GetAcceptLanguage

Reads the highest-ranked language from the request Accept-Language header. The header is a ranked list, and this returns the top of it after the quality values are applied, so nl;q=0.2,fr;q=0.9 yields fr rather than nl. Malformed tags and the * wildcard are discarded first, so it returns the best valid entry, and null only when the header is absent or holds no valid tag at all.

Usage

using Microsoft.AspNetCore.Mvc;
using AlmightyShogun.AspNet.Localization;

[ApiController]
[Route("preferences")]
public sealed class PreferencesController : ControllerBase
{
    [HttpGet("language")]
    public IActionResult Get() => Ok(Request.GetAcceptLanguage() ?? "en");
}

WARNING

Rejecting a malformed tag is a security boundary, not a formatting nicety. The returned value is used to build a filesystem path when message files are resolved, so an unvalidated header would allow directory traversal out of the messages directory.

Returns

The preferred language when the header contains a well-formed language tag; otherwise null.

Type signature

public string? GetAcceptLanguage();