739 lines
52 KiB
HTML
739 lines
52 KiB
HTML
|
|
|||
|
|
<!DOCTYPE html>
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
<html lang="en">
|
|||
|
|
<head>
|
|||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
|||
|
|
|
|||
|
|
<title>5.8. Extended Example: DNS Client — Computer Systems Fundamentals</title>
|
|||
|
|
|
|||
|
|
<link rel="stylesheet" href="_static/css/bootstrap.min.css" integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous" />
|
|||
|
|
<link rel="stylesheet" href="_static/css/pygments.css" type="text/css" />
|
|||
|
|
<link rel="stylesheet" href="_static/css/normalize.css" type="text/css" />
|
|||
|
|
<link rel="stylesheet" href="../../../JSAV/css/JSAV.css" type="text/css" />
|
|||
|
|
<link rel="stylesheet" href="../../../lib/odsaMOD-min.css" type="text/css" />
|
|||
|
|
<link rel="stylesheet" href="_static/css/jquery-1.11.4-smoothness-ui.css" type="text/css" />
|
|||
|
|
<link rel="stylesheet" href="../../../lib/odsaStyle-min.css" type="text/css" />
|
|||
|
|
<link rel="stylesheet" href="_static/css/csf.css" type="text/css" />
|
|||
|
|
|
|||
|
|
<style>
|
|||
|
|
.underline { text-decoration: underline; }
|
|||
|
|
</style>
|
|||
|
|
|
|||
|
|
<script type="text/javascript">
|
|||
|
|
var DOCUMENTATION_OPTIONS = {
|
|||
|
|
URL_ROOT: './',
|
|||
|
|
VERSION: '0.4.1',
|
|||
|
|
COLLAPSE_INDEX: false,
|
|||
|
|
FILE_SUFFIX: '.html',
|
|||
|
|
HAS_SOURCE: true
|
|||
|
|
};
|
|||
|
|
</script>
|
|||
|
|
|
|||
|
|
<script type="text/x-mathjax-config">
|
|||
|
|
MathJax.Hub.Config({
|
|||
|
|
tex2jax: {
|
|||
|
|
inlineMath: [['$','$'], ['\\(','\\)']],
|
|||
|
|
displayMath: [ ['$$','$$'], ["\\[","\\]"] ],
|
|||
|
|
processEscapes: true
|
|||
|
|
},
|
|||
|
|
"HTML-CSS": {
|
|||
|
|
scale: "80"
|
|||
|
|
}
|
|||
|
|
});
|
|||
|
|
</script>
|
|||
|
|
<link rel="shortcut icon" href="_static/favicon.ico"/>
|
|||
|
|
<link rel="index" title="Index" href="genindex.html" />
|
|||
|
|
<link rel="search" title="Search" href="search.html" />
|
|||
|
|
<link rel="index" title="Computer Systems Fundamentals" href="index.html" />
|
|||
|
|
<link rel="next" title="1. Concurrency with Multithreading" href="ThreadsOverview.html" />
|
|||
|
|
<link rel="prev" title="7. Wireless Connectivity: Wi-Fi, Bluetooth, and Zigbee" href="Wireless.html" />
|
|||
|
|
|
|||
|
|
</head><body>
|
|||
|
|
|
|||
|
|
<nav class="navbar navbar-expand-md navbar-dark navbar-custom fixed-top">
|
|||
|
|
|
|||
|
|
<a class="navbar-brand py-0" href="index.html"><img src="_static/CSF-Logo-Square-Text.png" alt="OpenCSF Logo" height="40em" class="py-1 px-2 mb-0 align-center rounded-lg bg-white" /></a>
|
|||
|
|
<!-- Show a navbar toggler on mobile -->
|
|||
|
|
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#defaultNavbars" aria-controls="defaultNavbars" aria-expanded="false" aria-label="Toggle navigation">
|
|||
|
|
<span class="navbar-toggler-icon"></span>
|
|||
|
|
</button>
|
|||
|
|
<div class="collapse navbar-collapse" id="defaultNavbars">
|
|||
|
|
<ul class="navbar-nav mr-auto">
|
|||
|
|
<li class="nav-item dropdown">
|
|||
|
|
<a class="nav-link dropdown-toggle jmu-gold rounded" href="Extended5DNS.html#" id="navbarDropdownChapters" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">Contents</a>
|
|||
|
|
<div class="dropdown-menu scrollable-menu" role="menu" aria-labelledby="navbarDropdownChapters">
|
|||
|
|
<a class="dropdown-item" tabindex="-1" href="Extended5DNS.html#"><b>Chapter 1</b></a>
|
|||
|
|
<a class="dropdown-item" href="IntroConcSysOverview.html"> 1.1. Introduction to Concurrent Systems</a>
|
|||
|
|
<a class="dropdown-item" href="SysAndModels.html"> 1.2. Systems and Models</a>
|
|||
|
|
<a class="dropdown-item" href="Themes.html"> 1.3. Themes and Guiding Principles</a>
|
|||
|
|
<a class="dropdown-item" href="Architectures.html"> 1.4. System Architectures</a>
|
|||
|
|
<a class="dropdown-item" href="StateModels.html"> 1.5. State Models in UML</a>
|
|||
|
|
<a class="dropdown-item" href="SequenceModels.html"> 1.6. Sequence Models in UML</a>
|
|||
|
|
<a class="dropdown-item" href="StateModelImplementation.html"> 1.7. Extended Example: State Model Implementation</a>
|
|||
|
|
<div class="dropdown-divider"></div>
|
|||
|
|
<a class="dropdown-item disabled"><b>Chapter 2</b></a>
|
|||
|
|
<a class="dropdown-item" href="ProcessesOverview.html"> 2.1. Processes and OS Basics</a>
|
|||
|
|
<a class="dropdown-item" href="Multiprogramming.html"> 2.2. Processes and Multiprogramming</a>
|
|||
|
|
<a class="dropdown-item" href="KernelMechanics.html"> 2.3. Kernel Mechanics</a>
|
|||
|
|
<a class="dropdown-item" href="Syscall.html"> 2.4. System Call Interface</a>
|
|||
|
|
<a class="dropdown-item" href="ProcessCycle.html"> 2.5. Process Life Cycle</a>
|
|||
|
|
<a class="dropdown-item" href="UnixFile.html"> 2.6. The UNIX File Abstraction</a>
|
|||
|
|
<a class="dropdown-item" href="EventsSignals.html"> 2.7. Events and Signals</a>
|
|||
|
|
<a class="dropdown-item" href="Extended2Processes.html"> 2.8. Extended Example: Listing Files with Processes</a>
|
|||
|
|
<div class="dropdown-divider"></div>
|
|||
|
|
<a class="dropdown-item disabled"><b>Chapter 3</b></a>
|
|||
|
|
<a class="dropdown-item" href="IPCOverview.html"> 3.1. Concurrency with IPC</a>
|
|||
|
|
<a class="dropdown-item" href="IPCModels.html"> 3.2. IPC Models</a>
|
|||
|
|
<a class="dropdown-item" href="Pipes.html"> 3.3. Pipes and FIFOs</a>
|
|||
|
|
<a class="dropdown-item" href="MMap.html"> 3.4. Shared Memory With Memory-mapped Files</a>
