NN_RECV(3) nanomsg manual NN_RECV(3)NAMEnn_recv - receive a message
SYNOPSIS
#include <nanomsg/nn.h>
int nn_recv (int s, void *buf, size_t len, int flags);
DESCRIPTION
Receive a message from the socket s and store it in the buffer
referenced by the buf argument. Any bytes exceeding the length
specified by the len argument will be truncated.
Alternatively, nanomsg can allocate the buffer for you. To do so, let
the buf parameter be a pointer to a void* variable (pointer to pointer)
to the receive buffer and set the len parameter to NN_MSG. If the call
is successful the user is responsible for deallocating the message
using the nn_freemsg(3) function.
The flags argument is a combination of the flags defined below:
NN_DONTWAIT
Specifies that the operation should be performed in non-blocking
mode. If the message cannot be received straight away, the function
will fail with errno set to EAGAIN.
RETURN VALUE
If the function succeeds number of bytes in the message is returned.
Otherwise, -1 is returned and errno is set to to one of the values
defined below.
ERRORS
EBADF
The provided socket is invalid.
ENOTSUP
The operation is not supported by this socket type.
EFSM
The operation cannot be performed on this socket at the moment
because socket is not in the appropriate state. This error may
occur with socket types that switch between several states.
EAGAIN
Non-blocking mode was requested and there’s no message to receive
at the moment.
EINTR
The operation was interrupted by delivery of a signal before the
message was received.
ETIMEDOUT
Individual socket types may define their own specific timeouts. If
such timeout is hit this error will be returned.
ETERM
The library is terminating.
EXAMPLES
Receiving a message into a buffer allocated by the user
This example code will retrieve a message of either 100 bytes or
less. If a larger message was sent it will be truncated to 100
bytes.
char buf [100];
nbytes = nn_recv (s, buf, sizeof (buf), 0);
Receiving a message into a buffer allocated by nanomsg
The following will get a message from the pipe with a buffer
allocated by the system. It is large enough to accommodate the
entire message. This is a good way to get the entire message
without truncating if the size of the message is unknown. It is the
user’s responsibility to call nn_freemsg(3) after processing the
message.
void *buf = NULL;
nbytes = nn_recv (s, &buf, NN_MSG, 0);
if (nbytes < 0) {
/* handle error */
...
}
else {
/* process message */
...
nn_freemsg (buf);
}
Note that this can be more efficient than manually allocating a buffer
since it is a zero-copy operation.
SEE ALSOnn_send(3)nn_recvmsg(3)nn_socket(3)nanomsg(7)AUTHORS
Martin Sustrik <sustrik@250bpm.com[1]>
NOTES
1. sustrik@250bpm.com
mailto:sustrik@250bpm.com
nanomsg Unknown 12/23/2015 NN_RECV(3)
