module

ContributorMural::SameImage

Whether two avatar data URIs draw the same picture.

GitHub resizes an avatar on request, and which of its servers does the resizing decides how the result is deflated: the same face comes back as one of two PNGs that differ in every compressed byte and in no pixel. The wall embeds the bytes, so a push that happened to reach the other server rewrote the file and committed a picture nobody could tell apart from the last one — on every push, alternating between the two, forever.

A PNG is compared with its compression taken off: every chunk except IDAT as written, and the IDAT stream inflated. Anything else, or a PNG that does not parse, is the same picture only when the bytes are.

Constants

MAX_INFLATED = (64 * 1024) * 1024

Past this, inflating is not worth it to save a commit: an avatar at the largest size any style fetches inflates to well under a megabyte.

SIGNATURE = Bytes[137, 80, 78, 71, 13, 10, 26, 10]

Class methods

same?(a : String, b : String) : Bool

Source