|
|||
|
|
<a class="dropdown-item" href="POSIXvSysV.html"> 3.5. POSIX vs. System V IPC</a>
|
|||
|
|
<a class="dropdown-item" href="MQueues.html"> 3.6. Message Passing With Message Queues</a>
|
|||
|
|
<a class="dropdown-item" href="ShMem.html"> 3.7. Shared Memory</a>
|
|||
|
|
<a class="dropdown-item" href="IPCSems.html"> 3.8. Semaphores</a>
|
|||
|
|
<a class="dropdown-item" href="Extended3Bash.html"> 3.9. Extended Example: Bash-lite: A Simple Command-line Shell</a>
|
|||
|
|
<div class="dropdown-divider"></div>
|
|||
|
|
<a class="dropdown-item disabled"><b>Chapter 4</b></a>
|
|||
|
|
<a class="dropdown-item" href="SocketsOverview.html"> 4.1. Networked Concurrency</a>
|
|||
|
|
<a class="dropdown-item" href="FiveLayer.html"> 4.2. The TCP/IP Internet Model</a>
|
|||
|
|
<a class="dropdown-item" href="NetApps.html"> 4.3. Network Applications and Protocols</a>
|
|||
|
|
<a class="dropdown-item" href="Sockets.html"> 4.4. The Socket Interface</a>
|
|||
|
|
<a class="dropdown-item" href="TCPSockets.html"> 4.5. TCP Socket Programming: HTTP</a>
|
|||
|
|
<a class="dropdown-item" href="UDPSockets.html"> 4.6. UDP Socket Programming: DNS</a>
|
|||
|
|
<a class="dropdown-item" href="AppBroadcast.html"> 4.7. Application-Layer Broadcasting: DHCP</a>
|
|||
|
|
<a class="dropdown-item" href="Extended4CGI.html"> 4.8. Extended Example: CGI Web Server</a>
|
|||
|
|
<div class="dropdown-divider"></div>
|
|||
|
|
<a class="dropdown-item disabled"><b>Chapter 5</b></a>
|
|||
|
|
<a class="dropdown-item" href="InternetOverview.html"> 5.1. The Internet and Connectivity</a>
|
|||
|
|
<a class="dropdown-item" href="AppLayer.html"> 5.2. Application Layer: Overlay Networks</a>
|
|||
|
|
<a class="dropdown-item" href="TransLayer.html"> 5.3. Transport Layer</a>
|
|||
|
|
<a class="dropdown-item" href="NetSec.html"> 5.4. Network Security Fundamentals</a>
|
|||
|
|
<a class="dropdown-item" href="NetLayer.html"> 5.5. Network Layer: IP</a>
|
|||
|
|
<a class="dropdown-item" href="LinkLayer.html"> 5.6. Link Layer</a>
|
|||
|
|
<a class="dropdown-item" href="Wireless.html"> 5.7. Wireless Connectivity: Wi-Fi, Bluetooth, and Zigbee</a>
|
|||
|
|
<a class="dropdown-item" href="Extended5DNS.html"> 5.8. Extended Example: DNS client</a>
|
|||
|
|
<div class="dropdown-divider"></div>
|
|||
|
|
<a class="dropdown-item disabled"><b>Chapter 6</b></a>
|
|||
|
|
<a class="dropdown-item" href="ThreadsOverview.html"> 6.1. Concurrency with Multithreading</a>
|
|||
|
|
<a class="dropdown-item" href="ProcVThreads.html"> 6.2. Processes vs. Threads</a>
|
|||
|
|
<a class="dropdown-item" href="RaceConditions.html"> 6.3. Race Conditions and Critical Sections</a>
|
|||
|
|
<a class="dropdown-item" href="POSIXThreads.html"> 6.4. POSIX Thread Library</a>
|
|||
|
|
<a class="dropdown-item" href="ThreadArgs.html"> 6.5. Thread Arguments and Return Values</a>
|
|||
|
|
<a class="dropdown-item" href="ImplicitThreads.html"> 6.6. Implicit Threading and Language-based Threads</a>
|
|||
|
|
<a class="dropdown-item" href="Extended6Input.html"> 6.7. Extended Example: Keyboard Input Listener</a>
|
|||
|
|
<a class="dropdown-item" href="Extended6Primes.html"> 6.8. Extended Example: Concurrent Prime Number Search</a>
|
|||
|
|
<div class="dropdown-divider"></div>
|
|||
|
|
<a class="dropdown-item disabled"><b>Chapter 7</b></a>
|
|||
|
|
<a class="dropdown-item" href="SynchOverview.html"> 7.1. Synchronization Primitives</a>
|
|||
|
|
<a class="dropdown-item" href="CritSect.html"> 7.2. Critical Sections and Peterson's Solution</a>
|
|||
|
|
<a class="dropdown-item" href="Locks.html"> 7.3. Locks</a>
|
|||
|
|
<a class="dropdown-item" href="Semaphores.html"> 7.4. Semaphores</a>
|
|||
|
|
<a class="dropdown-item" href="Barriers.html"> 7.5. Barriers</a>
|
|||
|
|
<a class="dropdown-item" href="Condvars.html"> 7.6. Condition Variables</a>
|
|||
|
|
<a class="dropdown-item" href="Deadlock.html"> 7.7. Deadlock</a>
|
|||
|
|
<a class="dropdown-item" href="Extended7Events.html"> 7.8. Extended Example: Event Log File</a>
|
|||
|
|
<div class="dropdown-divider"></div>
|
|||
|
|
<a class="dropdown-item disabled"><b>Chapter 8</b></a>
|
|||
|
|
<a class="dropdown-item" href="SynchProblemsOverview.html"> 8.1. Synchronization Patterns and Problems</a>
|
|||
|
|
<a class="dropdown-item" href="SynchDesign.html"> 8.2. Basic Synchronization Design Patterns</a>
|
|||
|
|
<a class="dropdown-item" href="ProdCons.html"> 8.3. Producer-Consumer Problem</a>
|
|||
|
|
<a class="dropdown-item" href="ReadWrite.html"> 8.4. Readers-Writers Problem</a>
|
|||
|
|
<a class="dropdown-item" href="DiningPhil.html"> 8.5. Dining Philosophers Problem and Deadlock</a>
|
|||
|
|
<a class="dropdown-item" href="CigSmokers.html"> 8.6. Cigarette Smokers Problem and the Limits of Semaphores and Locks</a>
|
|||
|
|
<a class="dropdown-item" href="Extended8ModExp.html"> 8.7. Extended Example: Parallel Modular Exponentiation</a>
|
|||
|
|
<div class="dropdown-divider"></div>
|
|||
|
|
<a class="dropdown-item disabled"><b>Chapter 9</b></a>
|
|||
|
|
<a class="dropdown-item" href="ParallelDistributedOverview.html"> 9.1. Parallel and Distributed Systems</a>
|
|||
|
|
<a class="dropdown-item" href="ParVConc.html"> 9.2. Parallelism vs. Concurrency</a>
|
|||
|
|
<a class="dropdown-item" href="ParallelDesign.html"> 9.3. Parallel Design Patterns</a>
|
|||
|
|
<a class="dropdown-item" href="Scaling.html"> 9.4. Limits of Parallelism and Scaling</a>
|
|||
|
|
<a class="dropdown-item" href="DistTiming.html"> 9.5. Timing in Distributed Environments</a>
