@hreintke : I don't know how generic the solution will be. I'm not that great at web development, and I'll probably end up reading the content of the file and splitting it on linebreak, as the code I have expects one line at the time from the HEX file. I want to validate the HEX as well (format and checksum) before sending as well. This means reading the content of the file to memory on the client, which is fine for me as they are ~30k, but might not be a good generic solution.
If I get that working ok, maybe I can try to modify it to a 'generic' solution though, that sends the file incrementally and possibly store it on the file system instead of 'consuming' the file.