[Bug 1934992] Re: rsync 3.2.x in Groovy depends on broken libxxhash 0.7.x

[Wayne Davison]

Anyone who has an rsync that supports the xxh128 hash using the xxhash
0.7 library did something very bad in their build. An rsync compiled
with that library only supports xxh64 & xxh32. Thus, this described
mismatch never occurs in a stock rsync (the 128-bit hash was unstable in
xxhash 0.7, and thus rsync doesn't use it).

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Title:
  rsync 3.2.x in Groovy depends on broken libxxhash 0.7.x

Status in xxhash package in Ubuntu:
  Triaged
Status in xxhash source package in Groovy:
  Won't Fix

Bug description:
  **Problem**

    $ rsync root at focal-system:/etc/.pwd.lock . 
    ERROR: .pwd.lock failed verification -- update discarded.
    rsync error: some files/attrs were not transferred (see previous errors)
      (code 23) at main.c(1816) [generator=3.2.3]

  
    $ rsync root at focal-system:/etc/.pwd.lock . --debug=all
    opening connection using: ssh -l root focal-system rsync --server --sender \
      -e.LsfxCIvu . /etc/.pwd.lock  (10 args)
    (Client) Protocol versions: remote=31, negotiated=31
    Client negotiated checksum: xxh128
    ...

  
  **Cause**

    focal-system# dpkg -l | grep -E 'libxxhash|rsync'
    ii  libxxhash0:amd64  0.7.3-1         amd64
    ii  rsync             3.2.3-2ubuntu1  amd64

  
  **Why this affects only us and not more people?**

  On Ubuntu/Focal, there is no rsync 3.2.3, only 3.1.3-8. But because we
  need the lz4 compression support we've fetched a newer rsync (from
  Groovy).

  However: the rsync 3.2.3 depends on libxxhash0 0.7.1+, while in fact
  it needs 0.8+.

  
  **Details**
    
  On a Ubuntu/Focal system we have installed a rsync 3.2.3 package from Ubuntu/Groovy because we need the lz4 compression support.

  
  focal-system# apt-cache show rsync
  Package: rsync
  ...
  Version: 3.2.3-2ubuntu1
  Depends: lsb-base, libacl1 (>= 2.2.23), libc6 (>= 2.15),
    liblz4-1 (>= 0.0~r130), libpopt0 (>= 1.14), libssl1.1 (>= 1.1.0),
    libxxhash0 (>= 0.7.1), libzstd1 (>= 1.3.8), zlib1g (>= 1:1.1.4)
  ...

  
  Alongside this we had libxxhash0 0.7.3-1 from Focal:

  focal-system# apt-cache policy libxxhash0
  libxxhash0:
    Installed: 0.7.3-1
    Candidate: 0.7.3-1
    Version table:
   *** 0.7.3-1 500
          500 http://ARCHIVE/ubuntu focal/universe amd64 Packages
          100 /var/lib/dpkg/status

  
  According to the dependencies, this should work. But the combination does not, as this quote from the rsync maintainer would tell you:
  https://github.com/WayneD/rsync/issues/122#issuecomment-737690913
  > Yeah, Cyan4973 could have told you that the 128-bit xxhash only
  > just stabilized in its 0.8.0 release, so anything older than
  > that isn't compatible.

  
  **The fix**

  As the maintainer points out, version 0.7 is not stable (= broken for
  our intents and purposes) and thus not fit for use with rsync 3.2.

  I would argue that it's a good idea to bump the dependency of rsync
  3.2.3 on Groovy to libxxhash0>=0.8

  After all, in Groovy there is a libxxhash0 0.8.0-1ubuntu1.20.10.1, so
  that would not be a problem. And it would fix issues for those mixing
  and matching packages.

  
  Thanks!

  Walter Doekes
  OSSO B.V.

  
  (*) possible patch:

  $ diff -pu debian/control{.orig,}
  --- debian/control.orig	2021-07-08 09:56:57.646861644 +0200
  +++ debian/control	2021-07-08 09:57:38.499029903 +0200
  @@ -8,7 +8,7 @@ Build-Depends: debhelper-compat (= 13),
                  libacl1-dev,
                  libpopt-dev,
                  liblz4-dev,
  -               libxxhash-dev,
  +               libxxhash-dev (>= 0.8),
                  libzstd-dev,
                  zlib1g-dev,
                  libssl-dev

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