Issue #9360: Cleanup and improvements to the nntplib module. The API

now conforms to the philosophy of bytes and unicode separation in Python 3.
A test suite has also been added.

1 files changed, 656 insertions, 290 deletions

diff --git a/Lib/nntplib.py b/Lib/nntplib.py
index 6ac2fcb..1055d06 100644
--- a/Lib/nntplib.py
+++ b/Lib/nntplib.py
@@ -1,4 +1,7 @@
-"""An NNTP client class based on RFC 977: Network News Transfer Protocol.
+"""An NNTP client class based on:
+- RFC 977: Network News Transfer Protocol
+- RFC 2980: Common NNTP Extensions
+- RFC 3977: Network News Transfer Protocol (version 2)
 
 Example:
 
@@ -27,15 +30,53 @@ are strings, not numbers, since they are rarely used for calculations.
 # RFC 977 by Brian Kantor and Phil Lapsley.
 # xover, xgtitle, xpath, date methods by Kevan Heydon
 
+# Incompatible changes from the 2.x nntplib:
+# - all commands are encoded as UTF-8 data (using the "surrogateescape"
+#   error handler), except for raw message data (POST, IHAVE)
+# - all responses are decoded as UTF-8 data (using the "surrogateescape"
+#   error handler), except for raw message data (ARTICLE, HEAD, BODY)
+# - the `file` argument to various methods is keyword-only
+#
+# - NNTP.date() returns a datetime object
+# - NNTP.newgroups() and NNTP.newnews() take a datetime (or date) object,
+#   rather than a pair of (date, time) strings.
+# - NNTP.newgroups() and NNTP.list() return a list of GroupInfo named tuples
+# - NNTP.descriptions() returns a dict mapping group names to descriptions
+# - NNTP.xover() returns a list of dicts mapping field names (header or metadata)
+#   to field values; each dict representing a message overview.
+# - NNTP.article(), NNTP.head() and NNTP.body() return a (response, ArticleInfo)
+#   tuple.
+# - the "internal" methods have been marked private (they now start with
+#   an underscore)
+
+# Other changes from the 2.x/3.1 nntplib:
+# - automatic querying of capabilities at connect
+# - New method NNTP.getcapabilities()
+# - New method NNTP.over()
+# - New helper function decode_header()
+# - NNTP.post() and NNTP.ihave() accept file objects, bytes-like objects and
+#   arbitrary iterables yielding lines.
+# - An extensive test suite :-)
+
+# TODO:
+# - return structured data (GroupInfo etc.) everywhere
+# - support HDR
 
 # Imports
 import re
 import socket
+import collections
+import datetime
+import warnings
 
-__all__ = ["NNTP","NNTPReplyError","NNTPTemporaryError",
-           "NNTPPermanentError","NNTPProtocolError","NNTPDataError",
-           "error_reply","error_temp","error_perm","error_proto",
-           "error_data",]
+from email.header import decode_header as _email_decode_header
+from socket import _GLOBAL_DEFAULT_TIMEOUT
+
+__all__ = ["NNTP",
+           "NNTPReplyError", "NNTPTemporaryError", "NNTPPermanentError",
+           "NNTPProtocolError", "NNTPDataError",
+           "decode_header",
+           ]
 
 # Exceptions raised when an error or invalid response is received
 class NNTPError(Exception):
@@ -67,39 +108,189 @@ class NNTPDataError(NNTPError):
     """Error in response data"""
     pass
 
-# for backwards compatibility
-error_reply = NNTPReplyError
-error_temp = NNTPTemporaryError
-error_perm = NNTPPermanentError
-error_proto = NNTPProtocolError
-error_data = NNTPDataError
-
-
 
 # Standard port used by NNTP servers
 NNTP_PORT = 119
 
 
 # Response numbers that are followed by additional text (e.g. article)
-LONGRESP = [b'100', b'215', b'220', b'221', b'222', b'224', b'230', b'231', b'282']
-
+_LONGRESP = {
+    '100',   # HELP
+    '101',   # CAPABILITIES
+    '211',   # LISTGROUP   (also not multi-line with GROUP)
+    '215',   # LIST
+    '220',   # ARTICLE
+    '221',   # HEAD, XHDR
+    '222',   # BODY
+    '224',   # OVER, XOVER
+    '225',   # HDR
+    '230',   # NEWNEWS
+    '231',   # NEWGROUPS
+    '282',   # XGTITLE
+}
+
+# Default decoded value for LIST OVERVIEW.FMT if not supported
+_DEFAULT_OVERVIEW_FMT = [
+    "subject", "from", "date", "message-id", "references", ":bytes", ":lines"]
+
+# Alternative names allowed in LIST OVERVIEW.FMT response
+_OVERVIEW_FMT_ALTERNATIVES = {
+    'bytes': ':bytes',
+    'lines': ':lines',
+}
 
 # Line terminators (we always output CRLF, but accept any of CRLF, CR, LF)
-CRLF = b'\r\n'
+_CRLF = b'\r\n'
 
+GroupInfo = collections.namedtuple('GroupInfo',
+                                   ['group', 'last', 'first', 'flag'])
 
+ArticleInfo = collections.namedtuple('ArticleInfo',
+                                     ['number', 'message_id', 'lines'])
 
