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Creating the protocol
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</ul>
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</nav>
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</div>
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</div>
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</div>
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<div class="md-content" data-md-component="content">
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<article class="md-content__inner md-typeset">
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<h1 id="protobuf-usage">Protobuf usage</h1>
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<p>In the <a href="../tutorial_2_customproto/">previous tutorial</a>, we created a simple "ping" protocol.
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Most real protocol want their messages to be structured and extensible, which is why
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most real protocols use <a href="https://developers.google.com/protocol-buffers">protobuf</a> to
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define their message structures.</p>
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<p>Here, we'll create a slightly more complex protocol, which parses & generate protobuf
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messages. Let's start by importing our dependencies, as usual:
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<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>
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<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><span class="w"> </span><span class="c"># for Opt[T]</span>
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<a id="__codelineno-0-3" name="__codelineno-0-3" href="#__codelineno-0-3"></a>
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<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>
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</code></pre></div></p>
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<h2 id="protobuf-encoding-decoding">Protobuf encoding & decoding</h2>
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<p>This will be the structure of our messages:
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<div class="highlight"><pre><span></span><code><a id="__codelineno-1-1" name="__codelineno-1-1" href="#__codelineno-1-1"></a><span class="kd">message</span><span class="w"> </span><span class="nc">MetricList</span><span class="w"> </span><span class="p">{</span>
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<a id="__codelineno-1-2" name="__codelineno-1-2" href="#__codelineno-1-2"></a><span class="w"> </span><span class="kd">message</span><span class="w"> </span><span class="nc">Metric</span><span class="w"> </span><span class="p">{</span>
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<a id="__codelineno-1-3" name="__codelineno-1-3" href="#__codelineno-1-3"></a><span class="w"> </span><span class="kt">string</span><span class="w"> </span><span class="na">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
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<a id="__codelineno-1-4" name="__codelineno-1-4" href="#__codelineno-1-4"></a><span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="na">value</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span>
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<a id="__codelineno-1-5" name="__codelineno-1-5" href="#__codelineno-1-5"></a><span class="w"> </span><span class="p">}</span>
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<a id="__codelineno-1-6" name="__codelineno-1-6" href="#__codelineno-1-6"></a>
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<a id="__codelineno-1-7" name="__codelineno-1-7" href="#__codelineno-1-7"></a><span class="w"> </span><span class="k">repeated</span><span class="w"> </span><span class="n">Metric</span><span class="w"> </span><span class="na">metrics</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span>
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<a id="__codelineno-1-8" name="__codelineno-1-8" href="#__codelineno-1-8"></a><span class="p">}</span>
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</code></pre></div>
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We'll create our protobuf types, encoders & decoders, according to this format.
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To create the encoders & decoders, we are going to use minprotobuf
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(included in libp2p).</p>
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<p>While more modern technics
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(such as <a href="https://github.com/status-im/nim-protobuf-serialization">nim-protobuf-serialization</a>)
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exists, minprotobuf is currently the recommended method to handle protobuf, since it has
|
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been used in production extensively, and audited.
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<div class="highlight"><pre><span></span><code><a id="__codelineno-2-1" name="__codelineno-2-1" href="#__codelineno-2-1"></a><span class="k">type</span>
