掌握Asterisk开发：AGI接口详解与高级应用
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更新于2025-01-03
收藏 529KB PDF 举报 本章节深入探讨了Asterisk Gateway Interface (AGI)，一个在Asterisk电话系统中发挥关键作用的接口。AGI提供了一个标准化的途径，使得外部程序能够控制Asterisk的呼叫路由和处理逻辑，从而实现复杂功能，如高级自动化操作、数据库交互（例如PostgreSQL或MySQL）以及访问其他外部资源。它极大地增强了Asterisk的灵活性和扩展性，使原本难以实现的任务变得简单可行。
对于已经具备编程技能的读者，这一章将着重于介绍如何利用AGI进行通信和编写脚本。章节内容不涉及基础编程教学，因此假设读者已具有编程能力。如果你是初学者或者对编程一无所知，那么这个章节可能不适合你，建议跳过直接阅读后续章节。
在本章中，我们将逐步讲解AGI的基本原理和工作流程，包括：
1. **AGI概述**：介绍AGI的概念，它是如何作为Asterisk与外部应用程序之间的一种交互方式。
2. **AGI通信协议**：讨论AGI使用的通信协议，包括命令行接口（CLI）和标准输入/输出，以及数据格式和编码。
3. **AGI脚本结构**：解析AGI脚本的语法和组成部分，如函数调用、变量管理以及错误处理机制。
4. **AGI与Asterisk事件处理**：了解AGI如何响应和触发Asterisk中的特定事件，如呼叫接通、挂断、转移等。
5. **数据库集成示例**：演示如何通过AGI与数据库交互，执行查询、更新操作来支持呼叫处理决策。
6. **外部资源访问**：介绍如何通过AGI调用API或其他外部服务，如邮件服务器、Web服务等，以扩展Asterisk的功能。
7. **安全性和权限管理**：讨论如何确保AGI脚本的安全性，以及如何设置权限，仅允许授权的程序执行特定任务。
8. **最佳实践和案例研究**：分享实际应用中使用AGI的案例，以便理解和应用到实际项目中。
通过本章的学习，读者将建立起对AGI的全面理解，并能够在自己的Asterisk项目中熟练地集成和定制AGI脚本，从而提升系统的效率和定制化能力。
This is the Title of the Book, eMatter Edition
Copyright © 2005 O’Reilly & Associates, Inc. All rights reserved.
Writing AGI Scripts in Perl
|
159
Writing AGI Scripts in Perl
Asterisk comes with a sample AGI script called agi-test.agi. Let’s step through the file
while we cover the core concepts of AGI programming. While this particular script is
written in Perl, please remember that your own AGI programs may be written in
almost any programming language. Just to prove it, we’re going to cover AGI pro-
gramming in a couple of other languages later in the chapter.
Let’s get started! We’ll look at each section of the code in turn, and describe what it
does.
#!/usr/bin/perl
This line tells the system that this particular script is written in Perl, so it should use
the Perl interpreter to execute the script. If you’ve done much Linux or Unix script-
ing, this line should be familiar to you. This line assumes, of course, that your Perl
binary is located in the /usr/bin/ directory. Change this to match the location of your
Perl interpreter.
use strict;
use strict tells Perl to act, well, strict about possible programming errors, such as
undeclared variables. While not absolutely necessary, enabling this will help you
avoid common programming pitfalls.
$|=1;
This line tells Perl not to buffer its output—in other words, that it should write any
data immediately, instead of waiting for a block of data before outputting it. You’ll
see this as a recurrent theme throughout the chapter.
You should always use unbuffered output when writing AGI scripts.
Otherwise, your AGI may not work as expected, because Asterisk may
be waiting for the output of your program, while your program thinks
it has sent the output to Asterisk and is waiting for a response.
# Set up some variables
my %AGI; my $tests = 0; my $fail = 0; my $pass = 0;
Here, we set up four variables. The first is a hash called AGI, which is used to store
the variables that Asterisk passes to our script at the beginning of the AGI session.
The next three are scalar values, used to count the total number of tests, the number
of failed tests, and the number of passed tests, respectively.
while(<STDIN>) {
chomp;
last unless length($_);
if (/^agi_(\w+)\:\s+(.*)$/) {
$AGI{$1} = $2;
}
}
,ch09.22228 Page 159 Wednesday, August 31, 2005 4:58 PM
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