-# The class itself
-class NNTP:
-    def __init__(self, host, port=NNTP_PORT, user=None, password=None,
-                 readermode=None, usenetrc=True):
+
+# Helper function(s)
+def decode_header(header_str):
+    """Takes an unicode string representing a munged header value
+    and decodes it as a (possibly non-ASCII) readable value."""
+    parts = []
+    for v, enc in _email_decode_header(header_str):
+        if isinstance(v, bytes):
+            parts.append(v.decode(enc or 'ascii'))
+        else:
+            parts.append(v)
+    return ' '.join(parts)
+
+def _parse_overview_fmt(lines):
+    """Parse a list of string representing the response to LIST OVERVIEW.FMT
+    and return a list of header/metadata names.
+    Raises NNTPDataError if the response is not compliant
+    (cf. RFC 3977, section 8.4)."""
+    fmt = []
+    for line in lines:
+        if line[0] == ':':
+            # Metadata name (e.g. ":bytes")
+            name, _, suffix = line[1:].partition(':')
+            name = ':' + name
+        else:
+            # Header name (e.g. "Subject:" or "Xref:full")
+            name, _, suffix = line.partition(':')
+        name = name.lower()
+        name = _OVERVIEW_FMT_ALTERNATIVES.get(name, name)
+        # Should we do something with the suffix?
+        fmt.append(name)
+    defaults = _DEFAULT_OVERVIEW_FMT
+    if len(fmt) < len(defaults):
+        raise NNTPDataError("LIST OVERVIEW.FMT response too short")
+    if fmt[:len(defaults)] != defaults:
+        raise NNTPDataError("LIST OVERVIEW.FMT redefines default fields")
+    return fmt
+
+def _parse_overview(lines, fmt, data_process_func=None):
+    """Parse the response to a OVER or XOVER command according to the
+    overview format `fmt`."""
+    n_defaults = len(_DEFAULT_OVERVIEW_FMT)
+    overview = []
+    for line in lines:
+        fields = {}
+        article_number, *tokens = line.split('\t')
+        article_number = int(article_number)
+        for i, token in enumerate(tokens):
+            if i >= len(fmt):
+                # XXX should we raise an error? Some servers might not
+                # support LIST OVERVIEW.FMT and still return additional
+                # headers.
+                continue
+            field_name = fmt[i]
+            is_metadata = field_name.startswith(':')
+            if i >= n_defaults and not is_metadata:
+                # Non-default header names are included in full in the response
+                h = field_name + ":"
+                if token[:len(h)].lower() != h:
+                    raise NNTPDataError("OVER/XOVER response doesn't include "
+                                        "names of additional headers")
+                token = token[len(h):].lstrip(" ")
+            fields[fmt[i]] = token
+        overview.append((article_number, fields))
+    return overview
+
+def _parse_datetime(date_str, time_str=None):
+    """Parse a pair of (date, time) strings, and return a datetime object.
+    If only the date is given, it is assumed to be date and time
+    concatenated together (e.g. response to the DATE command).
+    """
+    if time_str is None:
+        time_str = date_str[-6:]
+        date_str = date_str[:-6]
+    hours = int(time_str[:2])
+    minutes = int(time_str[2:4])
+    seconds = int(time_str[4:])
+    year = int(date_str[:-4])
+    month = int(date_str[-4:-2])
+    day = int(date_str[-2:])
+    # RFC 3977 doesn't say how to interpret 2-char years.  Assume that
+    # there are no dates before 1970 on Usenet.
+    if year < 70:
+        year += 2000
+    elif year < 100:
+        year += 1900
+    return datetime.datetime(year, month, day, hours, minutes, seconds)
+
+def _unparse_datetime(dt, legacy=False):
+    """Format a date or datetime object as a pair of (date, time) strings
+    in the format required by the NEWNEWS and NEWGROUPS commands.  If a
+    date object is passed, the time is assumed to be midnight (00h00).
+
+    The returned representation depends on the legacy flag:
+    * if legacy is False (the default):
+      date has the YYYYMMDD format and time the HHMMSS format
+    * if legacy is True:
+      date has the YYMMDD format and time the HHMMSS format.
+    RFC 3977 compliant servers should understand both formats; therefore,
+    legacy is only needed when talking to old servers.
+    """
+    if not isinstance(dt, datetime.datetime):
+        time_str = "000000"
+    else:
+        time_str = "{0.hour:02d}{0.minute:02d}{0.second:02d}".format(dt)
+    y = dt.year
+    if legacy:
+        y = y % 100
+        date_str = "{0:02d}{1.month:02d}{1.day:02d}".format(y, dt)
+    else:
+        date_str = "{0:04d}{1.month:02d}{1.day:02d}".format(y, dt)
+    return date_str, time_str
+
+
+# The classes themselves
+class _NNTPBase:
+    # UTF-8 is the character set for all NNTP commands and responses: they
+    # are automatically encoded (when sending) and decoded (and receiving)
+    # by this class.
+    # However, some multi-line data blocks can contain arbitrary bytes (for
+    # example, latin-1 or utf-16 data in the body of a message). Commands
+    # taking (POST, IHAVE) or returning (HEAD, BODY, ARTICLE) raw message
+    # data will therefore only accept and produce bytes objects.
+    # Furthermore, since there could be non-compliant servers out there,
+    # we use 'surrogateescape' as the error handler for fault tolerance
+    # and easy round-tripping. This could be useful for some applications
+    # (e.g. NNTP gateways).
+
+    encoding = 'utf-8'
+    errors = 'surrogateescape'
+
+    def __init__(self, file, user=None, password=None,
+                 readermode=None, usenetrc=True,
+                 timeout=_GLOBAL_DEFAULT_TIMEOUT):
         """Initialize an instance.  Arguments:
-        - host: hostname to connect to
-        - port: port to connect to (default the standard NNTP port)
+        - file: file-like object (open for read/write in binary mode)
         - user: username to authenticate with
         - password: password to use with username
         - readermode: if true, send 'mode reader' command after
                       connecting.
+        - usenetrc: allow loading username and password from ~/.netrc file
+                    if not specified explicitly
+        - timeout: timeout (in seconds) used for socket connections
 