|
|||
|
|
<a class="dropdown-item" href="DistDataStorage.html"> 9.6. Reliable Data Storage and Location</a>
|
|||
|
|
<a class="dropdown-item" href="DistConsensus.html"> 9.7. Consensus in Distributed Systems</a>
|
|||
|
|
<a class="dropdown-item" href="Extended9Blockchain.html"> 9.8. Extended Example: Blockchain Proof-of-Work</a>
|
|||
|
|
<div class="dropdown-divider"></div>
|
|||
|
|
<a class="dropdown-item disabled"><b>Appendix A</b></a>
|
|||
|
|
<a class="dropdown-item" href="CLangOverview.html"> A.1. C Language Reintroduction</a>
|
|||
|
|
<a class="dropdown-item" href="Debugging.html"> A.2. Documentation and Debugging</a>
|
|||
|
|
<a class="dropdown-item" href="BasicTypes.html"> A.3. Basic Types and Pointers</a>
|
|||
|
|
<a class="dropdown-item" href="Arrays.html"> A.4. Arrays, Structs, Enums, and Type Definitions</a>
|
|||
|
|
<a class="dropdown-item" href="Functions.html"> A.5. Functions and Scope</a>
|
|||
|
|
<a class="dropdown-item" href="Pointers.html"> A.6. Pointers and Dynamic Allocation</a>
|
|||
|
|
<a class="dropdown-item" href="Strings.html"> A.7. Strings</a>
|
|||
|
|
<a class="dropdown-item" href="FunctionPointers.html"> A.8. Function Pointers</a>
|
|||
|
|
<a class="dropdown-item" href="Files.html"> A.9. Files</a>
|
|||
|
|
</div>
|
|||
|
|
</li>
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
</ul>
|
|||
|
|
</div>
|
|||
|
|
|
|||
|
|
<ul class="navbar-nav flex-row ml-md-auto d-none d-md-flex">
|
|||
|
|
<li class="nav-item"><a class="nav-link jmu-gold" href="https://w3.cs.jmu.edu/kirkpams/OpenCSF/Books/csf/source/Extended5DNS.rst"
|
|||
|
|
target="_blank" rel="nofollow">Show Source</a></li>
|
|||
|
|
|
|||
|
|
</ul>
|
|||
|
|
</nav>
|
|||
|
|
|
|||
|
|
|
|||
|
|
<div class="container center">
|
|||
|
|
«  <a id="prevmod" href="Wireless.html">5.7. Wireless Connectivity: Wi-Fi, Bluetooth, and Zigbee</a>
|
|||
|
|
  ::  
|
|||
|
|
<a class="uplink" href="index.html">Contents</a>
|
|||
|
|
  ::  
|
|||
|
|
<a id="nextmod" href="ThreadsOverview.html">6.1. Concurrency with Multithreading</a>  »
|
|||
|
|
|
|||
|
|
</div>
|
|||
|
|
<br />
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
<script type="text/javascript" src="_static/js/jquery-2.1.4.min.js"></script>
|
|||
|
|
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
|
|||
|
|
<script type="text/javascript" src="_static/js/jquery-1.11.4-ui.min.js"></script>
|
|||
|
|
<script type="text/javascript" src="_static/js/forge-0.7.0.min.js"></script>
|
|||
|
|
<script type="text/javascript" src="../../../JSAV/lib/jquery.transit.js"></script>
|
|||
|
|
<script type="text/javascript" src="../../../JSAV/lib/raphael.js"></script>
|
|||
|
|
<script type="text/javascript" src="../../../JSAV/build/JSAV-min.js"></script>
|
|||
|
|
<script type="text/javascript" src="_static/js/config.js"></script>
|
|||
|
|
<script type="text/javascript" src="../../../lib/odsaUtils-min.js"></script>
|
|||
|
|
<script type="text/javascript" src="../../../lib/odsaMOD-min.js"></script>
|
|||
|
|
<script type="text/javascript" src="_static/js/d3-4.13.0.min.js"></script>
|
|||
|
|
<script type="text/javascript" src="_static/js/d3-selection-multi.v1.min.js"></script>
|
|||
|
|
<script type="text/javascript" src="../../../lib/dataStructures.js"></script>
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
<div class="container">
|
|||
|
|
|
|||
|
|
<script>ODSA.SETTINGS.DISP_MOD_COMP = true;ODSA.SETTINGS.MODULE_NAME = "Extended5DNS";ODSA.SETTINGS.MODULE_LONG_NAME = "Extended Example: DNS Client";ODSA.SETTINGS.MODULE_CHAPTER = "The Internet and Connectivity"; ODSA.SETTINGS.BUILD_DATE = "2021-06-14 17:15:25"; ODSA.SETTINGS.BUILD_CMAP = false;JSAV_OPTIONS['lang']='en';JSAV_EXERCISE_OPTIONS['code']='java';</script><div class="section" id="extended-example-dns-client">
|
|||
|
|
<h1>5.8. Extended Example: DNS Client<a class="headerlink" href="Extended5DNS.html#extended-example-dns-client" title="Permalink to this headline">¶</a></h1>
|
|||
|
|
<p>This Extended Example is a minimal client for performing a DNS query for IPv4
|
|||
|
|
addresses. Given a domain name (such as <code class="docutils literal notranslate"><span class="pre">example.com</span></code>), the client sets up
|
|||
|
|
the DNS question in <code class="docutils literal notranslate"><span class="pre">setup_dns_request()</span></code> (lines 200 – 234). The <code class="docutils literal notranslate"><span class="pre">packed</span></code>
|
|||
|
|
attribute of the <code class="docutils literal notranslate"><span class="pre">dns_record_a_t</span></code> (lines 31 – 39) ensures that the compiler
|
|||
|
|
does not add any unnecessary padding that would make the question improperly
|
|||
|
|
structured. The <code class="docutils literal notranslate"><span class="pre">build_domain_qname()</span></code> function (lines 95 – 134) replaces the
|
|||
|
|
dots in the domain name with an integer to denote the length of the next field.
|
|||
|
|
Lines 65 – 82 perform the actual query, sending the request to OpenDNS using a
|
|||
|
|
UDP socket. The client is only designed to support DNS <code class="docutils literal notranslate"><span class="pre">A</span></code> type records for
|
|||
|
|
IPv4. I.e., this client does not support <code class="docutils literal notranslate"><span class="pre">CNAME</span></code>, <code class="docutils literal notranslate"><span class="pre">NS</span></code>, or <code class="docutils literal notranslate"><span class="pre">MX</span></code> records.
