RE: [Question] Signature calculation ignoring parts of binary files

-----Original Message-----
From: git-owner@vger.kernel.org <redacted> On Behalf
Of Johannes Sixt
Sent: September 12, 2018 4:48 PM
To: Randall S. Becker <redacted>
Cc: git@vger.kernel.org
Subject: Re: [Question] Signature calculation ignoring parts of binary files

Am 12.09.18 um 21:16 schrieb Randall S. Becker:

quoted

I feel really bad asking this, and I should know the answer, and yet.

I have a binary file that needs to go into a repo intact (unchanged).
I also have a program that interprets the contents, like a textconv,
that can output the relevant portions of the file in whatever format I
like - used for diff typically, dumps in 1K chunks by file section.
What I'm looking for is to have the SHA1 signature calculated with
just the relevant portions of the file so that two actually different
files will be considered the same by git during a commit or status. In
real terms, I'm trying to ignore the Creator metadata of a JPG because
it is mutable and irrelevant to my repo contents.

I'm sorry to ask, but I thought this was in .gitattributes but I can't
confirm the SHA1 behaviour.

You are looking for a clean filter. See the 'filter' attribute in gitattributes(5).
Your clean filter program or script should strip the unwanted metadata or set
it to a constant known-good value.

(You shouldn't need a smudge filter.)

-- Hannes

Thanks Hannes. I thought about the clean filter, but I don't actually want to modify the file when going into git, just for SHA calculation. I need to be able to keep some origin metadata that might change with subsequent copies, so just cleaning the origin is not going to work - actually knowing the original author is important to our process. My objective is to keep the original file 100% exact as supplied and then ignore any changes to the metadata that I don't care about (like Creator) if the remainder of the file is the same.

Regards,
Randall