.net文件上传时实现通过文件头确认文件类型的方法

本文实例讲述了.net文件上传时实现通过文件头确认文件类型的方法，其中 script 用来返回给页面的数据，读者还可以根据自身需要对相关部分自行修改。另外，文件头也可以自行添加定义。

主要代码如下：

AppCode/FileUpload.cs
using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Text.RegularExpressions;
using System.Web;

/// <summary>
/// FileHeader 的摘要说明
/// </summary>
public static class FileUpload
{
 private static string script = string.Empty;
 private static bool autonamed = true;
 private static Random ra = new Random();

public static bool AutoNamed
 {
   get
   {
     return autonamed;
   }
   set
   {
     autonamed = value;
   }
 }
 public static string Script
 {
   get
   {
     return "var upload = [" + script + "];";
   }
 }
 public static Dictionary<string, byte[]> ImageHeader = new Dictionary<string, byte[]>();
 public static Dictionary<string, object> FilesHeader = new Dictionary<string, object>();

static FileUpload()
{
   ImageHeader.Add("gif", new byte[] { 71, 73, 70, 56, 57, 97 });
   ImageHeader.Add("bmp", new byte[] { 66, 77 });
   ImageHeader.Add("jpg", new byte[] { 255, 216, 255 });
   ImageHeader.Add("png", new byte[] { 137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82 });
   FilesHeader.Add("pdf", new byte[] { 37, 80, 68, 70, 45, 49, 46, 53 });
   FilesHeader.Add("docx", new object[] { new byte[] { 80, 75, 3, 4, 20, 0, 6, 0, 8, 0, 0, 0, 33 }, new Regex(@"word/_rels/document\.xml\.rels", RegexOptions.IgnoreCase) });
   FilesHeader.Add("xlsx", new object[] { new byte[] { 80, 75, 3, 4, 20, 0, 6, 0, 8, 0, 0, 0, 33 }, new Regex(@"xl/_rels/workbook\.xml\.rels", RegexOptions.IgnoreCase) });
   FilesHeader.Add("pptx", new object[] { new byte[] { 80, 75, 3, 4, 20, 0, 6, 0, 8, 0, 0, 0, 33 }, new Regex(@"ppt/_rels/presentation\.xml\.rels", RegexOptions.IgnoreCase) });
   FilesHeader.Add("doc", new object[] { new byte[] { 208, 207, 17, 224, 161, 177, 26, 225 }, new Regex(@"microsoft( office)? word(?![\s\S]*?microsoft)", RegexOptions.IgnoreCase) });
   FilesHeader.Add("xls", new object[] { new byte[] { 208, 207, 17, 224, 161, 177, 26, 225 }, new Regex(@"microsoft( office)? excel(?![\s\S]*?microsoft)", RegexOptions.IgnoreCase) });
   FilesHeader.Add("ppt", new object[] { new byte[] { 208, 207, 17, 224, 161, 177, 26, 225 }, new Regex(@"c.u.r.r.e.n.t. .u.s.e.r(?![\s\S]*?[a-z])", RegexOptions.IgnoreCase) });
   FilesHeader.Add("avi", new byte[] { 65, 86, 73, 32 });
   FilesHeader.Add("mpg", new byte[] { 0, 0, 1, 0xBA });
   FilesHeader.Add("mpeg", new byte[] { 0, 0, 1, 0xB3 });
   FilesHeader.Add("rar", new byte[] { 82, 97, 114, 33, 26, 7 });
   FilesHeader.Add("zip", new byte[] { 80, 75, 3, 4 });
 }

private static string DateTimeStamp()
 {
   return DateTime.Now.ToString("yyyyMMddHHmmss") + ra.Next(0, 99999).ToString("00000");
 }

private static string FileType(Stream str)
 {
   string FileExt = string.Empty;
   foreach (string ext in FilesHeader.Keys)
   {
     byte[] header = FilesHeader[ext].GetType() == (new byte[] { }).GetType() ? (byte[])FilesHeader[ext] : (byte[])(((object[])FilesHeader[ext])[0]);
     byte[] test = new byte[header.Length];
     str.Position = 0;
     str.Read(test, 0, test.Length);
     bool same = true;
     for (int i = 0; i < test.Length; i++)
     {
       if (test[i] != header[i])
       {
         same = false;
         break;
       }
     }
     if (FilesHeader[ext].GetType() != (new byte[] { }).GetType() && same)
     {
       object[] obj = (object[])FilesHeader[ext];
       bool exists = false;
       if (obj[1].GetType().ToString() == "System.Int32")
       {
         for (int ii = 2; ii < obj.Length; ii++)
         {
           if (str.Length >= (int)obj[1])
           {
             str.Position = str.Length - (int)obj[1];
             byte[] more = (byte[])obj[ii];
             byte[] testmore = new byte[more.Length];
             str.Read(testmore, 0, testmore.Length);
             if (Encoding.GetEncoding(936).GetString(more) == Encoding.GetEncoding(936).GetString(testmore))
             {
               exists = true;
               break;
             }
           }
         }
       }
       else if (obj[1].GetType().ToString() == "System.Text.RegularExpressions.Regex")
       {
         Regex re = (Regex)obj[1];
         str.Position = 0;
         byte[] buffer = new byte[(int)str.Length];
         str.Read(buffer, 0, buffer.Length);
         string txt = Encoding.ASCII.GetString(buffer);
         if (re.IsMatch(txt))
         {
           exists = true;
         }
       }
       if (!exists)
       {
         same = false;
       }
     }
     if (same)
     {
       FileExt = ext;
       break;
     }
   }
   return FileExt;
 }

