c# - 从相对路径获取绝对URL(重构方法)

Question

令我感到非常惊讶的是，没有 native .NET 方法可以从相对 URL 获取绝对 URL。我知道这已经被讨论过很多次，但从来没有遇到过一个令人满意的方法来很好地处理这个问题。你能帮忙微调下面的方法吗？

我想我只需要自动选择协议(protocol)而不是对其进行硬编码 (http/https)。我还有什么遗漏的吗(注意事项、性能等)？

public static string GetAbsoluteUrl(string url)
    {
        //VALIDATE INPUT FOR ALREADY ABSOLUTE URL
        if (url.StartsWith("http://", StringComparison.OrdinalIgnoreCase) 
           || url.StartsWith("https://", StringComparison.OrdinalIgnoreCase))
        { 
            return url;
        }

        //GET PAGE REFERENCE FOR CONTEXT PROCESSING
        Page page = HttpContext.Current.Handler as Page;

        //RESOLVE PATH FOR APPLICATION BEFORE PROCESSING
        if (url.StartsWith("~/"))
        {
            url = page.ResolveUrl(url);
        }

        //BUILD AND RETURN ABSOLUTE URL
        return "http://" + page.Request.ServerVariables["SERVER_NAME"] + "/" 
                         + url.TrimStart('/');
    }

Answer 1

这一直是我处理这个小麻烦的方法。注意 VirtualPathUtility.ToAbsolute(relativeUrl) 的使用允许将方法声明为静态类中的扩展。

/// <summary>
/// Converts the provided app-relative path into an absolute Url containing the 
/// full host name
/// </summary>
/// <param name="relativeUrl">App-Relative path</param>
/// <returns>Provided relativeUrl parameter as fully qualified Url</returns>
/// <example>~/path/to/foo to http://www.web.com/path/to/foo</example>
public static string ToAbsoluteUrl(this string relativeUrl) {
    if (string.IsNullOrEmpty(relativeUrl))
        return relativeUrl;

    if (HttpContext.Current == null)
        return relativeUrl;

    if (relativeUrl.StartsWith("/"))
        relativeUrl = relativeUrl.Insert(0, "~");
    if (!relativeUrl.StartsWith("~/"))
        relativeUrl = relativeUrl.Insert(0, "~/");

    var url = HttpContext.Current.Request.Url;
    var port = url.Port != 80 ? (":" + url.Port) : String.Empty;

    return String.Format("{0}://{1}{2}{3}",
        url.Scheme, url.Host, port, VirtualPathUtility.ToAbsolute(relativeUrl));
}