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<div class="section" id="eventmq-protocol-specification">
<h1>EventMQ Protocol Specification<a class="headerlink" href="#eventmq-protocol-specification" title="Permalink to this headline">¶</a></h1>
<p><em>The status of this document is alpha and subject to heavy change</em></p>
<div class="section" id="goals">
<h2>Goals<a class="headerlink" href="#goals" title="Permalink to this headline">¶</a></h2>
<p>The EventMQ Protocol (eMQP) defines a reliable service-oriented request-reply and pub-sub dialog between a set of clients, a broker, and a set of workers. This goal is to</p>
<p>The goals are to:</p>
<blockquote>
<div><ul class="simple">
<li>Specify a protocol to follow when implementing a component to EventMQ.</li>
<li>Allow requests to be routed to workers by an abstracted service name.</li>
<li>Detect disconnected peers through heartbeating.</li>
<li>Allow for message tracing and debugging.</li>
</ul>
</div></blockquote>
</div>
<div class="section" id="license">
<h2>License<a class="headerlink" href="#license" title="Permalink to this headline">¶</a></h2>
<p>This Specification is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.</p>
<p>This Specification is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.</p>
</div>
<div class="section" id="language">
<h2>Language<a class="headerlink" href="#language" title="Permalink to this headline">¶</a></h2>
<p>The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119[[1](<a class="reference external" href="http://tools.ietf.org/html/rfc2119">http://tools.ietf.org/html/rfc2119</a>)].</p>
</div>
<div class="section" id="architecture">
<h2>Architecture<a class="headerlink" href="#architecture" title="Permalink to this headline">¶</a></h2>
<p>insert pretty picture here</p>
<div class="section" id="topology">
<h3>Topology<a class="headerlink" href="#topology" title="Permalink to this headline">¶</a></h3>
<p>eMQP connects a set of client applications (e.g. web servers), a broker, and a pool of workers. Clients connect to the broker as well as the workers.</p>
<p>‘Clients’ is defined as application issuing requests and ‘workers’ as applications that process these requests. (Workers consist of a <cite>JobManager</cite> and a pool of <cite>Worker</cite> resources where the job executes.)</p>
<p>The EventMQ broker handles a set of named queues. The broker SHOULD serve clients on a fair request and MAY deliver requests to workers on any basis, including 0MQ’s built-in round robin or least-recently used.</p>
</div>
<div class="section" id="router-addressing">
<h3>ROUTER Addressing<a class="headerlink" href="#router-addressing" title="Permalink to this headline">¶</a></h3>
<p>In the case of request-reply, the broker MUST use a ROUTER socket to accept requests from both clients and workers. The broker MAY use a seperate socket implementing a subset of eMQP, or MAY use a single socket implementing all of eMQP.</p>
<p>From the 0MQ manual[[2](<a class="reference external" href="http://api.zeromq.org/master:zmq-socket">http://api.zeromq.org/master:zmq-socket</a>)]
> When receiving messages a ROUTER socket shall prepend a message part containing the identity of the originating peer to the message before passing it to the application. When sending messages a ROUTER socket shall remove the first part of the message and use it to determine the identity of the peer the message shall be routed to.</p>
<p>This extra frame is not shown in the specifications below.</p>
</div>
<div class="section" id="global-frames">
<h3>Global Frames<a class="headerlink" href="#global-frames" title="Permalink to this headline">¶</a></h3>
<p>An <strong>ACK</strong> command consists of a 4-frame multipart message, formatted as follows.</p>
<table border="1" class="docutils">
<colgroup>
<col width="8%" />
<col width="19%" />
<col width="73%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">FRAME</th>
<th class="head">Value</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>0</td>
<td>_EMPTY_</td>
<td>leave empty</td>
