Add WebSocket frame size limit & compression ratio

Add a new JSON configuration parameter "WEBSOCKET_MAX_FRAME_SIZE" to set
a limit for the maximum WebSocket frame size, as especially with the new
compression support, unbounded frame sizes pose a risk. The default is
left at 0 (unbounded) to keep compatibility with all existing uses, but
it is strongly recommended to set an appropriate limit.

Add a new API MultiProtocolJSONClient#getCompressionRatio() to retrieve
the current compression ratio for informational purposes.

Increase the WebSocket compression threshold from 0 to 64 bytes, as it
was observed that frames smaller than 64 bytes typically grow in size
when compression is applied.

Author: robert-s-ubi

ocpp-json/src/main/java/eu/chargetime/ocpp/JSONConfiguration.java

@@ -39,6 +39,7 @@ public class JSONConfiguration {
   public static final String CONNECT_NON_BLOCKING_PARAMETER = "CONNECT_NON_BLOCKING";
   public static final String CONNECT_TIMEOUT_IN_MS_PARAMETER = "CONNECT_TIMEOUT_IN_MS";
   public static final String WEBSOCKET_COMPRESSION_SUPPORT = "WEBSOCKET_COMPRESSION_SUPPORT";
+  public static final String WEBSOCKET_MAX_FRAME_SIZE = "WEBSOCKET_MAX_FRAME_SIZE";
   public static final String WEBSOCKET_WORKER_COUNT = "WEBSOCKET_WORKER_COUNT";
   public static final String HTTP_HEALTH_CHECK_ENABLED = "HTTP_HEALTH_CHECK_ENABLED";
   public static final String OCPPJ_CP_MIN_PASSWORD_LENGTH = "OCPPJ_CP_MIN_PASSWORD_LENGTH";

ocpp-v2/src/main/java/eu/chargetime/ocpp/MultiProtocolJSONClient.java

@@ -89,11 +89,14 @@ public MultiProtocolJSONClient(
       List<ProtocolVersion> protocolVersions, String identity, JSONConfiguration configuration) {
     this.identity = identity;
     featureRepository = new MultiProtocolFeatureRepository(protocolVersions);
+    int maxFrameSize = configuration.getParameter(JSONConfiguration.WEBSOCKET_MAX_FRAME_SIZE, 0);
     List<IExtension> inputExtensions = new ArrayList<>();
     if (configuration.getParameter(JSONConfiguration.WEBSOCKET_COMPRESSION_SUPPORT, false)) {
       PerMessageDeflateExtension perMessageDeflateExtension =
-          new PerMessageDeflateExtension(Deflater.BEST_COMPRESSION);
-      perMessageDeflateExtension.setThreshold(0);
+          maxFrameSize > 0
+              ? new PerMessageDeflateExtension(Deflater.BEST_COMPRESSION, maxFrameSize)
+              : new PerMessageDeflateExtension(Deflater.BEST_COMPRESSION);
+      perMessageDeflateExtension.setThreshold(64);
       perMessageDeflateExtension.setServerNoContextTakeover(false);
       perMessageDeflateExtension.setClientNoContextTakeover(false);
       inputExtensions.add(perMessageDeflateExtension);
@@ -102,7 +105,10 @@ public MultiProtocolJSONClient(
     for (ProtocolVersion protocolVersion : protocolVersions) {
       inputProtocols.add(new Protocol(protocolVersion.getSubProtocolName()));
     }
-    Draft draft = new Draft_6455(inputExtensions, inputProtocols);
+    Draft draft =
+        maxFrameSize > 0
+            ? new Draft_6455(inputExtensions, inputProtocols, maxFrameSize)
+            : new Draft_6455(inputExtensions, inputProtocols);
     transmitter = new MultiProtocolWebSocketTransmitter(featureRepository, configuration, draft);
     JSONCommunicator communicator = new JSONCommunicator(transmitter, false);
     ISessionFactory sessionFactory = new MultiProtocolSessionFactory(featureRepository);
@@ -216,6 +222,14 @@ public void disconnect() {
     client.disconnect();
   }
 
