Transport Stdio

AEP Transport Binding: stdio

> Status: draft. Part of the AEP 0.1 protocol specification.

Purpose

Define how AEP runs over standard input / standard output, supporting local process integration with no network dependency.

Framing

AEP over stdio uses newline-delimited JSON (NDJSON):

Each line is a complete, valid JSON-encoded AEP event.
Lines are separated by \n (LF).
Empty lines are ignored.
Neither side should emit partial or multi-line JSON.

Example stream:

{"aep_version":"0.1","id":"evt_01","type":"session.opened",...}
{"aep_version":"0.1","id":"evt_02","type":"session.ready",...}
{"aep_version":"0.1","id":"evt_03","type":"session.closed",...}

Direction

Stream	Direction	Purpose
`stdin`	Transport → Process	Inbound events (consumer receives)
`stdout`	Process → Transport	Outbound events (producer sends)
`stderr`	Process → Transport	Diagnostic output and error events

stderr may carry:

Non-JSON diagnostic messages
event.rejected or session.error events that could not be sent on stdout

Session Lifecycle

The process lifecycle maps directly to session lifecycle:

Process State	Session State	Notes
Start	`CREATED`
First `session.opened` on stdin	`OPENED`
`session.ready` sent on stdout	`READY`
Process exit (0)	`CLOSED`	Graceful shutdown
Process exit (non-0)	`ERROR`	Unexpected termination
stdin closed	`CLOSED`	Remote peer disconnected
Broken pipe on stdout	`CLOSED`	Remote peer disconnected

Error Handling

Malformed JSON (parse error): respond with event.rejected on stderr.
Write failure (broken pipe): treat as session close, exit cleanly.
Stdin closed unexpectedly: send session.closed on stdout if still open, then exit.

Implementation Notes

The transport binding is OS-independent. On Windows, the process must handle \r\n gracefully (the reader should accept \r\n as a line terminator).
Payload size is limited by available memory. Implementations may set a max_payload_size in capability negotiation.
See the session lifecycle specification for session state machine details.