Lab 9: Request Line

Task Outline

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

Background Theory

• 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.

Example Case

• 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.

Hints

• 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 indexOf(String word) function to discover the index of the first SPACE, and then use indexOf(String word, int start) to discover the index of the other SPACE.

Code Distribution

Description	File Size	File Name
Java Source Code for Request Line	5.0KB	lab09.zip

Contents of lab09.zip:

Lab09RequestLine/
├── package.bluej
├── README.TXT
├── RequestLine.class
├── RequestLine.ctxt
├── RequestLine.java
├── RequestLineJUnitTest.class
├── RequestLineJUnitTest.ctxt
└── RequestLineJUnitTest.java

Specification

• Write a Java program in the file RequestLine.java that determines the validity of an HTTP request line.
• You will write your solution in a function called parse(String 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

Testing

• Click on the Run Tests button to execute the JUnit test bench. JUnit indicates a successful test with a green bar, and an unsuccessful test with a red bar.

Submission

• Upload the file RequestLine.java to the Web-CAT automated grading platform.