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<a id="__codelineno-2-2" name="__codelineno-2-2" href="#__codelineno-2-2"></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>
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<a id="__codelineno-2-3" name="__codelineno-2-3" href="#__codelineno-2-3"></a><span class="w"> </span><span class="n">name</span><span class="p">:</span><span class="w"> </span><span class="nb">string</span>
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<a id="__codelineno-2-4" name="__codelineno-2-4" href="#__codelineno-2-4"></a><span class="w"> </span><span class="n">value</span><span class="p">:</span><span class="w"> </span><span class="nb">float</span>
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<a id="__codelineno-2-5" name="__codelineno-2-5" href="#__codelineno-2-5"></a>
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<a id="__codelineno-2-6" name="__codelineno-2-6" href="#__codelineno-2-6"></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>
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<a id="__codelineno-2-7" name="__codelineno-2-7" href="#__codelineno-2-7"></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>
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<a id="__codelineno-2-8" name="__codelineno-2-8" href="#__codelineno-2-8"></a>
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<a id="__codelineno-2-9" name="__codelineno-2-9" href="#__codelineno-2-9"></a><span class="sx">{.push</span><span class="w"> </span><span class="sx">raises</span>:<span class="w"> </span><span class="sx">[].}</span>
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<a id="__codelineno-2-10" name="__codelineno-2-10" href="#__codelineno-2-10"></a>
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<a id="__codelineno-2-11" name="__codelineno-2-11" href="#__codelineno-2-11"></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>
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<a id="__codelineno-2-12" name="__codelineno-2-12" href="#__codelineno-2-12"></a><span class="sx"> result</span><span class="w"> </span><span class="sx">= initProtoBuffer()</span>
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<a id="__codelineno-2-13" name="__codelineno-2-13" href="#__codelineno-2-13"></a><span class="sx"> result.write(1</span>,<span class="w"> </span><span class="sx">m.name)</span>
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<a id="__codelineno-2-14" name="__codelineno-2-14" href="#__codelineno-2-14"></a><span class="sx"> result.write(2</span>,<span class="w"> </span><span class="sx">m.value)</span>
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<a id="__codelineno-2-15" name="__codelineno-2-15" href="#__codelineno-2-15"></a><span class="sx"> result.finish()</span>
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<a id="__codelineno-2-16" name="__codelineno-2-16" href="#__codelineno-2-16"></a>
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<a id="__codelineno-2-17" name="__codelineno-2-17" href="#__codelineno-2-17"></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>
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<a id="__codelineno-2-18" name="__codelineno-2-18" href="#__codelineno-2-18"></a><span class="sx"> var</span><span class="w"> </span><span class="sx">res</span>:<span class="w"> </span><span class="sx">Metric</span>
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<a id="__codelineno-2-19" name="__codelineno-2-19" href="#__codelineno-2-19"></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>
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<a id="__codelineno-2-20" name="__codelineno-2-20" href="#__codelineno-2-20"></a><span class="sx"> # "getField" will</span><span class="w"> </span><span class="sx">return</span><span class="w"> </span><span class="sx">a</span><span class="w"> </span><span class="sx">Result[bool</span>,<span class="w"> </span><span class="sx">ProtoError].</span>
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<a id="__codelineno-2-21" name="__codelineno-2-21" href="#__codelineno-2-21"></a><span class="sx"> # The</span><span class="w"> </span><span class="sx">Result</span><span class="w"> </span><span class="sx">will</span><span class="w"> </span><span class="sx">hold</span><span class="w"> </span><span class="sx">an</span><span class="w"> </span><span class="sx">error</span><span class="w"> </span><span class="sx">if</span><span class="w"> </span><span class="sx">the</span><span class="w"> </span><span class="sx">protobuf</span><span class="w"> </span><span class="sx">is</span><span class="w"> </span><span class="sx">invalid.</span>
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<a id="__codelineno-2-22" name="__codelineno-2-22" href="#__codelineno-2-22"></a><span class="sx"> # The</span><span class="w"> </span><span class="sx">Result</span><span class="w"> </span><span class="sx">will</span><span class="w"> </span><span class="sx">hold</span><span class="w"> </span><span class="sx">"false" if</span><span class="w"> </span><span class="sx">the</span><span class="w"> </span><span class="sx">field</span><span class="w"> </span><span class="sx">is</span><span class="w"> </span><span class="sx">missing</span>
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<a id="__codelineno-2-23" name="__codelineno-2-23" href="#__codelineno-2-23"></a><span class="w"> </span><span class="sx">#</span>
