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<h1 id="gossipsub">GossipSub</h1>
<p>In this tutorial, we'll build a simple GossipSub network
to broadcast the metrics we built in the previous tutorial.</p>
<p>GossipSub is used to broadcast some messages in a network,
and allows to balance between latency, bandwidth usage,
privacy and attack resistance.</p>
<p>You'll find a good explanation of how GossipSub works
<a href="https://docs.libp2p.io/concepts/publish-subscribe/">here.</a> There are a lot
of parameters you can tweak to adjust how GossipSub behaves but here we'll
use the sane defaults shipped with libp2p.</p>
<p>We'll start by creating our metric structure like previously
<div class="highlight"><pre><span></span><code><a id="__codelineno-0-1" name="__codelineno-0-1" href="#__codelineno-0-1"></a><span class="kn">import</span><span class="w"> </span><span class="n">chronos</span>
<a id="__codelineno-0-2" name="__codelineno-0-2" href="#__codelineno-0-2"></a><span class="kn">import</span><span class="w"> </span><span class="n">stew</span><span class="o">/</span><span class="n">results</span>
<a id="__codelineno-0-3" name="__codelineno-0-3" href="#__codelineno-0-3"></a>
<a id="__codelineno-0-4" name="__codelineno-0-4" href="#__codelineno-0-4"></a><span class="kn">import</span><span class="w"> </span><span class="n">libp2p</span>
<a id="__codelineno-0-5" name="__codelineno-0-5" href="#__codelineno-0-5"></a><span class="kn">import</span><span class="w"> </span><span class="n">libp2p</span><span class="o">/</span><span class="n">protocols</span><span class="o">/</span><span class="n">pubsub</span><span class="o">/</span><span class="n">rpc</span><span class="o">/</span><span class="n">messages</span>
<a id="__codelineno-0-6" name="__codelineno-0-6" href="#__codelineno-0-6"></a>
<a id="__codelineno-0-7" name="__codelineno-0-7" href="#__codelineno-0-7"></a><span class="k">type</span>
<a id="__codelineno-0-8" name="__codelineno-0-8" href="#__codelineno-0-8"></a><span class="w"> </span><span class="n">Metric</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">object</span>
<a id="__codelineno-0-9" name="__codelineno-0-9" href="#__codelineno-0-9"></a><span class="w"> </span><span class="n">name</span><span class="p">:</span><span class="w"> </span><span class="nb">string</span>
<a id="__codelineno-0-10" name="__codelineno-0-10" href="#__codelineno-0-10"></a><span class="w"> </span><span class="n">value</span><span class="p">:</span><span class="w"> </span><span class="nb">float</span>
<a id="__codelineno-0-11" name="__codelineno-0-11" href="#__codelineno-0-11"></a>
<a id="__codelineno-0-12" name="__codelineno-0-12" href="#__codelineno-0-12"></a><span class="w"> </span><span class="n">MetricList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">object</span>
<a id="__codelineno-0-13" name="__codelineno-0-13" href="#__codelineno-0-13"></a><span class="w"> </span><span class="n">hostname</span><span class="p">:</span><span class="w"> </span><span class="nb">string</span>
<a id="__codelineno-0-14" name="__codelineno-0-14" href="#__codelineno-0-14"></a><span class="w"> </span><span class="n">metrics</span><span class="p">:</span><span class="w"> </span><span class="nb">seq</span><span class="o">[</span><span class="n">Metric</span><span class="o">]</span>
<a id="__codelineno-0-15" name="__codelineno-0-15" href="#__codelineno-0-15"></a>
