tradesocket

The point of "tradesocket" is to be able to create a socket in one process and then send it over to be used by another process. The primary use-case is when you have a server that starts off running as root and then drops down into another user but still wants to create special sockets like those using port 80. You have the process fork before it drops into its user, and now the user process will request the root process for sockets which can then be sent using tradesocket.

See "tests/test_tradesocket.py" for an example of this.

The module exposes two functions:

tradesocket.send_fd( fd_a, fd_b ):

Send a file descriptor fd_b over the file-descriptor fd_a.

Returns the number of characters sent over the socket or -1 if failed.

tradesocket.recv_fd( fd ):

Recieve a file descriptor over the file-descriptor fd.

Returns the recieved file-descriptor or a negative value if failed.

Example

Before forking:

server_unix_sock, client_unix_sock = socket.socketpair(socket.AF_UNIX, socket.SOCK_STREAM, 0)

... fork

Server:

socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.bind(('', 0))
sock.listen(5000)
tradesocket.send_fd( server_unix_sock.fileno(), sock.fileno())

Client:

fd = tradesocket.recv_fd(self._unix_socket.fileno())
if fd < 0:
    raise RuntimeError("Socket trading failed.")
sock = socket.fromfd( fd, socket.AF_INET, socket.SOCK_STREAM )