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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/nng.h>
+#include <nng/protocol/pubsub0/sub.h>
+
+int nng_sub0_open(nng_socket *s);
+----
+
+== DESCRIPTION
+
+(((protocol, _sub_)))
+The ((_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 _sub_ protocol is the subscriber side, and the
+<<nng_pub.7#,_pub_>> 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_sub_open.3#,`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`))(((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 _sub_ protocol has no protocol-specific headers.
+    
+== SEE ALSO
+
+<<nng_sub_open.3#,nng_sub_open(3)>>,
+<<nng_pub.7#,nng_pub(7)>>,
+<<nng.7#,nng(7)>>