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NNTP                                                          C. Feather
Internet-Draft                                                  Thus plc
Expires: October 24, 2003                                 April 25, 2003


                    Network News Transport Protocol
                       draft-ietf-nntpext-base-18

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   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 October 24, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

   The Network News Transport 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.

Administration

   This document is a product of the NNTP Working Group, chaired by Russ
   Allbery and Ned Freed.

Outstanding issues



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   OUTSTANDING ISSUE

      Outstanding substantive (as opposed to editorial) issues in the
      text are shown thus.


Author's Note

   This draft is written in XML using an NNTP-specific DTD. Custom
   software is used to convert this to RFC 2629 [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 draft.

Rights

   UNIX is a registered trademark of the X/Open Company Ltd.

































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Table of Contents

   1.      Introduction . . . . . . . . . . . . . . . . . . . . . . .  7
   2.      Notation . . . . . . . . . . . . . . . . . . . . . . . . .  8
   3.      Basic Concepts . . . . . . . . . . . . . . . . . . . . . .  9
   3.1     Commands and Responses . . . . . . . . . . . . . . . . . .  9
   3.2     Response Codes . . . . . . . . . . . . . . . . . . . . . . 11
   3.2.1   Generic Response Codes . . . . . . . . . . . . . . . . . . 13
   3.2.1.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 14
   3.3     Pipelining . . . . . . . . . . . . . . . . . . . . . . . . 16
   3.3.1   Examples . . . . . . . . . . . . . . . . . . . . . . . . . 17
   3.4     Articles . . . . . . . . . . . . . . . . . . . . . . . . . 17
   4.      The WILDMAT format . . . . . . . . . . . . . . . . . . . . 20
   4.1     Wildmat syntax . . . . . . . . . . . . . . . . . . . . . . 20
   4.2     Wildmat semantics  . . . . . . . . . . . . . . . . . . . . 20
   4.3     Extensions . . . . . . . . . . . . . . . . . . . . . . . . 21
   4.4     Examples . . . . . . . . . . . . . . . . . . . . . . . . . 22
   5.      Session administration commands  . . . . . . . . . . . . . 23
   5.1     Initial Connection . . . . . . . . . . . . . . . . . . . . 23
   5.1.1   Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 23
   5.1.2   Description  . . . . . . . . . . . . . . . . . . . . . . . 23
   5.1.3   Examples . . . . . . . . . . . . . . . . . . . . . . . . . 23
   5.2     MODE READER  . . . . . . . . . . . . . . . . . . . . . . . 24
   5.2.1   Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 24
   5.2.2   Description  . . . . . . . . . . . . . . . . . . . . . . . 24
   5.2.3   Examples . . . . . . . . . . . . . . . . . . . . . . . . . 25
   5.3     LIST EXTENSIONS  . . . . . . . . . . . . . . . . . . . . . 26
   5.3.1   Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 26
   5.3.2   Description  . . . . . . . . . . . . . . . . . . . . . . . 26
   5.3.3   Examples . . . . . . . . . . . . . . . . . . . . . . . . . 27
   5.4     QUIT . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
   5.4.1   Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 28
   5.4.2   Description  . . . . . . . . . . . . . . . . . . . . . . . 28
   5.4.3   Examples . . . . . . . . . . . . . . . . . . . . . . . . . 28
   6.      Article posting and retrieval  . . . . . . . . . . . . . . 29
   6.1     Group and article selection  . . . . . . . . . . . . . . . 29
   6.1.1   GROUP  . . . . . . . . . . . . . . . . . . . . . . . . . . 29
   6.1.1.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 29
   6.1.1.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 30
   6.1.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 31
   6.1.2   LAST . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
   6.1.2.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 32
   6.1.2.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 32
   6.1.2.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 33
   6.1.3   NEXT . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
   6.1.3.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 33
   6.1.3.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 34
   6.1.3.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 34



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   6.2     Retrieval of articles and article sections . . . . . . . . 35
   6.2.1   ARTICLE  . . . . . . . . . . . . . . . . . . . . . . . . . 35
   6.2.1.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 35
   6.2.1.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 36
   6.2.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 37
   6.2.2   HEAD . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
   6.2.2.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 38
   6.2.2.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 39
   6.2.2.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 39
   6.2.3   BODY . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
   6.2.3.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 40
   6.2.3.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 41
   6.2.3.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 41
   6.2.4   STAT . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
   6.2.4.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 42
   6.2.4.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 42
   6.2.4.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 43
   6.3     Article posting  . . . . . . . . . . . . . . . . . . . . . 44
   6.3.1   POST . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
   6.3.1.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 44
   6.3.1.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 44
   6.3.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 45
   6.3.2   IHAVE  . . . . . . . . . . . . . . . . . . . . . . . . . . 46
   6.3.2.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 46
   6.3.2.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 46
   6.3.2.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 47
   7.      Information commands . . . . . . . . . . . . . . . . . . . 50
   7.1     DATE . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
   7.1.1   Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 50
   7.1.2   Description  . . . . . . . . . . . . . . . . . . . . . . . 50
   7.1.3   Examples . . . . . . . . . . . . . . . . . . . . . . . . . 50
   7.2     HELP . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
   7.2.1   Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 50
   7.2.2   Description  . . . . . . . . . . . . . . . . . . . . . . . 51
   7.2.3   Examples . . . . . . . . . . . . . . . . . . . . . . . . . 51
   7.3     NEWGROUPS  . . . . . . . . . . . . . . . . . . . . . . . . 51
   7.3.1   Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 51
   7.3.2   Description  . . . . . . . . . . . . . . . . . . . . . . . 51
   7.3.3   Examples . . . . . . . . . . . . . . . . . . . . . . . . . 52
   7.4     NEWNEWS  . . . . . . . . . . . . . . . . . . . . . . . . . 53
   7.4.1   Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 53
   7.4.2   Description  . . . . . . . . . . . . . . . . . . . . . . . 53
   7.4.3   Examples . . . . . . . . . . . . . . . . . . . . . . . . . 53
   7.5     Time . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
   7.5.1   Examples . . . . . . . . . . . . . . . . . . . . . . . . . 54
   7.6     The LIST commands  . . . . . . . . . . . . . . . . . . . . 55
   7.6.1   LIST ACTIVE  . . . . . . . . . . . . . . . . . . . . . . . 55
   7.6.1.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 55



