Fix JPAN refactoring (#46)

Co-authored-by: Tilmann Zäschke <tilmann.zaeschke@inf.ethz.ch>

CHANGELOG.md

@@ -13,6 +13,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Support for `/etc/scion/hosts` and for OS search domains (e.g. `/etc/resolv.conf`). 
   [#40](https://github.com/netsec-ethz/scion-java-client/pull/40)
 - CI builds for Windows and MacOS. [#41](https://github.com/netsec-ethz/scion-java-client/pull/41)
+- Added support communicating with a dispatcher-endhost in the local AS, see 
+  `DatagramChannel.configureRemoteDispatcher`. 
+  [#46](https://github.com/netsec-ethz/scion-java-client/pull/46)
 
 ### Changed
 - BREAKING CHANGE: Changed maven artifactId to "client"
@@ -38,7 +41,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
   [#35](https://github.com/netsec-ethz/scion-java-client/pull/35)
 - **BREAKING CHANGE**: Renamed project to `jpan`. 
   [#43](https://github.com/netsec-ethz/scion-java-client/pull/43),
-  [#46](https://github.com/netsec-ethz/scion-java-client/pull/46)
+  [#45](https://github.com/netsec-ethz/scion-java-client/pull/45)
 - **BREAKING CHANGE**: `Path` now returns `InetAddress` instead of `byte[]`
   [#44](https://github.com/netsec-ethz/scion-java-client/pull/44)
 

README.md

@@ -41,7 +41,11 @@ JPAN can be used in one of the following ways:
 - You can use JPAN stand-alone (without local SCION installation),
   however it must listen on port 30041 for incoming SCION packets because
   SCION routers currently will forward data only to that port. 
-- If you need a local SCION installation (Go implementation),
+- If you are contacting an endhost within your own AS, and the endhost uses a dispatcher, then you 
+  must set the flag `DatagramChannel.configureRemoteDispatcher(true)`. This ensure that the outgoing
+  packet is sent to port 30041 on the remote machine. The flag has no effect on traffic sent to a 
+  remote AS. 
+- If you need a local SCION installation on your machine (Go implementation),
   consider using the dispatch-off branch/PR.
 - When you need to run a local system with dispatcher, you can try to use port forwarding
   to forward incoming data to your Java application port. The application port must not be 30041.

src/main/java/org/scion/jpan/AbstractDatagramChannel.java

@@ -45,6 +45,7 @@ abstract class AbstractDatagramChannel<C extends AbstractDatagramChannel<?>> imp
   // Whether we have a connectionPath is independent of whether the underlying channel is connected.
   private RequestPath connectionPath;
   private InetAddress localAddress;
+  private boolean isBoundToAddress = false;
   private boolean cfgReportFailedValidation = false;
   private PathPolicy pathPolicy = PathPolicy.DEFAULT;
   private ScionService service;
@@ -55,6 +56,7 @@ abstract class AbstractDatagramChannel<C extends AbstractDatagramChannel<?>> imp
           Constants.DEFAULT_PATH_EXPIRY_MARGIN);
   private int cfgTrafficClass;
   private Consumer<Scmp.Message> errorListener;
+  private boolean cfgRemoteDispatcher = false;
 
   protected AbstractDatagramChannel(ScionService service) throws IOException {
     this(service, DatagramChannel.open());
@@ -132,6 +134,7 @@ protected DatagramChannel channel() {
   public C bind(InetSocketAddress address) throws IOException {
     synchronized (stateLock) {
       channel.bind(address);
+      isBoundToAddress = address != null;
       localAddress = ((InetSocketAddress) channel.getLocalAddress()).getAddress();
       return (C) this;
     }
@@ -348,8 +351,32 @@ protected void checkListeners(Scmp.Message scmpMsg) {
     }
   }
 
-  protected void sendRaw(ByteBuffer buffer, InetSocketAddress address) throws IOException {
-    channel.send(buffer, address);
+  /**
+   * Assume that the destination host uses a dispatcher.
+   *
+   * <p>Calling this method sets an internal flag that forces the destination port of intra-AS
+   * packets to be 30041 independent of the UDP-overlay port. This flag has no effect for inter-AS
+   * packets or if the overlay port is already 30041.
+   *
+   * @param hasDispatcher Set to 'true' if remote end-host uses a dispatcher and requires using port
+   *     30041.
+   * @deprecated To be removed once dispatchers have been removed
+   */
+  @Deprecated
+  public void configureRemoteDispatcher(boolean hasDispatcher) {
+    this.cfgRemoteDispatcher = hasDispatcher;
+  }
+
+  protected int sendRaw(ByteBuffer buffer, InetSocketAddress address, Path path)
+      throws IOException {
+    if (cfgRemoteDispatcher && path != null && path.getRawPath().length == 0) {
+      return channel.send(buffer, new InetSocketAddress(address.getAddress(), 30041));
+    }
+    return channel.send(buffer, address);
+  }
+
+  protected int sendRaw(ByteBuffer buffer, InetSocketAddress address) throws IOException {
+    return sendRaw(buffer, address, null);
   }
 
   public Consumer<Scmp.Message> setScmpErrorListener(Consumer<Scmp.Message> listener) {
@@ -573,13 +600,15 @@ private void updateConnection(RequestPath newPath, boolean mustBeConnected) thro
     connectionPath = newPath;
     // update local address
     InetAddress oldLocalAddress = localAddress;
-    // TODO we should not change the local address if bind() was called with an explicit address!
-    // API: returning the localAddress should return non-ANY if we have a connection
-    //     I.e. getExternalIP() is fine if we have a connection.
-    //     It is NOT fine if we are bound to an explicit IP/port
-    localAddress = getOrCreateService().getExternalIP(newPath.getFirstHopAddress());
-    if (!Objects.equals(localAddress, oldLocalAddress)) {
-      resizeBuffers(localAddress);
+    // we should not change the local address if bind() was called with an explicit address!
+    if (!isBoundToAddress) {
+      // API: returning the localAddress should return non-ANY if we have a connection
+      //     I.e. getExternalIP() is fine if we have a connection.
+      //     It is NOT fine if we are bound to an explicit IP/port
+      localAddress = getOrCreateService().getExternalIP(newPath.getFirstHopAddress());
+      if (!Objects.equals(localAddress, oldLocalAddress)) {
+        resizeBuffers(localAddress);
+      }
     }
   }
 

src/main/java/org/scion/jpan/DatagramChannel.java

@@ -119,7 +119,7 @@ public Path send(ByteBuffer srcBuffer, Path path) throws IOException {
         throw new IOException("Packet is larger than max send buffer size.");
       }
       buffer.flip();
-      sendRaw(buffer, actualPath.getFirstHopAddress());
+      sendRaw(buffer, actualPath.getFirstHopAddress(), actualPath);
       return actualPath;
     } finally {
       writeLock().unlock();
@@ -173,7 +173,7 @@ public synchronized int write(ByteBuffer src) throws IOException {
       buffer.put(src);
       buffer.flip();
 
-      int sent = channel().send(buffer, getConnectionPath().getFirstHopAddress());
+      int sent = sendRaw(buffer, getConnectionPath().getFirstHopAddress(), getConnectionPath());
       if (sent < buffer.limit() || buffer.remaining() > 0) {
         throw new ScionException("Failed to send all data.");
       }