CS1103 Programming Assignment Unit 7 - A web server

Questions

Please write a web server that is capable of sending files to a web browser on request. The web server creates a listening socket and accepts connections. It implements just enough of the HTTP/1.1 protocol to enable it to read requests for files and to send the requested files. It is also capable of sending error responses to the client when appropriate.

1. Instructions for use

To test this program, you need to change the value of variable rootDirectory in the code to the directory where you store the test files. I use “F:” in my code, and you can change it. Then put the test files in the directory you choose, and then enter the corresponding URL in the browser, for example, using http://localhost:50505/text.txt to ask for a text.txt file from the server. Besides, you can find the test files in the attachment, which contains a text.txt file and a directory with an index.html.

2. Programs and Test Files

2.1. WebServer.java

import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Scanner;

/**
 * This program is web server that is capable of sending files to a web browser on request.
 * The web server creates a listening socket and accept connections.
 * It implements just enough of the HTTP/1.1 protocol to enable it to read requests for files and to send the requested files.
 * It is also capable of sending error responses to the client when appropriate.
 */
public class WebServer {

    /**
     * The server listens on this port.
     * Note that the port number must be greater than 1024 and lest than 65535.
     */
    private final static int LISTENING_PORT = 50505;

    /**
     * Main program opens a server socket and listens for connection requests.
     * It calls the handleConnection() method to respond to connection requests.
     *
     * @param args
     */
    public static void main(String[] args) {
        ServerSocket serverSocket;
        try {
            serverSocket = new ServerSocket(LISTENING_PORT);
        } catch (Exception e) {
            System.out.println("Failed to create listening socket.");
            return;
        }
        System.out.println("Listening on port " + LISTENING_PORT);
        try {
            while (true) {
                Socket connection = serverSocket.accept();
                System.out.println("\nConnection from " + connection.getRemoteSocketAddress());
                // Create multiple threads to handle requests
                ConnectionThread thread = new ConnectionThread(connection);
                thread.start();
            }
        } catch (Exception e) {
            System.out.println("Server socket shut down unexpectedly!");
            System.out.println("Error: " + e);
            System.out.println("Exiting.");
        }
    }

    /**
     * This method gets an already connected socket as a parameter. It can use that socket
     * to get an InputStream and an OutputStream for communicating over the connection.
     * It can read the request from the input stream and send a response to the output stream.
     * Finally, it can close the connection.
     *
     * @param connection the connected socket that will be used to communicate with the client.
     */
    public static void handleConnection(Socket connection) {
        try {
            String rootDirectory = "F:";

            Scanner in = new Scanner(connection.getInputStream()); // Create an input stream
            String line = in.nextLine().trim(); // Get the first line of the request

            System.out.println("The first line of the request: " + line);

            // Read the first three tokens: "GET", the file path, and "HTTP/1.1" or "HTTP/1.0"
            // If you can't read three tokens, you should consider that to be an error
            String[] tokens = line.trim().split("\\s+"); // Split the first line of the request
            String requestMethod = tokens[0].trim();
            String filePath = tokens[1].trim();
            String httpVersion = tokens[2].trim();

            System.out.println("requestMethod: " + requestMethod); // GET
            System.out.println("filePath: " + filePath); // /path/file.txt
            System.out.println("httpVersion: " + httpVersion); // HTTP/1.1

            // The method in the request is not 'GET', return 501
            if (!requestMethod.equals("GET")) {
                sendErrorResponse(501, connection.getOutputStream());
                in.close();
                connection.close();
                return; // exit handleConnection after sending the error response
            }

            // If the syntax of the request is bad, return 400
            if (!httpVersion.equals("HTTP/1.0") && !httpVersion.equals("HTTP/1.1")) {
                sendErrorResponse(400, connection.getOutputStream());
                in.close();
                connection.close();
                return; // exit handleConnection after sending the error response
            }