         readermode is sometimes necessary if you are connecting to an
         NNTP server on the local machine and intend to call
@@ -107,12 +298,9 @@ class NNTP:
         unexpected NNTPPermanentErrors, you might need to set
         readermode.
         """
-        self.host = host
-        self.port = port
-        self.sock = socket.create_connection((host, port))
-        self.file = self.sock.makefile('rb')
+        self.file = file
         self.debugging = 0
-        self.welcome = self.getresp()
+        self.welcome = self._getresp()
 
         # 'mode reader' is sometimes necessary to enable 'reader' mode.
         # However, the order in which 'mode reader' and 'authinfo' need to
@@ -122,12 +310,12 @@ class NNTP:
         readermode_afterauth = 0
         if readermode:
             try:
-                self.welcome = self.shortcmd('mode reader')
+                self.welcome = self._shortcmd('mode reader')
             except NNTPPermanentError:
                 # error 500, probably 'not implemented'
                 pass
             except NNTPTemporaryError as e:
-                if user and e.response.startswith(b'480'):
+                if user and e.response.startswith('480'):
                     # Need authorization before 'mode reader'
                     readermode_afterauth = 1
                 else:
@@ -144,29 +332,35 @@ class NNTP:
                     password = auth[2]
         except IOError:
             pass
-        # Perform NNRP authentication if needed.
+        # Perform NNTP authentication if needed.
         if user:
-            resp = self.shortcmd('authinfo user '+user)
-            if resp.startswith(b'381'):
+            resp = self._shortcmd('authinfo user '+user)
+            if resp.startswith('381'):
                 if not password:
                     raise NNTPReplyError(resp)
                 else:
-                    resp = self.shortcmd(
+                    resp = self._shortcmd(
                             'authinfo pass '+password)
-                    if not resp.startswith(b'281'):
+                    if not resp.startswith('281'):
                         raise NNTPPermanentError(resp)
             if readermode_afterauth:
                 try:
-                    self.welcome = self.shortcmd('mode reader')
+                    self.welcome = self._shortcmd('mode reader')
                 except NNTPPermanentError:
                     # error 500, probably 'not implemented'
                     pass
 
-
-    # Get the welcome message from the server
-    # (this is read and squirreled away by __init__()).
-    # If the response code is 200, posting is allowed;
-    # if it 201, posting is not allowed
+        # Inquire about capabilities (RFC 3977)
+        self.nntp_version = 1
+        try:
+            resp, caps = self.capabilities()
+        except NNTPPermanentError:
+            # Server doesn't support capabilities
+            self._caps = {}
+        else:
+            self._caps = caps
+            if 'VERSION' in caps:
+                self.nntp_version = int(caps['VERSION'][0])
 
     def getwelcome(self):
         """Get the welcome message from the server
@@ -177,6 +371,12 @@ class NNTP:
         if self.debugging: print('*welcome*', repr(self.welcome))
         return self.welcome
 
+    def getcapabilities(self):
+        """Get the server capabilities, as read by __init__().
+        If the CAPABILITIES command is not supported, an empty dict is
+        returned."""
+        return self._caps
+
     def set_debuglevel(self, level):
         """Set the debugging level.  Argument 'level' means:
         0: no debugging output (default)
@@ -186,121 +386,221 @@ class NNTP:
         self.debugging = level
     debug = set_debuglevel
 
-    def putline(self, line):
-        """Internal: send one line to the server, appending CRLF."""
-        line = line + CRLF
+    def _putline(self, line):
+        """Internal: send one line to the server, appending CRLF.
+        The `line` must be a bytes-like object."""
+        line = line + _CRLF
         if self.debugging > 1: print('*put*', repr(line))
-        self.sock.sendall(line)
+        self.file.write(line)
+        self.file.flush()
 
-    def putcmd(self, line):
-        """Internal: send one command to the server (through putline())."""
+    def _putcmd(self, line):
+        """Internal: send one command to the server (through _putline()).
+        The `line` must be an unicode string."""
         if self.debugging: print('*cmd*', repr(line))
-        line = bytes(line, "ASCII")
-        self.putline(line)
+        line = line.encode(self.encoding, self.errors)
+        self._putline(line)
 
-    def getline(self):
-        """Internal: return one line from the server, stripping CRLF.
-        Raise EOFError if the connection is closed."""
+    def _getline(self, strip_crlf=True):
+        """Internal: return one line from the server, stripping _CRLF.
+        Raise EOFError if the connection is closed.
+        Returns a bytes object."""
         line = self.file.readline()
         if self.debugging > 1:
             print('*get*', repr(line))
         if not line: raise EOFError
-        if line[-2:] == CRLF:
-            line = line[:-2]
-        elif line[-1:] in CRLF:
-            line = line[:-1]
+        if strip_crlf:
+            if line[-2:] == _CRLF:
+                line = line[:-2]
+            elif line[-1:] in _CRLF:
+                line = line[:-1]
         return line
 
