".webp": "image/webp",
	".xml":  "text/xml; charset=utf-8",
}

var once sync.Once // guards initMime

var testInitMime, osInitMime func()

func initMime() {
	if fn := testInitMime; fn != nil {
		fn()
	} else {
		setMimeTypes(builtinTypesLower, builtinTypesLower)
		osInitMime()
	}
}

// TypeByExtension returns the MIME type associated with the file extension ext.