如何正确规范化 ASP.NET MVC 应用程序中的 URL？

Question

我正在尝试找到一种很好的通用方法来规范化 ASP.NET MVC 2 应用程序中的 url。到目前为止，这是我想出的：

// Using an authorization filter because it is executed earlier than other filters
public class CanonicalizeAttribute : AuthorizeAttribute
{
    public bool ForceLowerCase { get;set; }

    public CanonicalizeAttribute()
        : base()
    {
        ForceLowerCase = true;
    }

    public override void OnAuthorization(AuthorizationContext filterContext)
    {
        RouteValueDictionary values = ExtractRouteValues(filterContext);
        string canonicalUrl = new UrlHelper(filterContext.RequestContext).RouteUrl(values);
        if (ForceLowerCase)
            canonicalUrl = canonicalUrl.ToLower();

        if (filterContext.HttpContext.Request.Url.PathAndQuery != canonicalUrl)
            filterContext.Result = new PermanentRedirectResult(canonicalUrl);
    }

    private static RouteValueDictionary ExtractRouteValues(AuthorizationContext filterContext)
    {
        var values = filterContext.RouteData.Values.Union(filterContext.RouteData.DataTokens).ToDictionary(x => x.Key, x => x.Value);
        var queryString = filterContext.HttpContext.Request.QueryString;
        foreach (string key in queryString.Keys)
        {
            if (!values.ContainsKey(key))
                values.Add(key, queryString[key]);
        }
        return new RouteValueDictionary(values);
    }
}

// Redirect result that uses permanent (301) redirect
public class PermanentRedirectResult : RedirectResult
{
    public PermanentRedirectResult(string url) : base(url) { }

    public override void ExecuteResult(ControllerContext context)
    {
        context.HttpContext.Response.RedirectPermanent(this.Url);
    }
}

现在我可以像这样标记我的控制器：

[Canonicalize]
public class HomeController : Controller { /* ... */ }

这一切似乎都运作良好，但我有以下顾虑：

1. 我仍然必须将CanonicalizeAttribute 添加到我想要规范化的每个控制器（或操作方法）中，当很难想到我不想要这种行为的情况时。似乎应该有一种方法可以在整个站点范围内获得这种行为，而不是一次一个控制器。

2. 我在过滤器中实施“强制小写”规则的事实似乎是错误的。当然，以某种方式将其添加到路由 url 逻辑中会更好，但我想不出在我的路由配置中执行此操作的方法。我想将@"[a-z]*" 约束添加到控制器和操作参数（以及任何其他字符串路由参数），但我认为这会导致路由不匹配。此外，因为小写规则没有在路由级别应用，所以可能会在我的页面中生成包含大写字母的链接，这看起来很糟糕。

我在这里忽略了什么明显的东西吗？

Answer 1

MVC 5 和 6 可以选择为您的路由生成小写 URL。我的路线配置如下所示：

public static class RouteConfig
{
    public static void RegisterRoutes(RouteCollection routes)
    {
        // Imprive SEO by stopping duplicate URL's due to case or trailing slashes.
        routes.AppendTrailingSlash = true;
        routes.LowercaseUrls = true;

        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

        routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}",
            defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional });
    }
}

使用此代码，您将不再需要规范化 URL，因为这是为您完成的。如果您使用 HTTP 和 HTTPS URL 并为此需要一个规范的 URL，则可能会出现一个问题。在这种情况下，很容易使用上述方法并将 HTTP 替换为 HTTPS，反之亦然。

另一个问题是链接到您网站的外部网站可能会省略尾部斜杠或添加大写字符，为此您应该执行 301 永久重定向到带有尾部斜杠的正确 URL。完整用法和源代码请参考我的blog post和RedirectToCanonicalUrlAttribute过滤器：

