server sendTo and sendToAll methods now will use fragments if needed

This change allows supporting sending large messages by sending keepalive messages in between fragments. Previously, the timeout mechanism in Java-WebSocket would close the connection automatically because no ping-pongs would be exchanged while the client was receiving a large message.

src/matlab-websocket/pom.xml

@@ -5,7 +5,7 @@
     <groupId>io.github.jebej.matlabwebsocket</groupId>
     <artifactId>matlab-websocket</artifactId>
     <packaging>jar</packaging>
-    <version>1.4</version>
+    <version>1.5</version>
 
     <name>matlab-websocket</name>
     <url>https://github.com/jebej/MatlabWebSocket</url>

src/matlab-websocket/src/main/java/io/github/jebej/matlabwebsocket/MatlabWebSocketServer.java

@@ -9,6 +9,8 @@
 import org.java_websocket.WebSocket;
 import org.java_websocket.handshake.ClientHandshake;
 import org.java_websocket.server.WebSocketServer;
+import org.java_websocket.framing.PongFrame;
+import org.java_websocket.enums.Opcode;
 
 public class MatlabWebSocketServer extends WebSocketServer {
     // The constructor creates a new WebSocketServer with the wildcard IP,
@@ -76,9 +78,9 @@ public void onClose( WebSocket conn, int code, String reason, boolean remote ) {
     public WebSocket getConnection( int hashCode ) {
 		Collection<WebSocket> conns = getConnections();
 		synchronized ( conns ) {
-			for( WebSocket c : conns ) {
-				if (c.hashCode() == hashCode) {
-                    return c;
+			for ( WebSocket conn : conns ) {
+				if (conn.hashCode() == hashCode) {
+                    return conn;
                 }
 			}
 		}
@@ -92,7 +94,8 @@ public void sendTo( int hashCode, String message ) {
 
     // Send binary message to a connection identified by a hashcode
     public void sendTo( int hashCode, ByteBuffer blob ) {
-		getConnection( hashCode ).send( blob );
+		WebSocket conn = getConnection( hashCode );
+		sendSplit( conn, blob );
 	}
 
     // Send binary message to a connection identified by a hashcode
@@ -104,8 +107,8 @@ public void sendTo( int hashCode, byte[] bytes ) {
     public void sendToAll( String message ) {
 		Collection<WebSocket> conns = getConnections();
 		synchronized ( conns ) {
-			for( WebSocket c : conns ) {
-				c.send( message );
+			for( WebSocket conn : conns ) {
+				conn.send( message );
 			}
 		}
 	}
@@ -114,8 +117,8 @@ public void sendToAll( String message ) {
     public void sendToAll( ByteBuffer blob ) {
 		Collection<WebSocket> conns = getConnections();
 		synchronized ( conns ) {
-			for( WebSocket c : conns ) {
-				c.send( blob );
+			for( WebSocket conn : conns ) {
+				sendSplit( conn, blob );
 			}
 		}
 	}
@@ -124,6 +127,28 @@ public void sendToAll( ByteBuffer blob ) {
     public void sendToAll( byte[] bytes ) {
         sendToAll( ByteBuffer.wrap( bytes ) );
 	}
+
+	// Method to send large messages in fragments if needed
+	public void sendSplit( WebSocket conn, ByteBuffer blob ) {
+		int FRAG_SIZE = 5*1024*1024; // 5MB
+		int blobSize = blob.capacity();
+		// Only send as fragments if message is larger than FRAG_SIZE
+		if ( blobSize <= FRAG_SIZE ) {
+			conn.send( blob );
+		} else {
+			int numFrags = (blobSize + FRAG_SIZE - 1)/FRAG_SIZE;
+			blob.rewind();
+			for ( int i = 0; i<numFrags; i++ ) {
+				blob.position( i*FRAG_SIZE );
+				blob.limit( Math.min( (i+1)*FRAG_SIZE, blobSize ) );
+				conn.sendFragmentedFrame( Opcode.BINARY, blob, (i+1)==numFrags );
+				// Send a ping AND an unpromted pong to keep connection alive
+				conn.sendPing();
+				conn.sendFrame( new PongFrame() );
+			}
+			assert( blob.position() == blobSize );
+		}
+	}
 
     // Close connection identified by a hashcode
     public void close( int hashCode ) {