Passing variables in a URL of a php page to JavaScript and to another PHP

Question

Based on the code in this link http://webaudiodemos.appspot.com/AudioRecorder/index.html, I am making changes to send the recorded audio file to server by passing a sessionId via URL. The php page is http://xxxxx/abc.php?sessionId=Sam. PHP versions: PHP 5.4 PHP 5.5.22. I am using the 2nd method from this link:How to pass variables and data from PHP to JavaScript?. The abc.php page has reference to a few JS codes as with the index.html from the link above. abc.php page process the URL values correctly with the following code:

  <div id="bottom">
        <?php
            $faid = $_GET["sessionId"];
            echo htmlspecialchars($faid);     // tested working
        ?>
  </div>

On the recorder.js JavaScript,I have a function that tries to pass the URL values to another PHP while uploading the audio file to server - The fname is not being passed on ... it seems .. can the xhr.send(blob) will still send the fname?

  Recorder.setupDownload = function(blob){
    var div = document.getElementById("bottom"); 
    var fname = div.textContent;                 

  var xhr = new XMLHttpRequest();
  xhr.open('POST', "./uploads.php?" + fname, true); 
  xhr.onload = function(e) {};
  // Listen to the upload progress.
  var progressBar = document.querySelector('progress');
  xhr.upload.onprogress = function(e) {
    if (e.lengthComputable) {
      progressBar.value = (e.loaded / e.total) * 100;
      progressBar.textContent = progressBar.value; // Fallback for unsupported browsers.
    }
  };

  xhr.send(blob); 

The uploads.php in the server has the following script to receive the value and to create an audio file - but it is not creating the audio file - however, if I fix the file name (eg: "filename123") it writes the audio file - so the issue is in passing the variable name - I am a newbie and I wonder what am I missing?:

    <?php
        ini_set("display_errors", true);
        error_reporting(E_ALL); 

    if(isset($_GET['fileId']) && !empty($_GET['fileId'])){
     $id = $_GET["fileId"];
    } 
        $fp = fopen( $id, 'wb' );   // writes the audio file 
        fwrite( $fp, $GLOBALS['HTTP_RAW_POST_DATA'] );   
        fclose( $fp );
    ?>

Update: It is working!

Answer 1

You didn't give your value a name, so you're passing a value that will appear as DIFFERENT key in every page.

e.g. each of your users will have something like

http://example.com?foo
http://example.com?bar

leading to $_GET['foo'] and $_GET['bar'] in PHP. But since foo/bar are some randomish value representing your session ID, you have no idea what that value will be. So... give it a name:

http://example.com?key=foo

Now you just do $key = $_GET['key'] and can always access your session value, no matter what value it really as - it'll always be assigned to the key.