smtp: add the class to verify the certificate of the SMTP server for STARTTLS

Original "smtplib.SMTP" has no route to pass "ca_certs" and
"cert_reqs" arguments to underlying SSL socket creation. This causes
that "getpeercert()" on SSL socket returns empty dict, so the peer
certificate for STARTTLS can't be verified.

This patch introduces the "STARTTLS" class derived from "smtplib.SMTP"
to pass "ca_certs" and "cert_reqs" arguments to underlying SSL socket
creation.

Almost all code of "starttls()" in this class is imported from
"smtplib.SMTP" of Python 2.7.3, but it differs from original code in
points below:

  - "self.ehlo_or_helo_if_needed()" invocation is omitted, because:

    - "ehlo_or_helo_if_needed()" is available with Python 2.6 or later, and
    - "ehlo()" is explicitly invoked in "mercurial.mail._smtp()"

  - "if not _have_ssl:" check is omitted, because:

    - "_have_ssl" is available with Python 2.6 or later, and
    - same checking is done in "mercurial.sslutil.ssl_wrap_socket()"

  - "ssl.wrap_socket()" is replaced by "sslutil.ssl_wrap_socket()" for
    compatibility between Python versions

  - use "sock.recv()" also as "sock.read()", if "sock" doesn't have
    "read()" method

    with Python 2.5.x or earlier, "sslutil.ssl_wrap_socket()" returns
    "httplib.FakeSocket"-ed object, and it doesn't have "read()"
    method, which is invoked via "smtplib.SSLFakeFile".

mercurial/mail.py

@@ -1,255 +1,282
 # mail.py - mail sending bits for mercurial
 #
 # Copyright 2006 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from i18n import _
-import util, encoding
+import util, encoding, sslutil
 import os, smtplib, socket, quopri, time
 import email.Header, email.MIMEText, email.Utils
 
 _oldheaderinit = email.Header.Header.__init__
 def _unifiedheaderinit(self, *args, **kw):
     """
     Python 2.7 introduces a backwards incompatible change
     (Python issue1974, r70772) in email.Generator.Generator code:
     pre-2.7 code passed "continuation_ws='\t'" to the Header
     constructor, and 2.7 removed this parameter.
 
     Default argument is continuation_ws=' ', which means that the
     behaviour is different in <2.7 and 2.7
 
     We consider the 2.7 behaviour to be preferable, but need
     to have an unified behaviour for versions 2.4 to 2.7
     """
     # override continuation_ws
     kw['continuation_ws'] = ' '
     _oldheaderinit(self, *args, **kw)
 
 email.Header.Header.__dict__['__init__'] = _unifiedheaderinit
 
+class STARTTLS(smtplib.SMTP):
+    '''Derived class to verify the peer certificate for STARTTLS.
+
+    This class allows to pass any keyword arguments to SSL socket creation.
+    '''
+    def __init__(self, sslkwargs, **kwargs):
+        smtplib.SMTP.__init__(self, **kwargs)
+        self._sslkwargs = sslkwargs
+
+    def starttls(self, keyfile=None, certfile=None):
+        if not self.has_extn("starttls"):
+            msg = "STARTTLS extension not supported by server"
+            raise smtplib.SMTPException(msg)
+        (resp, reply) = self.docmd("STARTTLS")
+        if resp == 220:
+            self.sock = sslutil.ssl_wrap_socket(self.sock, keyfile, certfile,
+                                                **self._sslkwargs)
+            if not util.safehasattr(self.sock, "read"):
+                # using httplib.FakeSocket with Python 2.5.x or earlier
+                self.sock.read = self.sock.recv
+            self.file = smtplib.SSLFakeFile(self.sock)
+            self.helo_resp = None
+            self.ehlo_resp = None
+            self.esmtp_features = {}
+            self.does_esmtp = 0
+        return (resp, reply)
+
 def _smtp(ui):
     '''build an smtp connection and return a function to send mail'''
     local_hostname = ui.config('smtp', 'local_hostname')
     tls = ui.config('smtp', 'tls', 'none')
     # backward compatible: when tls = true, we use starttls.
     starttls = tls == 'starttls' or util.parsebool(tls)
     smtps = tls == 'smtps'
     if (starttls or smtps) and not util.safehasattr(socket, 'ssl'):
         raise util.Abort(_("can't use TLS: Python SSL support not installed"))
     if smtps:
         ui.note(_('(using smtps)\n'))
         s = smtplib.SMTP_SSL(local_hostname=local_hostname)
     else:
         s = smtplib.SMTP(local_hostname=local_hostname)
     mailhost = ui.config('smtp', 'host')
     if not mailhost:
         raise util.Abort(_('smtp.host not configured - cannot send mail'))
     mailport = util.getport(ui.config('smtp', 'port', 25))
     ui.note(_('sending mail: smtp host %s, port %s\n') %
             (mailhost, mailport))
     s.connect(host=mailhost, port=mailport)
     if starttls:
         ui.note(_('(using starttls)\n'))
         s.ehlo()
         s.starttls()
         s.ehlo()
     username = ui.config('smtp', 'username')
     password = ui.config('smtp', 'password')
     if username and not password:
         password = ui.getpass()
     if username and password:
         ui.note(_('(authenticating to mail server as %s)\n') %
                   (username))
         try:
             s.login(username, password)
         except smtplib.SMTPException, inst:
             raise util.Abort(inst)
 
