Question

I have a javascript code like this

var testCanvas = document.getElementById('canvas-1');
var canvasData = testCanvas.toDataURL("image/png");
var ajax = new XMLHttpRequest();
ajax.open("POST",'http://www.domain.com/imgsave.php',true);
ajax.setRequestHeader('Content-Type', 'canvas/upload');
ajax.send("canvasData"+canvasData );

My php code is like this

if (isset($GLOBALS["HTTP_RAW_POST_DATA"]))
{
    // Get the data
    $imageData=$GLOBALS['HTTP_RAW_POST_DATA'];

    $filteredData=substr($imageData, strpos($imageData, ",")+1);

    $unencodedData=base64_decode($filteredData);
    $fp = fopen( 'test.png', 'wb' );
    fwrite( $fp, $unencodedData);
    fclose( $fp );
        echo "saved";
}
  else{

  echo "no raw data";
  }

When executing this code i got a zero size png file image? Whats the problem with my code?

Answer 1

I had to do this recently myself.

First I put my canvasData into a hidden field and posted it to my PHP page.

It comes back in this format: data:image/png;base64,iVBORw0......

You need to split the data up first, as this: data:image/png;base64, is header information. The rest is the encoded data.

$rawData = $_POST['imageData'];
$filteredData = explode(',', $rawData);

$unencoded = base64_decode($filteredData[1]);

I then create the image on my server:

//Create the image 
$fp = fopen('sigs/test1.png', 'w');
fwrite($fp, $unencoded);
fclose($fp); 

And then read it to do whatever I want with it.

$file_name = 'test1.png';
$file_size = strlen($filteredData[1])/1024; //This may be wrong, doesn't seem to break for me though.


$fh = fopen('sigs/test1.png', 'r');
$content = fread($fh, $file_size);
$content = base64_encode($content);
fclose($fh);

I’m more than sure there is a much more elegant solution to this, but this has been working for me!

Check this for more info (possibly): My own question