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.
Table of Contents (26 chapters)
Title Page
About Packt

Executing a remote command

The SSH protocol works using channels. After we've established an SSH connection, a channel must be opened to do any real work. The advantage is that many channels can be opened over one connection. This potentially allows an application to do multiple things (seemingly) simultaneously.

After the SSH session is open and the user is authenticated, a channel can be opened. A new channel is opened by calling the ssh_channel_new() function. The following code illustrates this:

/*ssh_command.c excerpt*/

    ssh_channel channel = ssh_channel_new(ssh);
    if (!channel) {
        fprintf(stderr, "ssh_channel_new() failed.\n");
        return 0;

The SSH protocol implements many types of channels. The session channel type is used for executing remote commands and transferring files. With libssh, we can request a session channel by using the ssh_channel_open_session() function. The following code shows calling ssh_channel_open_session():

/*ssh_command.c excerpt*/