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stbi/Lib/site-packages/pip/_vendor/urllib3/contrib/securetransport.py

+"""
+SecureTranport support for urllib3 via ctypes.
+
+This makes platform-native TLS available to urllib3 users on macOS without the
+use of a compiler. This is an important feature because the Python Package
+Index is moving to become a TLSv1.2-or-higher server, and the default OpenSSL
+that ships with macOS is not capable of doing TLSv1.2. The only way to resolve
+this is to give macOS users an alternative solution to the problem, and that
+solution is to use SecureTransport.
+
+We use ctypes here because this solution must not require a compiler. That's
+because pip is not allowed to require a compiler either.
+
+This is not intended to be a seriously long-term solution to this problem.
+The hope is that PEP 543 will eventually solve this issue for us, at which
+point we can retire this contrib module. But in the short term, we need to
+solve the impending tire fire that is Python on Mac without this kind of
+contrib module. So...here we are.
+
+To use this module, simply import and inject it::
+
+    import urllib3.contrib.securetransport
+    urllib3.contrib.securetransport.inject_into_urllib3()
+
+Happy TLSing!
+
+This code is a bastardised version of the code found in Will Bond's oscrypto
+library. An enormous debt is owed to him for blazing this trail for us. For
+that reason, this code should be considered to be covered both by urllib3's
+license and by oscrypto's:
+
+    Copyright (c) 2015-2016 Will Bond <will@wbond.net>
+
+    Permission is hereby granted, free of charge, to any person obtaining a
+    copy of this software and associated documentation files (the "Software"),
+    to deal in the Software without restriction, including without limitation
+    the rights to use, copy, modify, merge, publish, distribute, sublicense,
+    and/or sell copies of the Software, and to permit persons to whom the
+    Software is furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+    DEALINGS IN THE SOFTWARE.
+"""
+from __future__ import absolute_import
+
+import contextlib
+import ctypes
+import errno
+import os.path
+import shutil
+import socket
+import ssl
+import threading
+import weakref
+
+from .. import util
+from ._securetransport.bindings import Security, SecurityConst, CoreFoundation
+from ._securetransport.low_level import (
+    _assert_no_error,
+    _cert_array_from_pem,
+    _temporary_keychain,
+    _load_client_cert_chain,
+)
+
+try:  # Platform-specific: Python 2
+    from socket import _fileobject
+except ImportError:  # Platform-specific: Python 3
+    _fileobject = None
+    from ..packages.backports.makefile import backport_makefile
+
+__all__ = ["inject_into_urllib3", "extract_from_urllib3"]
+
+# SNI always works
+HAS_SNI = True
+
+orig_util_HAS_SNI = util.HAS_SNI
+orig_util_SSLContext = util.ssl_.SSLContext
+
+# This dictionary is used by the read callback to obtain a handle to the
+# calling wrapped socket. This is a pretty silly approach, but for now it'll
+# do. I feel like I should be able to smuggle a handle to the wrapped socket
+# directly in the SSLConnectionRef, but for now this approach will work I
+# guess.
+#
+# We need to lock around this structure for inserts, but we don't do it for
+# reads/writes in the callbacks. The reasoning here goes as follows:
+#
+#    1. It is not possible to call into the callbacks before the dictionary is
+#       populated, so once in the callback the id must be in the dictionary.
+#    2. The callbacks don't mutate the dictionary, they only read from it, and
+#       so cannot conflict with any of the insertions.
+#
+# This is good: if we had to lock in the callbacks we'd drastically slow down
+# the performance of this code.
+_connection_refs = weakref.WeakValueDictionary()
+_connection_ref_lock = threading.Lock()
+
+# Limit writes to 16kB. This is OpenSSL's limit, but we'll cargo-cult it over
+# for no better reason than we need *a* limit, and this one is right there.
+SSL_WRITE_BLOCKSIZE = 16384
+
+# This is our equivalent of util.ssl_.DEFAULT_CIPHERS, but expanded out to
+# individual cipher suites. We need to do this because this is how
+# SecureTransport wants them.
