FastSync/RSYNC_COMPAT.md

Rsync Feature Compatibility

This document maps rsync's full feature set to FastSync's current implementation status.

Summary

Status	Count	Description
✅ Implemented	35	Feature works end-to-end
🔀 Alt Arg	4	Functionality exists but under different flag/semantics
⚠️ Partial	5	Flag parsed/stored but behavior incomplete
🔄 Compatibility No-op	1	Flag is accepted for CLI compatibility but has no effect
❌ Not Implemented	95	Flag not recognized or no behavior
Total	141

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1. General Options

Flag	Rsync Description	FastSync Status	Notes
-a, --archive	Archive mode is -rlptgoD	🔀 Alt Arg	Maps to -c -m -M (compression + multithread + metadata)
-v, --verbose	Increase verbosity	✅ Implemented	Sets log_level=DEBUG
-q, --quiet	Suppress non-error messages	✅ Implemented	Suppresses client output while preserving errors
--help	Show help	✅ Implemented	Prints usage and exits; -h is not accepted
-V, --version	Print version	✅ Implemented
--info=FLAGS	Fine-grained info verbosity	✅ Implemented	Supports copy, misc, skip, stats, all, and none; explicit flags override --verbose, and none suppresses info output; unsupported names are rejected
--debug=FLAGS	Fine-grained debug verbosity	✅ Implemented	io, proto, pack, and util are supported; --debug=help lists flags; other rsync categories are rejected
--stderr=MODE	Change stderr output mode	⚠️ Partial	errors (default) and all are supported; client is rejected because FastSync has no rsync message channel
--no-motd	Suppress daemon MOTD	❌ Not Implemented
--exclude=PATTERN	Exclude files matching pattern	✅ Implemented	Glob matching in scanner
--include=PATTERN	Include files matching pattern	✅ Implemented	Glob matching in scanner
-C, --cvs-exclude	Auto-ignore CVS files	❌ Not Implemented	Removed because it had no effect

2. Modifying Output

Flag	Rsync Description	FastSync Status	Notes
--stats	Give transfer stats	✅ Implemented	Prints file/byte counts
-h, --human-readable	Human-readable numbers	✅ Implemented	Formats transfer byte sizes using binary units
-i, --itemize-changes	Per-file change summary	❌ Not Implemented	Removed because it had no effect
--progress	Show progress	✅ Implemented	Progress callback in sender
-P	Same as --partial --progress	⚠️ Partial	Parses and enables progress, but interrupted files are not retained for resumable transfers
--out-format=FORMAT	Custom output format	❌ Not Implemented	Removed because it had no effect
--log-file=FILE	Log to file	✅ Implemented	log_file config field
--log-file-format=FMT	Log format	❌ Not Implemented
--8-bit-output, -8	Leave high-bit chars unescaped	✅ Implemented	Applies to displayed paths and protocol debug output
--list-only	List files instead of copying	❌ Not Implemented	Removed because it had no effect

3. File Selection

Flag	Rsync Description	FastSync Status	Notes
--exclude-from=FILE	Read exclude patterns from file	✅ Implemented	Reads patterns from file
--include-from=FILE	Read include patterns from file	✅ Implemented	Reads patterns from file
--filter=RULE	Add file-filtering rule	❌ Not Implemented	Removed because it had no effect
--files-from=FILE	Read source file list from file	❌ Not Implemented	Removed because it had no effect
-0, --from0	Delimit *-from files with NULs	❌ Not Implemented
--max-size=SIZE	Skip files larger than SIZE	✅ Implemented	max_size in scanner
--min-size=SIZE	Skip files smaller than SIZE	✅ Implemented	min_size in scanner
-I, --ignore-times	Don't skip files matching size+time	❌ Not Implemented
--size-only	Skip based on size only	✅ Implemented	With --incremental, ignores mtime
-@, --modify-window=NUM	Mod-time comparison accuracy	✅ Implemented	Whole-second tolerance with nanosecond-aware comparisons
--existing	Skip creating new files on receiver	✅ Implemented	Existing destination files continue through normal update handling
--ignore-existing	Skip updating existing files	❌ Not Implemented
--remove-source-files	Sender removes regular files after confirmed transfer	✅ Implemented