-    def getresp(self):
+    def _getresp(self):
         """Internal: get a response from the server.
-        Raise various errors if the response indicates an error."""
-        resp = self.getline()
+        Raise various errors if the response indicates an error.
+        Returns an unicode string."""
+        resp = self._getline()
         if self.debugging: print('*resp*', repr(resp))
+        resp = resp.decode(self.encoding, self.errors)
         c = resp[:1]
-        if c == b'4':
+        if c == '4':
             raise NNTPTemporaryError(resp)
-        if c == b'5':
+        if c == '5':
             raise NNTPPermanentError(resp)
-        if c not in b'123':
+        if c not in '123':
             raise NNTPProtocolError(resp)
         return resp
 
-    def getlongresp(self, file=None):
+    def _getlongresp(self, file=None):
         """Internal: get a response plus following text from the server.
-        Raise various errors if the response indicates an error."""
+        Raise various errors if the response indicates an error.
+
+        Returns a (response, lines) tuple where `response` is an unicode
+        string and `lines` is a list of bytes objects.
+        If `file` is a file-like object, it must be open in binary mode.
+        """
 
         openedFile = None
         try:
             # If a string was passed then open a file with that name
-            if isinstance(file, str):
-                openedFile = file = open(file, "w")
+            if isinstance(file, (str, bytes)):
+                openedFile = file = open(file, "wb")
 
-            resp = self.getresp()
-            if resp[:3] not in LONGRESP:
+            resp = self._getresp()
+            if resp[:3] not in _LONGRESP:
                 raise NNTPReplyError(resp)
-            list = []
-            while 1:
-                line = self.getline()
-                if line == b'.':
-                    break
-                if line.startswith(b'..'):
-                    line = line[1:]
-                if file:
-                    file.write(line + b'\n')
-                else:
-                    list.append(line)
+
+            lines = []
+            if file is not None:
+                # XXX lines = None instead?
+                terminators = (b'.' + _CRLF, b'.\n')
+                while 1:
+                    line = self._getline(False)
+                    if line in terminators:
+                        break
+                    if line.startswith(b'..'):
+                        line = line[1:]
+                    file.write(line)
+            else:
+                terminator = b'.'
+                while 1:
+                    line = self._getline()
+                    if line == terminator:
+                        break
+                    if line.startswith(b'..'):
+                        line = line[1:]
+                    lines.append(line)
         finally:
             # If this method created the file, then it must close it
             if openedFile:
                 openedFile.close()
 
-        return resp, list
+        return resp, lines
 
-    def shortcmd(self, line):
-        """Internal: send a command and get the response."""
-        self.putcmd(line)
-        return self.getresp()
+    def _shortcmd(self, line):
+        """Internal: send a command and get the response.
+        Same return value as _getresp()."""
+        self._putcmd(line)
+        return self._getresp()
+
+    def _longcmd(self, line, file=None):
+        """Internal: send a command and get the response plus following text.
+        Same return value as _getlongresp()."""
+        self._putcmd(line)
+        return self._getlongresp(file)
+
+    def _longcmdstring(self, line, file=None):
+        """Internal: send a command and get the response plus following text.
+        Same as _longcmd() and _getlongresp(), except that the returned `lines`
+        are unicode strings rather than bytes objects.
+        """
+        self._putcmd(line)
+        resp, list = self._getlongresp(file)
+        return resp, [line.decode(self.encoding, self.errors)
+                      for line in list]
+
+    def _getoverviewfmt(self):
+        """Internal: get the overview format. Queries the server if not
+        already done, else returns the cached value."""
+        try:
+            return self._cachedoverviewfmt
+        except AttributeError:
+            pass
+        try:
+            resp, lines = self._longcmdstring("LIST OVERVIEW.FMT")
+        except NNTPPermanentError:
+            # Not supported by server?
+            fmt = _DEFAULT_OVERVIEW_FMT[:]
+        else:
+            fmt = _parse_overview_fmt(lines)
+        self._cachedoverviewfmt = fmt
+        return fmt
 
-    def longcmd(self, line, file=None):
-        """Internal: send a command and get the response plus following text."""
-        self.putcmd(line)
-        return self.getlongresp(file)
+    def _grouplist(self, lines):
+        # Parse lines into "group last first flag"
+        return [GroupInfo(*line.split()) for line in lines]
 
-    def newgroups(self, date, time, file=None):
-        """Process a NEWGROUPS command.  Arguments:
-        - date: string 'yymmdd' indicating the date
-        - time: string 'hhmmss' indicating the time
+    def capabilities(self):
+        """Process a CAPABILITIES command.  Not supported by all servers.
         Return:
         - resp: server response if successful
-        - list: list of newsgroup names"""
-
-        return self.longcmd('NEWGROUPS ' + date + ' ' + time, file)
+        - caps: a dictionary mapping capability names to lists of tokens
+        (for example {'VERSION': ['2'], 'OVER': [], LIST: ['ACTIVE', 'HEADERS'] })
+        """
+        caps = {}
+        resp, lines = self._longcmdstring("CAPABILITIES")
+        for line in lines:
+            name, *tokens = line.split()
+            caps[name] = tokens
+        return resp, caps
 