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   7.6.1.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 55
   7.6.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 56
   7.6.2   LIST ACTIVE.TIMES  . . . . . . . . . . . . . . . . . . . . 57
   7.6.2.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 57
   7.6.2.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 57
   7.6.2.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 58
   7.6.3   LIST DISTRIBUTIONS . . . . . . . . . . . . . . . . . . . . 58
   7.6.3.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 59
   7.6.3.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 59
   7.6.3.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 59
   7.6.4   LIST DISTRIB.PATS  . . . . . . . . . . . . . . . . . . . . 60
   7.6.4.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 60
   7.6.4.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 60
   7.6.4.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 60
   7.6.5   LIST NEWSGROUPS  . . . . . . . . . . . . . . . . . . . . . 61
   7.6.5.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 61
   7.6.5.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 61
   7.6.5.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 62
   8.      Framework for NNTP extensions  . . . . . . . . . . . . . . 63
   8.1     Initial IANA registry  . . . . . . . . . . . . . . . . . . 65
   8.2     Standard extensions  . . . . . . . . . . . . . . . . . . . 65
   8.3     The LISTGROUP extension  . . . . . . . . . . . . . . . . . 65
   8.3.1   LISTGROUP  . . . . . . . . . . . . . . . . . . . . . . . . 65
   8.3.1.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 65
   8.3.1.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 66
   8.3.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 66
   8.4     Article metadata . . . . . . . . . . . . . . . . . . . . . 67
   8.4.1   The :bytes metadata item . . . . . . . . . . . . . . . . . 68
   8.4.2   The :lines metadata item . . . . . . . . . . . . . . . . . 68
   8.5     The OVER extension . . . . . . . . . . . . . . . . . . . . 68
   8.5.1   OVER . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
   8.5.1.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 68
   8.5.1.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 69
   8.5.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 70
   8.5.2   LIST OVERVIEW.FMT  . . . . . . . . . . . . . . . . . . . . 72
   8.5.2.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 72
   8.5.2.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 72
   8.5.2.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 73
   8.6     The HDR extension  . . . . . . . . . . . . . . . . . . . . 74
   8.6.1   HDR  . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
   8.6.1.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . 74
   8.6.1.2 Description  . . . . . . . . . . . . . . . . . . . . . . . 74
   8.6.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 76
   9.      Augmented BNF Syntax for NNTP  . . . . . . . . . . . . . . 78
   9.1     Commands . . . . . . . . . . . . . . . . . . . . . . . . . 78
   9.2     Responses  . . . . . . . . . . . . . . . . . . . . . . . . 80
   9.3     Articles . . . . . . . . . . . . . . . . . . . . . . . . . 80
   9.4     General non-terminals  . . . . . . . . . . . . . . . . . . 80



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   10.     IANA Considerations  . . . . . . . . . . . . . . . . . . . 82
   11.     Security Considerations  . . . . . . . . . . . . . . . . . 83
   11.1    Personal and Proprietary Information . . . . . . . . . . . 83
   11.2    Abuse of Server Log Information  . . . . . . . . . . . . . 83
   11.3    Weak Authentication and Access Control . . . . . . . . . . 83
   11.4    DNS Spoofing . . . . . . . . . . . . . . . . . . . . . . . 84
   11.5    UTF-8 issues . . . . . . . . . . . . . . . . . . . . . . . 84
   12.     Acknowledgments  . . . . . . . . . . . . . . . . . . . . . 86
           Normative References . . . . . . . . . . . . . . . . . . . 88
           Informative References . . . . . . . . . . . . . . . . . . 89
           Author's Address . . . . . . . . . . . . . . . . . . . . . 89
           Intellectual Property and Copyright Statements . . . . . . 90







































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1. Introduction

   This document specifies the Network News Transport 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 977
   [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-8 [RFC2279] instead of US-ASCII [ANSI1986]. It now requires
   all articles to have a message-id, eliminating the "<0>" placeholder
   used in RFC 977. It also extends the newsgroup name matching
   capabilities already documented in RFC 977.

   Generally, new functionality is made available using new commands.
   Part of that 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 2119 [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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2. Notation

   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 parameter is optional;
     ellipsis...   indicates that the parameter may be repeated any
                   number of times (it must occur at least once);
     vertical|bar  indicates a choice of two mutually exclusive
                   parameters (exactly one must be provided).

   The name "message-id" for a command or response parameter indicates
   that it is the message-id of an article as described in Section 3.4,
   including the angle brackets.

   The name "wildmat" for a parameter indicates that it is a wildmat as
   defined in Section 4. If the parameter does not meet the requirements
   of that section (for example, if it does not fit the grammar of
   Section 4.1) 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
   with those codes in US-ASCII [ANSI1986] (that is, %x00, %x09, %x0A,
   %x0D, and %x20 respectively), as do quoted characters (so "." and "<"
   refer to %x2E and %x3C). 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.

   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 command (Section
   6.1.1)) is invalid; when so, this is indicated at the start of the
   example.








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3. Basic Concepts

3.1 Commands and Responses

   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-8 [RFC2279]. 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.

   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.

   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.

   Keywords are case-insensitive; the case of keywords for commands MUST
   be ignored by the server. Command and response parameters 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



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   in a single line.

   OUTSTANDING ISSUE

      Should the initial response line be limited to 512 octets as well?
       Possible text:

      The first or only line of the response MUST NOT exceed 512 octets,
      which includes the response code and the terminating CRLF pair.

      The text further down about "does not place any limit on the
      length" would need equivalent edits.

   All multi-line responses MUST adhere to the following format:

   1.  The response consists of a sequence of one or more "lines", each
       being a stream of octets ending with a CRLF pair. Apart from
       those line endings, the stream MUST NOT include the octets NUL,
       LF, or CR.

   2.  The first such line contains the response code as with a single
       line response.

   3.  If any subsequent line begins with the "termination octet" ("."
       or %x2E), that line MUST be "byte-stuffed" by pre-pending an
       additional termination octet to that line of the response.

   4.  The lines of the response MUST be followed by a terminating line
       consisting of a single termination octet followed by a CRLF pair
       in the normal way. Thus a multi-line response is always
       terminated with the five octets CRLF "." CRLF (%x0D.0A.2E.0D.0A).

   5.  When interpreting a multi-line response, the "byte stuffing" MUST
       be undone; i.e. the client MUST ensure that, in any line
       beginning with the termination octet followed by octets other
       than a CRLF pair, that initial termination octet is disregarded.

