issues of consistency and inconsistency apply as with the OVER extensionThe OVER extension and the LIST HEADERS command SHOULD take the same approach as the LIST OVERVIEW.FMT command in resolving them.
- Syntax
- HDR header message-id
HDR header range
HDR header- Responses
- First form (message-id specified)
- 225 Headers follow (multiline)
430 No article with that message-id- Second form (range specified)
- 225 Headers follow (multiline)
412 No newsgroup selected
423 No articles in that range- Third form (current article number used)
- 225 Headers follow (multiline)
412 No newsgroup selected
420 Current article number is invalid- Parameters
- header = name of header, without the colon
range = number(s) of articles
message-id = message-id of article
The HDR command retrieves specific headers from an article specified by message-id, or from a specified article or range of articles in the current selected newsgroup. It can also return certain metadata about the article or articles.
The required header argument is the name of a header (e.g. "subject") in an article, or the name of a metadata item, and is case-insensitive. Names of metadata items always begin with a colon. Except where stated otherwise, metadata items are treated as if they were header contents, and references to headers in this description apply equally to metadata items.
The message-id argument indicates a specific article. The range argument may be any of the following:
If neither is specified, the current article number is used.
If the information is available, it is returned as a multi-line response following the 225 response code and contains one line for each article in the range that exists (note that unless the argument is a range including a dash, there will be at most one line but it will still be in multi-line format). The line consists of the article number, a space, and then the contents of the header or metadata item. In the case of a header, the header name, colon, and the first space after the colon are all omitted.
If the article is specified by message-id (the first form of the command), the article number MUST be replaced with zero, except that if there is a current selected group and the article is present in that group, the server MAY use that article number (see the ARTICLE commandARTICLE and STAT examplesExamples for more details). In the other two forms of the command, the article number MUST be returned.
Header contents are modified as follows: all CRLF pairs are removed, and then each TAB is replaced with a single space (note that this is the same transformation as is performed by the OVER extensionDescription, and the same comment concerning NUL, CR, and LF applies).
The header content is in all cases taken from the article. This means that, for example, a request for the header "Lines" returns the contents of the "Lines" header of the specified articles, if any, not the line count metadata or any other server-generated value. If the header occurs in a given article multiple times, only the content of the first occurrence is returned by HDR.
If the requested header is not present in the article or if it is present but empty, a line for that article is included in the output but the header content portion of the line is empty (the space after the article number MAY be retained or omitted). If any article number in the provided range does not exist in the group, no line for that article number is included in the output.
If the second argument is a message-id and no such article exists, a 430 response MUST be returned. If the second argument is a range or is omitted and the current selected newsgroup is invalid, a 412 response MUST be returned. If the second argument is a range and no articles in that number range exist in the current selected newsgroup, a 423 response MUST be returned. If the second argument is omitted and the current article number is invalid, a 420 response MUST be returned.
A server MAY only allow HDR commands for a limited set of headers and metadata items; it may behave differently in this respect for the first (message-id) form than for the other forms. If so, it MUST respond with the generic 503 response to attempts to request other headers, rather than returning erroneous results such as a successful empty response.
If HDR uses a separate database and it is inconsistent for the requested header or metadata item, the server MAY return what results it can or it MAY respond with the generic 503 response; in the latter case, the field MUST NOT appear in the output from LIST HEADERS.
Example of a successful retrieval of subject lines from a range of articles (3000235 has no Subject header, and 3000236 is missing):
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HDR Subject 3000234-300238
[S] 225 Headers follow
[S] 3000234 I am just a test article
[S] 3000235
[S] 3000237 Re: I am just a test article
[S] 3000238 Ditto
[S] .
Example of a successful retrieval of line counts from a range of articles:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HDR :lines 3000234-300238
[S] 225 Headers follow
[S] 3000234 42
[S] 3000235 5
[S] 3000237 11
[S] 3000238 2378
[S] .
Example of a successful retrieval of the subject line from an article by message-id:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HDR subject <i.am.a.test.article@example.com>
[S] 225 Header information follows
[S] 0 I am just a test article
[S] .
Example of a successful retrieval of the subject line from the current article:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HDR subject
[S] 225 Header information follows
[S] 3000234 I am just a test article
[S] .
Example of an unsuccessful retrieval of a header from an article by message-id:
[C] HDR subject <i.am.not.there@example.com>
[S] 430 No Such Article Found
Example of an unsuccessful retrieval of headers from articles by number because no newsgroup was selected first:
[Assumes current selected newsgroup is invalid.]
[C] HDR subject 300256-
[S] 412 No newsgroup selected
Example of an unsuccessful retrieval of headers because the current selected newsgroup is empty:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] HDR subject 1-
[S] 423 No articles in that range
Example of an unsuccessful retrieval of headers because the server does not allow HDR commands for that header:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HDR Content-Type 3000234-300238
[S] 503 HDR not permitted on Content-Type
- Syntax
- LIST HEADERS [MSGID|RANGE]
- Responses
- 215 Header and metadata list follows (multiline)
- Parameters
- MSGID = requests list for access by message-id
RANGE = requests list for access by range
The LIST HEADERS command returns a list of headers and metadata items that may be retrieved using the HDR command.
