判断上传文件是否是图片文件

方法一：用image对象判断是否为图片

/// <summary>
/// 判断文件是否为图片
/// </summary>
/// <param name="path">文件的完整路径</param>
/// <returns>返回结果</returns>
public Boolean IsImage(string path)
{
try
{
 System.Drawing.Image img = System.Drawing.Image.FromFile(path);
 return true;
}
catch (Exception e)
{
 return false;
}
}

方法二，判断文件头

/// <summary>
/// 根据文件头判断上传的文件类型
/// </summary>
/// <param name="filePath">filePath是文件的完整路径 </param>
/// <returns>返回true或false</returns>
private bool IsPicture(string filePath)
{
try
{
 FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read);
 BinaryReader reader = new BinaryReader(fs);
 string fileClass;
 byte buffer;
 buffer = reader.ReadByte();
 fileClass = buffer.ToString();
 buffer = reader.ReadByte();
 fileClass += buffer.ToString();
 reader.Close();
 fs.Close();
 if (fileClass == "255216" || fileClass == "7173" || fileClass == "13780" || fileClass == "6677")
 //255216是jpg;7173是gif;6677是BMP,13780是PNG;7790是exe,8297是rar 
 {
 return true;
 }
 else
 {
 return false;
 }
}
catch
{
 return false;
}
}
public enum FileExtension
{
    JPG = 255216,
    GIF = 7173,
    BMP = 6677,
    PNG = 13780,
    COM = 7790,
    EXE = 7790,
    DLL = 7790,
    RAR = 8297,
    ZIP = 8075,
    XML = 6063,
    HTML = 6033,
    ASPX = 239187,
    CS = 117115,
    JS = 119105,
    TXT = 210187,
    SQL = 255254,
    BAT = 64101,
    BTSEED = 10056,
    RDP = 255254,
    PSD = 5666,
    PDF = 3780,
    CHM = 7384,
    LOG = 70105,
    REG = 8269,
    HLP = 6395,
    DOC = 208207,
    XLS = 208207,
    DOCX = 208207,
    XLSX = 208207,
}

据说方法二针对常规修改的木马有效，也就是直接修改扩展名的，比如把.asp改成.jpg这种。但是对于那种用工具生成的jpg木马没有效果。推荐大家用第一种好了。

主要代码如下：
 
需要引用
 
[csharp]
using System.IO; 
 
using System.IO;
 
[csharp]
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;  
            } 
} 
 
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：
 
[csharp]
/// <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); 
 
        } 
 
/// <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);
 
        }