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