The information is returned as a multi-line response following the 215 response code and contains one line for each header or metadata item name (excluding the colon in the former case). If the implementation allows any header to be retrieved, it MUST NOT include any header names in the list but MUST include the special entry ":" (a single colon on its own); it MUST still list any metadata items that are available. The order of items in the list is not significant; the server need not even consistently return the same order. The list MAY be empty (though in this circumstance there is little point in providing the extension).
An implementation that also supports the OVER extension SHOULD at least permit all the headers and metadata items listed in the output from the LIST OVERVIEW.FMT command.
If the server treats the first form of the HDR command (message-id specified) differently to the other two forms (range specified or current article number used) in respect of which headers or metadata items are available, then:
If the server does not treat the various forms differently, then it MUST always produce the same results and ignore any argument.
Example of an implementation providing access to only a few headers:
[C] LIST HEADERS
[S] 215 headers supported:
[S] Subject
[S] Message-ID
[S] Xref
[S] .
Example of an implementation providing access to the same fields as the first example in Section 8.5.2.3Examples:
[C] LIST EXTENSIONS
[S] 202 extensions supported:
[S] OVER
[S] HDR
[S] .
[C] LIST HEADERS
[S] 215 headers and metadata items supported:
[S] Date
[S] Distribution
[S] From
[S] Message-ID
[S] References
[S] Subject
[S] Xref
[S] :bytes
[S] :lines
[S] .
Example of an implementation providing access to all headers:
[C] LIST HEADERS
[S] 215 metadata items supported:
[S] :
[S] :lines
[S] :bytes
[S] :x-article-number
[S] .
Example of an implementation distinguishing the first form of the HDR command from the other two forms:
[C] LIST HEADERS RANGE
[S] 215 metadata items supported:
[S] :
[S] :lines
[S] :bytes
[S] .
[C] LIST HEADERS MSGID
[S] 215 headers and metadata items supported:
[S] Date
[S] Distribution
[S] From
[S] Message-ID
[S] References
[S] Subject
[S] :lines
[S] :bytes
[S] :x-article-number
[S] .
[C] LIST HEADERS
[S] 215 headers and metadata items supported:
[S] Date
[S] Distribution
[S] From
[S] Message-ID
[S] References
[S] Subject
[S] :lines
[S] :bytes
[S] .
Note how :x-article-number does not appear in the last set of output.
| TOC |
Each of the following sections describes the syntax of a major element of NNTP. This syntax extends and refines the descriptions elsewhere in this specification, and should be given precedence when resolving apparent conflicts. Note that ABNFCrocker, D. and P. Overell, Augmented BNF for Syntax Specifications: ABNF, November 1997.[RFC2234] strings are case-insensitive. Non-terminals used in several places are defined in a separate section at the end.
The non-terminals "command-line", "command-continuation", and "response" between them specify the text that flows between client and server. For each command, the sequence is:
This syntax defines the non-terminal "command-line", which represents what is sent from the client to the server.
command-line = command EOL
command = article-command /
body-command /
date-command /
group-command /
hdr-command /
head-command /
help-command /
ihave-command /
last-command /
list-active-command /
list-active-times-command /
list-distrib-pats-command /
list-distributions-command /
list-extensions-command /
list-headers-command /
list-newsgroups-command /
list-overview-fmt-command /
listgroup-command /
mode-reader-command /
newgroups-command /
newnews-command /
next-command /
over-command /
post-command /
quit-command /
stat-command /
x-command
article-command = "ARTICLE" [article-ref]
body-command = "BODY" [article-ref]
date-command = "DATE"
group-command = "GROUP" WS newsgroup-name
hdr-command = "HDR" WS header-meta-name [range-ref]
head-command = "HEAD" [article-ref]
help-command = "HELP"
ihave-command = "IHAVE" WS message-id
last-command = "LAST"
list-active-command = "LIST" [WS "ACTIVE" [WS wildmat]]
list-active-times-command = "LIST" WS "ACTIVE.TIMES" [WS wildmat]
list-distrib-pats-command = "LIST" WS "DISTRIB.PATS"
list-distributions-command = "LIST" WS "DISTRIBUTIONS"
list-extensions-command = "LIST" WS "EXTENSIONS"
list-headers-command = "LIST" WS "HEADERS" WS ["MSGID" / "RANGE"]
list-newsgroups-command = "LIST" WS "NEWSGROUPS" [WS wildmat]
list-overview-fmt-command = "LIST" WS "OVERVIEW.FMT"
listgroup-command = "LISTGROUP" [WS newsgroup-name]
mode-reader-command = "MODE" WS "READER"
newgroups-command = "NEWGROUPS" WS date-time
newnews-command = "NEWNEWS" WS wildmat WS date-time
next-command = "NEXT"
over-command = "OVER" [WS range-ref]
post-command = "POST"
quit-command = "QUIT"
stat-command = "STAT" [article-ref]
x-command = x-command-name *(WS x-argument)
; This is the generic syntax for an extension command.
