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PJSIP是一种用C语言编写的小型足迹、高性能的SIP栈，适合于需要实现信令协议的通信软件项目。PJSIP遵循GNU通用公共许可证（GPL），但同时也提供其他授权选项供选择。本文档是《PJSIP开发指南》的0.54版本，由Benny Prijono编写，并采用GNU自由文档许可证（GNU FDL）版本1.2发布。该文档详细介绍了PJSIP的架构、模块管理、消息元素等核心概念，同时提供了API、回调机制和事件处理的详细说明。在PJSIP的架构设计中，开发者需要了解以下几个方面： 1. **通信图和类图**：这是理解PJSIP通信机制的基础。通信图展示了不同组件间的消息流程，而类图则展示了系统中各个类的继承和依赖关系。这些图谱对于深入理解PJSIP的内部结构至关重要。 2. **终端点（Endpoint）**：包括内存池分配与回收、定时器管理和对栈的轮询等。理解这些机制对于开发高效、稳定的SIP应用程序至关重要，因为它直接关系到资源管理效率和系统的响应性能。 3. **线程安全和线程并发症**：PJSIP在设计上考虑了多线程环境下的线程安全问题。文档中提到了线程安全的概念，并阐述了在多线程环境下可能出现的并发症以及解决这些并发症的方法，如使用线程锁、线程局部存储等策略。在模块管理方面，文档详细讲解了模块的声明、优先级、消息处理以及事务用户和状态回调等概念。模块管理API允许开发者动态地加载、卸载和控制模块的行为，这对于提高系统的可扩展性和灵活性极为重要。此外，每个模块都有其特定的数据和回调函数，这些都是开发者需要关注的焦点。消息元素部分详细介绍了SIP消息结构，包括SIP方法的种类和作用，例如注册（REGISTER）、邀请（INVITE）、信息（MESSAGE）等。此外，文档还涉及了统一资源标识符（Uniform Resource Identifier, URI）和相关的处理逻辑，这对于实现SIP协议的请求和响应处理非常关键。文档还强调了开发者在使用PJSIP时应当遵循的API调用规则，例如在创建UAS（用户代理服务器）事务后必须调用pjsip_tsx_recv_msg()函数。对于软件设计者而言，理解这些API的使用时机和作用是实现正确SIP通信功能的前提。对于版本更新记录，文档列出了从0.5.0至0.5.4版的变更历史，包括新增的函数如dlg_terminate()和inv_terminate()等，以及对evsub API的回顾和IM和discomposing章节的添加。这些更新反映了PJSIP在功能上的不断进步和对开发者需求的响应。 PJSIP开发指南为开发者提供了一份详尽的参考文档，不仅介绍了PJSIP的核心架构和模块化设计，还包含了API的详细使用说明和通信机制的解释。通过这份文档，开发者可以获得关于如何有效地集成和使用PJSIP来构建SIP通信应用的深入知识。

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PJSIP

Developer’s Guide

Version 0.5.4

PJSIP Developer’s Guide
Table of Contents
 TABLE OF CONTENTS                                                                                                                            .......................................................................................................................   4  
 TABLE OF FIGURES                                                                                                                                 ............................................................................................................................   8  
 TABLE OF CODES                                                                                                                                     ................................................................................................................................   8  
CHAPTER 1: GENERAL DESIGN                                                                                                          .....................................................................................................   11  
1  ARCHITECTURE                                                                                                                                       ..................................................................................................................................   11  
1.1  Communication Diagram                                                                                                           ......................................................................................................   11  
1.2  Class Diagram                                                                                                                            .......................................................................................................................   11  
2  THE ENDPOINT                                                                                                                                       ..................................................................................................................................   12  
2.1  Pool Allocations and Deallocations                                                                                           ......................................................................................   12  
2.2  Timer Management                                                                                                                     ................................................................................................................   12  
2.3  Polling the Stack                                                                                                                         ....................................................................................................................   13  
3  THREAD SAFETY AND THREAD COMPLICATIONS                                                                                          .....................................................................................   13  
3.1  Thread Safety                                                                                                                              .........................................................................................................................   13  
3.2  The Complications                                                                                                                      .................................................................................................................   13  
3.3  The Relief                                                                                                                                    ...............................................................................................................................   14  
CHAPTER 2: MODULE                                                                                                                            .......................................................................................................................   15  
1.1  Module Declaration                                                                                                                    ...............................................................................................................   15  
1.2  Module Priorities                                                                                                                        ...................................................................................................................   16  
1.3  Incoming Message Processing by Modules                                                                                ...........................................................................   17  
1.4  Outgoing Message Processing by Modules                                                                                ...........................................................................   17  
1.5  Transaction User and State Callback                                                                                         ....................................................................................   18  
1.6  Module Specific Data                                                                                                                 ............................................................................................................   18  
1.7  Callback Summary                                                                                                                      .................................................................................................................   19  
1.8  Sample Callback Diagrams                                                                                                        ...................................................................................................   20  
2  MODULE MANAGEMENT                                                                                                                          .....................................................................................................................   21  
2.1  Module Management API                                                                                                           ......................................................................................................   21  
2.2  Module Capabilities                                                                                                                   ..............................................................................................................   21  
CHAPTER 3: MESSAGE ELEMENTS                                                                                                   ..............................................................................................   23  
1  UNIFORM RESOURCE INDICATOR (URI)                                                                                                    ...............................................................................................   23  
1.1  URI “Class Diagram”                                                                                                                ...........................................................................................................   23  
1.2  URI Context                                                                                                                                ...........................................................................................................................   23  
1.3  Base URI                                                                                                                                     ................................................................................................................................   24  
