Allow pointer channel args python

src/python/grpcio/grpc/_cython/_cygrpc/grpc.pxi

@@ -172,10 +172,14 @@ cdef extern from "grpc/grpc.h":
     GRPC_ARG_INTEGER
     GRPC_ARG_POINTER
 
-  ctypedef struct grpc_arg_value_pointer:
-    void *address "p"
+  ctypedef struct grpc_arg_pointer_vtable:
     void *(*copy)(void *)
     void (*destroy)(void *)
+    int (*cmp)(void *, void *)
+
+  ctypedef struct grpc_arg_value_pointer:
+    void *address "p"
+    grpc_arg_pointer_vtable *vtable
 
   union grpc_arg_value:
     char *string

src/python/grpcio/grpc/_cython/_cygrpc/records.pxd.pxi

@@ -84,6 +84,7 @@ cdef class SslPemKeyCertPair:
 cdef class ChannelArg:
 
   cdef grpc_arg c_arg
+  cdef grpc_arg_pointer_vtable ptr_vtable
   cdef readonly object key, value
 
 

src/python/grpcio/grpc/_cython/_cygrpc/records.pyx.pxi

@@ -27,6 +27,7 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+from libc.stdint cimport intptr_t
 
 class ConnectivityState:
   idle = GRPC_CHANNEL_IDLE
@@ -303,20 +304,49 @@ cdef class SslPemKeyCertPair:
     self.c_pair.certificate_chain = self.certificate_chain
 
 
+
+cdef void* copy_ptr(void* ptr):
+  return ptr
+
+
+cdef void destroy_ptr(void* ptr):
+  pass
+
+
+cdef int compare_ptr(void* ptr1, void* ptr2):
+  if ptr1 < ptr2:
+    return -1
+  elif ptr1 > ptr2:
+    return 1
+  else:
+    return 0
+
+
 cdef class ChannelArg:
 
   def __cinit__(self, bytes key, value):
     self.key = key
+    self.value = value
     self.c_arg.key = self.key
     if isinstance(value, int):
-      self.value = value
       self.c_arg.type = GRPC_ARG_INTEGER
       self.c_arg.value.integer = self.value
     elif isinstance(value, bytes):
-      self.value = value
       self.c_arg.type = GRPC_ARG_STRING
       self.c_arg.value.string = self.value
+    elif hasattr(value, '__int__'):
+      # Pointer objects must override __int__() to return
+      # the underlying C address (Python ints are word size).  The
+      # lifecycle of the pointer is fixed to the lifecycle of the 
+      # python object wrapping it.
+      self.ptr_vtable.copy = &copy_ptr
+      self.ptr_vtable.destroy = &destroy_ptr
+      self.ptr_vtable.cmp = &compare_ptr
+      self.c_arg.type = GRPC_ARG_POINTER
+      self.c_arg.value.pointer.vtable = &self.ptr_vtable
+      self.c_arg.value.pointer.address = <void*>(<intptr_t>int(self.value))
     else:
+      # TODO Add supported pointer types to this message
       raise TypeError('Expected int or bytes, got {}'.format(type(value)))
 
 

src/python/grpcio_tests/tests/unit/_channel_args_test.py

@@ -33,11 +33,18 @@ import unittest
 
 import grpc
 
+class TestPointerWrapper(object):
+
+  def __int__(self):
+    return 123456
+
+
 TEST_CHANNEL_ARGS = (
     ('arg1', b'bytes_val'),
     ('arg2', 'str_val'),
     ('arg3', 1),
     (b'arg4', 'str_val'),
+    ('arg6', TestPointerWrapper()),
 )