5.3 WireCompatibility and Envelope Decoding

WireCompatibility and Envelope Decoding

Fail-closed wire-schema gating in src/compatibility.rs. Crate semver (CARGO_PKG_VERSION) is independent of on-wire wire_version.

Constants

Constant	Value
WireCompatibility::CURRENT	1
WireCompatibility::MIN_SUPPORTED	1
WireCompatibility::LEGACY_UNVERSIONED	1

Classification

• classify_wire_version / WireCompatibility::classify → Compatibility::{Supported, TooOld, TooNew}
• accept_wire_version → SupportedWireVersion or CompatibilityError::TooOld{found, min} / TooNew{found, current}

Decode API

• decode_ipc_message_json(&[u8]) / decode_ipc_message_value(Value) — inspect wire_version before payload use; legacy unversioned tagged JSON accepted as wire v1.
• encode_ipc_message_json — non-canonical convenience encode (not the fixture generator).
• Canonical deterministic encode: encode_canonical_ipc_message.

Compatibility rules

1. Unknown fields ignored on structs and the top-level envelope.
2. Unknown IpcMessage variants fail deserialization (no Default, no catch-all).
3. Missing wire_version → treat as LEGACY_UNVERSIONED.

Errors

• CompatibilityError — version window miss
• EnvelopeError — wraps compatibility errors plus parse failures (NotAnObject, missing keys, payload/JSON errors)

See also 5.4 Canonical Wire-v1 Encoding.