SYNOPSIS
#include <nng/nng.h>
int nng_recv(nng_socket s, void *data, size_t *sizep int flags);DESCRIPTION
The nng_recv() receives a message.
If the special flag NNG_FLAG_ALLOC is not specified, then the caller must
set data to a buffer to receive the message body content, and must store
the size of that buffer at the location pointed to by sizep. When the
function returns, if it is successful, the size at sizep will be updated with
the actual message body length copied into data.
If the special flag NNG_FLAG_ALLOC is present, then a "zero-copy" mode is
used. In this case the caller must set the value of data to the location
of another pointer (of type void *), and the sizep pointer must be set
to a location to receive the size of the message body. The function will then
allocate a message buffer (as if by nng_alloc(3)), fill it with
the message body, and store it at the address referenced by data, and update
the size referenced by sizep. When this flag is present, the caller assumes
responsibility for disposing of the received buffer either by the function
nng_free(3) or reusing the message for sending (with the same
size) via nng_send(3).
| The semantics of what receiving a message means vary from protocol to protocol, so examination of the protocol documentation is encouraged. (For example, with an nng_req(7) socket a message may only be received after a request has been sent, and an nng_sub(7) socket may only receive messages corresponding to topics to which it has subscribed.) Furthermore, some protocols may not support receiving data at all, such as nng_pub(7). |
The NNG_FLAG_ALLOC flag can be used to reduce data copies, thereby
increasing performance, particularly if the buffer is reused to send
a response using the same flag.
|
RETURN VALUES
This function returns 0 on success, and non-zero otherwise.
ERRORS
NNG_EAGAIN-
The socket s cannot accept data for sending.
NNG_ECLOSED-
The socket s is not open.
NNG_EINVAL-
An invalid set of flags was specified.
NNG_EMSGSIZE-
The received message did not fit in the size provided.
NNG_ENOMEM-
Insufficient memory is available.
NNG_ENOTSUP-
The protocol for socket s does not support receiving.
NNG_ESTATE-
The socket s cannot receive data in this state.