An approach to exposing go functions over HTTP

program-fn.go

var RawFunctionMap = map[string]func(inputbytes []byte) (outputbytes []byte){}

func ProgramFnRegister[Input any, Output any](fn func(input Input) Output) {
	// e.g. "tt/pkg/student.FnCreateStudent"
	funcName := runtime.FuncForPC(reflect.ValueOf(fn).Pointer()).Name()

	rawFn := func(inputbytes []byte) []byte {
		var input Input
		if len(inputbytes) != 0 {
			check(json.Unmarshal(inputbytes, &input))
		}
		output := fn(input)
		return must(json.Marshal(output))
	}

	RawFunctionMap[funcName] = rawFn

	// POST /tt/pkg/student.FnCreateStudent
	http.HandleFunc(fmt.Sprintf("/%s", funcName), func(w http.ResponseWriter, r *http.Request) {
		defer func() {
			if r := recover(); r != nil {
				log.Println(funcName, "error:", r)
				w.WriteHeader(http.StatusInternalServerError)
				w.Write([]byte(fmt.Sprintf("%s", r)))
			}
		}()
		inputbytes := must(io.ReadAll(r.Body))
		outputbytes := rawFn(inputbytes)
		w.Header().Add("Content-Type", "application/json")
		w.Write(outputbytes)
	})
}

func check(err error) {
	if err != nil {
		panic(err)
	}
}

func must[T any](t T, err error) T {
	check(err)
	return t
}