<a id="__codelineno-0-16" name="__codelineno-0-16" href="#__codelineno-0-16"></a><span class="sx">{.push</span><span class="w"> </span><span class="sx">raises</span>:<span class="w"> </span><span class="sx">[].}</span>
<a id="__codelineno-0-17" name="__codelineno-0-17" href="#__codelineno-0-17"></a>
<a id="__codelineno-0-18" name="__codelineno-0-18" href="#__codelineno-0-18"></a><span class="sx">proc</span><span class="w"> </span><span class="sx">encode(m</span>:<span class="w"> </span><span class="sx">Metric): ProtoBuffer</span><span class="w"> </span><span class="sx">=</span>
<a id="__codelineno-0-19" name="__codelineno-0-19" href="#__codelineno-0-19"></a><span class="sx"> result</span><span class="w"> </span><span class="sx">= initProtoBuffer()</span>
<a id="__codelineno-0-20" name="__codelineno-0-20" href="#__codelineno-0-20"></a><span class="sx"> result.write(1</span>,<span class="w"> </span><span class="sx">m.name)</span>
<a id="__codelineno-0-21" name="__codelineno-0-21" href="#__codelineno-0-21"></a><span class="sx"> result.write(2</span>,<span class="w"> </span><span class="sx">m.value)</span>
<a id="__codelineno-0-22" name="__codelineno-0-22" href="#__codelineno-0-22"></a><span class="sx"> result.finish()</span>
<a id="__codelineno-0-23" name="__codelineno-0-23" href="#__codelineno-0-23"></a>
<a id="__codelineno-0-24" name="__codelineno-0-24" href="#__codelineno-0-24"></a><span class="sx">proc</span><span class="w"> </span><span class="sx">decode(_</span>:<span class="w"> </span><span class="sx">type</span><span class="w"> </span><span class="sx">Metric</span>,<span class="w"> </span><span class="sx">buf</span>:<span class="w"> </span><span class="sx">seq[byte]): Result[Metric</span>,<span class="w"> </span><span class="sx">ProtoError] =</span>
<a id="__codelineno-0-25" name="__codelineno-0-25" href="#__codelineno-0-25"></a><span class="sx"> var</span><span class="w"> </span><span class="sx">res</span>:<span class="w"> </span><span class="sx">Metric</span>
<a id="__codelineno-0-26" name="__codelineno-0-26" href="#__codelineno-0-26"></a><span class="w"> </span><span class="sx">let</span><span class="w"> </span><span class="sx">pb</span><span class="w"> </span><span class="sx">= initProtoBuffer(buf)</span>
<a id="__codelineno-0-27" name="__codelineno-0-27" href="#__codelineno-0-27"></a><span class="sx"> discard</span><span class="w"> </span><span class="sx">?pb.getField(1</span>,<span class="w"> </span><span class="sx">res.name)</span>
<a id="__codelineno-0-28" name="__codelineno-0-28" href="#__codelineno-0-28"></a><span class="sx"> discard</span><span class="w"> </span><span class="sx">?pb.getField(2</span>,<span class="w"> </span><span class="sx">res.value)</span>
<a id="__codelineno-0-29" name="__codelineno-0-29" href="#__codelineno-0-29"></a><span class="sx"> ok(res)</span>
<a id="__codelineno-0-30" name="__codelineno-0-30" href="#__codelineno-0-30"></a>
<a id="__codelineno-0-31" name="__codelineno-0-31" href="#__codelineno-0-31"></a><span class="sx">proc</span><span class="w"> </span><span class="sx">encode(m</span>:<span class="w"> </span><span class="sx">MetricList): ProtoBuffer</span><span class="w"> </span><span class="sx">=</span>
<a id="__codelineno-0-32" name="__codelineno-0-32" href="#__codelineno-0-32"></a><span class="sx"> result</span><span class="w"> </span><span class="sx">= initProtoBuffer()</span>
