Not throw an exception if subprotocol is not supported but just drop the header as stated in the RFC's

codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketServerHandshaker00.java

@@ -136,7 +136,9 @@ public class WebSocketServerHandshaker00 extends WebSocketServerHandshaker {
             if (subprotocols != null) {
                 String selectedSubprotocol = selectSubprotocol(subprotocols);
                 if (selectedSubprotocol == null) {
-                    throw new WebSocketHandshakeException("Requested subprotocol(s) not supported: " + subprotocols);
+                    if (logger.isDebugEnabled()) {
+                        logger.debug(String.format("Requested subprotocol(s) not supported: %s.", subprotocols));
+                    }
                 } else {
                     res.headers().add(SEC_WEBSOCKET_PROTOCOL, selectedSubprotocol);
                 }

codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketServerHandshaker07.java

@@ -121,7 +121,9 @@ public class WebSocketServerHandshaker07 extends WebSocketServerHandshaker {
         if (subprotocols != null) {
             String selectedSubprotocol = selectSubprotocol(subprotocols);
             if (selectedSubprotocol == null) {
-                throw new WebSocketHandshakeException("Requested subprotocol(s) not supported: " + subprotocols);
+                if (logger.isDebugEnabled()) {
+                    logger.debug(String.format("Requested subprotocol(s) not supported: %s.", subprotocols));
+                }
             } else {
                 res.headers().add(Names.SEC_WEBSOCKET_PROTOCOL, selectedSubprotocol);
             }

codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketServerHandshaker08.java

@@ -120,7 +120,9 @@ public class WebSocketServerHandshaker08 extends WebSocketServerHandshaker {
         if (subprotocols != null) {
             String selectedSubprotocol = selectSubprotocol(subprotocols);
             if (selectedSubprotocol == null) {
-                throw new WebSocketHandshakeException("Requested subprotocol(s) not supported: " + subprotocols);
+                if (logger.isDebugEnabled()) {
+                    logger.debug(String.format("Requested subprotocol(s) not supported: %s.", subprotocols));
+                }
             } else {
                 res.headers().add(Names.SEC_WEBSOCKET_PROTOCOL, selectedSubprotocol);
             }

codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketServerHandshaker13.java

@@ -118,8 +118,9 @@ public class WebSocketServerHandshaker13 extends WebSocketServerHandshaker {
         if (subprotocols != null) {
             String selectedSubprotocol = selectSubprotocol(subprotocols);
             if (selectedSubprotocol == null) {
-                throw new WebSocketHandshakeException(
+                if (logger.isDebugEnabled()) {
-                        "Requested subprotocol(s) not supported: " + subprotocols);
+                    logger.debug(String.format("Requested subprotocol(s) not supported: %s.", subprotocols));
+                }
             } else {
                 res.headers().add(Names.SEC_WEBSOCKET_PROTOCOL, selectedSubprotocol);
             }

codec-http/src/test/java/io/netty/handler/codec/http/websocketx/WebSocketServerHandshaker00Test.java

@@ -39,6 +39,15 @@ public class WebSocketServerHandshaker00Test {
 
     @Test
     public void testPerformOpeningHandshake() {
+        testPerformOpeningHandshake0(true);
+    }
+
+    @Test
+    public void testPerformOpeningHandshakeSubProtocolNotSupported() {
+        testPerformOpeningHandshake0(false);
+    }
+
+    private static void testPerformOpeningHandshake0(boolean subProtocol) {
         EmbeddedChannel ch = new EmbeddedChannel(
                 new HttpObjectAggregator(42), new HttpRequestDecoder(), new HttpResponseEncoder());
 
@@ -53,15 +62,24 @@ public class WebSocketServerHandshaker00Test {
         req.headers().set(Names.SEC_WEBSOCKET_KEY2, "12998 5 Y3 1  .P00");
         req.headers().set(Names.SEC_WEBSOCKET_PROTOCOL, "chat, superchat");
 
-        new WebSocketServerHandshaker00(
+        if (subProtocol) {
-                "ws://example.com/chat", "chat", Integer.MAX_VALUE).handshake(ch, req);
+            new WebSocketServerHandshaker00(
+                    "ws://example.com/chat", "chat", Integer.MAX_VALUE).handshake(ch, req);
+        } else {
+            new WebSocketServerHandshaker00(
+                    "ws://example.com/chat", null, Integer.MAX_VALUE).handshake(ch, req);
+        }
 
         EmbeddedChannel ch2 = new EmbeddedChannel(new HttpResponseDecoder());
         ch2.writeInbound(ch.readOutbound());
         HttpResponse res = (HttpResponse) ch2.readInbound();
 
         Assert.assertEquals("ws://example.com/chat", res.headers().get(Names.SEC_WEBSOCKET_LOCATION));
-        Assert.assertEquals("chat", res.headers().get(Names.SEC_WEBSOCKET_PROTOCOL));
+        if (subProtocol) {
+            Assert.assertEquals("chat", res.headers().get(Names.SEC_WEBSOCKET_PROTOCOL));
+        } else {
+            Assert.assertNull(res.headers().get(Names.SEC_WEBSOCKET_PROTOCOL));
+        }
         LastHttpContent content = (LastHttpContent) ch2.readInbound();
 