   6.  Likewise, the terminating line ("." CRLF or %x2E.0D.0A) MUST NOT
       be considered part of the multi-line response; i.e. the client
       MUST ensure that any line beginning with the termination octet
       followed immediately by a CRLF pair is disregarded; (the first
       CRLF pair of the terminating CRLF "." CRLF is, of course, part of
       the last line of the response).

   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. However, except when stated
   otherwise, this specification does not require the content to be



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   UTF-8 and it is possible for octets above and below 128 to be mixed
   arbitrarily.

   This document does not place any limit on the length of a line.
   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.

3.2 Response Codes

   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 correct, but couldn't be performed for some
      reason.
      5xx - Command unimplemented, or incorrect, or a serious program
      error occurred.

   OUTSTANDING ISSUE

      I proposed that we assign 6xx for extensions and future commands
      to use for multiline responses, thus at least limiting (if not
      eliminating) the problem clients have of working out whether one
      is coming up. Nobody was violently against the idea, but nobody
      was particularly in favour either.

   The next digit in the code indicates the function response category.

      x0x - Connection, setup, and miscellaneous messages
      x1x - Newsgroup selection
      x2x - Article selection



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      x3x - Distribution functions
      x4x - Posting
      x8x - Reserved for authentication and authorization extensions
      x9x - Reserved for private use (non-standard extensions)

   Certain responses contain parameters 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 parameters
   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 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.

   Parameters MUST be separated from the numeric status indicator and
   from each other by a single space. All numeric parameters MUST be in
   base 10 (decimal) format, and MAY have leading zeros. String
   parameters 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 parameter 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 parameter by at least one space.

   The server MUST respond to any command with the appropriate generic
   response (given in Section 3.2.1) 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 extension registered with IANA (see
   Section 8) will specify any response codes of the x9x pattern.



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   (Implementers of extensions are accordingly cautioned not to use such
   responses for extensions that may subsequently be submitted for
   registration.)

3.2.1 Generic Response Codes

   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, the response code 501 MUST be returned. 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 requested
   variant is not implemented but the base command is.

   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 recognises 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 command (Section 8.6.1) 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) or as a working command where the information is not
   available (response code 503).

   OUTSTANDING ISSUE

      Do we need to add text like:

         For backwards compatibility a server MAY return the response
         code 503 where this specification requires the response code
         403, and a client SHOULD be prepared for this. This waiver may
         be removed in a future revision of this specification.

   If the client is not authorized to use the specified facility when
   the server is in its current state, then either the response code 480
   or the response code 502 MUST be returned. The response code 480
   SHOULD be used if a different command (for example, an extension used
   to present credentials) might change the server state so that the
   command is permitted. The response code 502 SHOULD be used if the



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   server wishes to indicate that it is necessary to terminate the
   connection and start a new one with the appropriate authority before
   the command can be used. Since it is not always possible to clearly
   distinguish these two cases, a server MAY issue either of these
   response codes for either case. (Note that the server MUST NOT close
   the TCP connection immediately after a 502 response except at the
   initial connection (Section 5.1) and with the MODE READER (Section
   5.2) command.)

   OUTSTANDING ISSUE

      This isn't a complete solution to the 480 issue; what about the
      TLS extension, which uses 483 to mean "you need encryption".
      Should 480 be used for other than "you need authentication"? What
      code should be used to mean "can't do AUTH until after MODE
      READER"?

      Do we need a more generic mechanism for "you must invoke extension
      X to do Y"?

      The best proposal made so far is that all 48x codes, if returned
      from an existing command, mean "unavailable unless some
      authentication or privacy extension is invoked". Does this tie in
      with the issue of permitting existing commands not listed in an
      extension?

   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. It MAY give a 401 response code
   to any command to indicate that termination is imminent (following a
   401 response, it MUST NOT close the TCP connection immediately).

   OUTSTANDING ISSUE

      It's not clear that we need 401; it appears to have been an
      invention. If we do keep it, then text is needed to indicate what
      happens with commands that change the status (for example, if
      GROUP returns 401 what happens to the current selected newsgroup),
      and how to make those commands work.

   With the exception of mandatory commands and the 500 response, the
   client MUST be prepared to receive any of these responses for any
   command.

3.2.1.1 Examples

   Example of an unknown command:




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      [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 an attempt to access a restricted facility:

      [C] GROUP secret.group
      [S] 480 Permission denied

   followed by a successful attempt following 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 not available to this
   connection:

      [C] MODE READER



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      [S] 200 Reader mode, posting permitted
      [C] IHAVE <i.am.an.article.you.will.want@example.com>
      [S] 502 Permission denied

   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.]

   Example of imminent termination of the server:

      [C] STAT 123
      [S] 401 Pre-payment expired, you have 10 seconds
      [C] STAT 123
      [S] 423 No such article number in this group
      [C] NEXT
      [S] 400 Time expired
      [Server closes connection.]


3.3 Pipelining

   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.




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   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.

3.3.1 Examples

   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.

3.4 Articles

   OUTSTANDING ISSUE

      This section is new. If anyone has better wording, I won't
      complain.



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   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.
   In particular, where NNTP is used to transport articles that conform
   to other specifications such as RFC 1036 [RFC1036] or RFC 2822
   [RFC2822], articles must meet both this specification and that other.

   OUTSTANDING ISSUE

      Need to add an appendix that spells out how this document
      interacts with RFC 1036. That would allow us to remove some of the
      convoluted wording about "other specifications".

   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
   but is otherwise unrestricted; in particular, 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 (including the space after the colon after
   the header name), except that there MUST be at least one octet other
   than %x09 or %x20 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 value.

   Each article MUST have a unique message-id; two articles offered by
   an NNTP server MUST NOT have the same message-id. Note that RFC 1036
   [RFC1036] further requires that message-ids are globally unique for
   all time.



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   For the purposes of this specification, message-ids are opaque
   strings that MUST meet the following requirements:

   o  A message-id MUST begin with "<" and end with ">", and MUST NOT
      contain the latter except at the end.

   o  A message-id MUST be between 3 and 250 octets in length.

   o  A message-id MUST NOT contain octets other than printable US-ASCII
      characters.

   Two 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; an NNTP server that also conforms to such a
   specification must consistently use only one or the other. As an
   example, the message-ids:

      <abcd@example.com>
      <"abcd"@example.com>
      <"ab\cd"@example.com>

   are considered distinct by this specification even though they would
   be considered semantically identical according to the specification
   in RFC 2822 [RFC2822].

