examples: grpc-level proxy

examples/build.gradle

@@ -89,6 +89,7 @@ createStartScripts('io.grpc.examples.deadline.DeadlineClient')
 createStartScripts('io.grpc.examples.deadline.DeadlineServer')
 createStartScripts('io.grpc.examples.errordetails.ErrorDetailsExample')
 createStartScripts('io.grpc.examples.experimental.CompressingHelloWorldClient')
+createStartScripts('io.grpc.examples.grpcproxy.GrpcProxy')
 createStartScripts('io.grpc.examples.healthservice.HealthServiceClient')
 createStartScripts('io.grpc.examples.healthservice.HealthServiceServer')
 createStartScripts('io.grpc.examples.hedging.HedgingHelloWorldClient')

examples/src/main/java/io/grpc/examples/grpcproxy/GrpcProxy.java

@@ -0,0 +1,239 @@
+/*
+ * Copyright 2023, gRPC Authors All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.grpc.examples.grpcproxy;
+
+import com.google.common.io.ByteStreams;
+import io.grpc.CallOptions;
+import io.grpc.Channel;
+import io.grpc.ClientCall;
+import io.grpc.Grpc;
+import io.grpc.HandlerRegistry;
+import io.grpc.InsecureChannelCredentials;
+import io.grpc.InsecureServerCredentials;
+import io.grpc.ManagedChannel;
+import io.grpc.Metadata;
+import io.grpc.MethodDescriptor;
+import io.grpc.Server;
+import io.grpc.ServerCall;
+import io.grpc.ServerCallHandler;
+import io.grpc.ServerMethodDefinition;
+import io.grpc.Status;
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.concurrent.TimeUnit;
+import java.util.logging.Logger;
+
+/**
+ * A grpc-level proxy. GrpcProxy itself can be used unmodified to proxy any service for both unary
+ * and streaming. It doesn't care what type of messages are being used. The Registry class causes it
+ * to be called for any inbound RPC, and uses plain bytes for messages which avoids marshalling
+ * messages and the need for Protobuf schema information.
+ *
+ * <p>Route guide has unary and streaming RPCs which makes it a nice showcase. To test with route
+ * guide, run each in a separate terminal window:
+ * <pre>{@code
+ *   ./build/install/examples/bin/route-guide-server
+ *   ./build/install/examples/bin/grpc-proxy
+ *   ./build/install/examples/bin/route-guide-client localhost:8981
+ * }<pre>
+ *
+ * <p>You can verify the proxy is being used by shutting down the proxy and seeing the client fail.
+ */
+public final class GrpcProxy<ReqT, RespT> implements ServerCallHandler<ReqT, RespT> {
+  private static final Logger logger = Logger.getLogger(GrpcProxy.class.getName());
+
+  private final Channel channel;
+
+  public GrpcProxy(Channel channel) {
+    this.channel = channel;
+  }
+
+  @Override
+  public ServerCall.Listener<ReqT> startCall(
+      ServerCall<ReqT, RespT> serverCall, Metadata headers) {
+    ClientCall<ReqT, RespT> clientCall
+        = channel.newCall(serverCall.getMethodDescriptor(), CallOptions.DEFAULT);
+    CallProxy<ReqT, RespT> proxy = new CallProxy<ReqT, RespT>(serverCall, clientCall);
+    clientCall.start(proxy.clientCallListener, headers);
+    serverCall.request(1);
+    clientCall.request(1);
+    return proxy.serverCallListener;
+  }
+
+  private static class CallProxy<ReqT, RespT> {
+    final RequestProxy serverCallListener;
+    final ResponseProxy clientCallListener;
+
+    public CallProxy(ServerCall<ReqT, RespT> serverCall, ClientCall<ReqT, RespT> clientCall) {
+      serverCallListener = new RequestProxy(clientCall);
+      clientCallListener = new ResponseProxy(serverCall);
+    }
+
+    private class RequestProxy extends ServerCall.Listener<ReqT> {
+      private final ClientCall<ReqT, ?> clientCall;
+      // Hold 'this' lock when accessing
+      private boolean needToRequest;
+
+      public RequestProxy(ClientCall<ReqT, ?> clientCall) {
+        this.clientCall = clientCall;
+      }
+
+      @Override public void onCancel() {
+        clientCall.cancel("Server cancelled", null);
+      }
+
+      @Override public void onHalfClose() {
+        clientCall.halfClose();
+      }
+
+      @Override public void onMessage(ReqT message) {
+        clientCall.sendMessage(message);
+        synchronized (this) {
+          if (clientCall.isReady()) {
+            clientCallListener.serverCall.request(1);
+          } else {
+            // The outgoing call is not ready for more requests. Stop requesting additional data and
