FastSync/CHANGELOG.md

Changelog

All notable changes to FastSync are documented here. Versions match PROTOCOL_VERSION (printed by fastsync --version); the client and server must run the same version because the handshake is strict.

[Unreleased]

Wire backlog cycle (protocol 2.29.0 → 2.30.0; config-frame layout unchanged).

• --stderr=client client-message channel (#313): the client now accepts --stderr=client (and maps the deprecated --no-msgs2stderr to it), routing its own diagnostics over the new bounded STATUS_CLIENT_MSG client->server frame instead of writing them locally; the server writes each received message to its stderr (respecting the server log destination). errors/all behavior is unchanged.
• Receiver partial failures exit 23 (#320): a per-entry receiver failure that does not abort the stream (e.g. an unprivileged --devices mknod) now sends the terminal STATUS_PARTIAL; the client exits 23 like rsync and, under --remove-source-files, still removes the sources it successfully transferred. A clean run stays 0 and a fatal/connection error stays non-23.
• Directory/symlink destination-state itemize (#314): when report_dest_info is negotiated (now also for --progress), the receiver answers STATUS_MKDIR and STATUS_SYMLINK with the entry's pre-transfer destination snapshot (existence, type, perms/owner/group/time, and whether an existing symlink's target already matches), and the sender probes every ancestor directory before the receiver creates it implicitly. A re-run over an unchanged tree no longer emits per-directory cd+++++++++ or unchanged-symlink lines, a changed directory renders rsync's .d..t......, and a changed symlink renders cLc........ / .L..t....... Directory/symlink time comparison uses whole seconds (rsync's cmp_time). The STATUS_MKDIR body gains a probe flag and the STATUS_DEST_INFO record gains a symlink-target-match field; the config-frame layout is unchanged. Differential-tested against rsync 3.4.1.
• --stats deleted per-type breakdown (#316): STATUS_STATS gains deleted_reg/dir/link/special, tallied by the delete observers and rendered as rsync's Number of deleted files: X (reg: A, dir: B, link: C, special: D). Differential-tested against rsync 3.4.1 for a mixed-type --delete tree.

[2.29.0] - 2026-09-23

The rsync-parity cycle 2.29 (no wire change; PROTOCOL_VERSION stays 2.28.0). RSYNC_COMPAT.md moves from 116 ✅ / 14 ⚠️ / 27 ❌ to 120 ✅ / 10 ⚠️ / 27 ❌ of 157 rows.

An audit cycle follows on the same wire version (PROTOCOL_VERSION stays 2.28.0): a security-and-correctness pass over the parity-2.29 baseline, plus a set of audit follow-ups (filter merge modifiers, the --inplace/--partial-dir conflict, credential-file hardening, and small leak/log/test fixes). It fixes a --temp-dir symlink escape, gates client-controlled special permission bits, corrects --partial-dir/--bwlimit/-z behavior, handles unsupported filter modifiers, and tightens client and wire validation. The only parity reclassification is --filter=RULE moving ✅ → ⚠️, because its merge-only e/n/w/- modifiers are now accepted and consumed but their semantics remain unimplemented (accepted-but-ignored); the matrix is therefore 119 ✅ / 11 ⚠️ / 27 ❌ of 157 rows. The affected rows' notes and the summary tally in RSYNC_COMPAT.md were updated. A following triage-fix cycle (see Triage fixes below) moves -F and -i to ⚠️, for a final 117 ✅ / 13 ⚠️ / 27 ❌ of 157 rows.

A no-wire parity burn-down cycle follows on 2.28.0: it accepts --inc-recursive/--no-inc-recursive as inert no-ops, accepts an absolute --temp-dir that canonicalizes inside the receive root, closes the --delete-before phase-0 divergence (both the single-threaded and --threads data passes replay the pre-scan list), makes --fake-super interoperable with rsync's user.rsync.%stat key/grammar (regular files and char/block devices faked as regular files), turns a failed device mknod into a continuing per-entry failure, and accepts a practical subset of rsync's rsyncd.conf grammar (modules are read-only by default, and accepted-but-unenforced access-control keys emit a startup warning). The matrix moves to 119 ✅ / 14 ⚠️ / 24 ❌ of 157 rows.

A structural cycle then lands a transport I/O vtable over TCP/TLS (fixing the TLS-multithreaded sendfile path and making the per-thread SSL resolution explicit) and bumps the wire to 2.29.0: the STATUS_SYMLINK frame grows an optional symlink-xattr block (captured no-follow with llistxattr/lgetxattr, applied no-follow with lsetxattr). Because the handshake is strict, 2.28.0 and 2.29.0 peers are incompatible. Note: Linux refuses to associate xattrs with a symlink at all, so the symlink-xattr block is a no-op on Linux and is carried for correctness on platforms/filesystems that do support it; the config-frame layout is unchanged (golden length still 886).

