Crate zerodds_flatdata 

FlatStruct trait + slot header for zero-copy same-host pub/sub.

Crate zerodds-flatdata. Safety classification: STANDARD.

Spec: docs/specs/zerodds-flatdata-1.0.md.

Safety rationale

This crate implements an unsafe trait FlatStruct whose guarantees (Copy + repr(C) + ’static + no pointers/Vec/String) the implementer assures via unsafe impl. The as_bytes / from_bytes_unchecked helpers are then safe by layout — we localize the unsafe island here instead of scattering it into the DataWriter path.

Structs

FlatReader

Reads FlatStruct samples directly from SHM slots.

FlatSampleRef

Reference sample that holds its source slot for the duration of its lifetime and sets this reader’s bit on Drop (releasing the slot for recycling). Spec §9.2/§9.3. Returned by FlatReader::read_ref.

FlatSlot

Loaned slot. The caller sets the sample via write() and then calls commit(). Dropping without a commit discards the loan.

FlatWriter

Writes FlatStruct samples directly into SHM slots — without CDR encoding.

InMemorySlotAllocator

In-memory slot allocator. Provides the same SlotBackend interface as the POSIX mmap backend (posix.rs), but lives on the process heap — single-process pub/sub and test setups without an mmap dep.

PosixSlotAllocator

POSIX mmap slot allocator. An owner process creates the segment; consumer processes attach via attach.

ShmLocator

SHM locator: all the data a same-host reader needs to attach to a writer SHM segment.

SlotHandle

Slot identification: (segment_id, slot_index).

SlotHeader

Slot header — set by the writer in commit_slot and interpreted by the reader in read_flat.

Enums

LocatorError

Error during encode/decode.

PosixSlotError

Error while setting up the POSIX segment.

SlotError

Error during slot management.

Constants

SLOT_HEADER_SIZE

Size of the slot header in bytes.

Traits

FlatStruct

Marker trait for FlatData-capable types.

SlotBackend

Backend trait for the SHM slot allocator.

Functions

fnv1a_32

FNV-1a hash of the hostname (32-bit). Set by the writer during discovery; the reader checks it against its own.

is_same_host

Same-host match helper. The caller passes (local hostname, local uid) and a received ShmLocator; returns true when both match — i.e. we can mmap the segment.

Type Aliases

ReaderMask

Bitmap (32 bit) — one bit per reader slot. Bit set = reader has read. The slot becomes reservable again when all active reader bits are set, or the timeout has elapsed.