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Open Source MessagingApplication Development:

Building and Extending GaimSEAN EGAN

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Open Source Messaging Application Development: Building and Extending Gaim

Copyright 2005 by Sean Egan

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For Dad

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Contents at a Glance

About the Author. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xv

About the Technical Reviewer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii

Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi

CHAPTER 1 Getting Started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

CHAPTER 2 The Open Source Development Process . . . . . . . . . . . . . . . . . . . . . . 23

CHAPTER 3 Development Tools. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

CHAPTER 4 Programming Gaim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

CHAPTER 5 GTK+ Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

CHAPTER 6 Advanced GTK+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

CHAPTER 7 Sockets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237

CHAPTER 8 Protocol Plug-Ins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267

CHAPTER 9 Internationalization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299

CHAPTER 10 Portability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319

INDEX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337

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Contributing to Open Source Development . . . . . . . . . . . . . . . . . . . . . . . . . 31

Getting Started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Climbing the Ranks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Managing Your Own Open Source Project . . . . . . . . . . . . . . . . . . . . . . . . . 34

Becoming a Maintainer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Management Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

CHAPTER 3 Development Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Editors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

vi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

IDEs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

GCC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

How a Program Is Built. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Invoking GCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

make . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Makefile Rules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Implicit Rules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Multiple Directories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Autotools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Automake. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Autoconf. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Other Required Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

autogen.sh. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60Using the Build Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

GDB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Running Your Application Within GDB . . . . . . . . . . . . . . . . . . . . . . . . 61

Analyzing Core Dumps with GDB . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Debugging Segfaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

CVS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Versioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Branches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65Using CVS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

ViewCVS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

SourceForge.net. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Submitting a Tracker Item . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Managing Tracker Items . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

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CHAPTER 4 Programming Gaim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Compiling Your First Plug-In: helloworld.c. . . . . . . . . . . . . . . . . . . . . . 85Anatomy of a Gaim Plug-in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

GAIM_INIT_PLUGIN. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

GaimPluginInfo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89plugin_load(). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92#includeStatements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

Object-Oriented Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

Abstraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Inheritance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Polymorphism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Object-Oriented C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Inheritance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Accessor and Mutator Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . 100Data Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Linked Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Hash Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

Trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

The Gaim API . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

Core/UI Split. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

GaimAccount (account.h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108GaimConnection (connection.h). . . . . . . . . . . . . . . . . . . . . . 108GaimConversation (conversation.h) . . . . . . . . . . . . . . . . . 109GaimBuddyList (blist.h). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

CHAPTER 5 GTK+ Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

Overview of GTK+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

Language Bindings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

Anatomy of a GTK+ Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

The gtk_init()Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118The Main Loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

User Interface Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

Elegance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

GNOME HIG. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

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Creating Dialogs in GTK+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

Widget Packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

Container Widgets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

Event Listeners. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

Callbacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136A Sample GTK+ Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

Gaim Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

GTK+ Widgets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

GtkLabel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139GtkImage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140GtkProgressBar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141GtkEntry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143GtkSpinButton. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146GtkButton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147GtkToggleButton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150GtkCheckButton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151GtkRadioButton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152GtkTextView . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153GtkTreeView . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158GtkComboBox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163GtkToolbar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164GtkMenu. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167GtkDialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

GtkFileChooserDialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171A Gaim Plug-in Example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

Gaim Plug-in Boilerplate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

The Data Structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

Using Gaim Signals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

Scanning Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

Hooking into Account Actions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178

Creating the GUI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180

The Entire Plug-In . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

Potential Enhancements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

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CHAPTER 6 Advanced GTK+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

A Sample Plug-In . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

GObject. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

Object-Oriented Features of GObject. . . . . . . . . . . . . . . . . . . . . . . . 199

Using GObject. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202Creating a Composite Widget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217

GdkPixbuf. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219

Working with Image Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219

GdkPixbufLoader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220Animations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221

Pango . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222

PangoLayout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222PangoAttribute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223

GDK. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224

The X Window System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224GdkDrawable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226Drawing Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

OverridingGtkWidget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232Data Fields of GtkWidget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232Overriding Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233

Receiving Events. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235

CHAPTER 7 Sockets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237

Networking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237

The OSI Seven-Layer Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

Domain Name Service. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242

Sockets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242

Connecting to a Server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242

Accepting Connections from Clients. . . . . . . . . . . . . . . . . . . . . . . . . 248

Reading and Writing Data to a Socket. . . . . . . . . . . . . . . . . . . . . . . 252

Non-blocking I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253

select(). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253

fd_set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254timeval. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254Non-Blocking Sockets with select(). . . . . . . . . . . . . . . . . . . . . . 255

