Crate decmpfs 

decmpfs — apply the operating system’s transparent per-file compression to a file in place: macOS APFS (decmpfs), Linux btrfs, Windows NTFS. The kernel decompresses on read, so the file keeps its logical size + exact contents and loads at near-native speed while taking less space on disk.

compress_file(path) detects the filesystem, applies compression, then verifies the kernel reads the bytes back identically — rolling back on any failure. probe(path) is the detect-only / capability-reporting half.

Backends: btrfs (FS_COMPR_FL + the btrfs.compression property), NTFS (FSCTL_SET_COMPRESSION), and macOS decmpfs (resource fork, kernel-roundtrip verified); other targets report Unsupported.

Contract: every Outcome is a SUCCESS; Err is reserved for genuine I/O failures that leave the file’s integrity unknown. An unsupported FS, a permission/lock issue, an incompressible or too-large file are non-fatal Outcomes.

Panic-free invariant: the deny below keeps non-test code free of the obvious panic sources; all slice indexing is length-guarded.

Structs

Gate

The install-time gate: an optional glob AND an optional size predicate. A file matches only if BOTH present predicates pass (an absent half is vacuously true). Gate::default() is the fleet default — glob **/*.node, no size floor.

Enums

Error

Genuine failures only. A capability/permission gap is an Outcome, not an Error.

GateParseError

Why a Gate / SizePredicate string failed to parse.

Outcome

What happened to the file. Only Err is a hard failure.

SizePredicate

A >/>= comparison against a byte threshold.

SkipReason

Support

UnsupportedReason

Constants

DEFAULT_GLOB

The fleet default — every native addon, regardless of size.

Functions

compress_bytes

THE install-time entry point: write content to path as an OS-compressed file in ONE pass — never a write-then-read-back-recompress.

compress_file

THE entry point: detect → gate → apply → verify → rollback-on-failure. Idempotent. Never panics. Never corrupts the file.

probe

Detect-only, no mutation — for dry-run / capability reporting.