Book Image

Hands-On Network Programming with C

By : Lewis Van Winkle
Book Image

Hands-On Network Programming with C

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.

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Table of Contents (26 chapters)
Title Page
Title Page
Dedication
Dedication
About Packt
About Packt
Contributors
Contributors
Preface
Preface
Free Chapter
1
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
2
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
3
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
4
Establishing UDP Connections
Establishing UDP Connections
Technical requirements
How UDP sockets differ
A first UDP client/server
A UDP server
Summary
Questions
5
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
6
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
7
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
8
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
9
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
10
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
11
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
12
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
13
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
14
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
Leave a review - let other readers know what you think
Index
Index

Installing libssh

You can obtain the latest libssh library from https://www.libssh.org/. If you are proficient in installing C libraries, feel free to give it a go. Otherwise, read on for step-by-step instructions.

Before beginning, be sure that you've first installed the OpenSSL libraries successfully. These are required by the libssh library.

We will need CMake installed in order to build libssh. You can obtain CMake from https://cmake.org/. They provide a nice GUI installer, and you shouldn't run into any difficulties. Make sure you select the option to add CMake to your PATH during installation:

Once you have the CMake tool and the OpenSSL libraries installed, navigate to the libssh website to download the libssh source code. At the time of writing, Version 0.8.7 is the latest, and it is available from https://www.libssh.org/files/0.8/. Download and extract the libssh source code.

Take a look at the included INSTALL file.

Now, open a command window in the libssh source code directory. Create a new build folder with the following commands:

mkdir build
cd build

Keep this command window open. We'll do the build here in a minute.

Start CMake 3.14.3 (cmake-gui) from the start menu or desktop shortcut.

You need to set the source code and build locations using the Browse Source... and Browse Build... buttons. This is shown in the following screenshot:

Then, click Configure.

On the next screen, select MinGW Makefiles as the generator for this project. Click Finish.

It may take a moment to process.

From the configuration options, make the following changes:

  1. Uncheck WITH_NACL
  2. Uncheck WITH_GSSAPI
  3. Change CMAKE_INSTALL_PREFIX to c:\mingw

Then, click Configure again. It will take a moment. If everything worked, click Generate.

You should now be able to build libssh.

Go back to your command window in the build directory. Use the following command to complete the build:

mingw32-make

After the build completes, use the following command to copy the files over to your MinGW installation:

mingw32-make install

You can try building ssh_version.c from Chapter 11, Establishing SSH Connections with libssh, to test that everything is installed correctly. It should look like the following:

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