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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. we are.
To use this module, simply import and inject it::
import urllib3.contrib.securetransport
Happy TLSing!
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,
try: # Platform-specific: Python 2
from socket import _fileobject
except ImportError: # Platform-specific: Python 3
_fileobject = None
from ..packages.backports.makefile import backport_makefile
except NameError:
raise ImportError("SecureTransport only works on Pythons with memoryview")
__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.
# This is our equivalent of util.ssl_.DEFAULT_CIPHERS, but expanded out to
# individual cipher suites. We need to do this becuase this is how
# SecureTransport wants them.
# 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.
_protocol_to_min_max = {
ssl.PROTOCOL_SSLv23: (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
if hasattr(ssl, "PROTOCOL_TLS"):
_protocol_to_min_max[ssl.PROTOCOL_TLS] = _protocol_to_min_max[ssl.PROTOCOL_SSLv23]
def inject_into_urllib3():
Monkey-patch urllib3 with SecureTransport-backed SSL-support.
util.ssl_.SSLContext = SecureTransportContext
util.ssl_.HAS_SNI = HAS_SNI
def extract_from_urllib3():
Undo monkey-patching by :func:`inject_into_urllib3`.
util.ssl_.SSLContext = orig_util_SSLContext
util.HAS_SNI = orig_util_HAS_SNI
util.ssl_.HAS_SNI = orig_util_HAS_SNI
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
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
buffer = (ctypes.c_char * requested_length).from_address(data_buffer)
buffer_view = memoryview(buffer)
while read_count < requested_length:
if timeout is None or timeout >= 0:
readables = util.wait_for_read([base_socket], timeout)
if not readables:
raise socket.error(errno.EAGAIN, 'timed out')
# We need to tell ctypes that we have a buffer that can be
# written to. Upsettingly, we do that like this:
chunk_size = base_socket.recv_into(
read_count += chunk_size
if not chunk_size:
if not read_count:
return SecurityConst.errSSLClosedGraceful
except (socket.error) as e:
error = e.errno
if error is not None and error != errno.EAGAIN:
if error == errno.ECONNRESET:
return SecurityConst.errSSLClosedAbort
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
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
while sent < bytes_to_write:
if timeout is None or timeout >= 0:
writables = util.wait_for_write([base_socket], timeout)
if not writables:
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:
if error == errno.ECONNRESET:
return SecurityConst.errSSLClosedAbort
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()
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.
if self._exception is not None:
exception, self._exception = self._exception, None
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)
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:
# We want data in memory, so load it up.
if os.path.isfile(trust_bundle):
with open(trust_bundle, 'rb') as f:
trust_bundle =
cert_array = None
trust = Security.SecTrustRef()
# 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)
if not trust:
raise ssl.SSLError("Failed to copy trust reference")
result = Security.SecTrustSetAnchorCertificates(trust, cert_array)
result = Security.SecTrustSetAnchorCertificatesOnly(trust, True)
trust_result = Security.SecTrustResultType()
result = Security.SecTrustEvaluate(
trust, ctypes.byref(trust_result)
if trust:
if cert_array is None:
# Ok, now we can look at what the result was.
successes = (
if trust_result.value not in successes:
raise ssl.SSLError(
"certificate verify failed, error code: %d" %
def handshake(self,
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
# 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)
# 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)
# Setup the ciphers.
# Set the minimum and maximum TLS versions.
result = Security.SSLSetProtocolVersionMin(self.context, min_version)
result = Security.SSLSetProtocolVersionMax(self.context, max_version)
# 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(
# 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
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)
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:
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.
# 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")
# 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():
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:
self.context = None
if self._client_cert_chain:
self._client_cert_chain = None
if self._keychain:
self._keychain = self._keychain_dir = None
return self.socket.close()
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
# Grab the trust store.
result = Security.SSLCopyPeerTrust(
self.context, ctypes.byref(trust)
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)
if certdata:
if trust:
return der_bytes
def _reuse(self):
self._makefile_refs += 1
def _drop(self):
if self._makefile_refs < 1:
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
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
def check_hostname(self):
SecureTransport cannot have its hostname checking disabled. For more,
see the comment on getpeercert() in this file.
return True
def check_hostname(self, value):
SecureTransport cannot have its hostname checking disabled. For more,
see the comment on getpeercert() in this file.
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
def options(self, value):
# TODO: Update in line with above.
self._options = value
def verify_mode(self):
return ssl.CERT_REQUIRED if self._verify else ssl.CERT_NONE
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.
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,
# 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
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
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