Hypertext Transfer Protocol (HTTP) is the application protocol that powers the World Wide Web (WWW). Whenever you fire up your web browser to do an internet search, browse Wikipedia, or make a post on social media, you are using HTTP. Many mobile apps also use HTTP behind the scenes. It's safe to say that HTTP is one of the most widely used protocols on the internet.

In this chapter, we will look at the HTTP message format. We will then implement a C program, which can request and receive web pages.

The following topics are covered in this chapter:

• The HTTP message format
• HTTP request types
• Common HTTP headers
• HTTP response code
• HTTP message parsing
• Implementing an HTTP client
• Encoding form data (POST)
• HTTP file uploads