Doc/library/nntplib.rst

:mod:`nntplib` --- NNTP protocol client
=======================================

.. module:: nntplib
   :synopsis: NNTP protocol client (requires sockets).


.. index::
   pair: NNTP; protocol
   single: Network News Transfer Protocol

This module defines the class :class:`NNTP` which implements the client side of
the Network News Transfer Protocol.  It can be used to implement a news reader
or poster, or automated news processors.  It is compatible with :rfc:`3977`
as well as the older :rfc:`977` and :rfc:`2980`.

Here are two small examples of how it can be used.  To list some statistics
about a newsgroup and print the subjects of the last 10 articles::

   >>> s = nntplib.NNTP('news.gmane.org')
   >>> resp, count, first, last, name = s.group('gmane.comp.python.committers')
   >>> print('Group', name, 'has', count, 'articles, range', first, 'to', last)
   Group gmane.comp.python.committers has 1096 articles, range 1 to 1096
   >>> resp, overviews = s.over((last - 9, last))
   >>> for id, over in overviews:
   ...     print(id, nntplib.decode_header(over['subject']))
   ...
   1087 Re: Commit privileges for Łukasz Langa
   1088 Re: 3.2 alpha 2 freeze
   1089 Re: 3.2 alpha 2 freeze
   1090 Re: Commit privileges for Łukasz Langa
   1091 Re: Commit privileges for Łukasz Langa
   1092 Updated ssh key
   1093 Re: Updated ssh key
   1094 Re: Updated ssh key
   1095 Hello fellow committers!
   1096 Re: Hello fellow committers!
   >>> s.quit()
   '205 Bye!'

To post an article from a binary file (this assumes that the article has valid
headers, and that you have right to post on the particular newsgroup)::

   >>> s = nntplib.NNTP('news.gmane.org')
   >>> f = open('/tmp/article.txt', 'rb')
   >>> s.post(f)
   '240 Article posted successfully.'
   >>> s.quit()
   '205 Bye!'

The module itself defines the following classes:


.. class:: NNTP(host, port=119, user=None, password=None, readermode=None, usenetrc=True, [timeout])

   Return a new instance of the :class:`NNTP` class, representing a connection
   to the NNTP server running on host *host*, listening at port *port*.
   An optional *timeout* can be specified for the socket connection.
   If the optional *user* and *password* are provided, or if suitable
   credentials are present in :file:`/.netrc` and the optional flag *usenetrc*
   is true (the default), the ``AUTHINFO USER`` and ``AUTHINFO PASS`` commands
   are used to identify and authenticate the user to the server.  If the optional
   flag *readermode* is true, then a ``mode reader`` command is sent before
   authentication is performed.  Reader mode is sometimes necessary if you are
   connecting to an NNTP server on the local machine and intend to call
   reader-specific commands, such as ``group``.  If you get unexpected
   :exc:`NNTPPermanentError`\ s, you might need to set *readermode*.
   *readermode* defaults to ``None``. *usenetrc* defaults to ``True``.


.. exception:: NNTPError

   Derived from the standard exception :exc:`Exception`, this is the base
   class for all exceptions raised by the :mod:`nntplib` module.  Instances
   of this class have the following attribute:

   .. attribute:: response

      The response of the server if available, as a :class:`str` object.


.. exception:: NNTPReplyError

   Exception raised when an unexpected reply is received from the server.


.. exception:: NNTPTemporaryError

   Exception raised when a response code in the range 400--499 is received.


.. exception:: NNTPPermanentError

   Exception raised when a response code in the range 500--599 is received.


.. exception:: NNTPProtocolError

   Exception raised when a reply is received from the server that does not begin
   with a digit in the range 1--5.


.. exception:: NNTPDataError

   Exception raised when there is some error in the response data.


.. _nntp-objects:

NNTP Objects
------------

:class:`NNTP` instances have the following methods.  The *response* that is
returned as the first item in the return tuple of almost all methods is the
server's response: a string beginning with a three-digit code. If the server's
response indicates an error, the method raises one of the above exceptions.

.. note::
   Many of the following methods take an optional keyword-only argument *file*.
   When the *file* argument is supplied, it must be either a :term:`file object`
   opened for binary writing, or the name of an on-disk file to be written to.
   The method will then write any data returned by the server (except for the
   response line and the terminating dot) to the file; any list of lines,
   tuples or objects that the method normally returns will be empty.


