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Hands-On Network Programming with C

By : Lewis Van Winkle

4.5 (30)

Hands-On Network Programming with C

4.5 (30)

By: Lewis Van Winkle

Overview of this book

Network programming enables processes to communicate with each other over a computer network, but it is a complex task that requires programming with multiple libraries and protocols. With its support for third-party libraries and structured documentation, C is an ideal language to write network programs. Complete with step-by-step explanations of essential concepts and practical examples, this C network programming book begins with the fundamentals of Internet Protocol, TCP, and UDP. You’ll explore client-server and peer-to-peer models for information sharing and connectivity with remote computers. The book will also cover HTTP and HTTPS for communicating between your browser and website, and delve into hostname resolution with DNS, which is crucial to the functioning of the modern web. As you advance, you’ll gain insights into asynchronous socket programming and streams, and explore debugging and error handling. Finally, you’ll study network monitoring and implement security best practices. By the end of this book, you’ll have experience of working with client-server applications and be able to implement new network programs in C. The code in this book is compatible with the older C99 version as well as the latest C18 and C++17 standards. You’ll work with robust, reliable, and secure code that is portable across operating systems, including Winsock sockets for Windows and POSIX sockets for Linux and macOS.

Title Page

Title Page

Copyright and Credits

Copyright and Credits

Dedication

Dedication

About Packt

About Packt

Why subscribe?

Packt.com

Contributors

Contributors

About the author

About the reviewer

Packt is searching for authors like you

Preface

Preface

Who this book is for

What this book covers

To get the most out of this book

Get in touch

Free Chapter

Introducing Networks and Protocols

Introducing Networks and Protocols

Technical requirements

The internet and C

OSI layer model

TCP/IP layer model

Data encapsulation

Internet Protocol

Domain names

Internet routing

Port numbers

Clients and servers

Putting it together

What's your address?

Listing network adapters from C

Summary

Questions

Getting to Grips with Socket APIs

Getting to Grips with Socket APIs

Technical requirements

What are sockets?

Socket setup

Two types of sockets

Socket functions

Anatomy of a socket program

Berkeley sockets versus Winsock sockets

Our first program

Summary

Questions

An In-Depth Overview of TCP Connections

An In-Depth Overview of TCP Connections

Technical requirements

Multiplexing TCP connections

Synchronous multiplexing with select()

A TCP client

A TCP server

Blocking on send()

TCP is a stream protocol

Summary

Questions

Establishing UDP Connections

Establishing UDP Connections

Technical requirements

How UDP sockets differ

A first UDP client/server

A UDP server

Summary

Questions

Hostname Resolution and DNS

Hostname Resolution and DNS

Technical requirements

How hostname resolution works

Name/address translation functions

The DNS protocol

A DNS query program

Summary

Questions

Further reading

Building a Simple Web Client

Building a Simple Web Client

Technical requirements

The HTTP protocol

What's in a URL

Implementing a web client

HTTP POST requests

Summary

Questions

Further reading

Building a Simple Web Server

Building a Simple Web Server

Technical requirements

The HTTP server

Content types

Creating the server socket

Multiple connections buffering

The main loop

Security and robustness

Summary

Questions

Further reading

Making Your Program Send Email

Making Your Program Send Email

Technical requirements

Email servers

SMTP dialog

The format of an email

A simple SMTP client program

Enhanced emails

Spam-blocking pitfalls

Summary

Questions

Further reading

Loading Secure Web Pages with HTTPS and OpenSSL

Loading Secure Web Pages with HTTPS and OpenSSL

Technical requirements

HTTPS overview

Encryption basics

The TLS protocol

OpenSSL

A simple HTTPS client

Other examples

Summary

Questions

Further reading

Implementing a Secure Web Server

Implementing a Secure Web Server

Technical requirements

HTTPS and OpenSSL summary

HTTPS server with OpenSSL

HTTPS server challenges

Summary

Questions

Further reading

Establishing SSH Connections with libssh

Establishing SSH Connections with libssh

Technical requirements

The SSH protocol

libssh

SSH authentication

Executing a remote command

Downloading a file

Summary

Questions

Further reading

Network Monitoring and Security

Network Monitoring and Security

Technical requirements

The purpose of network monitoring

Testing reachability

Checking local connections

Snooping on connections

Network security

Network-testing etiquette

Summary

Questions

Further reading

Socket Programming Tips and Pitfalls

Socket Programming Tips and Pitfalls

Technical requirements

Error handling

TCP socket tips

Socket's local address

Multiplexing with a large number of sockets

Summary

Questions

Web Programming for the Internet of Things

Web Programming for the Internet of Things

Technical requirements

What is the IoT?

Connectivity options

Hardware choices

External transceivers and modems

IoT protocols

Firmware updates

Ethics of IoT

Summary

Questions

Answers to Questions

Answers to Questions

Chapter 1, Introducing Networks and Protocols

Chapter 2, Getting to Grips with Socket APIs

Chapter 3, An In-Depth Overview of TCP Connections

Chapter 4, Establishing UDP Connections

Chapter 5, Hostname Resolution and DNS

Chapter 6, Building a Simple Web Client

Chapter 7, Building a Simple Web Server

Chapter 8, Making Your Program Send Email

Chapter 9, Loading Secure Web Pages with HTTPS and OpenSSL

Chapter 10, Implementing a Secure Web Server

Chapter 11, Establishing SSH Connections with libssh

Chapter 12, Network Monitoring and Security

Chapter 13, Socket Programming Tips and Pitfalls

Chapter 14, Web Programming for the Internet of Things

Setting Up Your C Compiler on Windows

Setting Up Your C Compiler on Windows

Installing MinGW GCC

Installing Git

Installing OpenSSL

Installing libssh

Alternatives

Setting Up Your C Compiler on Linux

Setting Up Your C Compiler on Linux

Installing GCC

Installing Git

Installing OpenSSL

Installing libssh

Setting Up Your C Compiler on macOS

Setting Up Your C Compiler on macOS

Installing Homebrew and the C compiler

Installing OpenSSL

Installing libssh

Example Programs

Example Programs

Code license

Code included with this book

Other Book You May Enjoy

Other Book You May Enjoy

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External transceivers and modems

External transceivers and modems are available for Wi-Fi, cellular, Ethernet, Bluetooth, and any other protocol you can think of.

The following photo shows an industrial IoT device that uses a cellular modem:

In the preceding diagram, the lower circuit board implements the functionality of the device (monitoring cryogenic liquids, in this case). On this board, the power supply system, sensor electronics, and a low-cost, 16-bit microcontroller are found. A cellular modem is located on the top circuit board, which plugs into a socket on the lower board.

External modems often communicate with their host (microcontroller) through asynchronous serial. The protocols used vary considerably among systems.

One common protocol family for communicating with modems is the Hayes command set also called AT commands. These commands consist of short text-based...

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