Description

This bug was discovered by Claude (Anthropic's AI assistant) while I was investigating why header parameters were being silently ignored in a generated Java goolge-api-client.

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?

OpenAPI Generator Version

7.15.0

OpenAPI Declaration File Content

openapi: 3.1.0
info:
  title: Sample API
  version: '1.0'
paths:
  /v1/resource:
    post:
      operationId: createResource
      parameters:
        - name: X-Request-ID
          in: header
          description: Unique request identifier for tracing
          required: false
          schema:
            type: string
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateRequest'
        required: true
      responses:
        '200':
          description: Success
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/CreateResponse'
components:
  schemas:
    CreateRequest:
      type: object
      properties:
        name:
          type: string
    CreateResponse:
      type: object
      properties:
        id:
          type: string

Generation Details

openapi-generator generate \
  -g java \
  --library google-api-client \
  -i spec.yaml \
  -o ./generated

Actual Behavior (Bug)

The generated DefaultApi.java accepts the header parameter xRequestID but never adds it to the HTTP request:

public HttpResponse createResourceForHttpResponse(
    @javax.annotation.Nullable String xRequestID,  // Parameter accepted
    @javax.annotation.Nonnull CreateRequest createRequest
) throws IOException {
    // ... validation code ...

    // create a map of path variables
    final Map<String, Object> uriVariables = new HashMap<String, Object>();
    UriBuilder uriBuilder = UriBuilder.fromUri(apiClient.getBasePath() + "/v1/resource");

    String localVarUrl = uriBuilder.build().toString();
    GenericUrl genericUrl = new GenericUrl(localVarUrl);

    HttpContent content = apiClient.new JacksonJsonHttpContent(createRequest);

    // BUG: xRequestID is completely ignored here!
    // The header is never added to the request
    return apiClient.getHttpRequestFactory()
        .buildRequest(HttpMethods.POST, genericUrl, content)
        .execute();
}

The same issue exists in:

1. The main ForHttpResponse method with typed parameters
2. The InputStream variant method
3. The Map<String, Object> params variant method

Expected Behavior

Header parameters should be added to the HttpRequest before calling execute():

public HttpResponse createResourceForHttpResponse(
    @javax.annotation.Nullable String xRequestID,
    @javax.annotation.Nonnull CreateRequest createRequest
) throws IOException {
    // ... validation code ...

    HttpContent content = apiClient.new JacksonJsonHttpContent(createRequest);

    // Build the request
    com.google.api.client.http.HttpRequest httpRequest = apiClient
        .getHttpRequestFactory()
        .buildRequest(HttpMethods.POST, genericUrl, content);

    // ADD HEADER PARAMETERS (this is missing!)
    if (xRequestID != null) {
        httpRequest.getHeaders().set("X-Request-ID", xRequestID);
    }

    return httpRequest.execute();
}

Root Cause

In the template file modules/openapi-generator/src/main/resources/Java/libraries/google-api-client/api.mustache, the {{#headerParams}} block is never used to add headers to the request.

Suggested Fix

Update api.mustache to include header parameter handling. Replace:

HttpContent content = {{#isBodyAllowed}}...{{/isBodyAllowed}};
return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.{{httpMethod}}, genericUrl, content).execute();

With:

HttpContent content = {{#isBodyAllowed}}...{{/isBodyAllowed}};
com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.{{httpMethod}}, genericUrl, content);
{{#headerParams}}
if ({{paramName}} != null) {
    httpRequest.getHeaders().set("{{baseName}}", {{paramName}});
}
{{/headerParams}}
return httpRequest.execute();

This fix needs to be applied in 3 locations within the template:

1. Main ForHttpResponse method (~line 126)
2. InputStream variant method (~line 162)
3. Params map variant method (~line 204)

Related Issues

None found - this appears to be an unreported bug.

Impact

Any OpenAPI spec with in: header parameters will generate non-functional code when using the google-api-client library. The generated methods accept the header parameters but silently discard them.