.. versionchanged:: 3.2
   Many of the following methods have been reworked and fixed, which makes
   them incompatible with their 3.1 counterparts.


.. method:: NNTP.quit()

   Send a ``QUIT`` command and close the connection.  Once this method has been
   called, no other methods of the NNTP object should be called.


.. method:: NNTP.getwelcome()

   Return the welcome message sent by the server in reply to the initial
   connection.  (This message sometimes contains disclaimers or help information
   that may be relevant to the user.)


.. method:: NNTP.getcapabilities()

   Return the :rfc:`3977` capabilities advertised by the server, as a
   :class:`dict` instance mapping capability names to (possibly empty) lists
   of values. On legacy servers which don't understand the ``CAPABILITIES``
   command, an empty dictionary is returned instead.

      >>> s = NNTP('news.gmane.org')
      >>> 'POST' in s.getcapabilities()
      True

   .. versionadded:: 3.2


.. method:: NNTP.newgroups(date, *, file=None)

   Send a ``NEWGROUPS`` command.  The *date* argument should be a
   :class:`datetime.date` or :class:`datetime.datetime` object.
   Return a pair ``(response, groups)`` where *groups* is a list representing
   the groups that are new since the given *date*. If *file* is supplied,
   though, then *groups* will be empty.

      >>> from datetime import date, timedelta
      >>> resp, groups = s.newgroups(date.today() - timedelta(days=3))
      >>> len(groups)
      85
      >>> groups[0]
      GroupInfo(group='gmane.network.tor.devel', last='4', first='1', flag='m')


.. method:: NNTP.newnews(group, date, *, file=None)

   Send a ``NEWNEWS`` command.  Here, *group* is a group name or ``'*'``, and
   *date* has the same meaning as for :meth:`newgroups`.  Return a pair
   ``(response, articles)`` where *articles* is a list of message ids.

   This command is frequently disabled by NNTP server administrators.


.. method:: NNTP.list(*, file=None)

   Send a ``LIST`` command.  Return a pair ``(response, list)`` where *list* is a
   list of tuples representing all the groups available from this NNTP server.
   Each tuple has the form ``(group, last, first, flag)``, where
   *group* is a group name, *last* and *first* are the last and first article
   numbers, and *flag* usually takes one of these values:

   * ``y``: Local postings and articles from peers are allowed.
   * ``m``: The group is moderated and all postings must be approved.
   * ``n``: No local postings are allowed, only articles from peers.
   * ``j``: Articles from peers are filed in the junk group instead.
   * ``x``: No local postings, and articles from peers are ignored.
   * ``=foo.bar``: Articles are filed in the ``foo.bar`` group instead.

   If *flag* has another value, then the status of the newsgroup should be
   considered unknown.

   This command will often return very large results.  It is best to cache the
   results offline unless you really need to refresh them.


.. method:: NNTP.descriptions(grouppattern)

   Send a ``LIST NEWSGROUPS`` command, where *grouppattern* is a wildmat string as
   specified in :rfc:`3977` (it's essentially the same as DOS or UNIX shell wildcard
   strings).  Return a pair ``(response, descriptions)``, where *descriptions*
   is a dictionary mapping group names to textual descriptions.

      >>> resp, descs = s.descriptions('gmane.comp.python.*')
      >>> len(descs)
      295
      >>> descs.popitem()
      ('gmane.comp.python.bio.general', 'BioPython discussion list (Moderated)')


.. method:: NNTP.description(group)

   Get a description for a single group *group*.  If more than one group matches
   (if 'group' is a real wildmat string), return the first match.   If no group
   matches, return an empty string.

   This elides the response code from the server.  If the response code is needed,
   use :meth:`descriptions`.


.. method:: NNTP.group(name)

   Send a ``GROUP`` command, where *name* is the group name.  The group is
   selected as the current group, if it exists.  Return a tuple
   ``(response, count, first, last, name)`` where *count* is the (estimated)
   number of articles in the group, *first* is the first article number in
   the group, *last* is the last article number in the group, and *name*
   is the group name.