     def send(sender, recipients, msg):
         try:
             return s.sendmail(sender, recipients, msg)
         except smtplib.SMTPRecipientsRefused, inst:
             recipients = [r[1] for r in inst.recipients.values()]
             raise util.Abort('\n' + '\n'.join(recipients))
         except smtplib.SMTPException, inst:
             raise util.Abort(inst)
 
     return send
 
 def _sendmail(ui, sender, recipients, msg):
     '''send mail using sendmail.'''
     program = ui.config('email', 'method')
     cmdline = '%s -f %s %s' % (program, util.email(sender),
                                ' '.join(map(util.email, recipients)))
     ui.note(_('sending mail: %s\n') % cmdline)
     fp = util.popen(cmdline, 'w')
     fp.write(msg)
     ret = fp.close()
     if ret:
         raise util.Abort('%s %s' % (
             os.path.basename(program.split(None, 1)[0]),
             util.explainexit(ret)[0]))
 
 def _mbox(mbox, sender, recipients, msg):
     '''write mails to mbox'''
     fp = open(mbox, 'ab+')
     # Should be time.asctime(), but Windows prints 2-characters day
     # of month instead of one. Make them print the same thing.
     date = time.strftime('%a %b %d %H:%M:%S %Y', time.localtime())
     fp.write('From %s %s\n' % (sender, date))
     fp.write(msg)
     fp.write('\n\n')
     fp.close()
 
 def connect(ui, mbox=None):
     '''make a mail connection. return a function to send mail.
     call as sendmail(sender, list-of-recipients, msg).'''
     if mbox:
         open(mbox, 'wb').close()
         return lambda s, r, m: _mbox(mbox, s, r, m)
     if ui.config('email', 'method', 'smtp') == 'smtp':
         return _smtp(ui)
     return lambda s, r, m: _sendmail(ui, s, r, m)
 
 def sendmail(ui, sender, recipients, msg, mbox=None):
     send = connect(ui, mbox=mbox)
     return send(sender, recipients, msg)
 
 def validateconfig(ui):
     '''determine if we have enough config data to try sending email.'''
     method = ui.config('email', 'method', 'smtp')
     if method == 'smtp':
         if not ui.config('smtp', 'host'):
             raise util.Abort(_('smtp specified as email transport, '
                                'but no smtp host configured'))
     else:
         if not util.findexe(method):
             raise util.Abort(_('%r specified as email transport, '
                                'but not in PATH') % method)
 
 def mimetextpatch(s, subtype='plain', display=False):
     '''Return MIME message suitable for a patch.
     Charset will be detected as utf-8 or (possibly fake) us-ascii.
     Transfer encodings will be used if necessary.'''
 