4. Directory Options

Flag	Rsync Description	FastSync Status	Notes
-r, --recursive	Recurse into directories	✅ Implemented	Default behavior
-R, --relative	Use relative path names	❌ Not Implemented	Removed because it had no effect
--no-implied-dirs	Don't send implied dirs with -R	❌ Not Implemented
-d, --dirs, --old-dirs, --old-d	Transfer dirs without recursing	❌ Not Implemented	The aliases are recognized and rejected explicitly; they depend on the unimplemented --dirs behavior
--mkpath	Create missing path components	❌ Not Implemented

5. Transfer Modifications

Flag	Rsync Description	FastSync Status	Notes
-u, --update	Skip files newer on receiver	❌ Not Implemented	Removed because it had no effect
--inplace	Update files in-place	✅ Implemented	Direct write mode
--append	Append data to shorter files	❌ Not Implemented	Removed because it had no effect
--append-verify	Append with old-data checksum	❌ Not Implemented	Removed because it had no effect
-W, --whole-file	Copy whole file (no delta)	❌ Not Implemented
--block-size=SIZE	Force checksum block-size	⚠️ Partial	Parsed as --delta-block; controls delta transfer block size

6. Destination Handling

Flag	Rsync Description	FastSync Status	Notes
-n, --dry-run	Trial run with no changes	✅ Implemented	dry_run config field
-b, --backup	Make backups of overwritten files	✅ Implemented	Backup before overwrite
--backup-dir=DIR	Backup directory hierarchy	✅ Implemented	backup_dir config field
--suffix=SUFFIX	Backup suffix (default ~)	✅ Implemented	suffix config field
--delay-updates	Put updated files in place at end	❌ Not Implemented

7. Deletion

Flag	Rsync Description	FastSync Status	Notes
--delete	Delete extraneous files from dest	✅ Implemented	use_delete config field
--delete-before	Delete before transfer	❌ Not Implemented	Removed because it had no effect
--del, --delete-during	Delete during transfer	❌ Not Implemented	Both flags are recognized but rejected; delete timing is not implemented
--delete-delay	Find deletions during, delete after	❌ Not Implemented
--delete-after	Delete after transfer	❌ Not Implemented	Removed because it had no effect
--delete-excluded	Also delete excluded files	❌ Not Implemented	Removed because it had no effect
--max-delete=NUM	Max files to delete	❌ Not Implemented	Removed because it had no effect
--ignore-errors	Delete even with I/O errors	❌ Not Implemented
--force	Force deletion of non-empty dirs	❌ Not Implemented
--prune-empty-dirs	Prune empty dir chains	❌ Not Implemented	Removed because it had no effect

8. Metadata Preservation

Flag	Rsync Description	FastSync Status	Notes
-M, --preserve	Preserve file metadata	✅ Implemented	Mode, uid, gid, mtime
-p, --perms	Preserve permissions	🔀 Alt Arg	-p means SSH port; permissions preserved via -M/--preserve
-o, --owner	Preserve owner	✅ Implemented	Part of -M
-g, --group	Preserve group	✅ Implemented	Part of -M
-t, --times	Preserve modification times	✅ Implemented	Part of -M
-E, --executability	Preserve executability	✅ Implemented	Preserves executable permission bits (implies metadata preservation)
--chmod=CHMOD	Affect file permissions	✅ Implemented	Supports numeric and symbolic ugo rwx changes; retains receiver safety masking
-A, --acls	Preserve ACLs	❌ Not Implemented	Removed because it had no effect
-X, --xattrs	Preserve extended attributes	❌ Not Implemented	Removed because it had no effect
-H, --hard-links	Preserve hard links	❌ Not Implemented	Removed because it had no effect
-D	Same as --devices --specials	❌ Not Implemented	Removed because device-file handling is not implemented
--devices	Preserve device files	❌ Not Implemented	Removed because it had no effect
--specials	Preserve special files	❌ Not Implemented
--copy-devices	Copy device contents as file	❌ Not Implemented
--write-devices	Write to devices as files	❌ Not Implemented
-U, --atimes	Preserve access times	❌ Not Implemented
-N, --crtimes	Preserve create times	❌ Not Implemented
-O, --omit-dir-times	Omit dirs from --times	❌ Not Implemented
-J, --omit-link-times	Omit symlinks from --times	❌ Not Implemented
--super	Receiver attempts super-user activities	❌ Not Implemented
--fake-super	Store/recover privileged attrs via xattrs	❌ Not Implemented

