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<li class="toctree-l2"><a class="reference internal" href="RPC_method.html">RPC Methods</a></li>
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<li class="toctree-l2 current"><a class="current reference internal" href="#">Subscription</a><ul>
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<li class="toctree-l3"><a class="reference internal" href="#getapis">GetAPIs</a></li>
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<li class="toctree-l3"><a class="reference internal" href="#subscription-function">Subscription Function</a></li>
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<li class="toctree-l3"><a class="reference internal" href="#access">Access</a></li>
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<div class="section" id="subscription">
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<span id="id1"></span><h1>Subscription<a class="headerlink" href="#subscription" title="Permalink to this headline">¶</a></h1>
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<p>In addition to the initial template containing an intialize function, plugins providing <strong>Subscriptions</strong> will require two additional elements.</p>
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<div class="section" id="getapis">
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<h2>GetAPIs<a class="headerlink" href="#getapis" title="Permalink to this headline">¶</a></h2>
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<p>A GetAPIs method is required in the body of the plugin in order to make the plugin available. The bulk of the implementation will be in the MyService struct. MyService should be a struct which includes two public functions.</p>
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<div class="highlight-Go notranslate"><div class="highlight"><pre><span></span><span class="kd">type</span> <span class="nx">MyService</span> <span class="kd">struct</span> <span class="p">{</span>
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<span class="nx">backend</span> <span class="nx">core</span><span class="p">.</span><span class="nx">Backend</span>
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<span class="nx">stack</span> <span class="nx">core</span><span class="p">.</span><span class="nx">Node</span>
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<span class="p">}</span>
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<span class="kd">func</span> <span class="nx">GetAPIs</span><span class="p">(</span><span class="nx">stack</span> <span class="nx">core</span><span class="p">.</span><span class="nx">Node</span><span class="p">,</span> <span class="nx">backend</span> <span class="nx">core</span><span class="p">.</span><span class="nx">Backend</span><span class="p">)</span> <span class="p">[]</span><span class="nx">core</span><span class="p">.</span><span class="nx">API</span> <span class="p">{</span>
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<span class="k">return</span> <span class="p">[]</span><span class="nx">core</span><span class="p">.</span><span class="nx">API</span><span class="p">{</span>
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<span class="p">{</span>
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<span class="nx">Namespace</span><span class="p">:</span> <span class="s">"plugeth"</span><span class="p">,</span>
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<span class="nx">Version</span><span class="p">:</span> <span class="s">"1.0"</span><span class="p">,</span>
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<span class="nx">Service</span><span class="p">:</span> <span class="o">&</span><span class="nx">MyService</span><span class="p">{</span><span class="nx">backend</span><span class="p">,</span> <span class="nx">stack</span><span class="p">},</span>
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<span class="nx">Public</span><span class="p">:</span> <span class="kc">true</span><span class="p">,</span>
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<span class="p">},</span>
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<span class="p">}</span>
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<span class="p">}</span>
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</pre></div>
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</div>
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</div>
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<div class="section" id="subscription-function">
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<h2>Subscription Function<a class="headerlink" href="#subscription-function" title="Permalink to this headline">¶</a></h2>
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<p>For subscriptions (supported on IPC and websockets), a function should take MyService as a reciever and a context.Context object as an argument and return a channel and an error. The following is a subscription function that impliments a timer.</p>
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<div class="highlight-Go notranslate"><div class="highlight"><pre><span></span><span class="kd">func</span> <span class="p">(</span><span class="o">*</span><span class="nx">myservice</span><span class="p">)</span> <span class="nx">Timer</span><span class="p">(</span><span class="nx">ctx</span> <span class="nx">context</span><span class="p">.</span><span class="nx">Context</span><span class="p">)</span> <span class="p">(</span><span class="o"><-</span><span class="kd">chan</span> <span class="kt">int64</span><span class="p">,</span> <span class="kt">error</span><span class="p">)</span> <span class="p">{</span>
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<span class="nx">ticker</span> <span class="o">:=</span> <span class="nx">time</span><span class="p">.</span><span class="nx">NewTicker</span><span class="p">(</span><span class="nx">time</span><span class="p">.</span><span class="nx">Second</span><span class="p">)</span>
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<span class="nx">ch</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">(</span><span class="kd">chan</span> <span class="kt">int64</span><span class="p">)</span>
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<span class="k">go</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