/// <summary>
/// To improve Search Engine Optimization SEO, there should only be a single URL for each resource. Case 
/// differences and/or URL's with/without trailing slashes are treated as different URL's by search engines. This 
/// filter redirects all non-canonical URL's based on the settings specified to their canonical equivalent. 
/// Note: Non-canonical URL's are not generated by this site template, it is usually external sites which are 
/// linking to your site but have changed the URL case or added/removed trailing slashes.
/// (See Google's comments at http://googlewebmastercentral.blogspot.co.uk/2010/04/to-slash-or-not-to-slash.html
/// and Bing's at http://blogs.bing.com/webmaster/2012/01/26/moving-content-think-301-not-relcanonical).
/// </summary>
[AttributeUsage(AttributeTargets.Method | AttributeTargets.Class, Inherited = true, AllowMultiple = false)]
public class RedirectToCanonicalUrlAttribute : FilterAttribute, IAuthorizationFilter
{
    private readonly bool appendTrailingSlash;
    private readonly bool lowercaseUrls;

    #region Constructors

    /// <summary>
    /// Initializes a new instance of the <see cref="RedirectToCanonicalUrlAttribute" /> class.
    /// </summary>
    /// <param name="appendTrailingSlash">If set to <c>true</c> append trailing slashes, otherwise strip trailing 
    /// slashes.</param>
    /// <param name="lowercaseUrls">If set to <c>true</c> lower-case all URL's.</param>
    public RedirectToCanonicalUrlAttribute(
        bool appendTrailingSlash, 
        bool lowercaseUrls)
    {
        this.appendTrailingSlash = appendTrailingSlash;
        this.lowercaseUrls = lowercaseUrls;
    } 

    #endregion

    #region Public Methods

    /// <summary>
    /// Determines whether the HTTP request contains a non-canonical URL using <see cref="TryGetCanonicalUrl"/>, 
    /// if it doesn't calls the <see cref="HandleNonCanonicalRequest"/> method.
    /// </summary>
    /// <param name="filterContext">An object that encapsulates information that is required in order to use the 
    /// <see cref="RedirectToCanonicalUrlAttribute"/> attribute.</param>
    /// <exception cref="ArgumentNullException">The <paramref name="filterContext"/> parameter is <c>null</c>.</exception>
    public virtual void OnAuthorization(AuthorizationContext filterContext)
    {
        if (filterContext == null)
        {
            throw new ArgumentNullException("filterContext");
        }

        if (string.Equals(filterContext.HttpContext.Request.HttpMethod, "GET", StringComparison.Ordinal))
        {
            string canonicalUrl;
            if (!this.TryGetCanonicalUrl(filterContext, out canonicalUrl))
            {
                this.HandleNonCanonicalRequest(filterContext, canonicalUrl);
            }
        }
    }

    #endregion

    #region Protected Methods

    /// <summary>
    /// Determines whether the specified URl is canonical and if it is not, outputs the canonical URL.
    /// </summary>
    /// <param name="filterContext">An object that encapsulates information that is required in order to use the 
    /// <see cref="RedirectToCanonicalUrlAttribute" /> attribute.</param>
    /// <param name="canonicalUrl">The canonical URL.</param>
    /// <returns><c>true</c> if the URL is canonical, otherwise <c>false</c>.</returns>
    protected virtual bool TryGetCanonicalUrl(AuthorizationContext filterContext, out string canonicalUrl)
    {
        bool isCanonical = true;

        canonicalUrl = filterContext.HttpContext.Request.Url.ToString();
        int queryIndex = canonicalUrl.IndexOf(QueryCharacter);

        if (queryIndex == -1)
        {
            bool hasTrailingSlash = canonicalUrl[canonicalUrl.Length - 1] == SlashCharacter;

            if (this.appendTrailingSlash)
            {
                // Append a trailing slash to the end of the URL.
                if (!hasTrailingSlash)
                {
                    canonicalUrl += SlashCharacter;
                    isCanonical = false;
                }
            }
            else
            {
                // Trim a trailing slash from the end of the URL.
                if (hasTrailingSlash)
                {
                    canonicalUrl = canonicalUrl.TrimEnd(SlashCharacter);
                    isCanonical = false;
                }
            }
        }
        else
        {
            bool hasTrailingSlash = canonicalUrl[queryIndex - 1] == SlashCharacter;

