Structured Clone Algorithm for cross-thread data serialization #178

Phase 19: Web Workers#

Implement the WHATWG Structured Clone algorithm so JS values can be safely transferred across worker thread boundaries via postMessage.

What to implement#

Add a structured_clone module in crates/js/src/:

• Serialization (serialize(value: &JsValue) -> Result<SerializedData, CloneError>): walk the JS value graph and produce a self-contained, heap-allocation-free byte representation. Support:
  • Primitives: undefined, null, boolean, number, string, BigInt
  • Plain objects and arrays (recursively)
  • ArrayBuffer (copy bytes)
  • TypedArrays (Uint8Array, Int32Array, Float64Array, etc.) and DataView
  • Map, Set
  • Date (serialize as milliseconds since epoch)
  • Transferable placeholder for future ArrayBuffer transfer (mark as transferred, zero original)
• Deserialization (deserialize(data: SerializedData, context: &mut JsContext) -> JsValue): reconstruct the value in the target context's heap.
• Error handling: non-cloneable values (functions, DOM nodes, Symbols) return CloneError::NotSerializable which maps to a DataCloneError JS exception.

Acceptance criteria#

• Round-trip test: serialize then deserialize a deeply nested object with arrays, numbers, strings, and an ArrayBuffer; assert structural equality.
• Functions and DOM nodes produce CloneError::NotSerializable.
• cargo test -p we-js passes.