native_client/docs/replacing_bind_connect.md

   1 # Replacing use of host OSes' bind() and connect()
   2
   3 These are notes on how to address [issue 344]
   4 (http://code.google.com/p/nativeclient/issues/detail?id=344).
   5
   6 ## What I thought the current protocol was
   7
   8 In the server process: * imc\_makeboundsock() does the following: * `token =
   9 ChooseRandomToken()` * `fd = socket(AF_UNIX, SOCK_STREAM)` * `bind(fd, token)`
  10 // An error here means two processes chose the same token, which is not supposed
  11 to happen. * `listen(fd, backlog)` // Currently backlog=5 on Mac OS X. This is
  12 bad because it exposes an arbitrary limit to NaCl processes. * `return
  13 (SocketAddress(token), BoundSocket(fd))` * imc\_accept(BoundSocket(fd)) does: *
  14 `sock_fd1 = accept(fd)` * `return ConnectedSocket(sock_fd1)`
  15
  16 In a client process: * imc\_connect(SocketAddress(token)) does: * `sock_fd2 =
  17 socket(AF_UNIX, SOCK_STREAM)` * `connect(sock_fd2, token)` * `return
  18 ConnectedSocket(sock_fd2)`
  19
  20 ## Current protocol on Linux
  21
  22 In the server process: * imc\_makeboundsock() does the following: * `token =
  23 ChooseRandomToken()` * `fd = socket(AF_UNIX, SOCK_DGRAM)` * `bind(fd, token)` //
  24 An error here means two processes chose the same token, which is not supposed to
  25 happen. * `return (SocketAddress(token), BoundSocket(fd))` *
  26 imc\_accept(BoundSocket(fd)) does: * `sock_fd1 = recvmsg(fd)` * `return
  27 ConnectedSocket(sock_fd1)`
  28
  29 In a client process: * imc\_connect(SocketAddress(token)) does: * `sock_fd1,
  30 sock_fd2 = socketpair(AF_UNIX, SOCK_SEQPACKET)` * `sendmsg(global_fd, "",
  31 [sock_fd1], address=token)` // global\_fd is only available if sel\_ldr is run
  32 with "-X -1" * `close(sock_fd2)` * // The problem with this is that it succeeds
  33 immediately. We don't know if our connection request was received. * `return
  34 ConnectedSocket(sock_fd2)`
  35
  36 ## Replacement protocol
  37
  38 In the server process: * imc\_makeboundsock() does the following: * `client_fd,
  39 server_fd = socketpair(AF_UNIX, SOCK_STREAM)` * `return
  40 (SocketAddress(client_fd), BoundSocket(server_fd))` *
  41 imc\_accept(BoundSocket(server\_fd)) does: * `msg, sock_fd1 = recvmsg(server_fd,
  42 single_byte_buffer)` * `assert msg == "c"` * `return ConnectedSocket(sock_fd1)`
  43 // We assume that the FD that is sent to us behaves sanely.
  44
  45 In a client process: * imc\_connect(SocketAddress(client\_fd)) does: *
  46 `sock_fd1, sock_fd2 = socketpair()` * `sendmsg(client_fd, "c", [sock_fd1])` *
  47 `close(sock_fd1)` * // The problem with this is that it succeeds immediately. We
  48 don't know if our connection request was received. * `return
  49 ConnectedSocket(sock_fd2)`