HTTPServer0.java

package httpd.v1;

import java.io.PrintStream;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.URLDecoder;
import java.net.URLEncoder;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Scanner;

import com.google.gson.JsonArray;
import com.google.gson.JsonObject;


/**
 * HTTP Server example v0
 *
 * Implements a number of endpoints over HTTP. The root endpoint simply returns
 * a plaintext message "Hello! Welcome to the server.". The /calc endpoint does
 * simple arithmetic with the given query parameters. The various arithmetic
 * operations can be requested directly and will redirect to /calc. The
 * /students endpoint queries the SIS table in the Derby database and returns
 * the students in the given major with a GPA equal or greater than the value
 * given.
 *
 * Supports the following request:
 *
 *    - GET /
 *    - GET /students?major=<major>&gpa=<gpa>
 *    - GET /calc?op=<op>&a=<number>&b=<number>
 *    - GET /<op>?a=<number>&b=<number>
 *
 * where <op> is one of:
 *
 *    - add
 *    - subtract
 *    - multiply
 *    - divide
 *    - exponent
 *
 * **Important Note:**
 *
 * This is implementation is messy because the server logic, handling of the
 * HTTP protocol and the business logic are all mixed together in the same
 * class. In subsequent iterations of this code, we will decouple these parts,
 * and add abstraction and encapsulation to our implementation.
 */
public class HTTPServer0 extends Thread {

  private static final PrintStream log = System.out;
  private static final Map<Integer, String> httpResponseCodes = new HashMap<>();

  static {
    httpResponseCodes.put(100, "HTTP CONTINUE");
    httpResponseCodes.put(101, "SWITCHING PROTOCOLS");
    httpResponseCodes.put(200, "OK");
    httpResponseCodes.put(201, "CREATED");
    httpResponseCodes.put(202, "ACCEPTED");
    httpResponseCodes.put(203, "NON AUTHORITATIVE INFORMATION");
    httpResponseCodes.put(204, "NO CONTENT");
    httpResponseCodes.put(205, "RESET CONTENT");
    httpResponseCodes.put(206, "PARTIAL CONTENT");
    httpResponseCodes.put(300, "MULTIPLE CHOICES");
    httpResponseCodes.put(301, "MOVED PERMANENTLY");
    httpResponseCodes.put(302, "MOVED TEMPORARILY");
    httpResponseCodes.put(303, "SEE OTHER");
    httpResponseCodes.put(304, "NOT MODIFIED");
    httpResponseCodes.put(305, "USE PROXY");
    httpResponseCodes.put(400, "BAD REQUEST");
    httpResponseCodes.put(401, "UNAUTHORIZED");
    httpResponseCodes.put(402, "PAYMENT REQUIRED");
    httpResponseCodes.put(403, "FORBIDDEN");
    httpResponseCodes.put(404, "NOT FOUND");
    httpResponseCodes.put(405, "METHOD NOT ALLOWED");
    httpResponseCodes.put(406, "NOT ACCEPTABLE");
    httpResponseCodes.put(407, "PROXY AUTHENTICATION REQUIRED");
    httpResponseCodes.put(408, "REQUEST TIME OUT");
    httpResponseCodes.put(409, "CONFLICT");
    httpResponseCodes.put(410, "GONE");
    httpResponseCodes.put(411, "LENGTH REQUIRED");
    httpResponseCodes.put(412, "PRECONDITION FAILED");
    httpResponseCodes.put(413, "REQUEST ENTITY TOO LARGE");
    httpResponseCodes.put(414, "REQUEST URI TOO LARGE");
    httpResponseCodes.put(415, "UNSUPPORTED MEDIA TYPE");
    httpResponseCodes.put(500, "INTERNAL SERVER ERROR");
    httpResponseCodes.put(501, "NOT IMPLEMENTED");
    httpResponseCodes.put(502, "BAD GATEWAY");
    httpResponseCodes.put(503, "SERVICE UNAVAILABLE");
    httpResponseCodes.put(504, "GATEWAY TIME OUT");
    httpResponseCodes.put(505, "HTTP VERSION NOT SUPPORTED");
  }

  private Socket client;

  public HTTPServer0(Socket client) {
    this.client = client;
  }

  /// Request

  private String[] getURIComponents(String uri) {
    if (!uri.contains("?")) {
      return new String[]{ uri, "" };
    } else {
      return uri.split("\\?", 2);
    }
  }

  private Map<String, String> getHeaders(Scanner req) {
    Map<String, String> headers = new HashMap<>();

    String buffer;
    String[] pair;

    while (req.hasNextLine()) {
      buffer = req.nextLine();
      if (buffer.isEmpty()) break;
      pair = buffer.split(":\\s+", 2);
      if (pair.length != 2) continue; // malformed
      headers.put(pair[0], pair[1]);
    }
    return headers;
  }

  private Map<String, String> getQueryStrings(String qs) throws Exception {
    Map<String, String> queries = new HashMap<>();
    String[] fields = qs.split("&");

    for (String field : fields) {
      String[] pairs = field.split("=", 2);
      if (pairs.length == 2) {
        queries.put(pairs[0], URLDecoder.decode(pairs[1], "UTF-8"));
      }
    }

    return queries;
  }

  private String toQueryString(Map<String, String> qs) throws Exception {
    List<String> params = new ArrayList<>();
    for (String key : qs.keySet()) {
      params.add(key + "=" + URLEncoder.encode(qs.get(key), "UTF-8"));
    }
    return String.join("&", params);
  }

  private String getRequestBody(Scanner req) {
    String buffer;
    String body = "";

    while (req.hasNextLine()) {
      buffer = req.nextLine();
      if (buffer.isEmpty()) break;
      body += buffer;
    }
    return body;
  }