<a id="__codelineno-0-33" name="__codelineno-0-33" href="#__codelineno-0-33"></a><span class="sx"> for</span><span class="w"> </span><span class="sx">metric</span><span class="w"> </span><span class="sx">in</span><span class="w"> </span><span class="sx">m.metrics</span>:
<a id="__codelineno-0-34" name="__codelineno-0-34" href="#__codelineno-0-34"></a><span class="w"> </span><span class="sx">result.write(1</span>,<span class="w"> </span><span class="sx">metric.encode())</span>
<a id="__codelineno-0-35" name="__codelineno-0-35" href="#__codelineno-0-35"></a><span class="sx"> result.write(2</span>,<span class="w"> </span><span class="sx">m.hostname)</span>
<a id="__codelineno-0-36" name="__codelineno-0-36" href="#__codelineno-0-36"></a><span class="sx"> result.finish()</span>
<a id="__codelineno-0-37" name="__codelineno-0-37" href="#__codelineno-0-37"></a>
<a id="__codelineno-0-38" name="__codelineno-0-38" href="#__codelineno-0-38"></a><span class="sx">proc</span><span class="w"> </span><span class="sx">decode(_</span>:<span class="w"> </span><span class="sx">type</span><span class="w"> </span><span class="sx">MetricList</span>,<span class="w"> </span><span class="sx">buf</span>:<span class="w"> </span><span class="sx">seq[byte]): Result[MetricList</span>,<span class="w"> </span><span class="sx">ProtoError] =</span>
<a id="__codelineno-0-39" name="__codelineno-0-39" href="#__codelineno-0-39"></a><span class="sx"> var</span>
<a id="__codelineno-0-40" name="__codelineno-0-40" href="#__codelineno-0-40"></a><span class="w"> </span><span class="sx">res</span>:<span class="w"> </span><span class="sx">MetricList</span>
<a id="__codelineno-0-41" name="__codelineno-0-41" href="#__codelineno-0-41"></a><span class="w"> </span><span class="sx">metrics</span>:<span class="w"> </span><span class="sx">seq[seq[byte]]</span>
<a id="__codelineno-0-42" name="__codelineno-0-42" href="#__codelineno-0-42"></a><span class="sx"> let</span><span class="w"> </span><span class="sx">pb</span><span class="w"> </span><span class="sx">= initProtoBuffer(buf)</span>
<a id="__codelineno-0-43" name="__codelineno-0-43" href="#__codelineno-0-43"></a><span class="sx"> discard</span><span class="w"> </span><span class="sx">?pb.getRepeatedField(1</span>,<span class="w"> </span><span class="sx">metrics)</span>
<a id="__codelineno-0-44" name="__codelineno-0-44" href="#__codelineno-0-44"></a>
<a id="__codelineno-0-45" name="__codelineno-0-45" href="#__codelineno-0-45"></a><span class="sx"> for</span><span class="w"> </span><span class="sx">metric</span><span class="w"> </span><span class="sx">in</span><span class="w"> </span><span class="sx">metrics</span>:
<a id="__codelineno-0-46" name="__codelineno-0-46" href="#__codelineno-0-46"></a><span class="w"> </span><span class="sx">res.metrics</span><span class="w"> </span><span class="sx">&amp;= ?Metric.decode(metric)</span>
<a id="__codelineno-0-47" name="__codelineno-0-47" href="#__codelineno-0-47"></a><span class="sx"> ?pb.getRequiredField(2</span>,<span class="w"> </span><span class="sx">res.hostname)</span>
<a id="__codelineno-0-48" name="__codelineno-0-48" href="#__codelineno-0-48"></a><span class="sx"> ok(res)</span>
</code></pre></div>
This is exactly like the previous structure, except that we added
a <code>hostname</code> to distinguish where the metric is coming from.</p>
<p>Now we'll create a small GossipSub network to broadcast the metrics,
and collect them on one of the node.
