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<span class="target" id="imap-developer-api-index"></span><section id="index-api">
<h1>Index API<a class="headerlink" href="#index-api" title="Permalink to this heading"></a></h1>
<section id="intro">
<h2>Intro<a class="headerlink" href="#intro" title="Permalink to this heading"></a></h2>
<p>The Index API is implemented in <code class="docutils literal notranslate"><span class="pre">imap/index.h</span></code> and <code class="docutils literal notranslate"><span class="pre">imap/index.c</span></code>.
It provides a snapshot view into the underlying mailbox (see <cite>the
Mailbox API documentation <mailbox-api.html></cite>) which obeys IMAP
semantics, as well as all the searching and sorting logic.</p>
</section>
<section id="opening-and-closing">
<h2>Opening and closing<a class="headerlink" href="#opening-and-closing" title="Permalink to this heading"></a></h2>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">struct</span> <span class="n">index_state</span> <span class="o">*</span><span class="n">state</span> <span class="o">=</span> <span class="n">NULL</span><span class="p">;</span>
<span class="n">struct</span> <span class="n">index_init</span> <span class="n">init</span><span class="p">;</span>
<span class="nb">int</span> <span class="n">r</span><span class="p">;</span>
<span class="n">const</span> <span class="n">char</span> <span class="o">*</span><span class="n">mboxname</span> <span class="o">=</span> <span class="s2">"user.brong"</span><span class="p">;</span>
<span class="n">memset</span><span class="p">(</span><span class="o">&</span><span class="n">init</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="n">sizeof</span><span class="p">(</span><span class="n">struct</span> <span class="n">index_init</span><span class="p">));</span>
<span class="n">init</span><span class="o">.</span><span class="n">userid</span> <span class="o">=</span> <span class="n">imapd_userid</span><span class="p">;</span>
<span class="n">init</span><span class="o">.</span><span class="n">authstate</span> <span class="o">=</span> <span class="n">imapd_authstate</span><span class="p">;</span>
<span class="n">init</span><span class="o">.</span><span class="n">out</span> <span class="o">=</span> <span class="n">imapd_out</span><span class="p">;</span>
<span class="n">r</span> <span class="o">=</span> <span class="n">index_open</span><span class="p">(</span><span class="n">mboxname</span><span class="p">,</span> <span class="o">&</span><span class="n">init</span><span class="p">,</span> <span class="o">&</span><span class="n">state</span><span class="p">);</span>
<span class="k">if</span> <span class="p">(</span><span class="n">r</span><span class="p">)</span> <span class="k">return</span> <span class="n">r</span><span class="p">;</span>
<span class="n">do_stuff</span><span class="p">(</span><span class="n">state</span><span class="p">);</span>
<span class="n">index_close</span><span class="p">(</span><span class="o">&</span><span class="n">state</span><span class="p">);</span>
</pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">index_init</span></code> interface sucks. So does passing lots of parameters.
For now, this will do! Just pass NULL if you're only reading, or use the
code already in imapd and you'll be fine.</p>
</section>
<section id="the-index-model">
<h2>The Index Model<a class="headerlink" href="#the-index-model" title="Permalink to this heading"></a></h2>
<p>Ok - I think a few words about the index model and how it differs from
direct mailbox access are needed! In the past, index.c used pointers
directly into the mmaped <code class="docutils literal notranslate"><span class="pre">cyrus.index</span></code> file and maintained the old
mmaped copy if an expunge took place. Under the namelock regime, this is
no longer required because namelocks will avoid the file being
re-written.</p>
<p>Also, memory is now cheap. Rather than using locks to ensure
consistency, we just keep a copy of the <code class="docutils literal notranslate"><span class="pre">struct</span> <span class="pre">index_record</span></code> for even
message in the index, stored in memory. Since these are about 100 bytes
each, a 1 million email mailbox will take rougly 100Mb of memory. That's
not too bad on a modern server, and that's a <strong>huge</strong> mailbox.</p>
<p>So - the model works like this:</p>
<ul>
<li><p>Create the index state or re-lock (<code class="docutils literal notranslate"><span class="pre">index_lock</span></code>) the mailbox on an
existing index.</p></li>
<li><p>call <code class="docutils literal notranslate"><span class="pre">index_refresh</span></code></p></li>
<li><p>if any changes are to be made (i.e. flag updates for a store,
non-peek body fetch, expunge) then cycle through the refreshed state
map and update the records which are affected.</p></li>
<li><p>call <code class="docutils literal notranslate"><span class="pre">index_unlock</span></code> (unlock the underlying mailbox and commit the
statuscache changes)</p>
<p>At this point the index lock is <strong>released</strong> and we have not yet
generated any network traffic. Now start generating the response.</p>
</li>
<li><p>if expunges are allowed, call <code class="docutils literal notranslate"><span class="pre">index_tellexpunge</span></code></p></li>
<li><p>call <code class="docutils literal notranslate"><span class="pre">index_tellchanges</span></code> to tell about all other changes</p></li>
<li><p>return any response that the command itself required</p></li>
</ul>
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