nn_pubsub(7)
============

NAME
----
nn_pubsub - publish/subscribe scalability protocol


SYNOPSIS
--------
*#include <nanomsg/nn.h>*

*#include <nanomsg/pubsub.h>*


DESCRIPTION
-----------
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 incomming 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. 

The entire message, including the topic, is delivered to the user.

Socket Types
~~~~~~~~~~~~

NN_PUB::
    This socket is used to distribute messages to multiple destinations.
    Receive operation is not defined.
NN_SUB::
    Receives messages from the publisher. Only messages that the socket is
    subscribed to are received. When the socket is created there are no
    subscriptions and thus no messages will be received. Send operation is
    not defined on this socket.

Socket Options
~~~~~~~~~~~~~~

NN_SUB_SUBSCRIBE::
    Defined on full SUB socket. Subscribes for a particular topic. Type of the
    option is string. A single NN_SUB socket can handle multiple subscriptions.
NN_SUB_UNSUBSCRIBE::
    Defined on full SUB socket. Unsubscribes from a particular topic. Type of
    the option is string.

EXAMPLE
~~~~~~~

----
int pub = nn_socket (AF_SP, NN_PUB);
int sub = nn_socket (AF_SP, NN_SUB);
int nbytes;
void *buf = NULL;

nn_setsockopt (sub, NN_SUB, NN_SUB_SUBSCRIBE, "foo", 3);
nn_setsockopt (sub, NN_SUB, NN_SUB_SUBSCRIBE, "bar", 3);

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);
----


SEE ALSO
--------
linknanomsg:nn_bus[7]
linknanomsg:nn_reqrep[7]
linknanomsg:nn_pipeline[7]
linknanomsg:nn_survey[7]
linknanomsg:nn_pair[7]
linknanomsg:nanomsg[7]

AUTHORS
-------
Martin Sustrik <sustrik@250bpm.com>