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

Wires the generated transport stubs (GrpcServiceStub and HttpJsonServiceStub) to delegate resumable upload methods to the internal HTTP upload stub. In GrpcServiceStub, credentials, headers, and clocks are forwarded to the underlying HTTP client context. Clients initialize successfully without credentials; an exception results only if use of the HTTP upload stub is attempted.

Also declares the stub-side contract that the transports implement:

- In AbstractServiceStubClassComposer: emit public
  ResumableUploadCallable<RequestT, ResponseT> [method]Callable() throwing
  UnsupportedOperationException.

Author: whowes

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/main/java/com/google/api/generator/gapic/composer/common/AbstractServiceStubClassComposer.java

@@ -21,6 +21,7 @@
 import com.google.api.gax.rpc.ClientStreamingCallable;
 import com.google.api.gax.rpc.LongRunningClient;
 import com.google.api.gax.rpc.OperationCallable;
+import com.google.api.gax.rpc.ResumableUploadCallable;
 import com.google.api.gax.rpc.ServerStreamingCallable;
 import com.google.api.gax.rpc.UnaryCallable;
 import com.google.api.generator.engine.ast.AnnotationNode;
@@ -52,6 +53,7 @@
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.stream.Collectors;
 import javax.annotation.Generated;
 import org.jspecify.annotations.NullMarked;
@@ -162,22 +164,7 @@ private MethodDefinition createCallableGetter(Method method, TypeStore typeStore
 
   private MethodDefinition createCallableGetterHelper(
       Method method, TypeStore typeStore, boolean isLroCallable, boolean isPaged) {
-    TypeNode returnType;
-    switch (method.stream()) {
-      case CLIENT:
-        returnType = typeStore.get("ClientStreamingCallable");
-        break;
-      case SERVER:
-        returnType = typeStore.get("ServerStreamingCallable");
-        break;
-      case BIDI:
-        returnType = typeStore.get("BidiStreamingCallable");
-        break;
-      case NONE:
-      // Fall through.
-      default:
-        returnType = typeStore.get(isLroCallable ? "OperationCallable" : "UnaryCallable");
-    }
+    TypeNode returnType = getCallableType(method, typeStore, isLroCallable);
 
     String methodName =
         String.format(
@@ -270,6 +257,7 @@ private static TypeStore createTypes(Service service, Map<String, Message> messa
             Generated.class,
             Operation.class,
             OperationCallable.class,
+            ResumableUploadCallable.class,
             ServerStreamingCallable.class,
             UnaryCallable.class,
             UnsupportedOperationException.class,
@@ -328,4 +316,22 @@ protected MethodDefinition createOperationsStubGetterMethodDefinition(
                         .build())))
         .build();
   }
+
+  private static TypeNode getCallableType(
+      Method method, TypeStore typeStore, boolean isLroCallable) {
+    if (method.isResumableUpload()) {
+      return typeStore.get("ResumableUploadCallable");
+    }
+    switch (method.stream()) {
+      case CLIENT:
+        return typeStore.get("ClientStreamingCallable");
+      case SERVER:
+        return typeStore.get("ServerStreamingCallable");
+      case BIDI:
+        return typeStore.get("BidiStreamingCallable");
+      case NONE:
+      default:
+        return typeStore.get(isLroCallable ? "OperationCallable" : "UnaryCallable");
+    }
+  }
 }