1.4  SIP and SIPS URI                                                                                                                       ..................................................................................................................   25  
1.5  Tel URI                                                                                                                                       ..................................................................................................................................   25  
1.6  Name Address                                                                                                                             ........................................................................................................................   26  
1.7  Sample URI Manipulation Program                                                                                           ......................................................................................   26  
2  SIP METHODS                                                                                                                                       ..................................................................................................................................   27  
2.1  SIP Method Representation (pjsip_method)                                                                               ..........................................................................   27  
2.2  SIP Method API                                                                                                                          .....................................................................................................................   28  
3  HEADER FIELDS                                                                                                                                     ................................................................................................................................   29  
3.1  Header “Class Diagram”                                                                                                          .....................................................................................................   29  
3.2  Header Structure                                                                                                                        ...................................................................................................................   29  
3.3  Common Header Functions                                                                                                        ...................................................................................................   30  
3.4  Supported Header Fields                                                                                                            .......................................................................................................   31  
3.5  Header Array Elements                                                                                                              .........................................................................................................   31  
4  MESSAGE BODY (PJSIP_MSG_BODY)                                                                                                          .....................................................................................................   32  
5  MESSAGE (PJSIP_MSG)                                                                                                                            .......................................................................................................................   33  
6  SIP STATUS CODES                                                                                                                                ...........................................................................................................................   34  
7  NON-STANDARD PARAMETER ELEMENTS                                                                                                   ..............................................................................................   35  
7.1  Data Structure Representation (pjsip_param)                                                                           ......................................................................   36  
7.2  Non-Standard Parameter Manipulation                                                                                     ................................................................................   36  
8  ESCAPEMENT RULES                                                                                                                               ..........................................................................................................................   36  
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PJSIP Developer’s Guide
CHAPTER 4: PARSER                                                                                                                              .........................................................................................................................   38  
1  FEATURES                                                                                                                                              .........................................................................................................................................   38  
2  FUNCTIONS                                                                                                                                            .......................................................................................................................................   39  
2.1  Message Parsing                                                                                                                         ....................................................................................................................   39  
2.2  URI Parsing                                                                                                                                ...........................................................................................................................   39  
2.3  Header Parsing                                                                                                                           ......................................................................................................................   39  
3  EXTENDING PARSER                                                                                                                                ...........................................................................................................................   40  
CHAPTER 5: MESSAGE BUFFERS                                                                                                       ..................................................................................................   41  
1  RECEIVE DATA BUFFER                                                                                                                          .....................................................................................................................   41  
1.1  Receive Data Buffer Structure                                                                                                    ...............................................................................................   41  
2  TRANSMIT DATA BUFFER (PJSIP_TX_DATA)                                                                                               ..........................................................................................   42  
CHAPTER 6: TRANSPORT LAYER                                                                                                      .................................................................................................   43  
1  TRANSPORT LAYER DESIGN                                                                                                                     ................................................................................................................   43  
1.1  “Class Diagram”                                                                                                                       ..................................................................................................................   43  
1.2  Transport Manager                                                                                                                     ................................................................................................................   43  
1.3  Transport Factory                                                                                                                       ..................................................................................................................   44  
1.4  Transport                                                                                                                                    ..............................................................................................................................   44  
2  USING TRANSPORTS                                                                                                                                ...........................................................................................................................   46  