  /// Response

  private void sendHeaders(PrintStream res, int code, Map<String, Object> headers) {
    res.printf("HTTP/1.1 %d %s\n", code, httpResponseCodes.get(code));
    headers.entrySet().stream().forEach(e -> {
      res.printf("%s: %s\n", e.getKey(), e.getValue().toString());
    });
    res.println();
  }

  /// Thread

  public void run() {
    final String clientAddress = String.format("%s:%d", client.getInetAddress(), client.getPort());
    log.printf("Connected to %s\n", clientAddress);

    try (
      Socket client   = this.client; // Makes sure that client is closed at end of try-statement.
      Scanner req     = new Scanner(client.getInputStream());
      PrintStream res = new PrintStream(client.getOutputStream(), true);
    ) {
      String request = req.nextLine();
      String method, uri, version;

      StringWriter response = new StringWriter();
      PrintWriter  writer   = new PrintWriter(response);

      try (Scanner parse = new Scanner(request)) {
        method   = parse.next().toUpperCase();
        uri      = parse.next();
        version  = parse.next().toUpperCase();
      }

      int status = 200;

      @SuppressWarnings("unused")
      Map<String, String> reqHeaders = getHeaders(req);
      Map<String, Object> resHeaders = new HashMap<>();

      resHeaders.put("Server", "Java HTTP Server : 1.0");
      resHeaders.put("Date", new Date());
      resHeaders.put("Content-Type", "text/plain");

      try {
        if (!method.equals("GET") && !method.equals("HEAD") && !method.equals("POST")) {
          status = 501;
        } else if (!version.equals("HTTP/1.1")) {
          status = 505;
        } else {
          String[] components = getURIComponents(uri);
          uri = components[0];
          Map<String, String> qs = getQueryStrings(components[1]);
          
          @SuppressWarnings("unused")
          String body = null;
          if (method.equals("POST")) {
            body = getRequestBody(req);
          }

          switch (uri) {
            case "/":
              writer.println("Hello! Welcome to the server.");
              break;

            case "/calc":
              if (qs.containsKey("op") && qs.containsKey("a") && qs.containsKey("b")) {
                String op = qs.get("op");
                double a = Double.parseDouble(qs.get("a"));
                double b = Double.parseDouble(qs.get("b"));

                switch (op) {
                  case "add":      writer.println(a + b); break;
                  case "subtract": writer.println(a - b); break;
                  case "multiply": writer.println(a * b); break;
                  case "divide":   writer.println(a / b); break;
                  case "exponent": writer.println(Math.pow(a, b)); break;
                  default:
                    status = 400;
                }
              } else {
                status = 400;
              }
              break;

            case "/add":
            case "/subtract":
            case "/multiply":
            case "/divide":
            case "/exponent":
              resHeaders.put("Location", "/calc?op=" + uri.substring(1) + "&" + toQueryString(qs));
              status = 301;
              break;

            case "/students":
              if (qs.containsKey("major") && qs.containsKey("gpa")) {
                String url   = "jdbc:derby://localhost:64413/EECS";
                String query = "SELECT * FROM Roumani.Sis "
                              + "WHERE major = ? "
                              + "AND gpa >= ?";

                String major = qs.get("major");
                double gpa   = Double.parseDouble(qs.get("gpa"));

                try (Connection connection = DriverManager.getConnection(url)) {
                  log.printf("Connected to database: %s\n", connection.getMetaData().getURL());

                  try (PreparedStatement statement = connection.prepareStatement(query)) {
                    statement.setString(1, major);
                    statement.setDouble(2, gpa);

                    JsonArray students = new JsonArray();

                    try (ResultSet rs = statement.executeQuery()) {
                      while (rs.next()) {
                        JsonObject student = new JsonObject();

                        student.addProperty("id",           rs.getInt("id"));
                        student.addProperty("surname",      rs.getString("surname"));
                        student.addProperty("givenName",    rs.getString("givenname"));
                        student.addProperty("gpa",          rs.getDouble("gpa"));
                        student.addProperty("yearAdmitted", rs.getInt("yearadmitted"));

                        students.add(student);
                      }
                    }

                    JsonObject jsonRoot = new JsonObject();
                    jsonRoot.add("students", students);

                    resHeaders.put("Content-Type", "application/json");
                    writer.println(jsonRoot);
                  }
                } catch (SQLException e) {
                  log.println(e);
                  status = 500;
                } finally {
                  log.println("Disconnected from database.");
                }
              } else {
                status = 400;
              }
              break;

            default:
              status = 404;
          }
        }
      } catch (Exception err) {
        log.println(err.getMessage());
        err.printStackTrace(log);
        status = 500;
      }

      if (status != 200 && response.toString().length() == 0) {
        writer.println(httpResponseCodes.get(status));
      }

      String responseText = response.toString();
      resHeaders.put("Content-Length", responseText.getBytes().length);
      sendHeaders(res, status, resHeaders);

      if (!method.equals("HEAD")) {
        res.println(responseText);
      }

      res.flush(); // flush character output stream buffer
    } catch (Exception e) {
      log.println(e);
    } finally {
      log.printf("Disconnected from %s\n", clientAddress);
    }
  }

  /// Main

  public static void main(String[] args) throws Exception {
    int port = 0;
    InetAddress host = InetAddress.getLocalHost(); // .getLoopbackAddress();
    try (ServerSocket server = new ServerSocket(port, 0, host)) {
      log.printf("Server listening on %s:%d\n", server.getInetAddress(), server.getLocalPort());
      while (true) {
        (new HTTPServer0(server.accept())).start();
      }
    }
  }
}