fix(generator): use json_name when available

.gitignore

@@ -58,6 +58,7 @@ nosetests.xml
 .settings
 .DS_Store
 .classpath
+.vscode
 
 # API key file containing value of GOOGLE_API_KEY for integration tests
 api_key
@@ -79,4 +80,4 @@ monorepo
 *.tfstate.*.backup
 *.tfstate.lock.info
 
-.jqwik-database
+.jqwik-database

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

@@ -62,6 +62,7 @@
 import com.google.api.generator.gapic.model.Service;
 import com.google.api.generator.gapic.utils.JavaStyle;
 import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Strings;
 import com.google.common.collect.BiMap;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
@@ -723,7 +724,7 @@
             .build());
   }
 
   private Expr createBodyFieldsExtractorClassInstance(
       Method method,
       TypeNode extractorReturnType,
       Set<HttpBinding> httpBindingFieldNames,
@@ -763,7 +764,16 @@
       // Handle foo.bar cases by descending into the subfields.
       MethodInvocationExpr.Builder requestFieldMethodExprBuilder =
           MethodInvocationExpr.builder().setExprReferenceExpr(prevExpr);
-      bodyParamName = JavaStyle.toLowerCamelCase(httpBindingFieldName.name());
+      // Use explicit json_name if defined in the proto, prioritizing the actual wire name
+      // over Java-escaped identifiers. Note that trailing underscores (e.g., 'case_') result from:
+      // 1. protoc-gen-java:
+      // https://github.com/protocolbuffers/protobuf/blob/cecbbf41e43634c7c5b940dd336aa81b31fd4e5d/src/google/protobuf/compiler/java/names.cc#L189-L195
+      // 2. gapic-generator-java Keyword implementation:
+      // com/google/api/generator/engine/lexicon/Keyword.java#L92-L94
+      bodyParamName =
+          !Strings.isNullOrEmpty(httpBindingFieldName.jsonName())
+              ? httpBindingFieldName.jsonName()
+              : JavaStyle.toLowerCamelCase(httpBindingFieldName.name());
       String[] descendantFields = httpBindingFieldName.name().split("\\.");
       if (asteriskBody && descendantFields.length > 1) {
         // This is the `body: "*"` case, do not clean nested body fields as it a very rare, not
@@ -827,7 +837,7 @@
         .build();
   }
 
   private Expr createFieldsExtractorClassInstance(
       Method method,
       TypeNode extractorReturnType,
       Set<HttpBinding> httpBindingFieldNames,
@@ -926,7 +936,12 @@
       paramsPutArgs.add(
           ValueExpr.withValue(
               StringObjectValue.withValue(
-                  JavaStyle.toLowerCamelCase(httpBindingFieldName.name()))));
+                  // Use explicit json_name if defined in the proto, prioritizing the actual wire
+                  // name over Java-escaped identifiers (e.g., avoiding 'case_' generated to prevent
+                  // keywords conflict).
+                  (httpBindingFieldName.jsonName() != null)
+                      ? httpBindingFieldName.jsonName()
+                      : JavaStyle.toLowerCamelCase(httpBindingFieldName.name()))));
       paramsPutArgs.add(requestBuilderExpr);
 
       Expr paramsPutExpr =

sdk-platform-java/gapic-generator-java/src/main/java/com/google/api/generator/gapic/model/Field.java

@@ -31,6 +31,9 @@ public abstract class Field {
   // resolution behavior. For more context, please see the invocation site of the setter method.
   public abstract String originalName();
 
+  @Nullable
+  public abstract String jsonName();
+
   public abstract TypeNode type();
 
   // If the field is annotated with google.api.field_behavior = REQUIRED, then this is true. This is
@@ -92,6 +95,7 @@ public boolean equals(Object o) {
     Field other = (Field) o;
     return name().equals(other.name())
         && originalName().equals(other.originalName())
+        && Objects.equals(jsonName(), other.jsonName())
         && type().equals(other.type())
         && isRequired() == other.isRequired()
         && fieldInfoFormat() == other.fieldInfoFormat()
@@ -109,6 +113,7 @@ && isProto3Optional() == other.isProto3Optional()
   public int hashCode() {
     return 17 * name().hashCode()
         + 31 * originalName().hashCode()
+        + (jsonName() == null ? 0 : jsonName().hashCode())
         + 19 * type().hashCode()
         + (isMessage() ? 1 : 0) * 23
         + (isEnum() ? 1 : 0) * 29
@@ -141,6 +146,8 @@ public abstract static class Builder {
 
     public abstract Builder setOriginalName(String originalName);
 
+    public abstract Builder setJsonName(String jsonName);
+
     public abstract Builder setType(TypeNode type);
 
     public abstract Builder setIsRequired(boolean isRequired);

sdk-platform-java/gapic-generator-java/src/main/java/com/google/api/generator/gapic/model/HttpBindings.java

@@ -16,6 +16,7 @@
 
 import com.google.api.generator.gapic.utils.JavaStyle;
 import com.google.auto.value.AutoValue;
+import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableSet;
 import java.util.LinkedHashMap;
 import java.util.List;
@@ -42,6 +43,11 @@ public abstract static class HttpBinding implements Comparable<HttpBinding> {
 
     abstract String lowerCamelName();
 