<div class="highlight"><pre><span></span><code><a id="__codelineno-1-1" name="__codelineno-1-1" href="#__codelineno-1-1"></a><span class="k">type</span><span class="w"> </span><span class="n">Node</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">tuple</span><span class="o">[</span><span class="n">switch</span><span class="p">:</span><span class="w"> </span><span class="n">Switch</span><span class="p">,</span><span class="w"> </span><span class="n">gossip</span><span class="p">:</span><span class="w"> </span><span class="n">GossipSub</span><span class="p">,</span><span class="w"> </span><span class="n">hostname</span><span class="p">:</span><span class="w"> </span><span class="nb">string</span><span class="o">]</span>
<a id="__codelineno-1-2" name="__codelineno-1-2" href="#__codelineno-1-2"></a>
<a id="__codelineno-1-3" name="__codelineno-1-3" href="#__codelineno-1-3"></a><span class="k">proc</span><span class="w"> </span><span class="nf">oneNode</span><span class="p">(</span><span class="n">node</span><span class="p">:</span><span class="w"> </span><span class="n">Node</span><span class="p">,</span><span class="w"> </span><span class="n">rng</span><span class="p">:</span><span class="w"> </span><span class="k">ref</span><span class="w"> </span><span class="n">HmacDrbgContext</span><span class="p">)</span><span class="w"> </span><span class="sx">{.async.}</span><span class="w"> </span><span class="o">=</span>
<a id="__codelineno-1-4" name="__codelineno-1-4" href="#__codelineno-1-4"></a><span class="w"> </span><span class="c"># This procedure will handle one of the node of the network</span>
<a id="__codelineno-1-5" name="__codelineno-1-5" href="#__codelineno-1-5"></a><span class="w"> </span><span class="n">node</span><span class="p">.</span><span class="n">gossip</span><span class="p">.</span><span class="n">addValidator</span><span class="p">(</span>
<a id="__codelineno-1-6" name="__codelineno-1-6" href="#__codelineno-1-6"></a><span class="w"> </span><span class="o">[</span><span class="s">&quot;metrics&quot;</span><span class="o">]</span><span class="p">,</span>
<a id="__codelineno-1-7" name="__codelineno-1-7" href="#__codelineno-1-7"></a><span class="w"> </span><span class="n">proc</span><span class="p">(</span><span class="n">topic</span><span class="p">:</span><span class="w"> </span><span class="nb">string</span><span class="p">,</span><span class="w"> </span><span class="n">message</span><span class="p">:</span><span class="w"> </span><span class="n">Message</span><span class="p">):</span><span class="w"> </span><span class="n">Future</span><span class="o">[</span><span class="n">ValidationResult</span><span class="o">]</span><span class="w"> </span><span class="sx">{.async.}</span><span class="w"> </span><span class="o">=</span>
<a id="__codelineno-1-8" name="__codelineno-1-8" href="#__codelineno-1-8"></a><span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">decoded</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">MetricList</span><span class="p">.</span><span class="n">decode</span><span class="p">(</span><span class="n">message</span><span class="p">.</span><span class="n">data</span><span class="p">)</span>
<a id="__codelineno-1-9" name="__codelineno-1-9" href="#__codelineno-1-9"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">decoded</span><span class="p">.</span><span class="n">isErr</span><span class="p">:</span>
<a id="__codelineno-1-10" name="__codelineno-1-10" href="#__codelineno-1-10"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">ValidationResult</span><span class="p">.</span><span class="n">Reject</span>
<a id="__codelineno-1-11" name="__codelineno-1-11" href="#__codelineno-1-11"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">ValidationResult</span><span class="p">.</span><span class="n">Accept</span>
<a id="__codelineno-1-12" name="__codelineno-1-12" href="#__codelineno-1-12"></a><span class="w"> </span><span class="p">,</span>
<a id="__codelineno-1-13" name="__codelineno-1-13" href="#__codelineno-1-13"></a><span class="w"> </span><span class="p">)</span>
<a id="__codelineno-1-14" name="__codelineno-1-14" href="#__codelineno-1-14"></a><span class="w"> </span><span class="c"># This &quot;validator&quot; will attach to the `metrics` topic and make sure</span>
<a id="__codelineno-1-15" name="__codelineno-1-15" href="#__codelineno-1-15"></a><span class="w"> </span><span class="c"># that every message in this topic is valid. This allows us to stop</span>
