Lesson 1 HTTP

References:

• https://developer.mozilla.org/en-US/docs/Web/HTTP/Overview
• https://www.rfc-editor.org/rfc/rfc2616
• https://curl.se/docs/manpage.html

Overview

In the 1991 HTTP was created. Web browsers used HTTP to fetch static HTML, text and images from web servers. These static files were sitting in a directory on a server. The only way to change the website was to update these files.

You could type a URL like http://acme.com/products.html into a graphical web browser, the browser would then speak HTTP to the acme.com server to fetch the /products.html file. The user may then click a <a href="http://contoso.net/about.html"> to cause the browser to visit a different site, speaking HTTP to the contoso.net server to fetch the /about.html file.

Learning objective

The goal is to learn about HTTP, specifically what it does and what it looks like.
- What is an HTTP method?
- What is an HTTP status code?
- Identify the components of a URL, server, path.
- How does an HTTP server use the server and path from the URL?

Exercises

Run a simple web server using Python

• Make new directory with some text or html files, at least two. Eg demo.html and hello.txt.
• Open terminal in that directory. Right click, open in terminal.
• Start the web server: python -mhttp.server
• Keep this terminal window open for later.

Access the web server with a browser like Firefox

• Open web browser and visit: http://localhost:8000
• See what is happening in the web server terminal window.
• You can click on the files to view them.
• The browser is acting as an HTTP client to view the files being served by the Python HTTP server.

Access the web server with a command line client, curl

• Open a new terminal window in addition to the Python web server one.
• Run curl http://localhost:8000 to see the directory index generated by the web server.
• Run curl http://localhost:8000/demo.html to see a file you created in the web server directory.
• Try variations of this like: /hello.txt, or /missing.txt
• You can also try this on other web servers, like https://www.google.com
• Try in verbose mode to see the raw HTTP: curl -v http://localhost:8000

Access the web server by typing raw HTTP

• Run command nc localhost 8000
• Enter GET / HTTP/1.0, then press return twice
• Try with GET /hello.txt or other variations to see how the server responds.

HTTP is just text! When you click a link, all that Firefox does is send this text to the server and display the result on the screen.