Unexpected Flash Security Exception When Using URLLoader

Question

What I am trying to accomplish is to upload some binary data, specifically a ByteArray representing a PNG image, to a server using the URLLoader class in conjunction with UR

Answer 1

Just for completeness' sake, here is how I ended up setting up my URLRequest object (everything else stayed the same):

urlRequest.method = URLRequestMethod.POST;
urlRequest.data = UploadPostHelper.getPostData('filename', pngFile);
urlRequest.requestHeaders.push(new URLRequestHeader('Cache-Control', 'no-cache'));
urlRequest.requestHeaders.push(new URLRequestHeader('Content-Type', 'multipart/form-data; boundary=' + UploadPostHelper.getBoundary()));

The key, as pointed out by evilpenguin, was not to set the contentType property at all but to put it in the header. Using just 'multipart/form-data' however, I got an error on the server side about invalid POST boundaries, so I ended up using a class called UploadPostHelper to create a valid boundary and POST body for file uploads.

This fixed the mysterious security error (I still don't know why that happened), and the very long waits for uploads.

It should be noted that the example code for using UploadPostHelper involves setting the contentType property of the URLRequest object, and this apparently works for some people, but not in my case.