Add ALPN Buffering to support HTTP/2 Prior Knowledge (#11407)

Motivation:
Currently, Netty cannot handle HTTP/2 Preface messages if the client used the Prior knowledge technique. In Prior knowledge, the client sends an HTTP/2 preface message immediately after finishing TLS Handshake. But in Netty, when TLS Handshake is finished, ALPNHandler is triggered to configure the pipeline. And between these 2 operations, if an HTTP/2 preface message arrives, it gets dropped.

Modification:

Buffer messages until we are done with the ALPN handling.

Result:
Fixes #11403.

Co-authored-by: Norman Maurer <norman_maurer@apple.com>

handler/src/main/java/io/netty/handler/ssl/ApplicationProtocolNegotiationHandler.java

@@ -23,6 +23,7 @@ import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelInitializer;
 import io.netty.channel.ChannelPipeline;
 import io.netty.handler.codec.DecoderException;
+import io.netty.util.internal.RecyclableArrayList;
 import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
 
@@ -69,6 +70,8 @@ public abstract class ApplicationProtocolNegotiationHandler implements ChannelHa
             InternalLoggerFactory.getInstance(ApplicationProtocolNegotiationHandler.class);
 
     private final String fallbackProtocol;
+    private final RecyclableArrayList bufferedMessages = RecyclableArrayList.newInstance();
+    private ChannelHandlerContext ctx;
 
     /**
      * Creates a new instance with the specified fallback protocol name.
@@ -80,6 +83,36 @@ public abstract class ApplicationProtocolNegotiationHandler implements ChannelHa
         this.fallbackProtocol = requireNonNull(fallbackProtocol, "fallbackProtocol");
     }
 
+    @Override
+    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
+        this.ctx = ctx;
+    }
+
+    @Override
+    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
+        fireBufferedMessages();
+        bufferedMessages.recycle();
+    }
+
+    @Override
+    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
+        // Let's buffer all data until this handler will be removed from the pipeline.
+        bufferedMessages.add(msg);
+    }
+
+    /**
+     * Process all backlog into pipeline from List.
+     */
+    private void fireBufferedMessages() {
+        if (!bufferedMessages.isEmpty()) {
+            for (int i = 0; i < bufferedMessages.size(); i++) {
+                ctx.fireChannelRead(bufferedMessages.get(i));
+            }
+            ctx.fireChannelReadComplete();
+            bufferedMessages.clear();
+        }
+    }
+
     @Override
     public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
         if (evt instanceof SslHandshakeCompletionEvent) {
@@ -120,6 +153,7 @@ public abstract class ApplicationProtocolNegotiationHandler implements ChannelHa
             pipeline.remove(this);
         }
     }
+
     /**
      * Invoked on successful initial SSL/TLS handshake. Implement this method to configure your pipeline
      * for the negotiated application-level protocol.

handler/src/test/java/io/netty/handler/ssl/ApplicationProtocolNegotiationHandlerTest.java

@@ -24,11 +24,13 @@ import org.junit.Test;
 
 import java.security.NoSuchAlgorithmException;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
 import javax.net.ssl.SSLContext;
 import javax.net.ssl.SSLEngine;
 import javax.net.ssl.SSLHandshakeException;
 
 import static io.netty.handler.ssl.CloseNotifyTest.assertCloseNotify;
+import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNull;
@@ -99,4 +101,50 @@ public class ApplicationProtocolNegotiationHandlerTest {
             assertFalse(channel.finishAndReleaseAll());
         }
     }
+
+    @Test
+    public void testBufferMessagesUntilHandshakeComplete() throws Exception {
+        final AtomicReference<byte[]> channelReadData = new AtomicReference<byte[]>();
+        final AtomicBoolean channelReadCompleteCalled = new AtomicBoolean(false);
+        ChannelHandler alpnHandler = new ApplicationProtocolNegotiationHandler(ApplicationProtocolNames.HTTP_1_1) {
+            @Override
+            protected void configurePipeline(ChannelHandlerContext ctx, String protocol) {
+                assertEquals(ApplicationProtocolNames.HTTP_1_1, protocol);
+                ctx.pipeline().addLast(new ChannelHandler() {
+                    @Override
+                    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
+                        channelReadData.set((byte[]) msg);
+                    }
+
+                    @Override
+                    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
+                        channelReadCompleteCalled.set(true);
+                    }
+                });
+            }
+        };
+
+        SSLEngine engine = SSLContext.getDefault().createSSLEngine();
+        // This test is mocked/simulated and doesn't go through full TLS handshake. Currently only JDK SSLEngineImpl
+        // client mode will generate a close_notify.
+        engine.setUseClientMode(true);
+
+        final byte[] someBytes = new byte[1024];
+
+        EmbeddedChannel channel = new EmbeddedChannel(new SslHandler(engine), new ChannelHandler() {
+            @Override
+            public void userEventTriggered(ChannelHandlerContext ctx, Object evt) {
+                if (evt == SslHandshakeCompletionEvent.SUCCESS) {
+                    ctx.fireChannelRead(someBytes);
+                }
+                ctx.fireUserEventTriggered(evt);
+            }
+        }, alpnHandler);
+        channel.pipeline().fireUserEventTriggered(SslHandshakeCompletionEvent.SUCCESS);
+        assertNull(channel.pipeline().context(alpnHandler));
+        assertArrayEquals(someBytes, channelReadData.get());
+        assertTrue(channelReadCompleteCalled.get());
+        assertNull(channel.readInbound());
+        channel.finishAndReleaseAll();
+    }
 }