            // Use the exists() of the File class to test whether the file path in the request is legal and whether the file exists
            // If the path is a directory, and it has an index.html file, send the status line, headers and the index.html
            // If the path is a file, send the status line, headers and the index.html
            // If the path does exist, return 404
            File file = new File(rootDirectory + filePath);  // Create a File object to represent the file that is being requested
            if (file.exists()) { // Check if the file exists
                if (file.isDirectory()) { // If the file is a directory, and it has an index.html file, send this index.html
                    String[] content = file.list();
                    if (content != null) {
                        for (String name : content) {
                            if (name.equals("index.html")) {
                                //Send the status line, some headers, and an empty line.
                                String filePathOfIndex = filePath + "/index.html";
                                File fileIndex = new File(rootDirectory + filePathOfIndex);
                                sendStatusLineAndHeaders(fileIndex, connection, filePathOfIndex);
                                // Send the file
                                sendFile(fileIndex, connection.getOutputStream());
                            }
                        }
                    }
                } else {  // If the path is a file, send the file
                    File fileFromServer = new File(rootDirectory + filePath);
                    if (fileFromServer.canRead()) {
                        //Send the status line, some headers, and an empty line.
                        sendStatusLineAndHeaders(fileFromServer, connection, filePath);
                        // Send the file
                        sendFile(fileFromServer, connection.getOutputStream());
                    } else {
                        // You don't have permission to read the file, return 403
                        sendErrorResponse(403, connection.getOutputStream());
                        in.close();
                        connection.close();
                        return; // exit handleConnection after sending the error response
                    }
                }
            } else { // The file does not exit, return 404
                sendErrorResponse(404, connection.getOutputStream());
                in.close();
                connection.close();
                return; // exit handleConnection after sending the error response
            }
            in.close(); // Close the stream
        } catch (Exception e) {
            System.out.println("Error while communicating with client: " + e);
        } finally {
            try {
                connection.close(); // make SURE connection is closed before returning!
            } catch (Exception e) {
                e.printStackTrace();
            }
            System.out.println("Connection closed.");
        }
    }

    /**
     * Send a file to the client
     *
     * @param file
     * @param socketOut
     * @throws IOException
     */
    private static void sendFile(File file, OutputStream socketOut) throws IOException {
        InputStream in = new BufferedInputStream(new FileInputStream(file));
        OutputStream out = new BufferedOutputStream(socketOut);

        while (true) {
            int x = in.read(); // read one byte from file
            if (x < 0)
                break; // end of file reached
            out.write(x); // write the byte to the socket
        }

        out.flush();
    }

    /**
     * This program returns what kind of data is in the file
     *
     * @param fileName
     * @return
     */
    private static String getMimeType(String fileName) {
        int pos = fileName.lastIndexOf('.');
        if (pos < 0) // no file extension in name
            return "x-application/x-unknown";
        String ext = fileName.substring(pos + 1).toLowerCase();
        if (ext.equals("txt")) return "text/plain";
        else if (ext.equals("html")) return "text/html";
        else if (ext.equals("htm")) return "text/html";
        else if (ext.equals("css")) return "text/css";
        else if (ext.equals("js")) return "text/javascript";
        else if (ext.equals("java")) return "text/x-java";
        else if (ext.equals("jpeg")) return "image/jpeg";
        else if (ext.equals("jpg")) return "image/jpeg";
        else if (ext.equals("png")) return "image/png";
        else if (ext.equals("gif")) return "image/gif";
        else if (ext.equals("ico")) return "image/x-icon";
        else if (ext.equals("class")) return "application/java-vm";
        else if (ext.equals("jar")) return "application/java-archive";
        else if (ext.equals("zip")) return "application/zip";
        else if (ext.equals("xml")) return "application/xml";
        else if (ext.equals("xhtml")) return "application/xhtml+xml";
        else return "x-application/x-unknown";
        // Note: x-application/x-unknown is something made up;
        // it will probably make the browser offer to save the file.
    }

    /**
     * If there are no errors, send the status line with the code 200, headers, and an empty line
     *
     * @param file
     * @param connection
     * @param filePath
     * @throws IOException
     */
    private static void sendStatusLineAndHeaders(File file, Socket connection, String filePath) throws IOException {
        PrintWriter out = new PrintWriter(connection.getOutputStream());

        out.print("HTTP/1.1 200 OK" + "\r\n"); // tThe status line
        out.print("Connection: close" + "\r\n"); // Connection
        out.print("Content-Type: " + getMimeType(filePath) + "\r\n"); // Content-Type
        out.print("Content-Length: " + file.length() + "\r\n"); // Content-Length
        out.print("\r\n"); // An empty line

        out.flush();
    }

    /**
     * If something goes wrong with a request,
     * the server should send an error response with the headers and a page
     *
     * @param errorCode
     * @param socketOut
     */
    private static void sendErrorResponse(int errorCode, OutputStream socketOut) {
        PrintWriter out = new PrintWriter(socketOut);

        if (errorCode == 404) {
            // Send the headers
            out.print("HTTP/1.1 " + errorCode + " Not Found" + "\r\n"); // The status line
            out.print("Connection: close" + "\r\n"); // Connection
            out.print("Content-Type: text/html" + "\r\n"); // Content-Type
            out.print("\r\n"); // An empty line