         Assert.assertEquals("8jKS'y:G*Co,Wxa-", content.content().toString(CharsetUtil.US_ASCII));

codec-http/src/test/java/io/netty/handler/codec/http/websocketx/WebSocketServerHandshaker08Test.java

@@ -37,6 +37,15 @@ public class WebSocketServerHandshaker08Test {
 
     @Test
     public void testPerformOpeningHandshake() {
+        testPerformOpeningHandshake0(true);
+    }
+
+    @Test
+    public void testPerformOpeningHandshakeSubProtocolNotSupported() {
+        testPerformOpeningHandshake0(false);
+    }
+
+    private static void testPerformOpeningHandshake0(boolean subProtocol) {
         EmbeddedChannel ch = new EmbeddedChannel(
                 new HttpObjectAggregator(42), new HttpRequestDecoder(), new HttpResponseEncoder());
 
@@ -50,8 +59,13 @@ public class WebSocketServerHandshaker08Test {
         req.headers().set(Names.SEC_WEBSOCKET_PROTOCOL, "chat, superchat");
         req.headers().set(Names.SEC_WEBSOCKET_VERSION, "8");
 
-        new WebSocketServerHandshaker08(
+        if (subProtocol) {
-                "ws://example.com/chat", "chat", false, Integer.MAX_VALUE).handshake(ch, req);
+            new WebSocketServerHandshaker08(
+                    "ws://example.com/chat", "chat", false, Integer.MAX_VALUE).handshake(ch, req);
+        } else {
+            new WebSocketServerHandshaker08(
+                    "ws://example.com/chat", null, false, Integer.MAX_VALUE).handshake(ch, req);
+        }
 
         ByteBuf resBuf = (ByteBuf) ch.readOutbound();
 
@@ -61,7 +75,11 @@ public class WebSocketServerHandshaker08Test {
 
         Assert.assertEquals(
                 "s3pPLMBiTxaQ9kYGzzhZRbK+xOo=", res.headers().get(Names.SEC_WEBSOCKET_ACCEPT));
-        Assert.assertEquals("chat", res.headers().get(Names.SEC_WEBSOCKET_PROTOCOL));
+        if (subProtocol) {
+            Assert.assertEquals("chat", res.headers().get(Names.SEC_WEBSOCKET_PROTOCOL));
+        } else {
+            Assert.assertNull(res.headers().get(Names.SEC_WEBSOCKET_PROTOCOL));
+        }
         ReferenceCountUtil.release(res);
     }
 }

codec-http/src/test/java/io/netty/handler/codec/http/websocketx/WebSocketServerHandshaker13Test.java

@@ -37,6 +37,15 @@ public class WebSocketServerHandshaker13Test {
 
     @Test
     public void testPerformOpeningHandshake() {
+        testPerformOpeningHandshake0(true);
+    }
+
+    @Test
+    public void testPerformOpeningHandshakeSubProtocolNotSupported() {
+        testPerformOpeningHandshake0(false);
+    }
+
+    private static void testPerformOpeningHandshake0(boolean subProtocol) {
         EmbeddedChannel ch = new EmbeddedChannel(
                 new HttpObjectAggregator(42), new HttpRequestDecoder(), new HttpResponseEncoder());
 
@@ -50,8 +59,13 @@ public class WebSocketServerHandshaker13Test {
         req.headers().set(Names.SEC_WEBSOCKET_PROTOCOL, "chat, superchat");
         req.headers().set(Names.SEC_WEBSOCKET_VERSION, "13");
 
-        new WebSocketServerHandshaker13(
+        if (subProtocol) {
-                "ws://example.com/chat", "chat", false, Integer.MAX_VALUE).handshake(ch, req);
+            new WebSocketServerHandshaker13(
+                    "ws://example.com/chat", "chat", false, Integer.MAX_VALUE).handshake(ch, req);
+        } else {
+            new WebSocketServerHandshaker13(
+                    "ws://example.com/chat", null, false, Integer.MAX_VALUE).handshake(ch, req);
+        }
 
         ByteBuf resBuf = (ByteBuf) ch.readOutbound();
 
@@ -61,7 +75,11 @@ public class WebSocketServerHandshaker13Test {
 
         Assert.assertEquals(
                 "s3pPLMBiTxaQ9kYGzzhZRbK+xOo=", res.headers().get(Names.SEC_WEBSOCKET_ACCEPT));
-        Assert.assertEquals("chat", res.headers().get(Names.SEC_WEBSOCKET_PROTOCOL));
+        if (subProtocol) {
+            Assert.assertEquals("chat", res.headers().get(Names.SEC_WEBSOCKET_PROTOCOL));
+        } else {
+            Assert.assertNull(res.headers().get(Names.SEC_WEBSOCKET_PROTOCOL));
+        }
         ReferenceCountUtil.release(res);
     }
 }