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<a id="__codelineno-2-24" name="__codelineno-2-24" href="#__codelineno-2-24"></a><span class="sx"> # We</span><span class="w"> </span><span class="sx">are</span><span class="w"> </span><span class="sx">just</span><span class="w"> </span><span class="sx">checking</span><span class="w"> </span><span class="sx">the</span><span class="w"> </span><span class="sx">error</span>,<span class="w"> </span><span class="sx">and</span><span class="w"> </span><span class="sx">ignoring</span><span class="w"> </span><span class="sx">whether</span><span class="w"> </span><span class="sx">the</span><span class="w"> </span><span class="sx">value</span>
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<a id="__codelineno-2-25" name="__codelineno-2-25" href="#__codelineno-2-25"></a><span class="w"> </span><span class="sx"># is</span><span class="w"> </span><span class="sx">present</span><span class="w"> </span><span class="sx">or</span><span class="w"> </span><span class="sx">not</span><span class="w"> </span><span class="sx">(default</span><span class="w"> </span><span class="sx">values</span><span class="w"> </span><span class="sx">are</span><span class="w"> </span><span class="sx">valid).</span>
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<a id="__codelineno-2-26" name="__codelineno-2-26" href="#__codelineno-2-26"></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>
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<a id="__codelineno-2-27" name="__codelineno-2-27" href="#__codelineno-2-27"></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>
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<a id="__codelineno-2-28" name="__codelineno-2-28" href="#__codelineno-2-28"></a><span class="sx"> ok(res)</span>
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<a id="__codelineno-2-29" name="__codelineno-2-29" href="#__codelineno-2-29"></a>
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<a id="__codelineno-2-30" name="__codelineno-2-30" href="#__codelineno-2-30"></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>
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<a id="__codelineno-2-31" name="__codelineno-2-31" href="#__codelineno-2-31"></a><span class="sx"> result</span><span class="w"> </span><span class="sx">= initProtoBuffer()</span>
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<a id="__codelineno-2-32" name="__codelineno-2-32" href="#__codelineno-2-32"></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>:
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<a id="__codelineno-2-33" name="__codelineno-2-33" href="#__codelineno-2-33"></a><span class="w"> </span><span class="sx">result.write(1</span>,<span class="w"> </span><span class="sx">metric.encode())</span>
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<a id="__codelineno-2-34" name="__codelineno-2-34" href="#__codelineno-2-34"></a><span class="sx"> result.finish()</span>
|
|
<a id="__codelineno-2-35" name="__codelineno-2-35" href="#__codelineno-2-35"></a>
|
|
<a id="__codelineno-2-36" name="__codelineno-2-36" href="#__codelineno-2-36"></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>
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|
<a id="__codelineno-2-37" name="__codelineno-2-37" href="#__codelineno-2-37"></a><span class="sx"> var</span>
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<a id="__codelineno-2-38" name="__codelineno-2-38" href="#__codelineno-2-38"></a><span class="w"> </span><span class="sx">res</span>:<span class="w"> </span><span class="sx">MetricList</span>
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<a id="__codelineno-2-39" name="__codelineno-2-39" href="#__codelineno-2-39"></a><span class="w"> </span><span class="sx">metrics</span>:<span class="w"> </span><span class="sx">seq[seq[byte]]</span>
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<a id="__codelineno-2-40" name="__codelineno-2-40" href="#__codelineno-2-40"></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>
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<a id="__codelineno-2-41" name="__codelineno-2-41" href="#__codelineno-2-41"></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>
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<a id="__codelineno-2-42" name="__codelineno-2-42" href="#__codelineno-2-42"></a>
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<a id="__codelineno-2-43" name="__codelineno-2-43" href="#__codelineno-2-43"></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>:
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|
<a id="__codelineno-2-44" name="__codelineno-2-44" href="#__codelineno-2-44"></a><span class="w"> </span><span class="sx">res.metrics</span><span class="w"> </span><span class="sx">&= ? Metric.decode(metric)</span>
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<a id="__codelineno-2-45" name="__codelineno-2-45" href="#__codelineno-2-45"></a><span class="sx"> ok(res)</span>
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</code></pre></div></p>
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|
<h2 id="results-instead-of-exceptions">Results instead of exceptions</h2>
|
|
<p>As you can see, this part of the program also uses Results instead of exceptions for error handling.
