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= nng_sub(7)
//
// Copyright 2018 Staysail Systems, Inc. <info@staysail.tech>
// Copyright 2018 Capitar IT Group BV <info@capitar.com>
//
// This document is supplied under the terms of the MIT License, a
// copy of which should be located in the distribution where this
// file was obtained (LICENSE.txt). A copy of the license may also be
// found online at https://opensource.org/licenses/MIT.
//
== NAME
nng_sub - subscriber protocol
== SYNOPSIS
[source,c]
----------
#include <nng/protocol/pubsub0/sub.h>
int nng_sub0_open(nng_socket *s);
----------
== DESCRIPTION
The _nng_sub_ protocol is one half of a publisher/subscriber pattern.
In this pattern, a publisher sends data, which is broadcast to all
subscribers. The subscribing applications only see the data to which
they have subscribed.
The _nng_sub_ protocol is the subscriber side, and the
<<nng_pub#,nng_pub(7)>> protocol is the publisher side.
NOTE: In this implementation, the publisher delivers all messages to all
subscribers. The subscribers maintain their own subscriptions, and filter
them locally. Thus, this pattern should not be used in an attempt to
reduce bandwidth consumption.
The topics that subscribers subscribe to is just the first part of
the message body. Applications should construct their messages
accordingly.
=== Socket Operations
The `nng_sub0_open()` call creates a subscriber socket. This socket
may be used to receive messages, but is unable to send them. Attempts
to send messages will result in `NNG_ENOTSUP`.
=== Protocol Versions
Only version 0 of this protocol is supported. (At the time of writing,
no other versions of this protocol have been defined.)
=== Protocol Options
The following protocol-specific options are available.
`NNG_OPT_SUB_SUBSCRIBE`::
This option registers a topic that the subscriber is interested in.
The option is write-only, and takes an array of bytes, of arbitrary size.
Each incoming message is checked against the list of subscribed topics.
If the body begins with the entire set of bytes in the topic, then the
message is accepted. If no topic matches, then the message is
discarded.
+
TIP: To receive all messages, an empty topic (zero length) can be used.
`NNG_OPT_SUB_UNSUBSCRIBE`::
This option, also read-only, removes a topic from the subscription list.
Note that if the topic was not previously subscribed to with
`NNG_OPT_SUB_SUBSCRIBE` then an `NNG_ENOENT` error will result.
=== Protocol Headers
The _nng_sub_ protocol has no protocol-specific headers.
== SEE ALSO
<<nng#,nng(7)>>,
<<nng_pub#,nng_pub(7)>>
|
