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