+CIPHER_SUITES = [
+    SecurityConst.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
+    SecurityConst.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
+    SecurityConst.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
+    SecurityConst.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
+    SecurityConst.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256,
+    SecurityConst.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
+    SecurityConst.TLS_DHE_RSA_WITH_AES_256_GCM_SHA384,
+    SecurityConst.TLS_DHE_RSA_WITH_AES_128_GCM_SHA256,
+    SecurityConst.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384,
+    SecurityConst.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA,
+    SecurityConst.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256,
+    SecurityConst.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA,
+    SecurityConst.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384,
+    SecurityConst.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,
+    SecurityConst.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256,
+    SecurityConst.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,
+    SecurityConst.TLS_DHE_RSA_WITH_AES_256_CBC_SHA256,
+    SecurityConst.TLS_DHE_RSA_WITH_AES_256_CBC_SHA,
+    SecurityConst.TLS_DHE_RSA_WITH_AES_128_CBC_SHA256,
+    SecurityConst.TLS_DHE_RSA_WITH_AES_128_CBC_SHA,
+    SecurityConst.TLS_AES_256_GCM_SHA384,
+    SecurityConst.TLS_AES_128_GCM_SHA256,
+    SecurityConst.TLS_RSA_WITH_AES_256_GCM_SHA384,
+    SecurityConst.TLS_RSA_WITH_AES_128_GCM_SHA256,
+    SecurityConst.TLS_AES_128_CCM_8_SHA256,
+    SecurityConst.TLS_AES_128_CCM_SHA256,
+    SecurityConst.TLS_RSA_WITH_AES_256_CBC_SHA256,
+    SecurityConst.TLS_RSA_WITH_AES_128_CBC_SHA256,
+    SecurityConst.TLS_RSA_WITH_AES_256_CBC_SHA,
+    SecurityConst.TLS_RSA_WITH_AES_128_CBC_SHA,
+]
+
+# Basically this is simple: for PROTOCOL_SSLv23 we turn it into a low of
+# TLSv1 and a high of TLSv1.2. For everything else, we pin to that version.
+# TLSv1 to 1.2 are supported on macOS 10.8+
+_protocol_to_min_max = {
+    util.PROTOCOL_TLS: (SecurityConst.kTLSProtocol1, SecurityConst.kTLSProtocol12)
+}
+
+if hasattr(ssl, "PROTOCOL_SSLv2"):
+    _protocol_to_min_max[ssl.PROTOCOL_SSLv2] = (
+        SecurityConst.kSSLProtocol2,
+        SecurityConst.kSSLProtocol2,
+    )
+if hasattr(ssl, "PROTOCOL_SSLv3"):
+    _protocol_to_min_max[ssl.PROTOCOL_SSLv3] = (
+        SecurityConst.kSSLProtocol3,
+        SecurityConst.kSSLProtocol3,
+    )
+if hasattr(ssl, "PROTOCOL_TLSv1"):
+    _protocol_to_min_max[ssl.PROTOCOL_TLSv1] = (
+        SecurityConst.kTLSProtocol1,
+        SecurityConst.kTLSProtocol1,
+    )
+if hasattr(ssl, "PROTOCOL_TLSv1_1"):
+    _protocol_to_min_max[ssl.PROTOCOL_TLSv1_1] = (
+        SecurityConst.kTLSProtocol11,
+        SecurityConst.kTLSProtocol11,
+    )
+if hasattr(ssl, "PROTOCOL_TLSv1_2"):
+    _protocol_to_min_max[ssl.PROTOCOL_TLSv1_2] = (
+        SecurityConst.kTLSProtocol12,
+        SecurityConst.kTLSProtocol12,
+    )
+
+
+def inject_into_urllib3():
+    """
+    Monkey-patch urllib3 with SecureTransport-backed SSL-support.
