Lab 10: Request Line

Web-CAT: Submit Python programs to this automated grading platform.

Task Outline

Due Date: Friday, November 29, 2019
Total Points: 10
Implement a Python program that determines the validity of an HTTP request line.

HyperText Transfer Protocol(HTTP) is the protocol that web browsers and web servers use to communicate with each other over the Internet.
HTTP is an application level protocol, because it sits on top of the TCP layer in the protocol stack, and it is used by specific applications to talk to each other. In this particular case, those applications happen to be web browsers and web servers.
HTTP is a connectionless, text-based protocol, in which clients send requests to servers.
When you type a URL into a web browser, the following steps occur:
- If the URL contains a domain name, then the browser first connects to a Domain Name Server, and retrieves the corresponding IP address for that domain name.
- The web browser then connects to the web server, and sends an HTTP request for the desired web page. The HTTP request takes the following form: GET /hello.html HTTP/1.1
- The web server receives the request, verifies that it is properly formatted, and returns an appropriate error message if it is not. Then, it checks for the desired web page. If the requested page exists, then the web server sends it out. However, if the web server cannot find the requested web page, then it will send out an error message.

Network stack

According to Regulation rfc7230 from the Internet Enginering Task Force(IETF), a well-formed HTTP request line takes the following form:

delivery-method SPACE request-target SPACE HTTP-version

Your task is to verify that a given HTTP request conforms to this structure, and is consistent with the following rules:
- If delivery-method is not GET, then the function should return: 405 Method Not Allowed
- If request-target does not begin with a /, then the function should return: 501 Not Implemented
- If request-target contains a ", then the function should return: 400 Bad Request
- If HTTP-version is not HTTP/1.1, then the function should return: 505 HTTP Version Not Supported
If none of the above errors occur, then this means that the HTTP request line is well-formed, and that the parse() function should return the request-target.

You should use string slicing to separate the different parts of the request line. However, this means that you will need to discover the index locations of the SPACEs.
Use the find(item) function to discover the index of the first SPACE, and then use find(item, startindex) to discover the index of the other SPACE.

Description	File Size	File Name
`Python` Source Code for Request Line	1.3KB	lab10.zip

Contents of lab10.zip:

Lab10RequestLine/
├── requestline.py
└── testrequestline.py

Write a Python program in the file requestline.py that determines the validity of an HTTP request line.
You will write your solution in a function called parse(line) right below the place where it says: YOUR CODE HERE
When the function call parse("GET /hello.html HTTP/1.1") is executed, the output of the program should be: /hello.html

Run the file testrequestline.py to execute the PyUnit test bench. PyUnit indicates a successful test with an OK output, and an unsuccessful test with a FAIL output.