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 8, Making Your Program Send Email

  1. What port does SMTP operate on?

SMTP does mail transmission over TCP port 25. Many providers use alternative ports for mail submission.

  1. How do you determine which SMTP server receives mail for a given domain?

The mail servers responsible for receiving mail for a given domain are given by MX-type DNS records.

  1. How do you determine which SMTP server sends mail for a given provider?

It's not possible to determine that in the general case. In any case, several servers could be responsible. Sometimes these servers will be listed under a TXT-type DNS record using SPF, but that is certainly not universal.

  1. Why won't an SMTP server relay mail without authentication?

Open relay SMTP servers are targeted by spammers. SMTP servers require authentication to prevent abuse.

  1. How are binary files sent as email attachments when SMTP is a text-based protocol?

Binary files must be re-encoded as plain text. The most common method is with Content-Transfer-Encoding: base64.