+    // The dot-separated json_name of the field.
+    // e.g. parent.iceberg-catalog-id
+    @Nullable
+    public abstract String jsonName();
+
     // An object that contains all info of the leaf level field
     @Nullable
     public abstract Field field();
@@ -70,6 +76,8 @@ public abstract static class Builder {
 
       public abstract HttpBindings.HttpBinding.Builder setName(String name);
 
+      public abstract HttpBindings.HttpBinding.Builder setJsonName(String jsonName);
+
       public abstract HttpBindings.HttpBinding.Builder setField(Field field);
 
       abstract HttpBindings.HttpBinding.Builder setLowerCamelName(String lowerCamelName);
@@ -133,9 +141,11 @@ public List<String> lowerCamelAdditionalPatterns() {
   private static String lowerCamelPattern(String originalPattern, Set<HttpBinding> pathParameters) {
     String lowerCamelPattern = originalPattern;
     for (HttpBinding pathParam : pathParameters) {
-      lowerCamelPattern =
-          lowerCamelPattern.replaceAll(
-              "\\{" + pathParam.name(), "{" + JavaStyle.toLowerCamelCase(pathParam.name()));
+      String replacement =
+          !Strings.isNullOrEmpty(pathParam.jsonName())
+              ? pathParam.jsonName()
+              : JavaStyle.toLowerCamelCase(pathParam.name());
+      lowerCamelPattern = lowerCamelPattern.replaceAll("\\{" + pathParam.name(), "{" + replacement);
     }
     return lowerCamelPattern;
   }

sdk-platform-java/gapic-generator-java/src/main/java/com/google/api/generator/gapic/protoparser/HttpRuleParser.java

@@ -21,6 +21,7 @@
 import com.google.api.generator.gapic.model.HttpBindings;
 import com.google.api.generator.gapic.model.HttpBindings.HttpBinding;
 import com.google.api.generator.gapic.model.Message;
+import com.google.api.generator.gapic.utils.JavaStyle;
 import com.google.api.pathtemplate.PathTemplate;
 import com.google.common.base.Preconditions;
 import com.google.common.base.Strings;
@@ -29,8 +30,10 @@
 import com.google.common.collect.Sets;
 import com.google.protobuf.DescriptorProtos.MethodOptions;
 import com.google.protobuf.Descriptors.MethodDescriptor;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
@@ -126,7 +129,7 @@
         .build();
   }
 
   private static Set<HttpBinding> validateAndConstructHttpBindings(
       Set<String> paramNames,
       Message inputMessage,
       Map<String, Message> messageTypes,
@@ -144,10 +147,24 @@
         continue;
       }
       Message nestedMessage = inputMessage;
+      List<String> jsonNameParts = new ArrayList<>();
       for (int i = 0; i < subFields.length; i++) {
         String subFieldName = subFields[i];
+        Field field = nestedMessage.fieldMap().get(subFieldName);
+        Preconditions.checkState(
+            field != null,
+            "Expected message %s to contain field %s but none found",
+            nestedMessage.name(),
+            subFieldName);
+
+        // Each component of the JSON name uses the json_name annotation of the field,
+        // or default to the field name
+        jsonNameParts.add(
+            !Strings.isNullOrEmpty(field.jsonName())
+                ? field.jsonName()
+                : JavaStyle.toLowerCamelCase(field.name()));
+
         if (i < subFields.length - 1) {
-          Field field = nestedMessage.fieldMap().get(subFieldName);
           nestedMessage = messageTypes.get(field.type().reference().fullName());
           Preconditions.checkNotNull(
               nestedMessage,
@@ -160,9 +177,12 @@
             checkHttpFieldIsValid(subFieldName, nestedMessage, false);
             patternSampleValue = patternSampleValues.get(paramName);
           }
-          Field field = nestedMessage.fieldMap().get(subFieldName);
           httpBindings.add(
-              httpBindingBuilder.setValuePattern(patternSampleValue).setField(field).build());
+              httpBindingBuilder
+                  .setValuePattern(patternSampleValue)
+                  .setField(field)
+                  .setJsonName(String.join(".", jsonNameParts))
+                  .build());
         }
       }
     }

sdk-platform-java/gapic-generator-java/src/main/java/com/google/api/generator/gapic/protoparser/Parser.java

@@ -1181,6 +1181,7 @@ private static Field parseField(
     return fieldBuilder
         .setName(actualFieldName)
         .setOriginalName(fieldDescriptor.getName())
+        .setJsonName(fieldDescriptor.getJsonName())
         .setType(TypeParser.parseType(fieldDescriptor))
         .setIsMessage(fieldDescriptor.getJavaType() == FieldDescriptor.JavaType.MESSAGE)
         .setIsEnum(fieldDescriptor.getJavaType() == FieldDescriptor.JavaType.ENUM)

sdk-platform-java/gapic-generator-java/src/test/java/com/google/api/generator/gapic/composer/grpcrest/goldens/HttpJsonEchoStub.golden

@@ -362,7 +362,7 @@ public class HttpJsonEchoStub extends EchoStub {
                       })
                   .setRequestBodyExtractor(
                       request ->
-                          ProtoRestSerializer.create().toBody("case_", request.getCase(), false))
+                          ProtoRestSerializer.create().toBody("case", request.getCase(), false))
                   .build())
           .setResponseParser(
               ProtoMessageResponseParser.<Case>newBuilder()