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