1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
|
---
version: tip
layout: manpage_v2
title: nng_sub(7)
---
<h1>nng_sub(7)</h1>
<div class="sect1">
<h2 id="_name">NAME</h2>
<div class="sectionbody">
<div class="paragraph">
<p>nng_sub - subscriber protocol</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_synopsis">SYNOPSIS</h2>
<div class="sectionbody">
<div class="listingblock">
<div class="content">
<pre class="pygments highlight"><code data-lang="c"><span></span><span class="tok-cp">#include</span><span class="tok-w"> </span><span class="tok-cpf"><nng/nng.h></span>
<span class="tok-cp">#include</span><span class="tok-w"> </span><span class="tok-cpf"><nng/protocol/pubsub0/sub.h></span></code></pre>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_description">DESCRIPTION</h2>
<div class="sectionbody">
<div class="paragraph">
<p>
The <em>sub</em> 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.</p>
</div>
<div class="paragraph">
<p>The <em>sub</em> protocol is the subscriber side, and the
<a href="nng_pub.7.html"><em>pub</em></a> protocol is the publisher side.</p>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<i class="fa icon-note" title="Note"></i>
</td>
<td class="content">
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.
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>The topics that subscribers subscribe to is just the first part of
the message body.
Applications should construct their messages accordingly.</p>
</div>
<div class="sect2">
<h3 id="_socket_operations">Socket Operations</h3>
<div class="paragraph">
<p>The <a href="nng_sub_open.3.html"><code>nng_sub0_open()</code></a> functions create a subscriber socket.
This socket may be used to receive messages, but is unable to send them.
Attempts to send messages will result in <code>NNG_ENOTSUP</code>.</p>
</div>
</div>
<div class="sect2">
<h3 id="_protocol_versions">Protocol Versions</h3>
<div class="paragraph">
<p>Only version 0 of this protocol is supported.
(At the time of writing, no other versions of this protocol have been defined.)</p>
</div>
</div>
<div class="sect2">
<h3 id="_protocol_options">Protocol Options</h3>
<div class="paragraph">
<p>The following protocol-specific options are available.</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1"><code>NNG_OPT_SUB_SUBSCRIBE</code></dt>
<dd>
<p>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.</p>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<i class="fa icon-note" title="Note"></i>
</td>
<td class="content">
This option is a byte array. Thus if you use
<a href="nng_setopt.3.html"><code>nng_setopt_string()</code></a> the <code>NUL</code> terminator byte will
be included in the topic.
If that isn’t desired, consider using
<a href="nng_setopt.3.html"><code>nng_setopt()</code></a> and using <code>strlen()</code> of the topic
as the topic size.
</td>
</tr>
</table>
</div>
<div class="admonitionblock tip">
<table>
<tr>
<td class="icon">
<i class="fa icon-tip" title="Tip"></i>
</td>
<td class="content">
To receive all messages, an empty topic (zero length) can be used.
</td>
</tr>
</table>
</div>
</dd>
<dt class="hdlist1"><code>NNG_OPT_SUB_UNSUBSCRIBE</code></dt>
<dd>
<p>This option, also read-only, removes a topic from the subscription list.
Note that if the topic was not previously subscribed to with
<code>NNG_OPT_SUB_SUBSCRIBE</code> then an <code>NNG_ENOENT</code> error will result.</p>
</dd>
<dt class="hdlist1"><code>NNG_OPT_SUB_PREFNEW</code></dt>
<dd>
<p>(<code>bool</code>)
This read/write option specifies the behavior of the subscriber when the queue is full.
When <code>true</code> (the default), the subscriber will make room in the queue by removing the oldest message.
When <code>false</code>, the subscriber will reject messages if the message queue does not have room.</p>
</dd>
</dl>
</div>
</div>
<div class="sect2">
<h3 id="_protocol_headers">Protocol Headers</h3>
<div class="paragraph">
<p>The <em>sub</em> protocol has no protocol-specific headers.</p>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_see_also">SEE ALSO</h2>
<div class="sectionbody">
<div class="paragraph text-left">
<p><a href="nng_sub_open.3.html">nng_sub_open(3)</a>,
<a href="nng_pub.7.html">nng_pub(7)</a>,
<a href="nng.7.html">nng(7)</a></p>
</div>
</div>
</div>
|
