Multi-encoding response in Golang with fiber

main.go

package main

import (
	"github.com/gofiber/fiber/v2"
)

type SomethingDto struct {
	ID int `json:"id" xml:"id" protobuf:"int,1,opt,name=id"`
}

func somethingAPI(c *fiber.Ctx) (*SomethingDto, error) {
	return &SomethingDto{ID: 1}, nil
}

func encode[T any](c *fiber.Ctx, res T, accepts string) err {
	switch accepts {
	case "application/json":
		return c.JSON(res)

	case "application/x-protobuf":
		// TODO: encode as protobuf
		return c.SendString("TODO")

	case "application/xml":
		return c.XML(res)
	}
}

func wrap[T any](handler func(c *fiber.Ctx) (T, error)) func(c *fiber.Ctx) error {
	return func(c *fiber.Ctx) error {
		accepts := c.Accepts("application/json", "application/x-protobuf", "application/xml")
		if accepts == "" {
			return c.SendStatus(fiber.StatusNotAcceptable)
		}

		res, err := handler(c)
		if err != nil {
			// Just make sure you actually return data, otherwise this will panic
			return encode(c, res, accepts)
		}

		return encode(c, res, accepts)
	}
}

func main() {
	app := fiber.New()

	app.Get("/api/something", wrap(somethingAPI))

	if err := app.Listen(":3000"); err != nil {
		panic(err)
	}
}