+    """
+    util.SSLContext = SecureTransportContext
+    util.ssl_.SSLContext = SecureTransportContext
+    util.HAS_SNI = HAS_SNI
+    util.ssl_.HAS_SNI = HAS_SNI
+    util.IS_SECURETRANSPORT = True
+    util.ssl_.IS_SECURETRANSPORT = True
+
+
+def extract_from_urllib3():
+    """
+    Undo monkey-patching by :func:`inject_into_urllib3`.
+    """
+    util.SSLContext = orig_util_SSLContext
+    util.ssl_.SSLContext = orig_util_SSLContext
+    util.HAS_SNI = orig_util_HAS_SNI
+    util.ssl_.HAS_SNI = orig_util_HAS_SNI
+    util.IS_SECURETRANSPORT = False
+    util.ssl_.IS_SECURETRANSPORT = False
+
+
+def _read_callback(connection_id, data_buffer, data_length_pointer):
+    """
+    SecureTransport read callback. This is called by ST to request that data
+    be returned from the socket.
+    """
+    wrapped_socket = None
+    try:
+        wrapped_socket = _connection_refs.get(connection_id)
+        if wrapped_socket is None:
+            return SecurityConst.errSSLInternal
+        base_socket = wrapped_socket.socket
+
+        requested_length = data_length_pointer[0]
+
+        timeout = wrapped_socket.gettimeout()
+        error = None
+        read_count = 0
+
+        try:
+            while read_count < requested_length:
+                if timeout is None or timeout >= 0:
+                    if not util.wait_for_read(base_socket, timeout):
+                        raise socket.error(errno.EAGAIN, "timed out")
+
+                remaining = requested_length - read_count
+                buffer = (ctypes.c_char * remaining).from_address(
+                    data_buffer + read_count
+                )
+                chunk_size = base_socket.recv_into(buffer, remaining)
+                read_count += chunk_size
+                if not chunk_size:
+                    if not read_count:
+                        return SecurityConst.errSSLClosedGraceful
+                    break
+        except (socket.error) as e:
+            error = e.errno
+
+            if error is not None and error != errno.EAGAIN:
+                data_length_pointer[0] = read_count
+                if error == errno.ECONNRESET or error == errno.EPIPE:
+                    return SecurityConst.errSSLClosedAbort
+                raise
+
+        data_length_pointer[0] = read_count
+
+        if read_count != requested_length:
+            return SecurityConst.errSSLWouldBlock
+
+        return 0
+    except Exception as e:
+        if wrapped_socket is not None:
+            wrapped_socket._exception = e
+        return SecurityConst.errSSLInternal
+
+
+def _write_callback(connection_id, data_buffer, data_length_pointer):
+    """
+    SecureTransport write callback. This is called by ST to request that data
+    actually be sent on the network.
+    """
+    wrapped_socket = None
+    try:
+        wrapped_socket = _connection_refs.get(connection_id)
+        if wrapped_socket is None:
+            return SecurityConst.errSSLInternal
+        base_socket = wrapped_socket.socket
+
+        bytes_to_write = data_length_pointer[0]
+        data = ctypes.string_at(data_buffer, bytes_to_write)
+
+        timeout = wrapped_socket.gettimeout()
+        error = None
+        sent = 0
+
+        try:
+            while sent < bytes_to_write:
+                if timeout is None or timeout >= 0:
+                    if not util.wait_for_write(base_socket, timeout):
+                        raise socket.error(errno.EAGAIN, "timed out")
+                chunk_sent = base_socket.send(data)
+                sent += chunk_sent
+
+                # This has some needless copying here, but I'm not sure there's
+                # much value in optimising this data path.