|
|||
|
|
The <code class="docutils literal notranslate"><span class="pre">print_dns_response()</span></code> function (lines 153 – 198) will stop if any other
|
|||
|
|
record types are encountered.</p>
|
|||
|
|
<div class="highlight-c border border-dark rounded-lg bg-light px-0 mb-3 notranslate"><table class="highlighttable"><tr><td class="linenos px-0 mx-0"><div class="linenodiv"><pre class="mb-0"> 1
|
|||
|
|
2
|
|||
|
|
3
|
|||
|
|
4
|
|||
|
|
5
|
|||
|
|
6
|
|||
|
|
7
|
|||
|
|
8
|
|||
|
|
9
|
|||
|
|
10
|
|||
|
|
11
|
|||
|
|
12
|
|||
|
|
13
|
|||
|
|
14
|
|||
|
|
15
|
|||
|
|
16
|
|||
|
|
17
|
|||
|
|
18
|
|||
|
|
19
|
|||
|
|
20
|
|||
|
|
21
|
|||
|
|
22
|
|||
|
|
23
|
|||
|
|
24
|
|||
|
|
25
|
|||
|
|
26
|
|||
|
|
27
|
|||
|
|
28
|
|||
|
|
29
|
|||
|
|
30
|
|||
|
|
31
|
|||
|
|
32
|
|||
|
|
33
|
|||
|
|
34
|
|||
|
|
35
|
|||
|
|
36
|
|||
|
|
37
|
|||
|
|
38
|
|||
|
|
39
|
|||
|
|
40
|
|||
|
|
41
|
|||
|
|
42
|
|||
|
|
43
|
|||
|
|
44
|
|||
|
|
45
|
|||
|
|
46
|
|||
|
|
47
|
|||
|
|
48
|
|||
|
|
49
|
|||
|
|
50
|
|||
|
|
51
|
|||
|
|
52
|
|||
|
|
53
|
|||
|
|
54
|
|||
|
|
55
|
|||
|
|
56
|
|||
|
|
57
|
|||
|
|
58
|
|||
|
|
59
|
|||
|
|
60
|
|||
|
|
61
|
|||
|
|
62
|
|||
|
|
63
|
|||
|
|
64
|
|||
|
|
65
|
|||
|
|
66
|
|||
|
|
67
|
|||
|
|
68
|
|||
|
|
69
|
|||
|
|
70
|
|||
|
|
71
|
|||
|
|
72
|
|||
|
|
73
|
|||
|
|
74
|
|||
|
|
75
|
|||
|
|
76
|
|||
|
|
77
|
|||
|
|
78
|
|||
|
|
79
|
|||
|
|
80
|
|||
|
|
81
|
|||
|
|
82
|
|||
|
|
83
|
|||
|
|
84
|
|||
|
|
85
|
|||
|
|
86
|
|||
|
|
87
|
|||
|
|
88
|
|||
|
|
89
|
|||
|
|
90
|
|||
|
|
91
|
|||
|
|
92
|
|||
|
|
93
|
|||
|
|
94
|
|||
|
|
95
|
|||
|
|
96
|
|||
|
|
97
|
|||
|
|
98
|
|||
|
|
99
|
|||
|
|
100
|
|||
|
|
101
|
|||
|
|
102
|
|||
|
|
103
|
|||
|
|
104
|
|||
|
|
105
|
|||
|
|
106
|
|||
|
|
107
|
|||
|
|
108
|
|||
|
|
109
|
|||
|
|
110
|
|||
|
|
111
|
|||
|
|
112
|
|||
|
|
113
|
|||
|
|
114
|
|||
|
|
115
|
|||
|
|
116
|
|||
|
|
117
|
|||
|
|
118
|
|||
|
|
119
|
|||
|
|
120
|
|||
|
|
121
|
|||
|
|
122
|
|||
|
|
123
|
|||
|
|
124
|
|||
|
|
125
|
|||
|
|
126
|
|||
|
|
127
|
|||
|
|
128
|
|||
|
|
129
|
|||
|
|
130
|
|||
|
|
131
|
|||
|
|
132
|
|||
|
|
133
|
|||
|
|
134
|
|||
|
|
135
|
|||
|
|
136
|
|||
|
|
137
|
|||
|
|
138
|
|||
|
|
139
|
|||
|
|
140
|
|||
|
|
141
|
|||
|
|
142
|
|||
|
|
143
|
|||
|
|
144
|
|||
|
|
145
|
|||
|
|
146
|
|||
|
|
147
|
|||
|
|
148
|
|||
|
|
149
|
|||
|
|
150
|
|||
|
|
151
|
|||
|
|
152
|
|||
|
|
153
|
|||
|
|
154
|
|||
|
|
155
|
|||
|
|
156
|
|||
|
|
157
|
|||
|
|
158
|
|||
|
|
159
|
|||
|
|
160
|
|||
|
|
161
|
|||
|
|
162
|
|||
|
|
163
|
|||
|
|
164
|
|||
|
|
165
|
|||
|
|
166
|
|||
|
|
167
|
|||
|
|
168
|
|||
|
|
169
|
|||
|
|
170
|
|||
|
|
171
|
|||
|
|
172
|
|||
|
|
173
|
|||
|
|
174
|
|||
|
|
175
|
|||
|
|
176
|
|||
|
|
177
|
|||
|
|
178
|
|||
|
|
179
|
|||
|
|
180
|
|||
|
|
181
|
|||
|
|
182
|
|||
|
|
183
|
|||
|
|
184
|
|||
|
|
185
|
|||
|
|
186
|
|||
|
|
187
|
|||
|
|
188
|
|||
|
|
189
|
|||
|
|
190
|
|||
|
|
191
|
|||
|
|
192
|
|||
|
|
193
|
|||
|
|
194
|
|||
|
|
195
|
|||
|
|
196
|
|||
|
|
197
|
|||
|
|
198
|
|||
|
|
199
|
|||
|
|
200
|
|||
|
|
201
|
|||
|
|
202
|
|||
|
|
203
|
|||
|
|
204
|
|||
|
|
205
|
|||
|
|
206
|
|||
|
|
207
|
|||
|
|
208
|
|||
|
|
209
|
|||
|
|
210
|
|||
|
|
211
|
|||
|
|
212
|
|||
|
|
213
|
|||
|
|
214
|
|||
|
|
215
|
|||
|
|
216
|
|||
|
|
217
|
|||
|
|
218
|
|||
|
|
219
|
|||
|
|
220
|
|||
|
|
221
|
|||
|
|
222
|
|||
|
|
223
|
|||
|
|
224
|
|||
|
|
225
|
|||
|
|
226
|
|||
|
|
227
|
|||
|
|
228
|
|||
|
|
229
|
|||
|
|
230
|
|||
|
|
231
|
|||
|
|
232
|
|||
|
|
233
|
|||
|
|
234</pre></div></td><td class="code"><div class="highlight bg-light"><pre class="mb-0"><span></span><span class="cp">#include</span> <span class="cpf"><arpa/inet.h></span><span class="cp"></span>
|
|||
|
|
<span class="cp">#include</span> <span class="cpf"><assert.h></span><span class="cp"></span>
|
|||
|
|
<span class="cp">#include</span> <span class="cpf"><inttypes.h></span><span class="cp"></span>
|
|||
|
|
<span class="cp">#include</span> <span class="cpf"><netdb.h></span><span class="cp"></span>
|
|||
|
|
<span class="cp">#include</span> <span class="cpf"><netinet/in.h></span><span class="cp"></span>
|
|||
|
|
<span class="cp">#include</span> <span class="cpf"><stdint.h></span><span class="cp"></span>
|
|||
|
|
<span class="cp">#include</span> <span class="cpf"><stdio.h></span><span class="cp"></span>
|
|||
|
|
<span class="cp">#include</span> <span class="cpf"><stdint.h></span><span class="cp"></span>
|
|||
|
|
<span class="cp">#include</span> <span class="cpf"><stdlib.h></span><span class="cp"></span>
|
|||
|
|
<span class="cp">#include</span> <span class="cpf"><string.h></span><span class="cp"></span>
|
|||
|
|
<span class="cp">#include</span> <span class="cpf"><unistd.h></span><span class="cp"></span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* Structure of the bytes for a DNS header */</span>
|
|||
|
|
<span class="k">typedef</span> <span class="k">struct</span> <span class="p">{</span>
|
|||
|
|
<span class="kt">uint16_t</span> <span class="n">xid</span><span class="p">;</span>
|
|||
|
|
<span class="kt">uint16_t</span> <span class="n">flags</span><span class="p">;</span>
|
|||
|
|
<span class="kt">uint16_t</span> <span class="n">qdcount</span><span class="p">;</span>
|
|||
|
|
<span class="kt">uint16_t</span> <span class="n">ancount</span><span class="p">;</span>
|
|||
|
|
<span class="kt">uint16_t</span> <span class="n">nscount</span><span class="p">;</span>
|
|||
|
|
<span class="kt">uint16_t</span> <span class="n">arcount</span><span class="p">;</span>
|
|||
|
|
<span class="p">}</span> <span class="n">dns_header_t</span><span class="p">;</span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* Structure of the bytes for a DNS question */</span>
|
|||
|
|
<span class="k">typedef</span> <span class="k">struct</span>
|
|||
|
|
<span class="p">{</span>
|
|||
|
|
<span class="kt">char</span> <span class="o">*</span><span class="n">name</span><span class="p">;</span>
|
|||
|
|
<span class="kt">uint16_t</span> <span class="n">dnstype</span><span class="p">;</span>
|
|||
|
|
<span class="kt">uint16_t</span> <span class="n">dnsclass</span><span class="p">;</span>
|
|||
|
|
<span class="p">}</span> <span class="n">dns_question_t</span><span class="p">;</span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* Structure of the bytes for an IPv4 answer */</span>
|
|||
|
|
<span class="k">typedef</span> <span class="k">struct</span> <span class="p">{</span>
|
|||
|
|
<span class="kt">uint16_t</span> <span class="n">compression</span><span class="p">;</span>
|
|||
|
|
<span class="kt">uint16_t</span> <span class="n">type</span><span class="p">;</span>
|
|||
|
|
<span class="kt">uint16_t</span> <span class="n">class</span><span class="p">;</span>
|
|||
|
|
<span class="kt">uint32_t</span> <span class="n">ttl</span><span class="p">;</span>
|
|||
|
|
<span class="kt">uint16_t</span> <span class="n">length</span><span class="p">;</span>
|
|||
|
|
<span class="k">struct</span> <span class="n">in_addr</span> <span class="n">addr</span><span class="p">;</span>
|
|||
|
|
<span class="p">}</span> <span class="n">__attribute__</span><span class="p">((</span><span class="n">packed</span><span class="p">))</span> <span class="n">dns_record_a_t</span><span class="p">;</span>
|
|||
|
|
|
|||
|
|
<span class="kt">char</span> <span class="o">*</span> <span class="nf">build_domain_qname</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="p">);</span>
