Added boundary for size of packets read by extension server

- Also added documentation and refactored the code

G-Earth/src/main/java/gearth/services/extension_handler/extensions/implementations/network/NetworkExtensionsProducer.java

@@ -2,85 +2,125 @@ package gearth.services.extension_handler.extensions.implementations.network;
 
 import gearth.protocol.HPacket;
 import gearth.services.extension_handler.extensions.extensionproducers.ExtensionProducer;
+import gearth.services.extension_handler.extensions.extensionproducers.ExtensionProducerFactory;
 import gearth.services.extension_handler.extensions.extensionproducers.ExtensionProducerObserver;
 import gearth.services.extension_handler.extensions.implementations.network.authentication.Authenticator;
 
 import java.io.DataInputStream;
 import java.io.IOException;
-import java.io.InputStream;
 import java.net.ServerSocket;
 import java.net.Socket;
 
 /**
+ * Represents an {@link ExtensionProducer} that implements a server to which
+ * remotely-ran extensions can connect.
+ *
+ * @see ExtensionProducerFactory#getAll() for instance creation.
+ *
  * Created by Jonas on 21/06/18.
  */
-public class NetworkExtensionsProducer implements ExtensionProducer {
+public final class NetworkExtensionsProducer implements ExtensionProducer {
 
+    /**
+     * Initial port server tries to listen at, if {@link ServerSocket} creation fails,
+     * it tries next port.
+     */
+    private static final int PORT_ONSET = 9092;
+
+    /**
+     * Represents the number of bytes per boolean encoded in an incoming packet.
+     */
+    private static final int BOOLEAN_SIZE = 1;
+
+    /**
+     * Represents the maximum number of bytes per string encoded in an incoming packet.
+     */
+    private static final int MAX_STRING_SIZE = Character.BYTES * 100;
+
+    /**
+     * Represents the maximum number of bytes of an incoming packet.
+     * <p>
+     * Used as a form of validation for packets, prevents other Apps that connect
+     * with the server from sending unexpected data and inexplicably causing huge byte array allocations.
+     * <p>
+     * Since the server only accepts {@link NetworkExtensionInfo.INCOMING_MESSAGES_IDS#EXTENSIONINFO} packets,
+     * this value is calculated based on that packet.
+     */
+    private static final int MAX_PACKET_SIZE = (MAX_STRING_SIZE * 6) + (BOOLEAN_SIZE * 4);
+
+    /**
+     * The port at which the {@link #serverSocket} is listening for incoming connections.
+     */
     public static int extensionPort = -1;
 
-
     private ServerSocket serverSocket;
 
     @Override
     public void startProducing(ExtensionProducerObserver observer) {
-//        serverSocket = new ServerSocket(0);
-        int port = 9092;
-        boolean serverSetup = false;
-        while (!serverSetup) {
-            serverSetup = createServer(port);
-            port++;
-        }
 
+        /*
+        Initialise the serverSocket at the argued port.
+         */
+        int port = PORT_ONSET;
+        while (!createServer(port))
+            ++port;
 
+        /*
+        Start connection listener thread.
+         */
         new Thread(() -> {
+
             try {
+
                 while (!serverSocket.isClosed()) {
-                    Socket extensionSocket = serverSocket.accept();
+
+                    // accept a new connection
+                    final Socket extensionSocket = serverSocket.accept();
                     extensionSocket.setTcpNoDelay(true);
 
+                    /*
+                    Start client session handler thread.
+                     */
                     new Thread(() -> {
+
                         try {
+
+                            // write INFOREQUEST packet to client
                             synchronized (extensionSocket) {
                                 extensionSocket.getOutputStream().write((new HPacket(NetworkExtensionInfo.OUTGOING_MESSAGES_IDS.INFOREQUEST)).toBytes());
                             }
 
-                            InputStream inputStream = extensionSocket.getInputStream();
-                            DataInputStream dIn = new DataInputStream(inputStream);
+                            final DataInputStream dIn = new DataInputStream(extensionSocket.getInputStream());
 
+                            // listen to incoming data from client
                             while (!extensionSocket.isClosed()) {
 
-                                int length = dIn.readInt();
-                                byte[] headerandbody = new byte[length + 4];
+                                final int length = dIn.readInt();
 
-                                int amountRead = 0;
-                                while (amountRead < length) {
-                                    amountRead += dIn.read(headerandbody, 4 + amountRead, Math.min(dIn.available(), length - amountRead));
-                                }
+                                if (length > MAX_PACKET_SIZE)
+                                    break;
 
-                                HPacket packet = new HPacket(headerandbody);
-                                packet.fixLength();
+                                final HPacket packet = readPacket(dIn, length);
 
                                 if (packet.headerId() == NetworkExtensionInfo.INCOMING_MESSAGES_IDS.EXTENSIONINFO) {
-                                    NetworkExtension gEarthExtension = new NetworkExtension(
-                                            packet,
-                                            extensionSocket
-                                    );
 
-                                    if (Authenticator.evaluate(gEarthExtension)) {
+                                    final NetworkExtension gEarthExtension = new NetworkExtension(packet, extensionSocket);
+
+                                    if (Authenticator.evaluate(gEarthExtension))
                                         observer.onExtensionProduced(gEarthExtension);
-                                    }
-                                    else {
+                                    else
                                         gEarthExtension.close();
-                                    }
 
                                     break;
                                 }
                             }
-
-                        } catch (IOException ignored) {}
+                        } catch (IOException ignored) {
+                        }
                     }).start();
                 }
-            } catch (IOException e) {e.printStackTrace();}
+            } catch (IOException e) {
+                e.printStackTrace();
+            }
         }).start();
     }
 
@@ -94,6 +134,23 @@ public class NetworkExtensionsProducer implements ExtensionProducer {
         }
     }
 
+    private HPacket readPacket(DataInputStream dIn, int length) throws IOException {
+        final byte[] headerAndBody = new byte[length + 4];
+
+        int amountRead = 0;
+        while (amountRead < length)
+            amountRead += dIn.read(headerAndBody, 4 + amountRead, Math.min(dIn.available(), length - amountRead));
+
+        final HPacket packet = new HPacket(headerAndBody);
+        packet.fixLength();
+        return packet;
+    }
+
+    /**
+     * Retrieves the {@link ServerSocket#getLocalPort()} of {@link #serverSocket}.
+     *
+     * @return the port number to which {@link #serverSocket} is listening or -1 if the socket is not bound yet.
+     */
     public int getPort() {
         return serverSocket.getLocalPort();
     }