   This specification does not describe how the message-id of an article
   is determined (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). Many servers
   will extract the message-id from the contents of a header with name
   "Message-ID", but this is not required by this document. If the
   server does not have any way to determine a message-id from the
   article itself, it MUST synthesise one (it need not modify the
   article to add such a header unless required to by another
   specification).
















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4. The WILDMAT format

   The WILDMAT format described here is based on the version first
   developed by Rich Salz [SALZ1992], 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.

4.1 Wildmat syntax

   A wildmat is described by the following ABNF [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 9.

   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.

4.2 Wildmat semantics

   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



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   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.

4.3 Extensions

   An NNTP server or extension MAY extend the syntax or semantics of
   wildmats provided that all wildmats that meet the requirements of
   Section 4.1 have the meaning ascribed to them by Section 4.2. Future
   editions of this document may also extend wildmats.













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4.4 Examples

    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



























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5. Session administration commands

5.1 Initial Connection

5.1.1 Usage

   Responses
      200   Service available, posting allowed
      201   Service available, posting prohibited
      400   Service temporarily unavailable [1]
      502   Service permanently unavailable [1]

      These are the only valid response codes for the initial greeting;
      the server MUST not return any other generic response code.

   [1] Following a 400 or 502 response the server MUST immediately close
      the connection.


5.1.2 Description

   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. 502 MUST be used if the client is
   not permitted under any circumstances to interact with the server and
   400 otherwise.

5.1.3 Examples

   Example of a normal connection from an authorized client which then
   terminates the session (see Section 5.4):

      [Initial TCP connection setup completed.]
      [S] 200 NNTP Service Ready, posting permitted
      [C] QUIT
      [S] 205 NNTP Service exits normally
      [Server closes connection.]




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   Example of a normal connection from an authorized client that is not
   permitted to post; it also immediately terminates the session:

      [Initial TCP connection setup 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 setup 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 setup completed.]
      [S] 400 NNTP Service temporarily unavailable
      [Server closes connection.]


5.2 MODE READER

5.2.1 Usage

   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.


5.2.2 Description

   MODE READER SHOULD be sent by any client that intends to use any
   command other than IHAVE, HEAD, STAT, LIST ACTIVE, LIST EXTENSIONS,
   or a command advertised by the server as available via LIST
   EXTENSIONS.



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   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. Where an extension is only
   available after a MODE READER command, or where the effects of the
   extension will change, the LIST EXTENSIONS command MUST produce
   different results that indicate the change.

   The server MUST return a response using the same codes as the initial
   greeting (as described in Section 5.1.1) 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.

   Once MODE READER is sent, IHAVE (and any extensions intended for
   peer-to-peer article transfer) 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.

   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.

5.2.3 Examples

   Example of use of the MODE READER command by an authorized client
   which then terminates the session (see Section 5.4):

      [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:




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      [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.]


5.3 LIST EXTENSIONS

5.3.1 Usage

   This command is optional.

   This command MUST NOT be pipelined.

   Syntax
      LIST EXTENSIONS

   Responses
      202   Extension list follows (multiline)
      402   Server has no extensions


5.3.2 Description

   The LIST EXTENSIONS command allows a client to determine which
   extensions are supported by the server at any given time. See Section
   8 for further discussion of extensions.

   This command MUST be implemented by any server that implements any
   extensions defined in this document or any other extension in the
   IANA registry, and is optional otherwise.

   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
   MUST NOT cache (for use in another session) any information returned
   if the LIST EXTENSIONS command succeeds. That is, 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



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   response.

   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 parameters (separated by single spaces). The extension-label and
   the meaning of the parameters 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. Parameters 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,
   and MUST list all supported 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.

5.3.3 Examples

   Example of a successful response:

      [C] LIST EXTENSIONS
      [S] 202 Extensions supported:
      [S] OVER
      [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:




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      [C] LIST EXTENSIONS
      [S] 402 Server has no extensions


5.4 QUIT

5.4.1 Usage

   Syntax
      QUIT

   Responses
      205   Connection closing


5.4.2 Description

   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.

5.4.3 Examples

      [C] QUIT
      [S] 205 closing connection
      [Server closes connection.]




















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6. Article posting and retrieval

   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 SHOULD NOT use leading zeroes in specifying article
   numbers, and MUST NOT use more than 16 digits. In some situations,
   the value zero replaces an article number to show some special
   situation.

6.1 Group and article selection

   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".

6.1.1 GROUP

6.1.1.1 Usage

   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



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6.1.1.2 Description

   The required parameter 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 7.6.1).

   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 on file in the group.

   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 on
   file. 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.

   o  The high water mark will be one less than the low water mark, and
      the estimated article count will be zero. Servers SHOULD use this
      method to show an empty group. This is the only time that the high
      water mark can be less than the low water mark.

   o  All three numbers will be zero.

   o  The high water mark is greater than or equal to the low water
      mark. The estimated article count might be zero or non-zero; if
      non-zero, the same requirements apply as for a non-empty group.

   The set of articles in a group may change after the GROUP command is
   carried out. That is:

   o  articles may be removed from the group

   o  articles may be reinstated in the group with the same article
      number, but those articles MUST have numbers no less than the
      reported low water mark (note that this is a reinstatement of the
      previous article, not a new article reusing the number)

   o  new articles may be added with article numbers greater than the
      reported high water mark (if an article that was the one with the
      highest number has been removed, the next new article will not
      have the number one greater than the reported high water mark)



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   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 sent to any client. 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.

6.1.1.3 Examples

   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



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   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


6.1.2 LAST

6.1.2.1 Usage

   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


6.1.2.2 Description

   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.



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6.1.2.3 Examples

   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


6.1.3 NEXT

6.1.3.1 Usage

   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



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   Parameters
      n          = article number
      message-id = article message-id


6.1.3.2 Description

   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 command (Section 6.1.2).

6.1.3.3 Examples

   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:



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      [C] GROUP example.empty.newsgroup
      [S] 211 0 0 0 example.empty.newsgroup
      [C] NEXT
      [S] 420 No current article selected


6.2 Retrieval of articles and article sections

   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 3.4, 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.