; Each extension command is specified fully elsewhere
article-ref = WS (article-number / message-id)
date = date2y / date4y
date4y = 4DIGIT 2DIGIT 2DIGIT
date2y = 2DIGIT 2DIGIT 2DIGIT
date-time = date WS time [WS "GMT"]
header-meta-name = header-name / metadata-name
metadata-name = ":" 1*A-NOTCOLON
range = article-number ["-" [article-number]]
range-ref = WS (range / message-id)
time = 2DIGIT 2DIGIT 2DIGIT
x-command-name = 3*12A-CHAR
x-argument = 1*P-CHAR
This syntax defines the further material sent by the client in the case of multi-stage commands.
command-continuation = ihave-continuation /
post-continuation
ihave-continuation = encoded-article
post-continuation = encoded-article
encoded-article = content-lines termination
; after undoing the "byte-stuffing", this MUST match "article"
This syntax defines the non-terminal "response", which represents the generic form of responses - that is, what is sent from the server to the client in response to a command or a command-continuation.
response = simple-response / multiline-response
multiline-response = simple-response content-lines termination
simple-response =
simple-response-content [SP trailing-comment] CRLF
simple-response-content = 3DIGIT arguments
trailing-comment = *U-CHAR
arguments = *(SP argument) ; How many depends on the response
argument = 1*A-CHAR
This syntax defines the specific initial response lines for the various commands and extensions in this specification. Only those response codes with arguments are listed.
simple-response-content =/ response-111-content
response-211-content
response-22x-content
response-401-content
response-111-content = "111" SP date4y time
response-211-content = "211" 3(SP article-number) SP newsgroup-name
response-22x-content = ("220" / "221" / "222" / "223")
SP article-number SP message-id
response-401-content = "401" SP extension-label
This syntax defines the content of the various multi-line responses (more precisely, the part of the response in "content-lines"), in each case after any "byte-stuffing" has been undone.
multiline-response-content = article-response /
body-response /
hdr-response /
head-response /
help-response /
list-active-response /
list-active-times-response /
list-distrib-pats-response /
list-distributions-response /
list-extensions-response /
list-headers-response /
list-newsgroups-response /
list-overview-fmt-response /
listgroup-response /
newgroups-response /
newnews-response /
over-response
article-response = article
body-response = body
hdr-response = *(article-number SP hdr-content CRLF)
head-response = 1*header
help-response = *(*B-CHAR CRLF)
list-active-response = *(newsgroup-name SPA article-number
SPA article-number SPA newsgroup-status CRLF)
list-active-times-response =
*(newsgroup-name SPA 1*DIGIT SPA newsgroup-creator CRLF)
list-distrib-pats-response =
*(1*DIGIT ":" wildmat ":" distribution CRLF)
list-distributions-response =
*(distribution SPA distribution-description CRLF)
list-extensions-response =
*(extension-descriptor CRLF)
list-headers-response = *(header-meta-name CRLF) /
*((metadata-name / ":") CRLF)
list-newsgroups-response =
*(newsgroup-name WS newsgroup-description CRLF)
list-overview-fmt-response = list-overview-fmt-text
listgroup-response = *(article-number CRLF)
newgroups-response = list-active-response
newnews-response = *(message-id CRLF)
over-response = *(article-number over-content CRLF)
list-overview-fmt-text =
"Subject:" CRLF
"From:" CRLF
"Date:" CRLF
"Message-ID:" CRLF
"References:" CRLF
( ":bytes" CRLF ":lines" / "Bytes:" CRLF "Lines:") CRLF
*((header-name ":full" / metadata-name) CRLF)
distribution = 1*P-CHAR
distribution-description = U-TEXT
hdr-content = *S-NONTAB
hdr-n-content = [(header-name ":" / metadata-name) SP hdr-content]
newsgroup-creator = U-TEXT
newsgroup-description = S-TEXT
newsgroup-status = %x79 / %x6E / %x6D / private-status
over-content = 1*6(TAB hdr-content) /
7(TAB hdr-content) *(TAB hdr-n-content)
private-status = 1*P-CHAR ; except the values in newsgroup-status
This syntax defines the generic form of a LIST EXTENSIONS response line.
extension-argument = 1*P-CHAR
extension-descriptor = extension-generic-descriptor
extension-generic-descriptor =
extension-label *(SPA extension-argument)
extension-label = 1*12UPPER
This syntax defines the specific LIST EXTENSIONS response lines for the various extensions in this specification.
extension-descriptor =/ hdr-extension /
listgroup-extension /
over-extension
hdr-extension = %x48.44.52 ; "HDR"
listgroup-extension = %x4C.49.53.54.47.52.4F.55.50 ; "LISTGROUP"
over-extension = %x4F.56.45.52 [SPA "MSGID"] ; "OVER"
This syntax defines the non-terminal "article", which represents the format of an article as described in Section 3.4Articles.
article = 1*header CRLF body header = header-name ":" [CRLF] SP header-content CRLF header-content = *(S-CHAR / [CRLF] WS) body = *(*B-CHAR CRLF)
These non-terminals are used at various places in the syntax and are collected here for convenience. A few of these non-terminals are not used in this specification but are provided for the consistency and convenience of extension authors.
