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Motivation # In order for more efficient synchronization of conversational messages, information should be provided allowing a node to more effectively synchronize the dependencies for any given message.
Format # We introduce the metadata message which is used to convey information about a message and how it SHOULD be handled.">
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<meta property="og:description" content="In this specification, we describe a method to construct message history that will aid the consistency guarantees of 2/MVDS. Additionally, we explain how data sync can be used for more lightweight messages that do not require full synchronization.
Motivation # In order for more efficient synchronization of conversational messages, information should be provided allowing a node to more effectively synchronize the dependencies for any given message.
Format # We introduce the metadata message which is used to convey information about a message and how it SHOULD be handled." />
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<strong>4/MVDS-META</strong>
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<li><a href="#motivation">Motivation</a></li>
<li><a href="#format">Format</a>
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<li><a href="#fields">Fields</a></li>
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<li><a href="#parents"><code>parents</code></a></li>
<li><a href="#ephemeral"><code>ephemeral</code></a></li>
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<h1 id="4mvds-meta">
4/MVDS-META
<a class="anchor" href="#4mvds-meta">#</a>
</h1>
<h1 id="mvds-metadata-field">
MVDS Metadata Field
<a class="anchor" href="#mvds-metadata-field">#</a>
</h1>
<img src="https://img.shields.io/badge/status-draft-blue?style=flat-square" />
<ul>
<li>Status: draft</li>
<li>Editor: Sanaz Taheri <a href="mailto:sanaz@status.im">sanaz@status.im</a></li>
<li>Contributors:
Dean Eigenmann <a href="mailto:dean@status.im">dean@status.im</a>
,
Andrea Maria Piana <a href="mailto:andreap@status.im">andreap@status.im</a>
,
Oskar Thorén <a href="mailto:oskar@status.im">oskar@status.im</a>
</li>
</ul><p>In this specification, we describe a method to construct message history that will aid the consistency guarantees of <a href="/spec/2">2/MVDS</a>. Additionally, we explain how data sync can be used for more lightweight messages that do not require full synchronization.</p>
<h2 id="motivation">
Motivation
<a class="anchor" href="#motivation">#</a>
</h2>
<p>In order for more efficient synchronization of conversational messages, information should be provided allowing a node to more effectively synchronize the dependencies for any given message.</p>
<h2 id="format">
Format
<a class="anchor" href="#format">#</a>
</h2>
<p>We introduce the metadata message which is used to convey information about a message and how it SHOULD be handled.</p>
<div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-protobuf" data-lang="protobuf"><span style="display:flex;"><span><span style="color:#f92672">package</span> vac<span style="color:#f92672">.</span>mvds;<span style="color:#960050;background-color:#1e0010">
</span></span></span><span style="display:flex;"><span><span style="color:#960050;background-color:#1e0010">
</span></span></span><span style="display:flex;"><span><span style="color:#960050;background-color:#1e0010"></span><span style="color:#66d9ef">message</span> <span style="color:#a6e22e">Metadata</span> {<span style="color:#960050;background-color:#1e0010">
</span></span></span><span style="display:flex;"><span><span style="color:#960050;background-color:#1e0010"></span> <span style="color:#66d9ef">repeated</span> <span style="color:#66d9ef">bytes</span> parents <span style="color:#f92672">=</span> <span style="color:#ae81ff">1</span>;<span style="color:#960050;background-color:#1e0010">
</span></span></span><span style="display:flex;"><span><span style="color:#960050;background-color:#1e0010"></span> <span style="color:#66d9ef">bool</span> ephemeral <span style="color:#f92672">=</span> <span style="color:#ae81ff">2</span>;<span style="color:#960050;background-color:#1e0010">