6.2.1 ARTICLE

6.2.1.1 Usage

   Syntax
      ARTICLE message-id
      ARTICLE [number]

   Responses

      First form (message-id specified)
         220 0 message-id   Article follows (multiline)
         430                No article found with that message-id

      Second form (optional article number specified)
         220 n message-id   Article follows (multiline)
         412                No newsgroup selected
         420                Current article number is invalid [1]
         423                No such article in this newsgroup

   Parameters
      number     = Requested article number
      n          = Returned article number
      message-id = Article message-id

   [1] The 420 response can only occur if no article number has been
      specified.






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6.2.1.2 Description

   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 two forms.

   In the first form, a message-id is specified (including the angle
   brackets), 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 crossposted to more than one newsgroup.

   In the response, the article number is replaced with zero (that is,
   the server is not required to determine whether the article is in the
   current group or what article number(s) it has).

   In the second form, an article number may be specified. If so, and if
   there is an article with that number in the currently selected
   newsgroup, the server MUST set the current article number to that
   number.

   Then, whether or not a number was specified, the article indicated by
   the current article number is presented to the client.

   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 current article number is invalid, a 420 response MUST be
   returned. If there is no article with the specified number, a 423



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   response MUST be returned. If the current selected newsgroup is
   invalid, a 412 response MUST be returned.

6.2.1.3 Examples

   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



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      [S] 423 No such article number in this group

   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


6.2.2 HEAD

6.2.2.1 Usage

   Syntax
      HEAD message-id
      HEAD [number]

   Responses

      First form (message-id specified)
         221 0 message-id   Headers follow (multiline)
         430                No article found with that message-id

      Second form (optional article number specified)
         221 n message-id   Headers follow (multiline)
         412                No newsgroup selected
         420                Current article number is invalid [1]
         423                No such article in this newsgroup

   Parameters
      number     = Requested article number
      n          = Returned article number
      message-id = Article message-id

   [1] The 420 response can only occur if no article number has been
      specified.






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6.2.2.2 Description

   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).

6.2.2.3 Examples

   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:




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      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] HEAD 300256
      [S] 423 No such article number in this group

   Example of an unsuccessful retrieval 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


6.2.3 BODY

6.2.3.1 Usage

   Syntax
      BODY message-id
      BODY [number]

   Responses

      First form (message-id specified)
         222 0 message-id   Body follows (multiline)
         430                No article found with that message-id

      Second form (optional article number specified)
         222 n message-id   Body follows (multiline)
         412                No newsgroup selected
         420                Current article number is invalid [1]
         423                No such article in this newsgroup

   Parameters
      number     = Requested article number
      n          = Returned article number
      message-id = Article message-id






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   [1] The 420 response can only occur if no article number has been
      specified.


6.2.3.2 Description

   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).

6.2.3.3 Examples

   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 such article number in this group

   Example of an unsuccessful retrieval of the body of an article by
   number because no newsgroup was selected first:




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      [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


6.2.4 STAT

6.2.4.1 Usage

   Syntax
      STAT message-id
      STAT [number]

   Responses

      First form (message-id specified)
         223 0 message-id   Article exists
         430                No article found with that message-id

      Second form (optional article number specified)
         223 n message-id   Article exists
         412                No newsgroup selected
         420                Current article number is invalid [1]
         423                No such article in this newsgroup

   Parameters
      number     = Requested article number
      n          = Returned article number
      message-id = Article message-id

   [1] The 420 response can only occur if no article number has been
      specified.


6.2.4.2 Description

   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.



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   This command allows the client to determine whether an article
   exists, and in the second form what its message-id is, without having
   to process an arbitrary amount of text.

6.2.4.3 Examples

   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 a STAT of an existing article by message-id:

      [C] STAT <45223423@example.com>
      [S] 223 0 <45223423@example.com>

   Example of an STAT of 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 of 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 such article number in this group

   Example of STAT of 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 of 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







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6.3 Article posting

   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.

6.3.1 POST

6.3.1.1 Usage

   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


6.3.1.2 Description

   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 3.4 and MUST be sent by the client to the server in the
   manner specified in (Section 3.1) 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 unforseen server



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   errors, the posted article will be made available on the server and/
   or transferred to other servers as appropriate. In other words,
   articles not wanted by the server SHOULD be rejected with a 441
   response and not accepted and silently discarded.

   No attempt shall be made by the server to filter characters, fold or
   limit lines, or otherwise process incoming text. The intent is that
   the server just passes the incoming message to be posted to the
   server installation's news posting software, which is not defined by
   this document.

   The client SHOULD NOT assume that the article has been successfully
   transferred unless it receives an affirmative response from the
   server. 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, if the client supplied a message-id in the
   original article, ensure it supplies the same message-id - 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). In particular, if the article contained a header
   with name "Message-ID", the client SHOULD ensure that the contents of
   this header are identical when resending it and the server SHOULD
   ensure that the re-sent article is recognised as a duplicate and not
   assigned a different message-id to the original.

6.3.1.3 Examples

   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



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      [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


6.3.2 IHAVE

6.3.2.1 Usage

   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


6.3.2.2 Description

   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,



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   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 3.1) 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.

6.3.2.3 Examples

   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>



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      [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.a.test.article@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:

      [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.a.test.article@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.a.test.article@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




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   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














































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7. Information commands

   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.

7.1 DATE

7.1.1 Usage

   Syntax
      DATE

   Responses
      111 yyyymmddhhmmss   server date and time

   Parameters
      yyyymmddHHmmss = Current UTC date and time on server


7.1.2 Description

   This command exists to help clients find out the current Coordinated
   Universal Time [TF.686-1] from the server's perspective. This command
   SHOULD NOT be used as a substitute for NTP [RFC1305] but to provide
   information that might be useful when using the NEWNEWS command (see
   Section 7.4). 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.

7.1.3 Examples

      [C] DATE
      [S] 111 19990623135624


7.2 HELP

7.2.1 Usage







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   Syntax
      HELP

   Responses
      100   Help text follows (multiline)


7.2.2 Description

   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 5.3

7.2.3 Examples

      [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] .


7.3 NEWGROUPS

7.3.1 Usage

   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


7.3.2 Description

   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 7.6.1). However, they MAY



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   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 command (Section 7.6.2), 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 Time [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" parameter) when possible.

7.3.3 Examples

   Example where there are new groups:

      [C] NEWGROUPS 19990624 000000 GMT
      [S] 231 list of new newsgroups follows
      [S] alt.fc-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] .





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7.4 NEWNEWS

7.4.1 Usage

   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


7.4.2 Description

   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 7.3).

   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" parameter) when possible.