9. Symlink Handling

Flag	Rsync Description	FastSync Status	Notes
-l, --links	Copy symlinks as symlinks	⚠️ Partial	Scanner includes symlinks; target path not transmitted
-L, --copy-links	Transform symlink to referent	✅ Implemented	copy_links config field
--copy-unsafe-links	Transform unsafe symlinks	✅ Implemented	copy_unsafe_links config field
--safe-links	Ignore symlinks outside tree	✅ Implemented	safe_links config field
--munge-links	Munge symlinks for safety	❌ Not Implemented
-k, --copy-dirlinks	Transform symlink to dir	❌ Not Implemented
-K, --keep-dirlinks	Treat symlinked dir as dir	❌ Not Implemented

10. Sparse & Device

Flag	Rsync Description	FastSync Status	Notes
-S, --sparse	Sparse block handling	⚠️ Partial	Flag is accepted, but full hole preservation is not implemented
--preallocate	Allocate dest files before writing	❌ Not Implemented

11. Checksum & Comparison

Flag	Rsync Description	FastSync Status	Notes
--checksum	Skip based on checksum	✅ Implemented	With --incremental, compares xxHash64 content checksums; -c remains compression
--checksum-choice=STR	Choose checksum algorithm	❌ Not Implemented	xxHash used internally
--compare-dest=DIR	Compare dest files relative to DIR	❌ Not Implemented	Removed because it had no effect
--copy-dest=DIR	Include copies of unchanged files	❌ Not Implemented	Removed because it had no effect
--link-dest=DIR	Hardlink to files when unchanged	❌ Not Implemented	Removed because it had no effect
--fuzzy, --no-fuzzy	Find similar file for basis	❌ Not Implemented

12. Compression

Flag	Rsync Description	FastSync Status	Notes
-z, --compress	Compress file data	🔀 Alt Arg	Always uses zstd (rsync supports multiple algorithms)
--compress-choice=STR, --zc=STR	Choose compression algorithm	✅ Implemented	FastSync supports zstd and none
--compress-level=NUM, --zl=NUM	Set compression level	✅ Implemented	1-22, default 5
--compress-threads=NUM	Set compression threads	❌ Not Implemented
--skip-compress=LIST	Skip compress for suffixes	✅ Implemented	Comma-separated, case-insensitive suffix list; empty list skips none; incompatible with FastSync chunk serialization (-s)

13. Connectivity

Flag	Rsync Description	FastSync Status	Notes
-e, --rsh=COMMAND	Remote shell to use	❌ Not Implemented	Removed; SSH invokes ssh directly
--rsync-path=PROGRAM	rsync binary on remote	❌ Not Implemented	Removed; use --fastsync-server-path
--port=PORT	Alternate daemon port	✅ Implemented	server_port config field
--sockopts=OPTIONS	Custom TCP options	❌ Not Implemented
--blocking-io	Use blocking I/O for remote shell	❌ Not Implemented
--outbuf=N|L|B	Set output buffering	❌ Not Implemented
--address=ADDRESS	Bind address for outgoing socket	❌ Not Implemented	Removed because it had no effect
-4, --ipv4	Prefer IPv4	❌ Not Implemented	Removed because it had no effect
-6, --ipv6	Prefer IPv6	❌ Not Implemented	Removed because it had no effect

