request S3 Credentials and build formdata

gistfile1.coffee

			@_requestCredentials( @format, _fName, ( res ) =>
				# building html5 / formdata object for use with xhr transport
				formData = new FormData
				formData.append( "key", "#{res.FileDescriptor}.#{@ext}" )
				formData.append( "acl", "public-read" )
				formData.append( "Content-Disposition", "" )
				formData.append( "Content-Type", res.ContentType )
				formData.append( "success_action_status", res.ActionStatus )
				formData.append( "AWSAccessKeyId", res.Key )
				formData.append( "Policy", res.PolicyBase64 )
				formData.append( "Signature", res.Signature )
				formData.append( "file", @images[_id] )

				try
					xhr = new XMLHttpRequest

					xhr.onreadystatechange = =>
						#xhr request has finished - one way or another
						if xhr.readyState is 4 
							if xhr.status is 200 or xhr.status is 201
								@_uploadFinished( _id, "http://#{res.Bucket}.s3.amazonaws.com/#{res.FileDescriptor}.#{@ext}" )
							else
								@_uploadError( _id, xhr.status )
						return

					xhr.onprogress = ( progress ) =>
						# do something fancy here - maybe an animated progress bar?
						return

					xhr.open "POST", "http://#{res.Bucket}.s3.amazonaws.com", true
					xhr.send formData
				catch e
					@_uploadError( _id, e ) 
				return