</tr>
<tr class="row-odd"><td>1</td>
<td>eMQP/1.0</td>
<td>Protocol version</td>
</tr>
<tr class="row-even"><td>2</td>
<td>ACK</td>
<td>command</td>
</tr>
<tr class="row-odd"><td>3</td>
<td>_MSGID_</td>
<td>A unique id for the msg</td>
</tr>
<tr class="row-even"><td>4</td>
<td>_MSGID_</td>
<td>The message id of the message this ACK is acknowledging</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="emqp-client">
<h3>eMQP / Client<a class="headerlink" href="#emqp-client" title="Permalink to this headline">¶</a></h3>
<p>A <strong>REQUEST</strong> command consists of a 7-frame multipart message, formatted as follows.</p>
<table border="1" class="docutils">
<colgroup>
<col width="10%" />
<col width="22%" />
<col width="68%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">FRAME</th>
<th class="head">Value</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>0</td>
<td>_EMPTY_</td>
<td>leave empty</td>
</tr>
<tr class="row-odd"><td>1</td>
<td>eMQP/1.0</td>
<td>Protocol version</td>
</tr>
<tr class="row-even"><td>2</td>
<td>READY</td>
<td>command</td>
</tr>
<tr class="row-odd"><td>3</td>
<td>_MSGID_</td>
<td>A unique id for the msg</td>
</tr>
<tr class="row-even"><td>4</td>
<td>_QUEUE_NAME_</td>
<td>the name of the queue the worker belongs to</td>
</tr>
<tr class="row-odd"><td>5</td>
<td>_HEADERS_</td>
<td>dictionary of headers. can be an empty set</td>
</tr>
<tr class="row-even"><td>6</td>
<td>_MSG_</td>
<td>The message to send</td>
</tr>
</tbody>
</table>
<p>A <strong>PUBLISH</strong> command consists of a 7-frame multipart messag, formatted as follows.</p>
<table border="1" class="docutils">
<colgroup>
<col width="10%" />
<col width="22%" />
<col width="68%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">FRAME</th>
<th class="head">Value</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>0</td>
<td>_EMPTY_</td>
<td>leave empty</td>
</tr>
<tr class="row-odd"><td>1</td>
<td>eMQP/1.0</td>
<td>Protocol version</td>
</tr>
<tr class="row-even"><td>2</td>
<td>PUBLISH</td>
<td>command</td>
</tr>
<tr class="row-odd"><td>3</td>
<td>_MSGID_</td>
<td>A unique id for the msg</td>
</tr>
<tr class="row-even"><td>4</td>
<td>_TOPIC_NAME_</td>
<td>the name of the queue the worker belongs to</td>
</tr>
<tr class="row-odd"><td>5</td>
<td>_HEADERS_</td>
<td>dictionary of headers. can be an empty set</td>
</tr>
<tr class="row-even"><td>6</td>
<td>_MSG_</td>
<td>The message to send</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="emqp-worker">
<h3>eMQP / Worker<a class="headerlink" href="#emqp-worker" title="Permalink to this headline">¶</a></h3>
<p>An <strong>INFORM</strong> command consists of a 5-frame multipart message, formatted as follows.</p>
<table border="1" class="docutils">
<colgroup>
<col width="9%" />
<col width="20%" />
<col width="71%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">FRAME</th>
<th class="head">Value</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>0</td>
<td>_EMPTY_</td>
<td>leave empty</td>
</tr>
<tr class="row-odd"><td>1</td>
<td>eMQP/1.0</td>
<td>Protocol version</td>
</tr>
<tr class="row-even"><td>2</td>
<td>INFORM</td>
<td>command</td>
</tr>
<tr class="row-odd"><td>3</td>
<td>_MSGID_</td>
<td>A unique id for the msg</td>
</tr>
<tr class="row-even"><td>4</td>
<td>_QUEUE_NAME_</td>
<td>csv seperated names of queue the worker belongs to</td>
</tr>
</tbody>
</table>
<p>A <strong>READY</strong> frame consists of a 4-frame multipart message, formatted as follows.</p>
<table border="1" class="docutils">
<colgroup>
<col width="14%" />
<col width="33%" />
<col width="53%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">FRAME</th>
<th class="head">Value</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>0</td>
<td>_EMPTY_</td>
<td>leave empty</td>
</tr>
<tr class="row-odd"><td>1</td>
<td>eMQP/1.0</td>
<td>Protocol version</td>
</tr>
<tr class="row-even"><td>2</td>
<td>READY</td>
<td>command</td>
</tr>
<tr class="row-odd"><td>3</td>
<td>_MSGID_</td>
<td>A unique id for the msg</td>
</tr>
</tbody>
</table>
