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The Codex »
Stop Building Synchronous Web Containers
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stop-building-synchronous-web-containers
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<h1 id="stop-building-synchronous-web-containers">Stop Building Synchronous Web Containers</h1>
<p>Seriously, stop it. It's surreally difficult to build a sane ansynchronous service on top of a synchronous API, but building a synchronous service on top of an asynchronous API is easy.</p>
<ul>
<li>
<p>WSGI: container calls the application as a function, and uses the return
value for the response body. Asynchronous apps generally use a non-WSGI
base (see for example <a href="http://bottlepy.org/docs/dev/async.html">Bottle</a>).</p>
</li>
<li>
<p>Rack: container calls the application as a method, and uses the return
value for the complete response. Asynchronous apps generally use a non-Rack
base (see <a href="https://github.com/rkh/async-rack/issues/5">this Github ticket</a>).</p>
</li>
<li>
<p>Java Servlets: container calls the application as a method, passing a
callback-bearing object as a parameter. The container commits and closes
the response as soon as the application method returns. Asynchronous apps
can use a standard API that operates by <em>re-invoking</em> the servlet method as
needed.</p>
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<li>
<p>What does .Net do?</p>
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<p>vs</p>
<ul>
<li>ExpressJS: container calls the application as a function, passing a
callback-bearing object as a parameter. The application is responsible for
indicating that the response is complete.</li>
</ul>
<h2 id="synchronous-web-containers-are-bad-api-design">Synchronous web containers are bad API design</h2>
<ul>
<li>
<p>Make the easy parts easy (this works)</p>
</li>
<li>
<p>Make the hard parts possible (OH SHIT)</p>
</li>
</ul>
<h2 id="writing-synchronous-adapters-for-async-apis-is-easy">Writing synchronous adapters for async APIs is easy</h2>
<pre><code>def adapter(request, response_callback):
synchronous_response = synchronous_entry_point(request)
return response_callback(synchronous_response)
</code></pre>
<p>Going the other way is more or less impossible, which is why websocket
support, HTML5 server-sent event support, and every other async tool for the
web has an awful server interface.</p>
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