How to use picture ETag to judge users

Principle: Do not use Javascript,session,cookies,flash.

Using picture ETag to identify users

1. Generate a unique etag based on the user's remote_addr and http_user_agent.

2. Output the ETag to the client.

3. Get Http_if_none_match to determine whether to access the same user.

. htaccess rewrite

<ifmodule mod_rewrite.c>  
      
rewriteengine on  
      
rewriterule ^pic.png$ index.php?pic=1 [NC]  
      
</ Ifmodule>

SOURCE index.php:

?  Define (' SECRET ', ' j8s91slksd9ab ');          Secret define (' LOG ', ' data.log ');  
    Save user Data//Generate ETag//More Highlights: Http://www.bianceng.cnhttp://www.bianceng.cn/web/Skills/function Genetag () {  
    if (!empty ($_server[' Http_if_none_match ')) {$etag = $_server[' Http_if_none_match ']; }else{$etag = substr (MD5 (SECRET. substr MD5 ($_server[' REMOTE_ADDR ')), 0,16). substr (MD5 ' $_server[' Http_user_agen  
    T ']), 0,16), 0, 16);  
return $etag;  
    //Show Picture function Showpic ($etag) {header (' content-type:image/png ');  
      
    Header (' Etag: '. $etag); $im = Imagecreate (1, 1);  
    Generate 1x1px transparent picture Imagecolorallocatealpha ($im, 0, 0, 0, 127);  
    Imagepng ($im);  
      
    Imagedestroy ($im);  
Exit ();  
    //Get Stored data function GetData () {$logdata = file_exists (log) file_get_contents (log): ';  
    if (! $logdata) {$data = array ();  
    }else{$data = Json_decode ($logdata, true); }  
    return $data;  
      
} $etag = Genetag (); $pic = isset ($_get[' pic ')?  
$_get[' pic ']: 0;  
if ($pic ==1) {showpic ($etag);  
      
} $data = GetData (); Submit Form $send = isset ($_post[' send '])?  
      
$_post[' send ']: 0;  
    if ($send ==1) {$txt = isset ($_post[' txt '])? $_post[' txt ']: ';  
        if ($txt!= ') {$data [$etag] = $txt;  
    File_put_contents (LOG, Json_encode ($data), true); }} $txt = Isset ($data [$etag])? $data [$etag]: '; User-entered data?> <!  
 DOCTYPE HTML PUBLIC "-//w3c//dtd HTML 4.01 transitional//en" "Http://www.w3.org/TR/html4/loose.dtd" >