<a id="__codelineno-1-16" name="__codelineno-1-16" href="#__codelineno-1-16"></a><span class="w"> </span><span class="c"># propagation of invalid messages quickly in the network, and punish</span>
<a id="__codelineno-1-17" name="__codelineno-1-17" href="#__codelineno-1-17"></a><span class="w"> </span><span class="c"># peers sending them.</span>
<a id="__codelineno-1-18" name="__codelineno-1-18" href="#__codelineno-1-18"></a>
<a id="__codelineno-1-19" name="__codelineno-1-19" href="#__codelineno-1-19"></a><span class="w"> </span><span class="c"># `John` will be responsible to log the metrics, the rest of the nodes</span>
<a id="__codelineno-1-20" name="__codelineno-1-20" href="#__codelineno-1-20"></a><span class="w"> </span><span class="c"># will just forward them in the network</span>
<a id="__codelineno-1-21" name="__codelineno-1-21" href="#__codelineno-1-21"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">node</span><span class="p">.</span><span class="n">hostname</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">&quot;John&quot;</span><span class="p">:</span>
<a id="__codelineno-1-22" name="__codelineno-1-22" href="#__codelineno-1-22"></a><span class="w"> </span><span class="n">node</span><span class="p">.</span><span class="n">gossip</span><span class="p">.</span><span class="n">subscribe</span><span class="p">(</span>
<a id="__codelineno-1-23" name="__codelineno-1-23" href="#__codelineno-1-23"></a><span class="w"> </span><span class="s">&quot;metrics&quot;</span><span class="p">,</span>
<a id="__codelineno-1-24" name="__codelineno-1-24" href="#__codelineno-1-24"></a><span class="w"> </span><span class="n">proc</span><span class="p">(</span><span class="n">topic</span><span class="p">:</span><span class="w"> </span><span class="nb">string</span><span class="p">,</span><span class="w"> </span><span class="n">data</span><span class="p">:</span><span class="w"> </span><span class="nb">seq</span><span class="o">[</span><span class="n">byte</span><span class="o">]</span><span class="p">)</span><span class="w"> </span><span class="sx">{.async.}</span><span class="w"> </span><span class="o">=</span>
<a id="__codelineno-1-25" name="__codelineno-1-25" href="#__codelineno-1-25"></a><span class="w"> </span><span class="n">echo</span><span class="w"> </span><span class="n">MetricList</span><span class="p">.</span><span class="n">decode</span><span class="p">(</span><span class="n">data</span><span class="p">).</span><span class="n">tryGet</span><span class="p">()</span>
<a id="__codelineno-1-26" name="__codelineno-1-26" href="#__codelineno-1-26"></a><span class="w"> </span><span class="p">,</span>
<a id="__codelineno-1-27" name="__codelineno-1-27" href="#__codelineno-1-27"></a><span class="w"> </span><span class="p">)</span>
<a id="__codelineno-1-28" name="__codelineno-1-28" href="#__codelineno-1-28"></a><span class="w"> </span><span class="k">else</span><span class="p">:</span>
<a id="__codelineno-1-29" name="__codelineno-1-29" href="#__codelineno-1-29"></a><span class="w"> </span><span class="n">node</span><span class="p">.</span><span class="n">gossip</span><span class="p">.</span><span class="n">subscribe</span><span class="p">(</span><span class="s">&quot;metrics&quot;</span><span class="p">,</span><span class="w"> </span><span class="kp">nil</span><span class="p">)</span>
<a id="__codelineno-1-30" name="__codelineno-1-30" href="#__codelineno-1-30"></a>
<a id="__codelineno-1-31" name="__codelineno-1-31" href="#__codelineno-1-31"></a><span class="w"> </span><span class="c"># Create random metrics 10 times and broadcast them</span>
<a id="__codelineno-1-32" name="__codelineno-1-32" href="#__codelineno-1-32"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="err">_ in 0 ..&lt; 10:</span>
<a id="__codelineno-1-33" name="__codelineno-1-33" href="#__codelineno-1-33"></a><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">sleepAsync</span><span class="p">(</span><span class="mf">500.</span><span class="n">milliseconds</span><span class="p">)</span>
<a id="__codelineno-1-34" name="__codelineno-1-34" href="#__codelineno-1-34"></a><span class="w"> </span><span class="kd">var</span><span class="w"> </span><span class="n">metricList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">MetricList</span><span class="p">(</span><span class="n">hostname</span><span class="p">:</span><span class="w"> </span><span class="n">node</span><span class="p">.</span><span class="n">hostname</span><span class="p">)</span>