|
|||
|
|
<span class="kt">void</span> <span class="nf">print_byte_block</span> <span class="p">(</span><span class="kt">uint8_t</span> <span class="o">*</span><span class="p">,</span> <span class="kt">size_t</span><span class="p">);</span>
|
|||
|
|
<span class="kt">void</span> <span class="nf">print_dns_response</span> <span class="p">(</span><span class="kt">uint8_t</span> <span class="o">*</span><span class="p">);</span>
|
|||
|
|
<span class="kt">uint8_t</span> <span class="o">*</span> <span class="nf">setup_dns_request</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="p">,</span> <span class="kt">size_t</span> <span class="o">*</span><span class="p">);</span>
|
|||
|
|
|
|||
|
|
<span class="kt">int</span>
|
|||
|
|
<span class="nf">main</span> <span class="p">(</span><span class="kt">int</span> <span class="n">argc</span><span class="p">,</span> <span class="kt">char</span> <span class="o">*</span><span class="n">argv</span><span class="p">[])</span>
|
|||
|
|
<span class="p">{</span>
|
|||
|
|
<span class="k">if</span> <span class="p">(</span><span class="n">argc</span> <span class="o">!=</span> <span class="mi">2</span><span class="p">)</span>
|
|||
|
|
<span class="p">{</span>
|
|||
|
|
<span class="n">fprintf</span> <span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"ERROR: Must pass a domain name</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
|
|||
|
|
<span class="k">return</span> <span class="mi">1</span><span class="p">;</span>
|
|||
|
|
<span class="p">}</span>
|
|||
|
|
|
|||
|
|
<span class="kt">char</span> <span class="o">*</span><span class="n">hostname</span> <span class="o">=</span> <span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">];</span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* Set up the packet and get the length */</span>
|
|||
|
|
<span class="kt">size_t</span> <span class="n">packetlen</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
|
|||
|
|
<span class="kt">uint8_t</span> <span class="o">*</span><span class="n">packet</span> <span class="o">=</span> <span class="n">setup_dns_request</span> <span class="p">(</span><span class="n">hostname</span><span class="p">,</span> <span class="o">&</span><span class="n">packetlen</span><span class="p">);</span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* Print the raw bytes formatted as 0000 0000 0000 ... */</span>
|
|||
|
|
<span class="n">printf</span> <span class="p">(</span><span class="s">"Lookup %s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">hostname</span><span class="p">);</span>
|
|||
|
|
<span class="n">print_byte_block</span> <span class="p">(</span><span class="n">packet</span><span class="p">,</span> <span class="n">packetlen</span><span class="p">);</span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* Send the packet to OpenDNS. Create an IPv4 UDP socket to</span>
|
|||
|
|
<span class="cm"> 208.67.222.222 (0xd043dede), the IP address for OpenDNS.</span>
|
|||
|
|
<span class="cm"> DNS servers listen on port 53. */</span>
|
|||
|
|
<span class="kt">int</span> <span class="n">socketfd</span> <span class="o">=</span> <span class="n">socket</span> <span class="p">(</span><span class="n">AF_INET</span><span class="p">,</span> <span class="n">SOCK_DGRAM</span><span class="p">,</span> <span class="mi">0</span><span class="p">);</span>
|
|||
|
|
<span class="k">struct</span> <span class="n">sockaddr_in</span> <span class="n">address</span><span class="p">;</span>
|
|||
|
|
<span class="n">address</span><span class="p">.</span><span class="n">sin_family</span> <span class="o">=</span> <span class="n">AF_INET</span><span class="p">;</span>
|
|||
|
|
<span class="n">address</span><span class="p">.</span><span class="n">sin_addr</span><span class="p">.</span><span class="n">s_addr</span> <span class="o">=</span> <span class="n">htonl</span> <span class="p">(</span><span class="mh">0xd043dede</span><span class="p">);</span>
|
|||
|
|
<span class="n">address</span><span class="p">.</span><span class="n">sin_port</span> <span class="o">=</span> <span class="n">htons</span> <span class="p">(</span><span class="mi">53</span><span class="p">);</span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* Send the request and get the response */</span>
|
|||
|
|
<span class="n">sendto</span> <span class="p">(</span><span class="n">socketfd</span><span class="p">,</span> <span class="n">packet</span><span class="p">,</span> <span class="n">packetlen</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="p">(</span><span class="k">struct</span> <span class="n">sockaddr</span> <span class="o">*</span><span class="p">)</span><span class="o">&</span><span class="n">address</span><span class="p">,</span>
|
|||
|
|
<span class="p">(</span><span class="kt">socklen_t</span><span class="p">)</span><span class="k">sizeof</span> <span class="p">(</span><span class="n">address</span><span class="p">));</span>
|
|||
|
|
|
|||
|
|
<span class="kt">socklen_t</span> <span class="n">length</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
|
|||
|
|
<span class="kt">uint8_t</span> <span class="n">response</span><span class="p">[</span><span class="mi">512</span><span class="p">];</span>
|
|||
|
|
<span class="n">memset</span> <span class="p">(</span><span class="o">&</span><span class="n">response</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">512</span><span class="p">);</span>
|
|||
|
|
<span class="kt">ssize_t</span> <span class="n">bytes</span> <span class="o">=</span> <span class="n">recvfrom</span> <span class="p">(</span><span class="n">socketfd</span><span class="p">,</span> <span class="n">response</span><span class="p">,</span> <span class="mi">512</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span>
|
|||
|
|
<span class="p">(</span><span class="k">struct</span> <span class="n">sockaddr</span> <span class="o">*</span><span class="p">)</span><span class="o">&</span><span class="n">address</span><span class="p">,</span> <span class="o">&</span><span class="n">length</span><span class="p">);</span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* Print the raw bytes formatted as 0000 0000 0000 ... */</span>
|
|||
|
|
<span class="n">printf</span> <span class="p">(</span><span class="s">"Received %zd bytes from %s:</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">bytes</span><span class="p">,</span>
|
|||
|
|
<span class="n">inet_ntoa</span> <span class="p">(</span><span class="n">address</span><span class="p">.</span><span class="n">sin_addr</span><span class="p">));</span>
|
|||
|
|
<span class="n">print_byte_block</span> <span class="p">(</span><span class="n">response</span><span class="p">,</span> <span class="n">bytes</span><span class="p">);</span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* Parse the DNS response into a struct and print the result */</span>
|
|||
|
|
<span class="n">print_dns_response</span> <span class="p">(</span><span class="n">response</span><span class="p">);</span>
|
|||
|
|
|
|||
|
|
<span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
|
|||
|
|
<span class="p">}</span>
|
|||
|
|
|
|||
|
|
<span class="kt">char</span> <span class="o">*</span>
|
|||
|
|
<span class="nf">build_domain_qname</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="n">hostname</span><span class="p">)</span>
|
|||
|
|
