Example http handler with api client dep

example.go

type APIClient struct {
	baseUrl url.URL
}

type Something struct {
	Id string // the response data
}

// NewAPIClient is a constructor and instantiating our api
// client once. See you can use url.URL to handle urls which
// has a lot of positive side effects.
func NewAPIClient(baseUrl url.URL) APIClient {
	return APIClient{baseUrl: baseUrl}
}

func (c *APIClient) Get(id string) (Something, error) {
	// TBD API call to your external service and return the result you want
	return Something{}, nil
}

type WebHandler struct{ apiClient APIClient }

// NewWebHandler is a constructor instantiating our http handler
// implementation and accepting our api client dependency
func NewWebHandler(apiClient APIClient) WebHandler {
	return WebHandler{apiClient: apiClient}
}

func (h *WebHandler) GetWrapper(w http.ResponseWriter, r *http.Request) {
	// TBD get id from request or whatever, we define it here for simplicity
	id := "123"
	// TBD call api client
	res, err := h.apiClient.Get(id)
	if err != nil {
		// TBD handle error
		w.WriteHeader(http.StatusInternalServerError)
		_, _ = w.Write([]byte(err.Error())) // something like this
	}

	//TBD transform your data

	// write response
	w.WriteHeader(http.StatusOK)
	_, _ = w.Write([]byte(res.Id)) // do not forget to check write errs
}