-    def newnews(self, group, date, time, file=None):
+    def newgroups(self, date, *, file=None):
+        """Process a NEWGROUPS command.  Arguments:
+        - date: a date or datetime object
+        Return:
+        - resp: server response if successful
+        - list: list of newsgroup names
+        """
+        if not isinstance(date, (datetime.date, datetime.date)):
+            raise TypeError(
+                "the date parameter must be a date or datetime object, "
+                "not '{:40}'".format(date.__class__.__name__))
+        date_str, time_str = _unparse_datetime(date, self.nntp_version < 2)
+        cmd = 'NEWGROUPS {0} {1}'.format(date_str, time_str)
+        resp, lines = self._longcmdstring(cmd, file)
+        return resp, self._grouplist(lines)
+
+    def newnews(self, group, date, *, file=None):
         """Process a NEWNEWS command.  Arguments:
         - group: group name or '*'
-        - date: string 'yymmdd' indicating the date
-        - time: string 'hhmmss' indicating the time
+        - date: a date or datetime object
         Return:
         - resp: server response if successful
-        - list: list of message ids"""
-
-        cmd = 'NEWNEWS ' + group + ' ' + date + ' ' + time
-        return self.longcmd(cmd, file)
-
-    def list(self, file=None):
-        """Process a LIST command.  Return:
+        - list: list of message ids
+        """
+        if not isinstance(date, (datetime.date, datetime.date)):
+            raise TypeError(
+                "the date parameter must be a date or datetime object, "
+                "not '{:40}'".format(date.__class__.__name__))
+        date_str, time_str = _unparse_datetime(date, self.nntp_version < 2)
+        cmd = 'NEWNEWS {0} {1} {2}'.format(group, date_str, time_str)
+        return self._longcmdstring(cmd, file)
+
+    def list(self, *, file=None):
+        """Process a LIST command. Argument:
+        - file: Filename string or file object to store the result in
+        Returns:
         - resp: server response if successful
-        - list: list of (group, last, first, flag) (strings)"""
+        - list: list of (group, last, first, flag) (strings)
+        """
+        resp, lines = self._longcmdstring('LIST', file)
+        return resp, self._grouplist(lines)
 
-        resp, list = self.longcmd('LIST', file)
-        for i in range(len(list)):
-            # Parse lines into "group last first flag"
-            list[i] = tuple(list[i].split())
-        return resp, list
+    def _getdescriptions(self, group_pattern, return_all):
+        line_pat = re.compile('^(?P<group>[^ \t]+)[ \t]+(.*)$')
+        # Try the more std (acc. to RFC2980) LIST NEWSGROUPS first
+        resp, lines = self._longcmdstring('LIST NEWSGROUPS ' + group_pattern)
+        if not resp.startswith('215'):
+            # Now the deprecated XGTITLE.  This either raises an error
+            # or succeeds with the same output structure as LIST
+            # NEWSGROUPS.
+            resp, lines = self._longcmdstring('XGTITLE ' + group_pattern)
+        groups = {}
+        for raw_line in lines:
+            match = line_pat.search(raw_line.strip())
+            if match:
+                name, desc = match.group(1, 2)
+                if not return_all:
+                    return desc
+                groups[name] = desc
+        if return_all:
+            return resp, groups
+        else:
+            # Nothing found
+            return ''
 
     def description(self, group):
-
         """Get a description for a single group.  If more than one
         group matches ('group' is a pattern), return the first.  If no
         group matches, return an empty string.
@@ -311,42 +611,24 @@ class NNTP:
 
         NOTE: This neither checks for a wildcard in 'group' nor does
         it check whether the group actually exists."""
-
-        resp, lines = self.descriptions(group)
-        if len(lines) == 0:
-            return b''
-        else:
-            return lines[0][1]
+        return self._getdescriptions(group, False)
 
     def descriptions(self, group_pattern):
         """Get descriptions for a range of groups."""
-        line_pat = re.compile(b'^(?P<group>[^ \t]+)[ \t]+(.*)$')
-        # Try the more std (acc. to RFC2980) LIST NEWSGROUPS first
-        resp, raw_lines = self.longcmd('LIST NEWSGROUPS ' + group_pattern)
-        if not resp.startswith(b'215'):
-            # Now the deprecated XGTITLE.  This either raises an error
-            # or succeeds with the same output structure as LIST
-            # NEWSGROUPS.
-            resp, raw_lines = self.longcmd('XGTITLE ' + group_pattern)
-        lines = []
-        for raw_line in raw_lines:
-            match = line_pat.search(raw_line.strip())
-            if match:
-                lines.append(match.group(1, 2))
-        return resp, lines
+        return self._getdescriptions(group_pattern, True)
 
     def group(self, name):
         """Process a GROUP command.  Argument:
         - group: the group name
         Returns:
         - resp: server response if successful
-        - count: number of articles (string)
-        - first: first article number (string)
-        - last: last article number (string)
-        - name: the group name"""
-
-        resp = self.shortcmd('GROUP ' + name)
-        if not resp.startswith(b'211'):
+        - count: number of articles
+        - first: first article number
+        - last: last article number
+        - name: the group name
+        """
+        resp = self._shortcmd('GROUP ' + name)
+        if not resp.startswith('211'):
             raise NNTPReplyError(resp)
         words = resp.split()
         count = first = last = 0
@@ -359,151 +641,177 @@ class NNTP:
                     last = words[3]
                     if n > 4:
                         name = words[4].lower()
-        return resp, count, first, last, name
+        return resp, int(count), int(first), int(last), name
 
-    def help(self, file=None):
-        """Process a HELP command.  Returns:
+    def help(self, *, file=None):
+        """Process a HELP command. Argument:
+        - file: Filename string or file object to store the result in
+        Returns:
         - resp: server response if successful
-        - list: list of strings"""
-
-        return self.longcmd('HELP',file)
+        - list: list of strings returned by the server in response to the
+                HELP command
+        """
+        return self._longcmdstring('HELP', file)
 