<p>A <strong>REPLY</strong> frame consists of a 5-frame multipart message, formatted as follows.</p>
<table border="1" class="docutils">
<colgroup>
<col width="13%" />
<col width="31%" />
<col width="56%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">FRAME</th>
<th class="head">Value</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>0</td>
<td>_EMPTY_</td>
<td>leave empty</td>
</tr>
<tr class="row-odd"><td>1</td>
<td>eMQP/1.0</td>
<td>Protocol version</td>
</tr>
<tr class="row-even"><td>2</td>
<td>REPLY</td>
<td>command</td>
</tr>
<tr class="row-odd"><td>3</td>
<td>_MSGID_</td>
<td>A unique id for the msg</td>
</tr>
<tr class="row-even"><td>4</td>
<td>_MSG_</td>
<td>The reply to respond with</td>
</tr>
</tbody>
</table>
<p>A <strong>HEARTBEAT</strong> frame consists of a</p>
<table border="1" class="docutils">
<colgroup>
<col width="14%" />
<col width="33%" />
<col width="53%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">FRAME</th>
<th class="head">Value</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>0</td>
<td>_EMPTY_</td>
<td>leave empty</td>
</tr>
<tr class="row-odd"><td>1</td>
<td>eMQP/1.0</td>
<td>Protocol version</td>
</tr>
<tr class="row-even"><td>2</td>
<td>HEARTBEAT</td>
<td>command</td>
</tr>
<tr class="row-odd"><td>3</td>
<td>_MSGID_</td>
<td>A unique id for the msg</td>
</tr>
<tr class="row-even"><td>4</td>
<td>_UNIX_TS_</td>
<td>A unix timestamp</td>
</tr>
</tbody>
</table>
<p>A <strong>DISCONNECT</strong> frame consists of</p>
<table border="1" class="docutils">
<colgroup>
<col width="14%" />
<col width="33%" />
<col width="53%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">FRAME</th>
<th class="head">Value</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>0</td>
<td>_EMPTY_</td>
<td>leave empty</td>
</tr>
<tr class="row-odd"><td>1</td>
<td>eMQP/1.0</td>
<td>Protocol version</td>
</tr>
<tr class="row-even"><td>2</td>
<td>DISCONNECT</td>
<td>command</td>
</tr>
<tr class="row-odd"><td>3</td>
<td>_MSGID_</td>
<td>A unique id for the msg</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="heartbeating">
<h3>Heartbeating<a class="headerlink" href="#heartbeating" title="Permalink to this headline">¶</a></h3>
<blockquote>
<div><ul class="simple">
<li>HEARTBEAT commands are valid at any time after an INFORM command</li>
<li>Any command except DISCONNECT act as a heartbeat. Peers SHOULD NOT send HEARTBEAT commands while sending other commands.</li>
<li>Both worker and broker MUST send heartbeats at regular and agreed-upon intervals.</li>
<li>If the worker detects that the broker disconnected it SHOULD restart the conversation.</li>
<li>If the broker detects that a worker has disconnected it should stop sending it a message of any type.</li>
</ul>
</div></blockquote>
</div>
<div class="section" id="request-headers">
<h3>Request Headers<a class="headerlink" href="#request-headers" title="Permalink to this headline">¶</a></h3>
<p>Headers MUST be 0 to many comma seperated values inserted into the header field. If there are no headers requried, send an empty string MUST be sent where headers are required.</p>
<p>Below is a table which defines and describes the headers.</p>
<table border="1" class="docutils">
<colgroup>
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<tr class="row-odd"><th class="head">Header</th>
<th class="head">REQUEST</th>
<th class="head">PUBLISH</th>
<th class="head">Default</th>
<th class="head">Description</th>
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<tr class="row-even"><td>reply-requested</td>
<td>X</td>
<td> </td>
<td>False</td>
<td>Once the job is finished, send a reply back with information from the job. If there is no information reply with a True value.</td>
</tr>
<tr class="row-odd"><td>retry-count:#</td>
<td>X</td>
<td> </td>
<td>0</td>
<td>Retry a failed job this many times before accepting defeat.</td>
</tr>
<tr class="row-even"><td>guarantee</td>
<td>X</td>
<td> </td>
<td>False</td>
<td>Ensure the job completes by letting someone else worry about a success reply.</td>
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