+                data = data[chunk_sent:]
+        except (socket.error) as e:
+            error = e.errno
+
+            if error is not None and error != errno.EAGAIN:
+                data_length_pointer[0] = sent
+                if error == errno.ECONNRESET or error == errno.EPIPE:
+                    return SecurityConst.errSSLClosedAbort
+                raise
+
+        data_length_pointer[0] = sent
+
+        if sent != bytes_to_write:
+            return SecurityConst.errSSLWouldBlock
+
+        return 0
+    except Exception as e:
+        if wrapped_socket is not None:
+            wrapped_socket._exception = e
+        return SecurityConst.errSSLInternal
+
+
+# We need to keep these two objects references alive: if they get GC'd while
+# in use then SecureTransport could attempt to call a function that is in freed
+# memory. That would be...uh...bad. Yeah, that's the word. Bad.
+_read_callback_pointer = Security.SSLReadFunc(_read_callback)
+_write_callback_pointer = Security.SSLWriteFunc(_write_callback)
+
+
+class WrappedSocket(object):
+    """
+    API-compatibility wrapper for Python's OpenSSL wrapped socket object.
+
+    Note: _makefile_refs, _drop(), and _reuse() are needed for the garbage
+    collector of PyPy.
+    """
+
+    def __init__(self, socket):
+        self.socket = socket
+        self.context = None
+        self._makefile_refs = 0
+        self._closed = False
+        self._exception = None
+        self._keychain = None
+        self._keychain_dir = None
+        self._client_cert_chain = None
+
+        # We save off the previously-configured timeout and then set it to
+        # zero. This is done because we use select and friends to handle the
+        # timeouts, but if we leave the timeout set on the lower socket then
+        # Python will "kindly" call select on that socket again for us. Avoid
+        # that by forcing the timeout to zero.
+        self._timeout = self.socket.gettimeout()
+        self.socket.settimeout(0)
+
+    @contextlib.contextmanager
+    def _raise_on_error(self):
+        """
+        A context manager that can be used to wrap calls that do I/O from
+        SecureTransport. If any of the I/O callbacks hit an exception, this
+        context manager will correctly propagate the exception after the fact.
+        This avoids silently swallowing those exceptions.
+
+        It also correctly forces the socket closed.
+        """
+        self._exception = None
+
+        # We explicitly don't catch around this yield because in the unlikely
+        # event that an exception was hit in the block we don't want to swallow
+        # it.
+        yield
+        if self._exception is not None:
+            exception, self._exception = self._exception, None
+            self.close()
+            raise exception
+
+    def _set_ciphers(self):
+        """
+        Sets up the allowed ciphers. By default this matches the set in
+        util.ssl_.DEFAULT_CIPHERS, at least as supported by macOS. This is done
+        custom and doesn't allow changing at this time, mostly because parsing
+        OpenSSL cipher strings is going to be a freaking nightmare.
+        """
+        ciphers = (Security.SSLCipherSuite * len(CIPHER_SUITES))(*CIPHER_SUITES)
+        result = Security.SSLSetEnabledCiphers(
+            self.context, ciphers, len(CIPHER_SUITES)
+        )
+        _assert_no_error(result)
+
+    def _custom_validate(self, verify, trust_bundle):
+        """
+        Called when we have set custom validation. We do this in two cases:
+        first, when cert validation is entirely disabled; and second, when
+        using a custom trust DB.
+        """
+        # If we disabled cert validation, just say: cool.
+        if not verify:
+            return
+
+        # We want data in memory, so load it up.
+        if os.path.isfile(trust_bundle):
+            with open(trust_bundle, "rb") as f:
+                trust_bundle = f.read()
+
+        cert_array = None
+        trust = Security.SecTrustRef()
+
+        try:
+            # Get a CFArray that contains the certs we want.
+            cert_array = _cert_array_from_pem(trust_bundle)
+
+            # Ok, now the hard part. We want to get the SecTrustRef that ST has
+            # created for this connection, shove our CAs into it, tell ST to
+            # ignore everything else it knows, and then ask if it can build a
+            # chain. This is a buuuunch of code.