Changed

• rsync-exact traversal order. The sequential scanner now walks each directory's entries in rsync 3.4.1's flist order (non-directories ascending, then directories ascending, depth-first), so --info=name, the --delete-during/--delete-delay/-n would-delete order and the partial --max-delete survivor set match rsync byte-for-byte. --threads has no rsync analogue and stays unordered.
• Delete timing. The complete --delete-during/--delete-delay per-directory plan set is transmitted before the first data frame, so a mid-transfer abort has already removed every planned extra like rsync's generator; -d/--dirs uses per-directory plans (shielded untraversed subdirectories) instead of the end-of-transfer commit. -n, --delete, --del/--delete-during and --delete-delay are now ✅ Parity.
• Basis directories. A relative --compare-dest/--copy-dest/--link-dest DIR resolves against the destination directory with the transfer-relative name appended, exactly like rsync 3.4.1.
• -y/--fuzzy. The candidate search no longer inherits the ordinary delta engine's 16 KiB minimum or 10× size-ratio bound, so an oversized or sub-16-KiB sibling is reused exactly as rsync reuses it.
• --info=mount prints rsync's mount-point skip line (repeated -xx drops the mount-point directory); --info=stats enables the --stats block; -x is repeatable. --stats counts traversed directories for the Number of files breakdown under a plain -r scan. --debug emits real output for flist/del/hash/deltasum/recv/filter/send.

Known residuals

• --progress and --info still need a receiver→sender event channel for the root ./ line, ancestor-directory suppression, receiver-side skip/backup wording, and symlink/empty-directory quick-checks.
• --delete-before's phase-0 late-file divergence remains (rsync's pre-scan fixes the file list before the data pass).
• A whole-file sender that cannot stream its codec (lz4's one-shot block format) or a --append/delta source above the bound still buffers; the default zstd/zlib and the uncompressed paths stream (see #318).
• --stats byte totals and --msgs2stderr stay documented divergences.

Security

• --temp-dir symlink escape fixed. The receiver's scratch directory was opened with a bare open(), so a symlink planted under the receive root could redirect receiver scratch files outside the authorized root. The opened directory is now judged by the real path of its fd (/proc/self/fd via realpath) and an escaping target is refused (EACCES, logged); an in-root link to another filesystem (the EXDEV fallback case) still works.
• Client-controlled special bits masked when super-user activities are not permitted. Setuid/setgid/sticky bits (--perms, --chmod, the symlink and special-node paths, and deferred directory modes) are now stripped when the connection forbids super activities (--no-super, a non-opted daemon module, a privileged listener without --allow-super); exact rsync semantics are preserved wherever super activities are permitted.
• Daemon umask no longer forced to 0. daemonize() now sets the conventional 022, so implied parent directories created without -p are no longer world-writable 0777.
• Daemon modules are read-only by default. A --daemon module is now served read-only unless it sets read only = no (or rsync's write only = yes), matching rsync: a real rsyncd.conf that omits read only is no longer silently writable. A global read only still sets the default for later modules, and an explicit module value wins. This is a behavior change for existing FastSync-native configs that relied on the old writable default; add read only = no to keep them writable. An rsync write only = yes is mapped to writability (FastSync is push-only, so a module can never be read from the network).
• Accepted-but-unenforced rsync security keys now warn at startup. The rsync keys FastSync recognizes but does not implement — secrets file, refuse options, exclude/include/filter, max size/min size, pre-xfer exec/post-xfer exec, incoming chmod/outgoing chmod, name converter, use chroot, uid/gid, and the rest of the access-control set — load for migration compatibility but now emit a WARN naming the key (and module) so an operator does not believe the restriction is enforced. auth users/secrets file stay fail-closed: a module declaring auth users still requires a FastSync credential store.
• Credentials and signal handling hardened. Secret files are opened with O_NOFOLLOW|O_NONBLOCK (while allowing fd-backed store paths and bound-waiting a FIFO read for ~3 s so a slow process substitution works but a connected-but- silent FIFO cannot hang), and signal handlers use sigaction with async-signal-safe bodies.

