Fix Per-Message Compression Extension support

The per-message compression extension was badly broken, leading to
exceptions and loss of communication between client and server.

Fix the extension negotiation to correctly send the current state of the
client_no_context_takeover and server_no_context_takeover configuration
variables, and ORing the received extensions with the received ones, to
ensure client and server end up with the same configuration.

Fix the application of these configuration variables, which must be
swapped on the client vs. the server: The configuration of the deflater
on the client side must affect the inflater on the server side, and vice
versa.

Remove the requestedParameters map as there is no need for it.

This fixes issue #1496

Author: robert-s-ubi

src/main/java/org/java_websocket/extensions/permessage_deflate/PerMessageDeflateExtension.java

@@ -2,7 +2,6 @@
 
 import java.io.ByteArrayOutputStream;
 import java.nio.ByteBuffer;
-import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.zip.DataFormatException;
 import java.util.zip.Deflater;
@@ -47,15 +46,14 @@ public class PerMessageDeflateExtension extends CompressionExtension {
   private boolean serverNoContextTakeover = true;
   private boolean clientNoContextTakeover = false;
 
-  // For WebSocketServers, this variable holds the extension parameters that the peer client has requested.
-  // For WebSocketClients, this variable holds the extension parameters that client himself has requested.
-  private Map<String, String> requestedParameters = new LinkedHashMap<>();
-
   private final int compressionLevel;
 
   private final Inflater inflater;
   private final Deflater deflater;
 
+  private boolean resetDeflater = false;
+  private boolean resetInflater = false;
+
   /**
    * Constructor for the PerMessage Deflate Extension (<a href="https://tools.ietf.org/html/rfc7692#section-7">7&#46; Thepermessage-deflate" Extension</a>)
    *
@@ -184,8 +182,8 @@ We can check the getRemaining() method to see whether the data we supplied has b
 
       if (inputFrame.isFin()) {
         decompress(TAIL_BYTES, output);
-        // If context takeover is disabled, inflater can be reset.
-        if (clientNoContextTakeover) {
+        // If context takeover is disabled for the other side, inflater must be reset.
+        if (resetInflater) {
           inflater.reset();
         }
       }
@@ -254,8 +252,8 @@ public void encodeFrame(Framedata inputFrame) {
       if (endsWithTail(outputBytes)) {
         outputLength -= TAIL_BYTES.length;
       }
-
-      if (serverNoContextTakeover) {
+      // If context takeover is disabled for this side, deflater must be reset.
+      if (resetDeflater) {
         deflater.reset();
       }
     }
@@ -294,11 +292,19 @@ public boolean acceptProvidedExtensionAsServer(String inputExtension) {
 
       // Holds parameters that peer client has sent.
       Map<String, String> headers = extensionData.getExtensionParameters();
-      requestedParameters.putAll(headers);
-      if (requestedParameters.containsKey(CLIENT_NO_CONTEXT_TAKEOVER)) {
+      if (headers.containsKey(SERVER_NO_CONTEXT_TAKEOVER)) {
+        serverNoContextTakeover = true;
+      }
+      if (headers.containsKey(CLIENT_NO_CONTEXT_TAKEOVER)) {
         clientNoContextTakeover = true;
       }
 
+      // RFC 7692:
+      // server_ prefix parameters configure the server compressor (deflater)
+      // client_ prefix parameters configure the server decompressor (inflater)
+      resetDeflater = serverNoContextTakeover;
+      resetInflater = clientNoContextTakeover;
+
       return true;
     }
 
@@ -316,7 +322,19 @@ public boolean acceptProvidedExtensionAsClient(String inputExtension) {
 
       // Holds parameters that are sent by the server, as a response to our initial extension request.
       Map<String, String> headers = extensionData.getExtensionParameters();
-      // After this point, parameters that the server sent back can be configured, but we don't use them for now.
+      if (headers.containsKey(SERVER_NO_CONTEXT_TAKEOVER)) {
+        serverNoContextTakeover = true;
+      }
+      if (headers.containsKey(CLIENT_NO_CONTEXT_TAKEOVER)) {
+        clientNoContextTakeover = true;
+      }
+
+      // RFC 7692:
+      // client_ prefix parameters configure the client compressor (deflater)
+      // server_ prefix parameters configure the client decompressor (inflater)
+      resetDeflater = clientNoContextTakeover;
+      resetInflater = serverNoContextTakeover;
+
       return true;
     }
 
@@ -325,17 +343,15 @@ public boolean acceptProvidedExtensionAsClient(String inputExtension) {
 
   @Override
   public String getProvidedExtensionAsClient() {
-    requestedParameters.put(CLIENT_NO_CONTEXT_TAKEOVER, ExtensionRequestData.EMPTY_VALUE);
-    requestedParameters.put(SERVER_NO_CONTEXT_TAKEOVER, ExtensionRequestData.EMPTY_VALUE);
-
-    return EXTENSION_REGISTERED_NAME + "; " + SERVER_NO_CONTEXT_TAKEOVER + "; "
-        + CLIENT_NO_CONTEXT_TAKEOVER;
+    return EXTENSION_REGISTERED_NAME
+        + (serverNoContextTakeover ? "; " + SERVER_NO_CONTEXT_TAKEOVER : "")
+        + (clientNoContextTakeover ? "; " + CLIENT_NO_CONTEXT_TAKEOVER : "");
   }
 
   @Override
   public String getProvidedExtensionAsServer() {
     return EXTENSION_REGISTERED_NAME
-        + "; " + SERVER_NO_CONTEXT_TAKEOVER
+        + (serverNoContextTakeover ? "; " + SERVER_NO_CONTEXT_TAKEOVER : "")
         + (clientNoContextTakeover ? "; " + CLIENT_NO_CONTEXT_TAKEOVER : "");
   }