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<div class="title">Design </div> </div>
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<div class="textblock"><p>The following image shows the various modules of libdns and their functionality.</p>
<div class="image">
<img src="libdnsoverview.png" alt="libdnsoverview.png"/>
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<h2><a class="anchor" id="central_structures"></a>
Central structures</h2>
<ul>
<li><a class="el" href="packet_8h.html#a6b137fb9a86468d16cf66130db3b9da2">ldns_pkt</a> A DNS Packet, which can contain a query, answers, and additional information.</li>
<li><a class="el" href="rr_8h.html#a34d846d44506c86bc94f244445605e98">ldns_rr</a> A Resource Record, which holds a bit of information about a specific domain name.</li>
<li><a class="el" href="rdata_8h.html#adb9c97875196c13e6d1996ae0fd17f86">ldns_rdf</a> An RDATA field, every Resource Record contains one or more RDATA fields, depending on the type of RR. These are the 'basic types' of DNS data.</li>
<li><a class="el" href="rr_8h.html#a99b7150f3167c5df552095a8f7144f33">ldns_rr_list</a> A list of resource records</li>
<li><a class="el" href="zone_8h.html#af8077ee2090d473d6c598fa95c2826b3">ldns_zone</a> A representation of a DNS Zone.</li>
</ul>
<p>The actual structure definitions are named <code>ldns_struct_<name></code> which are all typedeffed to <code>ldns_<name></code> </p>
<p>A DNS Resource record looks like this:</p>
<pre>
nlnetlabs.nl. 600 IN MX 10 open.nlnetlabs.nl.
\ \ \ \ \ /
owner ttl class type \ rdf[] /
(rdf) (uint32_t) (rr_class) (rr_type)
10 := rdf[0]
open.nlnetlabs.nl. := rdf[1]
</pre><p>Owner: The owner name is put in an <code>ldns_rdf</code> structure, which is a normal rdata field but always has the type LDNS_RDF_TYPE_DNAME.</p>
<p>An <a class="el" href="rdata_8h.html#adb9c97875196c13e6d1996ae0fd17f86">ldns_rdf</a> structure has 3 members; the size, the type of rdata and a void * pointer to the data. The data is always in uncompressed wireformat.</p>
<p>The RSH (rdata) is put in an array of rdf's (in this case 2).</p>
<p>The entire resource record is put in a RR structure, which has the fields described above (under the RR):</p>
<ul>
<li>owner (nlnetlabs.nl.)</li>
<li>ttl (600)</li>
<li>class (LDNS_RR_CLASS_IN: 'IN')</li>
<li>type (LDNS_RR_TYPE_MX: 'MX')</li>
<li>rd_count (2)</li>
<li>rdata_fields[rd_count]<ul>
<li>rdf[0] (10)</li>
<li>rdf[1] (open.nlnetlabs.nl.)</li>
</ul>
</li>
</ul>
<p>RR list structure: An RR list structure is simply a structure with a counter and an array of RR structures. Different kinds of RR's can be grouped together this way.</p>
<p>RRset structure: An RRset structure is an RR list structure, but its accessor function checks if the <code>ldns_rr</code> structures in there are:</p>
<ul>
<li>from the same type</li>
<li>have the same TTL</li>
<li>have the same ownername</li>
</ul>
<p>This is the RFC definition of an RRset.</p>
<p>pkt structure: A pkt structure consists out of a header structure where packet specific flags are kept, TC, RD, IP from the server which sent the packet, etc. Further more it is divided in 4 sections: question, authority, answer and additional.</p>
<p>All four sections have the type RRlist that simply hold a list of RR's</p>
<h2><a class="anchor" id="wire_module"></a>
Wire module and central structures Interface</h2>
<p>As the WIRE module takes care of the compression/decompression it needs a buffer which holds all the binary DNS data. All functions will operate on such a buffer to extract specific information which is then stored in RR structures.</p>
<h2><a class="anchor" id="resolver_module"></a>
Resolver module and central structures Interface</h2>
<p>The resolver module always returns a pkt structure. Either with the answer or a SERVFAIL pkt.</p>
<p>The exact function-call parameters have not yet been decided on.</p>
<p>Also the resolver module will need to access some of the to_wire and from_wire function to creates ldn_pkt's from the data it receives (arrow not drawn).</p>
<h2><a class="anchor" id="str_module"></a>
str module and central structures Interface</h2>
<p>Convert to and from strings. This module could be used to read in a zone file (list of RRs) and convert the text strings to the format used by ldns. Or the other way around.</p>
<h2><a class="anchor" id="net_module"></a>
Net module and resolver module interface</h2>
<p>The resolver module will get a packet and will mold it so that it can be sent off to a nameserver. It might need to interface with the wire module (arrow not drawn).</p>
<h2><a class="anchor" id="Net"></a>
module and OS/libc interface</h2>
<p>OS/network calls will be used here. The Net module is the only part of the library where the underlying OS matters.</p>
<h2><a class="anchor" id="Client"></a>
program ldns interface</h2>
<p>Any client program will have access to</p>
<ul>
<li>Wire module</li>
<li>Central structures</li>
<li>Resolver module</li>
<li>str module (arrow not drawn in the above figure)</li>
</ul>
<h2><a class="anchor" id="dnssec_module"></a>
DNSSEC module</h2>
<p>The DNSSEC types are handled in the RR module, but the crypto routines are contained in this module. This module will depend on OpenSSL for the crypto routines. </p>
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