feat: implement snapshot-integrated custom LRO error parsing

Author: nnicolee

java-compute/google-cloud-compute/src/main/java/com/google/cloud/compute/v1/stub/ComputeLroErrorParser.java

@@ -0,0 +1,73 @@
+/*
+ * 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
+ *
+ *      https://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.cloud.compute.v1.stub;
+
+import com.google.api.core.BetaApi;
+import com.google.api.gax.httpjson.HttpJsonLroErrorParser;
+import com.google.api.gax.rpc.ErrorDetails;
+import com.google.cloud.compute.v1.Errors;
+import com.google.cloud.compute.v1.Operation;
+import com.google.protobuf.Any;
+import com.google.rpc.ErrorInfo;
+import java.util.ArrayList;
+import java.util.List;
+
+@BetaApi("The surface for custom LRO error parsing is not stable yet and may change.")
+class ComputeLroErrorParser implements HttpJsonLroErrorParser {
+
+  @Override
+  public ErrorDetails parse(Object response) {
+    if (!(response instanceof Operation)) {
+      return null;
+    }
+    Operation operation = ((Operation) response);
+    if (!operation.hasError()) {
+      return null;
+    }
+    List<Any> rawErrorMessages = new ArrayList<>();
+    for (Errors error : operation.getError().getErrorsList()) {
+      ErrorInfo errorInfo =
+          ErrorInfo.newBuilder()
+              .setReason(error.getCode())
+              .setDomain("googleapis.com")
+              .putMetadata("message", error.getMessage())
+              .putMetadata("location", error.getLocation())
+              .build();
+      rawErrorMessages.add(Any.pack(errorInfo));
+    }
+    return ErrorDetails.builder().setRawErrorMessages(rawErrorMessages).build();
+  }
+
+  @Override
+  public String parseErrorMessage(Object response) {
+    if (!(response instanceof Operation)) {
+      return null;
+    }
+    Operation operation = ((Operation) response);
+    if (!operation.hasError() || operation.getError().getErrorsCount() == 0) {
+      return null;
+    }
+    StringBuilder sb = new StringBuilder();
+    for (Errors error : operation.getError().getErrorsList()) {
+      if (sb.length() > 0) {
+        sb.append("; ");
+      }
+      sb.append(error.getCode()).append(": ").append(error.getMessage());
+    }
+    return sb.toString();
+  }
+}

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

@@ -170,7 +170,7 @@ protected Statement createMethodDescriptorVariableDecl(
           methodMaker
               .apply(
                   "setOperationSnapshotFactory",
-                  setOperationSnapshotFactoryExpr(protoMethod, messageTypes))
+                  setOperationSnapshotFactoryExpr(service, protoMethod, messageTypes))
               .apply(expr);
     }
 
@@ -453,7 +453,7 @@ private MethodInvocationExpr getExpr(VariableExpr var, String num) {
   }
 
   private List<Expr> setOperationSnapshotFactoryExpr(
-      Method protoMethod, Map<String, Message> messageTypes) {
+      Service service, Method protoMethod, Map<String, Message> messageTypes) {
 
     // Generate input variables for create()
     VariableExpr requestVarExpr =
@@ -598,6 +598,20 @@ private List<Expr> setOperationSnapshotFactoryExpr(
               .apply("setError", Arrays.asList(getHttpErrorStatusCodeExpr, getHttpErrorMessageExpr))
               .apply(newBuilderExpr);
 
+      if (service.pakkage().startsWith("com.google.cloud.compute.v1")) {
+        TypeNode parserType =
+            TypeNode.withReference(
+                VaporReference.builder()
+                    .setName("ComputeLroErrorParser")
+                    .setPakkage(service.pakkage() + ".stub")
+                    .build());
+        Expr newParserExpr = NewObjectExpr.builder().setType(parserType).build();
+        newBuilderExpr =
+            methodMaker
+                .apply("setErrorParser", Collections.singletonList(newParserExpr))
+                .apply(newBuilderExpr);
+      }
+
       buildExpr =
           MethodInvocationExpr.builder()
               .setExprReferenceExpr(newBuilderExpr)