-    def statparse(self, resp):
-        """Internal: parse the response of a STAT, NEXT or LAST command."""
-        if not resp.startswith(b'22'):
+    def _statparse(self, resp):
+        """Internal: parse the response line of a STAT, NEXT, LAST,
+        ARTICLE, HEAD or BODY command."""
+        if not resp.startswith('22'):
             raise NNTPReplyError(resp)
         words = resp.split()
-        nr = 0
-        id = b''
-        n = len(words)
-        if n > 1:
-            nr = words[1]
-            if n > 2:
-                id = words[2]
-        return resp, nr, id
+        art_num = int(words[1])
+        message_id = words[2]
+        return resp, art_num, message_id
 
-    def statcmd(self, line):
+    def _statcmd(self, line):
         """Internal: process a STAT, NEXT or LAST command."""
-        resp = self.shortcmd(line)
-        return self.statparse(resp)
+        resp = self._shortcmd(line)
+        return self._statparse(resp)
 
-    def stat(self, id):
+    def stat(self, message_spec=None):
         """Process a STAT command.  Argument:
-        - id: article number or message id
+        - message_spec: article number or message id (if not specified,
+          the current article is selected)
         Returns:
         - resp: server response if successful
-        - nr:   the article number
-        - id:   the message id"""
-
-        return self.statcmd('STAT {0}'.format(id))
+        - art_num: the article number
+        - message_id: the message id
+        """
+        if message_spec:
+            return self._statcmd('STAT {0}'.format(message_spec))
+        else:
+            return self._statcmd('STAT')
 
     def next(self):
         """Process a NEXT command.  No arguments.  Return as for STAT."""
-        return self.statcmd('NEXT')
+        return self._statcmd('NEXT')
 
     def last(self):
         """Process a LAST command.  No arguments.  Return as for STAT."""
-        return self.statcmd('LAST')
+        return self._statcmd('LAST')
 
-    def artcmd(self, line, file=None):
+    def _artcmd(self, line, file=None):
         """Internal: process a HEAD, BODY or ARTICLE command."""
-        resp, list = self.longcmd(line, file)
-        resp, nr, id = self.statparse(resp)
-        return resp, nr, id, list
+        resp, lines = self._longcmd(line, file)
+        resp, art_num, message_id = self._statparse(resp)
+        return resp, ArticleInfo(art_num, message_id, lines)
 
-    def head(self, id):
+    def head(self, message_spec=None, *, file=None):
         """Process a HEAD command.  Argument:
-        - id: article number or message id
+        - message_spec: article number or message id
+        - file: filename string or file object to store the headers in
         Returns:
         - resp: server response if successful
-        - nr: article number
-        - id: message id
-        - list: the lines of the article's header"""
-
-        return self.artcmd('HEAD {0}'.format(id))
+        - ArticleInfo: (article number, message id, list of header lines)
+        """
+        if message_spec is not None:
+            cmd = 'HEAD {0}'.format(message_spec)
+        else:
+            cmd = 'HEAD'
+        return self._artcmd(cmd, file)
 
-    def body(self, id, file=None):
+    def body(self, message_spec=None, *, file=None):
         """Process a BODY command.  Argument:
-        - id: article number or message id
-        - file: Filename string or file object to store the article in
+        - message_spec: article number or message id
+        - file: filename string or file object to store the body in
         Returns:
         - resp: server response if successful
-        - nr: article number
-        - id: message id
-        - list: the lines of the article's body or an empty list
-                if file was used"""
-
-        return self.artcmd('BODY {0}'.format(id), file)
+        - ArticleInfo: (article number, message id, list of body lines)
+        """
+        if message_spec is not None:
+            cmd = 'BODY {0}'.format(message_spec)
+        else:
+            cmd = 'BODY'
+        return self._artcmd(cmd, file)
 
-    def article(self, id):
+    def article(self, message_spec=None, *, file=None):
         """Process an ARTICLE command.  Argument:
-        - id: article number or message id
+        - message_spec: article number or message id
+        - file: filename string or file object to store the article in
         Returns:
         - resp: server response if successful
-        - nr: article number
-        - id: message id
-        - list: the lines of the article"""
-
-        return self.artcmd('ARTICLE {0}'.format(id))
+        - ArticleInfo: (article number, message id, list of article lines)
+        """
+        if message_spec is not None:
+            cmd = 'ARTICLE {0}'.format(message_spec)
+        else:
+            cmd = 'ARTICLE'
+        return self._artcmd(cmd, file)
 
     def slave(self):
         """Process a SLAVE command.  Returns:
-        - resp: server response if successful"""
-
-        return self.shortcmd('SLAVE')
+        - resp: server response if successful
+        """
+        return self._shortcmd('SLAVE')
 
-    def xhdr(self, hdr, str, file=None):
+    def xhdr(self, hdr, str, *, file=None):
         """Process an XHDR command (optional server extension).  Arguments:
         - hdr: the header type (e.g. 'subject')
         - str: an article nr, a message id, or a range nr1-nr2
+        - file: Filename string or file object to store the result in
         Returns:
         - resp: server response if successful
-        - list: list of (nr, value) strings"""
-
-        pat = re.compile(b'^([0-9]+) ?(.*)\n?')
-        resp, lines = self.longcmd('XHDR {0} {1}'.format(hdr, str), file)
-        for i in range(len(lines)):
-            line = lines[i]
+        - list: list of (nr, value) strings
+        """
+        pat = re.compile('^([0-9]+) ?(.*)\n?')
+        resp, lines = self._longcmdstring('XHDR {0} {1}'.format(hdr, str), file)
+        def remove_number(line):
             m = pat.match(line)
-            if m:
-                lines[i] = m.group(1, 2)
-        return resp, lines
+            return m.group(1, 2) if m else line
+        return resp, [remove_number(line) for line in lines]
 