2.1  Function Reference                                                                                                                     ................................................................................................................   46  
3  EXTENDING TRANSPORTS                                                                                                                         ....................................................................................................................   46  
4  INITIALIZING TRANSPORTS                                                                                                                        ...................................................................................................................   46  
4.1  UDP Transport Initialization                                                                                                     ................................................................................................   47  
4.2  TCP Transport Initialization                                                                                                      .................................................................................................   47  
4.3  TLS Transport Initialization                                                                                                       ..................................................................................................   47  
4.4  SCTP Transport Initialization                                                                                                    ...............................................................................................   47  
CHAPTER 7: SENDING MESSAGES                                                                                                     ................................................................................................   48  
1  SENDING MESSAGES OVERVIEW                                                                                                               ..........................................................................................................   48  
1.1  Creating Messages                                                                                                                     ................................................................................................................   48  
1.2  Sending Messages                                                                                                                       ..................................................................................................................   48  
2  FUNCTION REFERENCE                                                                                                                             ........................................................................................................................   49  
2.1  Sending Response                                                                                                                       ..................................................................................................................   49  
2.2  Sending Request                                                                                                                          .....................................................................................................................   50  
2.3  Stateless Proxy Forwarding                                                                                                       ..................................................................................................   52  
3  EXAMPLES                                                                                                                                             ........................................................................................................................................   53  
3.1  Sending Responses                                                                                                                      .................................................................................................................   53  
3.2  Sending Requests                                                                                                                        ...................................................................................................................   54  
3.3  Stateless Forwarding                                                                                                                  .............................................................................................................   55  
CHAPTER 8: TRANSACTIONS                                                                                                              .........................................................................................................   56  
1  DESIGN                                                                                                                                                 ............................................................................................................................................   56  
1.1  Introduction                                                                                                                                ...........................................................................................................................   56  
1.2  Timers and Retransmissions                                                                                                       ..................................................................................................   56  
1.3  INVITE Final Response and ACK Request                                                                                 ............................................................................   56  
1.4  Incoming ACK Request                                                                                                               ..........................................................................................................   57  
1.5  Server Resolution and Transports                                                                                              .........................................................................................   57  
1.6  Via Header                                                                                                                                  .............................................................................................................................   58  
2  REFERENCE                                                                                                                                            .......................................................................................................................................   58  
2.1  Base Functions                                                                                                                           ......................................................................................................................   58  
2.2  Composite Functions                                                                                                                  .............................................................................................................   59  
3  SENDING STATEFULL RESPONSES                                                                                                              .........................................................................................................   60  
3.1  Usage Examples                                                                                                                         ....................................................................................................................   60  
4  SENDING STATEFULL REQUEST                                                                                                                 ............................................................................................................   60  
4.1  Usage Examples                                                                                                                         ....................................................................................................................   61  
5  STATEFULL PROXY FORWARDING                                                                                                              .........................................................................................................   61  
5.1  Usage Examples                                                                                                                         ....................................................................................................................   61  
CHAPTER 9: AUTHENTICATION FRAMEWORK                                                                            .......................................................................   63  
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