feat(generator): wire transport stub delegation to resumable upload stubs

sdk-platform-java/gapic-generator-java/src/main/java/com/google/api/generator/gapic/composer/Composer.java

@@ -29,10 +29,12 @@
 import com.google.api.generator.gapic.composer.grpcrest.HttpJsonServiceClientTestClassComposer;
 import com.google.api.generator.gapic.composer.resourcename.ResourceNameHelperClassComposer;
 import com.google.api.generator.gapic.composer.rest.HttpJsonServiceCallableFactoryClassComposer;
+import com.google.api.generator.gapic.composer.rest.HttpJsonServiceResumableUploadStubClassComposer;
 import com.google.api.generator.gapic.composer.rest.HttpJsonServiceStubClassComposer;
 import com.google.api.generator.gapic.model.GapicClass;
 import com.google.api.generator.gapic.model.GapicContext;
 import com.google.api.generator.gapic.model.GapicPackageInfo;
+import com.google.api.generator.gapic.model.Method;
 import com.google.api.generator.gapic.model.ReflectConfig;
 import com.google.api.generator.gapic.model.Sample;
 import com.google.api.generator.gapic.model.Service;
@@ -91,6 +93,11 @@ public static List<GapicClass> generateStubClasses(GapicContext context) {
         .services()
         .forEach(
             s -> {
+              if (s.methods().stream().anyMatch(Method::isResumableUpload)) {
+                clazzes.add(
+                    HttpJsonServiceResumableUploadStubClassComposer.instance()
+                        .generate(context, s));
+              }
               if (context.transport() == Transport.REST) {
                 clazzes.add(
                     com.google.api.generator.gapic.composer.rest.ServiceStubClassComposer.instance()

sdk-platform-java/gapic-generator-java/src/test/java/com/google/api/generator/gapic/composer/common/ResumableUploadTransportStubComposerTest.java