-    def xover(self, start, end, file=None):
+    def xover(self, start, end, *, file=None):
         """Process an XOVER command (optional server extension) Arguments:
         - start: start of range
         - end: end of range
+        - file: Filename string or file object to store the result in
+        Returns:
+        - resp: server response if successful
+        - list: list of dicts containing the response fields
+        """
+        resp, lines = self._longcmdstring('XOVER {0}-{1}'.format(start, end),
+                                          file)
+        fmt = self._getoverviewfmt()
+        return resp, _parse_overview(lines, fmt)
+
+    def over(self, message_spec, *, file=None):
+        """Process an OVER command.  If the command isn't supported, fall
+        back to XOVER. Arguments:
+        - message_spec:
+            - either a message id, indicating the article to fetch
+              information about
+            - or a (start, end) tuple, indicating a range of article numbers;
+              if end is None, information up to the newest message will be
+              retrieved
+            - or None, indicating the current article number must be used
+        - file: Filename string or file object to store the result in
         Returns:
         - resp: server response if successful
-        - list: list of (art-nr, subject, poster, date,
-                         id, references, size, lines)"""
+        - list: list of dicts containing the response fields
 
-        resp, lines = self.longcmd('XOVER {0}-{1}'.format(start, end), file)
-        xover_lines = []
-        for line in lines:
-            elem = line.split(b'\t')
-            try:
-                xover_lines.append((elem[0],
-                                    elem[1],
-                                    elem[2],
-                                    elem[3],
-                                    elem[4],
-                                    elem[5].split(),
-                                    elem[6],
-                                    elem[7]))
-            except IndexError:
-                raise NNTPDataError(line)
-        return resp,xover_lines
-
-    def xgtitle(self, group, file=None):
+        NOTE: the "message id" form isn't supported by XOVER
+        """
+        cmd = 'OVER' if 'OVER' in self._caps else 'XOVER'
+        if isinstance(message_spec, (tuple, list)):
+            start, end = message_spec
+            cmd += ' {0}-{1}'.format(start, end or '')
+        elif message_spec is not None:
+            cmd = cmd + ' ' + message_spec
+        resp, lines = self._longcmdstring(cmd, file)
+        fmt = self._getoverviewfmt()
+        return resp, _parse_overview(lines, fmt)
+
+    def xgtitle(self, group, *, file=None):
         """Process an XGTITLE command (optional server extension) Arguments:
         - group: group name wildcard (i.e. news.*)
         Returns:
         - resp: server response if successful
         - list: list of (name,title) strings"""
-
-        line_pat = re.compile(b'^([^ \t]+)[ \t]+(.*)$')
-        resp, raw_lines = self.longcmd('XGTITLE ' + group, file)
+        warnings.warn("The XGTITLE extension is not actively used, "
+                      "use descriptions() instead",
+                      PendingDeprecationWarning, 2)
+        line_pat = re.compile('^([^ \t]+)[ \t]+(.*)$')
+        resp, raw_lines = self._longcmdstring('XGTITLE ' + group, file)
         lines = []
         for raw_line in raw_lines:
             match = line_pat.search(raw_line.strip())
@@ -511,15 +819,18 @@ class NNTP:
                 lines.append(match.group(1, 2))
         return resp, lines
 
-    def xpath(self,id):
+    def xpath(self, id):
         """Process an XPATH command (optional server extension) Arguments:
         - id: Message id of article
         Returns:
         resp: server response if successful
-        path: directory path to article"""
+        path: directory path to article
+        """
+        warnings.warn("The XPATH extension is not actively used",
+                      PendingDeprecationWarning, 2)
 
-        resp = self.shortcmd('XPATH {0}'.format(id))
-        if not resp.startswith(b'223'):
+        resp = self._shortcmd('XPATH {0}'.format(id))
+        if not resp.startswith('223'):
             raise NNTPReplyError(resp)
         try:
             [resp_num, path] = resp.split()
@@ -528,89 +839,144 @@ class NNTP:
         else:
             return resp, path
 
-    def date (self):
-        """Process the DATE command. Arguments:
-        None
+    def date(self):
+        """Process the DATE command.
         Returns:
-        resp: server response if successful
-        date: Date suitable for newnews/newgroups commands etc.
-        time: Time suitable for newnews/newgroups commands etc."""
-
-        resp = self.shortcmd("DATE")
-        if not resp.startswith(b'111'):
+        - resp: server response if successful
+        - date: datetime object
+        """
+        resp = self._shortcmd("DATE")
+        if not resp.startswith('111'):
             raise NNTPReplyError(resp)
         elem = resp.split()
         if len(elem) != 2:
             raise NNTPDataError(resp)
-        date = elem[1][2:8]
-        time = elem[1][-6:]
-        if len(date) != 6 or len(time) != 6:
+        date = elem[1]
+        if len(date) != 14:
             raise NNTPDataError(resp)
-        return resp, date, time
+        return resp, _parse_datetime(date, None)
 
     def _post(self, command, f):
-        resp = self.shortcmd(command)
-        # Raises error_??? if posting is not allowed
-        if not resp.startswith(b'3'):
+        resp = self._shortcmd(command)
+        # Raises a specific exception if posting is not allowed
+        if not resp.startswith('3'):
             raise NNTPReplyError(resp)
-        while 1:
-            line = f.readline()
-            if not line:
-                break
-            if line.endswith(b'\n'):
-                line = line[:-1]
+        if isinstance(f, (bytes, bytearray)):
+            f = f.splitlines()
+        # We don't use _putline() because:
+        # - we don't want additional CRLF if the file or iterable is already
+        #   in the right format
+        # - we don't want a spurious flush() after each line is written
+        for line in f:
+            if not line.endswith(_CRLF):
+                line = line.rstrip(b"\r\n") + _CRLF
             if line.startswith(b'.'):
                 line = b'.' + line
-            self.putline(line)
-        self.putline(b'.')
-        return self.getresp()
+            self.file.write(line)
+        self.file.write(b".\r\n")
+        self.file.flush()
+        return self._getresp()
 