<span class="p">{</span>
|
|||
|
|
<span class="n">assert</span> <span class="p">(</span><span class="n">hostname</span> <span class="o">!=</span> <span class="nb">NULL</span><span class="p">);</span>
|
|||
|
|
|
|||
|
|
<span class="kt">char</span> <span class="o">*</span><span class="n">name</span> <span class="o">=</span> <span class="n">calloc</span> <span class="p">(</span><span class="n">strlen</span> <span class="p">(</span><span class="n">hostname</span><span class="p">)</span> <span class="o">+</span> <span class="mi">2</span><span class="p">,</span> <span class="k">sizeof</span> <span class="p">(</span><span class="kt">uint8_t</span><span class="p">));</span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* Leave the first byte blank for the first field length */</span>
|
|||
|
|
<span class="n">memcpy</span> <span class="p">(</span><span class="n">name</span> <span class="o">+</span> <span class="mi">1</span><span class="p">,</span> <span class="n">hostname</span><span class="p">,</span> <span class="n">strlen</span> <span class="p">(</span><span class="n">hostname</span><span class="p">));</span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* Example:</span>
|
|||
|
|
<span class="cm"> +---+---+---+---+---+---+---+---+---+---+---+</span>
|
|||
|
|
<span class="cm"> | a | b | c | . | d | e | . | c | o | m | \0|</span>
|
|||
|
|
<span class="cm"> +---+---+---+---+---+---+---+---+---+---+---+</span>
|
|||
|
|
|
|||
|
|
<span class="cm"> becomes:</span>
|
|||
|
|
<span class="cm"> +---+---+---+---+---+---+---+---+---+---+---+---+</span>
|
|||
|
|
<span class="cm"> | 3 | a | b | c | 2 | d | e | 3 | c | o | m | 0 |</span>
|
|||
|
|
<span class="cm"> +---+---+---+---+---+---+---+---+---+---+---+---+</span>
|
|||
|
|
<span class="cm"> */</span>
|
|||
|
|
|
|||
|
|
<span class="kt">uint8_t</span> <span class="n">count</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
|
|||
|
|
<span class="kt">uint8_t</span> <span class="o">*</span><span class="n">prev</span> <span class="o">=</span> <span class="p">(</span><span class="kt">uint8_t</span> <span class="o">*</span><span class="p">)</span><span class="n">name</span><span class="p">;</span>
|
|||
|
|
<span class="k">for</span> <span class="p">(</span><span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="n">i</span> <span class="o"><</span> <span class="n">strlen</span> <span class="p">(</span><span class="n">hostname</span><span class="p">);</span> <span class="n">i</span><span class="o">++</span><span class="p">)</span>
|
|||
|
|
<span class="p">{</span>
|
|||
|
|
<span class="cm">/* Look for the next ., then copy the length back to the</span>
|
|||
|
|
<span class="cm"> location of the previous . */</span>
|
|||
|
|
<span class="k">if</span> <span class="p">(</span><span class="n">hostname</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">==</span> <span class="sc">'.'</span><span class="p">)</span>
|
|||
|
|
<span class="p">{</span>
|
|||
|
|
<span class="o">*</span><span class="n">prev</span> <span class="o">=</span> <span class="n">count</span><span class="p">;</span>
|
|||
|
|
<span class="n">prev</span> <span class="o">=</span> <span class="p">(</span><span class="kt">uint8_t</span> <span class="o">*</span><span class="p">)</span><span class="n">name</span> <span class="o">+</span> <span class="n">i</span> <span class="o">+</span> <span class="mi">1</span><span class="p">;</span>
|
|||
|
|
<span class="n">count</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
|
|||
|
|
<span class="p">}</span>
|
|||
|
|
<span class="k">else</span>
|
|||
|
|
<span class="n">count</span><span class="o">++</span><span class="p">;</span>
|
|||
|
|
<span class="p">}</span>
|
|||
|
|
<span class="o">*</span><span class="n">prev</span> <span class="o">=</span> <span class="n">count</span><span class="p">;</span>
|
|||
|
|
|
|||
|
|
<span class="k">return</span> <span class="n">name</span><span class="p">;</span>
|
|||
|
|
<span class="p">}</span>
|
|||
|
|
|
|||
|
|
<span class="kt">void</span>
|
|||
|
|
<span class="nf">print_byte_block</span> <span class="p">(</span><span class="kt">uint8_t</span> <span class="o">*</span><span class="n">bytes</span><span class="p">,</span> <span class="kt">size_t</span> <span class="n">length</span><span class="p">)</span>
|
|||
|
|
<span class="p">{</span>
|
|||
|
|
<span class="n">printf</span> <span class="p">(</span><span class="s">" "</span><span class="p">);</span>
|
|||
|
|
<span class="k">for</span> <span class="p">(</span><span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="n">i</span> <span class="o"><</span> <span class="n">length</span><span class="p">;</span> <span class="n">i</span><span class="o">++</span><span class="p">)</span>
|
|||
|
|
<span class="p">{</span>
|
|||
|
|
<span class="n">printf</span> <span class="p">(</span><span class="s">"%02x"</span><span class="p">,</span> <span class="n">bytes</span><span class="p">[</span><span class="n">i</span><span class="p">]);</span>
|
|||
|
|
<span class="k">if</span> <span class="p">(</span><span class="n">i</span> <span class="o">==</span> <span class="n">length</span> <span class="o">-</span> <span class="mi">1</span><span class="p">)</span>
|
|||
|
|
<span class="n">printf</span> <span class="p">(</span><span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
|
|||
|
|
<span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">i</span> <span class="o">+</span> <span class="mi">1</span><span class="p">)</span> <span class="o">%</span> <span class="mi">16</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
|
|||
|
|
<span class="n">printf</span> <span class="p">(</span><span class="s">"</span><span class="se">\n</span><span class="s"> "</span><span class="p">);</span>
|
|||
|
|
<span class="k">else</span> <span class="k">if</span> <span class="p">((</span><span class="n">i</span> <span class="o">%</span> <span class="mi">2</span><span class="p">)</span> <span class="o">!=</span> <span class="mi">0</span><span class="p">)</span>
|
|||
|
|
<span class="n">printf</span> <span class="p">(</span><span class="s">" "</span><span class="p">);</span>
|
|||
|
|
<span class="p">}</span>
|
|||
|
|
<span class="n">printf</span> <span class="p">(</span><span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
|
|||
|
|
<span class="p">}</span>
|
|||
|
|
|
|||
|
|
<span class="kt">void</span>
|
|||
|
|
<span class="nf">print_dns_response</span> <span class="p">(</span><span class="kt">uint8_t</span> <span class="o">*</span><span class="n">response</span><span class="p">)</span>
|
|||
|
|
<span class="p">{</span>
|
|||
|
|
<span class="cm">/* First, check the header for an error response code */</span>
|
|||
|
|
<span class="n">dns_header_t</span> <span class="o">*</span><span class="n">response_header</span> <span class="o">=</span> <span class="p">(</span><span class="n">dns_header_t</span> <span class="o">*</span><span class="p">)</span><span class="n">response</span><span class="p">;</span>
|
|||
|
|
<span class="k">if</span> <span class="p">((</span><span class="n">ntohs</span> <span class="p">(</span><span class="n">response_header</span><span class="o">-></span><span class="n">flags</span><span class="p">)</span> <span class="o">&</span> <span class="mh">0xf</span><span class="p">)</span> <span class="o">!=</span> <span class="mi">0</span><span class="p">)</span>
|
|||
|
|
<span class="p">{</span>
|
|||
|
|
