Add real implementations for the rsync 3.4.1 checksum and compression
breadth: a self-contained MD4 (RFC 1320), OpenSSL-backed SHA1, a
no-digest mode, and LZ4/zlib codecs alongside zstd. Compressed buffers
are now self-describing (a leading codec id), so every existing
decompression call site keeps working through a process-global codec
selection. zlibx shares the zlib codec because FastSync compresses only
delta/token bytes (never matched file data), matching the 'x' intent.
#289 checksum/compression:
- -c/--checksum now implies the incremental content quick-check (without
implying -t), so an unchanged file is skipped like rsync.
- --checksum-choice/--cc accepts xxh64/xxhash, xxh3, xxh128, md5 and auto;
md4/sha1/none and the two-name form are rejected by name.
- --compress-choice/--zc rejects lz4/zlib/zlibx by name (zstd/none/auto kept).
- --checksum-seed=0 is randomized per transfer and sent on the wire.
- --skip-compress uses rsync 3.4.1's default suffix list; slash separators and
dot-less suffixes are accepted.
- add --no-whole-file.
#295 timeouts/alloc/temp-dir:
- --timeout default 0 (disabled), --contimeout default 60; 0 disables both,
plus --no-timeout/--no-contimeout.
- --max-alloc=0 means no allocation limit (was rejected).
- --temp-dir accepts any dir, requires it to exist, and falls back to a
non-atomic copy on EXDEV instead of aborting.
#296 connectivity/daemon:
- -M/--remote-option is rejected for daemon/TCP destinations (SSH-only).
- --trust-sender clarified as receiver-local; server-path tests added.
- --stop-at accepts rsync's full date form (y-m-dTh:m etc.).
Adds unit and integration coverage; no wire-field change, PROTOCOL_VERSION stays
2.22.0.
Adds real algorithm selection (xxh64 default, plus md5 via OpenSSL EVP) and a
64-bit seed for the per-file whole-file digest used by the --incremental/
--checksum handshake and basis-dir content verification. The seed also feeds
the delta path's per-block xxHash32 strong checksum (low 32 bits) so an
explicit seed deterministically changes those digests too. Sender and receiver
hash identically: the algorithm id and seed cross the config wire frame and the
STATUS_CHECK handshake now carries a length-prefixed, bounded digest instead of
a fixed 64-bit value. Unsupported algorithm names are rejected at parse time
(never a silent no-op). PROTOCOL_VERSION bumped 2.9.0 -> 2.10.0; defaults
(xxh64, seed 0) preserve prior byte-for-byte behavior.
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