Fixed

• -z on 100–256 MiB files. The decompressor's internal ceiling was 100 MiB while the receiver advertises and the sender compresses whole files up to MAX_RECEIVE_WHOLE_FILE_SIZE (256 MiB), so -z on a 100–256 MiB regular file failed with Declared decompressed size exceeds 104857600 bytes. The ceiling is now defined in terms of the protocol whole-file bound (still an allocation-clamped bomb guard).
• --bwlimit now paces --sendfile. The plaintext-TCP --sendfile fast path bypassed the protocol's token bucket, so the limit was ignored there. It now throttles through the same per-session leaky bucket as the TLS path.
• --partial-dir implies --partial. Matching rsync 3.4.1 (which sets keep_partial after option parsing), --partial-dir=DIR alone retains an interrupted transfer's partial and wins over an explicit --no-partial; --inplace still bypasses the partial machinery, and combining --inplace with --partial-dir is now rejected up front with rsync's message (--inplace cannot be used with --partial-dir).
• Filter modifiers handled. The x xattr-name modifier is rejected with a clear error everywhere. The merge-only e/n/w and - modifiers are now accepted and consumed on merge/dir-merge rules (so they no longer leak into the merge filename) while still being rejected on non-merge rules, matching rsync; their semantics remain unimplemented (accepted-but-ignored). Glued patterns (-newfile, -e2e) and mixed tokens (H,!secret) keep their historical parsing.
• Credential-file reads hardened. Secret files (--password-file/ --early-input/--hash-credentials input) are opened with O_NOFOLLOW, so a symlinked credential path now fails closed (ELOOP) instead of being followed before the owner/mode gate; literal fd-backed paths (/dev/fd/<digits>, /proc/self/fd/<digits>) are exempt so process substitution still works. A FIFO/process-substitution read now waits under a bounded ~3 s deadline for its writer, so a slow producer works while a connected-but-silent FIFO fails instead of hanging.
• Miscellaneous correctness fixes: --filter rule count is checked client-side against MAX_FILTER_RULES before any network I/O (the receiver still re-checks the expanded count); unknown wire Status values are rejected as protocol errors; a mutex leak on an init-failure path, an errno read after free() in deferred delete application, log_perror misuse for non-errno conditions, and a NULL server_host/ssh_destination allocation path were fixed (the config_create failure now releases through config_delete); the decompression-limit log now prints the effective bound rather than the compile-time ceiling; the daemon umask and root test fixtures were hardened; SSL_read length is clamped and sendfile poll() retries on EINTR.

Refactored / Docs

• Dropped dead filter_rules_apply and dead --old-args plumbing, unified set_error, deduplicated path_is_within and shared constants, and added printf format attributes (fixing format mismatches). RSYNC_COMPAT.md, CHANGELOG.md and HANDOFF.md were updated for the audit cycle; the RSYNC_COMPAT.md summary tally was corrected to match the rows.

Triage fixes

• --dirs directory xattrs applied inline. A -d/--dirs transfer now applies captured directory -X/-A xattrs fd-relative on the directory entry instead of dropping them, so directory xattrs survive the non-recursive path (src/shared/file_save.c, tests/test_xattr.c).
• Directory/root itemize and --out-format lines. -i/--itemize-changes and --out-format now emit the transfer-root ./ line and per-directory cd.../.d..t... lines, rendered by the shared itemize code. This matches rsync's fresh-transfer output; because the root line is unconditional and an incremental re-run may itemize directories/symlinks that rsync's quick-check leaves silent, -i is now a ⚠️ Caveat row.
• FROM name globs for identity maps. --usermap/--groupmap FROM tokens now accept */?/[...] globs, expanded sender-side against the passwd/group database and collapsed into bounded numeric ranges (MAX_IDENTITY_MAP), matching rsync.
• Transport fallback unit tests. Added unit coverage for the TCP/TLS transport fallback paths (tests/test_transport_tcp.c, tests/test_transport_tls.c).
• Docs corrections. RSYNC_COMPAT.md/README.md corrected stale parity claims for issues #286–#297: the -F and -i reclassifications, the --munge-links direction, the accepted checksum/compression name sets, --bwlimit parsing, --stop-at grammar, --trust-sender, symlink xattrs, and the native/non-interoperable batch and credential notes. The summary tally is now 117 ✅ / 13 ⚠️ / 27 ❌ of 157 rows.

[2.28.0] - 2026-09-20

The rsync-parity cycle. PROTOCOL_VERSION moves 2.26.0 → 2.27.0 → 2.28.0; client and server must run the same version (the handshake is strict). See RSYNC_COMPAT.md for the per-option matrix, now 116 ✅ / 14 ⚠️ / 27 ❌ of 157 rows.