<a id="__codelineno-1-35" name="__codelineno-1-35" href="#__codelineno-1-35"></a><span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">metricCount</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">rng</span><span class="o">[]</span><span class="p">.</span><span class="n">generate</span><span class="p">(</span><span class="n">uint32</span><span class="p">)</span><span class="w"> </span><span class="ow">mod</span><span class="w"> </span><span class="mi">4</span>
<a id="__codelineno-1-36" name="__codelineno-1-36" href="#__codelineno-1-36"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="ow">in</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">..</span><span class="o">&lt;</span><span class="w"> </span><span class="n">metricCount</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">:</span>
<a id="__codelineno-1-37" name="__codelineno-1-37" href="#__codelineno-1-37"></a><span class="w"> </span><span class="n">metricList</span><span class="p">.</span><span class="n">metrics</span><span class="p">.</span><span class="n">add</span><span class="p">(</span>
<a id="__codelineno-1-38" name="__codelineno-1-38" href="#__codelineno-1-38"></a><span class="w"> </span><span class="n">Metric</span><span class="p">(</span><span class="n">name</span><span class="p">:</span><span class="w"> </span><span class="s">&quot;metric_&quot;</span><span class="w"> </span><span class="o">&amp;</span><span class="w"> </span><span class="o">$</span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">value</span><span class="p">:</span><span class="w"> </span><span class="nb">float</span><span class="p">(</span><span class="n">rng</span><span class="o">[]</span><span class="p">.</span><span class="n">generate</span><span class="p">(</span><span class="n">uint16</span><span class="p">))</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">1000.0</span><span class="p">)</span>
<a id="__codelineno-1-39" name="__codelineno-1-39" href="#__codelineno-1-39"></a><span class="w"> </span><span class="p">)</span>
<a id="__codelineno-1-40" name="__codelineno-1-40" href="#__codelineno-1-40"></a>
<a id="__codelineno-1-41" name="__codelineno-1-41" href="#__codelineno-1-41"></a><span class="w"> </span><span class="k">discard</span><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">node</span><span class="p">.</span><span class="n">gossip</span><span class="p">.</span><span class="n">publish</span><span class="p">(</span><span class="s">&quot;metrics&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">encode</span><span class="p">(</span><span class="n">metricList</span><span class="p">).</span><span class="n">buffer</span><span class="p">)</span>
<a id="__codelineno-1-42" name="__codelineno-1-42" href="#__codelineno-1-42"></a><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">node</span><span class="p">.</span><span class="n">switch</span><span class="p">.</span><span class="n">stop</span><span class="p">()</span>
</code></pre></div>
For our main procedure, we'll create a few nodes, and connect them together.
Note that they are not all interconnected, but GossipSub will take care of
broadcasting to the full network nonetheless.
<div class="highlight"><pre><span></span><code><a id="__codelineno-2-1" name="__codelineno-2-1" href="#__codelineno-2-1"></a><span class="k">proc</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span><span class="w"> </span><span class="sx">{.async.}</span><span class="w"> </span><span class="o">=</span>
<a id="__codelineno-2-2" name="__codelineno-2-2" href="#__codelineno-2-2"></a><span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">rng</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">newRng</span><span class="p">()</span>
<a id="__codelineno-2-3" name="__codelineno-2-3" href="#__codelineno-2-3"></a><span class="w"> </span><span class="kd">var</span><span class="w"> </span><span class="n">nodes</span><span class="p">:</span><span class="w"> </span><span class="nb">seq</span><span class="o">[</span><span class="n">Node</span><span class="o">]</span>
<a id="__codelineno-2-4" name="__codelineno-2-4" href="#__codelineno-2-4"></a>
<a id="__codelineno-2-5" name="__codelineno-2-5" href="#__codelineno-2-5"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">hostname</span><span class="w"> </span><span class="ow">in</span><span class="w"> </span><span class="o">[</span><span class="s">&quot;John&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Walter&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;David&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Thuy&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Amy&quot;</span><span class="o">]</span><span class="p">:</span>
