[BUG] go-server doesn't honour the provided headers within EncodeJSONResponse

[mgoltzsche]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• 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?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When the option addResponseHeaders is enabled for the go-server generator it generates a ResponseWithHeaders method that calls an EncodeJSONResponse method which however ignores the headers that are provided to it.
The generated method looks as follows:

func EncodeJSONResponse(i interface{}, status *int, headers map[string][]string, w http.ResponseWriter) error {
	w.Header().Set("Content-Type", "application/json; charset=UTF-8")
	if status != nil {
		w.WriteHeader(*status)
	} else {
		w.WriteHeader(http.StatusOK)
	}

	return json.NewEncoder(w).Encode(i)
}

This stops me from specifying response headers within my controller implementation.

I would expect this method to apply the headers I provided.

openapi-generator version

openapi-generator 5.1.1

OpenAPI declaration file content or url

This is the example OpenAPI schema example-openapi.yaml - though you could use any other to reproduce the bug that is described here:

openapi: "3.0.3"

info:
  title: "Example API"
  version: "1.0.0"

paths:
  "/path/{myparam}/myresource":
    post:
      operationId: createResource
      parameters:
      - name: myparam
        in: path
        required: true
        schema:
          type: string
      requestBody:
        content:
          "application/json":
            schema:
              type: object
              properties:
                name:
                  type: string
      responses:
        '201':
          description: response with headers
          headers:
            myheader:
              schema:
                type: string

Generation Details

java -jar ./openapi-generator-5.1.1.jar generate -i ./example-openapi.yaml -g go-server -o ./generated --api-name-suffix API --package-name generated -p addResponseHeaders=true

Steps to reproduce

see generation details

Related issues/PRs

Suggest a fix

Generate the EncodeJSONResponse method so that it applies the provided headers to the ResponseWriter:

func EncodeJSONResponse(i interface{}, status *int, headers map[string][]string, w http.ResponseWriter) error {
	w.Header().Set("Content-Type", "application/json; charset=UTF-8")
	if headers != nil {
		for k, v := range headers {
			w.Header()[k] = v
		}
	}
	if status != nil {
		w.WriteHeader(*status)
	} else {
		w.WriteHeader(http.StatusOK)
	}

	return json.NewEncoder(w).Encode(i)
}

[mgoltzsche]

Apparently this is caused by a typo within the mustache template here where the condition refers to addResponseHeader instead of addResponseHeaders as the documentation says and as it is the case other parts of the template.

Fortunately this also means that there's a workaround already by specifying both addResponseHeaders=true and addResponseHeader=true ;)