article-number = 1*16DIGIT
content-lines = *([content-text] CRLF)
content-text = (".." / B-NONDOT) *B-CHAR
header-name = 1*A-NOTCOLON
message-id = "<" 1*248A-NOTGT ">"
newsgroup-name = 1*wildmat-exact
termination = "." CRLF
wildmat = wildmat-pattern *("," ["!"] wildmat-pattern)
wildmat-pattern = 1*wildmat-item
wildmat-item = wildmat-exact / wildmat-wild
wildmat-exact = %x21-29 / %x2B / %x2D-3E / %x40-5A / %x5E-7E /
UTF8-non-ascii ; exclude * , ? [ \ ]
wildmat-wild = "*" / "?"
base64 = *(4base64-char) [base64-terminal]
base64-char = UPPER / LOWER / DIGIT / "+" / "/"
base64-terminal = 2base64-char "==" / 3base64-char "="
; Assorted special character sets
; A- means based on US-ASCII, excluding controls and SP
; P- means based on UTF-8, excluding controls and SP
; U- means based on UTF-8, excluding NUL CR and LF
; B- means based on bytes, excluding NUL CR and LF
A-CHAR = %x21-7E
A-NOTCOLON = %x21-39 / %x3B-7E ; exclude ":"
A-NOTGT = %x21-3D / %x3F-7E ; exclude ">"
P-CHAR = A-CHAR / UTF8-non-ascii
U-CHAR = CTRL / TAB / SP / A-CHAR / UTF8-non-ascii
U-NONTAB = CTRL / SP / A-CHAR / UTF8-non-ascii
U-TEXT = P-CHAR *U-CHAR
B-CHAR = CTRL / TAB / SP / %x21-FF
B-NONDOT = CTRL / TAB / SP / %x21-2D / %x2F-FF ; exclude "."
ALPHA = UPPER / LOWER ; use only when case-insensitive
CR = %x0D
CRLF = CR LF
CTRL = %x01-08 / %x0B-0C / %x0E-1F
DIGIT = %x30-39
EOL = *(SP / TAB) CRLF
LF = %x0A
LOWER = %x61-7A
SP = %x20
SPA = 1*SP
TAB = %x09
UPPER = %x41-5A
UTF8-non-ascii = UTF8-2 / UTF8-3 / UTF8-4
UTF8-2 = %xC2-DF UTF8-tail
UTF8-3 = %xE0 %xA0-BF UTF8-tail / %xE1-EC 2UTF8-tail /
%xED %x80-9F UTF8-tail / %xEE-EF 2UTF8-tail
UTF8-4 = %xF0 %x90-BF 2UTF8-tail / %xF1-F3 3UTF8-tail /
%xF4 %x80-8F 2UTF8-tail
UTF8-tail = %x80-BF
WS = 1*(SP / TAB)
The following non-terminals require special consideration. They represent situations where material SHOULD be restricted to UTF-8, but implementations MUST be able to cope with other character encodings. Therefore there are two sets of definitions for them.
Implementations MUST accept any content that meets this syntax:
S-CHAR = %x21-FF S-NONTAB = CTRL / SP / S-CHAR S-TEXT = (CTRL / S-CHAR) *B-CHAR
Implementations SHOULD only generate content that meets this syntax:
S-CHAR = P-CHAR S-NONTAB = U-NONTAB S-TEXT = U-TEXT
| TOC |
This specification requires IANA to keep a registry of extension-labels. The initial contents of this registry are specified in Section 8.1Initial IANA registry. As described in Section 8Framework for NNTP extensions, names beginning with X are reserved for private use while all other names are expected to be associated with a specification in an RFC on the standards-track or defining an IESG-approved experimental protocol.
Different entries in the registry MUST use different extension-labels.
Different entries in the registry MUST NOT use the same command name. For this purpose, variants distinguished by a second or subsequent keyword (e.g. "LIST HEADERS" and "LIST OVERVIEW.FMT") count as different commands. If there is a need for two extensions to use the same command, a single harmonised specification MUST be registered.
| TOC |
This section is meant to inform application developers, information providers, and users of the security limitations in NNTP as described by this document. The discussion does not include definitive solutions to the problems revealed, though it does make some suggestions for reducing security risks.
NNTP, because it was created to distribute network news articles, will forward whatever information is stored in those articles. Specification of that information is outside this scope of this document, but it is likely that some personal and/or proprietary information is available in some of those articles. It is very important that designers and implementers provide informative warnings to users so personal and/or proprietary information in material that is added automatically to articles (e.g. in headers) is not disclosed inadvertently. Additionally, effective and easily understood mechanisms to manage the distribution of news articles SHOULD be provided to NNTP Server administrators, so that they are able to report with confidence the likely spread of any particular set of news articles.
A server is in the position to save session data about a user's requests that might identify their reading patterns or subjects of interest. This information is clearly confidential in nature and its handling can be constrained by law in certain countries. People using the NNTP protocol to provide data are responsible for ensuring that such material is not distributed without the permission of any individuals that are identifiable by the published results.