     cs = 'us-ascii'
     if not display:
         try:
             s.decode('us-ascii')
         except UnicodeDecodeError:
             try:
                 s.decode('utf-8')
                 cs = 'utf-8'
             except UnicodeDecodeError:
                 # We'll go with us-ascii as a fallback.
                 pass
 
     return mimetextqp(s, subtype, cs)
 
 def mimetextqp(body, subtype, charset):
     '''Return MIME message.
     Quoted-printable transfer encoding will be used if necessary.
     '''
     enc = None
     for line in body.splitlines():
         if len(line) > 950:
             body = quopri.encodestring(body)
             enc = "quoted-printable"
             break
 
     msg = email.MIMEText.MIMEText(body, subtype, charset)
     if enc:
         del msg['Content-Transfer-Encoding']
         msg['Content-Transfer-Encoding'] = enc
     return msg
 
 def _charsets(ui):
     '''Obtains charsets to send mail parts not containing patches.'''
     charsets = [cs.lower() for cs in ui.configlist('email', 'charsets')]
     fallbacks = [encoding.fallbackencoding.lower(),
                  encoding.encoding.lower(), 'utf-8']
     for cs in fallbacks: # find unique charsets while keeping order
         if cs not in charsets:
             charsets.append(cs)
     return [cs for cs in charsets if not cs.endswith('ascii')]
 
 def _encode(ui, s, charsets):
     '''Returns (converted) string, charset tuple.
     Finds out best charset by cycling through sendcharsets in descending
     order. Tries both encoding and fallbackencoding for input. Only as
     last resort send as is in fake ascii.
     Caveat: Do not use for mail parts containing patches!'''
     try:
         s.decode('ascii')
     except UnicodeDecodeError:
         sendcharsets = charsets or _charsets(ui)
         for ics in (encoding.encoding, encoding.fallbackencoding):
             try:
                 u = s.decode(ics)
             except UnicodeDecodeError:
                 continue
             for ocs in sendcharsets:
                 try:
                     return u.encode(ocs), ocs
                 except UnicodeEncodeError:
                     pass
                 except LookupError:
                     ui.warn(_('ignoring invalid sendcharset: %s\n') % ocs)
     # if ascii, or all conversion attempts fail, send (broken) ascii
     return s, 'us-ascii'
 
 def headencode(ui, s, charsets=None, display=False):
     '''Returns RFC-2047 compliant header from given string.'''
     if not display:
         # split into words?
         s, cs = _encode(ui, s, charsets)
         return str(email.Header.Header(s, cs))
     return s
 
 def _addressencode(ui, name, addr, charsets=None):
     name = headencode(ui, name, charsets)
     try:
         acc, dom = addr.split('@')
         acc = acc.encode('ascii')
         dom = dom.decode(encoding.encoding).encode('idna')
         addr = '%s@%s' % (acc, dom)
     except UnicodeDecodeError:
         raise util.Abort(_('invalid email address: %s') % addr)
     except ValueError:
         try:
             # too strict?
             addr = addr.encode('ascii')
         except UnicodeDecodeError:
             raise util.Abort(_('invalid local address: %s') % addr)
     return email.Utils.formataddr((name, addr))
 
 def addressencode(ui, address, charsets=None, display=False):
     '''Turns address into RFC-2047 compliant header.'''
     if display or not address:
         return address or ''
     name, addr = email.Utils.parseaddr(address)
     return _addressencode(ui, name, addr, charsets)
 
 def addrlistencode(ui, addrs, charsets=None, display=False):
     '''Turns a list of addresses into a list of RFC-2047 compliant headers.
     A single element of input list may contain multiple addresses, but output
     always has one address per item'''
     if display:
         return [a.strip() for a in addrs if a.strip()]
 
     result = []
     for name, addr in email.Utils.getaddresses(addrs):
         if name or addr:
             result.append(_addressencode(ui, name, addr, charsets))
     return result
 
 def mimeencode(ui, s, charsets=None, display=False):
     '''creates mime text object, encodes it if needed, and sets
     charset and transfer-encoding accordingly.'''
     cs = 'us-ascii'
     if not display:
         s, cs = _encode(ui, s, charsets)
     return mimetextqp(s, 'plain', cs)