Do not alter json in docker save

[vieux]

Fix #6455
Fix #6340
Close #6385

[vieux]

ping @vbatts what about this ?

[crosbymichael]

Do you know of a good way to test this? Maybe validate the json structure by parsing?

[vieux]

@crosbymichael test added, look at commit 614c57c it's much more readable.

[vbatts]

As for a way to unit test it, that may be a little more tricky.

root@jellyroll:/var/lib/docker/graph# docker save a9eb172552348a9a49180694790b33a1097f546456d041b6e82e4d7716ddb721 | tar xO -- a9eb172552348a9a49180694790b33a1097f546456d041b6e82e4d7716ddb721/json | md5sum
6191105cf0ea6f9273aa2de7b7fc6465  -
root@jellyroll:/var/lib/docker/graph# cat a9eb172552348a9a49180694790b33a1097f546456d041b6e82e4d7716ddb721/json | md5sum
715465f178b591dbe580e3da421bd3b4  -

Close, but they aren't the same. I'm thinking that there be a be a interface in image.Image like https://github.com/vbatts/docker/compare/vbatts-gh6385

[crosbymichael]

LGTM

[vbatts]

@crosbymichael but the json is still not the same. It should just do a copy of the file from the image graph.

[vieux]

@vbatts the only change is the create/mod/access time of the json file, not the content. So I don't see the issue.

[vbatts]

@vieux I can test this PR again, but #6461 (comment) has the output of the json on disk and the one from docker save, and they are different ...

[vieux]

@vbatts can you provide me a failing test ?
My test compares the content, and it's the same.

[vbatts]

@vieux i will work on getting a test. Your test's look good, but there are other use-cases in the life of an image to account for, and not affecting the layer's TarSum calculation (for the docker client or registry)

[vbatts]

@vieux here is a branch that uses this branch of yours, and expressly does a raw json for docker save https://github.com/vbatts/docker/compare/vbatts-raw_json