roboto.formats.mcap.msgpack_decoder_factory

MCAP decoder factory for msgpack-encoded messages.

Exposes an mcap.decoder.DecoderFactory that decodes msgpack messages (typically described by a jsonschema schema), for use by McapReader. Decoding is delegated to the shared Rust decoder (the mcap_codec extension built from roboto-mcap-codec), which returns nested dict / list / scalar values.

Known limitation: msgpack-numpy ndarray fields — nested maps with binary keys (nd/type/shape/data), used by compressed-video packet payloads — are silently dropped by the codec: the field decodes to an empty {} and the payload bytes are unrecoverable downstream. Every other field of such a message decodes normally. Tracked in roboto-ai/roboto-mcap-codec#5; until that lands, consumers must treat non-bytes payload fields as undecodable rather than assume frame data is present.

Module Contents

exception roboto.formats.mcap.msgpack_decoder_factory.MsgpackDecodeError

Bases: mcap.exceptions.McapError

Raised when a msgpack message cannot be decoded.

class roboto.formats.mcap.msgpack_decoder_factory.MsgpackDecoderFactory

Bases: mcap.decoder.DecoderFactory

Decode msgpack-encoded MCAP messages via the shared Rust mcap_codec decoder.

Supply an instance to mcap.reader.make_reader(). The schema is parsed once per schema id; the returned callable then decodes each message into nested dict / list / scalar values.

decoder_for(message_encoding, schema)

If the message encoding and schema arguments can be decoded by this decoder factory, returns a callable to decode message bytes.

Parameters:

• message_encoding (str)

• schema (Optional[mcap.records.Schema])

Return type:

Optional[Callable[[bytes], Any]]

roboto.formats.mcap.msgpack_decoder_factory.make_msgpack_decoder_factory()

Build a decoder factory for msgpack-encoded messages, backed by the shared Rust mcap_codec decoder.

Return type:

MsgpackDecoderFactory