Protocol

The Talos protocol is defined in talos-common.

The protocol module owns schema and framing types: request/response enums, topic data types, DynValue, stream headers, and the length-prefixed bincode codec. The application-facing client API lives in session, while socket and stream setup lives in transport.

Control messages use a four-byte big-endian length prefix followed by a bincode-encoded payload. The codec is implemented around Tokio async I/O and is used by both UDS and QUIC control paths.

Requests

Clients send Request values:

• ListTopics
• ListNodes
• ListPoses
• Subscribe { topics }
• Unsubscribe { topics }
• SetJointPosition { joint, position }
• ExecutePose { name }
• ListParameters { node }
• GetParameters { node, names }
• SetParameter { node, name, value }
• GetTopicStats
• GetTopicEndpoints { topic }
• GetLoggerLevel { node, logger }
• SetLoggerLevel { node, logger, level }

Responses

The agent replies with Response values:

• TopicList
• NodeList
• PoseList
• Subscribed
• Unsubscribed
• TopicData
• Parameters { node, parameters }
• ParameterSet { node, name, successful, reason }
• Ok
• Error
• TopicStats (list of { topic, rate_hz, bandwidth_bps, latency_ms })
• TopicEndpoints { topic, publishers, subscribers }. Each endpoint has its node, type and QoS (reliability, durability, history, deadline).
• LoggerLevel { node, logger, level }
• LoggerLevelSet { node, logger, successful, reason }

UDS carries control responses and topic data on the same framed connection. Because that connection carries data for multiple topics, UDS topic frames keep the topic name and type in each TopicData response.

QUIC uses a bidirectional stream for control and server-initiated unidirectional streams for topic data. A topic stream starts with a StreamHeader containing the topic and type name, then carries TopicFrame values with timestamp and data.

DynValue

DynValue is the generic representation clients receive for ROS 2 message payloads. It can represent:

• Booleans.
• Signed and unsigned integer primitives.
• f32 and f64.
• Strings.
• Byte arrays.
• Arrays of other DynValue values.
• Structs with an ordered field list.

The agent handles typed ROS 2 subscriptions and conversions. Clients render or print the resulting DynValue tree without knowing the original ROS 2 message type at compile time.

Frame Limits

Oversized frames are rejected by the codec. The default maximum frame size is intended to protect the agent and clients from unbounded buffering.