kurz/web/i18n/i18ner.go

package i18n

import (
	"context"
	"errors"
	"log"
	"net/http"

	"github.com/nicksnyder/go-i18n/v2/i18n"
	"golang.org/x/text/language"
	"gopkg.in/yaml.v2"
)

var Bundle = &i18n.Bundle{
	DefaultLanguage: language.English,
	UnmarshalFuncs: map[string]i18n.UnmarshalFunc{
		"yaml": yaml.Unmarshal,
	},
}

const localizerKey = "localizer"

/*
WithLocalizer() is a higher-order function injecting into the request context a
printer for the language best matching the Accept-Language header in the incoming
request.

The wrapped handler can use Localizer() to get a message printer instance
configured for the best available language for the request.
*/
func WithLocalizer(h http.Handler) http.Handler {
	h2 := func(w http.ResponseWriter, r *http.Request) {
		localizer := i18n.NewLocalizer(Bundle, r.Header.Get("Accept-Language"))

		c := context.WithValue(r.Context(), localizerKey, localizer)
		h.ServeHTTP(w, r.WithContext(c))
	}
	return http.HandlerFunc(h2)
}

/*
Localizer() returns a message printer configured for the language best matching the
Accept-Language in the request, or panic if the handler invoking it was not
wrapped by a WithLocalizer() call.
*/
func Localizer(r *http.Request) *i18n.Localizer {
	ip := r.Context().Value(localizerKey)
	p, ok := ip.(*i18n.Localizer)
	if !ok {
		log.Println(errors.New("trying to use i18n.Localizer in a handler not wrapped with i18.WithLocalizer"))
		// In that case, p will be nil, which is a valid localizer doing no localization.
	}
	return p
}