GUACAMOLE-2228: Write stream blobs asynchronously.

guacamole/src/main/java/org/apache/guacamole/tunnel/OutputStreamInterceptingFilter.java

@@ -23,6 +23,8 @@
 import java.io.IOException;
 import java.io.OutputStream;
 import java.util.List;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
 import org.apache.guacamole.GuacamoleException;
 import org.apache.guacamole.net.GuacamoleTunnel;
 import org.apache.guacamole.protocol.GuacamoleInstruction;
@@ -37,14 +39,21 @@
  * sent automatically.
  */
 public class OutputStreamInterceptingFilter
-        extends StreamInterceptingFilter<OutputStream> {
+        extends StreamInterceptingFilter<OutputStream>
+        implements OutputStreamWriter.ExecutionListener {
 
     /**
      * Logger for this class.
      */
     private static final Logger logger =
             LoggerFactory.getLogger(OutputStreamInterceptingFilter.class);
 
+    /**
+     * File download stream writers which will send data asynchronosly.
+     */
+    private final ConcurrentMap<String, OutputStreamWriter> streamWriters =
+            new ConcurrentHashMap<>();
+
     /**
      * Whether this OutputStreamInterceptingFilter should respond to received
      * blobs with "ack" messages on behalf of the client. If false, blobs will
@@ -95,6 +104,23 @@ private void sendAck(String index, String message, GuacamoleStatus status) {
 
     }
 
+    @Override
+    public void onBlobWritten(String streamIndex, boolean requiresAck) {
+        if (requiresAck) {
+            sendAck(streamIndex, "OK", GuacamoleStatus.SUCCESS);
+        }
+    }
+
+    @Override
+    public void onWriteFailed(String streamIndex) {
+        sendAck(streamIndex, "FAIL", GuacamoleStatus.SERVER_ERROR);
+    }
+
+    @Override
+    public void onStreamEnd(String streamIndex) {
+        closeInterceptedStream(streamIndex);
+    }
+
     /**
      * Handles a single "blob" instruction, decoding its base64 data,
      * sending that data to the associated OutputStream, and ultimately
@@ -117,10 +143,12 @@ private GuacamoleInstruction handleBlob(GuacamoleInstruction instruction) {
         if (args.size() < 2)
             return instruction;
 
-        // Pull associated stream
-        String index = args.get(0);
-        InterceptedStream<OutputStream> stream = getInterceptedStream(index);
-        if (stream == null)
+        // Get the stream index
+        String streamIndex = args.get(0);
+
+        // Process the blob asynchornously if there is a worker
+        OutputStreamWriter streamWriter = streamWriters.get(streamIndex);
+        if (streamWriter == null)
             return instruction;
 
         // Decode blob
@@ -134,31 +162,25 @@ private GuacamoleInstruction handleBlob(GuacamoleInstruction instruction) {
             return null;
         }
 
-        try {
-
-            // Attempt to write data to stream
-            stream.getStream().write(blob);
-
-            // Force client to respond with their own "ack" if we need to
-            // confirm that they are not falling behind with respect to the
-            // graphical session
-            if (!acknowledgeBlobs) {
-                acknowledgeBlobs = true;
-                return new GuacamoleInstruction("blob", index, "");
-            }
-
-            // Otherwise, acknowledge the blob on the client's behalf
-            sendAck(index, "OK", GuacamoleStatus.SUCCESS);
-
-        }
-        catch (IOException e) {
-            sendAck(index, "FAIL", GuacamoleStatus.SERVER_ERROR);
-            logger.debug("Write failed for intercepted stream.", e);
+        // Force client to respond with their own "ack" to confirm they are not
+        // falling behind with respect to the graphical session, only if
+        // - There are no blobs in the queue currently
+        // - Previous blob required server side acknowledgement 
+        // This may lead to more than one blob in the writer queue temporarily,
+        // but not more than two blobs anyways.
+        if (!acknowledgeBlobs &&
+                streamWriter.getQueuedMessageCount() == 0 &&
+                streamWriter.didPrevBlobRequireAck()) {
+            streamWriter.handleBlob(blob, false);
+            acknowledgeBlobs = true;
+
+            // Send an empty blob to trigger client "ack"
+            return new GuacamoleInstruction("blob", streamIndex, "");
         }
 
-        // Instruction was handled purely internally
+        // Put the blob to the writer queue
+        streamWriter.handleBlob(blob, true);
         return null;
-
     }
 
     /**
@@ -176,9 +198,13 @@ private void handleEnd(GuacamoleInstruction instruction) {
         if (args.size() < 1)
             return;
 
-        // Terminate stream
-        closeInterceptedStream(args.get(0));
-
+        OutputStreamWriter streamWriter = streamWriters.get(args.get(0));
+        if (streamWriter == null)
+            return;
+
+        // Notify the writer that the end marker has been received.
+        // it will terminate the stream once all blobs are written.
+        streamWriter.handleEnd();
     }
 
     /**
@@ -221,9 +247,30 @@ public GuacamoleInstruction filter(GuacamoleInstruction instruction)
     @Override
     protected void handleInterceptedStream(InterceptedStream<OutputStream> stream) {
 
+        // Create the stream writer
+        OutputStreamWriter streamWriter = new OutputStreamWriter(stream, this);
+
+        // Put it into the container and check if there was another writer for the index
+        OutputStreamWriter old = streamWriters.put(stream.getIndex(), streamWriter);
+        if (old != null) {
+            logger.debug("Found an older stream #{}; will close it", stream.getIndex());
+            // Close the stream to be sure it does not get stuck on write
+            closeInterceptedStream(old.getStream());
+            // Stop it
+            old.stop();
+        }
+
         // Acknowledge that the stream is ready to receive data
         sendAck(stream.getIndex(), "OK", GuacamoleStatus.SUCCESS);
 
-    }
+        // This will block the thread until the stream is closed by
+        // disconnection, or the end instruction is received.
+        streamWriter.run();
+
+        // Close the stream if not closed yet
+        closeInterceptedStream(stream);
 
+        // Remove the stream from the container
+        streamWriters.entrySet().removeIf(entry -> entry.getValue().equals(streamWriter));        
+    }
 }