+            result = Security.SSLCopyPeerTrust(self.context, ctypes.byref(trust))
+            _assert_no_error(result)
+            if not trust:
+                raise ssl.SSLError("Failed to copy trust reference")
+
+            result = Security.SecTrustSetAnchorCertificates(trust, cert_array)
+            _assert_no_error(result)
+
+            result = Security.SecTrustSetAnchorCertificatesOnly(trust, True)
+            _assert_no_error(result)
+
+            trust_result = Security.SecTrustResultType()
+            result = Security.SecTrustEvaluate(trust, ctypes.byref(trust_result))
+            _assert_no_error(result)
+        finally:
+            if trust:
+                CoreFoundation.CFRelease(trust)
+
+            if cert_array is not None:
+                CoreFoundation.CFRelease(cert_array)
+
+        # Ok, now we can look at what the result was.
+        successes = (
+            SecurityConst.kSecTrustResultUnspecified,
+            SecurityConst.kSecTrustResultProceed,
+        )
+        if trust_result.value not in successes:
+            raise ssl.SSLError(
+                "certificate verify failed, error code: %d" % trust_result.value
+            )
+
+    def handshake(
+        self,
+        server_hostname,
+        verify,
+        trust_bundle,
+        min_version,
+        max_version,
+        client_cert,
+        client_key,
+        client_key_passphrase,
+    ):
+        """
+        Actually performs the TLS handshake. This is run automatically by
+        wrapped socket, and shouldn't be needed in user code.
+        """
+        # First, we do the initial bits of connection setup. We need to create
+        # a context, set its I/O funcs, and set the connection reference.
+        self.context = Security.SSLCreateContext(
+            None, SecurityConst.kSSLClientSide, SecurityConst.kSSLStreamType
+        )
+        result = Security.SSLSetIOFuncs(
+            self.context, _read_callback_pointer, _write_callback_pointer
+        )
+        _assert_no_error(result)
+
+        # Here we need to compute the handle to use. We do this by taking the
+        # id of self modulo 2**31 - 1. If this is already in the dictionary, we
+        # just keep incrementing by one until we find a free space.
+        with _connection_ref_lock:
+            handle = id(self) % 2147483647
+            while handle in _connection_refs:
+                handle = (handle + 1) % 2147483647
+            _connection_refs[handle] = self
+
+        result = Security.SSLSetConnection(self.context, handle)
+        _assert_no_error(result)
+
+        # If we have a server hostname, we should set that too.
+        if server_hostname:
+            if not isinstance(server_hostname, bytes):
+                server_hostname = server_hostname.encode("utf-8")
+
+            result = Security.SSLSetPeerDomainName(
+                self.context, server_hostname, len(server_hostname)
+            )
+            _assert_no_error(result)
+
+        # Setup the ciphers.
+        self._set_ciphers()
+
+        # Set the minimum and maximum TLS versions.
+        result = Security.SSLSetProtocolVersionMin(self.context, min_version)
+        _assert_no_error(result)
+
+        result = Security.SSLSetProtocolVersionMax(self.context, max_version)
+        _assert_no_error(result)
+
+        # If there's a trust DB, we need to use it. We do that by telling
+        # SecureTransport to break on server auth. We also do that if we don't
+        # want to validate the certs at all: we just won't actually do any
+        # authing in that case.
+        if not verify or trust_bundle is not None:
+            result = Security.SSLSetSessionOption(
+                self.context, SecurityConst.kSSLSessionOptionBreakOnServerAuth, True
+            )
+            _assert_no_error(result)
+
+        # If there's a client cert, we need to use it.
