Support mmap objects for reading with from_bytes

capnp/lib/capnp.pyx

@@ -29,6 +29,7 @@ import threading as _threading
 import socket as _socket
 import random as _random
 import collections as _collections
+import mmap as _mmap
 
 _CAPNP_VERSION_MAJOR = capnp.CAPNP_VERSION_MAJOR
 _CAPNP_VERSION_MINOR = capnp.CAPNP_VERSION_MINOR
@@ -277,6 +278,8 @@ ctypedef fused PromiseTypes:
 cdef extern from "Python.h":
     cdef int PyObject_AsReadBuffer(object, void** b, Py_ssize_t* c)
     cdef int PyObject_AsWriteBuffer(object, void** b, Py_ssize_t* c)
+    cdef int PyObject_GetBuffer(object, Py_buffer *view, int flags)
+    cdef void PyBuffer_Release(Py_buffer *view)
 
 # Templated classes are weird in cython. I couldn't put it in a pxd header for some reason
 cdef extern from "capnp/list.h" namespace " ::capnp":
@@ -3682,6 +3685,19 @@ cdef class _AlignedBuffer:
         if self.allocated:
             free(self.buf)
 
+
+@cython.internal
+cdef class _BufferView:
+    cdef Py_buffer view
+    cdef char * buf
+
+    def __init__(self, other):
+        PyObject_GetBuffer(other, &self.view, 0)
+        self.buf = <char*>self.view.buf
+
+    def __dealloc__(self):
+        PyBuffer_Release(&self.view)
+
 @cython.internal
 cdef class _FlatArrayMessageReader(_MessageReader):
     cdef object _object_to_pin
@@ -3698,7 +3714,13 @@ cdef class _FlatArrayMessageReader(_MessageReader):
         if sz % 8 != 0:
             raise ValueError("input length must be a multiple of eight bytes")
 
-        cdef char * ptr = buf
+        cdef char * ptr
+        if type(buf) == _mmap.mmap:
+            view = _BufferView(buf)
+            ptr = <char*>view.view.buf
+            self._object_to_pin = view
+        else:
+            ptr = buf
             if (<uintptr_t>ptr) % 8 != 0:
                 aligned = _AlignedBuffer(buf)
                 ptr = aligned.buf

test/test_serialization.py

@@ -5,6 +5,7 @@ import platform
 import test_regression
 import tempfile
 import pickle
+import mmap
 
 this_dir = os.path.dirname(__file__)
 
@@ -40,6 +41,20 @@ def test_roundtrip_bytes(all_types):
     msg = all_types.TestAllTypes.from_bytes(message_bytes)
     test_regression.check_all_types(msg)
 
+def test_roundtrip_bytes_mmap(all_types):
+    msg = all_types.TestAllTypes.new_message()
+    test_regression.init_all_types(msg)
+
+    with tempfile.TemporaryFile() as f:
+        msg.write(f)
+        length = f.tell()
+
+        f.seek(0)
+        memory = mmap.mmap(f.fileno(), length)
+
+        msg = all_types.TestAllTypes.from_bytes(memory)
+        test_regression.check_all_types(msg)
+
 def test_roundtrip_bytes_packed(all_types):
     msg = all_types.TestAllTypes.new_message()
     test_regression.init_all_types(msg)