@@ -0,0 +1,215 @@
+// Copyright 2026 Google LLC
+//
+// 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 com.google.api.generator.gapic.composer.common;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.api.generator.engine.writer.JavaWriterVisitor;
+import com.google.api.generator.gapic.composer.grpc.GrpcServiceStubClassComposer;
+import com.google.api.generator.gapic.composer.rest.HttpJsonServiceStubClassComposer;
+import com.google.api.generator.gapic.model.GapicClass;
+import com.google.api.generator.gapic.model.GapicClass.Kind;
+import com.google.api.generator.gapic.model.GapicContext;
+import com.google.api.generator.gapic.model.Service;
+import com.google.api.generator.test.protoloader.GrpcTestProtoLoader;
+import com.google.api.generator.test.protoloader.RestTestProtoLoader;
+import org.junit.jupiter.api.Test;
+
+class ResumableUploadTransportStubComposerTest {
+
+  private static String generateGrpcStubCode() {
+    GapicContext context = GrpcTestProtoLoader.instance().parseShowcaseResumableUpload();
+    Service service = context.services().get(0);
+
+    GapicClass clazz = GrpcServiceStubClassComposer.instance().generate(context, service);
+    assertThat(clazz.kind()).isEqualTo(Kind.STUB);
+
+    JavaWriterVisitor visitor = new JavaWriterVisitor();
+    clazz.classDefinition().accept(visitor);
+    return visitor.write();
+  }
+
+  private static String generateRestStubCode() {
+    GapicContext context = RestTestProtoLoader.instance().parseShowcaseResumableUpload();
+    Service service = context.services().get(0);
+
+    GapicClass clazz = HttpJsonServiceStubClassComposer.instance().generate(context, service);
+    assertThat(clazz.kind()).isEqualTo(Kind.STUB);
+
+    JavaWriterVisitor visitor = new JavaWriterVisitor();
+    clazz.classDefinition().accept(visitor);
+    return visitor.write();
+  }
+
+  @Test
+  void generate_grpcStub_withCredentials_initializesHttpStub() {
+    String code = generateGrpcStubCode();
+
+    // Verify key imports
+    assertThat(code).contains("import com.google.api.gax.grpc.GrpcStatusCode;");
+    assertThat(code).contains("import com.google.api.gax.httpjson.HttpJsonCallContext;");
+    assertThat(code).contains("import com.google.api.gax.httpjson.HttpJsonTransportChannel;");
+    assertThat(code).contains("import com.google.api.gax.httpjson.ManagedHttpJsonChannel;");
+    assertThat(code).contains("import com.google.api.gax.rpc.FailedPreconditionException;");
+    assertThat(code).contains("import com.google.api.gax.rpc.ResumableUploadCallable;");
+    assertThat(code).contains("import com.google.common.collect.ImmutableList;");
+    assertThat(code).contains("import io.grpc.Status;");
+    assertThat(code).contains("import java.util.Arrays;");
+
+    // Verify class declaration and nullable stub field
+    assertThat(code)
+        .contains("public class GrpcResumableUploadServiceStub extends ResumableUploadServiceStub");
+    assertThat(code)
+        .contains(
+            "private final @Nullable HttpJsonResumableUploadServiceResumableUploadStub"
+                + " resumableUploadStub;");
+
+    // Verify constructor credentials check and HTTP channel instantiation
+    assertThat(code).contains("if (clientContext.getCredentials() != null) {");
+    assertThat(code).contains("ManagedHttpJsonChannel httpJsonManagedChannel =");
+    assertThat(code).contains("HttpJsonTransportChannel httpJsonTransportChannel =");
+    assertThat(code).contains("ClientContext httpJsonClientContext =");
+    assertThat(code).contains(".setCredentials(clientContext.getCredentials())");
+    assertThat(code).contains(".setEndpoint(settings.getEndpoint())");
+    assertThat(code).contains(".setExecutor(clientContext.getExecutor())");
+    assertThat(code).contains(".setHeaders(clientContext.getHeaders())");
+    assertThat(code).contains(".setInternalHeaders(clientContext.getInternalHeaders())");
+    assertThat(code).contains(".setTransportChannel(httpJsonTransportChannel)");
+    assertThat(code).contains(".withTransportChannel(httpJsonTransportChannel)");
+    assertThat(code).contains(".setBackgroundResources(Arrays.asList(httpJsonTransportChannel))");
+    assertThat(code).contains("this.resumableUploadStub =");
+    assertThat(code)
+        .contains(
+            "HttpJsonResumableUploadServiceResumableUploadStub.create(httpJsonClientContext,"
+                + " settings);");
+  }
+
+  @Test
+  void generate_grpcStub_withoutCredentials_assignsNull() {
+    String code = generateGrpcStubCode();
+
+    assertThat(code).contains("} else {");
+    assertThat(code).contains("this.resumableUploadStub = null;");
+  }
+
+  @Test
+  void generate_grpcStub_uploadMediaCallable_guardsNullWithFailedPrecondition() {
+    String code = generateGrpcStubCode();
+
+    // Verify callable getter throwing FailedPreconditionException when resumableUploadStub == null
+    assertThat(code)
+        .contains(
+            "public ResumableUploadCallable<UploadMediaRequest, UploadMediaResponse>"
+                + " uploadMediaCallable() {");
+    assertThat(code).contains("if (resumableUploadStub == null) {");