-    def post(self, f):
+    def post(self, data):
         """Process a POST command.  Arguments:
-        - f: file containing the article
+        - data: bytes object, iterable or file containing the article
         Returns:
         - resp: server response if successful"""
-        return self._post('POST', f)
+        return self._post('POST', data)
 
-    def ihave(self, id, f):
+    def ihave(self, message_id, data):
         """Process an IHAVE command.  Arguments:
-        - id: message-id of the article
-        - f:  file containing the article
+        - message_id: message-id of the article
+        - data: file containing the article
         Returns:
         - resp: server response if successful
         Note that if the server refuses the article an exception is raised."""
-        return self._post('IHAVE {0}'.format(id), f)
+        return self._post('IHAVE {0}'.format(message_id), data)
+
+    def _close(self):
+        self.file.close()
+        del self.file
 
     def quit(self):
         """Process a QUIT command and close the socket.  Returns:
         - resp: server response if successful"""
-
-        resp = self.shortcmd('QUIT')
-        self.file.close()
-        self.sock.close()
-        del self.file, self.sock
+        try:
+            resp = self._shortcmd('QUIT')
+        finally:
+            self._close()
         return resp
 
 
+class NNTP(_NNTPBase):
+
+    def __init__(self, host, port=NNTP_PORT, user=None, password=None,
+                 readermode=None, usenetrc=True,
+                 timeout=_GLOBAL_DEFAULT_TIMEOUT):
+        """Initialize an instance.  Arguments:
+        - host: hostname to connect to
+        - port: port to connect to (default the standard NNTP port)
+        - user: username to authenticate with
+        - password: password to use with username
+        - readermode: if true, send 'mode reader' command after
+                      connecting.
+        - usenetrc: allow loading username and password from ~/.netrc file
+                    if not specified explicitly
+        - timeout: timeout (in seconds) used for socket connections
+
+        readermode is sometimes necessary if you are connecting to an
+        NNTP server on the local machine and intend to call
+        reader-specific comamnds, such as `group'.  If you get
+        unexpected NNTPPermanentErrors, you might need to set
+        readermode.
+        """
+        self.host = host
+        self.port = port
+        self.sock = socket.create_connection((host, port), timeout)
+        file = self.sock.makefile("rwb")
+        _NNTPBase.__init__(self, file, user, password,
+                           readermode, usenetrc, timeout)
+
+    def _close(self):
+        try:
+            _NNTPBase._close(self)
+        finally:
+            self.sock.close()
+
+
 # Test retrieval when run as a script.
-# Assumption: if there's a local news server, it's called 'news'.
-# Assumption: if user queries a remote news server, it's named
-# in the environment variable NNTPSERVER (used by slrn and kin)
-# and we want readermode off.
 if __name__ == '__main__':
-    import os
-    newshost = 'news' and os.environ["NNTPSERVER"]
-    if newshost.find('.') == -1:
-        mode = 'readermode'
-    else:
-        mode = None
-    s = NNTP(newshost, readermode=mode)
-    resp, count, first, last, name = s.group('comp.lang.python')
-    print(resp)
+    import argparse
+    from email.utils import parsedate
+
+    parser = argparse.ArgumentParser(description="""\
+        nntplib built-in demo - display the latest articles in a newsgroup""")
+    parser.add_argument('-g', '--group', default='gmane.comp.python.general',
+                        help='group to fetch messages from (default: %(default)s)')
+    parser.add_argument('-s', '--server', default='news.gmane.org',
+                        help='NNTP server hostname (default: %(default)s)')
+    parser.add_argument('-p', '--port', default=NNTP_PORT, type=int,
+                        help='NNTP port number (default: %(default)s)')
+    parser.add_argument('-n', '--nb-articles', default=10, type=int,
+                        help='number of articles to fetch (default: %(default)s)')
+    args = parser.parse_args()
+
+    s = NNTP(host=args.server, port=args.port)
+    resp, count, first, last, name = s.group(args.group)
     print('Group', name, 'has', count, 'articles, range', first, 'to', last)
-    resp, subs = s.xhdr('subject', '{0}-{1}'.format(first, last))
-    print(resp)
-    for item in subs:
-        print("%7s %s" % item)
-    resp = s.quit()
-    print(resp)
+
+    def cut(s, lim):
+        if len(s) > lim:
+            s = s[:lim - 4] + "..."
+        return s
+
+    first = str(int(last) - args.nb_articles + 1)
+    resp, overviews = s.xover(first, last)
+    for artnum, over in overviews:
+        author = decode_header(over['from']).split('<', 1)[0]
+        subject = decode_header(over['subject'])
+        lines = int(over[':lines'])
+        print("{:7} {:20} {:42} ({})".format(
+              artnum, cut(author, 20), cut(subject, 42), lines)
+              )
+
+    s.quit()