+        if client_cert:
+            self._keychain, self._keychain_dir = _temporary_keychain()
+            self._client_cert_chain = _load_client_cert_chain(
+                self._keychain, client_cert, client_key
+            )
+            result = Security.SSLSetCertificate(self.context, self._client_cert_chain)
+            _assert_no_error(result)
+
+        while True:
+            with self._raise_on_error():
+                result = Security.SSLHandshake(self.context)
+
+                if result == SecurityConst.errSSLWouldBlock:
+                    raise socket.timeout("handshake timed out")
+                elif result == SecurityConst.errSSLServerAuthCompleted:
+                    self._custom_validate(verify, trust_bundle)
+                    continue
+                else:
+                    _assert_no_error(result)
+                    break
+
+    def fileno(self):
+        return self.socket.fileno()
+
+    # Copy-pasted from Python 3.5 source code
+    def _decref_socketios(self):
+        if self._makefile_refs > 0:
+            self._makefile_refs -= 1
+        if self._closed:
+            self.close()
+
+    def recv(self, bufsiz):
+        buffer = ctypes.create_string_buffer(bufsiz)
+        bytes_read = self.recv_into(buffer, bufsiz)
+        data = buffer[:bytes_read]
+        return data
+
+    def recv_into(self, buffer, nbytes=None):
+        # Read short on EOF.
+        if self._closed:
+            return 0
+
+        if nbytes is None:
+            nbytes = len(buffer)
+
+        buffer = (ctypes.c_char * nbytes).from_buffer(buffer)
+        processed_bytes = ctypes.c_size_t(0)
+
+        with self._raise_on_error():
+            result = Security.SSLRead(
+                self.context, buffer, nbytes, ctypes.byref(processed_bytes)
+            )
+
+        # There are some result codes that we want to treat as "not always
+        # errors". Specifically, those are errSSLWouldBlock,
+        # errSSLClosedGraceful, and errSSLClosedNoNotify.
+        if result == SecurityConst.errSSLWouldBlock:
+            # If we didn't process any bytes, then this was just a time out.
+            # However, we can get errSSLWouldBlock in situations when we *did*
+            # read some data, and in those cases we should just read "short"
+            # and return.
+            if processed_bytes.value == 0:
+                # Timed out, no data read.
+                raise socket.timeout("recv timed out")
+        elif result in (
+            SecurityConst.errSSLClosedGraceful,
+            SecurityConst.errSSLClosedNoNotify,
+        ):
+            # The remote peer has closed this connection. We should do so as
+            # well. Note that we don't actually return here because in
+            # principle this could actually be fired along with return data.
+            # It's unlikely though.
+            self.close()
+        else:
+            _assert_no_error(result)
+
+        # Ok, we read and probably succeeded. We should return whatever data
+        # was actually read.
+        return processed_bytes.value
+
+    def settimeout(self, timeout):
+        self._timeout = timeout
+
+    def gettimeout(self):
+        return self._timeout
+
+    def send(self, data):
+        processed_bytes = ctypes.c_size_t(0)
+
+        with self._raise_on_error():
+            result = Security.SSLWrite(
+                self.context, data, len(data), ctypes.byref(processed_bytes)
+            )
+
+        if result == SecurityConst.errSSLWouldBlock and processed_bytes.value == 0:
+            # Timed out
+            raise socket.timeout("send timed out")
+        else:
+            _assert_no_error(result)
+
+        # We sent, and probably succeeded. Tell them how much we sent.
+        return processed_bytes.value
+
+    def sendall(self, data):
+        total_sent = 0
+        while total_sent < len(data):
+            sent = self.send(data[total_sent : total_sent + SSL_WRITE_BLOCKSIZE])
+            total_sent += sent
+
+    def shutdown(self):
+        with self._raise_on_error():
+            Security.SSLClose(self.context)
+
+    def close(self):
+        # TODO: should I do clean shutdown here? Do I have to?
+        if self._makefile_refs < 1:
+            self._closed = True
+            if self.context:
+                CoreFoundation.CFRelease(self.context)
+                self.context = None
+            if self._client_cert_chain:
+                CoreFoundation.CFRelease(self._client_cert_chain)
+                self._client_cert_chain = None
+            if self._keychain:
+                Security.SecKeychainDelete(self._keychain)
+                CoreFoundation.CFRelease(self._keychain)
+                shutil.rmtree(self._keychain_dir)
+                self._keychain = self._keychain_dir = None
+            return self.socket.close()
+        else:
+            self._makefile_refs -= 1
+
+    def getpeercert(self, binary_form=False):
+        # Urgh, annoying.
