Async transport trait, frame wire format, codecs, mock transport, Unix sockets, vsock ports, and TEE protocol types.

Common Transport

a3s_common::transport provides a small async framed transport abstraction for local IPC, test transports, and TEE-oriented protocol messages.

Frame Format

Frames use a fixed header:

[type:u8][length:u32 big-endian][payload:length bytes]

Item	Current value
Header size	5 bytes
Max payload	16 MiB
Frame types	`Data`, `Control`, `Heartbeat`, `Error`, `Close`

Frame::decode returns None for incomplete buffers and errors on unknown frame types or payloads above the maximum.

Codec

Type	Role
`FrameReader<R>`	Buffers any `AsyncRead` stream and yields complete frames.
`FrameWriter<W>`	Writes frames to any `AsyncWrite` stream.
`FrameCodec<R, W>`	Combines split read/write halves.

FrameWriter includes helpers for data frames, control frames, and JSON-serializable payloads.

Transport Trait

Transport is Send + Sync + Debug and provides async connect, send, recv, close, and connection-state methods. The default frame methods bridge raw byte send/receive with Frame values.

MockTransport is an in-memory implementation with an optional response handler and a sent-message log for tests.

On Unix platforms, UnixTransport wraps tokio::net::UnixStream and uses the common frame codec. UnixListener binds a socket path, removes a stale socket file if present, and yields accepted UnixTransport connections.

Well-Known Ports

The crate exposes vsock port constants:

Constant	Port	Purpose
`GRPC_AGENT`	`4088`	gRPC agent control channel.
`EXEC_SERVER`	`4089`	Guest command execution.
`PTY_SERVER`	`4090`	Interactive terminal.
`TEE_CHANNEL`	`4091`	Secure channel.

TEE Protocol Types

TEE messages include requests, responses, heartbeats, and errors. Request types cover session initialization, message processing, tool execution, protected value storage/retrieval/deletion, session state, and termination.

Transport