NAME

       nng_recv - recv data

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.

       The flags is a bit mask that may contain any of the following values:

       NNG_FLAG_NONBLOCK
           The function returns immediately, even if no message is available. Without this flag,
           the function will wait until a message is received by the socket s, or any configured
           timer expires.

       NNG_FLAG_ALLOC
           If this flag 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()), fill it with the
           message body, and store it at the address referenced by data, and update the size
           referenced by sizep. The caller is responsible for disposing of the received buffer
           either by the nng_free() function or passing the message (also with the NNG_FLAG_ALLOC
           flag) in a call to nng_send().

       If the special flag NNG_FLAG_ALLOC (see above) 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.

           Note
           The semantics of what receiving a message means vary from protocol to protocol, so
           examination of the protocol documentation is encouraged. (For example, with a req
           socket a message may only be received after a request has been sent, and a sub 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 pub.

           Tip
           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 operation would block, but NNG_FLAG_NONBLOCK was specified.

       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.

       NNG_ETIMEDOUT
           The operation timed out.

SEE ALSO

       nng_alloc(3), nng_free(3), nng_recvmsg(3), nng_send(3), nng_strerror(3), nng(7)

                                            2024-10-11                                NNG_RECV(3)