+    assertThat(code).contains("throw new FailedPreconditionException(");
+    assertThat(code)
+        .contains("\"Resumable uploads execute over HTTP/REST and require credentials.");
+    assertThat(code).contains("GrpcStatusCode.of(Status.Code.FAILED_PRECONDITION)");
+    assertThat(code).contains("return resumableUploadStub.uploadMediaCallable();");
+  }
+
+  @Test
+  void generate_grpcStub_implementsBackgroundResource() {
+    String code = generateGrpcStubCode();
+
+    // Verify BackgroundResource aggregation with fallback
+    assertThat(code).contains("if (resumableUploadStub != null) {");
+    assertThat(code).contains("this.backgroundResources =");
+    assertThat(code).contains("new BackgroundResourceAggregation(");
+    assertThat(code).contains("ImmutableList.<BackgroundResource>builder()");
+    assertThat(code).contains(".addAll(clientContext.getBackgroundResources())");
+    assertThat(code).contains(".add(resumableUploadStub)");
+    assertThat(code).contains(".build());");
+    assertThat(code)
+        .contains(
+            "this.backgroundResources =\n"
+                + "          new"
+                + " BackgroundResourceAggregation(clientContext.getBackgroundResources());");
+
+    // Verify close() delegates only to backgroundResources
+    assertThat(code).contains("backgroundResources.close();");
+    assertThat(code).doesNotContain("resumableUploadStub.close();");
+  }
+
+  @Test
+  void generate_restStub_delegatesToResumableUploadStub() {
+    String code = generateRestStubCode();
+
+    // Verify class declaration and non-null stub field
+    assertThat(code)
+        .contains(
+            "public class HttpJsonResumableUploadServiceStub extends ResumableUploadServiceStub");
+    assertThat(code)
+        .contains(
+            "private final HttpJsonResumableUploadServiceResumableUploadStub resumableUploadStub;");
+    assertThat(code)
+        .doesNotContain(
+            "private final @Nullable HttpJsonResumableUploadServiceResumableUploadStub"
+                + " resumableUploadStub;");
+
+    // Verify REST constructor directly creates the upload stub
+    assertThat(code).contains("this.resumableUploadStub =");
+    assertThat(code)
+        .contains(
+            "HttpJsonResumableUploadServiceResumableUploadStub.create(clientContext, settings);");
+
+    // Verify callable getter delegates directly
+    assertThat(code)
+        .contains(
+            "public ResumableUploadCallable<UploadMediaRequest, UploadMediaResponse>"
+                + " uploadMediaCallable() {");
+    assertThat(code).contains("return resumableUploadStub.uploadMediaCallable();");
+
+    // Verify BackgroundResource aggregation
+    assertThat(code).contains("ImmutableList.<BackgroundResource>builder()");
+    assertThat(code).contains(".addAll(clientContext.getBackgroundResources())");
+    assertThat(code).contains(".add(resumableUploadStub)");
+    assertThat(code).contains("backgroundResources.close();");
+    assertThat(code).doesNotContain("resumableUploadStub.close();");
+  }
+
+  @Test
+  void generateGrpcServiceStubClass_serviceWithoutResumableUpload_noUploadStub() {
+    GapicContext context = GrpcTestProtoLoader.instance().parseShowcaseEcho();
+    Service service = context.services().get(0);
+
+    GapicClass clazz = GrpcServiceStubClassComposer.instance().generate(context, service);
+    assertThat(clazz.kind()).isEqualTo(Kind.STUB);
+
+    JavaWriterVisitor visitor = new JavaWriterVisitor();
+    clazz.classDefinition().accept(visitor);
+    String code = visitor.write();
+
+    assertThat(code).doesNotContain("resumableUploadStub");
+    assertThat(code).doesNotContain("HttpJsonCallContext");
+    assertThat(code).doesNotContain("FailedPreconditionException");
+  }
+
+  @Test
+  void generateHttpJsonServiceStubClass_serviceWithoutResumableUpload_noUploadStub() {
+    GapicContext context = RestTestProtoLoader.instance().parseCompliance();
+    Service service = context.services().get(0);
+
+    GapicClass clazz = HttpJsonServiceStubClassComposer.instance().generate(context, service);
+    assertThat(clazz.kind()).isEqualTo(Kind.STUB);
+
+    JavaWriterVisitor visitor = new JavaWriterVisitor();
+    clazz.classDefinition().accept(visitor);
+    String code = visitor.write();
+
+    assertThat(code).doesNotContain("resumableUploadStub");
+  }
+}

sdk-platform-java/gapic-generator-java/src/test/java/com/google/api/generator/gapic/composer/grpc/GrpcServiceStubClassComposerTest.java

@@ -122,4 +122,14 @@ void generateGrpcServiceStubClass_clientResourceNameExtractor() {
     Assert.assertGoldenClass(this.getClass(), clazz, "GrpcResourceNameExtractorStub.golden");
     Assert.assertEmptySamples(clazz.samples());
   }
+
+  @Test
+  void generateGrpcServiceStubClass_resumableUpload() {
+    GapicContext context = GrpcTestProtoLoader.instance().parseShowcaseResumableUpload();
+    Service service = context.services().get(0);
+    GapicClass clazz = GrpcServiceStubClassComposer.instance().generate(context, service);
+
+    Assert.assertGoldenClass(this.getClass(), clazz, "GrpcResumableUploadServiceStub.golden");
+    Assert.assertEmptySamples(clazz.samples());
+  }
 }