ASP. NET 2.0 File Download (support for large files and anti-leech)

1. File Download
There are two main methods to download HTTP files:

• Direct URL download, with the advantage of low server resource occupation and high speed. The disadvantage is that files in the data library are not allowed to be downloaded, and files in the format of .html can be opened directly in the browser and cannot be downloaded directly.
• The binary data stream output method has the following advantages: Accurate Measurement of downloads, anti-leeching, direct download of all file formats rather than opening, and medium non-file data stored in the database can be downloaded as files; the disadvantage is that it occupies many server resources.

The principle of large file download is to cut the file into small data streams for download. Microsoft msdn provides an example of large file download, but there is a problem with the Chinese file name garbled, just a slight change.CodeIs:

 Protected     Void  Responsefile (  String  Path)
{
System. Io. Stream istream  =     Null ;
  Byte  [] Buffer  =     New  Byte [  10000  ];
  Int  Length;
  Long  Datatoread;
  String  Filename  =  System. Io. Path. getfilename (PATH );

 Try  
{
Istream  =     New  System. Io. filestream (path, system. Io. filemode. Open,
System. Io. fileaccess. Read, system. Io. fileshare. Read );
Datatoread  =  Istream. length;
Response. contenttype  =     "  Application/octet-stream  "  ;
Response. addheader (  " Content-Disposition  "  ,  "  Attachment; filename =  "     +   
Httputility. urlencode (filename, system. Text. encoding. utf8 ));
  While  (Datatoread  >     0  )
{
  If (Response. isclientconnected)
{
Length  =  Istream. Read (buffer,  0  ,  10000  );
Response. outputstream. Write (buffer,  0  , Length );
Response. Flush ();

Buffer  =     New  Byte [  10000  ];
Datatoread  = Datatoread  -  Length;
}
  Else  
{
Datatoread  =     -  1  ;
}
}
}
  Catch  (Exception ex)
{
Response. Write (  "  An error occurred while downloading the file!  "  );
}
 Finally  
{
  If  (Istream  ! =     Null  )
{
Istream. Close ();
}
}
} 

2. Prevent leeching

 Protected     Void  Page_load (  Object  Sender, eventargs E)
{
  /* --------------------------------------------------------------*\
* Large file downloads and anti-leech protection *
**
* Tda7264@163.com *
**
* Floating blog  Http://xianfen.net  *
\*-------------------------------------------------------------  */  

  If  (Request. querystring [  "  Filename  "  ]  =     Null )
{
Invalidredirect ();
}

  String  Filename  =  Request. querystring [  "  Filename  "  ];

  If  (Filename  =     String  . Empty)
{
Invalidredirect ();
}

  // Determine whether the configuration file is directly downloaded  
     String  Downdirect  =  Configurationmanager. deleettings [  "  Down  "  ]. Tolower ();

  If  (Downdirect  =     "  True "  )
{
Updatehits (filename );  //  Update downloads  
  Response. Redirect (  "  Upload/  "     +  Filename );
  Return  ;
}

  String  Path  = Server. mappath (request. applicationpath  +     "  /Upload/  "     +  Filename );
  String  Referrer  =     String  . Empty;

  If  (Request. urlreferrer ! =     Null  )
{
Referrer  =  Request. urlreferrer. tostring (). tolower ();
}

  String  D  =  Configurationmanager. deleettings [  "  Valid  "  ]. Tolower ();
  String  [] Domainname =   
Configurationmanager. deleettings [  "  Refers  "  ]. Tolower (). Split (  New     Char  [] {  '  ,  '  });

  //  If it is set to prevent leeching, determine whether the access source is legal  
    If  (D  =     "  False  "  )
{
  Foreach  (  String  S  In  Domainname)
{
  If  (Referrer. indexof (S. tolower ()) >     0  )
{
Updatehits (filename );  //  Update downloads  
  Responsefile (PATH );
  Return  ;
}
}

Invalidredirect ();
}
  Else  
{
Responsefile (PATH );
}
}

  Protected     Void Updatehits (  String  Filename)
{
  //  Code for updating the number of file downloads  
  }

  Protected     Void  Invalidredirect ()
{
  String  Defaultpage  =  Configurationmanager. deleettings [  " Defaultredirect  "  ];

Response. Redirect (defaultpage,  True  );
} 

3. Configuration File
In the configuration file, configure the download method, whether the leeching function is enabled, and the default page address for leeching:

 <  Appsettings  >  
  <  Add  Key  = "Down"  Value  = "False"  /> 
  <! --  Direct download?  -->  
  <  Add  Key  = "Valid"  Value  = "False"  />  
  <! --  Whether leeching is allowed  -->  
  < Add  Key  = "Refers"  Value  = "Localhost, google.cn"  />  
  <! --  Multiple allowed access sources are separated by commas (,).  -->  
  <  Add  Key  = "Defaultredirect"  Value  = "Error.htm" />  
  <! --  Default redirection page  -->  
  </  Appsettings  > 

Complete example: Click to download