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<title>Multiplexer — AMC Traffic Server Documentation</title>
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<ul>
<li><a class="reference internal" href="#">Multiplexer</a><ul>
<li><a class="reference internal" href="#description">Description</a></li>
<li><a class="reference internal" href="#implementation">Implementation</a><ul>
<li><a class="reference internal" href="#parsing-chunk-encoded-data">Parsing Chunk Encoded Data</a></li>
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<h1>Multiplexer<a class="headerlink" href="#name" title="Permalink to this headline">¶</a></h1>
<p>Multiplexer is a remap plug-in that allows a request to be multiplexed one or more times and sent to
different remap entries. Both headers and body (in case of POST or PUT methods, only) are copied
into the new requests.</p>
<div class="section" id="description">
<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
<p>Actions:</p>
<ol class="arabic simple">
<li>Adds <code class="docutils literal"><span class="pre">X-Multiplexer:</span> <span class="pre">original</span></code> header into client’s request.</li>
<li>Copies client’s request (bodies are copied by transforming the request)</li>
<li>Changes <code class="docutils literal"><span class="pre">Host</span></code> header of the copy according to <code class="docutils literal"><span class="pre">pparam</span></code> from the remap rule.</li>
<li>Changes <code class="docutils literal"><span class="pre">X-Multiplexer</span> <span class="pre">header</span></code> to “copy”.</li>
<li>Sends the copied request with <code class="code docutils literal"><span class="pre">TSHttpConnect</span></code>.</li>
</ol>
<p>Multiplexer dispatches the request in background without blocking the original request. Multiplexed
responses are drained and discarded.</p>
<p>A global timeout can be overwritten through <code class="docutils literal"><span class="pre">multiplexer__timeout</span></code> environment variable representing how many nanoseconds to wait. A default 1s timeout is hard-coded.</p>
<p>Please use <code class="docutils literal"><span class="pre">multiplexer</span></code> tag for debugging purposes. While debugging, multiplexed requests and
responses are printed into the logs.</p>
<p>Multiplexer produces the following statistics consumed with <code class="docutils literal"><span class="pre">traffic_ctl</span></code>:</p>
<ul class="simple">
<li>failures: number of failed multiplexed requests</li>
<li>hits: number of successful multiplexed requests</li>
<li>requests: total number of multiplexed requests</li>
<li>time(avg): average time taken between multiplexed requests and their responses</li>
<li>timeouts: number of multiplexed requests which timed-out</li>
<li>size(avg): average size of multiplexed responses</li>
</ul>
<p>Example remap.config:</p>
<div class="highlight-cpp"><div class="highlight"><pre><span></span><span class="n">map</span> <span class="nl">http</span><span class="p">:</span><span class="c1">//www.example.com/a http://www.example.com/ @plugin=multiplexer.so @pparam=host1.example.com</span>
<span class="n">map</span> <span class="nl">http</span><span class="p">:</span><span class="c1">//www.example.com/b http://www.example.com/ @plugin=multiplexer.so @pparam=host2.example.com</span>
<span class="n">map</span> <span class="nl">http</span><span class="p">:</span><span class="c1">//www.example.com/c http://www.example.com/ @plugin=multiplexer.so @pparam=host1.example.com @pparam=host2.example.com</span>
</pre></div>
</div>
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<div class="section" id="implementation">
<h2>Implementation<a class="headerlink" href="#implementation" title="Permalink to this headline">¶</a></h2>
<div class="section" id="parsing-chunk-encoded-data">
<h3>Parsing Chunk Encoded Data<a class="headerlink" href="#parsing-chunk-encoded-data" title="Permalink to this headline">¶</a></h3>
<p>Multiplexer parses chunked data with its own home brew parser. In the parser <code class="code docutils literal"><span class="pre">size_</span></code> is the size of
a chunk to be consumed. The local variable / parameter <code class="code docutils literal"><span class="pre">size</span></code> is raw input size as read from an
<code class="code docutils literal"><span class="pre">TSIOBufferBlock</span></code>. The “size states” are marked blue.</p>
<div class="figure align-center">
<p class="plantuml">
<object data="_images/plantuml-6458582619ff10545b8cd05d88310480a79e0bc7.svg" type="image/svg+xml" style="width:495px;height:894px;">
<img src="_images/plantuml-6458582619ff10545b8cd05d88310480a79e0bc7.png" alt="@startuml
skinparam state {
backgroundColor<<SIZE_STATE>> SkyBlue
}
state kSize <<SIZE_STATE>>
kSize : Accumulate size_\nfrom hex input.
[*] --> kSize
kSize --> kSize : hex digit
kSize --> kDataN : CR,size_ > 0
kSize --> kEndN : CR, size_ == 0
kSize --> kInvalid : *
state kDataN <<SIZE_STATE>>
kDataN --> kData : LF
kDataN --> kInvalid : *
kDataN : ASSERT(size_ > 0)
state kEndN <<SIZE_STATE>>
kEndN --> kEnd : LF
kEndN --> kInvalid : *
kData : Consume size_\nbytes of input.
kData --> kSizeR : Input consumed
state kSizeR <<SIZE_STATE>>
kSizeR --> kSizeN : CR
kSizeR --> kInvalid : *
state kSizeN <<SIZE_STATE>>
kSizeN --> kSize : LF
kSizeN --> kInvalid : *
kInvalid --> [*]
kEnd --> [*]
@enduml" />
</object></p>
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<div class="section" id="notes">
<h2>Notes<a class="headerlink" href="#notes" title="Permalink to this headline">¶</a></h2>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">This should be moved to the Traffic Server documentation.</p>
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