Added

• Differential rsync 3.4.1 parity gate (tests/integration/ test_differential_parity.py, parity_harness.py, parity_caveats.py): runs real rsync and FastSync over generated corpora and diffs the destination tree, normalized stdout and exit code. A fast subset runs on pull requests and the full strict set on push; the residual allowlist is empty.
• FastSync-only long option --verify-basis: require a --compare-dest/--copy-dest/--link-dest hit to match the source by whole-file digest instead of trusting the size+mtime quick-check.
• FastSync-only long option --delete-commit (implies --delete): the old atomic late whole-tree commit.
• --bwlimit now parses rsync's units exactly and paces like rsync's leaky bucket; --ignore-errors reproduces rsync's skip-unreadable-subdir and IO-error-suppressed deletion (exit 23).
• --info=name/flist/del/remove/nonreg/progress emit rsync's line format, including real-run deleting/*deleting lines carried by a new report_deletes wire bool.
• Receiver-observed --stats counters: Number of created files now carries rsync's (reg/dir/link/special) breakdown and Literal data is exact for a delta transfer (extended STATUS_STATS).
• --progress uses an opt-in paths-only pre-count so the to-chk denominator counts every entry like rsync, and emits per-directory/symlink/special names.
• Receiver-side protect/risk filter engine (new bounded filter-rule wire block): --filter='P ...' now shields a destination-only entry like rsync.
• auto for --compress-choice/--checksum-choice honors RSYNC_COMPRESS_LIST/RSYNC_CHECKSUM_LIST, and per-codec compression-level defaults match rsync.
• Empty source directories are recreated recursively; -R --no-implied-dirs --files-from places listed files under missing implied parents; --iconv matches rsync's push direction; --delete-delay reports actual removals and recursively removes a refilled deferred directory.

Changed

• --delete now defaults to delete-during (rsync --del) timing. With no explicit timing flag, a plain --delete removes each directory's extras as that directory is processed instead of committing one whole-tree deletion only after the entire transfer succeeds. This matches rsync, frees destination space progressively, and avoids the whole-old+new-tree peak that could ENOSPC a tight destination. The client maps the default onto the existing delete_during wire boolean, so PROTOCOL_VERSION stays 2.28.0.
• Basis directories (--compare-dest/--copy-dest/--link-dest) now default to rsync's metadata quick-check (equal size and mtime; --size-only drops the mtime leg) instead of FastSync's historical always-verify content hash. --copy-dest re-applies the source attributes, and basis materialization is streamed so the 256 MiB whole-file cap no longer applies to a basis hit.
• The per-directory STATUS_DELETE_PLAN frame gained a one-int apply flag: the one-shot per-run config block (protected prefixes, size-pruned mirrors, --delete-missing-args exact paths) is now always transmitted first on a config-only carrier (apply=false), fixing a latent bug where a --delete-missing-args run whose --files-from list synchronized no directory never sent its exact deletions.

Notes

• --delete/--delete-during remain caveats for the mid-transfer abort boundary (rsync's generator removes all planned extras ahead of its throttled sender; FastSync removes only reached directories — final trees agree). --delete-before, --progress, --stats, --fuzzy and the basis rows keep their documented residuals in RSYNC_COMPAT.md; --filter and --delete-excluded are now parity, including protection of a destination-only excluded entry under default --delete.

Migration

• Scripts that relied on plain --delete deleting nothing until the transfer fully succeeded must pass --delete-commit (or --delete-after) to keep that behavior. Plain --delete now removes reached directories' extras during the transfer, exactly like rsync's default; on a completed run the final tree is unchanged.
• Deployments that relied on FastSync's stricter basis verification should pass --verify-basis; the default now trusts the size+mtime quick-check like rsync.

