Question

I need to be able to send an image and some form fields from a client side canvas element to a PHP script, ending up in $_POST and $_FILES. When I send it like this:

<script type="text/javascript">
var img = canvas.toDataURL("image/png");
...
ajax.setRequestHeader('Content-Type', "multipart/form-data; boundary=" + boundary_str);
var request_body = boundary + '\n' 
+ 'Content-Disposition: form-data; name="formfield"' + '\n' 
+ '\n' 
+ formfield + '\n' 
+ '\n' 
+ boundary + '\n'
+ 'Content-Disposition: form-data; name="async-upload"; filename="' 
+ "ajax_test64_2.png" + '"' + '\n' 
+ 'Content-Type: image/png' + '\n' 
+ '\n' 
+ img
+ '\n' 
+ boundary;
ajax.send(request_body);
</script>

$_POST and $_FILES both come back populated, but the image data in $_FILES still needs decoding like this:

$loc = $_FILES['async-upload']['tmp_name'];
$file = fopen($loc, 'rb');
$contents = fread($file, filesize($loc));
fclose($file);
$filteredData=substr($contents, strpos($contents, ",")+1);
$unencodedData=base64_decode($filteredData);

…in order to save it as a readable PNG. This isn’t an option as I’m trying to pass the image to WordPress’s media_handle_upload() function, which requires an index to $_FILES pointing to a readable image. I also can’t decode, save and alter ‘tmp_name’ accordingly, as it falls foul of security checks.

So, I found this:
http://www.webtoolkit.info/javascript-base64.html
and tried to do the decode on the client side:

img_split = img.split(",",2)[1];
img_decoded = Base64.decode( img_split );

but for some reason I still don’t end up with a readable file when it gets to the PHP.
So the question is: “Why?” or “What am I doing wrong?” or “Is this even possible?” 🙂

Any help very much appreciated!

Thanks,
Kane

Answer 1

Building on Nathan’s excellent answer, I was able to finnagle it so that it is still going through jQuery.ajax. Just add this to the ajax request:

            xhr: function () {
                var myXHR = new XMLHttpRequest();
                if (myXHR.sendAsBinary == undefined) {
                    myXHR.legacySend = myXHR.send;
                    myXHR.sendAsBinary = function (string) {
                        var bytes = Array.prototype.map.call(string, function (c) {
                            return c.charCodeAt(0) & 0xff;
                        });
                        this.legacySend(new Uint8Array(bytes).buffer);
                    };
                }
                myXHR.send = myXHR.sendAsBinary;
                return myXHR;
            },

Basically, you just return back an xhr object that is overriden so that “send” means “sendAsBinary”. Then jQuery does the right thing.