21.16. "nntplib" --- NNTP protocol client
*****************************************

**Source code:** Lib/nntplib.py

======================================================================

This module defines the 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('article.txt', 'rb')
   >>> s.post(f)
   '240 Article posted successfully.'
   >>> s.quit()
   '205 Bye!'

The module itself defines the following classes:

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

   Return a new "NNTP" object, 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 "/.netrc" and the optional flag
   *usenetrc* is true, 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 "NNTPPermanentError"s, you
   might need to set *readermode*. The "NNTP" class supports the
   "with" statement to unconditionally consume "OSError" exceptions
   and to close the NNTP connection when done, e.g.:

   >>> from nntplib import NNTP
   >>> with NNTP('news.gmane.org') as n:
   ...     n.group('gmane.comp.python.committers')
   ... 
   ('211 1755 1 1755 gmane.comp.python.committers', 1755, 1, 1755, 'gmane.comp.python.committers')
   >>>

   在 3.2 版更改: *usenetrc* is now "False" by default.

   在 3.3 版更改: 支持了 "with" 语句。

class nntplib.NNTP_SSL(host, port=563, user=None, password=None, ssl_context=None, readermode=None, usenetrc=False[, timeout])

   Return a new "NNTP_SSL" object, representing an encrypted
   connection to the NNTP server running on host *host*, listening at
   port *port*.  "NNTP_SSL" objects have the same methods as "NNTP"
   objects.  If *port* is omitted, port 563 (NNTPS) is used.
   *ssl_context* is also optional, and is a "SSLContext" object.
   Please read 安全考量 for best practices. All other parameters
   behave the same as for "NNTP".

   Note that SSL-on-563 is discouraged per **RFC 4642**, in favor of
   STARTTLS as described below.  However, some servers only support
   the former.

   3.2 新版功能.

   在 3.4 版更改: 本类现在支持通过 "ssl.SSLContext.check_hostname" 和
   *服务器名称提示* （参阅 "ssl.HAS_SNI"）进行主机名检查。

exception nntplib.NNTPError

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

   response

      The response of the server if available, as a "str" object.

exception nntplib.NNTPReplyError

   从服务器收到意外答复时，将引发本异常。

exception nntplib.NNTPTemporaryError

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

exception nntplib.NNTPPermanentError

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

exception nntplib.NNTPProtocolError

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

exception nntplib.NNTPDataError

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


21.16.1. NNTP Objects
=====================

When connected, "NNTP" and "NNTP_SSL" objects support the following
methods and attributes.


21.16.1.1. Attributes
---------------------

NNTP.nntp_version

   An integer representing the version of the NNTP protocol supported
   by the server.  In practice, this should be "2" for servers
   advertising **RFC 3977** compliance and "1" for others.

   3.2 新版功能.

NNTP.nntp_implementation

   A string describing the software name and version of the NNTP
   server, or "None" if not advertised by the server.

   3.2 新版功能.


21.16.1.2. 方法
---------------

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.

Many of the following methods take an optional keyword-only argument
*file*. When the *file* argument is supplied, it must be either a
*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.

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

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.

NNTP.getwelcome()

   返回服务器发送的欢迎消息，作为连接开始的回复。（该消息有时包含与用
   户有关的免责声明或帮助信息。）

NNTP.getcapabilities()

   Return the **RFC 3977** capabilities advertised by the server, as a
   "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

   3.2 新版功能.

NNTP.login(user=None, password=None, usenetrc=True)

   Send "AUTHINFO" commands with the user name and password.  If
   *user* and *password* are "None" and *usenetrc* is true,
   credentials from "~/.netrc" will be used if possible.

   Unless intentionally delayed, login is normally performed during
   the "NNTP" object initialization and separately calling this
   function is unnecessary.  To force authentication to be delayed,
   you must not set *user* or *password* when creating the object, and
   must set *usenetrc* to False.

   3.2 新版功能.

NNTP.starttls(context=None)

   Send a "STARTTLS" command.  This will enable encryption on the NNTP
   connection.  The *context* argument is optional and should be a
   "ssl.SSLContext" object.  Please read 安全考量 for best practices.

   Note that this may not be done after authentication information has
   been transmitted, and authentication occurs by default if possible
   during a "NNTP" object initialization.  See "NNTP.login()" for
   information on suppressing this behavior.

   3.2 新版功能.

   在 3.4 版更改: 此方法现在支持使用 "ssl.SSLContext.check_hostname"
   和 *服务器名称指示* (参见 "ssl.HAS_SNI") 进行主机名检查。

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

   Send a "NEWGROUPS" command.  The *date* argument should be a
   "datetime.date" or "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')

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 "newgroups()".  Return a
   pair "(response, articles)" where *articles* is a list of message
   ids.

   This command is frequently disabled by NNTP server administrators.

NNTP.list(group_pattern=None, *, file=None)

   Send a "LIST" or "LIST ACTIVE" command.  Return a pair "(response,
   list)" where *list* is a list of tuples representing all the groups
   available from this NNTP server, optionally matching the pattern
   string *group_pattern*.  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 can return very large results, especially if
   *group_pattern* is not specified.  It is best to cache the results
   offline unless you really need to refresh them.

   在 3.2 版更改: *group_pattern* was added.

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)')

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 "descriptions()".

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.

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

   Send an "OVER" command, or an "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 "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 "None" if not
   present.

   It is advisable to use the "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>'

   3.2 新版功能.

NNTP.help(*, file=None)

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

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 "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>')

NNTP.next()

   Send a "NEXT" command.  Return as for "stat()".

NNTP.last()

   Send a "LAST" command.  Return as for "stat()".

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

   Send an "ARTICLE" command, where *message_spec* has the same
   meaning as for "stat()".  Return a tuple "(response, info)" where
   *info* is a "namedtuple" with three attributes *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']

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

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

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

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

NNTP.post(data)

   Post an article using the "POST" command.  The *data* argument is
   either a *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 "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 "NNTPReplyError" is raised.

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 "post()".

NNTP.date()

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

NNTP.slave()

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

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**.

NNTP.xhdr(hdr, str, *, file=None)

   Send an "XHDR" command.  The *hdr* argument is a header keyword,
   e.g. "'subject'".  The *str* 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 *file object*, then it will start calling
   "write()" on it to store the lines of the command output. If *file*
   is supplied, then the returned *list* is an empty list.

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 "over()".  It is recommended to use "over()"
   instead, since it will automatically use the newer "OVER" command
   if available.

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.

   3.3 版后已移除: The XPATH extension is not actively used.


21.16.2. 工具函数
=================

The module also defines the following utility function:

nntplib.decode_header(header_str)

   Decode a header value, un-escaping any escaped non-ASCII
   characters. *header_str* must be a "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'
