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