ASP.NET中如何检测一个图片是否是真实图片 防范病毒上传

主要是用来判断客户端上传的图片是否为真实的图片，以防病毒侵入，保证上传的文件的安全。

主要代码如下：

需要引用using System.IO;

public void UploadFile()
{
try
{
HttpPostedFile postfile = Request.Files["file"];
string savepath = Server.MapPath("Image/" + postfile.FileName);
postfile.SaveAs(savepath);
FileStream fs = new FileStream(savepath, FileMode.Open, FileAccess.Read);
BinaryReader reader = new BinaryReader(fs);
string fileClass;
byte buffer;
byte[] b = new byte[2];
buffer = reader.ReadByte();
b[0] = buffer;
fileClass = buffer.ToString();
buffer = reader.ReadByte();
b[1] = buffer;
fileClass += buffer.ToString();
reader.Close();
fs.Close();

if (fileClass == "255216" || fileClass == "7173" || fileClass == "6677" || fileClass == "13780")
{
//255216是jpg;7173是gif;6677是BMP,13780是PNG;7790是exe,8297是rar
//Response.Write("图片可用");
//保存到数据库中
}
else
{
//Response.Write("图片非法");
File.Delete(savepath); //删除文件
return;
}
}
catch (Exception)
{ //Response.Write("图片非法！");
return;
throw;
}
}

MVC 中的代码如下，在这里我返回的JSON格式，当然可以返回Content或其他：

/// <summary>
/// 上传头像
/// </summary>
/// <param name="userId">用户编号</param>
/// <returns>Json(-1表示系统异常，-2表示文件不合法)</returns>
[HttpPost]
public JsonResult UploadAvatar(string userId)
{
//上传头像
string folderPath = "/upload/avatar/";
//判断路径是否存在
if (!Directory.Exists(folderPath))
Directory.CreateDirectory(folderPath);//创建文件路径
HttpPostedFileBase uploadFile = Request.Files["avatars"];
if (uploadFile != null)
{
string oriFileName = uploadFile.FileName;//原始文件名
string fileName = userId + "_" + oriFileName;
uploadFile.SaveAs(Server.MapPath(folderPath + fileName));
FileStream fs = new FileStream(Server.MapPath(folderPath + fileName), FileMode.Open, FileAccess.Read);
BinaryReader reader = new BinaryReader(fs);
string fileClass;
byte buffer;
byte[] b = new byte[2];
buffer = reader.ReadByte();
b[0] = buffer;
fileClass = buffer.ToString();
buffer = reader.ReadByte();
b[1] = buffer;
fileClass += buffer.ToString();
reader.Close();
fs.Close();
if (fileClass == "255216" || fileClass == "7173" || fileClass == "6677" || fileClass == "13780")
{
//255216是jpg;7173是gif;6677是BMP,13780是PNG;7790是exe,8297是rar
//Response.Write("图片可用");
//保存到数据库中
}
else
{

//Response.Write("图片非法");
FileInfo f = new FileInfo(Server.MapPath(folderPath + fileName));
f.Delete(); //删除文件
return Json(-2, JsonRequestBehavior.AllowGet);
}
return Json(Server.HtmlEncode(folderPath + fileName), JsonRequestBehavior.AllowGet);
}
return Json(-1, JsonRequestBehavior.AllowGet);

}