There is no user-based or token-based authentication in the basic NNTP specification. Access is normally controlled by server configuration files. Those files specify access by using domain names or IP addresses. However, this specification does permit the creation of extensions to the NNTP protocol itself for such purposes; one such extension is [NNTP-AUTH]Vinocur, J., Newman, C. and K. Murchinson, NNTP Authentication, July 2004.. While including such mechanisms is optional, doing so is strongly encouraged.
Other mechanisms are also available. For example, a proxy server could be put in place that requires authentication before connecting via the proxy to the NNTP server.
Many existing NNTP implementations authorize incoming connections by checking the IP address of that connection against the IP addresses obtained via DNS lookups of lists of domain names given in local configuration files. Servers that use this type of authentication, and clients that find a server by doing a DNS lookup of the server name, rely very heavily on the Domain Name Service, and are thus generally prone to security attacks based on the deliberate misassociation of IP addresses and DNS names. Clients and servers need to be cautious in assuming the continuing validity of an IP number/DNS name association.
In particular, NNTP clients and servers SHOULD rely on their name resolver for confirmation of an IP number/DNS name association, rather than caching the result of previous host name lookups. Many platforms already can cache host name lookups locally when appropriate, and they SHOULD be configured to do so. It is proper for these lookups to be cached, however, only when the TTL (Time To Live) information reported by the name server makes it likely that the cached information will remain useful.
If NNTP clients or servers cache the results of host name lookups in order to achieve a performance improvement, they MUST observe the TTL information reported by DNS. If NNTP clients or servers do not observe this rule, they could be spoofed when a previously accessed server's IP address changes. As network renumbering is expected to become increasingly common, the possibility of this form of attack will grow. Observing this requirement thus reduces this potential security vulnerability.
This requirement also improves the load-balancing behaviour of clients for replicated servers using the same DNS name and reduces the likelihood of a user's experiencing failure in accessing sites that use that strategy.
UTF-8Yergeau, F., UTF-8, a transformation format of ISO 10646, November 2003.[RFC3629] permits only certain sequences of octets and designates others as either malformed or "illegal". The Unicode standard identifies a number of security issues related to illegal sequences and forbids their generation by conforming implementations.
Implementations of this specification MUST NOT generate malformed or illegal sequences and SHOULD detect them and take some appropriate action. This could include:
In the last case, the implementation MUST ensure that any replacement cannot be used to bypass validity or security checks. For example, the illegal sequence %xC0.A0 is an over-long encoding for space (%x20). If it is replaced by the latter in a command line, this needs to happen before the command line is parsed into individual arguments. If the replacement came after parsing, it would be possible to generate an argument with an embedded space, which is forbidden. Use of the "replacement character" does not have this problem, since it is permitted wherever non-US-ASCII characters are. Implementations SHOULD use one of the first two solutions where the general structure of the NNTP stream remains intact, and close the connection if it is no longer possible to parse it sensibly.
The LIST EXTENSIONS command provides information about the extensions currently available from the server. Whenever there is a relevant change to the server state, the results of this command are required to change accordingly.
In most situations the results from this command in a given server state will not change from session to session; a given extension will be installed permanently on a server. Some clients may therefore wish to remember which extensions a server supports to avoid the delay of an additional command and response, particularly if they open multiple connections in the same session.
However, information about extensions related to security and privacy MUST NOT be cached, since this could allow a variety of attacks.
For example, consider a server which permits the use of cleartext passwords on links that are encrypted but not otherwise:
[Initial TCP connection set-up completed.]
[S] 200 NNTP Service Ready, posting permitted
[C] LIST EXTENSIONS
[S] 202 Extensions supported:
[S] XENCRYPT
[S] .
[C] XENCRYPT
[Client and server negotiate encryption on the link]
[S] 283 Encrypted link established
[C] LIST EXTENSIONS
[S] 202 Extensions supported:
[S] XSECRET
[S] .
[C] XSECRET fred flintstone
[S] 290 Password for fred accepted
If the client caches the last LIST EXTENSIONS result, then on the next session it will attempt to use XSECRET on an unencrypted link:
[Initial TCP connection set-up completed.]
[S] 200 NNTP Service Ready, posting permitted
[C] XSECRET fred flintstone
[S] 483 Only permitted on secure links
exposing the password to any eavesdropper. While the primary cause of this is passing a secret without first checking the security of the link, caching of LIST EXTENSIONS results can increase the risk.
Any security extension should include requirements to check the security state of the link in a manner appropriate to that extension.
Caching should normally only be considered for anonymous clients that do not use any security or privacy extensions and for which the time required for an additional command and response is a noticeable issue.
| TOC |
This document is the result of much effort by the present and past members of the NNTP Working Group, chaired by Russ Allbery and Ned Freed. It could not have been produced without them.
The author acknowledges the original authors of NNTP as documented in RFC 977Kantor, B. and P. Lapsley, Network News Transfer Protocol, February 1986.[RFC977]: Brian Kantor and Phil Lapsey.
