zeroinstall/support/ssl_match_hostname.py

   1 """This is a temporary hack to fix an SSL bug in Python versions before 3.2.
   2 It is used automatically when you download an HTTPS URL using a Fetcher.
   3
   4 Copyright: Python Software Foundation
   5 License: MIT License
   6 Downloaded from: http://pypi.python.org/pypi/backports.ssl_match_hostname/"""
   7
   8 # pylint: disable=W0312
   9
  10 import re
  11
  12 class CertificateError(ValueError):
  13     pass
  14
  15 def _dnsname_to_pat(dn):
  16     pats = []
  17     for frag in dn.split(r'.'):
  18         if frag == '*':
  19             # When '*' is a fragment by itself, it matches a non-empty dotless
  20             # fragment.
  21             pats.append('[^.]+')
  22         else:
  23             # Otherwise, '*' matches any dotless fragment.
  24             frag = re.escape(frag)
  25             pats.append(frag.replace(r'\*', '[^.]*'))
  26     return re.compile(r'\A' + r'\.'.join(pats) + r'\Z', re.IGNORECASE)
  27
  28 def match_hostname(cert, hostname):
  29     """Verify that *cert* (in decoded format as returned by
  30     SSLSocket.getpeercert()) matches the *hostname*.  RFC 2818 rules
  31     are mostly followed, but IP addresses are not accepted for *hostname*.
  32
  33     CertificateError is raised on failure. On success, the function
  34     returns nothing.
  35     """
  36     if not cert:
  37         raise ValueError("empty or no certificate")
  38     dnsnames = []
  39     san = cert.get('subjectAltName', ())
  40     for key, value in san:
  41         if key == 'DNS':
  42             if _dnsname_to_pat(value).match(hostname):
  43                 return
  44             dnsnames.append(value)
  45     if not san:
  46         # The subject is only checked when subjectAltName is empty
  47         for sub in cert.get('subject', ()):
  48             for key, value in sub:
  49                 # XXX according to RFC 2818, the most specific Common Name
  50                 # must be used.
  51                 if key == 'commonName':
  52                     if _dnsname_to_pat(value).match(hostname):
  53                         return
  54                     dnsnames.append(value)
  55     if len(dnsnames) > 1:
  56         raise CertificateError("hostname %r "
  57             "doesn't match either of %s"
  58             % (hostname, ', '.join(map(repr, dnsnames))))
  59     elif len(dnsnames) == 1:
  60         raise CertificateError("hostname %r "
  61             "doesn't match %r"
  62             % (hostname, dnsnames[0]))
  63     else:
  64         raise CertificateError("no appropriate commonName or "
  65             "subjectAltName fields were found")