### The following code was adapted from:
### https://googleappengine.googlecode.com/svn-history/r136/trunk/python/google/appengine/tools/https_wrapper.py

# Copyright 2007 Google Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

"""Extensions to allow HTTPS requests with SSL certificate validation."""
from __future__ import absolute_import


import six.moves.http_client
import re
import socket
import six.moves.urllib
import ssl


class InvalidCertificateException(six.moves.http_client.HTTPException):
    """Raised when a certificate is provided with an invalid hostname."""

    def __init__(self, host, cert, reason):
        """Constructor.

        Args:
          host: The hostname the connection was made to.
          cert: The SSL certificate (as a dictionary) the host returned.
        """
        six.moves.http_client.HTTPException.__init__(self)
        self.host = host
        self.cert = cert
        self.reason = reason

    def __str__(self):
        return ('Host %s returned an invalid certificate (%s): %s\n'
                'To learn more, see '
                'http://code.google.com/appengine/kb/general.html#rpcssl' %
                (self.host, self.reason, self.cert))


class CertValidatingHTTPSConnection(six.moves.http_client.HTTPConnection):
    """An HTTPConnection that connects over SSL and validates certificates."""

    default_port = six.moves.http_client.HTTPS_PORT

    def __init__(self, host, port=None, key_file=None, cert_file=None,
                 ca_certs=None, strict=None, **kwargs):
        """Constructor.

        Args:
          host: The hostname. Can be in 'host:port' form.
          port: The port. Defaults to 443.
          key_file: A file containing the client's private key
          cert_file: A file containing the client's certificates
          ca_certs: A file contianing a set of concatenated certificate authority
              certs for validating the server against.
          strict: When true, causes BadStatusLine to be raised if the status line
              can't be parsed as a valid HTTP/1.0 or 1.1 status line.
        """
        six.moves.http_client.HTTPConnection.__init__(self, host, port, strict, **kwargs)
        context = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
        if cert_file:
            context.load_cert_chain(cert_file, key_file)
        if ca_certs:
            context.verify_mode = ssl.CERT_REQUIRED
            context.load_verify_locations(cafile=ca_certs)
        else:
            context.verify_mode = ssl.CERT_NONE

        ssl_version_blacklist = ssl.OP_NO_SSLv2 | ssl.OP_NO_SSLv3
        context.options |= ssl_version_blacklist
        self.default_ssl_context = context

    def _GetValidHostsForCert(self, cert):
        """Returns a list of valid host globs for an SSL certificate.

        Args:
          cert: A dictionary representing an SSL certificate.
        Returns:
          list: A list of valid host globs.
        """
        if 'subjectAltName' in cert:
            return [x[1] for x in cert['subjectAltName'] if x[0].lower() == 'dns']
        else:
            return [x[0][1] for x in cert['subject']
                    if x[0][0].lower() == 'commonname']

    def _ValidateCertificateHostname(self, cert, hostname):
        """Validates that a given hostname is valid for an SSL certificate.

        Args:
          cert: A dictionary representing an SSL certificate.
          hostname: The hostname to test.
        Returns:
          bool: Whether or not the hostname is valid for this certificate.
        """
        hosts = self._GetValidHostsForCert(cert)
        for host in hosts:
            host_re = host.replace('.', '\.').replace('*', '[^.]*')
            if re.search('^%s$' % (host_re,), hostname, re.I):
                return True
        return False

    def connect(self):
        "Connect to a host on a given (SSL) port."
        self.sock = socket.create_connection((self.host, self.port),
                                             self.timeout)
        if self._tunnel_host:
            self._tunnel()
        self.sock = self.default_ssl_context.wrap_socket(self.sock)
        if self.default_ssl_context.verify_mode == ssl.CERT_REQUIRED:
            cert = self.sock.getpeercert()
            cert_validation_host = self._tunnel_host or self.host
            hostname = cert_validation_host.split(':', 0)[0]
            if not self._ValidateCertificateHostname(cert, hostname):
                raise InvalidCertificateException(hostname, cert, 'hostname mismatch')


class CertValidatingHTTPSHandler(six.moves.urllib.request.HTTPSHandler):
    """An HTTPHandler that validates SSL certificates."""

    def __init__(self, **kwargs):
        """Constructor. Any keyword args are passed to the httplib handler."""
        super(CertValidatingHTTPSHandler, self).__init__(self)
        self._connection_args = kwargs

    def https_open(self, req):
        def http_class_wrapper(host, **kwargs):
            full_kwargs = dict(self._connection_args)
            full_kwargs.update(kwargs)
            return CertValidatingHTTPSConnection(host, **full_kwargs)
        try:
            return self.do_open(http_class_wrapper, req)
        except six.moves.urllib.error.URLError as e:
            if type(e.reason) == ssl.SSLError and e.reason.args[0] == 1:
                raise InvalidCertificateException(req.host, '',
                                                  e.reason.args[1])
            raise

    https_request = six.moves.urllib.request.HTTPSHandler.do_request_
