comparison mercurial/chgserver.py @ 49275:c6a3243567b6

chg: replace mercurial.util.recvfds() by simpler pure Python implementation

On Python 3, we have socket.socket.recvmsg(). This makes it possible to receive
FDs in pure Python code. The new code behaves like the previous
implementations, except that it’s more strict about the format of the ancillary
data. This works because we know in which format the FDs are passed.

Because the code is (and always has been) specific to chg (payload is 1 byte,
number of passed FDs is limited) and we now have only one implementation and
the code is very short, I decided to stop exposing a function in
mercurial.util.

Note on terminology: The SCM_RIGHTS mechanism is used to share open file
descriptions to another process over a socket. The sending side passes an array
of file descriptors and the receiving side receives an array of file
descriptors. The file descriptors are different in general on both sides but
refer to the same open file descriptions. The two terms are often conflated,
even in the official documentation. That’s why I used “FD” above, which could
mean both “file descriptor” and “file description”.

49273:34020d1f1635

        channels except cresult will no longer be used
        """
        # tell client to sendmsg() with 1-byte payload, which makes it
        # distinctive from "attachio\n" command consumed by client.read()
        self.clientsock.sendall(struct.pack(b'>cI', b'I', 1))
        clientfds = util.recvfds(self.clientsock.fileno())
        self.ui.log(b'chgserver', b'received fds: %r\n', clientfds)

        ui = self.ui
        ui.flush()
        self._saveio()

49275:c6a3243567b6

        channels except cresult will no longer be used
        """
        # tell client to sendmsg() with 1-byte payload, which makes it
        # distinctive from "attachio\n" command consumed by client.read()
        self.clientsock.sendall(struct.pack(b'>cI', b'I', 1))

        data, ancdata, msg_flags, address = self.clientsock.recvmsg(1, 256)
        assert len(ancdata) == 1
        cmsg_level, cmsg_type, cmsg_data = ancdata[0]
        assert cmsg_level == socket.SOL_SOCKET
        assert cmsg_type == socket.SCM_RIGHTS
        # memoryview.cast() was added in typeshed 61600d68772a, but pytype
        # still complains
        # pytype: disable=attribute-error
        clientfds = memoryview(cmsg_data).cast('i').tolist()
        # pytype: enable=attribute-error
        self.ui.log(b'chgserver', b'received fds: %r\n', clientfds)

        ui = self.ui
        ui.flush()
        self._saveio()