imagehandler.cs

个人博客系统

#region Using

using System;
using System.IO;
using System.Web;

#endregion

namespace BlogEngine.Core.Web.HttpHandlers
{
  /// <summary>
  /// The ImageHanlder serves all images that is uploaded from
  /// the admin pages. 
  /// </summary>
  /// <remarks>
  /// By using a HttpHandler to serve images, it is very easy
  /// to add the capability to stop bandwidth leeching or
  /// to create a statistics analysis feature upon it.
  /// </remarks>
  public class ImageHandler : IHttpHandler
  {

    #region IHttpHandler Members

    /// <summary>
    /// Gets a value indicating whether another request can use the <see cref="T:System.Web.IHttpHandler"></see> instance.
    /// </summary>
    /// <value></value>
    /// <returns>true if the <see cref="T:System.Web.IHttpHandler"></see> instance is reusable; otherwise, false.</returns>
    public bool IsReusable
    {
      get { return false; }
    }

    /// <summary>
    /// Enables processing of HTTP Web requests by a custom HttpHandler that 
    /// implements the <see cref="T:System.Web.IHttpHandler"></see> interface.
    /// </summary>
    /// <param name="context">An <see cref="T:System.Web.HttpContext"></see> object 
    /// that provides references to the intrinsic server objects 
    /// (for example, Request, Response, Session, and Server) used to service HTTP requests.
    /// </param>
    public void ProcessRequest(HttpContext context)
    {
      if (!string.IsNullOrEmpty(context.Request.QueryString["picture"]))
      {
        string fileName = context.Request.QueryString["picture"];
        string folder = BlogSettings.Instance.StorageLocation + "files/";
        FileInfo fi = new FileInfo(context.Server.MapPath(folder) + fileName);

        OnServing(fileName);

        if (fi.Exists && fi.Directory.FullName.ToLowerInvariant().Contains("\\files"))
        { 
          int index = fileName.LastIndexOf(".") + 1;
          string extension = fileName.Substring(index).ToUpperInvariant();
          
          // Fix for IE not handling jpg image types
          if (string.Compare(extension, "JPG") == 0)
            context.Response.ContentType = "image/jpeg";
          else
            context.Response.ContentType = "image/" + extension;

          string etag = "\"" + fi.CreationTimeUtc.GetHashCode() + "\"";
          string incomingEtag = context.Request.Headers["If-None-Match"];

          context.Response.Cache.SetCacheability(HttpCacheability.Public);
          context.Response.Cache.SetExpires(DateTime.Now.AddYears(1));
          context.Response.Cache.SetLastModified(fi.CreationTimeUtc);
          context.Response.Cache.SetETag(etag);

          if (String.Compare(incomingEtag, etag) == 0)
          {
            context.Response.StatusCode = (int)System.Net.HttpStatusCode.NotModified;
            context.Response.End();
          }

          context.Server.Transfer(folder + fileName, false);
          OnServed(fileName);
        }
        else
        {
          OnBadRequest(fileName);
          context.Response.Status = "404 Bad Request";
        }
      }
    }

    #endregion

    #region Events

    /// <summary>
    /// Occurs when the requested file does not exist;
    /// </summary>
    public static event EventHandler<EventArgs> Serving;
    private static void OnServing(string file)
    {
      if (Serving != null)
      {
        Serving(file, EventArgs.Empty);
      }
    }

    /// <summary>
    /// Occurs when a file is served;
    /// </summary>
    public static event EventHandler<EventArgs> Served;
    private static void OnServed(string file)
    {
      if (Served != null)
      {
        Served(file, EventArgs.Empty);
      }
    }

    /// <summary>
    /// Occurs when the requested file does not exist;
    /// </summary>
    public static event EventHandler<EventArgs> BadRequest;
    private static void OnBadRequest(string file)
    {
      if (BadRequest != null)
      {
        BadRequest(file, EventArgs.Empty);
      }
    }

    #endregion

  }
}