14. Daemon Mode

Flag	Rsync Description	FastSync Status	Notes
--daemon	Run as rsync daemon	❌ Not Implemented	Removed because it had no effect
--config=FILE	Alternate rsyncd.conf file	❌ Not Implemented	Removed because it had no effect
--dparam=OVERRIDE	Override global daemon config	❌ Not Implemented
--no-detach	Don't detach from parent	❌ Not Implemented
--password-file=FILE	Read daemon password from file	❌ Not Implemented
--early-input=FILE	Use FILE for daemon early exec	❌ Not Implemented

15. Safety & Security

Flag	Rsync Description	FastSync Status	Notes
Path escape detection	Ensure files stay within root	✅ Implemented	has_path_traversal() + realpath
Symlink-safe delete	Skip symlinks in delete walk	✅ Implemented	delete_extras_walk()
Protocol version check	Verify compatible versions	✅ Implemented	config_receive()
Max data/string/chunk sizes	Prevent OOM attacks	✅ Implemented	Per-message limits
Per-connection memory limit	1GB per connection	✅ Implemented	MAX_CONNECTION_MEMORY
--trust-sender	Trust remote sender's file list	❌ Not Implemented
--old-args	Disable modern arg protection	✅ Implemented	SSH-only legacy mode; restores raw remote command construction and permits shell interpretation of the configured server path
--ignore-missing-args	Ignore missing source args	❌ Not Implemented
--delete-missing-args	Delete missing source args	❌ Not Implemented

16. Batch Operations

Flag	Rsync Description	FastSync Status	Notes
--write-batch=FILE	Write batched update to file	❌ Not Implemented
--only-write-batch=FILE	Write batch without updating dest	❌ Not Implemented
--read-batch=FILE	Read batched update from file	❌ Not Implemented

17. Advanced

Flag	Rsync Description	FastSync Status	Notes
--stop-after=MINS	Stop after N minutes	❌ Not Implemented
--stop-at=TIME	Stop at specified time	❌ Not Implemented
--fsync	Fsync every written file before publication	✅ Implemented
--protocol=NUM	Force older protocol version	❌ Not Implemented
--iconv=CONVERT_SPEC	Charset conversion	❌ Not Implemented
--checksum-seed=NUM	Set checksum seed	❌ Not Implemented
--secluded-args	Use protocol to send args	🔄 Compatibility No-op	Accepted for CLI compatibility; it does not change FastSync transport or protocol behavior. -s remains chunk serialization.
--no-OPTION	Turn off implied option	✅ Supported	Supported boolean FastSync options and archive-implied options; unsafe or value-taking options are rejected.

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Recommendations: Top Features to Implement Next

Ranked by user demand, implementation complexity, and interoperability impact:

Priority	Feature	Effort	Impact
1	--whole-file / -W	Low	High — users expect opt-out of delta
2	--ignore-times / -I	Low	Medium — useful for forcing re-transfer
3	--size-only	Low	Medium — common migration scenario
4	--ignore-existing	Low	Medium — common sync patterns
5	--existing	Low	Medium — common sync patterns
6	--remove-source-files	Low	High — common for moves/backup
7	--delete-during	Medium	High — performance improvement
8	--delay-updates	Medium	High — atomic updates
9	--chmod	Low	Medium — permission flexibility
10	--executability / -E	Low	Low — simple flag
11	--skip-compress	Low	Medium — performance tuning

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FastSync-Specific Features (Not in rsync)

Feature	Description
-m	Multithreaded pipeline (scanner/loader/sender)
-s	Chunk serialization mode
-f / --sendfile	Zero-copy sendfile() syscall (TCP only)
-c [level]	zstd compression level (1-22)
--chunk-size	Configurable chunk size
--tls	TLS encryption (mutual auth)
--fastsync-server-path	Path to fastsync-server binary
--server-host / --server-port	Direct TCP connection
Incremental sync	Skip unchanged files (size+mtime)
Delta transfer	Block-level delta for changed files