9.4 Decoding and validation

A missing required field → DecodeError.Missing.
A value that fails the invariant of a refined type or an invariant → DecodeError.Invalid.
Unknown fields are skipped; with @preserve_unknown on the type they are preserved and written back on re-serialisation. @preserve_unknown is allowed only on data (otherwise the compile error schema-attr) and acts only in the OxL binary format: the preserved raw records (tag and value) are written after the known fields in the order they were read; JSON, MessagePack and CBOR neither read nor write unknown fields. Nested messages keep their own unknown fields if they have the attribute. Preserved fields do not take part in ==, the hash and Show (D-8053; DIV-005; D-7610).
An unknown variant of an @open enum is mapped to the automatic variant Unknown(tag: u32).
In an rpc, a request decoding error is returned to the client as ProtocolError.InvalidArgument; the handler is not called.

See also