The author gratefully acknowledges:
Russ Allbery <rra@stanford.edu>
Wayne Davison <davison@armory.com>
Chris Lewis <clewis@bnr.ca>
Tom Limoncelli <tal@mars.superlink.net>
Eric Schnoebelen <eric@egsner.cirr.com>
Rich Salz <rsalz@osf.org>
This work was motivated by the work of various news reader authors and news server authors, which includes those listed below:
- Rick Adams
- Original author of the NNTP extensions to the RN news reader and last maintainer of Bnews
- Stan Barber
- Original author of the NNTP extensions to the news readers that are part of Bnews
- Geoff Collyer
- Original author of the OVERVIEW database proposal and one of the original authors of CNEWS
- Dan Curry
- Original author of the xvnews news reader
- Wayne Davison
- Author of the first threading extensions to the RN news reader (commonly called TRN)
- Geoff Huston
- Original author of ANU NEWS
- Phil Lapsey
- Original author of the UNIX reference implementation for NNTP
- Iain Lea
- Original maintainer of the TIN news reader
- Chris Lewis
- First known implementer of the AUTHINFO GENERIC extension
- Rich Salz
- Original author of INN
- Henry Spencer
- One of the original authors of CNEWS
- Kim Storm
- Original author of the NN news reader
Other people who contributed to this document include:
Matthias Andree
Greg Andruk
Maurizio Codogno
Andrew Gierth
Juergen Helbing
Scott Hollenbeck
Charles Lindsey
Ade Lovett
Ken Murchinson
Francois Petillon
Peter Robinson
Rob Siemborski
Howard Swinehart
Ruud van Tol
Jeffrey Vinocur
The author thanks them all and apologises to anyone omitted.
Finally, the present author gratefully acknowledges the vast amount of work put into previous drafts by the previous author:
Stan Barber <sob@academ.com>
| TOC |
| TOC |
| [ANSI1986] | American National Standards Institute, "Coded Character Set - 7-bit American Standard Code for Information Interchange", ANSI X3.4, 1986. |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 (TXT, HTML, XML). |
| [RFC2234] | Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. |
| [RFC3548] | Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 3548, July 2003. |
| [RFC3629] | Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. |
| [RFC977] | Kantor, B. and P. Lapsley, "Network News Transfer Protocol", RFC 977, February 1986. |
| [TF.686-1] | International Telecommunications Union - Radio, "Glossary, ITU-R Recommendation TF.686-1", ITU-R Recommendation TF.686-1, October 1997. |
| TOC |
| [NNTP-AUTH] | Vinocur, J., Newman, C. and K. Murchinson, "NNTP Authentication", draft-ietf-nntpext-authinfo-02 (work in progress), July 2004. |
| [NNTP-TLS] | Vinocur, J. and C. Newman, "Using TLS with NNTP", draft-ietf-nntpext-tls-nntp-01 (work in progress), October 2003. |
| [RFC1036] | Horton, M. and R. Adams, "Standard for interchange of USENET messages", RFC 1036, December 1987. |
| [RFC1305] | Mills, D., "Network Time Protocol (Version 3) Specification, Implementation", RFC 1305, March 1992 (TXT, PDF). |
| [RFC1869] | Klensin, J., Freed, N., Rose, M., Stefferud, E. and D. Crocker, "SMTP Service Extensions", STD 10, RFC 1869, November 1995. |
| [RFC2616] | Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999 (TXT, PS, PDF). |
| [RFC2629] | Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, June 1999 (TXT, HTML, XML). |
| [RFC2822] | Resnick, P., "Internet Message Format", RFC 2822, April 2001. |
| [RFC2980] | Barber, S., "Common NNTP Extensions", RFC 2980, October 2000. |
| [ROBE1995] | Robertson, R., "FAQ: Overview database / NOV General Information", January 1995 (TXT, TXT). There is no definitive copy of this document known to the author. It was previously posted as the Usenet article <news:nov-faq-1-930909720@agate.Berkeley.EDU> |
| [SALZ1992] | Salz, R., "Manual Page for wildmat(3)
from the INN 1.4 distribution, Revision 1.10", April 1992. There is no definitive copy of this document known to the author. |
| TOC |
| Clive D.W. Feather | |
| Thus plc | |
| 322 Regents Park Road | |
| London N3 2QQ | |
| GB | |
| Phone: | +44 20 8495 6138 |
| Fax: | +44 870 051 9937 |
| EMail: | clive@demon.net |
| URI: | http://www.davros.org/ |
| TOC |
It has been proposed that the response code range 6xx be used for multiline responses. While existing commands and extensions do not use this, it would at least limit the problem clients would face in dealing with an unknown response.
| TOC |
NNTP is most often used for transferring articles that conform to RFC 1036Horton, M. and R. Adams, Standard for interchange of USENET messages, December 1987.[RFC1036] (such articles are called "Netnews articles" here). It is also sometimes used for transferring email messages that conform to RFC 2822Resnick, P., Internet Message Format, April 2001.[RFC2822] (such articles are called "email articles" here). In this situation, articles must conform both to this specification and to that other one; this appendix describes some relevant issues.
NNTP allows a header line to be folded (by inserting a CRLF pair) before any space or TAB character.
