instead of using ProtocolNegotiator interface, mimic the behavior to …

…avoid adding other handlers such as WaitUntilActive and KickProtocolNegotiationHandler (no longer exists)

netty/build.gradle

@@ -13,6 +13,7 @@ configurations {
     alpnagent
 }
 
+evaluationDependsOn(':grpc-core')
 dependencies {
     compile project(':grpc-core'),
             libraries.netty,

netty/src/main/java/io/grpc/netty/ProtocolNegotiators.java

@@ -34,13 +34,10 @@
 import io.grpc.internal.GrpcAttributes;
 import io.grpc.internal.GrpcUtil;
 import io.netty.channel.ChannelDuplexHandler;
-import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelFutureListener;
 import io.netty.channel.ChannelHandler;
 import io.netty.channel.ChannelHandlerContext;
-import io.netty.channel.ChannelInboundHandler;
 import io.netty.channel.ChannelInboundHandlerAdapter;
-import io.netty.channel.ChannelPromise;
 import io.netty.handler.codec.http.DefaultHttpRequest;
 import io.netty.handler.codec.http.HttpClientCodec;
 import io.netty.handler.codec.http.HttpClientUpgradeHandler;
@@ -60,12 +57,9 @@
 import io.netty.util.AsciiString;
 import io.netty.util.Attribute;
 import io.netty.util.AttributeMap;
-import io.netty.util.ReferenceCountUtil;
 import java.net.SocketAddress;
 import java.net.URI;
-import java.util.ArrayDeque;
 import java.util.Arrays;
-import java.util.Queue;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 import javax.annotation.Nullable;
@@ -196,9 +190,9 @@ private void fireProtocolNegotiationEvent(ChannelHandlerContext ctx, SSLSession
   public static ProtocolNegotiator httpProxy(final SocketAddress proxyAddress,
       final @Nullable String proxyUsername, final @Nullable String proxyPassword,
       final ProtocolNegotiator negotiator) {
+    checkNotNull(negotiator, "negotiator");
+    checkNotNull(proxyAddress, "proxyAddress");
     final AsciiString scheme = negotiator.scheme();
-    Preconditions.checkNotNull(proxyAddress, "proxyAddress");
-    Preconditions.checkNotNull(negotiator, "negotiator");
     class ProxyNegotiator implements ProtocolNegotiator {
       @Override
       public ChannelHandler newHandler(GrpcHttp2ConnectionHandler http2Handler) {
@@ -222,25 +216,31 @@ public void close() {
     return new ProxyNegotiator();
   }
 
-  static final class ProxyProtocolNegotiationHandler extends ProtocolNegotiationHandler {
+  /**
+   * A Proxy handler follows {@link ProtocolNegotiationHandler} pattern. Upon successful proxy
+   * connection, this handler will install {@code next} handler which should be a handler from
+   * other type of {@link ProtocolNegotiator} to continue negotiating protocol using proxy.
+   */
+  static final class ProxyProtocolNegotiationHandler extends ChannelDuplexHandler {
 
     private final SocketAddress address;
     @Nullable private final String userName;
     @Nullable private final String password;
+    private final ChannelHandler next;
 
     public ProxyProtocolNegotiationHandler(
         SocketAddress address,
         @Nullable String userName,
         @Nullable String password,
         ChannelHandler next) {
-      super(next);
       this.address = checkNotNull(address, "address");
       this.userName = userName;
       this.password = password;
+      this.next = checkNotNull(next, "next");
     }
 
     @Override
-    protected void protocolNegotiationEventTriggered(ChannelHandlerContext ctx) {
+    public void handlerAdded(ChannelHandlerContext ctx) {
       HttpProxyHandler nettyProxyHandler;
       if (userName == null || password == null) {
         nettyProxyHandler = new HttpProxyHandler(address);
@@ -251,11 +251,11 @@ protected void protocolNegotiationEventTriggered(ChannelHandlerContext ctx) {
     }
 
     @Override
-    protected void userEventTriggered0(ChannelHandlerContext ctx, Object evt) throws Exception {
+    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
       if (evt instanceof ProxyConnectionEvent) {
-        fireProtocolNegotiationEvent(ctx);
+        ctx.pipeline().replace(ctx.name(), /* newName= */ null, next);
       } else {
-        super.userEventTriggered0(ctx, evt);
+        super.userEventTriggered(ctx, evt);
       }
     }
   }