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<html><head><title>Araneida - Handlers</title>
<LINK rel="stylesheet" href="/doc/araneida.css">
<title>Araneida - HTTP Listeners</title>
</head><body>
<h1>HTTP Listeners</h1>
<p>HTTP-LISTENER is the object in Araneida responsible for listening
to a TCP port and reading requests that come in. When it gets a
request, it calls a handler to process it.
<p>It is possible to have more than one http-listener if you are
publishing on more than one address or port. Multiple http-listeners
may share the same handler, if you wich to publish the same content on
many endpoints.
<p>There are presently two concrete implementations of the
http-listener interface: THREADED-HTTP-LISTENER (only available if
your SBCL has the SB-THREAD feature) and SERVE-EVENT-HTTP-LISTENER.
Both of these operate 'in the background' - i.e. without interfering
with your interactive use of Lisp, but the serve-event listener blocks
requests while it's processing, so is only appropriate if your
responses come back in reasonably short time. On the other hand, it's
seen a lot more use and is likely to be much more stable at present.
<h2>Proxies</h2>
<p>If you are using a reverse proxy (e.g. Apache's mod_proxy) in front
of Araneida, you will probably want to use
{THREADED,SERVE-EVENT}-REVERSE-PROXY-LISTENER. These have an
additional TRANSLATIONS slot - this is a list whose elements are
urlstrings mapping from the external URL hierarchy that the proxy is
configured for to the internal URL that Araneida is listening for.
For example,
<pre>
:translations '(("http://www.examples.com/" "http://www.internal:8000/")
("http://images.examples.com/" "http://images.internal:8000/")
</pre>
<p>There are two reasons to use this:
<ol>
<li>Araneida handlers now believe the requests they are seeing are
from the public interface, so for example REQUEST-URL will return
www.examples.com instead of www.internal. This means that URLs
can safely be displayed to the browser and will not cause subsequent
requests to bypass the proxy.
<li>the APACHE-CONF-SEGMENT function can be used to print out a chunk
of apache.conf syntax containing VirtualHost definitions for the
specified translations.
</ol>
<p>Apache mod_proxy can also cache your responses when so configured.
See the documentation on <a href="caching.html">HTTP caching</a> for details.
<p>See <a href="example.lisp">example.lisp</a> to learn most of
what you need to know about http listeners.
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