Both email and Netnews articles are required to have at least one octet other than space or TAB on each header line. Thus folding can only happen at one point in each sequence of consecutive spaces or TABs. Netnews articles are further required to have the header name, colon, and following space all on the first line; folding may only happen beyond that space. Finally, some non-conforming software will remove trailing spaces and TABs from a line. Therefore it might be inadvisable to fold a header after a space or TAB.
For maximum safety, header lines SHOULD conform to the following syntax rather than that in Section 9.5Articles.
header = header-name ":" SP [header-content] CRLF header-content = [WS] 1*P-CHAR *( [CRLF] WS 1*P-CHAR )
Every article handled by an NNTP server MUST have a unique message-id. For the purposes of this specification, a message-id is an arbitrary opaque string that merely needs to meet certain syntactic requirements and is just a way to refer to the article.
Because there is a significant risk of old articles being reinjected into the global Usenet system, RFC 1036Horton, M. and R. Adams, Standard for interchange of USENET messages, December 1987.[RFC1036] requires that message-ids are globally unique for all time.
This specification states that message-ids are the same if and only if they consist of the same sequence of octets. Other specifications may define two different sequences as being equal because they are putting an interpretation on particular characters. RFC 2822Resnick, P., Internet Message Format, April 2001.[RFC2822] has a concept of "quoted" and "escaped" characters. It therefore considers the three message-ids:
<abcd@example.com>
<"abcd"@example.com>
<"ab\cd"@example.com>
as being identical. Therefore an NNTP implementation handing email articles must ensure that only one of these three appears in the protocol and the other two are converted to it as and when necessary, such as when a client checks the results of a NEWNEWS command against an internal database of message-ids. Note that RFC 1036Horton, M. and R. Adams, Standard for interchange of USENET messages, December 1987.[RFC1036] never treats two different strings as being identical. Its draft successor restricts the syntax of message-ids so that, whenever RFC 2822 would treat two strings as equivalent, only one of them is valid (in the above example only the first string is valid).
This specification does not describe how the message-id of an article is determined; it may be deduced from the contents of the article or derived from some external source. If the server is also conforming to another specification that contains a definition of message-id compatible with this one, the server SHOULD use those message-ids. A common approach, and one that SHOULD be used for email and Netnews articles, is to extract the message-id from the contents of a header with name "Message-ID". This may not be as simple as copying the entire header contents; it may be necessary to strip off comments and undo quoting, or to reduce "equivalent" message-ids to a canonical form.
If an article is obtained through the IHAVE command, there will be a message-id provided with the command. The server MAY either use it or determine one from the article contents. However, whichever it does it SHOULD ensure that, if the IHAVE command is repeated with the same argument and article, it will be recognized as a duplicate.
If an article does not contain a message-id that the server can identify, it MUST synthesize one. This could, for example, be a simple sequence number or based on the date and time that the article arrived. When handling email or Netnews articles, a Message-ID header SHOULD be added to ensure global consistency and uniqueness.
As far as NNTP is concerned, the POST and IHAVE commands provide the same basic facilities in a slightly different way. However they have rather different intentions.
The IHAVE command is intended for transmitting conforming articles between a system of NNTP servers, with all articles perhaps also conforming to another specification (e.g. all articles are Netnews articles). It is expected that the client will have already done any necessary validation (or has in turn obtained the article from a third party which has done so); therefore the contents SHOULD be left unchanged.
In contrast, the POST command is intended for use when an end-user is injecting a newly-created article into a such a system. The article being transferred might not be a conforming email or Netnews article, and the server is expected to validate it and, if necessary, convert it to the right form for onward distribution. This is often done by a separate piece of software on the server installation; if so, the NNTP server SHOULD pass the incoming article to that software unaltered, making no attempt to filter characters, fold or limit lines, or otherwise process the incoming text.
The POST command can fail in various ways and clients should be prepared to re-send an article. When doing so, however, it is often important to ensure - as far as possible - that the same message-id is allocated to both attempts so that the server, or other servers, can recognize the two articles as being duplicates. In the case of email or Netnews articles, therefore, the posted article SHOULD contain a header with name "Message-ID" and the contents of this header SHOULD be identical on each attempt. The server SHOULD ensure that two POSTed articles with the same contents for this header are recognized as identical and the same message-id allocated, whether or not those contents are suitable for use as the message-id.
| TOC |
This section contains a list of every response code defined in this document, whether it is multi-line, which commands can generate it, what arguments it has, and what its meaning is.
