add workaround for Rebex SSH server (described workaround in code);

add  possibility to activate the workaround by setting an entry in the specificConfig;

Signed-off-by: Stefan Maute <stefan.maute@bosch.io>

connectivity/service/src/main/java/org/eclipse/ditto/connectivity/service/messaging/tunnel/SshTunnelActor.java

@@ -177,7 +177,8 @@ private void handleConnectResult(final ConnectFuture connectFuture) throws IOExc
             logger.debug("SSH session connected successfully.");
             sshSession = connectFuture.getClientSession();
             sshSession.addSessionListener(new TunnelSessionListener(getSelf(), logger));
-            sshSession.addChannelListener(new TunnelChannelListener(getSelf(), logger));
+            sshSession.addChannelListener(new TunnelChannelListener(getSelf(),
+                    this.connection.getSpecificConfig().getOrDefault("initialWindowSize","0"), logger));
             sshSession.setServerKeyVerifier(serverKeyVerifier);
             sshSession.setUserAuthFactoriesNames(sshUserAuthMethod);
             connection.getSshTunnel()

connectivity/service/src/main/java/org/eclipse/ditto/connectivity/service/messaging/tunnel/TunnelChannelListener.java

@@ -25,18 +25,29 @@
  */
 final class TunnelChannelListener implements ChannelListener {
 
+    private static final String TUNNEL_EXCEPTION_MESSAGE = "Opening SSH channel failed with exception";
     private final ActorRef sshTunnelActor;
     private final LoggingAdapter logger;
+    private int initialWindowSize;
 
     /**
      * Instantiates a new {@code TunnelChannelListener}.
      *
      * @param sshTunnelActor actor reference of SshTunnelActor to notify about errors
+     * @param initialWindowSize the initial window size to use for the Remote Window
      * @param logger the logger
      */
-    TunnelChannelListener(final ActorRef sshTunnelActor, final LoggingAdapter logger) {
+    TunnelChannelListener(final ActorRef sshTunnelActor, final String initialWindowSize, final LoggingAdapter logger) {
         this.sshTunnelActor = sshTunnelActor;
         this.logger = logger;
+        try {
+            this.initialWindowSize = Integer.parseInt(initialWindowSize);
+        }
+        catch (final NumberFormatException e) {
+            final SshTunnelActor.TunnelClosed tunnelClosed =
+                    new SshTunnelActor.TunnelClosed(TUNNEL_EXCEPTION_MESSAGE, e);
+            sshTunnelActor.tell(tunnelClosed, ActorRef.noSender());
+        }
     }
 
     @Override
@@ -46,14 +57,22 @@ public void channelInitialized(final Channel channel) {
 
     @Override
     public void channelOpenSuccess(final Channel channel) {
+        if (initialWindowSize > 0) {
+            // workaround for Rebex SSH server
+            // SSH server sends initial window size of 0 which causes problems when sending data over
+            // the SSH channel right after creation. Write results in SocketTimeoutException and
+            // SSH_MSG_CHANNEL_WINDOW_ADJUST from server is not handled properly.
+            // Expanding the remote window fixes the problem
+            channel.getRemoteWindow().expand(initialWindowSize);
+        }
         logger.debug("SSH channel opened successfully: {}", channel);
     }
 
     @Override
     public void channelOpenFailure(final Channel channel, final Throwable reason) {
         if (reason != null) {
             final SshTunnelActor.TunnelClosed tunnelClosed =
-                    new SshTunnelActor.TunnelClosed("Opening SSH channel failed with exception", reason);
+                    new SshTunnelActor.TunnelClosed(TUNNEL_EXCEPTION_MESSAGE, reason);
             sshTunnelActor.tell(tunnelClosed, ActorRef.noSender());
         }
     }
@@ -83,8 +102,7 @@ public void channelClosed(final Channel channel, final Throwable reason) {
                             final Throwable exception = future.getException();
                             if (exception != null) {
                                 final SshTunnelActor.TunnelClosed tunnelClosed =
-                                        new SshTunnelActor.TunnelClosed("Opening SSH channel failed with exception",
-                                                exception);
+                                        new SshTunnelActor.TunnelClosed(TUNNEL_EXCEPTION_MESSAGE, exception);
                                 sshTunnelActor.tell(tunnelClosed, ActorRef.noSender());
                             }
                         });