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<span class="k">defer</span> <span class="nx">ticker</span><span class="p">.</span><span class="nx">Stop</span><span class="p">()</span>
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<span class="k">for</span> <span class="p">{</span>
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<span class="k">select</span> <span class="p">{</span>
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<span class="k">case</span> <span class="o"><-</span><span class="nx">ctx</span><span class="p">.</span><span class="nx">Done</span><span class="p">():</span>
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<span class="nb">close</span><span class="p">(</span><span class="nx">ch</span><span class="p">)</span>
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<span class="k">return</span>
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<span class="k">case</span> <span class="nx">t</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">ticker</span><span class="p">.</span><span class="nx">C</span><span class="p">:</span>
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<span class="nx">ch</span> <span class="o"><-</span> <span class="nx">t</span><span class="p">.</span><span class="nx">UnixNano</span><span class="p">()</span>
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<span class="p">}</span>
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<span class="p">}</span>
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<span class="p">}()</span>
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<span class="k">return</span> <span class="nx">ch</span><span class="p">,</span> <span class="kc">nil</span>
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<span class="p">}</span>
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</pre></div>
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</div>
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<div class="admonition warning">
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<p class="admonition-title">Warning</p>
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<p>Notice in the example above, the <code class="docutils literal notranslate"><span class="pre">ctx.Done()</span></code> or
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Context.Done() method closes the channel. If this is not present the go routine will run for the life of the process.</p>
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</div>
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</div>
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<div class="section" id="access">
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<h2>Access<a class="headerlink" href="#access" title="Permalink to this headline">¶</a></h2>
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<div class="admonition note">
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<p class="admonition-title">Note</p>
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<p>Plugins providing subscriptions can be accessed via IPC
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and websockets. In the below example we will be using <a class="reference external" href="https://www.npmjs.com/package/wscat">wscat</a> to connect a websocket to a local Geth node.</p>
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</div>
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<p>As with pre-built plugins, a <code class="docutils literal notranslate"><span class="pre">.so</span></code> will need to be built from <code class="docutils literal notranslate"><span class="pre">main.go</span></code> and moved into <code class="docutils literal notranslate"><span class="pre">~/.ethereum/plugins</span></code>. Geth will need to be started with with <code class="docutils literal notranslate"><span class="pre">--ws</span> <span class="pre">--ws.api=mynamespace``flags.</span> <span class="pre">Additionally</span> <span class="pre">you</span> <span class="pre">will</span> <span class="pre">need</span> <span class="pre">to</span> <span class="pre">include</span> <span class="pre">a</span> <span class="pre">``--http</span></code> flag in order to access the standard json rpc methods.</p>
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<p>After starting Geth, from a seperate terminal run:</p>
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<div class="highlight-shell notranslate"><div class="highlight"><pre><span></span>wscat -c ws://127.0.0.1:8546
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</pre></div>
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</div>
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<div class="admonition note">
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<p class="admonition-title">Note</p>
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<p>Websockets are available via port 8546</p>
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</div>
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<p>Once the connection has been established from the websocket cursor enter the following argument:</p>
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<div class="highlight-shell notranslate"><div class="highlight"><pre><span></span><span class="o">{</span><span class="s2">"jsonrpc"</span>:<span class="s2">"2.0"</span>,<span class="s2">"method"</span>:<span class="s2">"mynamespace_hello"</span>,<span class="s2">"params"</span>:<span class="o">[]</span>,<span class="s2">"id"</span>:0<span class="o">}</span>
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You should see that the network has responded with:
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</pre></div>
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</div>
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<div class="highlight-shell notranslate"><div class="highlight"><pre><span></span><span class="sb">``</span><span class="o">{</span><span class="s2">"jsonrpc"</span>:<span class="s2">"2.0"</span>,<span class="s2">"id"</span>:0,<span class="s2">"result"</span>:<span class="s2">"Hello world"</span><span class="o">}</span><span class="sb">``</span>
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</pre></div>
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