core/kg/api/rest/handler.go

package rest

import (
	"encoding/json"
	"net/http"
)

type HandlerFunc func(w http.ResponseWriter, r *http.Request) error

// ServeHTTP calls f(w, r) and handles error
func (f HandlerFunc) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if err := f(w, r); err != nil {
		jsoner(w, http.StatusBadRequest, err.Error()) // TODO detect the correct statusCode from error
	}
}

func jsoner(w http.ResponseWriter, statusCode int, payload interface{}) error {
	w.Header().Set("Content-Type", "application/json")

	// If there is nothing to marshal then set status code and return.
	if payload == nil {
		_, err := w.Write([]byte("{}"))
		return err
	}

	if statusCode != http.StatusOK {
		w.WriteHeader(statusCode)
	}

	encoder := json.NewEncoder(w)
	encoder.SetEscapeHTML(true)
	encoder.SetIndent("", "")

	if err := encoder.Encode(payload); err != nil {
		return err
	}

	if f, ok := w.(http.Flusher); ok {
		f.Flush()
	}

	return nil
}