Merge pull request #768 from reaperhulk/cffi-modulename-fix

Workaround for cffi issue 140

1 files changed, 30 insertions, 8 deletions

diff --git a/cryptography/hazmat/bindings/utils.py b/cryptography/hazmat/bindings/utils.py
index b8253483..318b82bb 100644
--- a/cryptography/hazmat/bindings/utils.py
+++ b/cryptography/hazmat/bindings/utils.py
@@ -13,6 +13,8 @@
 
 from __future__ import absolute_import, division, print_function
 
+import binascii
+
 import sys
 
 import cffi
@@ -50,7 +52,8 @@ def build_ffi(module_prefix, modules, pre_include, post_include, libraries):
         includes.append(module.INCLUDES)
         customizations.append(module.CUSTOMIZATIONS)
 
-    ffi.cdef("\n".join(types + functions + macros))
+    cdef_sources = types + functions + macros
+    ffi.cdef("\n".join(cdef_sources))
 
     # We include functions here so that if we got any of their definitions
     # wrong, the underlying C compiler will explode. In C you are allowed
@@ -60,14 +63,16 @@ def build_ffi(module_prefix, modules, pre_include, post_include, libraries):
     # is legal, but the following will fail to compile:
     #   int foo(int);
     #   int foo(short);
+    source = "\n".join(
+        [pre_include] +
+        includes +
+        [post_include] +
+        functions +
+        customizations
+    )
     lib = ffi.verify(
-        source="\n".join(
-            [pre_include] +
-            includes +
-            [post_include] +
-            functions +
-            customizations
-        ),
+        source=source,
+        modulename=_create_modulename(cdef_sources, source, sys.version),
         libraries=libraries,
         ext_package="cryptography",
     )
@@ -81,3 +86,20 @@ def build_ffi(module_prefix, modules, pre_include, post_include, libraries):
                     delattr(lib, name)
 
     return ffi, lib
+
+
+def _create_modulename(cdef_sources, source, sys_version):
+    """
+    cffi creates a modulename internally that incorporates the cffi version.
+    This will cause cryptography's wheels to break when the version of cffi
+    the user has does not match what was used when building the wheel. To
+    resolve this we build our own modulename that uses most of the same code
+    from cffi but elides the version key.
+    """
+    key = '\x00'.join([sys_version[:3], source] + cdef_sources)
+    key = key.encode('utf-8')
+    k1 = hex(binascii.crc32(key[0::2]) & 0xffffffff)
+    k1 = k1.lstrip('0x').rstrip('L')
+    k2 = hex(binascii.crc32(key[1::2]) & 0xffffffff)
+    k2 = k2.lstrip('0').rstrip('L')
+    return '_Cryptography_cffi_{0}{1}'.format(k1, k2)