Integrating into GLibs Main Loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255

GIOChannel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256g_io_add_watch(). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256

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A Sample Gaim Plug-in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257

The Boilerplate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257

plugin_load(). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258incoming_cb(). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259create_response() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260

The Final Plug-In . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261Possible Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265

CHAPTER 8 Protocol Plug-Ins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267

Protocol Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267

Packet Framing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267

Packet Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269

Packet Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271

Protocol Implementation in C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275Binary Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275

Text Protocols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277

Learning Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280

Reverse Engineering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280

Legal Ramifications of Reverse Engineering . . . . . . . . . . . . . . . . . . 281

Packet Sniffing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283

Reverse Engineering Techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . 286

Interfacing with Gaim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288

server.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288

GaimPluginProtocolInfo. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289Command Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294

Program Flow of a prpl. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

CHAPTER 9 Internationalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299

Internationalization Defined . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300

Text Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301

ASCII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302

Foreign Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302iconv. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303

Knowing What Encodings to Use . . . . . . . . . . . . . . . . . . . . . . . . . . . 305

Unicode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306

Code Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306

Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

UTF-8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

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Translations with gettext . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308

An Overview of gettext . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

Setting Up gettext . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310

Coding with gettext. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312

Translating with gettext . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314

Using Translations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316gettext Summarized . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317

CHAPTER 10 Portability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319

The C Programming Language. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319

History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

K&R, ANSI, and C99 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321

libc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323

Tips on Writing Portable C Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324

POSIX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325

Porting to Windows with MinGW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326

Cygwin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327

Windows Compatibility Libraries. . . . . . . . . . . . . . . . . . . . . . . . . . . . 327

GLib . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327

Portable Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328

Utility Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329

Memory Allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330

File Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331

Plug-Ins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331

GDK. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333

X11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333

Win32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334

WIMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337

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About the Author

SEAN EGANmaintains the Gaim project, http://gaim.sourceforge.net.He is

a major contributor to the project, managing a team of 10 core developers,

and reviewing and incorporating patches from over 200 contributors. A

Long Island, NY native, Sean has a bachelors degree in computer science

from Binghamton Universtiy.

Sean has been involved in Gaim development for five years and learned

most of what he knows about software development from his experience

with the project.

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About the Technical Reviewer

NATHAN WALPis a software engineer at Recognition Research, Inc. in Blacksburg, VA. He has

more than five years experience writing software, and has been working on Gaim since 2001; he

is responsible for Jabber support, among many other things.

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Acknowledgments

Id like to thank my friends and family for their support while I was writing this book, especiallymy parents Doug and Lynn, and my sister Erin.

Id like to thank everyone at Apress for their support and patience with me, especially

those I worked with directly: Beth Christmas, Jason Gilmore, Candace English, Julie Miller,

and Kelly Winquist.

Mostly, Id like to thank everyone whos contributed to Gaim, making this book possible;

especially Nathan Walp (who is also the technical reviewer for this book), Mark Spencer,

Jim Duchek, Rob Flynn, Syd Logan, Eric Warmenhoven, Adam Fritzler, Benjamin Miller,

Decklin Foster, Mark Doliner, Luke Schierer, Ethan Blanton, Etan Reisner, Tim Ringenbach,

Daniel Atallah, Robert McQueen, Christian Hammond, Herman Bloggs, Stu Tomlinson,

Gary Kramlich, Ka-Hing Cheung, Kevin Stange, and Felipe Contreras.

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Introduction

Idiscovered Gaim in the AOL Instant Messenger (AIM) user profile of a friend about five yearsago. I didnt know a lot about Linux then. I knew that it was a free implementation of UNIX with

publicly available source code, but my previous experiences with UNIX comprised staring at a

shell prompt, trying to type cryptic commands into a DOS-like console. Likewise, I assumed

that Linux was primitive compared to the high-tech, state-of-the-art Windows 98 I was using

that day when I read my friends profile.

Visit the Gaim Web page, it invited me. I followed the link and found my preconceptions

were wrong. On what I had seen as a platform solely for Web servers and corporate mainframes,

I could perform such everyday tasks as chatting with my friends. I expected nothing but text

commands, but I found Web browsers, e-mail clients, and gamesall with windows to scroll

and buttons to click. Linux no longer looked like DOS; it was an actively developed desktop

operating system. Wanting to contribute to that development process, I quickly downloaded

the Gaim source code and started coding.

At the time, though, I had just started learning how to use my operating system and didnt

know any C (the language Gaim is written in). This didnt stop me; I quickly taught myself all the

skills necessary to write this hugely popular desktop application, using Gaim as an example.

