Proxy Cache Assignment Level 1

This assignment involves implementing a proxy cache in Java. The provided code includes three Java files: ProxyCache.java, HttpRequest.java, and HttpResponse.java. ProxyCache.java handles client connections, forwards requests to the server, and sends responses back to the client. HttpRequest.java parses HTTP requests from clients, extracting information like the method, URL, and headers. HttpResponse.java reads responses from the server, handling headers and the response body. The assignment requires filling in missing code sections within these files to complete the proxy cache functionality. The code is designed to handle GET requests and includes error handling for various scenarios, such as unknown hosts and I/O exceptions. The solution provided on the website offers a complete implementation of the missing code sections, allowing students to understand the concepts and complete their assignment.

Code for proxy cache Assignment
This page contains the code for the proxy cache assignment level 1 implementation. You can
copy the code into the appropriate java files.
ProxyCache.java
import java.net.*;
import java.io.*;
import java.util.*;
public class ProxyCache {
/** Port for the proxy */
private static int port;
/** Socket for client connections */
private static ServerSocket socket;
/** Create the ProxyCache object and the socket */
public static void init(int p) {
port = p;
try {
socket = /* Fill in */;
} catch (IOException e) {
System.out.println("Error creating socket: " + e);
System.exit(-1);
}
}
public static void handle(Socket client) {
Socket server = null;
HttpRequest request = null;
HttpResponse response = null;
/* Process request. If there are any exceptions, then simply
* return and end this request. This unfortunately means the
* client will hang for a while, until it timeouts. */
/* Read request */
try {
BufferedReader fromClient = /* Fill in */;
request = /* Fill in */;
} catch (IOException e) {
System.out.println("Error reading request from client: "
+ e);
return;
}
/* Send request to server */
try {
/* Open socket and write request to socket */
server = /* Fill in */;
DataOutputStream toServer = /* Fill in */;
/* Fill in */
} catch (UnknownHostException e) {
System.out.println("Unknown host: " + request.getHost());

System.out.println(e);
return;
} catch (IOException e) {
System.out.println("Error writing request to server: " +
e);
return;
}
/* Read response and forward it to client */
try {
DataInputStream fromServer = /* Fill in */;
response = /* Fill in */;
DataOutputStream toClient = /* Fill in */;
/* Fill in */
/* Write response to client. First headers, then body */
client.close();
server.close();
} catch (IOException e) {
System.out.println("Error writing response to client: " +
e);
}
}
/* -------------------------------------------------- */
/** Read command line arguments and start proxy */
public static void main(String args[]) {
int myPort = 0;
try {
myPort = Integer.parseInt(args[0]);
} catch (ArrayIndexOutOfBoundsException e) {
System.out.println("Need port number as argument");
System.exit(-1);
} catch (NumberFormatException e) {
System.out.println("Please give port number as
integer.");
System.exit(-1);
}
init(myPort);
/** Main loop. Listen for incoming connections and spawn a
new
* thread for handling them */
Socket client = null;
while (true) {
try {
client = /* Fill in */;
handle(client);
} catch (IOException e) {
System.out.println("Error reading request from
client: " + e);
/* Definitely cannot continue processing this
request,
* so skip to next iteration of while loop. */
continue;
}
}

}
}

HttpRequest.java
import java.io.*;
import java.net.*;
import java.util.*;
public class HttpRequest {
/** Help variables */
final static String CRLF = "\r\n";
final static int HTTP_PORT = 80;
/** Store the request parameters */
String method;
String URL;
String version;
String headers = "";
/** Server and port */
private String host;
private int port;
/** Create HttpRequest by reading it from the client socket */
public HttpRequest(BufferedReader from) {
String firstLine = "";
try {
firstLine = from.readLine();
} catch (IOException e) {
System.out.println("Error reading request line: " + e);
}
String[] tmp = firstLine.split(" ");
method = /* Fill in */;
URL = /* Fill in */;
version = /* Fill in */;
System.out.println("URL is: " + URL);
if (!method.equals("GET")) {
System.out.println("Error: Method not GET");
}
try {
String line = from.readLine();
while (line.length() != 0) {
headers += line + CRLF;
/* We need to find host header to know which server
to
* contact in case the request URL is not complete.
*/
if (line.startsWith("Host:")) {
tmp = line.split(" ");
if (tmp[1].indexOf(':') > 0) {
String[] tmp2 = tmp[1].split(":");
host = tmp2[0];
port = Integer.parseInt(tmp2[1]);
} else {
host = tmp[1];
port = HTTP_PORT;
}
}
line = from.readLine();
}

