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

Chapter 3, An In-Depth Overview of TCP Connections

  1. How can we tell if the next call to recv() will block?

We use the select() function to indicate which sockets are ready to be read from without blocking.

  1. How can you ensure that select() doesn't block for longer than a specified time?

You can pass select() a timeout parameter.

  1. When we used our tcp_client program to connect to a web server, why did we need to send a blank line before the web server responded?

HTTP, the web server's protocol, expects a blank line to indicate the end of the request. Without this blank line, it wouldn't know if the client was going to keep sending additional request headers.

  1. Does send() ever block?

Yes. You can use select() to determine when a socket is ready to be written to without blocking. Alternatively, sockets can be put into non-blocking mode. See Chapter 13Socket Programming Tips and Pitfalls, for more information.

  1. How can we tell if a socket has been disconnected by our peer?

The return value of recv() can indicate if a socket has been disconnected.

  1. Is data received by recv() always the same size as data sent with send()?

No. TCP is a stream protocol. There is no way to tell if the data returned from one recv() call was sent with one or many calls to send().

  1. Consider this code:
recv(socket_peer, buffer, 4096, 0);

What is wrong with it?Also see what is wrong with this code:

recv(socket_peer, buffer, 4096, 0);
printf("%s", buffer);

The data returned by recv() is not null terminated! Both of the preceding code excerpts will likely causeprintf()to read past the end of the data returned by recv(). Additionally, in the first code example the data received could contain format specifiers (for example %d), which would cause additional memory access violations.