feat: add api client headers to outbound requests

google-cloud-pubsublite/src/main/java/com/google/cloud/pubsublite/Stubs.java

@@ -16,13 +16,28 @@
 
 package com.google.cloud.pubsublite;
 
+import com.google.api.gax.core.GaxProperties;
+import com.google.api.gax.grpc.GaxGrpcProperties;
+import com.google.api.gax.rpc.ApiClientHeaderProvider;
 import com.google.auth.oauth2.GoogleCredentials;
 import com.google.cloud.pubsublite.internal.ChannelCache;
 import com.google.common.collect.ImmutableList;
+import io.grpc.CallOptions;
 import io.grpc.Channel;
+import io.grpc.ClientCall;
+import io.grpc.ClientInterceptor;
+import io.grpc.ClientInterceptors;
+import io.grpc.ForwardingClientCall.SimpleForwardingClientCall;
+import io.grpc.Metadata;
+import io.grpc.Metadata.Key;
+import io.grpc.MethodDescriptor;
 import io.grpc.auth.MoreCallCredentials;
 import io.grpc.stub.AbstractStub;
 import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
 import java.util.function.Function;
 
 public class Stubs {
@@ -31,13 +46,44 @@ public class Stubs {
   public static <StubT extends AbstractStub<StubT>> StubT defaultStub(
       String target, Function<Channel, StubT> stubFactory) throws IOException {
     return stubFactory
-        .apply(channels.get(target))
+        .apply(ClientInterceptors.intercept(channels.get(target), getClientInterceptors()))
         .withCallCredentials(
             MoreCallCredentials.from(
                 GoogleCredentials.getApplicationDefault()
                     .createScoped(
                         ImmutableList.of("https://www.googleapis.com/auth/cloud-platform"))));
   }
 
+  private static List<ClientInterceptor> getClientInterceptors() {
+    List<ClientInterceptor> clientInterceptors = new ArrayList<>();
+    Map<String, String> apiClientHeaders =
+        ApiClientHeaderProvider.newBuilder()
+            .setClientLibToken("gccl", GaxProperties.getLibraryVersion(Stubs.class))
+            .setTransportToken(
+                GaxGrpcProperties.getGrpcTokenName(), GaxGrpcProperties.getGrpcVersion())
+            .build()
+            .getHeaders();
+    clientInterceptors.add(
+        new ClientInterceptor() {
+          @Override
+          public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(
+              MethodDescriptor<ReqT, RespT> method, CallOptions callOptions, Channel next) {
+            ClientCall<ReqT, RespT> call = next.newCall(method, callOptions);
+            return new SimpleForwardingClientCall<ReqT, RespT>(call) {
+              @Override
+              public void start(ClientCall.Listener<RespT> responseListener, Metadata headers) {
+                for (Entry<String, String> apiClientHeader : apiClientHeaders.entrySet()) {
+                  headers.put(
+                      Key.of(apiClientHeader.getKey(), Metadata.ASCII_STRING_MARSHALLER),
+                      apiClientHeader.getValue());
+                }
+                super.start(responseListener, headers);
+              }
+            };
+          }
+        });
+    return clientInterceptors;
+  }
+
   private Stubs() {}
 }