} catch (IOException e) {
System.out.println("Error reading from socket: " + e);
return;
}
System.out.println("Host to contact is: " + host + " at port
" + port);
}
/** Return host for which this request is intended */
public String getHost() {
return host;
}
/** Return port for server */
public int getPort() {
return port;
}
/** Return URL to connect to */
public String getURL() {
return URL;
}
/**
* Convert request into a string for easy re-sending.
*/
public String toString() {
String req = "";
req = method + " " + URL + " " + version + CRLF;
req += headers;
/* This proxy does not support persistent connections */
req += "Connection: close" + CRLF;
req += CRLF;
return req;
}
}

HttpResponse.java
import java.io.*;
import java.net.*;
import java.util.*;
public class HttpResponse {
final static String CRLF = "\r\n";
/** How big is the buffer used for reading the object */
final static int BUF_SIZE = 8192;
/** Maximum size of objects that this proxy can handle. For the
* moment set to 100 KB. You can adjust this as needed. */
final static int MAX_OBJECT_SIZE = 100000;
/** Reply status and headers */
String version;
int status;
String statusLine = "";
String headers = "";
/* Body of reply */
byte[] body = new byte[MAX_OBJECT_SIZE];
/** Read response from server. */
public HttpResponse(DataInputStream fromServer) {
/* Length of the object */
int length = -1;
boolean gotStatusLine = false;
/* First read status line and response headers */
try {
String line = /* Fill in */;
while (line.length() != 0) {
if (!gotStatusLine) {
statusLine = line;
gotStatusLine = true;
} else {
headers += line + CRLF;
}
/* Get length of content as indicated by
* Content-Length header. Unfortunately this is not
* present in every response. Some servers return the
* header "Content-Length", others return
* "Content-length". You need to check for both
* here. */
if (line.startsWith(/* Fill in */) ||
line.startsWith(/* Fill in */)) {
String[] tmp = line.split(" ");
length = Integer.parseInt(tmp[1]);
}
line = fromServer.readLine();
}
} catch (IOException e) {
System.out.println("Error reading headers from server: "
+ e);
return;
}
try {
int bytesRead = 0;

byte buf[] = new byte[BUF_SIZE];
boolean loop = false;
/* If we didn't get Content-Length header, just loop
until
* the connection is closed. */
if (length == -1) {
loop = true;
}
/* Read the body in chunks of BUF_SIZE and copy the chunk
* into body. Usually replies come back in smaller chunks
* than BUF_SIZE. The while-loop ends when either we have
* read Content-Length bytes or when the connection is
* closed (when there is no Connection-Length in the
* response. */
while (bytesRead < length || loop) {
/* Read it in as binary data */
int res = /* Fill in */;
if (res == -1) {
break;
}
/* Copy the bytes into body. Make sure we don't
exceed
* the maximum object size. */
for (int i = 0;
i < res && (i + bytesRead) < MAX_OBJECT_SIZE;
i++) {
/* Fill in */
}
bytesRead += res;
}
} catch (IOException e) {
System.out.println("Error reading response body: " + e);
return;
}
}
/**
* Convert response into a string for easy re-sending. Only
* converts the response headers, body is not converted to a
* string.
*/
public String toString() {
String res = "";
res = statusLine + CRLF;
res += headers;
res += CRLF;
return res;
}
}