[2.26.0] - 2026-09-17

Added

• Parity-completion wave. Closed the remaining rsync-parity gaps against rsync 3.4.1 and reclassified the inherently non-rsync rows. It moved the wire protocol three times (2.23.0 → 2.24.0 → 2.25.0 → 2.26.0).
  • Delete timing (2.24.0): per-directory delete plans (STATUS_DELETE_PLAN) for --delete-during/--delete-delay. An interrupted during-transfer has already removed the reached directories' extras, while a delayed transfer commits per directory only after the whole transfer succeeds (a late-created extra survives --delete-delay but not --delete-after). -R --delete is scoped to the transferred prefix; empty in-scope source directories survive; dry-run never deletes.
  • Wire stats (2.25.0): STATUS_STATS carries the receiver counters (matched data, deleted files) and the dry-run would-delete list. --stats prints rsync's protocol-independent lines; --progress/-P print per-file blocks; --out-format gains %b (wire bytes), %c (block-sum bytes) and %C (whole-file digest); -n --delete prints escaped *deleting lines in the sequential and --threads paths.
  • Codecs (2.26.0): lz4/zlib/zlibx compression and md4/sha1/ none checksums, with rsync-style auto negotiation (default xxh128 + zstd) and exit-4 rejection of unknown names; the resolved compression_algo crosses the wire.
  • General -R/--relative (including the /./ cut) and --no-implied-dirs; one-level -d/--dirs listing for dir, dir/ and .; the full filter grammar (merge/dir-merge/hide/show/protect/risk/clear and modifiers) with -f bound to --filter; a single -F transfers .rsync-filter and -FF excludes it.
  • Receiver-side --chown/--usermap/--groupmap TO-name resolution; absolute basis directories and a --link-dest relink of an up-to-date destination; a receiver-side --ignore-existing short-circuit before any payload; --preallocate now wins over --sparse via fallocate(2).
  • Client quick wins: --iconv=./-/--no-iconv, a lone -h prints help, an empty --files-from succeeds (exit 0), a broken referent under -L/--copy-unsafe-links exits 23, the full --info/--debug vocabularies, and the aliases --ignore-non-existing, --protect-args, --msgs2stderr.

Changed

• PROTOCOL_VERSION bumped 2.23.0 → 2.24.0 (delete plans), 2.24.0 → 2.25.0 (STATUS_STATS + report_stats), and 2.25.0 → 2.26.0 (codec negotiation + md4/sha1/none).
• --checksum-choice/--cc now accepts md4, sha1, none and the two-name form; the negotiated whole-file default is xxh128.
• --compress-choice/--zc now accepts lz4, zlib, zlibx.
• RSYNC_COMPAT.md reclassifies the matrix: 9 already-parity rows to ✅, 17 inherently non-rsync rows to ❌ (native daemon config/auth, batch, privileged xattr namespaces, and the safe-subset device/privilege flags), and the genuine fixes to ✅; new rows cover --bwlimit, --partial, --partial-dir, --no-whole-file, --inc-recursive/--no-inc-recursive, --protect-args and --msgs2stderr.
• The client --help --max-delete text now describes the implemented partial semantics (delete up to N, skip the rest, exit 25).

Notes

• Remaining documented divergences include the --stats per-type file-count breakdown, %b/%c being FastSync wire counts, -n --delete line ordering, the default --delete timing (delete-after, not rsync's delete-during), destination-only exclude protection (still sender-derived), --temp-dir absolute paths, basis-dir attribute re-application and the 256 MiB whole-file cap, --fuzzy tie-breaking, --bwlimit=0/decimal rates, zlibx==zlib, and recursive empty-directory creation.
• Build: adds zlib and lz4 as link dependencies.

[2.23.0] - 2026-09-16

Added

• Rsync-parity wave. Closed the remaining CLI, filesystem, ownership, deletion, and output gaps against rsync 3.4.1.
  • Short options -r (--recursive), -b (--backup), -L (--copy-links), and -B (--block-size/--delta-block); rsync short-option clustering (-av, -aAX, -rlpt) and attached/inline values (--opt=value, -B1000, -essh, -MOPT). A value that starts with - is not mistaken for a cluster.
  • -c/--checksum now implies the incremental checksum quick-check (and, like rsync, does not imply -t).
  • --checksum-choice/--cc accepts xxh64/xxhash/xxh3/xxh128/md5/ auto and rejects md4/sha1/none and the two-name form by name; --checksum-seed=0 (the default) is randomized per transfer and the chosen seed is sent to the receiver.
  • --compress-choice/--zc accepts zstd/none/auto and rejects lz4/zlib/zlibx by name; --skip-compress defaults to rsync 3.4.1's built-in suffix list; --no-whole-file is accepted.
  • --timeout defaults to 0 (disabled) and --contimeout to 60 s (both 0 disables), matching rsync; --max-alloc=0 means no local limit.
  • --temp-dir is confined to the receive root (absolute/.. rejected by the receiver) and an EXDEV install falls back to a non-atomic copy.
  • --numeric-ids is documented as a mapping modifier only; --usermap/--groupmap support inclusive LOW-HIGH ranges, *, empty-FROM (unnamed ids), and receiver-resolved TO names; --chown conflicts with a map on the same side are rejected.
  • --fake-super records the resolved owner (never a real chown) and replays mode/time; directory ownership and directory xattrs/ACLs are preserved.
  • -l/--links stores symlink targets verbatim (absolute and ..-bearing included), matching rsync; --safe-links/--copy-unsafe-links are applied sender-side and --munge-links uses rsync's /rsyncd-munged/ marker; --trust-sender no longer affects symlink targets.
  • --specials recreates unix sockets with mknod(S_IFSOCK) (so -D covers the full rsync node set).
  • Deletion: the manifest carries a synchronized-directory section so --files-from subsets no longer delete untransmitted paths; --delete-excluded leaves size-pruned mirrors protected; extraneous destination symlinks are unlinked (never followed); --max-delete=N is partial (delete up to N, skip the rest, exit 25) and --delete-missing-args removals draw from the same budget; --force is honored during --delay-updates publication.
  • -x/--one-file-system emits the mount-point directory entry; the --include/--exclude layers are an ordered first-match rule list.
  • --chmod is a faithful port of rsync 3.4.1 (numeric/symbolic, D/F/X, s/t, append semantics, no -p implication, no sanitization).