|
|
We start by <code>{.push raises: [].}</code>, which will prevent every non-async function from raising
|
|
exceptions.</p>
|
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<p>Then, we use <a href="https://github.com/arnetheduck/nim-result">nim-result</a> to convey
|
|
errors to function callers. A <code>Result[T, E]</code> will either hold a valid result of type
|
|
T, or an error of type E.</p>
|
|
<p>You can check if the call succeeded by using <code>res.isOk</code>, and then get the
|
|
value using <code>res.value</code> or the error by using <code>res.error</code>.</p>
|
|
<p>Another useful tool is <code>?</code>, which will unpack a Result if it succeeded,
|
|
or if it failed, exit the current procedure returning the error.</p>
|
|
<p>nim-result is packed with other functionalities that you'll find in the
|
|
nim-result repository.</p>
|
|
<p>Results and exception are generally interchangeable, but have different semantics
|
|
that you may or may not prefer.</p>
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<h2 id="creating-the-protocol">Creating the protocol</h2>
|
|
<p>We'll next create a protocol, like in the last tutorial, to request these metrics from our host
|
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<div class="highlight"><pre><span></span><code><a id="__codelineno-3-1" name="__codelineno-3-1" href="#__codelineno-3-1"></a><span class="k">type</span>
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|
<a id="__codelineno-3-2" name="__codelineno-3-2" href="#__codelineno-3-2"></a><span class="w"> </span><span class="n">MetricCallback</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">proc</span><span class="p">:</span><span class="w"> </span><span class="n">Future</span><span class="o">[</span><span class="n">MetricList</span><span class="o">]</span><span class="w"> </span><span class="sx">{.raises</span>:<span class="w"> </span><span class="sx">[], gcsafe.}</span>
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|
<a id="__codelineno-3-3" name="__codelineno-3-3" href="#__codelineno-3-3"></a><span class="w"> </span><span class="n">MetricProto</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">ref</span><span class="w"> </span><span class="k">object</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">LPProtocol</span>
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|
<a id="__codelineno-3-4" name="__codelineno-3-4" href="#__codelineno-3-4"></a><span class="w"> </span><span class="n">metricGetter</span><span class="p">:</span><span class="w"> </span><span class="n">MetricCallback</span>
|
|
<a id="__codelineno-3-5" name="__codelineno-3-5" href="#__codelineno-3-5"></a>
|
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<a id="__codelineno-3-6" name="__codelineno-3-6" href="#__codelineno-3-6"></a><span class="k">proc</span><span class="w"> </span><span class="nf">new</span><span class="p">(</span><span class="err">_: typedesc[MetricProto], cb: MetricCallback): MetricProto =</span>
|
|
<a id="__codelineno-3-7" name="__codelineno-3-7" href="#__codelineno-3-7"></a><span class="w"> </span><span class="kd">var</span><span class="w"> </span><span class="n">res</span><span class="p">:</span><span class="w"> </span><span class="n">MetricProto</span>
|
|
<a id="__codelineno-3-8" name="__codelineno-3-8" href="#__codelineno-3-8"></a><span class="w"> </span><span class="k">proc</span><span class="w"> </span><span class="nf">handle</span><span class="p">(</span><span class="n">conn</span><span class="p">:</span><span class="w"> </span><span class="n">Connection</span><span class="p">,</span><span class="w"> </span><span class="n">proto</span><span class="p">:</span><span class="w"> </span><span class="nb">string</span><span class="p">)</span><span class="w"> </span><span class="sx">{.async</span>,<span class="w"> </span><span class="sx">gcsafe.}</span><span class="w"> </span><span class="o">=</span>
|
|
<a id="__codelineno-3-9" name="__codelineno-3-9" href="#__codelineno-3-9"></a><span class="w"> </span><span class="k">let</span>
|
|
<a id="__codelineno-3-10" name="__codelineno-3-10" href="#__codelineno-3-10"></a><span class="w"> </span><span class="n">metrics</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="n">metricGetter</span><span class="p">()</span>
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<a id="__codelineno-3-11" name="__codelineno-3-11" href="#__codelineno-3-11"></a><span class="w"> </span><span class="n">asProtobuf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">metrics</span><span class="p">.</span><span class="n">encode</span><span class="p">()</span>
|
|
<a id="__codelineno-3-12" name="__codelineno-3-12" href="#__codelineno-3-12"></a><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">conn</span><span class="p">.</span><span class="n">writeLp</span><span class="p">(</span><span class="n">asProtobuf</span><span class="p">.</span><span class="n">buffer</span><span class="p">)</span>
|
|
<a id="__codelineno-3-13" name="__codelineno-3-13" href="#__codelineno-3-13"></a><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">conn</span><span class="p">.</span><span class="n">close</span><span class="p">()</span>
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<a id="__codelineno-3-14" name="__codelineno-3-14" href="#__codelineno-3-14"></a>
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<a id="__codelineno-3-15" name="__codelineno-3-15" href="#__codelineno-3-15"></a><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">MetricProto</span><span class="p">.</span><span class="n">new</span><span class="p">(</span><span class="o">@[</span><span class="s">"/metric-getter/1.0.0"</span><span class="o">]</span><span class="p">,</span><span class="w"> </span><span class="n">handle</span><span class="p">)</span>
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<a id="__codelineno-3-16" name="__codelineno-3-16" href="#__codelineno-3-16"></a><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="n">metricGetter</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">cb</span>