+            // wait for it to catch up.
+            needToRequest = true;
+          }
+        }
+      }
+
+      @Override public void onReady() {
+        clientCallListener.onServerReady();
+      }
+
+      // Called from ResponseProxy, which is a different thread than the ServerCall.Listener
+      // callbacks.
+      synchronized void onClientReady() {
+        if (needToRequest) {
+          clientCallListener.serverCall.request(1);
+          needToRequest = false;
+        }
+      }
+    }
+
+    private class ResponseProxy extends ClientCall.Listener<RespT> {
+      private final ServerCall<?, RespT> serverCall;
+      // Hold 'this' lock when accessing
+      private boolean needToRequest;
+
+      public ResponseProxy(ServerCall<?, RespT> serverCall) {
+        this.serverCall = serverCall;
+      }
+
+      @Override public void onClose(Status status, Metadata trailers) {
+        serverCall.close(status, trailers);
+      }
+
+      @Override public void onHeaders(Metadata headers) {
+        serverCall.sendHeaders(headers);
+      }
+
+      @Override public void onMessage(RespT message) {
+        serverCall.sendMessage(message);
+        synchronized (this) {
+          if (serverCall.isReady()) {
+            serverCallListener.clientCall.request(1);
+          } else {
+            // The incoming call is not ready for more responses. Stop requesting additional data
+            // and wait for it to catch up.
+            needToRequest = true;
+          }
+        }
+      }
+
+      @Override public void onReady() {
+        serverCallListener.onClientReady();
+      }
+
+      // Called from RequestProxy, which is a different thread than the ClientCall.Listener
+      // callbacks.
+      synchronized void onServerReady() {
+        if (needToRequest) {
+          serverCallListener.clientCall.request(1);
+          needToRequest = false;
+        }
+      }
+    }
+  }
+
+  private static class ByteMarshaller implements MethodDescriptor.Marshaller<byte[]> {
+    @Override public byte[] parse(InputStream stream) {
+      try {
+        return ByteStreams.toByteArray(stream);
+      } catch (IOException ex) {
+        throw new RuntimeException();
+      }
+    }
+
+    @Override public InputStream stream(byte[] value) {
+      return new ByteArrayInputStream(value);
+    }
+  };
+
+  public static class Registry extends HandlerRegistry {
+    private final MethodDescriptor.Marshaller<byte[]> byteMarshaller = new ByteMarshaller();
+    private final ServerCallHandler<byte[], byte[]> handler;
+
+    public Registry(ServerCallHandler<byte[], byte[]> handler) {
+      this.handler = handler;
+    }
+
+    @Override
+    public ServerMethodDefinition<?,?> lookupMethod(String methodName, String authority) {
+      MethodDescriptor<byte[], byte[]> methodDescriptor
+          = MethodDescriptor.newBuilder(byteMarshaller, byteMarshaller)
+          .setFullMethodName(methodName)
+          .setType(MethodDescriptor.MethodType.UNKNOWN)
+          .build();
+      return ServerMethodDefinition.create(methodDescriptor, handler);
+    }
+  }
+
+  public static void main(String[] args) throws IOException, InterruptedException {
+    String target = "localhost:8980";
+    ManagedChannel channel = Grpc.newChannelBuilder(target, InsecureChannelCredentials.create())
+        .build();
+    logger.info("Proxy will connect to " + target);
+    GrpcProxy<byte[], byte[]> proxy = new GrpcProxy<byte[], byte[]>(channel);
+    int port = 8981;
+    Server server = Grpc.newServerBuilderForPort(port, InsecureServerCredentials.create())
+        .fallbackHandlerRegistry(new Registry(proxy))
+        .build()
+        .start();
+    logger.info("Proxy started, listening on " + port);
+    Runtime.getRuntime().addShutdownHook(new Thread() {
+      @Override
+      public void run() {
+        server.shutdown();
+        try {
+          server.awaitTermination(10, TimeUnit.SECONDS);
+        } catch (InterruptedException ex) {
+          Thread.currentThread().interrupt();
+        }
+        server.shutdownNow();
+        channel.shutdownNow();
+      }
+    });
+    server.awaitTermination();
+    if (!channel.awaitTermination(1, TimeUnit.SECONDS)) {
+      System.out.println("Channel didn't shut down promptly");
+    }
+  }
+}