Changed

• PROTOCOL_VERSION bumped 2.22.0 → 2.23.0: the delete manifest gains a synchronized-directory section and the terminal status gains STATUS_DELETE_LIMIT (client exit 25 on a --max-delete-capped commit).
• The 2.22.0 mode-masking divergence is removed. Under -p the source mode is copied exactly, including S_IWGRP/S_IWOTH and setuid/setgid/sticky; --chmod no longer implies -p. New files without -p still use source_mode & ~umask when metadata is present (else 0644), and new directories without -p still use the 0755 creation default.
• --protocol=NUM accepts only the current 2.23.0 version string.

Notes

• The rsync-compatibility matrix (RSYNC_COMPAT.md) now classifies every row as parity, caveat (works with a documented divergence), or divergent (not supported/no-op/impossible), replacing the previous misleading "N implemented / 0 divergence" summary. Durable documented divergences remain: receiver-side symlink target containment is not enforced by default (verbatim storage is rsync parity; use --safe-links), --temp-dir rejects absolute/foreign-filesystem paths, --copy-devices reads a bounded st_size, a broken referent under --copy-links exits 0, new directories without -p use 0755, --stats receiver-only counters are 0, and --password-file/--early-input/--hash-credentials/--iterations and the batch format are FastSync-native.

[2.22.0] - 2026-09-15

Added

• Per-attribute metadata preservation (protocol 2.22.0). The former single metadata bundle is split into four independent, rsync-compatible flags: -p/--perms, -t/--times, -o/--owner, and -g/--group, each applied independently on the receiver, with negations --no-perms/--no-times/ --no-owner/--no-group (short --no-p/--no-t/--no-o/--no-g) and --no-preserve clearing all four. -a/--archive is now full rsync -rlptgoD (owner and group included; their application stays privilege-gated). -A/--acls and --chmod imply -p, -X/--xattrs does not, -E/--executability sets only executability, and -U/-N do not imply -t. --incremental/--delta still auto-preserve perms+times unless the user explicitly negated them.
• Receiver applies directory modes under -p (at the end of the transfer, alongside the deferred directory times) and symlink mode under -p; -O suppresses directory times only.

Changed

• PROTOCOL_VERSION bumped 2.21.0 → 2.22.0: the binary config frame gains four appended booleans (preserve_perms/preserve_times/preserve_owner/ preserve_group) after omit_link_times. The fixed-width FileMetadata layout is unchanged; the receiver derives the metadata-frame gate (use_metadata) from the four attributes.

Notes

• Documented divergences from rsync: a client-supplied mode never grants group/other write (S_IWGRP|S_IWOTH are stripped for files, directories, symlinks, and specials; rsync's -p preserves them exactly); a brand-new file without -p gets source_mode & ~umask (sanitized) when metadata is present, else the historical fixed 0644; --chmod implies -p (rsync does not); -o/-g map by name on the receiver with a raw-numeric fallback (only numeric ids cross the wire); and a daemon module without client owner = yes does not refuse a plain -a/-o/-g but forces super-user activities off, applies no ownership, and logs a warning (explicit --chown/--usermap/ --groupmap/--numeric-ids/--copy-as/--super are still refused).