private static string ImageType(Stream str)
 {
   string FileExt = string.Empty;
   foreach (string ext in ImageHeader.Keys)
   {
     byte[] header = ImageHeader[ext];
     byte[] test = new byte[header.Length];
     str.Position = 0;
     str.Read(test, 0, test.Length);
     bool same = true;
     for (int i = 0; i < test.Length; i++)
     {
       if (test[i] != header[i])
       {
         same = false;
         break;
       }
     }
     if (same)
     {
       FileExt = ext;
       break;
     }
   }
   if (!string.IsNullOrEmpty(FileExt))
   {
     Encoding[] chkList = new Encoding[] { Encoding.ASCII, Encoding.UTF8, Encoding.GetEncoding(936) };
     for (int i = 0; i < chkList.Length; i++)
     {
       str.Position = 0;
       string str_test = new StreamReader(str, chkList[i]).ReadToEnd();
       if (Regex.IsMatch(str_test, @"^[^\u0000-\u0008\u000B-\u000C\u000E-\u001F]*$"))
       {
         FileExt = string.Empty;
         break;
       }
     }
   }
   return FileExt;
 }

private static void CreateFolder(string path)
 {
   string t_path = HttpContext.Current.Server.MapPath(path);
   if (!Directory.Exists(t_path))
   {
     Directory.CreateDirectory(t_path);
   }
 }

private static string CreateFileName(string name, string ext)
 {
   string filename = "/Upload/" + DateTime.Now.ToString("yyyy/MM/dd") + "/" + ext + "/" + (autonamed ? DateTimeStamp() + "." + ext : name);
   if (File.Exists(HttpContext.Current.Server.MapPath(filename)))
   {
     return CreateFileName(name, ext);
   }
   else
   {
     return filename;
   }
 }

private static string SaveAs(HttpPostedFile file, string Ext)
 {
   string filename = CreateFileName(file.FileName, Ext);
   CreateFolder(Regex.Match(filename, @"^[\s\S]*?(?=[^\\/]+$)").Value);
   file.SaveAs(HttpContext.Current.Server.MapPath(filename));
   return Regex.Match(HttpContext.Current.Request.Url.ToString(), @"^[\s\S]*?(?=(?<!/)/(?!/))").Value + filename;
 }

private static void SaveInvalid(HttpPostedFile file)
 {
 }
 // 每次提交之前调用此方法，确认返回内容正确
 public static void Clear()
 {
   script = string.Empty;
 }

public static void Save(HttpPostedFile file)
 {
   if (file.ContentLength == 0)
   {
     if (file.FileName.Length > 0)
     {
       script += (script.Length > 0 ? "," : "") + "{filename:'" + file.FileName + "',upload:false,length:0,target:null,type:''}";
     }
   }
   else
   {
     if (Regex.IsMatch(file.ContentType, @"^image/"))
     {
       string ext = ImageType(file.InputStream);
       if (string.IsNullOrEmpty(ext))
       {
         SaveInvalid(file);
         script += (script.Length > 0 ? "," : "") + "{filename:'" + file.FileName + "',upload:false,length:" + file.ContentLength + ",target:null,type:''}";
       }
       else
       {
         string filename = SaveAs(file, ext);
         script += (script.Length > 0 ? "," : "") + "{filename:'" + file.FileName + "',upload:true,length:" + file.ContentLength + ",target:'" + filename + "',type:'" + ext + "'}";
       }
     }
     else if (Regex.IsMatch(file.ContentType, @"^text/"))
     {
     }
     else
     {
       string ext = FileType(file.InputStream);
       if (string.IsNullOrEmpty(ext))
       {
         SaveInvalid(file);
         script += (script.Length > 0 ? "," : "") + "{filename:'" + file.FileName + "',upload:false,length:" + file.ContentLength + ",target:null,type:'',header:[" + "" + "]}";
       }
       else
       {
         string filename = SaveAs(file, ext);
         script += (script.Length > 0 ? "," : "") + "{filename:'" + file.FileName + "',upload:true,length:" + file.ContentLength + ",target:'" + filename + "',type:'" + ext + "'}";
       }
     }
   }
 }
}

调用页面：

using System;
using System.Web;

public partial class _Default : System.Web.UI.Page
{
 protected void Page_Load(object sender, EventArgs e)
 {
   HttpFileCollection files = Request.Files;
   FileUpload.Clear();
   for (int i = 0; i < files.Count; i++)
   {
     FileUpload.Save(files[i]);
   }
   Response.Write(FileUpload.Script);
 }
}

功能至此完成，读者还可以根据自身需要进一步作出修改与完善。