feat: add cython def for unmarshaller read_sock for fd passing (#143)

src/dbus_fast/_private/unmarshaller.pxd

@@ -5,6 +5,12 @@ import cython
 from ..signature import SignatureType
 
 
+cdef object MAX_UNIX_FDS_SIZE
+cdef object ARRAY
+cdef object UNIX_FDS_CMSG_LENGTH
+cdef object SOL_SOCKET
+cdef object SCM_RIGHTS
+
 cdef unsigned int UINT32_SIZE
 cdef unsigned int INT16_SIZE
 cdef unsigned int UINT16_SIZE
@@ -106,7 +112,10 @@ cdef class Unmarshaller:
 
     cpdef reset(self)
 
-    cdef bytes _read_sock(self, unsigned long length)
+    @cython.locals(
+        msg=cython.bytes,
+    )
+    cdef bytes _read_sock(self, object length)
 
     @cython.locals(
         start_len=cython.ulong,

src/dbus_fast/_private/unmarshaller.py

@@ -12,6 +12,8 @@ from ..signature import SignatureType, Variant, get_signature_tree
 from .constants import BIG_ENDIAN, LITTLE_ENDIAN, PROTOCOL_VERSION
 
 MAX_UNIX_FDS = 16
+MAX_UNIX_FDS_SIZE = array.array("i").itemsize
+UNIX_FDS_CMSG_LENGTH = socket.CMSG_LEN(MAX_UNIX_FDS_SIZE)
 
 UNPACK_SYMBOL = {LITTLE_ENDIAN: "<", BIG_ENDIAN: ">"}
 
@@ -88,6 +90,10 @@ TOKEN_O_AS_INT = ord("o")
 TOKEN_S_AS_INT = ord("s")
 TOKEN_G_AS_INT = ord("g")
 
+ARRAY = array.array
+SOL_SOCKET = socket.SOL_SOCKET
+SCM_RIGHTS = socket.SCM_RIGHTS
+
 HEADER_MESSAGE_ARG_NAME = {
     1: "path",
     2: "interface",
@@ -229,22 +235,20 @@ class Unmarshaller:
     def _read_sock(self, length: int) -> bytes:
         """reads from the socket, storing any fds sent and handling errors
         from the read itself"""
-        unix_fd_list = array.array("i")
 
         try:
-            msg, ancdata, *_ = self._sock.recvmsg(
-                length, socket.CMSG_LEN(MAX_UNIX_FDS * unix_fd_list.itemsize)
+            msg, ancdata, _flags, _addr = self._sock.recvmsg(
+                length, UNIX_FDS_CMSG_LENGTH
             )
         except BlockingIOError:
             raise MarshallerStreamEndError()
 
         for level, type_, data in ancdata:
-            if not (level == socket.SOL_SOCKET and type_ == socket.SCM_RIGHTS):
+            if not (level == SOL_SOCKET and type_ == SCM_RIGHTS):
                 continue
-            unix_fd_list.frombytes(
-                data[: len(data) - (len(data) % unix_fd_list.itemsize)]
+            self._unix_fds.extend(
+                ARRAY("i", data[: len(data) - (len(data) % MAX_UNIX_FDS_SIZE)])
             )
-            self._unix_fds.extend(list(unix_fd_list))
 
         return msg