PJSIP C++开发指南：PJSUA2 高级API概述

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"PJSUA2Doc.pdf 是一份关于PJSIP的C++开发文档，它详细介绍了PJSIP的关键类和API接口。这份文档由Sauw Ming Liong和Benny Prijono于2018年9月5日发布，版本为1.0-alpha。" PJSIP是一个开源的多媒体通信库，它提供了SIP（会话初始化协议）的实现，支持VoIP、即时消息、视频通话等多种功能。PJSUA2是PJSIP的一个高级API，以C++编写，便于开发者构建跨平台的应用程序。文档首先介绍了PJSIP的基础知识，包括如何开始使用PJSIP以及获取相关文档的途径。接着，它提供了开发指导和注意事项，如遵循的开发原则、平台兼容性考虑、选择合适的API、网络和基础设施的考量、以及声音设备的处理。在“PJSUA2 - 高级API”部分，文档详细阐述了PJSUA2的主要类，如Endpoint、Account、Uri、Call等，这些都是构建PJSIP应用的核心组件。其中，Endpoint是PJSIP的核心，它代表了一个运行SIP协议栈的实例。开发人员需要实例化Endpoint来创建SIP库，并进行初始化设置，包括配置传输方式（如TCP、UDP或TLS）。创建Transport是实现网络通信的关键，可以支持不安全和安全的连接。启动Endpoint后，就可以开始处理SIP会话和账户。账户管理是PJSIP应用的重要部分，文档详细讲解了如何创建和管理账户，包括继承Account类来自定义行为、创建无用户账户以及添加认证信息。此外，还涉及到了呼叫管理，包括发起、接收、挂断和转移呼叫，以及媒体操作如音频和视频的处理。 PJSUA2也支持与其他语言的互操作，如Java、Python和C#，文档中给出了这些语言的SWIG模块构建方法，使得PJSIP的功能可以无缝集成到多语言环境中。这份PJSIP的C++开发文档为开发者提供了一个全面的指南，涵盖了从基础概念到实际开发的各个环节，帮助他们理解并有效地利用PJSIP库来构建功能丰富的通信应用程序。通过深入学习和实践，开发者可以掌握如何在各种环境中构建高效的SIP解决方案。

PJSUA2 Documentation, Release 1.0-alpha

3.1.4 Call

This class represents an ongoing call (or speaking technically, an INVITE session) and can be used to manipulate it,

such as to answer the call, hangup the call, put the call on hold, transfer the call, etc.

3.1.5 Buddy

This class represents a remote buddy (a person, or a SIP endpoint). You can subscribe to presence status of a buddy to

know whether the buddy is online/ofﬂine/etc., and you can send and receive instant messages to/from the buddy.

3.2 General Concepts

3.2.1 Class Usage Patterns

With the methods of the main classes above, you will be able to invoke various operations to the object quite easily. But

how can we get events/notiﬁcations from these classes? Each of the main classes above (except Media) will get their

events in the callback methods. So to handle these events, just derive a class from the corresponding class (Endpoint,

Call, Account, or Buddy) and implement/override the relevant method (depending on which event you want to handle).

More will be explained in later sections.

3.2.2 Error Handling

We use exceptions as means to report error, as this would make the program ﬂows more naturally. Operations which

yield error will raise Error exception. If you prefer to display the error in more structured manner, the Error class has

several members to explain the error, such as the operation name that raised the error, the error code, and the error

message itself.

3.2.3 Asynchronous Operations

If you have developed applications with PJSIP, you’ll know about this already. In PJSIP, all operations that involve

sending and receiving SIP messages are asynchronous, meaning that the function that invokes the operation will

complete immediately, and you will be given the completion status as callbacks.

Take a look for example the makeCall() method of the Call class. This function is used to initiate outgoing call to a

destination. When this function returns successfully, it does not mean that the call has been established, but rather it

means that the call has been initiated successfully. You will be given the report of the call progress and/or completion

in the onCallState() callback method of Call class.

3.2.4 Threading

For platforms that require polling, the PJSUA2 module provides its own worker thread to poll PJSIP, so it is not

necessary to instantiate own your polling thread. Having said that the application should be prepared to have the

callbacks called by different thread than the main thread. The PJSUA2 module itself is thread safe.

Often though, especially if you use PJSUA2 with high level languages such as Python, it is required to disable PJSUA2

internal worker threads by setting EpConﬁg.uaConﬁg.threadCnt to 0, because the high level environment doesn’t like

to be called by external thread (such as PJSIP’s worker thread).

12 Chapter 3. PJSUA2-High Level API

PJSUA2 Documentation, Release 1.0-alpha

3.2.5 Problems with Garbage Collection

Garbage collection (GC) exists in Java and Python (and other languages, but we don’t support those for now), and

there are some problems with it when it comes to PJSUA2 usage:

1. premature destruction of PJSUA2 objects which are created in Java and Python space and passed to the native

space without keeping reference to the object

2. it delays the destruction of objects (including PJSUA2 objects), causing the code in object’s destructor to be

executed out of order

3. the destruction operation by GC may run on different thread not previously registered to PJLIB, causing assertion

Some examples for problem 1 are (these examples are by no means a complete list) when adding Buddy object to

an account using Account.addBuddy() or setting LogWriter by calling EpConﬁg.LogConﬁg.setLogWriter(). To avoid

this problem, application needs to maintain an explicit reference on objects created in its application, instead of relying

on PJSUA2 native library to keep track of those objects, i.e. :

class MyApp {

private MyLogWriter logWriter;

public void init()

{

Maintain reference to log writer to avoid premature cleanup by GC

logWriter = new MyLogWriter();

epConfig.getLogConfig.setWriter(logWriter);

}

While for problems 2 and 3, application ‘’‘MUST immediately destroy PJSUA2 objects using object’s delete() method

(in Java)’‘’, instead of relying on the GC to clean up the object. For example, to delete an Account, it’s NOT enough

to just let it go out of scope. Application MUST delete it manually like this (in Java):

acc.delete();

3.2.6 Objects Persistence

PJSUA2 includes PersistentObject class to provide functionality to read/write data from/to a document (string or

ﬁle). The data can be simple data types such as boolean, number, string, and string arrays, or a user deﬁned object.

Currently the implementation supports reading and writing from/to JSON document ([http://tools.ietf.org/html/rfc4627

RFC 4627]), but the framework allows application to extend the API to support other document formats.

As such, classes which inherit from PersistentObject, such as EpConﬁg (endpoint conﬁguration), AccountConﬁg

(account conﬁguration), and BuddyConﬁg (buddy conﬁguration) can be loaded/saved from/to a ﬁle. Heres an example

to save a conﬁg to a ﬁle:

EpConfig epCfg;

JsonDocument jDoc;

epCfg.uaConfig.maxCalls = 61;

epCfg.uaConfig.userAgent = "Just JSON Test";

jDoc.writeObject(epCfg);

jDoc.saveFile("jsontest.js");

To load from the ﬁle:

3.2. General Concepts 13

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