本文实例讲述了C#检测上传文件真正类型的方法。分享给大家供大家参考。具体分析如下：
对于用户上传的文件如果只是根据扩展名判断，很容易上传上来可执行文件，这是非常危险的，这段代码可以在服务器端检测上传文件的真实类型。
<%@ Page Language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
void Alert(string s)
{
Page.ClientScript.RegisterStartupScript(Page.GetType(), "js", "alert('" + s + "')", true);
}
protected void Button1_Click(object sender, EventArgs e)
{
saveFile();
}
protected String saveFile()
{
String MaxSize = "1024";
//最大文件大小
int imgMaxSize = Convert.ToInt32(MaxSize) * 1024 * 1024;
HttpPostedFile imgFile = FuImg.PostedFile;
if (imgFile == null || FuImg.FileName == "")
{
Alert("请选择文件。");
return "";
}
String dirPath = Server.MapPath("~/");
string saveUrl = Page.ResolveUrl("~/");
if (!System.IO.Directory.Exists(dirPath))
{
Alert("上传目录不存在。");
return "";
}
String fileName = imgFile.FileName;
String fileExt = System.IO.Path.GetExtension(fileName).ToLower();
if (imgFile.InputStream == null || imgFile.InputStream.Length > imgMaxSize)
{
Alert("上传文件大小超过限制。");
return "";
}
//验证文件格式
String fpath = IsAllowedExtension(imgFile);
if ("" == fpath)
{
Alert("图片格式不正确。");
return "";
}
String ymd = DateTime.Now.ToString("yyyyMMdd", System.Globalization.DateTimeFormatInfo.InvariantInfo);
dirPath += ymd + "/";
saveUrl = saveUrl + ymd + "/";
//判断目录是否存在
if (!System.IO.Directory.Exists(dirPath))
{
//创建目录
System.IO.Directory.CreateDirectory(dirPath);
}
String newFileName = Guid.NewGuid().ToString() + fileExt;
//图片名字
String filePath = dirPath + newFileName;
System.IO.File.Move(fpath, filePath);
String fileUrl = saveUrl + newFileName;
Img.ImageUrl = fileUrl;
//ImageUrl = saveUrl + newFileName;
return fileUrl;
}
public String IsAllowedExtension(HttpPostedFile f)
{
String newFile = Server.MapPath("~/" + System.Guid.NewGuid().ToString("D") + ".tmp");
f.SaveAs(newFile);
System.IO.FileStream fs = new System.IO.FileStream(newFile, System.IO.FileMode.Open, System.IO.FileAccess.Read);
System.IO.BinaryReader r = new System.IO.BinaryReader(fs);
string fileclass = "";
byte buffer;
buffer = r.ReadByte();
fileclass = buffer.ToString();
buffer = r.ReadByte();
fileclass += buffer.ToString();
r.Close();
fs.Close();
/* 文件扩展名说明
*7173 gif
*255216 jpg
*13780 png
*6677 bmp
*/
Dictionary<String, String> ftype = new Dictionary<string, string>();
//添加允许的文件类型
ftype.Add("7173", "gif");
ftype.Add("255216", "jpg");
ftype.Add("13780", "png");
ftype.Add("6677", "bmp");
if (ftype.ContainsKey(fileclass))
{
return newFile;
}
else
{
System.IO.File.Delete(newFile);
return "";
}
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
</head>
<body>
<form id="form1" runat="server">
<asp:FileUpload ID="FuImg" runat="server" />
<asp:Button ID="Button1" runat="server"
OnClick="Button1_Click" Text="上传测试" />
<asp:Image ID="Img" runat="server" />
</form>
</body>
</html>
希望本文所述对大家的C#程序设计有所帮助。