DragonFly On-Line Manual Pages

XS_RECVMSG(3)                Crossroads I/O Manual               XS_RECVMSG(3)

NAME
       xs_recvmsg - receive a message part from a socket (zero-copy)

SYNOPSIS
       int xs_recvmsg (void *socket, xs_msg_t *msg, int flags);

DESCRIPTION
       The xs_recvmsg() function shall receive a message part from the socket
       referenced by the socket argument and store it in the message
       referenced by the msg argument. Any content previously stored in msg
       shall be properly deallocated. If there are no message parts available
       on the specified socket the xs_recvmsg() function shall block until the
       request can be satisfied. The flags argument is a combination of the
       flags defined below:

       XS_DONTWAIT
           Specifies that the operation should be performed in non-blocking
           mode. If there are no messages available on the specified socket,
           the xs_recvmsg() function shall fail with errno set to EAGAIN.

   Multi-part messages
       A Crossroads message is composed of 1 or more message parts. Each
       message part is an independent xs_msg_t in its own right. Crossroads
       ensures atomic delivery of messages; peers shall receive either all
       message parts of a message or none at all. The total number of message
       parts is unlimited except by available memory.

       An application that processes multipart messages must use the
       XS_RCVMORE xs_getsockopt(3) option after calling xs_recvmsg() to
       determine if there are further parts to receive.

RETURN VALUE
       The xs_recvmsg() function shall return the number of bytes in the
       received message if successful. Otherwise it shall return -1 and set
       errno to one of the values defined below.

ERRORS
       EAGAIN
           Non-blocking mode was requested and no messages are available at
           the moment.

       ENOTSUP
           The xs_recvmsg() operation is not supported by this socket type.

       EFSM
           The xs_recvmsg() operation cannot be performed on this socket at
           the moment due to the socket not being in the appropriate state.
           This error may occur with socket types that switch between several
           states, such as XS_REP. See the messaging patterns section of
           xs_socket(3) for more information.

       ETERM
           The context associated with the specified socket was terminated.

       ENOTSOCK
           The provided socket was invalid.

       EINTR
           The operation was interrupted by delivery of a signal before a
           message was available.

       EFAULT
           The message passed to the function was invalid.

       ETIMEDOUT
           Survey has timed out. (Applicable only to XS_SURVEYOR socket.)

EXAMPLE
       Receiving a message from a socket.

           /* Create an empty message */
           xs_msg_t msg;
           int rc = xs_msg_init (&msg);
           assert (rc == 0);
           /* Block until a message is available to be received from socket */
           rc = xs_recvmsg (socket, &msg, 0);
           assert (rc != -1);
           /* Release message */
           xs_msg_close (&msg);

       Receiving a multi-part message.

           int64_t more;
           size_t more_size = sizeof more;
           do {
               /* Create an empty message to hold the message part */
               xs_msg_t part;
               int rc = xs_msg_init (&part);
               assert (rc == 0);
               /* Block until a message is available to be received from socket */
               rc = xs_recvmsg (socket, &part, 0);
               assert (rc != -1);
               /* Determine if more message parts are to follow */
               rc = xs_getsockopt (socket, XS_RCVMORE, &more, &more_size);
               assert (rc == 0);
               xs_msg_close (&part);
           } while (more);

SEE ALSO
       Applications that do not require zero-copy messaging can use the
       simpler xs_recv(3) instead of xs_recvmsg().

       xs_sendmsg(3) xs_getsockopt(3) xs_socket(7) xs(7)

AUTHORS
       This man page was written by Martin Sustrik <sustrik@250bpm.com[1]>,
       Martin Lucina <martin@lucina.net[2]> and Pieter Hintjens
       <ph@imatix.com[3]>.

NOTES
        1. sustrik@250bpm.com
           mailto:sustrik@250bpm.com

        2. martin@lucina.net
           mailto:martin@lucina.net

        3. ph@imatix.com
           mailto:ph@imatix.com

Crossroads I/O 1.2.0              02/17/2016                     XS_RECVMSG(3)