Options to strip EXIF metadata from media uploads.

[ara4n]

A really useful privacy feature would be to be able to strip off any metadata from images (or audio or video) before uploading them to the server. This could be done at the server itself, but then the server would be able to sniff it and it wouldn't work with E2E uploads which are probably the most important ones anyway.

So instead we should probably implement it as an option for the client to mangle the image before uploading to strip it out.

[ara4n]

(Given we already have the ability to mangle file-uploads before sending them to the server, when we do E2E encryption on them clientside before sending, this isn't impossible, although could be quite fiddly to get right and not pose performance problems).

[ara4n]

http://jsfiddle.net/mowglisanu/frhwm2xe/3/ has a relatively plausible looking example of stripping exif metadata from JPEGs. The right place to insert this is around https://github.com/matrix-org/matrix-react-sdk/blob/443ab1add73390176478fc7ecd1a334aa157e833/src/ContentMessages.js#L293 - either replacing the file with a new file object pointing to the updated data stream, or changing all the downstream code to work on data streams rather than file objects.

[ara4n]

actually, https://github.com/matrix-org/matrix-react-sdk/blob/443ab1add73390176478fc7ecd1a334aa157e833/src/ContentMessages.js#L237 is another option: just before we do the upload, we could check the mime type here for image/jpeg etc and then load the file into RAM and mangle it before sending (and then pass the same buffer to the e2e code as needed).

[ara4n]

another complication is that if we strip off EXIF colour profile metadata we should be re-compressing the image to 'bake in' the correct profile first. the right solution here is probably to leave colour profile meta intact.

[turt2live]

One concern with loading it into RAM would be issues like #4264

[ara4n]

For some reason i couldn't get this out of my head, so i've pushed a totally untested and almost certainly broken proof-of-concept to matrix-org/matrix-react-sdk@a0eea2a. If someone felt like picking it up and testing/finishing it it'd be hugely appreciated, as I should be focusing on organisational stuff atm rather than writing code, sadly :(

[ara4n]

(see also https://github.com/matrix-org/matrix-doc/issues/558)

[ara4n]

matrix-org/matrix-react-sdk#1307 ended up being the PR for this, but we couldn't get it to work, and it bitrotted and got closed :( It should still be resurrectable by some kind soul in future though.