Static messages

Static messages is a simple go library/command that helps with the translation of messages and errors in your application.

It converts simple translations files like this:

NotFound:
    default: User %(ID)d not found
    nl: Gebruiker %(ID)d niet gevonden

Into go code like this:

func UserNotFound(ctx context.Context, ID int) string {
    switch messages.GetLocale(ctx) {
    case "nl":
        return fmt.Sprintf("Gebruiker %(ID)d niet gevonden", ID)
    }

    return fmt.Sprintf("User %d not found.", ID)
}

This means that using this in your code is type safe.

func GetUser(ctx context.Context, ID int64) (*User, error) {
    user := db.GetUser(ID)
    if user == nil {
        return nil, errors.New(translations.UserNotFound(ctx, ID))
    }

    return user, nil
}

Usage

Install the latest version of msggen.

$ go install github.com/wvell/staticmessages/cmd/msggen@latest

# Test your installation.
$ msggen --help

# Write a sample file (in a new empty directory).
$ cat > sample.yml << EOF
NotFound:
  default: User %(ID)d not found
  nl: Gebruiker %(ID)d niet gevonden
EOF

# Generate the template file inside the same directory.
$ msggen -pkg translations

Integrating inside your application.

Add a simple middleware to your http server to set the locale based on the accept language header.

var localeRe = regexp.MustCompile(`([a-z]{2})([\-_]{1}[A-Z]{2})?`)

func requestLanguage(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// The format is mostly: en-GB,en-US.....
		// We are only interested in picking the first item that matches the regex.
		// The regex matches en as well as en_GB.
		matches := localeRe.FindStringSubmatch(r.Header.Get("Accept-Language"))
		if len(matches) > 1 {
			// Set the locale in the ctx to allow handlers along the chain to fetch the correct translation.
			r = r.WithContext(messages.WrapLocale(r.Context(), matches[1]))
		}

		next.ServeHTTP(w, r)
	})
}

Inspiration

The inspiration for this package comes from this talk by Alan Shreve.