[2.21.0] - 2026-09-14

Added

• Optional server→client rejection detail (protocol 2.21.0). A rejected operation may now carry a bounded human-readable reason via STATUS_ERROR_DETAIL instead of a bare STATUS_ERROR, so the client can report why the server refused (daemon module gate, config validation, receiver-side path/node validation). receive_status() transparently maps the new status back to STATUS_ERROR for every existing call site and captures the reason into a thread-local buffer exposed by protocol_last_error(). The detail body is always consumed, so the stream cannot desynchronize, and messages are sliced to MAX_ERROR_DETAIL_BYTES (4096) on send.
• Server-contacting --dry-run (protocol 2.21.0). --dry-run now performs a real handshake with a remote/daemon receiver and reports exactly what WOULD change based on receiver state (existing destination files, mtimes, checksums, basis dirs). The wire config carries the dry-run intent (Config.dry_run) and the receiver answers each per-file check with STATUS_DRY_RUN_TRANSFER (would transfer) or STATUS_OK (already up to date); the sender prints the would-transfer set and its trailer without sending any file data. The receiver performs the normal read-only incremental decision but mutates nothing: no temp files, writes, renames, deletes, metadata/xattr/chown, or directory creation. A plain local destination (no explicit --server-port/remote) keeps the original client-side dry-run. Would-delete reporting for --delete* is deferred to a follow-up; dry-run never deletes.
• Daemon max connections per host (per-source-IP concurrent cap, default 0 = unlimited), auth lockout threshold (default 10; 0 disables) and auth lockout duration (default 300 s) config keys.
• fastsync-server --allow-super opt-in for a privileged standalone TCP server; without it a root standalone receiver forces super-user activities off (device nodes, --write-devices, ownership). The --stdio SSH argv is client-composed, so super activities always stay off there.

Changed

• Config wire fields are now declared once in an X-macro table (CONFIG_WIRE_FIELDS in src/shared/config.h) that generates the struct members, defaults, and the send/receive sequence, removing the manual six-site field sync. Wire bytes and PROTOCOL_VERSION are unchanged.
• receive_incremental_check() (the per-file STATUS_CHECK fast path) is split into small static helpers with a short linear orchestrator. Pure refactor: the wire byte stream and all cleanup are unchanged.
• authorized_root state has a single owner (utils.c) with read accessors; the duplicated statics in file.c and the server were removed.
• Data records its owning ProtocolSession so its memory charge is returned to the session that reserved it, regardless of the destroying thread.
• The receiver pipeline moved out of shared into server/receiver_pipeline.[ch]; the build now uses explicit fastsync_shared / fastsync_client_core / fastsync_server_core targets instead of a GLOB, and the client no longer links server code.
• The benchmark tool generates the requested random/compressible data mix accurately, verifies each transfer before recording it, computes correct percentiles, adds a MB/s column, handles tc/netem without requiring sudo when already root, builds into a dedicated build-bench/ directory, and adds a --warm incremental-transfer mode.
• The nix-shell dev environment provides the full toolchain (clang-format, cppcheck, pytest-xdist, OpenSSH, rsync, iproute2, valgrind, lcov) and no longer builds on entry.

Security

• Enforce the daemon's per-module max connections cap (0 = unlimited) and add the shared per-source max connections per host cap plus a cross-process auth lockout. Because the listener forks one child per connection, the counters live in an anonymous shared mapping created before the accept loop and reclaimed by the parent's SIGCHLD handler, so the per-module, per-source and auth-failure state is shared across every child (including after SIGKILL). The per-source table has a bounded lifetime (expired/idle entries are reclaimed, with a rate-limited warning when genuinely full), and the occupancy counters are re-derived from the shared slot table on every child exit. Trusted loopback peers are exempt (they share one address); clients behind a shared NAT/proxy share a single per-host budget and lockout, which is documented.
• Hardening from a full security audit:
  • Fail a truncated zstd frame instead of spinning forever (remote DoS).
  • Open receiver destination/basis/hard-link entries O_NONBLOCK so a client-planted FIFO cannot block a worker indefinitely.
  • Require a regular file before --inplace writes, closing a FIFO-hang and a raw-device write that bypassed the --write-devices gate.
  • Reject SSH destinations whose user/host begins with - and insert -- before the host token, closing -o ProxyCommand=… argument injection (RCE).
  • Gate client --force recursive removal behind the server --allow-delete policy.
  • Reject empty hosts allow/hosts deny/auth users values instead of silently meaning "unrestricted".
  • Restrict TLS 1.2 to AEAD suites and set server cipher preference; load the private key TOCTOU-safely from an O_NOFOLLOW fd; verify IP literals against IP SANs; guard client-cert CN truncation.
  • Make --dry-run content-blind: it neither reads destination files nor hashes basis files, removing a 1-bit content oracle against read only modules.
  • Bound glob matching (iterative DP, no exponential backtracking) and bound line reads for filter/--files-from/pattern files.
  • Gate system.posix_acl_* xattrs on --acls and charge decompression/chunk allocations against the per-connection memory budget.