            if (this.appendTrailingSlash)
            {
                // Append a trailing slash to the end of the URL but before the query string.
                if (!hasTrailingSlash)
                {
                    canonicalUrl = canonicalUrl.Insert(queryIndex, SlashCharacter.ToString());
                    isCanonical = false;
                }
            }
            else
            {
                // Trim a trailing slash to the end of the URL but before the query string.
                if (hasTrailingSlash)
                {
                    canonicalUrl = canonicalUrl.Remove(queryIndex - 1, 1);
                    isCanonical = false;
                }
            }
        }

        if (this.lowercaseUrls)
        {
            foreach (char character in canonicalUrl)
            {
                if (char.IsUpper(character))
                {
                    canonicalUrl = canonicalUrl.ToLower();
                    isCanonical = false;
                    break;
                }
            }
        }

        return isCanonical;
    }

    /// <summary>
    /// Handles HTTP requests for URL's that are not canonical. Performs a 301 Permanent Redirect to the canonical URL.
    /// </summary>
    /// <param name="filterContext">An object that encapsulates information that is required in order to use the 
    /// <see cref="RedirectToCanonicalUrlAttribute" /> attribute.</param>
    /// <param name="canonicalUrl">The canonical URL.</param>
    protected virtual void HandleNonCanonicalRequest(AuthorizationContext filterContext, string canonicalUrl)
    {
        filterContext.Result = new RedirectResult(canonicalUrl, true);
    }

    #endregion
}

确保所有请求都被 301 重定向到正确的规范 URL 的使用示例：

filters.Add(new RedirectToCanonicalUrlAttribute(
    RouteTable.Routes.AppendTrailingSlash, 
    RouteTable.Routes.LowercaseUrls));

Answer 2

对于默认 ASP.NET MVC 路由的宽松性质、忽略字母大小写、尾部斜杠等，我也感到同样“痒”。和你一样，我想要一个通用的解决方案，最好是作为我的应用程序中的路由逻辑。

在网上到处搜索后，没有找到有用的库，我决定自己推出一个。结果是Canonicalize，一个补充了 ASP.NET 路由引擎的开源类库。

您可以通过 NuGet 安装库：Install-Package Canonicalize

并在您的路线注册中：routes.Canonicalize().Lowercase();

除了小写字母之外，包中还包含其他几个 URL 规范化策略。强制www域前缀打开或关闭，强制特定主机名，尾部斜杠等。添加自定义URL规范化策略也很容易，我非常愿意接受补丁添​​加更多策略到“官方” 规范化分布。

我希望你或其他人会觉得这很有帮助，即使这个问题已经存在一年了:)

Answer 3

以下是我如何在 MVC2 中创建规范 URL。我使用 IIS7 重写模块 v2 将我的所有 URL 设为小写，并去除尾部斜杠，因此不需要从我的代码中执行此操作。 (Full blog post)

将其添加到 head 部分的母版页中，如下所示：

<%=ViewData["CanonicalURL"] %>
<!--Your other head info here-->

创建过滤器属性 (CanonicalURL.cs)：

public class CanonicalURL : ActionFilterAttribute
{
    public string Url { get; private set; }

    public CanonicalURL(string url)
    {
       Url = url;
    }

    public override void OnResultExecuting(ResultExecutingContext filterContext)
    {
        string fullyQualifiedUrl = "http://www.example.com" + this.Url;
        filterContext.Controller.ViewData["CanonicalUrl"] = @"<link rel='canonical' href='" + fullyQualifiedUrl + "' />";
        base.OnResultExecuting(filterContext);
    }
}

从你的行动中调用它：

[CanonicalURL("Contact-Us")]
public ActionResult Index()
 {
      ContactFormViewModel contact = new ContactFormViewModel(); 
      return View(contact);
}

有关搜索引擎相关帖子的其他一些有趣文章，请查看 Matt Cutts 博客