<a id="__codelineno-2-6" name="__codelineno-2-6" href="#__codelineno-2-6"></a><span class="w"> </span><span class="k">let</span>
<a id="__codelineno-2-7" name="__codelineno-2-7" href="#__codelineno-2-7"></a><span class="w"> </span><span class="n">switch</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">newStandardSwitch</span><span class="p">(</span><span class="n">rng</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">rng</span><span class="p">)</span>
<a id="__codelineno-2-8" name="__codelineno-2-8" href="#__codelineno-2-8"></a><span class="w"> </span><span class="n">gossip</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">GossipSub</span><span class="p">.</span><span class="n">init</span><span class="p">(</span><span class="n">switch</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">switch</span><span class="p">,</span><span class="w"> </span><span class="n">triggerSelf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="kp">true</span><span class="p">)</span>
<a id="__codelineno-2-9" name="__codelineno-2-9" href="#__codelineno-2-9"></a><span class="w"> </span><span class="n">switch</span><span class="p">.</span><span class="n">mount</span><span class="p">(</span><span class="n">gossip</span><span class="p">)</span>
<a id="__codelineno-2-10" name="__codelineno-2-10" href="#__codelineno-2-10"></a><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">switch</span><span class="p">.</span><span class="n">start</span><span class="p">()</span>
<a id="__codelineno-2-11" name="__codelineno-2-11" href="#__codelineno-2-11"></a>
<a id="__codelineno-2-12" name="__codelineno-2-12" href="#__codelineno-2-12"></a><span class="w"> </span><span class="n">nodes</span><span class="p">.</span><span class="n">add</span><span class="p">((</span><span class="n">switch</span><span class="p">,</span><span class="w"> </span><span class="n">gossip</span><span class="p">,</span><span class="w"> </span><span class="n">hostname</span><span class="p">))</span>
<a id="__codelineno-2-13" name="__codelineno-2-13" href="#__codelineno-2-13"></a>
<a id="__codelineno-2-14" name="__codelineno-2-14" href="#__codelineno-2-14"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="n">node</span><span class="w"> </span><span class="ow">in</span><span class="w"> </span><span class="n">nodes</span><span class="p">:</span>
<a id="__codelineno-2-15" name="__codelineno-2-15" href="#__codelineno-2-15"></a><span class="w"> </span><span class="c"># Connect to a few neighbors</span>
<a id="__codelineno-2-16" name="__codelineno-2-16" href="#__codelineno-2-16"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">otherNodeIdx</span><span class="w"> </span><span class="ow">in</span><span class="w"> </span><span class="n">index</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">..</span><span class="w"> </span><span class="n">index</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">2</span><span class="p">:</span>
<a id="__codelineno-2-17" name="__codelineno-2-17" href="#__codelineno-2-17"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">otherNodeIdx</span><span class="w"> </span><span class="ow">notin</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">..</span><span class="o">&lt;</span><span class="w"> </span><span class="n">nodes</span><span class="p">.</span><span class="n">len</span><span class="w"> </span><span class="ow">or</span><span class="w"> </span><span class="n">otherNodeIdx</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">index</span><span class="p">:</span>
<a id="__codelineno-2-18" name="__codelineno-2-18" href="#__codelineno-2-18"></a><span class="w"> </span><span class="k">continue</span>
<a id="__codelineno-2-19" name="__codelineno-2-19" href="#__codelineno-2-19"></a><span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">otherNode</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">nodes</span><span class="o">[</span><span class="n">otherNodeIdx</span><span class="o">]</span>
<a id="__codelineno-2-20" name="__codelineno-2-20" href="#__codelineno-2-20"></a><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">node</span><span class="p">.</span><span class="n">switch</span><span class="p">.</span><span class="n">connect</span><span class="p">(</span>
