Recently on his blog Cormac has posted a quick little tutorial on making things a bit faster when rejecting file uploads in PHP that are just a bit too large.

Discovered today you can report to a user if the file(s) he/she is uploading is too large without having to wait for the file to finish uploading by checking $_FILES.

The key is the "error" field in the $_FILES array that actually returns its value before the upload is finished if the size of the file is larger than the MAX_FILE_SIZE set in the POSTed information of the form. The Content-length header is sent before the actual payload (the file upload data) so PHP can interpret that before the upload starts and kick it back with an error if it's too large.