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<h2 class="title"><a id="libmailapi" shape="rect" name="libmailapi"> </a> <span class="application">LibMAIL</span> APIs</h2>
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<p>The <span class="application">LibMAIL</span> library
provides two alternative interfaces: called the
“<span class="quote">native</span>” and the
“<span class="quote">synchronous</span>” interfaces
(API). The native API is based on two fundamental objects:
<span class="structname">mail::account</span> - an
“<span class="quote">account</span>”; and
<span class="structname">mail::folder</span> - a
“<span class="quote">folder</span>”. The syncronous
API uses <span class="structname">mail::ACCOUNT</span> objects
instead of <span class="structname">mail::account</span>
objects; the synchronous API also uses <span class="structname">mail::folder</span> objects, but they are used in
a different manner: instead of invoking <span class="structname">mail::folder</span>'s methods, the synchronous API
provides additional <span class="structname">mail::ACCOUNT</span> methods that take a
<span class="structname">mail::folder</span> object as an
additional parameter.</p>
<p>Both APIs fulfill the same function, but use fundamentally
different approaches. The synchronous, <span class="structname">mail::ACCOUNT</span>-based API, is a traditional,
function-oriented interface: each function completes its given
task, and returns. The native, <span class="structname">mail::account</span>-based API uses an
event-driven paradigm. <span class="structname">mail::account</span> (and <span class="structname">mail::folder</span>) methods receive a
<span class="structname">mail::callback</span> object, or one
of its subclasses, as an extra parameter. The methods always
return immediately, without waiting for the requested operation
to complete. The <span class="structname">mail::callback</span>
object has two methods: <code class="function">success</code>
and <code class="function">fail</code>. One of these methods
will be invoked when the original task is completed.</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>In some cases it's possible that the requested task can be
completed immediately, but this mechanism is still used: the
callback method will be invoked before the original method
returns to the application, instead of afterwards.</p>
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<p>The native API is designed for interactive, event-driven
applications. The application's main event loop should invoke
the <a class="link" href="mail-process.html" title="mail::account::process" shape="rect"><span class="citerefentry"><span class="refentrytitle">mail::account::process</span>(3x)</span></a>
method. This method checks all pending requests, and invokes
the completed requests' callback methods.</p>
<p>The native API is not convenient for single-purpose command
line based mail processing tools . That's the purpose of the
alternative <span class="structname">mail::ACCOUNT</span>-based
API. The <span class="structname">mail::ACCOUNT</span>
synchronous API is designed specifically for single-purpose
command line tools. It should NOT be used by interactive,
event-driven applications. This is because open mail accounts
usually require some sort of periodic, regularly-scheduled
processing (such as checking for new mail). This processing is
automatically handled by <a class="link" href="mail-process.html" title="mail::account::process" shape="rect"><span class="citerefentry"><span class="refentrytitle">mail::account::process</span>(3x)</span></a>.
An interactive application that uses the synchronous API will
exhibit random failures because it will be regularly
disconnected from mail servers, for inactivity, when no mail
processing occurs for a significant period of time.</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>The synchronous API is really nothing more than a small
wrapper around the native API. <span class="structname">mail::ACCOUNT</span> methods closely parallel
their equivalent <span class="structname">mail::account</span>-based methods. A given
<span class="structname">mail::ACCOUNT</span> method is
implemented by creating a callback object, invoking the
corresponding <span class="structname">mail::account</span>
(or <span class="structname">mail::folder</span>) method,
then repeatedly calling <a class="link" href="mail-process.html" title="mail::account::process" shape="rect"><span class="citerefentry"><span class="refentrytitle">mail::account::process</span>(3x)</span></a>,
until the callback object is invoked.</p>
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