bpo-28724: Add methods send_fds, recv_fds to the socket module

Doc/library/socket.rst

@@ -1564,6 +1564,29 @@ to sockets.
 
  .. versionadded:: 3.6
 
+.. method:: socket.send_fds(sock, buffers, fds[, flags[, address]])
+
+ Send the list of file descriptors *fds* over an :const:`AF_UNIX` socket.
+ The *fds* parameter is a sequence of file descriptors.
+ Consult :meth:`sendmsg` for the documentation of these parameters.
+
+ .. availability:: Unix supporting :meth:`~socket.sendmsg` and :const:`SCM_RIGHTS` mechanism.
+
+ .. versionadded:: 3.9
+
+.. method:: socket.recv_fds(sock, bufsize, maxfds[, flags])
+
+ Receive up to *maxfds* file descriptors. Return ``(msg, list(fds), flags, addr)``. Consult
+ :meth:`recvmsg` for the documentation of these parameters.
+
+ .. availability:: Unix supporting :meth:`~socket.recvmsg` and :const:`SCM_RIGHTS` mechanism.
+
+ .. versionadded:: 3.9
+
+ .. note::
+
+ Any truncated integers at the end of the list of file descriptors.
+
 .. method:: socket.sendfile(file, offset=0, count=None)
 
  Send a file until EOF is reached by using high-performance

Lib/socket.py

@@ -12,6 +12,8 @@
 socket() -- create a new socket object
 socketpair() -- create a pair of new socket objects [*]
 fromfd() -- create a socket object from an open file descriptor [*]
+send_fds() -- Send file descriptor to the socket.
+recv_fds() -- Recieve file descriptors from the socket.
 fromshare() -- create a socket object from data received from socket.share() [*]
 gethostname() -- return the current hostname
 gethostbyname() -- map a hostname to its IP number
@@ -463,6 +465,40 @@ def fromfd(fd, family, type, proto=0):
  nfd = dup(fd)
  return socket(family, type, proto, nfd)
 
+if hasattr(_socket.socket, "sendmsg"):
+ import array
+
+ def send_fds(sock, buffers, fds, flags=0, address=None):
+ """ send_fds(sock, buffers, fds[, flags[, address]]) -> integer
+
+ Send the list of file descriptors fds over an AF_UNIX socket.
+ """
+ return sock.sendmsg(buffers, [(_socket.SOL_SOCKET,
+ _socket.SCM_RIGHTS, array.array("i", fds))])
+ __all__.append("send_fds")
+
+if hasattr(_socket.socket, "recvmsg"):
+ import array
+
+ def recv_fds(sock, bufsize, maxfds, flags=0):
+ """ recv_fds(sock, bufsize, maxfds[, flags]) -> (data, list of file
+ descriptors, msg_flags, address)
+
+ Receive up to maxfds file descriptors returning the message
+ data and a list containing the descriptors.
+ """
+ # Array of ints
+ fds = array.array("i")
+ msg, ancdata, flags, addr = sock.recvmsg(bufsize,
+ _socket.CMSG_LEN(maxfds * fds.itemsize))
+ for cmsg_level, cmsg_type, cmsg_data in ancdata:
+ if (cmsg_level == _socket.SOL_SOCKET and cmsg_type == _socket.SCM_RIGHTS):
+ fds.frombytes(cmsg_data[:
+ len(cmsg_data) - (len(cmsg_data) % fds.itemsize)])
+
+ return msg, list(fds), flags, addr
+ __all__.append("recv_fds")
+
 if hasattr(_socket.socket, "share"):
  def fromshare(info):
  """ fromshare(info) -> socket object

Lib/test/test_socket.py

@@ -6186,11 +6186,53 @@ def test_dual_stack_client_v6(self):
  self.echo_server(sock)
  self.echo_client(("::1", port), socket.AF_INET6)
 
+@requireAttrs(socket, "send_fds")
+@requireAttrs(socket, "recv_fds")
+@requireAttrs(socket, "AF_UNIX")
+class SendRecvFdsTests(unittest.TestCase):
+ def testSendAndRecvFds(self):
+ def close_pipes(pipes):
+ for fd1, fd2 in pipes:
+ os.close(fd1)
+ os.close(fd2)
+
+ def close_fds(fds):
+ for fd in fds:
+ os.close(fd)
+
+ # send 10 file descriptors
+ pipes = [os.pipe() for _ in range(10)]
+ self.addCleanup(close_pipes, pipes)
+ fds = [rfd for rfd, wfd in pipes]
+
+ # use a UNIX socket pair to exchange file descriptors locally
+ sock1, sock2 = socket.socketpair(socket.AF_UNIX, socket.SOCK_STREAM)
+ with sock1, sock2:
+ socket.send_fds(sock1, [MSG], fds)
+ # request more data and file descriptors than expected
+ msg, fds2, flags, addr = socket.recv_fds(sock2, len(MSG) * 2, len(fds) * 2)
+ self.addCleanup(close_fds, fds2)
+
+ self.assertEqual(msg, MSG)
+ self.assertEqual(len(fds2), len(fds))
+ self.assertEqual(flags, 0)
+ # don't test addr
+
+ # test that file descriptors are connected
+ for index, fds in enumerate(pipes):
+ rfd, wfd = fds
+ os.write(wfd, str(index).encode())
+
+ for index, rfd in enumerate(fds2):
+ data = os.read(rfd, 100)
+ self.assertEqual(data, str(index).encode())
+
 
 def test_main():
  tests = [GeneralModuleTests, BasicTCPTest, TCPCloserTest, TCPTimeoutTest,
  TestExceptions, BufferIOTest, BasicTCPTest2, BasicUDPTest,
- UDPTimeoutTest, CreateServerTest, CreateServerFunctionalTest]
+ UDPTimeoutTest, CreateServerTest, CreateServerFunctionalTest,
+ SendRecvFdsTests]
 
  tests.extend([
  NonBlockingTCPTests,
@@ -6254,5 +6296,6 @@ def test_main():
  support.run_unittest(*tests)
  support.threading_cleanup(*thread_info)
 
+
 if __name__ == "__main__":
  test_main()

Misc/NEWS.d/next/Library/2019-05-30-15-51-42.bpo-28724.34TrS8.rst

@@ -0,0 +1,2 @@
+The socket module now has the :func:`socket.send_fds` and :func:`socket.recv.fds` methods.
+Contributed by Joannah Nanjekye, Shinya Okano and Victor Stinner.