            // Send a page that is to be displayed in the browser to inform the user of the error
            out.print("<html><head><title>Error</title></head><body>" + "\r\n");
            out.print("<h2>Error: 404 Not Found</h2>" + "\r\n");
            out.print("<p>The resource that you requested does not exist on this server.</p>" + "\r\n");
            out.print("</body></html>" + "\r\n");
        }

        if (errorCode == 403) {
            // Send the headers
            out.print("HTTP/1.1 " + errorCode + " Forbidden" + "\r\n"); // The status line
            out.print("Connection: close" + "\r\n"); // Connection
            out.print("Content-Type: text/html" + "\r\n"); // Content-Type
            out.print("\r\n"); // An empty line

            // Send a page that is to be displayed in the browser to inform the user of the error
            out.print("<html><head><title>Error</title></head><body>" + "\r\n");
            out.print("<h2>Error: Forbidden</h2>" + "\r\n");
            out.print("<p> You don't have permission to read the file </p>" + "\r\n");
            out.print("</body></html>" + "\r\n");
        }

        if (errorCode == 400) {
            // Send the headers
            out.print("HTTP/1.1 " + errorCode + " Bad Request" + "\r\n"); // The status line
            out.print("Connection: close" + "\r\n"); // Connection
            out.print("Content-Type: text/html" + "\r\n"); // Content-Type
            out.print("\r\n"); // An empty line

            // Send a page that is to be displayed in the browser to inform the user of the error
            out.print("<html><head><title>Error</title></head><body>" + "\r\n");
            out.print("<h2>Error: Bad Request</h2>" + "\r\n");
            out.print("<p> The syntax of the request is bad </p>" + "\r\n");
            out.print("</body></html>" + "\r\n");
        }

        if (errorCode == 501) {
            // Send the headers
            out.print("HTTP/1.1 " + errorCode + " Not Implemented" + "\r\n"); // The status line
            out.print("Connection: close" + "\r\n"); // Connection
            out.print("Content-Type: text/html" + "\r\n"); // Content-Type
            out.print("\r\n"); // An empty line

            // Send a page that is to be displayed in the browser to inform the user of the error
            out.print("<html><head><title>Error</title></head><body>" + "\r\n");
            out.print("<h2>Error: Not Implemented</h2>" + "\r\n");
            out.print("<p> The method in the request is not \"GET\" </p>" + "\r\n");
            out.print("</body></html>" + "\r\n");
        }

        if (errorCode == 500) {
            // Send the headers
            out.print("HTTP/1.1 " + errorCode + " Internal Server Error" + "\r\n"); // The status line
            out.print("Connection: close" + "\r\n"); // Connection
            out.print("Content-Type: text/html" + "\r\n"); // Content-Type
            out.print("\r\n"); // An empty line

            // Send a page that is to be displayed in the browser to inform the user of the error
            out.print("<html><head><title>Error</title></head><body>" + "\r\n");
            out.print("<h2>Error: Internal Server Error</h2>" + "\r\n");
            out.print("<p> Some unexpected error happened in the server </p>" + "\r\n");
            out.print("</body></html>" + "\r\n");
        }

        out.flush();
        out.close();
    }

    /**
     * This class is used to create multiple threads for requests
     */
    private static class ConnectionThread extends Thread {
        Socket connection;

        ConnectionThread(Socket connection) {
            this.connection = connection;
        }

        public void run() {
            handleConnection(connection);
        }
    }
}

2.2. Test files

Please click here to download the test files.

3. Outputs

3.1. Case 1

Use the browser to send a request to the server, and ask for the text.txt file. After the server receives the request, it returns the text.txt file to the browser, and the browser displays the content of text.txt

The outputs of the browser:

The outputs of the WebServer program:

3.2. Case 2

Use the browser to send a request to the server, but the path in the file is a directory instead of a file. After the server receives the request, it returns the index.html file in that directory to the browser, and the browser displays the content of the index.html

The outputs of the browser:

The outputs of the WebServer program:

3.3. Case 3

Use the browser to send a request to the server, but if the path is illegal or the file does not exist, the server returns a 404 error and the corresponding HTML file to the browser, and the browser displays the content of the HTML file.

The outputs of the browser:

The outputs of the WebServer program:

3.4. Case 4

For other error types, such as 501 error, which means that the method in the request is not “GET”, we need to use telnet to test. My specific approach is to use the command (telnet localhost 50505) to connect to the server WebServer, and then enter the command (POST /text.txt HTTP/1.1). Because the method in the request header is “POST” instead of “GET“, the server will return a 501 error and the corresponding HTML, and then the telnet side will display the content of the HTML.

The outputs of the telnet:

The outputs of the WebServer program:

​

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This is the ending, thanks for reading.

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