Fixed

• Pre-auth NULL dereference in config_delete() when an over-long basis_count (and the analogous count fields) was received and then failed validation; received counts are now validated before being published.
• Leaked inherited Data in the forked compression-truncation unit test (valgrind definite leak).
• receive_status() no longer loses a captured rejection reason when owed keepalives are drained.

[2.20.0] - 2026-09-13

Security

• Cap cumulative DirTimeList growth and bound pre-auth config-string memory (remote memory-exhaustion DoS).
• Daemon host access control (hosts allow/hosts deny, IPv4/IPv6/CIDR), configurable global max connections, connection audit logging, and a bounded auth failure delay throttle. IPv4-mapped peers are normalized and invalid patterns are rejected at parse time (no silent fail-open).
• Honor --timeout for protocol I/O and bound idle/session time to defeat keepalive slowloris; child-safe signal handling in the forked daemon.
• Compiler/linker hardening (_FORTIFY_SOURCE, stack protector, PIE, RELRO) and pinned build dependencies.

Fixed

• Use-after-free in the basis-dir oversize preflight.
• Placeholder Data leaks, missing_args leak, scanner chunk leak.
• Thread-safe logging; single fd owner and cleanup epilogue in the server handler.

Performance

• Metadata now crosses the wire as one packed frame (protocol 2.20.0).
• Delete keep-set and --files-from lookups indexed (O(n*m) → O(n)).
• Reused per-thread zstd contexts; TCP_NODELAY by default.
• Byte-bounded sender queues; removed a redundant scanner stat().

[2.19.0] - 2026-09-12

Security

• Daemon authentication rewritten as SCRAM-SHA-256 challenge/response (STATUS_AUTH_CHALLENGE → STATUS_AUTH_RESPONSE → STATUS_AUTH_OK/STATUS_AUTH_FAILED), replacing the old replayable static SHA-256(password) bearer credential. Each proof is bound to a fresh per-connection server nonce plus a client nonce, so a captured response can never be reused.
• Salted verifier store. --password-file/--early-input now hold user:$fastsync$1$pbkdf2-sha256$<iters>$<salt>$<stored_key>$<server_key> (PBKDF2-HMAC-SHA256, default 600000 iterations, range 100000–10000000). The legacy user:SHA256HEX form is hard-rejected; there is no auto-upgrade. Generate stores offline with fastsync-server --hash-credentials FILE [--iterations N].
• Username-enumeration hardening. Unknown/off-list users are answered with a dummy verifier whose salt is a deterministic per-username value (HMAC-SHA256(dummy_key, username)), using the store-wide uniform iteration count and a constant-time full-length membership scan. The dummy key is persisted in an owner-only <store>.dummykey sidecar (atomic publish, exact mode 0600) so challenges are stable across restarts.
• Verified transport for auth-required modules. A module with auth users accepts credentials only over verified TLS whose client certificate matches --client-cn, or — when --allow-unauthenticated is explicitly set — plaintext from a loopback peer. Remote plaintext is refused before any challenge. Clients must use --tls to send --password-file credentials to a non-loopback daemon; --client-cn is mandatory with --tls.
• Secret hygiene. The plaintext password, derived keys, nonces/proofs and the dummy key are wiped from memory on every path and never logged.
• Carried-over hardening: -K TOCTOU-safe directory walk (openat(O_NOFOLLOW) per component), always shell-quoted SSH remote path, TLS compression/renegotiation disabled, race-free (open-then-fstat) --password-file/--early-input checks, log-injection escaping, and lazy protocol debug escaping.

Added

• fastsync-server --hash-credentials FILE [--iterations N] offline tool.
• <store>.dummykey sidecar (auto-created, owner-only, 0600).
• Integration tests for auth replay rejection, malformed frames, legacy-store refusal, and the loopback/TLS transport policy; fuzz targets for config receive and daemon-auth parsing.

Changed

• Protocol version 2.18.0 → 2.19.0 (breaking). The config-frame auth block is now [present][username] (digest removed) and the auth challenge/response frames are interleaved between the config frame and its STATUS_OK. A 2.19.0 client and a 2.18.0 server (or vice versa) fail cleanly at the handshake.
• Daemon modules declaring auth users require a configured credential store at startup (fail closed); operators regenerate stores from plaintext with --hash-credentials.

Notes

• First tagged release. FastSync implements rsync-compatible file synchronization over TCP and SSH with TLS (OpenSSL), streaming zstd compression, multithreaded transfers, and incremental sync. See RSYNC_COMPAT.md for the flag-parity matrix.