'''SSL with SNI_-support for Python 2. Follow these instructions if you would
like to verify SSL certificates in Python 2. Note, the default libraries do
*not* do certificate checking; you need to do additional work to validate
certificates yourself.

This needs the following packages installed:

* pyOpenSSL (tested with 0.13)
* ndg-httpsclient (tested with 0.3.2)
* pyasn1 (tested with 0.1.6)

You can install them with the following command:

    pip install pyopenssl ndg-httpsclient pyasn1

To activate certificate checking, call
:func:`~urllib3.contrib.pyopenssl.inject_into_urllib3` from your Python code
before you begin making HTTP requests. This can be done in a ``sitecustomize``
module, or at any other time before your application begins using ``urllib3``,
like this::

    try:
        import urllib3.contrib.pyopenssl
        urllib3.contrib.pyopenssl.inject_into_urllib3()
    except ImportError:
        pass

Now you can use :mod:`urllib3` as you normally would, and it will support SNI
when the required modules are installed.

Activating this module also has the positive side effect of disabling SSL/TLS
compression in Python 2 (see `CRIME attack`_).

If you want to configure the default list of supported cipher suites, you can
set the ``urllib3.contrib.pyopenssl.DEFAULT_SSL_CIPHER_LIST`` variable.

Module Variables
----------------

:var DEFAULT_SSL_CIPHER_LIST: The list of supported SSL/TLS cipher suites.
    Default: ``ECDH+AESGCM:DH+AESGCM:ECDH+AES256:DH+AES256:ECDH+AES128:DH+AES:
    ECDH+3DES:DH+3DES:RSA+AESGCM:RSA+AES:RSA+3DES:!aNULL:!MD5:!DSS``

.. _sni: https://en.wikipedia.org/wiki/Server_Name_Indication
.. _crime attack: https://en.wikipedia.org/wiki/CRIME_(security_exploit)

'''

try:
    from ndg.httpsclient.ssl_peer_verification import SUBJ_ALT_NAME_SUPPORT
    from ndg.httpsclient.subj_alt_name import SubjectAltName as BaseSubjectAltName
except SyntaxError as e:
    raise ImportError(e)

import OpenSSL.SSL
from pyasn1.codec.der import decoder as der_decoder
from pyasn1.type import univ, constraint
from socket import _fileobject, timeout
import ssl
import select

from .. import connection
from .. import util

__all__ = ['inject_into_urllib3', 'extract_from_urllib3']

# SNI only *really* works if we can read the subjectAltName of certificates.
HAS_SNI = SUBJ_ALT_NAME_SUPPORT

# Map from urllib3 to PyOpenSSL compatible parameter-values.
_openssl_versions = {
    ssl.PROTOCOL_SSLv23: OpenSSL.SSL.SSLv23_METHOD,
    ssl.PROTOCOL_TLSv1: OpenSSL.SSL.TLSv1_METHOD,
}

try:
    _openssl_versions.update({ssl.PROTOCOL_SSLv3: OpenSSL.SSL.SSLv3_METHOD})
except AttributeError:
    pass

_openssl_verify = {
    ssl.CERT_NONE: OpenSSL.SSL.VERIFY_NONE,
    ssl.CERT_OPTIONAL: OpenSSL.SSL.VERIFY_PEER,
    ssl.CERT_REQUIRED: OpenSSL.SSL.VERIFY_PEER
                       + OpenSSL.SSL.VERIFY_FAIL_IF_NO_PEER_CERT,
}

# A secure default.
# Sources for more information on TLS ciphers:
#
# - https://wiki.mozilla.org/Security/Server_Side_TLS
# - https://www.ssllabs.com/projects/best-practices/index.html
# - https://hynek.me/articles/hardening-your-web-servers-ssl-ciphers/
#
# The general intent is:
# - Prefer cipher suites that offer perfect forward secrecy (DHE/ECDHE),
# - prefer ECDHE over DHE for better performance,
# - prefer any AES-GCM over any AES-CBC for better performance and security,
# - use 3DES as fallback which is secure but slow,
# - disable NULL authentication, MD5 MACs and DSS for security reasons.
DEFAULT_SSL_CIPHER_LIST = "ECDH+AESGCM:DH+AESGCM:ECDH+AES256:DH+AES256:" + \
    "ECDH+AES128:DH+AES:ECDH+3DES:DH+3DES:RSA+AESGCM:RSA+AES:RSA+3DES:" + \
    "!aNULL:!MD5:!DSS"


orig_util_HAS_SNI = util.HAS_SNI
orig_connection_ssl_wrap_socket = connection.ssl_wrap_socket


def inject_into_urllib3():
    'Monkey-patch urllib3 with PyOpenSSL-backed SSL-support.'

    connection.ssl_wrap_socket = ssl_wrap_socket
    util.HAS_SNI = HAS_SNI


def extract_from_urllib3():
    'Undo monkey-patching by :func:`inject_into_urllib3`.'

    connection.ssl_wrap_socket = orig_connection_ssl_wrap_socket
    util.HAS_SNI = orig_util_HAS_SNI


