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Hands-On Network Programming with C

You're reading from  Hands-On Network Programming with C

Product type Book
Published in May 2019
Publisher Packt
ISBN-13 9781789349863
Pages 478 pages
Edition 1st Edition
Languages
Concepts
Author (1):
Lewis Van Winkle Lewis Van Winkle
Profile icon Lewis Van Winkle

Table of Contents (26) Chapters

Title Page
Dedication
About Packt
Contributors
Preface
1. Introducing Networks and Protocols 2. Getting to Grips with Socket APIs 3. An In-Depth Overview of TCP Connections 4. Establishing UDP Connections 5. Hostname Resolution and DNS 6. Building a Simple Web Client 7. Building a Simple Web Server 8. Making Your Program Send Email 9. Loading Secure Web Pages with HTTPS and OpenSSL 10. Implementing a Secure Web Server 11. Establishing SSH Connections with libssh 12. Network Monitoring and Security 13. Socket Programming Tips and Pitfalls 14. Web Programming for the Internet of Things 1. Answers to Questions 2. Setting Up Your C Compiler on Windows 3. Setting Up Your C Compiler on Linux 4. Setting Up Your C Compiler on macOS 5. Example Programs 6. Other Book You May Enjoy Index

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*/

  ...
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