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<a id="__codelineno-3-17" name="__codelineno-3-17" href="#__codelineno-3-17"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span>
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<a id="__codelineno-3-18" name="__codelineno-3-18" href="#__codelineno-3-18"></a>
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<a id="__codelineno-3-19" name="__codelineno-3-19" href="#__codelineno-3-19"></a><span class="k">proc</span><span class="w"> </span><span class="nf">fetch</span><span class="p">(</span><span class="n">p</span><span class="p">:</span><span class="w"> </span><span class="n">MetricProto</span><span class="p">,</span><span class="w"> </span><span class="n">conn</span><span class="p">:</span><span class="w"> </span><span class="n">Connection</span><span class="p">):</span><span class="w"> </span><span class="n">Future</span><span class="o">[</span><span class="n">MetricList</span><span class="o">]</span><span class="w"> </span><span class="sx">{.async.}</span><span class="w"> </span><span class="o">=</span>
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<a id="__codelineno-3-20" name="__codelineno-3-20" href="#__codelineno-3-20"></a><span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">protobuf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">conn</span><span class="p">.</span><span class="n">readLp</span><span class="p">(</span><span class="mi">2048</span><span class="p">)</span>
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<a id="__codelineno-3-21" name="__codelineno-3-21" href="#__codelineno-3-21"></a><span class="w"> </span><span class="c"># tryGet will raise an exception if the Result contains an error.</span>
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<a id="__codelineno-3-22" name="__codelineno-3-22" href="#__codelineno-3-22"></a><span class="w"> </span><span class="c"># It's useful to bridge between exception-world and result-world</span>
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<a id="__codelineno-3-23" name="__codelineno-3-23" href="#__codelineno-3-23"></a><span class="w"> </span><span class="k">return</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">protobuf</span><span class="p">).</span><span class="n">tryGet</span><span class="p">()</span>
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</code></pre></div>
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We can now create our main procedure:
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<div class="highlight"><pre><span></span><code><a id="__codelineno-4-1" name="__codelineno-4-1" href="#__codelineno-4-1"></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="sx">gcsafe.}</span><span class="w"> </span><span class="o">=</span>
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<a id="__codelineno-4-2" name="__codelineno-4-2" href="#__codelineno-4-2"></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>
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<a id="__codelineno-4-3" name="__codelineno-4-3" href="#__codelineno-4-3"></a><span class="w"> </span><span class="k">proc</span><span class="w"> </span><span class="nf">randomMetricGenerator</span><span class="p">:</span><span class="w"> </span><span class="n">Future</span><span class="o">[</span><span class="n">MetricList</span><span class="o">]</span><span class="w"> </span><span class="sx">{.async.}</span><span class="w"> </span><span class="o">=</span>
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<a id="__codelineno-4-4" name="__codelineno-4-4" href="#__codelineno-4-4"></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">16</span>
|
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<a id="__codelineno-4-5" name="__codelineno-4-5" href="#__codelineno-4-5"></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"><</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>
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<a id="__codelineno-4-6" name="__codelineno-4-6" href="#__codelineno-4-6"></a><span class="w"> </span><span class="n">result</span><span class="p">.</span><span class="n">metrics</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">Metric</span><span class="p">(</span>
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<a id="__codelineno-4-7" name="__codelineno-4-7" href="#__codelineno-4-7"></a><span class="w"> </span><span class="n">name</span><span class="p">:</span><span class="w"> </span><span class="s">"metric_"</span><span class="w"> </span><span class="o">&</span><span class="w"> </span><span class="o">$</span><span class="n">i</span><span class="p">,</span>
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<a id="__codelineno-4-8" name="__codelineno-4-8" href="#__codelineno-4-8"></a><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>
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<a id="__codelineno-4-9" name="__codelineno-4-9" href="#__codelineno-4-9"></a><span class="w"> </span><span class="p">))</span>
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<a id="__codelineno-4-10" name="__codelineno-4-10" href="#__codelineno-4-10"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">result</span>
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<a id="__codelineno-4-11" name="__codelineno-4-11" href="#__codelineno-4-11"></a><span class="w"> </span><span class="k">let</span>
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<a id="__codelineno-4-12" name="__codelineno-4-12" href="#__codelineno-4-12"></a><span class="w"> </span><span class="n">metricProto1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">MetricProto</span><span class="p">.</span><span class="n">new</span><span class="p">(</span><span class="n">randomMetricGenerator</span><span class="p">)</span>
