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

Downloading a file

The Secure Copy Protocol (SCP) provides a method to transfer files. It supports both uploading and downloading files.

libssh makes using SCP easy. This chapter's code repository contains an example, ssh_download.c, which shows the basic method for downloading a file over SCP with libssh.

After the SSH session is started and the user is authenticated, ssh_download.c prompts the user for the remote filename using the following code:

/*ssh_download.c excerpt*/

    printf("Remote file to download: ");
    char filename[128];
    fgets(filename, sizeof(filename), stdin);
    filename[strlen(filename)-1] = 0;

A new SCP session is initialized by calling the libssh library function ssh_scp_new(), as shown in the following code:

/*ssh_download.c excerpt*/

    ssh_scp scp = ssh_scp_new(ssh, SSH_SCP_READ, filename);
    if (!scp) {
        fprintf(stderr, "ssh_scp_new() failed.\n%s\n",
        return 1;

In the preceding code, SSH_SCP_READ is...