</span></span></span><span style="display:flex;"><span><span style="color:#960050;background-color:#1e0010"></span>}<span style="color:#960050;background-color:#1e0010">
</span></span></span></code></pre></div><p>Nodes MAY transmit a <code>Metadata</code> message by extending the MVDS <a href="/spec/2#payloads">message</a> with a <code>metadata</code> field.</p>
<div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-diff" data-lang="diff"><span style="display:flex;"><span>message Message {
</span></span><span style="display:flex;"><span> bytes group_id = 6001;
</span></span><span style="display:flex;"><span> int64 timestamp = 6002;
</span></span><span style="display:flex;"><span> bytes body = 6003;
</span></span><span style="display:flex;"><span><span style="color:#a6e22e">+ Metadata metadata = 6004;
</span></span></span><span style="display:flex;"><span><span style="color:#a6e22e"></span>}
</span></span></code></pre></div><h3 id="fields">
Fields
<a class="anchor" href="#fields">#</a>
</h3>
<table>
<thead>
<tr>
<th>Name</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td><code>parents</code></td>
<td>list of parent <a href="/spec/2#payloads"><code>message identifier</code>s</a> for the specific message.</td>
</tr>
<tr>
<td><code>ephemeral</code></td>
<td>indicates whether a message is ephemeral or not.</td>
</tr>
</tbody>
</table>
<h2 id="usage">
Usage
<a class="anchor" href="#usage">#</a>
</h2>
<h3 id="parents">
<code>parents</code>
<a class="anchor" href="#parents">#</a>
</h3>
<p>This field contains a list of parent <a href="/spec/2#payloads"><code>message identifier</code>s</a> for the specific message. It MUST NOT contain any messages as parent whose <code>ack</code> flag was set to <code>false</code>. This establishes a directed acyclic graph (DAG)<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup> of persistent messages.</p>
<p>Nodes MAY buffer messages until dependencies are satisfied for causal consistency<sup id="fnref:2"><a href="#fn:2" class="footnote-ref" role="doc-noteref">2</a></sup>, they MAY also pass the messages straight away for eventual consistency<sup id="fnref:3"><a href="#fn:3" class="footnote-ref" role="doc-noteref">3</a></sup>.</p>
<p>A parent is any message before a new message that a node is aware of that has no children.</p>
<p>The number of parents for a given message is bound by [0, N], where N is the number of nodes participating in the conversation, therefore the space requirements for the <code>parents</code> field is O(N).</p>
<p>If a message has no parents it is considered a root. There can be multiple roots, which might be disconnected, giving rise to multiple DAGs.</p>
<h3 id="ephemeral">
<code>ephemeral</code>
<a class="anchor" href="#ephemeral">#</a>
</h3>
<p>When the <code>ephemeral</code> flag is set to <code>false</code>, a node MUST send an acknowledgment when they have received and processed a message. If it is set to <code>true</code>, it SHOULD NOT send any acknowledgment. The flag is <code>false</code> by default.</p>
<p>Nodes MAY decide to not persist ephemeral messages, however they MUST NOT be shared as part of the message history.</p>
<p>Nodes SHOULD send ephemeral messages in batch mode. As their delivery is not needed to be guaranteed.</p>
<h2 id="copyright">
Copyright
<a class="anchor" href="#copyright">#</a>
</h2>
<p>Copyright and related rights waived via <a href="https://creativecommons.org/publicdomain/zero/1.0/">CC0</a>.</p>
<h2 id="footnotes">
Footnotes
<a class="anchor" href="#footnotes">#</a>
</h2>
<div class="footnotes" role="doc-endnotes">
<hr>
<ol>
<li id="fn:1">
<p><a href="https://en.wikipedia.org/wiki/Directed_acyclic_graph">https://en.wikipedia.org/wiki/Directed_acyclic_graph</a>&#160;<a href="#fnref:1" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p>
</li>
<li id="fn:2">
<p>Jepsen. <a href="https://jepsen.io/consistency/models/causal">Causal Consistency</a>. Jepsen, LLC.&#160;<a href="#fnref:2" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p>
</li>
<li id="fn:3">
<p><a href="https://en.wikipedia.org/wiki/Eventual_consistency">https://en.wikipedia.org/wiki/Eventual_consistency</a>&#160;<a href="#fnref:3" class="footnote-backref" role="doc-backlink">&#x21a9;&#xfe0e;</a></p>
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