testsuite/abdiff.py runs the same benign transfer with two rsync binaries
(A = build under test, B = a baseline) and compares the OUTCOME -- exit code,
stderr, --stats "Literal data", the destination tree (content + full metadata),
the --itemize list, and (with --cost) peak process-group RSS. For benign input
the two must be indistinguishable; any divergence is a regression candidate.
It is a developer tool, NOT a runtests.py test (does not end in _test.py).
Capabilities:
- Scenario sweeps over options / path shapes / file types / sizes / modes /
selection / placement / wire / transports, plus domain-knowledge pairwise +
combo sweeps and a stochastic fuzzer/role matrix.
- Transport lanes: local, ssh split (lsh.sh), stdio-pipe daemon, a REAL TCP
daemon (bound port + greeting/handshake/auth challenge-response), and the
restricted rrsync wrapper (support/rrsh.sh; each binary paired with its own
version's rrsync via --rrsync-a/--rrsync-b, since rrsync ships in the script).
- Stability gate: each binary is run N times and escalated on a candidate diff;
nondeterministic scenarios are quarantined FLAKY, never reported as regressions.
- Parallel (-j, default 20) with a per-run findings log; --loop runs until
--timelimit (or Ctrl-C), feeding the pool a half-random / half-systematic
stream of new combinations. As root an "all" run also folds in the root-only
sweeps (priv, daemonchroot).
- General coverage levers: a cost oracle (--cost, peak RSS over the whole process
group), transport lifted as an orthogonal axis, a resume/redo sweep, and
type-transition / nanosecond-mtime / scale (--scale N) fixtures.
Documented in testsuite/README.md.
