Send Image File via XHR on Chrome - html

Question

I'm using HTML5 drag&drop to get images from a user's computer and want to upload them to my Rails server (using Carrierwave on that end). I don't know exactly what I'm doing here, but cobbled together this code from these instructions http://code.google.com/p/html5uploader/wiki/HTML5Uploader
This returns a 500 error - can anyone take a look and help me out with what I'm doing wrong?
var files = e.dataTransfer.files;
if (files.length){
for (var i = 0; i<files.length; i++) {
var file = files[i];
var reader = new FileReader();
reader.readAsBinaryString(file);
reader.onload = function() {
var bin = reader.result;
var xhr = new XMLHttpRequest();
var boundary = 'xxxxxxxxx';
xhr.open('POST', '/images?up=true&base64=true', true);
xhr.setRequestHeader('content-type', 'multipart/form-data; boundary=' + boundary);
xhr.setRequestHeader('UP-FILENAME', file.name);
xhr.setRequestHeader('UP-SIZE', file.size);
xhr.setRequestHeader('UP-TYPE', file.type);
xhr.send(window.btoa(bin));
};
};
};

Answer 1

There are a couple of things that could be the culprit. You're reading the file as a binary string, then creating a multipart request, then sending a base64 encoded value.
There's no need to read the file or mess with base64 encoding. Instead, just construct a FormData object, append the file, and send that directly using xhr.send(formData). See my response here.