7.4.3 Examples

   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



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      [S] 230 list of new articles by message-id follows
      [S] .


7.5 Time

   As described in Section 6, 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
   reponses.

   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.

7.5.1 Examples

   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):




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      [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.

7.6 The LIST commands

7.6.1 LIST ACTIVE

7.6.1.1 Usage

   Syntax
      LIST ACTIVE [wildmat]

   Responses
      215   Information follows (multiline)

   Parameters
      wildmat = groups of interest


7.6.1.2 Description

   The LIST ACTIVE command with no parameters returns a list of valid
   newsgroups and associated information. The server MUST include every
   group that the client is permitted to select with the GROUP (Section
   6.1.1) 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;






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   "status" is the current status of the group on this server.

   Each field in the line is separated from its neighboring 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 6.1.1).

   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
   unrecognised 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 parameter is specified, the list is limited
   to only the groups whose names match the wildmat. If no wildmat is
   specified, the keyword ACTIVE MAY be omitted without altering the
   effect of the command.

7.6.1.3 Examples

   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.fc-writers.recovery 4 1 y
      [S] tx.natives.recovery 89 56 y
      [S] tx.natives.recovery.d 11 9 n
      [S] .



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   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.fc-writers.recovery 4 1 y
      [S] tx.natives.recovery 89 56 y
      [S] .


7.6.2 LIST ACTIVE.TIMES

7.6.2.1 Usage

   This command is optional.

   Syntax
      LIST ACTIVE.TIMES [wildmat]

   Responses
      215   Information follows (multiline)

   Parameters
      wildmat = groups of interest


7.6.2.2 Description

   The active.times file is maintained by some news transport systems to
   contain information about who created a particular newsgroup and
   when. Each line of this file 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 the email address of the entity that created the
   newsgroup, and must be a mailbox as defined in RFC 2822 [RFC2822].

   OUTSTANDING ISSUE

      Should the third field simply be free-form, or should it be
      recommended usage rather than mandatory? The problem with
      "mailbox" is that mailbox requires that it be fully qualified, and



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      unqualified addresses are apparently very common for groups
      created directly by the administrator.

   The file MAY omit newsgroups for which the information is unavailable
   and MAY include groups not available on the server; in particular,
   the file 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
   command (Section 7.3) 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 parameter is specified, the list is limited
   to only the groups in the file whose names match the wildmat. Note
   that an empty list is a possible valid response, and indicates that
   there are no groups in the file, or that match the wildmat.

7.6.2.3 Examples

   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
   recognised 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


7.6.3 LIST DISTRIBUTIONS






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7.6.3.1 Usage

   This command is optional.

   Syntax
      LIST DISTRIBUTIONS

   Responses
      215   Information follows (multiline)


7.6.3.2 Description

   The distributions file is maintained by some news transport 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 file 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.

7.6.3.3 Examples

   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
   recognised 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






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7.6.4 LIST DISTRIB.PATS

7.6.4.1 Usage

   This command is optional.

   Syntax
      LIST DISTRIB.PATS

   Responses
      215   Information follows (multiline)


7.6.4.2 Description

   The distrib.pats file is maintained by some news transport systems to
   choose a value for the content of the Distribution header of a news
   article being posted. Each line of this file 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.

7.6.4.3 Examples

   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
   recognised but the software does not maintain this information:

      [C] LIST DISTRIB.PATS



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      [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


7.6.5 LIST NEWSGROUPS

7.6.5.1 Usage

   This command is optional.

   Syntax
      LIST NEWSGROUPS [wildmat]

   Responses
      215   Information follows (multiline)

   Parameters
      wildmat = groups of interest


7.6.5.2 Description

   The newsgroups file is maintained by some news transport 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 file 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. Note that an empty list is a possible valid
   response, and indicates that there are currently no valid newsgroups.

   The file 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 parameter is specified, the list is limited
   to only the groups in the file whose names match the wildmat. Note
   that an empty list is a possible valid response, and indicates that
   there are no groups in the file, or that match the wildmat.



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7.6.5.3 Examples

   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
   recognised 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





























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8. Framework for NNTP extensions

   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:

   o  a mechanism for clients to determine a server's available
      extensions

   o  a registry of NNTP service extensions

   The LIST EXTENSIONS command is described in this document (see
   Section 5.3) and is the mechanism for clients to use to determine
   what extensions are available.

   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. Such RFCs either must be
   on the standards-track or must define an IESG-approved experimental
   protocol.

   The definition of an extension must include:

   o  a descriptive name for the extension




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   o  the extension-label (which is returned by LIST EXTENSIONS to
      indicate to the client that the server supports this particular
      extension)

   o  the syntax, values, and meanings of any parameters following the
      extension-label in the output of LIST EXTENSIONS

   o  any new NNTP commands associated with the extension

   o  the syntax and possible values of parameters associated with the
      new NNTP commands

   o  the response codes and possible values of parameters for the
      responses of the new NNTP commands

   o  any new parameters the extension associates with any other
      pre-existing NNTP commands

   o  how support for the extension affects the behavior of a server and
      NNTP client

   o  any increase in the maximum length of commands over the value
      specified in this document

   o  a specific statement about the effect on pipelining this extension
      may have (if any)

   The extension-label of private extensions MUST begin with "X". The
   extension-label of registered extensions MUST NOT begin with "X".

   A server MUST NOT provide any extension, whether or not listed in the
   output from LIST EXTENSIONS, unless it is either a registered
   extension or a private extension.

   OUTSTANDING ISSUE

      As worded, this forbids commands like MODE SLAVE that servers
      already provide but that aren't part of an existing extension. We
      can't simply make these illegal.

      The wording about starting keywords with an X could be reduced to
      a SHOULD, except for backwards compatibility (with a pointer to
      RFC 2980). But is that the right answer?

   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.



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   A server MAY provide additional keywords - either for new commands or
   new variants of existing commands - as part of a private extension.
   These new keywords MUST begin with "X".

   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.

8.1 Initial IANA registry

    The IANA's initial registry of NNTP service extensions consists of
   these entries:

     Extension                   Label        Added behavior
     Specific article numbers    LISTGROUP    Defined in this document
     Overview support            OVER         Defined in this document
     Header pattern matching     HDR          Defined in this document


8.2 Standard extensions

   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.

   If the server provides an extension, it MUST implement all of the
   commands in the specification of the extension except for those
   marked as optional. If it does not provide an extension, it MUST NOT
   implement any of the commands in the specification of that extension.

