xs_send(3)

# xs_send(3) Manual Page

## NAME

xs_send - send a message part on a socket

## SYNOPSIS

int xs_send (void *socket, void *buf, size_t len, int flags);

## DESCRIPTION

The xs_send() function shall queue a message created from the buffer referenced by the buf and len arguments. 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_send() 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.

Note | A successful invocation of xs_send() 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. 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 sends multipart messages must use the XS_SNDMORE flag when sending each message part except the final one.

## RETURN VALUE

The xs_send() 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_send() operation is not supported by this socket type.

EFSM

  The xs_send() 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.

## EXAMPLE

Sending a multi-part message

    /* Send a multi-part message consisting of three parts to socket */
    rc = xs_send (socket, "ABC", 3, XS_SNDMORE);
    assert (rc == 3);
    rc = xs_send (socket, "DEFGH", 5, XS_SNDMORE);
    assert (rc == 5);
    /* Final part; no more parts to follow */
    rc = xs_send (socket, "JK", 2, 0);
    assert (rc == 2);

## SEE ALSO

Applications that wish to use zero-copy messaging must use xs_sendmsg(3) instead of xs_send().

xs_recv(3) xs_socket(7) xs(7)

## AUTHORS

This man page was written by Martin Sustrik <sustrik@250bpm.com>, Martin Lucina <martin@lucina.net> and Pieter Hintjens <ph@imatix.com>.