sdk-platform-java/gax-java/gax-httpjson/src/main/java/com/google/api/gax/httpjson/HttpJsonLroErrorParser.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google LLC nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package com.google.api.gax.httpjson;
+
+import com.google.api.core.BetaApi;
+import com.google.api.gax.rpc.ErrorDetails;
+import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
+
+@NullMarked
+@BetaApi("The surface for custom LRO error parsing is not stable yet and may change.")
+public interface HttpJsonLroErrorParser {
+  /** Parses custom LRO response object into standard ErrorDetails. */
+  @Nullable ErrorDetails parse(Object response);
+
+  /** Concatenates custom LRO response errors into a single descriptive message. */
+  @Nullable String parseErrorMessage(Object response);
+}

sdk-platform-java/gax-java/gax-httpjson/src/main/java/com/google/api/gax/httpjson/HttpJsonOperationSnapshot.java

@@ -37,6 +37,7 @@
 import com.google.longrunning.Operation;
 import java.util.Collections;
 import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Implementation of OperationSnapshot based on REST transport.
@@ -130,6 +131,7 @@ public static class Builder {
     private String errorMessage;
     private ErrorDetails errorDetails =
         ErrorDetails.builder().setRawErrorMessages(Collections.emptyList()).build();
+    private @Nullable HttpJsonLroErrorParser errorParser;
 
     /**
      * Sets the LRO error details.
@@ -142,6 +144,17 @@ Builder setErrorDetails(final ErrorDetails errorDetails) {
       return this;
     }
 
+    /**
+     * Sets the LRO error parser.
+     *
+     * @param errorParser the LRO error parser
+     * @return the builder instance
+     */
+    public Builder setErrorParser(final HttpJsonLroErrorParser errorParser) {
+      this.errorParser = errorParser;
+      return this;
+    }
+
     public Builder setName(String name) {
       this.name = name;
       return this;
@@ -183,8 +196,20 @@ private Builder setOperation(Operation operation) {
     }
 
     public HttpJsonOperationSnapshot build() {
+      ErrorDetails finalErrorDetails = this.errorDetails;
+      String finalErrorMessage = this.errorMessage;
+      if (errorParser != null && response != null) {
+        ErrorDetails parsedDetails = errorParser.parse(response);
+        if (parsedDetails != null) {
+          finalErrorDetails = parsedDetails;
+        }
+        String parsedMsg = errorParser.parseErrorMessage(response);
+        if (parsedMsg != null && !parsedMsg.isEmpty()) {
+          finalErrorMessage = parsedMsg;
+        }
+      }
       return new HttpJsonOperationSnapshot(
-          name, metadata, done, response, errorCode, errorMessage, errorDetails);
+          name, metadata, done, response, errorCode, finalErrorMessage, finalErrorDetails);
     }
   }
 }

sdk-platform-java/test/integration/goldens/compute/src/com/google/cloud/compute/v1small/stub/HttpJsonAddressesStub.java

@@ -161,6 +161,7 @@ public class HttpJsonAddressesStub extends AddressesStub {
                     .setDone(Status.DONE.equals(response.getStatus()))
                     .setResponse(response)
                     .setError(response.getHttpErrorStatusCode(), response.getHttpErrorMessage())
+                    .setErrorParser(new ComputeLroErrorParser())
                     .build();
               })
           .build();
@@ -213,6 +214,7 @@ public class HttpJsonAddressesStub extends AddressesStub {
                     .setDone(Status.DONE.equals(response.getStatus()))
                     .setResponse(response)
                     .setError(response.getHttpErrorStatusCode(), response.getHttpErrorMessage())
+                    .setErrorParser(new ComputeLroErrorParser())
                     .build();
               })
           .build();

sdk-platform-java/test/integration/goldens/compute/src/com/google/cloud/compute/v1small/stub/HttpJsonRegionOperationsStub.java

@@ -101,6 +101,7 @@ public class HttpJsonRegionOperationsStub extends RegionOperationsStub {
                         .setDone(Status.DONE.equals(response.getStatus()))
                         .setResponse(response)
                         .setError(response.getHttpErrorStatusCode(), response.getHttpErrorMessage())
+                        .setErrorParser(new ComputeLroErrorParser())
                         .build();
                   })
               .setPollingRequestFactory(