Le protocole NNTP: Common Implementation Issues

4.0. Common Implementation Issues

   Many NNTP implementations do not follow the specifications in RFC
   977 .  In this section, some common implementation issues are
   summarized.

4.1. The Response to the LIST command

   RFC 977 says that the fourth field of the "list of valid newsgroups
   associated information" returned must be "either 'y' or 'n'
   indicating whether posting to this newsgroup is allowed ('y') or
   prohibited ('n').  Most implementations simply output the exact
   contents of the transport system's active newsgroup list.  For more
   implementations, the fourth field usually has more values that 'y' or
   'n'.

4.2. The Required Headers in an Article and the POST command

   RFC 977 notes in section 3.10.1 that articles presented "should
   include all required header lines." In fact, modern implementations
   only require From, Subject, and Newsgroups header lines and will
   supply the rest; further, many implementers believe that it is best
   for clients to generate as few headers as possible, since clients
   often do not format other headers correctly.

   This implementation behavior is consistent with both Bnews and Cnews
   which would supply missing headers for articles directly submitted to
   them.

4.3. Article Numbering

   RFC 977 does not directly address the rules concerning articles
   number.  However, the current practice is simple: article numbers are
   monotonically increasing, articles may disappear, and therefore the
   high and low water marks returned in a GROUP command should be
   treated as maximum minima, and minimum maxima, respectively.

   Some implementations permit administrators to disable commands
   defined RFC 977.  Some implementations have some set of commands
   disabled by default.  This means that client implementations cannot
   depend on the availability of the disabled set of commands.  This
   increases the complexity of the client and does not encourage
   implementors to optimize the implementation of commands that don't
   perform well.

   NEWNEWS is one of the commands frequently disabled.

4.5. The Distribution header and NEWNEWS

   In section 12.4 of RFC 977, the optional distributions argument is
   described.  This argument, according to RFC 977, would limit the
   responses to articles that were in newsgroups with prefixes that
   matched the optional distributions argument.

   Some implementations implement this by matching the Distributions
   header in articles to the distribution argument.  Others do the match
   against segments of the newsgroup's name.

   This variation is probably best explained by the evolution of the
   USENET article format.  At the time RFC 977 was specified, the
   newsgroup name defined how the group was distributed throughout
   USENET.  RFC 1036 changed this convention.  So, those that are

   strictly implementing RFC 977 would match the newsgroup name prefix
   against the distribution argument and only display matches.  Those
   that implement against the intent of the command (as modified by the
   redefinition of the article format)would match the Distributions
   header against the distribution argument and only display those
   matches.