xs_recv(3) receive a message part from a socket


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


The xs_recv() function shall receive a message from the socket referenced by the socket argument and store it in the buffer referenced by the buf argument. Any bytes exceeding the length specified by the len argument shall be truncated. If there are no messages available on the specified socket the xs_recv() function shall block until the request can be satisfied. The flags argument is a combination of the flags defined below:


Specifies that the operation should be performed in non-blocking mode. If there are no messages available on the specified socket, the xs_recv() function shall fail with errno set to EAGAIN.

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 processes multipart messages must use the XS_RCVMORE xs_getsockopt(3) option on the socket after calling xs_recv() to determine if there are further parts to receive.


The xs_recv() function shall return the number of bytes in the received message if successful. Note that the value can exceed the value of the len parameter, in this case the message was truncated. If not successful the function shall return -1 and set errno to one of the values defined below.



Non-blocking mode was requested and no messages are available at the moment.


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


The xs_recv() 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.


The context associated with the specified socket was terminated.


The provided socket was invalid.


The operation was interrupted by delivery of a signal before a message was available.


Survey has timed out. (Applicable only to XS_SURVEYOR socket.)


Receiving a message from a socket.

char buf [256];
nbytes = xs_recv (socket, buf, 256, 0);
assert (nbytes != -1);


This man page was written by Martin Sustrik <m[blue][email protected]m[][1]>, Martin Lucina <m[blue][email protected]m[][2]> and Pieter Hintjens <m[blue][email protected]m[][3]>.