.. method:: NNTP.over(message_spec, *, file=None)

   Send a ``OVER`` command, or a ``XOVER`` command on legacy servers.
   *message_spec* can be either a string representing a message id, or
   a ``(first, last)`` tuple of numbers indicating a range of articles in
   the current group, or a ``(first, None)`` tuple indicating a range of
   articles starting from *first* to the last article in the current group,
   or :const:`None` to select the current article in the current group.

   Return a pair ``(response, overviews)``.  *overviews* is a list of
   ``(article_number, overview)`` tuples, one for each article selected
   by *message_spec*.  Each *overview* is a dictionary with the same number
   of items, but this number depends on the server.  These items are either
   message headers (the key is then the lower-cased header name) or metadata
   items (the key is then the metadata name prepended with ``":"``).  The
   following items are guaranteed to be present by the NNTP specification:

   * the ``subject``, ``from``, ``date``, ``message-id`` and ``references``
     headers
   * the ``:bytes`` metadata: the number of bytes in the entire raw article
     (including headers and body)
   * the ``:lines`` metadata: the number of lines in the article body

   The value of each item is either a string, or :const:`None` if not present.

   It is advisable to use the :func:`decode_header` function on header
   values when they may contain non-ASCII characters::

      >>> _, _, first, last, _ = s.group('gmane.comp.python.devel')
      >>> resp, overviews = s.over((last, last))
      >>> art_num, over = overviews[0]
      >>> art_num
      117216
      >>> list(over.keys())
      ['xref', 'from', ':lines', ':bytes', 'references', 'date', 'message-id', 'subject']
      >>> over['from']
      '=?UTF-8?B?Ik1hcnRpbiB2LiBMw7Z3aXMi?= <martin@v.loewis.de>'
      >>> nntplib.decode_header(over['from'])
      '"Martin v. Löwis" <martin@v.loewis.de>'

   .. versionadded:: 3.2


.. method:: NNTP.help(*, file=None)

   Send a ``HELP`` command.  Return a pair ``(response, list)`` where *list* is a
   list of help strings.


.. method:: NNTP.stat(message_spec=None)

   Send a ``STAT`` command, where *message_spec* is either a message id
   (enclosed in ``'<'`` and ``'>'``) or an article number in the current group.
   If *message_spec* is omitted or :const:`None`, the current article in the
   current group is considered.  Return a triple ``(response, number, id)``
   where *number* is the article number and *id* is the message id.

      >>> _, _, first, last, _ = s.group('gmane.comp.python.devel')
      >>> resp, number, message_id = s.stat(first)
      >>> number, message_id
      (9099, '<20030112190404.GE29873@epoch.metaslash.com>')


.. method:: NNTP.next()

   Send a ``NEXT`` command.  Return as for :meth:`stat`.


.. method:: NNTP.last()

   Send a ``LAST`` command.  Return as for :meth:`stat`.


.. method:: NNTP.article(message_spec=None, *, file=None)

   Send an ``ARTICLE`` command, where *message_spec* has the same meaning as
   for :meth:`stat`.  Return a tuple ``(response, info)`` where *info*
   is a :class:`~collections.namedtuple` with three members *number*,
   *message_id* and *lines* (in that order).  *number* is the article number
   in the group (or 0 if the information is not available), *message_id* the
   message id as a string, and *lines* a list of lines (without terminating
   newlines) comprising the raw message including headers and body.

      >>> resp, info = s.article('<20030112190404.GE29873@epoch.metaslash.com>')
      >>> info.number
      0
      >>> info.message_id
      '<20030112190404.GE29873@epoch.metaslash.com>'
      >>> len(info.lines)
      65
      >>> info.lines[0]
      b'Path: main.gmane.org!not-for-mail'
      >>> info.lines[1]
      b'From: Neal Norwitz <neal@metaslash.com>'
      >>> info.lines[-3:]
      [b'There is a patch for 2.3 as well as 2.2.', b'', b'Neal']


.. method:: NNTP.head(message_spec=None, *, file=None)

   Same as :meth:`article()`, but sends a ``HEAD`` command.  The *lines*
   returned (or written to *file*) will only contain the message headers, not
   the body.


.. method:: NNTP.body(message_spec=None, *, file=None)

   Same as :meth:`article()`, but sends a ``BODY`` command.  The *lines*
   returned (or written to *file*) will only contain the message body, not the
   headers.