- Response code 100
- (multi-line) Generated by: HELPHELP
Meaning: help text follows.- Response code 111
- Generated by: DATEDATE
1 argument: yyyymmddhhmmss
Meaning: server date and time.- Response code 200
- Generated by: initial connectionInitial Connection, MODE READERMODE READER
Meaning: service available, posting allowed.- Response code 201
- Generated by: initial connectionInitial Connection, MODE READERMODE READER
Meaning: service available, posting prohibited.- Response code 202
- (multi-line) Generated by: LIST EXTENSIONSLIST EXTENSIONS
Meaning: extension list follows.- Response code 205
- Generated by: QUITQUIT
Meaning: connection closing (the server immediately closes the connection).- Response code 211
- The 211 response code has two completely different forms depending on which command generated it:
Generated by: GROUPGROUP
4 arguments: number low high group
Meaning: group selected.(multi-line)
Generated by: LISTGROUPLISTGROUP
4 arguments: number low high group
Meaning: article numbers follow.- Response code 215
- (multi-line) Generated by: LIST ACTIVELIST ACTIVE, LIST ACTIVE.TIMESLIST ACTIVE.TIMES, LIST DISTRIB.PATSLIST DISTRIB.PATS, LIST DISTRIBUTIONSLIST DISTRIBUTIONS, LIST HEADERSLIST HEADERS, LIST NEWSGROUPSLIST NEWSGROUPS, LIST OVERVIEW.FMTLIST OVERVIEW.FMT
Meaning: information follows.- Response code 220
- (multi-line) Generated by: ARTICLEARTICLE
2 arguments: n message-id
Meaning: article follows.- Response code 221
- (multi-line) Generated by: HEADHEAD
2 arguments: n message-id
Meaning: article headers follow.- Response code 222
- (multi-line) Generated by: BODYBODY
2 arguments: n message-id
Meaning: article body follows.- Response code 223
- Generated by: LASTLAST, NEXTNEXT, STATSTAT
2 arguments: n message-id
Meaning: article exists and selected.- Response code 224
- (multi-line) Generated by: OVEROVER
Meaning: overview information follows.- Response code 225
- (multi-line) Generated by: HDRHDR
Meaning: headers follow.- Response code 230
- (multi-line) Generated by: NEWNEWSNEWNEWS
Meaning: list of new articles follows.- Response code 231
- (multi-line) Generated by: NEWGROUPSNEWGROUPS
Meaning: list of new newsgroups follows.- Response code 235
- Generated by: IHAVE (second stage)IHAVE
Meaning: article transferred OK.- Response code 240
- Generated by: POST (second stage)POST
Meaning: article received OK.- Response code 335
- Generated by: IHAVE (first stage)IHAVE
Meaning: send article to be transferred.- Response code 340
- Generated by: POST (first stage)POST
Meaning: send article to be posted.- Response code 400
- Generic response and generated by initial connectionInitial Connection
Meaning: service not available or no longer available (the server immediately closes the connection).- Response code 401
- Generic response
1 argument: extension-label
Meaning: the server is in the wrong mode; the indicated extension should be used to change the mode.- Response code 402
- Generated by: LIST EXTENSIONSLIST EXTENSIONS
Meaning: server has no extensions.- Response code 403
- Generic response
Meaning: internal fault or problem preventing action being taken.- Response code 411
- Generated by: GROUPGROUP, LISTGROUPLISTGROUP
Meaning: no such newsgroup.- Response code 412
- Generated by: ARTICLEARTICLE, BODYBODY, HDRHDR, HEADHEAD, LASTLAST, LISTGROUPLISTGROUP, NEXTNEXT, OVEROVER, STATSTAT
Meaning: no newsgroup selected.- Response code 420
- Generated by: ARTICLEARTICLE, BODYBODY, HDRHDR, HEADHEAD, LASTLAST, NEXTNEXT, OVEROVER, STATSTAT
Meaning: current article number is invalid.- Response code 421
- Generated by: NEXTNEXT
Meaning: no next article in this group.- Response code 422
- Generated by: LASTLAST
Meaning: no previous article in this group.- Response code 423
- Generated by: ARTICLEARTICLE, BODYBODY, HDRHDR, HEADHEAD, OVEROVER, STATSTAT
Meaning: no article with that number or in that range.- Response code 430
- Generated by: ARTICLEARTICLE, BODYBODY, HDRHDR, HEADHEAD, OVEROVER, STATSTAT
Meaning: no article with that message-id.- Response code 435
- Generated by: IHAVE (first stage)IHAVE
Meaning: article not wanted.- Response code 436
- Generated by: IHAVE (either stage)IHAVE
Meaning: transfer not possible (first stage) or failed (second stage); try again later.- Response code 437
- Generated by: IHAVE (second stage)IHAVE
Meaning: transfer rejected; do not retry.- Response code 440
- Generated by: POST (first stage)POST
Meaning: posting not permitted.- Response code 441
- Generated by: POST (second stage)POST
Meaning: posting failed.- Response code 480
- Generic response
Meaning: command unavailable until the client has authenticated itself.- Response code 483
- Generic response
Meaning: command unavailable until suitable privacy has been arranged.- Response code 500
- Generic response
Meaning: unknown command.- Response code 501
- Generic response
Meaning: syntax error in command.- Response code 502
- Generic response and generated by initial connectionInitial Connection
Meaning for the initial connectionInitial Connection and the MODE READER commandMODE READER: service permanently unavailable (the server immediately closes the connection).
Meaning for all other commands: command not permitted (and there is no way for the client to change this).- Response code 503
- Generic response
Meaning: feature not supported.- Response code 504
- Generic response
Meaning: error in base64-encoding [RFC3548]Josefsson, S., The Base16, Base32, and Base64 Data Encodings, July 2003. of an argument
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This section gives a formal definition of each of the extensions in Section 8.2Standard extensions as required by Section 8Framework for NNTP extensions for the IANA registry.
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