+        #
+        # Here's how we do this:
+        #
+        # 1. Call SSLCopyPeerTrust to get hold of the trust object for this
+        #    connection.
+        # 2. Call SecTrustGetCertificateAtIndex for index 0 to get the leaf.
+        # 3. To get the CN, call SecCertificateCopyCommonName and process that
+        #    string so that it's of the appropriate type.
+        # 4. To get the SAN, we need to do something a bit more complex:
+        #    a. Call SecCertificateCopyValues to get the data, requesting
+        #       kSecOIDSubjectAltName.
+        #    b. Mess about with this dictionary to try to get the SANs out.
+        #
+        # This is gross. Really gross. It's going to be a few hundred LoC extra
+        # just to repeat something that SecureTransport can *already do*. So my
+        # operating assumption at this time is that what we want to do is
+        # instead to just flag to urllib3 that it shouldn't do its own hostname
+        # validation when using SecureTransport.
+        if not binary_form:
+            raise ValueError("SecureTransport only supports dumping binary certs")
+        trust = Security.SecTrustRef()
+        certdata = None
+        der_bytes = None
+
+        try:
+            # Grab the trust store.
+            result = Security.SSLCopyPeerTrust(self.context, ctypes.byref(trust))
+            _assert_no_error(result)
+            if not trust:
+                # Probably we haven't done the handshake yet. No biggie.
+                return None
+
+            cert_count = Security.SecTrustGetCertificateCount(trust)
+            if not cert_count:
+                # Also a case that might happen if we haven't handshaked.
+                # Handshook? Handshaken?
+                return None
+
+            leaf = Security.SecTrustGetCertificateAtIndex(trust, 0)
+            assert leaf
+
+            # Ok, now we want the DER bytes.
+            certdata = Security.SecCertificateCopyData(leaf)
+            assert certdata
+
+            data_length = CoreFoundation.CFDataGetLength(certdata)
+            data_buffer = CoreFoundation.CFDataGetBytePtr(certdata)
+            der_bytes = ctypes.string_at(data_buffer, data_length)
+        finally:
+            if certdata:
+                CoreFoundation.CFRelease(certdata)
+            if trust:
+                CoreFoundation.CFRelease(trust)
+
+        return der_bytes
+
+    def version(self):
+        protocol = Security.SSLProtocol()
+        result = Security.SSLGetNegotiatedProtocolVersion(
+            self.context, ctypes.byref(protocol)
+        )
+        _assert_no_error(result)
+        if protocol.value == SecurityConst.kTLSProtocol13:
+            raise ssl.SSLError("SecureTransport does not support TLS 1.3")
+        elif protocol.value == SecurityConst.kTLSProtocol12:
+            return "TLSv1.2"
+        elif protocol.value == SecurityConst.kTLSProtocol11:
+            return "TLSv1.1"
+        elif protocol.value == SecurityConst.kTLSProtocol1:
+            return "TLSv1"
+        elif protocol.value == SecurityConst.kSSLProtocol3:
+            return "SSLv3"
+        elif protocol.value == SecurityConst.kSSLProtocol2:
+            return "SSLv2"
+        else:
+            raise ssl.SSLError("Unknown TLS version: %r" % protocol)
+
+    def _reuse(self):
+        self._makefile_refs += 1
+
+    def _drop(self):
+        if self._makefile_refs < 1:
+            self.close()
+        else:
+            self._makefile_refs -= 1
+
+
+if _fileobject:  # Platform-specific: Python 2
+
+    def makefile(self, mode, bufsize=-1):
+        self._makefile_refs += 1
+        return _fileobject(self, mode, bufsize, close=True)
+
+
+else:  # Platform-specific: Python 3
+
+    def makefile(self, mode="r", buffering=None, *args, **kwargs):
+        # We disable buffering with SecureTransport because it conflicts with
+        # the buffering that ST does internally (see issue #1153 for more).