.. method:: NNTP.post(data)

   Post an article using the ``POST`` command.  The *data* argument is either
   a :term:`file object` opened for binary reading, or any iterable of bytes
   objects (representing raw lines of the article to be posted).  It should
   represent a well-formed news article, including the required headers.  The
   :meth:`post` method automatically escapes lines beginning with ``.`` and
   appends the termination line.

   If the method succeeds, the server's response is returned.  If the server
   refuses posting, a :class:`NNTPReplyError` is raised.


.. method:: NNTP.ihave(message_id, data)

   Send an ``IHAVE`` command. *message_id* is the id of the message to send
   to the server (enclosed in  ``'<'`` and ``'>'``).  The *data* parameter
   and the return value are the same as for :meth:`post()`.


.. method:: NNTP.date()

   Return a pair ``(response, date)``.  *date* is a :class:`~datetime.datetime`
   object containing the current date and time of the server.


.. method:: NNTP.slave()

   Send a ``SLAVE`` command.  Return the server's *response*.


.. method:: NNTP.set_debuglevel(level)

   Set the instance's debugging level.  This controls the amount of debugging
   output printed.  The default, ``0``, produces no debugging output.  A value of
   ``1`` produces a moderate amount of debugging output, generally a single line
   per request or response.  A value of ``2`` or higher produces the maximum amount
   of debugging output, logging each line sent and received on the connection
   (including message text).


The following are optional NNTP extensions defined in :rfc:`2980`.  Some of
them have been superseded by newer commands in :rfc:`3977`.


.. method:: NNTP.xhdr(header, string, *, file=None)

   Send an ``XHDR`` command.  The *header* argument is a header keyword, e.g.
   ``'subject'``.  The *string* argument should have the form ``'first-last'``
   where *first* and *last* are the first and last article numbers to search.
   Return a pair ``(response, list)``, where *list* is a list of pairs ``(id,
   text)``, where *id* is an article number (as a string) and *text* is the text of
   the requested header for that article. If the *file* parameter is supplied, then
   the output of the  ``XHDR`` command is stored in a file.  If *file* is a string,
   then the method will open a file with that name, write to it  then close it.
   If *file* is a :term:`file object`, then it will start calling :meth:`write` on
   it to store the lines of the command output. If *file* is supplied, then the
   returned *list* is an empty list.


.. method:: NNTP.xover(start, end, *, file=None)

   Send an ``XOVER`` command.  *start* and *end* are article numbers
   delimiting the range of articles to select.  The return value is the
   same of for :meth:`over()`.  It is recommended to use :meth:`over()`
   instead, since it will automatically use the newer ``OVER`` command
   if available.


.. method:: NNTP.xpath(id)

   Return a pair ``(resp, path)``, where *path* is the directory path to the
   article with message ID *id*.  Most of the time, this extension is not
   enabled by NNTP server administrators.


.. XXX deprecated:

   .. method:: NNTP.xgtitle(name, *, file=None)

      Process an ``XGTITLE`` command, returning a pair ``(response, list)``, where
      *list* is a list of tuples containing ``(name, title)``. If the *file* parameter
      is supplied, then the output of the  ``XGTITLE`` command is stored in a file.
      If *file* is a string,  then the method will open a file with that name, write
      to it  then close it.  If *file* is a :term:`file object`, then it will start
      calling :meth:`write` on it to store the lines of the command output. If *file*
      is supplied, then the returned *list* is an empty list. This is an optional NNTP
      extension, and may not be supported by all servers.

      RFC2980 says "It is suggested that this extension be deprecated".  Use
      :meth:`descriptions` or :meth:`description` instead.


Utility functions
-----------------

The module also defines the following utility function:


.. function:: decode_header(header_str)

   Decode a header value, un-escaping any escaped non-ASCII characters.
   *header_str* must be a :class:`str` object.  The unescaped value is
   returned.  Using this function is recommended to display some headers
   in a human readable form::

      >>> decode_header("Some subject")
      'Some subject'
      >>> decode_header("=?ISO-8859-15?Q?D=E9buter_en_Python?=")
      'Débuter en Python'
      >>> decode_header("Re: =?UTF-8?B?cHJvYmzDqG1lIGRlIG1hdHJpY2U=?=")
      'Re: problème de matrice'