DragonFly On-Line Manual Pages

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

NAME
       xs_sendmsg - send a message part on a socket (zero-copy)

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

DESCRIPTION
       The xs_sendmsg() function shall queue the message referenced by the msg
       argument to be sent to the socket referenced by the socket argument.
       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 the message cannot be queued on the socket, the
           xs_sendmsg() function shall fail with errno set to EAGAIN.

       XS_SNDMORE
           Specifies that the message being sent is a multi-part message, and
           that further message parts are to follow. Refer to the section
           regarding multi-part messages below for a detailed description.

       The xs_msg_t structure passed to xs_sendmsg() is nullified during the
       call. If you want to send the same message to multiple sockets you have
       to copy it using (e.g. using xs_msg_copy()).

           Note

           A successful invocation of xs_sendmsg() does not indicate that the
           message has been transmitted to the network, only that it has been
           queued on the socket and Crossroads have assumed responsibility for
           the message.

   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
       ensure 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 sends multipart messages must use the XS_SNDMORE
       flag when sending each data part except the final one.

RETURN VALUE
       The xs_sendmsg() function shall return number of bytes in the 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 the message cannot be sent at
           the moment.

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

       EFSM
           The xs_sendmsg() 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 the
           message was sent.

       EFAULT
           Invalid message.

EXAMPLE
       Filling in a message and sending it to a socket.

           /* Create a new message, allocating 6 bytes for message content */
           xs_msg_t msg;
           int rc = xs_msg_init_size (&msg, 6);
           assert (rc == 0);
           /* Fill in message content with 'AAAAAA' */
           memset (xs_msg_data (&msg), 'A', 6);
           /* Send the message to the socket */
           rc = xs_sendmsg (socket, &msg, 0);
           assert (rc == 6);

       Sending a multi-part message.

           /* Send a multi-part message consisting of three parts to socket */
           rc = xs_sendmsg (socket, &part1, XS_SNDMORE);
           rc = xs_sendmsg (socket, &part2, XS_SNDMORE);
           /* Final part; no more parts to follow */
           rc = xs_sendmsg (socket, &part3, 0);

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

       xs_recvmsg(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_SENDMSG(3)