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