Broadcasts messages to multiple destinations.
Messages are sent from NN_PUB sockets and will only be received by NN_SUB sockets that have subscribed to the matching topic. Topic is an arbitrary sequence of bytes at the beginning of the message body. The NN_SUB socket will determine whether a message should be delivered to the user by comparing the subscribed topics (using NN_SUB_SUBSCRIBE on a full SUB socket) to the bytes initial bytes in the incoming message, up to the size of the topic.
nn_setsockopt (s, NN_SUB, NN_SUB_SUBSCRIBE, "Hello", 5);
Will match any message with intial 5 bytes being "Hello", for example, message "Hello, World!" will match.
Topic with zero length matches any message.
If the socket is subscribed to multiple topics, message matching any of them will be delivered to the user.
Since the filtering is performed on the Subscriber side, all the messages from Publisher will be sent over the transport layer.
int pub = nn_socket (AF_SP, NN_PUB); int sub = nn_socket (AF_SP, NN_SUB); int nbytes; void *buf = NULL; char *addr = "inproc://example"; nn_setsockopt (sub, NN_SUB, NN_SUB_SUBSCRIBE, "foo", 3); nn_setsockopt (sub, NN_SUB, NN_SUB_SUBSCRIBE, "bar", 3); nn_bind(pub, addr); nn_connect(sub, addr); nbytes = nn_send (pub, "foo|Hello!", 10); assert(nbytes == 10); nbytes = nn_recv (sub, &buf, NN_MSG, 0); assert (nbytes == 10); nn_freemsg (buf); nbytes = nn_send (pub, "baz|World!", 10); /* Message is not delivered because if matches no subscription. */ nbytes = nn_recv(sub, &buf, NN_MSG, 0);