pkg/archive:CopyTo(): fix for long dest filename

[kolyshkin]

relates to #35739

As reported in docker/for-linux/issues/484, since Docker 18.06
docker cp with a destination file name fails with the following error:

archive/tar: cannot encode header: Format specifies USTAR; and USTAR cannot encode Name="a_very_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx_long_filename_that_is_101_characters"

The problem is caused by changes in Go 1.10 archive/tar, which
mis-guesses the tar stream format as USTAR (rather than PAX),
which, in turn, leads to inability to specify file names
longer than 100 characters.

This tar stream is sent by TarWithOptions() (which, since we switched to
Go 1.10, explicitly sets format=PAX for every file, see FileInfoHeader(),
and before Go 1.10 it was PAX by default). Unfortunately, the receiving
side, RebaseArchiveEntries(), which calls tar.Next(), mistakenly guesses
header format as USTAR, which leads to the above error.

The fix is easy: set the format to PAX in RebaseArchiveEntries()
where we read the tar stream and change the file name.

A unit test is added to prevent future regressions.

NOTE this code is not used by dockerd, but rather but docker cli
(also possibly other clients), so this needs to be re-vendored
to cli in order to take effect.

- A picture of a cute animal (not mandatory but encouraged)

from Cheburashka

[kolyshkin]

janky failure

01:23:29.240 FAIL: docker_api_swarm_test.go:297: DockerSwarmSuite.TestAPISwarmLeaderElection

is well known flaky test, #32673

[kolyshkin]

reserved for Derek commands

[alexellis]

Nice to see Derek being put to use 👍

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[cyphar]

hdr.Format = tar.FormatPAX

This might cause image-cache breakage because mtime and atime were ignored under USTAR but in PAX they can be represented. The Go 1.10 fix was actually because of a bug report I submitted about the above, but as a result you might end up with different images.

[thaJeztah]

This might cause image-cache breakage because mtime and atime were ignored under USTAR but in PAX they can be represented.

hmf.

I wonder; I recall some older PR's addressing those to be ignored; #12031 (possibly related #11422). So wondering if this will be an issue 🤔

[thaJeztah]

ping @tonistiigi @dmcgowan PTAL

[thaJeztah]

LGTM (issue is indeed fix with this change)

[thaJeztah]

Caught up with @tonistiigi to verify if this would affect caching, and we should be good to go, so I'll go ahead and merge.

Feel free to continue the discussion though if there are things we overlooked

[kolyshkin]

hdr.Format = tar.FormatPAX

This might cause image-cache breakage because mtime and atime were ignored under USTAR but in PAX they can be represented.

@cyphar as far as I remember, the sending side already takes care of this, see

moby/pkg/archive/archive.go

Lines 365 to 368 in 44af96c

	hdr.Format = tar.FormatPAX
	hdr.ModTime = hdr.ModTime.Truncate(time.Second)
	hdr.AccessTime = time.Time{}
	hdr.ChangeTime = time.Time{}