+        buffering = 0
+        return backport_makefile(self, mode, buffering, *args, **kwargs)
+
+
+WrappedSocket.makefile = makefile
+
+
+class SecureTransportContext(object):
+    """
+    I am a wrapper class for the SecureTransport library, to translate the
+    interface of the standard library ``SSLContext`` object to calls into
+    SecureTransport.
+    """
+
+    def __init__(self, protocol):
+        self._min_version, self._max_version = _protocol_to_min_max[protocol]
+        self._options = 0
+        self._verify = False
+        self._trust_bundle = None
+        self._client_cert = None
+        self._client_key = None
+        self._client_key_passphrase = None
+
+    @property
+    def check_hostname(self):
+        """
+        SecureTransport cannot have its hostname checking disabled. For more,
+        see the comment on getpeercert() in this file.
+        """
+        return True
+
+    @check_hostname.setter
+    def check_hostname(self, value):
+        """
+        SecureTransport cannot have its hostname checking disabled. For more,
+        see the comment on getpeercert() in this file.
+        """
+        pass
+
+    @property
+    def options(self):
+        # TODO: Well, crap.
+        #
+        # So this is the bit of the code that is the most likely to cause us
+        # trouble. Essentially we need to enumerate all of the SSL options that
+        # users might want to use and try to see if we can sensibly translate
+        # them, or whether we should just ignore them.
+        return self._options
+
+    @options.setter
+    def options(self, value):
+        # TODO: Update in line with above.
+        self._options = value
+
+    @property
+    def verify_mode(self):
+        return ssl.CERT_REQUIRED if self._verify else ssl.CERT_NONE
+
+    @verify_mode.setter
+    def verify_mode(self, value):
+        self._verify = True if value == ssl.CERT_REQUIRED else False
+
+    def set_default_verify_paths(self):
+        # So, this has to do something a bit weird. Specifically, what it does
+        # is nothing.
+        #
+        # This means that, if we had previously had load_verify_locations
+        # called, this does not undo that. We need to do that because it turns
+        # out that the rest of the urllib3 code will attempt to load the
+        # default verify paths if it hasn't been told about any paths, even if
+        # the context itself was sometime earlier. We resolve that by just
+        # ignoring it.
+        pass
+
+    def load_default_certs(self):
+        return self.set_default_verify_paths()
+
+    def set_ciphers(self, ciphers):
+        # For now, we just require the default cipher string.
+        if ciphers != util.ssl_.DEFAULT_CIPHERS:
+            raise ValueError("SecureTransport doesn't support custom cipher strings")
+
+    def load_verify_locations(self, cafile=None, capath=None, cadata=None):
+        # OK, we only really support cadata and cafile.
+        if capath is not None:
+            raise ValueError("SecureTransport does not support cert directories")
+
+        self._trust_bundle = cafile or cadata
+
+    def load_cert_chain(self, certfile, keyfile=None, password=None):
+        self._client_cert = certfile
+        self._client_key = keyfile
+        self._client_cert_passphrase = password
+
+    def wrap_socket(
+        self,
+        sock,
+        server_side=False,
+        do_handshake_on_connect=True,
+        suppress_ragged_eofs=True,
+        server_hostname=None,
+    ):
+        # So, what do we do here? Firstly, we assert some properties. This is a
+        # stripped down shim, so there is some functionality we don't support.
+        # See PEP 543 for the real deal.
+        assert not server_side
+        assert do_handshake_on_connect
+        assert suppress_ragged_eofs
+
+        # Ok, we're good to go. Now we want to create the wrapped socket object
+        # and store it in the appropriate place.
+        wrapped_socket = WrappedSocket(sock)
+
+        # Now we can handshake
+        wrapped_socket.handshake(
+            server_hostname,
+            self._verify,
+            self._trust_bundle,
+            self._min_version,
+            self._max_version,
+            self._client_cert,
+            self._client_key,
+            self._client_key_passphrase,
+        )
+        return wrapped_socket