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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<meta content="text/html; charset=ISO-8859-1" http-equiv="content-type" /><title>Class Hierarchy</title>

<meta name="generator" content="LompoZer" /><!-- <link rel="stylesheet" type="text/css" href="ss-font.css">
rlt-doc uses white borders for cells!  --></head><body style="width: 600px; font-family: sans-serif;">

<h3>Class Hierarchy</h3>
<span style="font-style: italic;">libtrace</span> is a C API, i.e.a
library of functions that allow you to create Traces and Packets, to
read Packets, and to extract 'decodes' for various parts of the
Packets, e.g. IP (i.e. IPv4), TDP and UDP headers, etc.  That means
that in C, you need to keep pointers to each part of the Packet you're
interested in.

<p><span style="font-style: italic;">python-libtrace (plt)</span> provides Python access to <span style="font-style: italic;">libtrace</span> objects via a set of Python classes.  Each class
has methods that provide access to
various <span style="font-style: italic;">libtrace</span> functions,
and to fields in <span style="font-style: italic;">libtrace's</span>
  'decodes.' &nbsp;

  Trace objects read or write libtrace <span style="font-style: italic;">python-libtrace</span> Packets; the Trace class functions only specify
  details of the trace itself.  

From the Packet object, the classes are arranged in an
  inheritance hierarchy, as shown in the diagram below.  

</p><table style="text-align: left; background-image: url(table-image.svg); background-color: transparent; height: 355px; width: 555px;" class="indent1" border="0" cellpadding="1" cellspacing="2"><tbody>
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  <td style="width: 88px; text-align: center;"><a href="Packet.html">Packet</a></td>
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  <td style="width: 96px; text-align: center;"><a href="Internet.html">Internet</a></td>
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<tr><td style="width: 94px;">&nbsp; </td>
  <td style="width: 88px; text-align: right;"><a href="IP.html">IP</a></td>
  <td style="width: 92px; text-align: center;"><a href="IP6.html">IP6</a></td>
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<tr><td style="width: 94px; text-align: center;"><a href="Layers.html">Transport</a> </td>
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  <td style="text-align: center; width: 96px;"><a href="TCP.html">TCP</a></td>
  <td style="width: 71px;"><a href="UDP.html">UDP</a></td>
  <td style="width: 100px;"><a href="ICMP.html">ICMP</a>, 
  <a href="ICMP6.html">ICMP6</a></td></tr>
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</table>

<p><br />The important thing about this is that classes at lower levels
in the Hierarchy can use all the methods in any of their predecessor
classes, i.e. any that can be reached by tracing up the black lines
in the diagram.
</p><p>For example:</p><ul>
<li>Packet &nbsp; provides &nbsp;<span style="font-style: italic;">.wire_len</span> &nbsp;&nbsp; (on-the-wire packet length in bytes)</li>
<li>Internet &nbsp;provides <span style="font-style: italic;">&nbsp;.src_prefix</span>&nbsp; (IPv4 or IPv6 source address)</li>
<li>TCP &nbsp; &nbsp; &nbsp; provides&nbsp; <span style="font-style: italic;">.src_port</span> &nbsp; &nbsp; (TCP source port)</li>
</ul>
Therefore, classes IP, IPv6, TCP, UDP and ICMP can all use <span style="font-style: italic;">.wire_len</span> and <span style="font-style: italic;">.src_prefix</span>.

<p>If you are writing methods that work on a TCP object, you
should use the higher-level methods within your own methods. Doing that
means that you don't have to make, for example, an IP6 object within
your method - which Python will later have to garbage-collect.
<br /></p><p /><p>Nevil Brownlee
<br />Mon, &nbsp;6 Jan 14 (NZDT)<br />
</p>

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