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I am trying to create an image using DataURL of a Canvas (using JavaScript). When a user hits submit, the value gets sent to an Input type text tag (e.g., <input type='text'>), however, apparently on Chrome, the text gets cut off when it is at length 524,288 characters.

I am sending it to an input tag because I need to obtain the value in PHP (as a $_POST['dataurltext'];), so that I can create an image and upload it to my web server.

Any ideas on how to bypass this length?

Should I use a comment box instead, maybe?

Thank you for any help, it will be greatly appreciated.

Kelsey
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1 Answers1

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Try sending canvas as Blob at javascript; use fopen() with php://input as parameter to read Blob, stream_copy_to_stream or file_get_contents() , file_put_contents() to process file at php

See HTMLCanvasElement.toBlob()

if (!HTMLCanvasElement.prototype.toBlob) {
 Object.defineProperty(HTMLCanvasElement.prototype, 'toBlob', {
  value: function (callback, type, quality) {

    var binStr = atob( this.toDataURL(type, quality).split(',')[1] ),
        len = binStr.length,
        arr = new Uint8Array(len);

    for (var i=0; i<len; i++ ) {
     arr[i] = binStr.charCodeAt(i);
    }

    callback( new Blob( [arr], {type: type || 'image/png'} ) );
  }
 });
}

Beyond $_POST, $_GET and $_FILE: Working with Blob in JavaScript and PHP

<?php

// choose a filename
$filename = "hello.json";

// the Blob will be in the input stream, so we use php://input
$input = fopen('php://input', 'rb');
$file = fopen($filename, 'wb'); 

// Note: we don't need open and stream to stream, we could've used file_get_contents and file_put_contents
stream_copy_to_stream($input, $file);
fclose($input);
fclose($file);

?>
guest271314
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  • In my JS code, I ended up using `var dataURL = bottleCanvas.toDataURL("image/jpeg", 0.5);` instead of `var dataURL = bottleCanvas.toDataURL("image/png");`, and that seemed to make it a lot less characters (which solved my problem). But thank you for your answer. – Kelsey May 27 '16 at 21:39