8.3 The LISTGROUP extension

   This extension provides one command and has the extension label
   LISTGROUP.

8.3.1 LISTGROUP

8.3.1.1 Usage

   Syntax
      LISTGROUP [group]





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   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.


8.3.1.2 Description

   The LISTGROUP command is used to get a listing of all the article
   numbers in a particular newsgroup.

   The optional parameter 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.

   The list of article numbers is returned as a multi-line response
   following the 211 response code (the parameters on the initial
   response line are the same as for the GROUP command (see Section
   6.1.1). 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.

8.3.1.3 Examples

   Example of LISTGROUP on an empty group:



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      [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


8.4 Article metadata

   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).

   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.)

   This specification defines two metadata items: ":bytes" and ":lines".
   Implementations and other extensions may define other metadata items.

   OUTSTANDING ISSUE

      Do we need a separate private namespace? For example, we could
      reserve :name for extensions and ::name for implementation use.



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8.4.1 The :bytes metadata item

   The :bytes metadata item for an article is a decimal integer. It MUST
   equal the number of octets in the entire article - headers, body, and
   separating empty line - except that each CRLF pair MAY (but SHOULD
   NOT) be counted as a single octet.

   OUTSTANDING ISSUE

      Should this be called ":octets" instead?


8.4.2 The :lines metadata item

   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).

8.5 The OVER extension

   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. The LIST OVERVIEW.FMT command
   describes the information that would be stored for an article
   arriving at the same time as the command was executed.

   This extension is based on the Overview/NOV database [ROBE1995]
   developed by Geoff Collyer.

8.5.1 OVER

8.5.1.1 Usage

   Syntax
      OVER [range]

   Responses
      224   Overview information follows (multiline)
      412   No newsgroup selected
      420   Current article number is invalid



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      423   No articles in that range

   Parameters
      range = Article(s) to return information for


8.5.1.2 Description

   The OVER command returns the contents of the headers and metadata in
   the database for the article(s) specified from the current selected
   newsgroup.

   The optional range argument may be any of the following:

   o  an article number

   o  an article number followed by a dash to indicate all following

   o  an article number followed by a dash followed by another article
      number

   If no argument is specified, then the current article number is used.

   If the information is available, it is returned as a multi-line
   response following the 224 response code. If the current selected
   newsgroup is invalid, a 412 response MUST be returned. If there are
   no articles in the range specified, a 423 response MUST be returned.
   If OVER is sent without any arguments and the current article number
   is invalid, a 420 response MUST be returned.

   For a successful response, the output consists of one line per
   article, sorted in numerical order of article number. 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:

      article number
      Subject header content
      From header content
      Date header content
      Message-ID header content
      References header content
      :bytes metadata item
      :lines metadata item

   Any subsequent fields are the contents of the other headers and



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   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 may permit these characters to appear in articles.

   The server SHOULD NOT produce output for articles that no longer
   exist.

8.5.1.3 Examples

   In the first two 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|



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      17|Xref: news.example.com misc.test:3000363
      [S] .

   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] 420 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



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8.5.2 LIST OVERVIEW.FMT

8.5.2.1 Usage

   Syntax
      LIST OVERVIEW.FMT

   Responses
      215   Information follows (multiline)


8.5.2.2 Description

   OUTSTANDING ISSUE

      Should this be optional even when the OVER extension is provided?
      Or even just removed entirely? What do we want to require about
      the OVER contents being consistent with the output of this
      command?

   The LIST OVERVIEW.FMT command returns a description of the fields in
   the database. The fields MUST be listed in the order that they will
   be returned by the OVER command for a newly-received article (the
   information stored for articles may change over time).

   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 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.



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   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 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.

8.5.2.3 Examples

   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:

      [C] LIST OVERVIEW.FMT
      [S] 503 overview.fmt not available




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8.6 The HDR extension

   This extension provides one new command: HDR. The label for this
   extension is HDR.

   OUTSTANDING ISSUE

      There is ongoing discussion about whether this extension should
      have a parameter and, if so, what it means.


8.6.1 HDR

8.6.1.1 Usage

   Syntax
      HDR header range
      HDR header message-id
      HDR header

   Responses

      First form (range specified)
         225   Headers follow (multiline)
         412   No newsgroup selected
         423   No articles in that range

      Second form (message-id specified)
         225   Headers follow (multiline)
         430   No article with that message-id

      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


8.6.1.2 Description

   The HDR command retrieves specific headers from an article or
   specified range of articles in the current selected newsgroup, or
   from an article specified by message-id. It can also return certain
   metadata about the article or articles.



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   The required header parameter 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 range parameter may be any of the following:

   o  an article number

   o  an article number followed by a dash to indicate all following

   o  an article number followed by a dash followed by another article
      number

   The message-id argument indicates a specific article. As shown by the
   syntax, the range and message-id arguments are mutually exclusive; 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 where the relevant header line exists. The line consists
   of the article number, a space, and then the contents of the header
   (without the header name or the colon and space that follow it) or
   metadata item. If the article is specified by message-id rather than
   by article range, the article number is given as "0".

   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 extension
   (Section 8.5.1.2), 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.




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   If the optional argument is a message-id and no such article exists,
   a 430 response MUST be returned. If the optional argument is not a
   message-id and the current selected newsgroup is invalid, a 412
   response MUST be returned. If the optional argument is an article
   number or number range and no article with that number or in that
   number range exists in the current selected newsgroup, a 423 response
   MUST be returned. If HDR is sent without any arguments 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 (such as those present in the overview database). If
   so, it MUST respond with a 503 response to attempts to request other
   headers, rather than returning erroneous results such as a successful
   empty response.

8.6.1.3 Examples

   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



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      [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








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9. Augmented BNF Syntax for NNTP

   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 ABNF [RFC2234] strings are
   case insensitive. Non-terminals used in several places are defined in
   a separate section at the end.

9.1 Commands

    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-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]



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     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-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]
     post-command = "POST"
     quit-command = "QUIT"
     stat-command = "STAT" [article-ref]
     x-command = x-command-name *(WS x-argument)
         ; Each extension command is specified fully elsewhere

     article-ref = WS (article-number / message-id)
     article-number = 1*16DIGIT
     date = [2DIGIT] 6DIGIT
     date-time = date WS time [WS "GMT"]
     header-meta-name = header-name / metadata-name
     metadata-name = ":" 1*A-NOTCOLON
     newsgroup-name = 1*wildmat-exact
     range = article-number ["-" [article-number]]
     range-ref = WS (range / message-id)
     time = 6DIGIT
     x-command-name = 3*12A-CHAR
     x-argument = 1*P-CHAR

     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 = "*" / "?"