<span class="n">fprintf</span> <span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"Failed to get response</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
|
|||
|
|
<span class="k">return</span><span class="p">;</span>
|
|||
|
|
<span class="p">}</span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* Reconstruct the question */</span>
|
|||
|
|
<span class="kt">uint8_t</span> <span class="o">*</span><span class="n">start_of_question</span> <span class="o">=</span> <span class="n">response</span> <span class="o">+</span> <span class="k">sizeof</span> <span class="p">(</span><span class="n">dns_header_t</span><span class="p">);</span>
|
|||
|
|
<span class="n">dns_question_t</span> <span class="o">*</span><span class="n">questions</span>
|
|||
|
|
<span class="o">=</span> <span class="n">calloc</span> <span class="p">(</span><span class="k">sizeof</span> <span class="p">(</span><span class="n">dns_question_t</span><span class="p">),</span> <span class="n">response_header</span><span class="o">-></span><span class="n">ancount</span><span class="p">);</span>
|
|||
|
|
<span class="k">for</span> <span class="p">(</span><span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="n">i</span> <span class="o"><</span> <span class="n">ntohs</span> <span class="p">(</span><span class="n">response_header</span><span class="o">-></span><span class="n">ancount</span><span class="p">);</span> <span class="n">i</span><span class="o">++</span><span class="p">)</span>
|
|||
|
|
<span class="p">{</span>
|
|||
|
|
<span class="n">questions</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">name</span> <span class="o">=</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="p">)</span><span class="n">start_of_question</span><span class="p">;</span>
|
|||
|
|
<span class="kt">uint8_t</span> <span class="n">total</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
|
|||
|
|
<span class="kt">uint8_t</span> <span class="o">*</span><span class="n">field_length</span> <span class="o">=</span> <span class="p">(</span><span class="kt">uint8_t</span> <span class="o">*</span><span class="p">)</span><span class="n">questions</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">name</span><span class="p">;</span>
|
|||
|
|
<span class="k">while</span> <span class="p">(</span><span class="o">*</span><span class="n">field_length</span> <span class="o">!=</span> <span class="mi">0</span><span class="p">)</span>
|
|||
|
|
<span class="p">{</span>
|
|||
|
|
<span class="n">total</span> <span class="o">+=</span> <span class="o">*</span><span class="n">field_length</span> <span class="o">+</span> <span class="mi">1</span><span class="p">;</span>
|
|||
|
|
<span class="o">*</span><span class="n">field_length</span> <span class="o">=</span> <span class="sc">'.'</span><span class="p">;</span>
|
|||
|
|
<span class="n">field_length</span> <span class="o">=</span> <span class="p">(</span><span class="kt">uint8_t</span> <span class="o">*</span><span class="p">)</span><span class="n">questions</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">name</span> <span class="o">+</span> <span class="n">total</span><span class="p">;</span>
|
|||
|
|
<span class="p">}</span>
|
|||
|
|
<span class="n">questions</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">name</span><span class="o">++</span><span class="p">;</span>
|
|||
|
|
<span class="cm">/* Skip null byte, qtype, and qclass */</span>
|
|||
|
|
<span class="n">start_of_question</span> <span class="o">=</span> <span class="n">field_length</span> <span class="o">+</span> <span class="mi">5</span><span class="p">;</span>
|
|||
|
|
<span class="p">}</span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* The records start right after the question section. For each record,</span>
|
|||
|
|
<span class="cm"> confirm that it is an A record (only type supported). If any are not</span>
|
|||
|
|
<span class="cm"> an A-type, then return. */</span>
|
|||
|
|
<span class="n">dns_record_a_t</span> <span class="o">*</span><span class="n">records</span> <span class="o">=</span> <span class="p">(</span><span class="n">dns_record_a_t</span> <span class="o">*</span><span class="p">)</span><span class="n">start_of_question</span><span class="p">;</span>
|
|||
|
|
<span class="k">for</span> <span class="p">(</span><span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="n">i</span> <span class="o"><</span> <span class="n">ntohs</span> <span class="p">(</span><span class="n">response_header</span><span class="o">-></span><span class="n">ancount</span><span class="p">);</span> <span class="n">i</span><span class="o">++</span><span class="p">)</span>
|
|||
|
|
<span class="p">{</span>
|
|||
|
|
<span class="n">printf</span> <span class="p">(</span><span class="s">"Record for %s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">questions</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">name</span><span class="p">);</span>
|
|||
|
|
<span class="n">printf</span> <span class="p">(</span><span class="s">" TYPE: %"</span> <span class="n">PRId16</span> <span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">ntohs</span> <span class="p">(</span><span class="n">records</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">type</span><span class="p">));</span>
|
|||
|
|
<span class="n">printf</span> <span class="p">(</span><span class="s">" CLASS: %"</span> <span class="n">PRId16</span> <span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">ntohs</span> <span class="p">(</span><span class="n">records</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">class</span><span class="p">));</span>
|
|||
|
|
<span class="n">printf</span> <span class="p">(</span><span class="s">" TTL: %"</span> <span class="n">PRIx32</span> <span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">ntohl</span> <span class="p">(</span><span class="n">records</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">ttl</span><span class="p">));</span>
|
|||
|
|
<span class="n">printf</span> <span class="p">(</span><span class="s">" IPv4: %08"</span> <span class="n">PRIx32</span> <span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span>
|
|||
|
|
<span class="n">ntohl</span> <span class="p">((</span><span class="kt">uint32_t</span><span class="p">)</span><span class="n">records</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">addr</span><span class="p">.</span><span class="n">s_addr</span><span class="p">));</span>
|
|||
|
|
<span class="n">printf</span> <span class="p">(</span><span class="s">" IPv4: %s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">inet_ntoa</span> <span class="p">(</span><span class="n">records</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">addr</span><span class="p">));</span>
|
|||
|
|
<span class="p">}</span>
|
|||
|
|
<span class="p">}</span>
|
|||
|
|
|
|||
|
|
<span class="kt">uint8_t</span> <span class="o">*</span>
|
|||
|
|
<span class="nf">setup_dns_request</span> <span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="n">hostname</span><span class="p">,</span> <span class="kt">size_t</span> <span class="o">*</span><span class="n">packetlen</span><span class="p">)</span>
|
|||
|
|
<span class="p">{</span>
|
|||
|
|
<span class="cm">/* Set up the DNS header */</span>
|
|||
|
|
<span class="n">dns_header_t</span> <span class="n">header</span><span class="p">;</span>
|
|||
|
|