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<a id="__codelineno-4-13" name="__codelineno-4-13" href="#__codelineno-4-13"></a><span class="w"> </span><span class="n">metricProto2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">MetricProto</span><span class="p">.</span><span class="n">new</span><span class="p">(</span><span class="n">randomMetricGenerator</span><span class="p">)</span>
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<a id="__codelineno-4-14" name="__codelineno-4-14" href="#__codelineno-4-14"></a><span class="w"> </span><span class="n">switch1</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="o">=</span><span class="n">rng</span><span class="p">)</span>
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<a id="__codelineno-4-15" name="__codelineno-4-15" href="#__codelineno-4-15"></a><span class="w"> </span><span class="n">switch2</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="o">=</span><span class="n">rng</span><span class="p">)</span>
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<a id="__codelineno-4-16" name="__codelineno-4-16" href="#__codelineno-4-16"></a>
|
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<a id="__codelineno-4-17" name="__codelineno-4-17" href="#__codelineno-4-17"></a><span class="w"> </span><span class="n">switch1</span><span class="p">.</span><span class="n">mount</span><span class="p">(</span><span class="n">metricProto1</span><span class="p">)</span>
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<a id="__codelineno-4-18" name="__codelineno-4-18" href="#__codelineno-4-18"></a>
|
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<a id="__codelineno-4-19" name="__codelineno-4-19" href="#__codelineno-4-19"></a><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">switch1</span><span class="p">.</span><span class="n">start</span><span class="p">()</span>
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<a id="__codelineno-4-20" name="__codelineno-4-20" href="#__codelineno-4-20"></a><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">switch2</span><span class="p">.</span><span class="n">start</span><span class="p">()</span>
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<a id="__codelineno-4-21" name="__codelineno-4-21" href="#__codelineno-4-21"></a>
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<a id="__codelineno-4-22" name="__codelineno-4-22" href="#__codelineno-4-22"></a><span class="w"> </span><span class="k">let</span>
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<a id="__codelineno-4-23" name="__codelineno-4-23" href="#__codelineno-4-23"></a><span class="w"> </span><span class="n">conn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">switch2</span><span class="p">.</span><span class="n">dial</span><span class="p">(</span><span class="n">switch1</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">switch1</span><span class="p">.</span><span class="n">peerInfo</span><span class="p">.</span><span class="n">addrs</span><span class="p">,</span><span class="w"> </span><span class="n">metricProto2</span><span class="p">.</span><span class="n">codecs</span><span class="p">)</span>
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<a id="__codelineno-4-24" name="__codelineno-4-24" href="#__codelineno-4-24"></a><span class="w"> </span><span class="n">metrics</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">metricProto2</span><span class="p">.</span><span class="n">fetch</span><span class="p">(</span><span class="n">conn</span><span class="p">)</span>
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<a id="__codelineno-4-25" name="__codelineno-4-25" href="#__codelineno-4-25"></a><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">conn</span><span class="p">.</span><span class="n">close</span><span class="p">()</span>
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<a id="__codelineno-4-26" name="__codelineno-4-26" href="#__codelineno-4-26"></a>
|
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<a id="__codelineno-4-27" name="__codelineno-4-27" href="#__codelineno-4-27"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">metric</span><span class="w"> </span><span class="ow">in</span><span class="w"> </span><span class="n">metrics</span><span class="p">.</span><span class="n">metrics</span><span class="p">:</span>
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<a id="__codelineno-4-28" name="__codelineno-4-28" href="#__codelineno-4-28"></a><span class="w"> </span><span class="n">echo</span><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">" = "</span><span class="p">,</span><span class="w"> </span><span class="n">metric</span><span class="p">.</span><span class="n">value</span>
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<a id="__codelineno-4-29" name="__codelineno-4-29" href="#__codelineno-4-29"></a>
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<a id="__codelineno-4-30" name="__codelineno-4-30" href="#__codelineno-4-30"></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">switch1</span><span class="p">.</span><span class="n">stop</span><span class="p">(),</span><span class="w"> </span><span class="n">switch2</span><span class="p">.</span><span class="n">stop</span><span class="p">())</span><span class="w"> </span><span class="c"># close connections and shutdown all transports</span>
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<a id="__codelineno-4-31" name="__codelineno-4-31" href="#__codelineno-4-31"></a>
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<a id="__codelineno-4-32" name="__codelineno-4-32" href="#__codelineno-4-32"></a><span class="n">waitFor</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
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</code></pre></div>
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If you run this program, you should see random metrics being sent from the switch1 to the switch2.</p>
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