Struct CodecCaps 

pub struct CodecCaps {
    pub encode: bool,
    pub decode: bool,
    pub parallel_encode: bool,
    pub parallel_decode: bool,
    pub frame_index: bool,
    pub detects_corruption: CorruptionDetection,
    pub memory_per_worker: Option<u64>,
    pub weak_encoder: bool,
    pub truncation_undetectable: bool,
}

What a codec can do. Every field defaults to false (or, for detects_corruption, its equivalent conservative variant): a backend must opt in.

Fields

encode: bool

decode: bool

parallel_encode: bool

parallel_decode: bool

frame_index: bool

Stream carries a frame/block index enabling random access.

detects_corruption: CorruptionDetection

See CorruptionDetection for what each state promises.

memory_per_worker: Option<u64>

Rough working-set cost of one encode worker, in bytes, when the codec knows it. None means unknown — assume modest.

A static, conservative HIGH figure for callers who introspect CodecCaps without encoding anything (property 12’s own governor sizing, and each codec’s clamp test) — it is not what the governor actually divides by during a real encode. The four codecs Phase 1f gave a multi-threaded encoder (zstd-c, xz-c, xz-pure, lzip) each call their own level-aware per_worker_bytes(level) for that, because the true cost varies by preset (roughly 128 MiB below preset 7, ~896 MiB at 7 and above, for xz and lzip) and this field’s contract is to round up to a single figure that covers every level a caller might ask for.

weak_encoder: bool

This build’s encoder for the format is markedly worse than the format’s usual one — a fallback that produces valid output nobody would choose.

ops refuses to use it unless the caller opts in, because the output is indistinguishable afterwards: a user who asked for .xz expects xz ratios, and two builds of stuffr would otherwise produce very different files from an identical command with no way to tell which they got.

truncation_undetectable: bool

True only when the format itself carries no signal whatsoever — no checksum, no length, no structural decode constraint, no end-of-stream marker — that could ever distinguish a truncated stream from a complete one. This does NOT exempt a codec from conformance property 10 (truncation, conformance.rs) — property 10 has no bare skip for any declaration, deliberately: conformance.rs’s own mod broken_codecs keeps testing::MockCodec, a bare unframed XOR pass-through, specifically UNABLE to clear property 10 (mock_codec_clears_every_property_up_to_truncation), and a codec that answered nothing at all about truncation would be indistinguishable from one that never checked.

What this field switches property 10 to instead is a WEAKER, but still falsifiable, property: on truncated input, the decoder must either error, or produce a byte sequence that is a genuine prefix of what the same decoder produces from the untruncated input — one that never shrinks as a less severe truncation is tried (monotonicity across the several cut lengths property 10 already sweeps), and that is not trivially empty when the untruncated decode is not (closing the residual gap a bare prefix check alone leaves: the empty string is a prefix of everything). That still catches real defect classes — a decoder that mishandles a partial final unit and emits wrong trailing bytes, reordered bytes, or fabricated padding fails this exactly as it would fail the strict “must always error” property, and one that always answers empty on truncation fails it too — while not demanding a guarantee the format cannot give. conformance.rs’s a_decoder_that_returns_a_non_prefix_on_truncation_is_caught and a_decoder_that_always_answers_empty_on_truncation_is_caught prove the weaker check still fires, by mutation, the same way mock_codec_clears_every_property_up_to_truncation proves the strict one does.

Every real codec so far closes the gap the strict property demands: a mandatory checksum (gzip, zlib, bzip2, snappy), a per-writer optional one this build’s own encoder always turns on (zstd, xz, lz4), structural invalidity from a range coder (LZMA1), or, for a codec with neither, an explicit end-of-stream signal (raw deflate’s BFINAL bit — see deflate.rs).

legacy::compress_z (Phase 3b) is the first exception, and this field exists because of it, not in anticipation of it: Unix compress’s LZW code stream has none of the above. A prefix of a valid stream decodes via the identical state machine as the full stream and simply runs out of bits, producing a shorter but otherwise byte-correct PREFIX of the real output with no error — measured directly, at the bit level, on this project’s own hello.Z fixture: cutting 1, 25 or 50 of its 51 bytes left between 5 and 7 leftover, unconsumed bits in every case, including the GENUINE, untruncated end (6 leftover bits) — no leftover count or value distinguishes a real ending from a truncated one, because both stop for the identical reason (too few bits left for the next code). Confirmed independently against two production reference tools, not just this crate: /usr/bin/uncompress and /usr/bin/gzip -dc on macOS both exit 0 with silently-partial output on the same cut files, and in every case what they emit is a strict prefix of the untruncated decode — never garbage, never a differently-ordered or padded result. This is a real, external, cross-validated fact about the format, not a gap in compress_z’s own decoder — see that module’s doc for the full measurement.

Defaults to false (the strict property applies) via Self::round_trip and Self::decode_only, so every existing codec’s behavior — including testing::MockCodec’s own deliberate failure above — is unchanged; only compress_z::CompressZ sets this explicitly.

Implementations

impl CodecCaps

pub const fn round_trip() -> Self

A codec that both compresses and decompresses, with no parallelism and no frame index. The common shape.

pub const fn decode_only() -> Self

A decode-only codec — the pure-Rust fallbacks that let a build with no C toolchain still open a .zst or .xz.

Trait Implementations

impl Clone for CodecCaps

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for CodecCaps

impl Debug for CodecCaps

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for CodecCaps

fn default() -> Self

Returns the “default value” for a type.

impl Eq for CodecCaps

impl PartialEq for CodecCaps

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for CodecCaps