<span class="n">memset</span> <span class="p">(</span><span class="o">&</span><span class="n">header</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="k">sizeof</span> <span class="p">(</span><span class="n">dns_header_t</span><span class="p">));</span>
|
|||
|
|
<span class="n">header</span><span class="p">.</span><span class="n">xid</span><span class="o">=</span> <span class="n">htons</span> <span class="p">(</span><span class="mh">0x1234</span><span class="p">);</span> <span class="cm">/* Randomly chosen ID */</span>
|
|||
|
|
<span class="n">header</span><span class="p">.</span><span class="n">flags</span> <span class="o">=</span> <span class="n">htons</span> <span class="p">(</span><span class="mh">0x0100</span><span class="p">);</span> <span class="cm">/* Q=0, RD=1 */</span>
|
|||
|
|
<span class="n">header</span><span class="p">.</span><span class="n">qdcount</span> <span class="o">=</span> <span class="n">htons</span> <span class="p">(</span><span class="mi">1</span><span class="p">);</span> <span class="cm">/* Sending 1 question */</span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* Set up the DNS question */</span>
|
|||
|
|
<span class="n">dns_question_t</span> <span class="n">question</span><span class="p">;</span>
|
|||
|
|
<span class="n">question</span><span class="p">.</span><span class="n">dnstype</span> <span class="o">=</span> <span class="n">htons</span> <span class="p">(</span><span class="mi">1</span><span class="p">);</span> <span class="cm">/* QTYPE 1=A */</span>
|
|||
|
|
<span class="n">question</span><span class="p">.</span><span class="n">dnsclass</span> <span class="o">=</span> <span class="n">htons</span> <span class="p">(</span><span class="mi">1</span><span class="p">);</span> <span class="cm">/* QCLASS 1=IN */</span>
|
|||
|
|
<span class="n">question</span><span class="p">.</span><span class="n">name</span> <span class="o">=</span> <span class="n">build_domain_qname</span> <span class="p">(</span><span class="n">hostname</span><span class="p">);</span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* Copy all fields into a single, concatenated packet */</span>
|
|||
|
|
<span class="o">*</span><span class="n">packetlen</span> <span class="o">=</span> <span class="k">sizeof</span> <span class="p">(</span><span class="n">header</span><span class="p">)</span> <span class="o">+</span> <span class="n">strlen</span> <span class="p">(</span><span class="n">hostname</span><span class="p">)</span> <span class="o">+</span> <span class="mi">2</span>
|
|||
|
|
<span class="o">+</span> <span class="k">sizeof</span> <span class="p">(</span><span class="n">question</span><span class="p">.</span><span class="n">dnstype</span><span class="p">)</span> <span class="o">+</span> <span class="k">sizeof</span> <span class="p">(</span><span class="n">question</span><span class="p">.</span><span class="n">dnsclass</span><span class="p">);</span>
|
|||
|
|
<span class="kt">uint8_t</span> <span class="o">*</span><span class="n">packet</span> <span class="o">=</span> <span class="n">calloc</span> <span class="p">(</span><span class="o">*</span><span class="n">packetlen</span><span class="p">,</span> <span class="k">sizeof</span> <span class="p">(</span><span class="kt">uint8_t</span><span class="p">));</span>
|
|||
|
|
<span class="kt">uint8_t</span> <span class="o">*</span><span class="n">p</span> <span class="o">=</span> <span class="p">(</span><span class="kt">uint8_t</span> <span class="o">*</span><span class="p">)</span><span class="n">packet</span><span class="p">;</span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* Copy the header first */</span>
|
|||
|
|
<span class="n">memcpy</span> <span class="p">(</span><span class="n">p</span><span class="p">,</span> <span class="o">&</span><span class="n">header</span><span class="p">,</span> <span class="k">sizeof</span> <span class="p">(</span><span class="n">header</span><span class="p">));</span>
|
|||
|
|
<span class="n">p</span> <span class="o">+=</span> <span class="k">sizeof</span> <span class="p">(</span><span class="n">header</span><span class="p">);</span>
|
|||
|
|
|
|||
|
|
<span class="cm">/* Copy the question name, QTYPE, and QCLASS fields */</span>
|
|||
|
|
<span class="n">memcpy</span> <span class="p">(</span><span class="n">p</span><span class="p">,</span> <span class="n">question</span><span class="p">.</span><span class="n">name</span><span class="p">,</span> <span class="n">strlen</span> <span class="p">(</span><span class="n">hostname</span><span class="p">)</span> <span class="o">+</span> <span class="mi">2</span><span class="p">);</span>
|
|||
|
|
<span class="n">p</span> <span class="o">+=</span> <span class="n">strlen</span> <span class="p">(</span><span class="n">hostname</span><span class="p">)</span> <span class="o">+</span> <span class="mi">2</span><span class="p">;</span>
|
|||
|
|
<span class="n">memcpy</span> <span class="p">(</span><span class="n">p</span><span class="p">,</span> <span class="o">&</span><span class="n">question</span><span class="p">.</span><span class="n">dnstype</span><span class="p">,</span> <span class="k">sizeof</span> <span class="p">(</span><span class="n">question</span><span class="p">.</span><span class="n">dnstype</span><span class="p">));</span>
|
|||
|
|
<span class="n">p</span> <span class="o">+=</span> <span class="k">sizeof</span> <span class="p">(</span><span class="n">question</span><span class="p">.</span><span class="n">dnstype</span><span class="p">);</span>
|
|||
|
|
<span class="n">memcpy</span> <span class="p">(</span><span class="n">p</span><span class="p">,</span> <span class="o">&</span><span class="n">question</span><span class="p">.</span><span class="n">dnsclass</span><span class="p">,</span> <span class="k">sizeof</span> <span class="p">(</span><span class="n">question</span><span class="p">.</span><span class="n">dnsclass</span><span class="p">));</span>
|
|||
|
|
|
|||
|
|
<span class="k">return</span> <span class="n">packet</span><span class="p">;</span>
|
|||
|
|
<span class="p">}</span>
|
|||
|
|
</pre></div>
|
|||
|
|
</td></tr></table></div>
|
|||
|
|
</div>
|
|||
|
|
|
|||
|
|
|
|||
|
|
</div>
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
<div class="container">
|
|||
|
|
|
|||
|
|
<div class="mt-4 container center">
|
|||
|
|
«  <a id="prevmod1" href="Wireless.html">5.7. Wireless Connectivity: Wi-Fi, Bluetooth, and Zigbee</a>
|
|||
|
|
  ::  
|
|||
|
|
<a class="uplink" href="index.html">Contents</a>
|
|||
|
|
  ::  
|
|||
|
|
<a id="nextmod1" href="ThreadsOverview.html">6.1. Concurrency with Multithreading</a>  »
|
|||
|
|
</div>
|
|||
|
|
|
|||
|
|
|
|||
|
|
</div>
|
|||
|
|
|
|||
|
|
<br />
|
|||
|
|
|
|||
|
|
<div class="row jmu-dark-purple-bg">
|
|||
|
|
<div class="col-md-12">
|
|||
|
|
<center>
|
|||
|
|
<a id="contact_us" class="btn button-link-no-blue jmu-gold" rel="nofollow" href="mailto:webmaster@opencsf.org" role="button">Contact Us</a>
|
|||
|
|
<a id="license" class="btn button-link-no-blue jmu-gold" rel="nofollow" href="https://w3.cs.jmu.edu/kirkpams/OpenCSF/lib/license.html" target="_blank">License</a>
|
|||
|
|
</center>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
<script src="_static/js/popper.js-1.14.7-min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script>
|
|||
|
|
<script src="_static/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script>
|
|||
|
|
</body>
|
|||
|
|
</html>
|