rsync - Feb 2020 - [Bug 14267] New: rsync produces unhelpful errors on remote copy to OS with different ACL format

https://bugzilla.samba.org/show_bug.cgi?id=14267

            Bug ID: 14267
           Summary: rsync produces unhelpful errors on remote copy to OS
                    with different ACL format
           Product: rsync
           Version: 3.1.3
          Hardware: All
                OS: All
            Status: NEW
          Severity: minor
          Priority: P5
         Component: core
          Assignee: wayne at opencoder.net
          Reporter: s.adam at diffingo.com
        QA Contact: rsync-qa at samba.org

# Issue Description
Between two systems (different OSs) both with rsync 3.1.3, copies fail with an
unhelpful error when they use different ACL formats:

rsync: [sender] write error: Broken pipe (32)
rsync: connection unexpectedly closed (56591 bytes received so far) [generator]
rsync error: error in rsync protocol data stream (code 12) at io.c(820)
[sender=3.1.3]

This is a nondescript error that sends the user down a rabbit hole debugging
the wrong issue (are my rsync versions mismatched? why is there a
protocol-level error? is my ssh connection failing? is my disk full?).

It doesn't help that by default logs or increasing sender-side verbose
produces
no further hints; it's only by increasing receiver-side verbosity with
-M-vvv
that I got to the bottom of it -- incompatible ACL systems:

recv_acl_access: "value out of range": 129a000

Once it became clear that it was an ACL issue, per the man page
'-M--fake-super' fixes the issue.

# Repro steps
rsync -aAX macos-timemachine-backups-folder user at linuxhost:/path/to/dst

# Actual Results
rsync produces a bogus error about protocol failure, when in reality the
protocol communication itself is just fine (receiver just has an unsupported
ACL error)

# Expected Results
rsync produces a more appropriate error message, along the lines of "ACL
unsupported by receiver"

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