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9.2 Responses

    This syntax defines the non-terminal "response", which represents
   what is sent from the server to the client in response to a command.

     response = simple-response / multiline-response
     multiline-response = simple-response *content-line termination
     termination = "." CRLF
     content-line = [content-text] CRLF
     content-text = (".." / B-NONDOT) B-CHAR

     simple-response = 3DIGIT parameters [ SP trailing-comment ] CRLF
     trailing-comment = *U-CHAR
     parameters = *( SP parameter ) ; How many depends on the response
     parameter = 1*A-CHAR


9.3 Articles

    This syntax defines the non-terminal "article", which represents the
   format of an article as described in Section 3.4.

     article = 1*header CRLF body
     body = *(*B-CHAR CRLF)
     header = header-name ":" header-tail CRLF
     header-tail = SP header-content-u / CRLF SP header-content-f
     header-content-u = *( header-gap header-text) *WS
     header-content-f = *WS header-text header-content-u
     header-gap = *WS [CRLF] 1*WS
     header-text = 1*P-CHAR


9.4 General non-terminals


















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     header-name = 1*A-NOTCOLON
     message-id = "<" 1*248A-NOTGT ">"

     ; Assorted special character sets
     ;   A- means based on 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     = %x01-09 / %x0B-0C / %x0E-7F / UTF8-non-ascii
     B-CHAR     = %x01-09 / %x0B-0C / %x0E-FF
     B-NONDOT   = %x01-09 / %x0B-0C / %x0E-2D / %x2F-FF  ; exclude "."

     CR = %x0D
     CRLF = CR LF
     DIGIT = %x30-39
     EOL = *(SP / HT) CRLF
     HT = %x09
     LF = %x0A
     SP = %x20
     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 / HT)

   OUTSTANDING ISSUE

      When draft-yergeau-rfc2279bis-04.txt replaces 2279, need to update
      references.















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10. IANA Considerations

   This specification requires IANA to keep a registry of
   extension-labels. The initial contents of this registry are specified
   in Section 8.1. As described in Section 8, names beginning with X are
   reserved for private use while all other names are to be associated
   with a specification in an RFC on the standards-track or defining an
   IESG-approved experimental protocol.











































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11. Security Considerations

   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.

11.1 Personal and Proprietary Information

   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.

11.2 Abuse of Server Log Information

   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.

11.3 Weak Authentication and Access Control

   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. 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.




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11.4 DNS Spoofing

   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 behavior 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.

11.5 UTF-8 issues

   UTF-8 [RFC2279] 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:

   o  replacing such sequences by a "guessed" valid sequence (based on



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      properties of the UTF-8 encoding);

   o  replacing such sequences by the sequence %xEF.BF.BD, which encodes
      the "replacement character" U+FFFD;

   o  closing the connection;

   o  generating a 501 response code.

   In the first 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.

   OUTSTANDING ISSUE

      Yergeau says that you MUST detect illegal sequences. He also
      rejects the first bullet point and consequent text; I'm discussing
      it with him now.



























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12. Acknowledgments

   The author acknowledges the original authors of NNTP as documented in
   RFC 977 [RFC977]: Brian Kantor and Phil Lapsey.

   The author gratefully acknowledges the work of the NNTP committee
   chaired by Eliot Lear. The organization of this document was
   influenced by the last available draft from this working group. A
   special thanks to Eliot for generously providing the original
   machine-readable sources for that document.

   The author gratefully acknowledges the work of Marshall Rose & John
   G. Meyers in RFC 1939 [RFC1939] and the work of the DRUMS working
   group, specifically RFC 1869 [RFC1869], which is the basis of the
   NNTP extensions mechanism detailed in this document.

   OUTSTANDING ISSUE

      Why RFC 1939?

   The author gratefully acknowledges the authors of RFC 2616 [RFC2616]
   for providing specific and relevant examples of security issues that
   should be considered for HTTP. Since many of the same considerations
   exist for NNTP, those examples that are relevant have been included
   here with some minor rewrites.

   The author gratefully acknowledges the comments and additional
   information provided by the following individuals in preparing one or
   more of the progenitors of this document:

      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




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   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

   Finally, the present author gratefully acknowledges the vast amount
   of work put into previous drafts by the previous author:

      Stan Barber <sob@academ.com>















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Normative References

   [ANSI1986]
              American National Standards Institute, "Coded Character
              Set - 7-bit American Standard Code for Information
              Interchange", ANSI X3.4, 1986.

   [RFC1305]  Mills, D., "Network Time Protocol (Version 3)
              Specification, Implementation", RFC 1305, March 1992.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 2234, November 1997.

   [RFC2279]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", RFC 2279, January 1998.

   [RFC2822]  Resnick, P., "Internet Message Format", RFC 2822, April
              2001.

   [RFC977]   Kantor, B. and P. Lapsley, "Network News Transfer
              Protocol", RFC 977, February 1986.

   [ROBE1995]
              Robertson, R., "FAQ: Overview database / NOV General
              Information", January 1995.

   [TF.686-1]
              International Telecommunications Union - Radio, "Glossary,
              ITU-R Recommendation TF.686-1", ITU-R Recommendation
              TF.686-1, October 1997.


















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Informative References

   [RFC1036]  Horton, M. and R. Adams, "Standard for interchange of
              USENET messages", RFC 1036, December 1987.

   [RFC1869]  Klensin, J., Freed, N., Rose, M., Stefferud, E. and D.
              Crocker, "SMTP Service Extensions", STD 10, RFC 1869,
              November 1995.

   [RFC1939]  Myers, J. and M. Rose, "Post Office Protocol - Version 3",
              STD 53, RFC 1939, May 1996.

   [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.

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              June 1999.

   [SALZ1992]
              Salz, R., "Manual Page for wildmat(3) from the INN 1.4
              distribution, Revision 1.10", April 1992.


Author's Address

   Clive D.W. Feather
   Thus plc
   322 Regents Park Road
   London  N3 2QQ
   GB

   Phone: +44 20 8495 6138
   Fax:   +44 870 051 9937
   URI:   http://www.davros.org/
















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Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.











































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