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<link title="Get" rel="Chapter" href="Get.html"><title>Ocamlnet 4 Reference Manual : Foreword</title>
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<h1>Foreword</h1>
<div class="info-desc">
<h2 id="1_Foreword">Foreword</h2>
<p>A few words about this and that...</p>
<h3 id="2_OrganizationofOcamlnet">Organization of Ocamlnet</h3>
<p>Ocamlnet has grown a lot, and it may look a bit confusing to
beginners. Fortunately, Ocamlnet follows a few organizational
principles:</p>
<p><b>String routines are often factored out</b></p>
<p>String routines like URL parsing, buffer handling, message decoding
etc. are often not directly included in the protocol interpreter, but
defined in separate modules. Actually, there is a whole library,
Netstring, only consisting of string functions.</p>
<p>The advantage is obvious: String functions can be reused, for example
from within clients and servers, but also from user code wishing to do
certain string manipulations directly.</p>
<p><b>Common types ease plugging parts together</b></p>
<p>It is encouraged that one can plug together various parts of Ocamlnet
to create new functionality. Ocamlnet tries to use the same types for
the same kind of values throughout the whole library to make this
easier. Examples:</p>
<ul>
<li><a href="Netmime.html"><code class="code">Netmime</code></a> defines mail messages, but as this data format is also
used in HTTP, <a href="Nethttp_client.html"><code class="code">Nethttp_client</code></a> represents requests and responses
with the same classes</li>
<li><a href="Netchannels.html"><code class="code">Netchannels</code></a> defines object-oriented I/O channels. These are
used almost everywhere in Ocamlnet.</li>
</ul>
<p><b>Common infrastructure for logging, exception printing, and signal handling</b></p>
<p>All Ocamlnet modules use this infrastructure:</p>
<ul>
<li><a href="Netlog.html"><code class="code">Netlog</code></a> is a simple logging module and redirector</li>
<li><a href="Netexn.html"><code class="code">Netexn</code></a> provides extended support for exception printing</li>
<li><a href="Netsys_signal.html"><code class="code">Netsys_signal</code></a> is a little framework for coordinating signal handlers</li>
</ul>
<p>These modules are as simple as possible to do their task. It is up
to the user to extend them, e.g. by plugging in fancier logging
modules.</p>
<p><b>Pluggable name resolver</b></p>
<p>All Ocamlnet modules use a single module for network name resolution:</p>
<ul>
<li><a href="Uq_resolver.html"><code class="code">Uq_resolver</code></a> defines a type for resolvers, and the current default resolver</li>
</ul>
<p><b>Preference of asynchronous protocol interpreters</b></p>
<p>A number of protocol interpreters are written in asynchronous style.
This is generally preferred because of better timeout and error
handling, but also because it makes it possible to run several
instances of these protocol interpreters in the same thread
concurrently (i.e. it is a kind of micro-threading). Ocamlnet
includes the Equeue library as support library for asynchronous
network programming (see <a href="Equeue_intro.html"><code class="code">Equeue_intro</code></a> for more information).</p>
<p>Nevertheless, nobody is forced to use these protocol interpreters
asynchronously. There is always also a simple way for synchronous
calls (i.e. where the execution of the caller blocks until the
network function is completely done).</p>
<p><b>Parallelization is done at a single place</b></p>
<p>In other network environments, often every protocol interpreter
defines functions for parallelizing its use, e.g. by using thread
pools. In Ocamlnet we avoid that. For parallelization there is only
the Netplex library which supports both multi-threading and
multi-processing.</p>
<p>It is easy to use Netplex with the available server implementations:</p>
<ul>
<li><a href="Nethttpd_plex.html"><code class="code">Nethttpd_plex</code></a> allows it to run a webserver inside Netplex</li>
<li><a href="Rpc_netplex.html"><code class="code">Rpc_netplex</code></a> can run SunRPC servers inside Netplex</li>
<li><a href="Netcgi_plex.html"><code class="code">Netcgi_plex</code></a> can run FCGI, SCGI, and AJP connectors inside Netplex</li>
</ul>
<p>There are a number of advantages. First, one can easily create
compound servers running a number of protocol interpreters at the
same time. All interpreters are configured from a single place.
All interpreters use the same logging mechanism. All interpreters
share the same workload mechanism. All interpreters can be
administered with the same command, <code class="code">netplex-admin</code>.</p>
<p>Second, one does not need to develop the parallelization code anew
for each protocol implementation. It is difficult enough.</p>
<p>Third, this approach makes it first possible to provide a serious
implementation of multi-processing. For this kind of parallelism, more
coordination between the interacting components is required than for
multi-threading. For example, when child processes are forked off, it
must be clear which protocol interpreter are run within them.</p>
<p>At Mylife, we have developed a server program that integrates dozens
of different protocols under the same roof. The Netplex approach is
scalable!</p>
<p><b>Pick what you like, and omit things you don't understand</b></p>
<p>Ocamlnet is modular enough that one can cherry-pick the parts one
needs. After all, it is only a library, i.e. a collection of Ocaml
modules, and by using one module there is no strict requirement to
use another module.</p>
<p>Of course, there is also a "use hierarchy" in Ocamlnet - the
HTTP code uses Equeue, for instance. However, the user of HTTP
needs not to know this or care about it. Equeue is then simply
an internally used helper library.</p>
<h3 id="2_FutureDirections">Future Directions</h3>
<p>Ocamlnet is already focused on Internet protocols. Current activities
especially try to</p>
<ul>
<li>focus even more on datacenters as computing environments (affecting
scalability, selection of protocols, etc.)</li>
<li>provide more support to get high availability (e.g. utilities to
detect failed services quickly, or a common directory service)</li>
<li>improve multi-core support (especially speed up interprocess
communication)</li>
</ul>
<h3 id="2_LibrariesUsingOcamlnet">Libraries Using Ocamlnet</h3>
<p>There a number of libraries using and extending Ocamlnet:</p>
<ul>
<li><a href="http://oss.wink.com/hydro"> Hydro</a> implements the ICE remote procedure
call system</li>
<li><a href="http://oss.wink.com/netdns"> Netdns</a> implements much of a DNS client
and client cache</li>
<li><a href="http://oss.wink.com/webdav/"> Webdav</a> is a WebDAV client</li>
<li><a href="http://oss.wink.com/netamqp/"> NetAMQP</a> is an AMQP client</li>
<li><a href="http://code.google.com/p/orpc2"> orpc</a> is another language mapping layer
for SunRPC</li>
<li><a href="http://merjis.com/_file/simplesoap-doc.html"> SimpleSOAP</a> provides a
simple SOAP client</li>
<li><a href="http://ne-fat-s.org/soss/index.html"> SOSS</a> is a SOAP server</li>
<li><a href="http://raevnos.pennmush.org/code/ocaml-xml-rpc"> ocaml-xml-rpc</a> is an
XMLRPC client</li>
<li><a href="http://code.google.com/p/xmlrpc-light"> xmlrpc-light</a> another XMLRPC
library</li>
<li><a href="http://ocamldap.sourceforge.net/"> Ocamlldap</a> is an LDAP client and
an LDAP server framework
</li>
</ul>
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