Today, Im the lead developer of the Gaim project, and I work closely with a group of developers

to maintain and enhance the most popular open source instant messaging application on the

planet.

About GaimGaim is a modular instant messaging client that supports a wide variety of IM protocols,

including AIM, ICQ, MSN, Yahoo!, and Jabber. Although it was originally written for Linux, it

now runs on most popular operating systems, including Windows and Mac OS X. Although

exact user statistics are impossible to obtain, its users number in the hundreds of thousands, if

not over a million. Its so popular because, in addition to functionality available in other clients,

it offers many unique features and is infinitely extensible through a powerful plug-in API. Most

importantly in the context of this book is that Gaim is free and open source software.

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xxii I N T R O D U C T I O N

Figure 1.A screenshot of the Gaim application

Free software and open source software are terms that differ slightly in semantics but

describe essentially the same thing. When downloading Gaim, you are offered the source code.Having unfettered access to the source code is quite valuable for understanding how Gaim

works, and is necessary should you wish to make any modifications. The only major provision

is that you grant this same right to modify your changes. This way, Gaim benefits from

hundreds of talented developers around the world, offering their contributions back to the

community. Because Gaim is built entirely with open source tools, involving yourself in its

development is easy, and it makes an excellent example to learn from.

About This BookThis book will help you to learn the same important programming skills I learned using Gaim

as an example. Ill explore the various techniques and technologies used by Gaim, and afterreading this book you will be able to use what youve learned to create your own networked,

cross-platform desktop application.

This book introduces GTK+, the library used to create Gaims graphical user interface. You

will understand the principles behind it, and will know enough of its API to make changes to

Gaims GUI and to develop interfaces for your own applications.

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xxiv I N T R O D U C T I O N

Chapter 6: Advanced GTK+

Now that youre equipped with a basic of understanding of GTK+, I will explore its internal

workings more thoroughly. You will learn how to create your own GUI objects, or widgets, byfollowing a sample plug-in that radically changes Gaims File Transfer dialog with three such

custom objects.

Chapter 7: Sockets

In Chapter 7, Ill introduce sockets, the programmatic interface to the Internet. You will learn

some basic principles of networking, and how to communicate over a network. I will explain

how to hook your networking code to GTK+s GLib library to integrate it into GTK+s main loop

and ensure cross-platform compatibility.

Chapter 8: Protocol Plug-Ins

After learning how to communicate over the Internet, you will learn about various protocols,

including IM protocols. You will learn how to intercept and interpret Internet traffic used by IM

clientsa process called reverse engineering. I will then teach you how to add a new protocolto Gaim as a protocol plug-in. I will review how Gaim and the plug-in communicate events

between each other.

Chapter 9: Internationalization

In this chapter, you will learn how to write programs that speakers of any language can use. I

will review the gettext system for providing translation of your program at runtime. I will

explain the concept of text encodings, why they are significant, and how to write code that

understands them.

Chapter 10: Portability

Chapter 10 will address portability; that is, making your program run on as many systems aspossible, regardless of hardware or operating system. I will discuss major differences you needto concern yourself with and how to use the portability functions of GTK+.

PrerequisitesI mentioned that when I started working on Gaim I was a complete amateur who didnt even

know the language its programmed in. As such, I dont expect you to be very experienced

either. Youll learn as we go.

However, I wont be introducing basic concepts of C, the language used to build Gaim.

Therefore,you should possess at least a rudimentary understanding of the language, and have

a basic knowledge of underlying principles of computer programming. Although I learned C by

example, there are other books that will do a better job of teaching you This book will focus on

higher-level aspects of the development process. However, you can most likely get by with

knowing C++, Java, or another language with a C-like syntax, as I will elaborate on more-

difficult or obscure techniques.

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I NT R ODU C T I ON

Because Gaim is created entirely with free software, everything you need is freely available

for download on the Internet. In Chapter 1, you will install the tools youll need for developing

Gaim and your own applications.

With a basic understanding of programming and a few free tools, you should be able to

follow this book and to write large programs like Gaim on your own.

Summary

Gaim has many advantages over other clients, but its major asset is that its open source.

Because of this, anyone with an idea and the ability to code can make it a better program. Also,it acts as a teaching toola real-life, practical example of a large codebase from which you can

learn to write similar code. This book will use Gaims example to teach you exactly that. I amalso available to answer any questions you may have. To e-mail or IM me, see my contact

information at http://gaim.sourceforge.net/contactinfo.php.