+  public double getCompressionRatio() {
+    IExtension extension = transmitter.getExtension();
+    if (extension instanceof PerMessageDeflateExtension) {
+      return ((PerMessageDeflateExtension) extension).getCompressionRatio();
+    }
+    return 1;
+  }
+
   public Exception getLastError() {
     return transmitter.getLastError();
   }

ocpp-v2/src/main/java/eu/chargetime/ocpp/MultiProtocolJSONServer.java

@@ -67,12 +67,14 @@ public MultiProtocolJSONServer(
       List<ProtocolVersion> protocolVersions, JSONConfiguration configuration) {
     featureRepository = new MultiProtocolFeatureRepository(protocolVersions);
     MultiProtocolSessionFactory sessionFactory = new MultiProtocolSessionFactory(featureRepository);
-
+    int maxFrameSize = configuration.getParameter(JSONConfiguration.WEBSOCKET_MAX_FRAME_SIZE, 0);
     List<IExtension> extensions = new ArrayList<>();
     if (configuration.getParameter(JSONConfiguration.WEBSOCKET_COMPRESSION_SUPPORT, true)) {
       PerMessageDeflateExtension perMessageDeflateExtension =
-          new PerMessageDeflateExtension(Deflater.BEST_COMPRESSION);
-      perMessageDeflateExtension.setThreshold(0);
+          maxFrameSize > 0
+              ? new PerMessageDeflateExtension(Deflater.BEST_COMPRESSION, maxFrameSize)
+              : new PerMessageDeflateExtension(Deflater.BEST_COMPRESSION);
+      perMessageDeflateExtension.setThreshold(64);
       perMessageDeflateExtension.setServerNoContextTakeover(false);
       perMessageDeflateExtension.setClientNoContextTakeover(false);
       extensions.add(perMessageDeflateExtension);
@@ -81,8 +83,10 @@ public MultiProtocolJSONServer(
     for (ProtocolVersion protocolVersion : protocolVersions) {
       protocols.add(new Protocol(protocolVersion.getSubProtocolName()));
     }
-    Draft draft = new Draft_6455(extensions, protocols);
-
+    Draft draft =
+        maxFrameSize > 0
+            ? new Draft_6455(extensions, protocols, maxFrameSize)
+            : new Draft_6455(extensions, protocols);
     if (configuration.getParameter(JSONConfiguration.HTTP_HEALTH_CHECK_ENABLED, true)) {
       logger.info("JSONServer with HttpHealthCheckDraft");
       listener =

ocpp-v2/src/main/java/eu/chargetime/ocpp/MultiProtocolWebSocketTransmitter.java

@@ -35,9 +35,12 @@ of this software and associated documentation files (the "Software"), to deal
 import java.util.HashMap;
 import java.util.Map;
 import javax.net.SocketFactory;
+import org.java_websocket.WebSocket;
 import org.java_websocket.client.WebSocketClient;
 import org.java_websocket.drafts.Draft;
+import org.java_websocket.drafts.Draft_6455;
 import org.java_websocket.exceptions.WebsocketNotConnectedException;
+import org.java_websocket.extensions.IExtension;
 import org.java_websocket.handshake.ServerHandshake;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -264,6 +267,20 @@ public void send(Object request) throws NotConnectedException {
     }
   }
 
+  public IExtension getExtension() {
+    WebSocketClient webSocketClient = client;
+    if (webSocketClient != null) {
+      WebSocket webSocket = webSocketClient.getConnection();
+      if (webSocket != null) {
+        Draft draft = webSocket.getDraft();
+        if (draft instanceof Draft_6455) {
+          return ((Draft_6455) draft).getExtension();
+        }
+      }
+    }
+    return null;
+  }
+
   public Exception getLastError() {
     return lastError;
   }