<a id="__codelineno-2-21" name="__codelineno-2-21" href="#__codelineno-2-21"></a><span class="w"> </span><span class="n">otherNode</span><span class="p">.</span><span class="n">switch</span><span class="p">.</span><span class="n">peerInfo</span><span class="p">.</span><span class="n">peerId</span><span class="p">,</span><span class="w"> </span><span class="n">otherNode</span><span class="p">.</span><span class="n">switch</span><span class="p">.</span><span class="n">peerInfo</span><span class="p">.</span><span class="n">addrs</span>
<a id="__codelineno-2-22" name="__codelineno-2-22" href="#__codelineno-2-22"></a><span class="w"> </span><span class="p">)</span>
<a id="__codelineno-2-23" name="__codelineno-2-23" href="#__codelineno-2-23"></a>
<a id="__codelineno-2-24" name="__codelineno-2-24" href="#__codelineno-2-24"></a><span class="w"> </span><span class="kd">var</span><span class="w"> </span><span class="n">allFuts</span><span class="p">:</span><span class="w"> </span><span class="nb">seq</span><span class="o">[</span><span class="n">Future</span><span class="o">[</span><span class="n">void</span><span class="o">]]</span>
<a id="__codelineno-2-25" name="__codelineno-2-25" href="#__codelineno-2-25"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">node</span><span class="w"> </span><span class="ow">in</span><span class="w"> </span><span class="n">nodes</span><span class="p">:</span>
<a id="__codelineno-2-26" name="__codelineno-2-26" href="#__codelineno-2-26"></a><span class="w"> </span><span class="n">allFuts</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">oneNode</span><span class="p">(</span><span class="n">node</span><span class="p">,</span><span class="w"> </span><span class="n">rng</span><span class="p">))</span>
<a id="__codelineno-2-27" name="__codelineno-2-27" href="#__codelineno-2-27"></a>
<a id="__codelineno-2-28" name="__codelineno-2-28" href="#__codelineno-2-28"></a><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">allFutures</span><span class="p">(</span><span class="n">allFuts</span><span class="p">)</span>
<a id="__codelineno-2-29" name="__codelineno-2-29" href="#__codelineno-2-29"></a>
<a id="__codelineno-2-30" name="__codelineno-2-30" href="#__codelineno-2-30"></a><span class="n">waitFor</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
</code></pre></div>
If you run this program, you should see something like:
<div class="highlight"><pre><span></span><code><a id="__codelineno-3-1" name="__codelineno-3-1" href="#__codelineno-3-1"></a>(hostname: &quot;John&quot;, metrics: @[(name: &quot;metric_0&quot;, value: 42.097), (name: &quot;metric_1&quot;, value: 50.99), (name: &quot;metric_2&quot;, value: 47.86), (name: &quot;metric_3&quot;, value: 5.368)])
<a id="__codelineno-3-2" name="__codelineno-3-2" href="#__codelineno-3-2"></a>(hostname: &quot;Walter&quot;, metrics: @[(name: &quot;metric_0&quot;, value: 39.452), (name: &quot;metric_1&quot;, value: 15.606), (name: &quot;metric_2&quot;, value: 14.059), (name: &quot;metric_3&quot;, value: 6.68)])
<a id="__codelineno-3-3" name="__codelineno-3-3" href="#__codelineno-3-3"></a>(hostname: &quot;David&quot;, metrics: @[(name: &quot;metric_0&quot;, value: 9.82), (name: &quot;metric_1&quot;, value: 2.862), (name: &quot;metric_2&quot;, value: 15.514)])
<a id="__codelineno-3-4" name="__codelineno-3-4" href="#__codelineno-3-4"></a>(hostname: &quot;Thuy&quot;, metrics: @[(name: &quot;metric_0&quot;, value: 59.038)])
<a id="__codelineno-3-5" name="__codelineno-3-5" href="#__codelineno-3-5"></a>(hostname: &quot;Amy&quot;, metrics: @[(name: &quot;metric_0&quot;, value: 55.616), (name: &quot;metric_1&quot;, value: 23.52), (name: &quot;metric_2&quot;, value: 59.081), (name: &quot;metric_3&quot;, value: 2.516)])
</code></pre></div></p>
<p>This is John receiving &amp; logging everyone's metrics.</p>
<h2 id="going-further">Going further</h2>
<p>Building efficient &amp; safe GossipSub networks is a tricky subject. By tweaking the <a href="https://status-im.github.io/nim-libp2p/master/libp2p/protocols/pubsub/gossipsub/types.html#GossipSubParams">gossip params</a>
and <a href="https://status-im.github.io/nim-libp2p/master/libp2p/protocols/pubsub/gossipsub/types.html#TopicParams">topic params</a>,
you can achieve very different properties.</p>
<p>Also see reports for <a href="https://gateway.ipfs.io/ipfs/QmRAFP5DBnvNjdYSbWhEhVRJJDFCLpPyvew5GwCCB4VxM4">GossipSub v1.1</a></p>
<p>If you are interested in broadcasting for your application, you may want to use <a href="https://waku.org/">Waku</a>, which builds on top of GossipSub,
and adds features such as history, spam protection, and light node friendliness.</p>
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