cse15l-lab-reports

Lab Report 2 - Servers and Bugs

Part 1 - Web Server

This is my code for my web server called StringServer

import java.io.IOException;
import java.net.URI;

class Handler3 implements URLHandler {
    
    String str = "";

    public String handleRequest(URI url) {
        if (url.getPath().equals("/")) {
            return String.format("%s", str);
        }

        else {
            System.out.println("Path: " + url.getPath());
            if (url.getPath().contains("/add-message")) {
                String[] parameters = url.getQuery().split("=");
                if (parameters[0].equals("s")) {
                    str += parameters[1]+ "\n";
                    
                    return String.format("%s",str);
                }
            }
            return "404 Not Found!";
        }
    }
}

class StringServer {
    public static void main(String[] args) throws IOException {
        if(args.length == 0){
            System.out.println("Missing port number! Try any number between 1024 to 49151");
            return;
        }

        int port = Integer.parseInt(args[0]);

        Server.start(port, new Handler3());
    }
}

The first message I added was “Hello” to my web server.

Methods called: handleRequest is called when adding the message “Hello”.

Arguement to handleRequest: “http://localhost:4000/add-message?s=Hello” is the argument passed to handleRequest.

Relevant Fields: String[] parameters holds the query which is split by “=” so it contains “s” in the first index and “Hello” in the second index. String str holds all of the messages added to the web server and starts out as “”. After handleRequest is called, str contains “Hello\n”.

The second message I added was “How’s it going 1” to my web server.

Methods called: handleRequest is called when adding the message “How’s it going 1”.

Arguement to handleRequest: “http://localhost:4000/add-message?s=How’s it going 1” is the argument passed to handleRequest.

Relevant Fields: String[] parameters contains “s” in the first index and “How’s it going 1” in the second index. String str contains previously added messages so it contains “Hello\n”. After handleRequest is called again, str contains “Hello\nHow’s it going 1\n”.

Part 2 - Bugs

Failure Inducing Input:

@Test 
	public void testReverseInPlaceFail() {
    int[] input2 = {1,2,3};
    ArrayExamples.reverseInPlace(input2);
    assertArrayEquals(new int[]{ 3,2,1 }, input2);
	}

Non-Failure Inducing Input:

@Test 
	public void testReverseInPlaceNonFail() {
    int[] input1 = { 3 };
    ArrayExamples.reverseInPlace(input1);
    assertArrayEquals(new int[]{ 3 }, input1);

Symptom:

Buggy Program:

static void reverseInPlace(int[] arr) {
    for(int i = 0; i < arr.length; i += 1) {
      arr[i] = arr[arr.length - i - 1];
    }
  }

Bug-Fixed Program:

static void reverseInPlace(int[] arr) {
    for(int i = 0; i < arr.length/2; i += 1) {
      int temp = arr[i];
      arr[i] = arr[arr.length - i - 1];
      arr[arr.length - i-1] = temp;
    }
  }

Fix Explanation:
Originally, the buggy program was replacing the first half of elements in the array with the second half of the elements without containing the elements being replaced somewhere else first. This meant the elements being replaced were essentially erased from the array and could no longer be swapped to the index of the element taking its place. The fix was to create a temp variable to temporarily hold the element being replaced (int temp = arr[i];). Then, after the element is replaced, the index of the element that replaced it is set to element in temp (arr[arr.length - i-1] = temp;). Finally, to ensure once the array is reversed that the program does not reverse it back to the original order, the loop needs to end after swapping the first half of the elements with the second half of elements (i < arr.length/2).

Testing Bug-Fixed Program:

Part 3 - Something New I Learned

Something new I learned about in the past two weeks that I did not know before what how to run my own web server. I had never tried to create my own before CSE 15L, so I never took the time to figure out how to code it. I found it really intriguing even though the servers we created in lab were very basic. Eventually, I hope to code a much more complex web server to increase my understanding of them.