### Note: This is a slightly bug-fixed version of same from ndg-httpsclient.
class SubjectAltName(BaseSubjectAltName):
    '''ASN.1 implementation for subjectAltNames support'''

    # There is no limit to how many SAN certificates a certificate may have,
    #   however this needs to have some limit so we'll set an arbitrarily high
    #   limit.
    sizeSpec = univ.SequenceOf.sizeSpec + \
        constraint.ValueSizeConstraint(1, 1024)


### Note: This is a slightly bug-fixed version of same from ndg-httpsclient.
def get_subj_alt_name(peer_cert):
    # Search through extensions
    dns_name = []
    if not SUBJ_ALT_NAME_SUPPORT:
        return dns_name

    general_names = SubjectAltName()
    for i in range(peer_cert.get_extension_count()):
        ext = peer_cert.get_extension(i)
        ext_name = ext.get_short_name()
        if ext_name != 'subjectAltName':
            continue

        # PyOpenSSL returns extension data in ASN.1 encoded form
        ext_dat = ext.get_data()
        decoded_dat = der_decoder.decode(ext_dat,
                                         asn1Spec=general_names)

        for name in decoded_dat:
            if not isinstance(name, SubjectAltName):
                continue
            for entry in range(len(name)):
                component = name.getComponentByPosition(entry)
                if component.getName() != 'dNSName':
                    continue
                dns_name.append(str(component.getComponent()))

    return dns_name


class WrappedSocket(object):
    '''API-compatibility wrapper for Python OpenSSL's Connection-class.

    Note: _makefile_refs, _drop() and _reuse() are needed for the garbage
    collector of pypy.
    '''

    def __init__(self, connection, socket, suppress_ragged_eofs=True):
        self.connection = connection
        self.socket = socket
        self.suppress_ragged_eofs = suppress_ragged_eofs
        self._makefile_refs = 0

    def fileno(self):
        return self.socket.fileno()

    def makefile(self, mode, bufsize=-1):
        self._makefile_refs += 1
        return _fileobject(self, mode, bufsize, close=True)

    def recv(self, *args, **kwargs):
        try:
            data = self.connection.recv(*args, **kwargs)
        except OpenSSL.SSL.SysCallError as e:
            if self.suppress_ragged_eofs and e.args == (-1, 'Unexpected EOF'):
                return b''
            else:
                raise
        except OpenSSL.SSL.WantReadError:
            rd, wd, ed = select.select(
                [self.socket], [], [], self.socket.gettimeout())
            if not rd:
                raise timeout('The read operation timed out')
            else:
                return self.recv(*args, **kwargs)
        else:
            return data

    def settimeout(self, timeout):
        return self.socket.settimeout(timeout)

    def sendall(self, data):
        return self.connection.sendall(data)

    def close(self):
        if self._makefile_refs < 1:
            return self.connection.shutdown()
        else:
            self._makefile_refs -= 1

    def getpeercert(self, binary_form=False):
        x509 = self.connection.get_peer_certificate()

        if not x509:
            return x509

        if binary_form:
            return OpenSSL.crypto.dump_certificate(
                OpenSSL.crypto.FILETYPE_ASN1,
                x509)

        return {
            'subject': (
                (('commonName', x509.get_subject().CN),),
            ),
            'subjectAltName': [
                ('DNS', value)
                for value in get_subj_alt_name(x509)
            ]
        }

    def _reuse(self):
        self._makefile_refs += 1

    def _drop(self):
        if self._makefile_refs < 1:
            self.close()
        else:
            self._makefile_refs -= 1


def _verify_callback(cnx, x509, err_no, err_depth, return_code):
    return err_no == 0


def ssl_wrap_socket(sock, keyfile=None, certfile=None, cert_reqs=None,
                    ca_certs=None, server_hostname=None,
                    ssl_version=None):
    ctx = OpenSSL.SSL.Context(_openssl_versions[ssl_version])
    if certfile:
        ctx.use_certificate_file(certfile)
    if keyfile:
        ctx.use_privatekey_file(keyfile)
    if cert_reqs != ssl.CERT_NONE:
        ctx.set_verify(_openssl_verify[cert_reqs], _verify_callback)
    if ca_certs:
        try:
            ctx.load_verify_locations(ca_certs, None)
        except OpenSSL.SSL.Error as e:
            raise ssl.SSLError('bad ca_certs: %r' % ca_certs, e)
    else:
        ctx.set_default_verify_paths()

    # Disable TLS compression to migitate CRIME attack (issue #309)
    OP_NO_COMPRESSION = 0x20000
    ctx.set_options(OP_NO_COMPRESSION)

    # Set list of supported ciphersuites.
    ctx.set_cipher_list(DEFAULT_SSL_CIPHER_LIST)

    cnx = OpenSSL.SSL.Connection(ctx, sock)
    cnx.set_tlsext_host_name(server_hostname)
    cnx.set_connect_state()
    while True:
        try:
            cnx.do_handshake()
        except OpenSSL.SSL.WantReadError:
            select.select([sock], [], [])
            continue
        except OpenSSL.SSL.Error as e:
            raise ssl.SSLError('bad handshake', e)
        break

    return WrappedSocket(cnx, sock)
