Files
codex/codex-rs/app-server-client
Eric Traut 79ea577156 TUI: Keep remote app-server events draining (#18932)
Addresses #18860

Problem: Remote app-server clients could stop draining websocket events
when their bounded local event channel filled, leaving clients stuck on
stale in-progress turns after a disconnect.

Solution: Use an unbounded local event channel for the remote client so
the websocket reader can keep forwarding disconnect and progress events
instead of blocking or dropping them.

Why this is reasonable: This does not make the remote websocket itself
unbounded. The changed queue lives inside the remote client, between the
task that reads the remote websocket and the API consumer in the same
client process. Once an event has been received from the remote server,
preserving it is preferable to blocking websocket reads or dropping
disconnect/lifecycle events; network-level backpressure still happens at
the websocket boundary if the remote side outpaces the client.
2026-04-22 09:29:34 -07:00
..

codex-app-server-client

Shared in-process app-server client used by conversational CLI surfaces:

  • codex-exec
  • codex-tui

Purpose

This crate centralizes startup and lifecycle management for an in-process codex-app-server runtime, so CLI clients do not need to duplicate:

  • app-server bootstrap and initialize handshake
  • in-memory request/event transport wiring
  • lifecycle orchestration around caller-provided startup identity
  • graceful shutdown behavior

Startup identity

Callers pass both the app-server SessionSource and the initialize client_info.name explicitly when starting the facade.

That keeps thread metadata (for example in thread/list and thread/read) aligned with the originating runtime without baking TUI/exec-specific policy into the shared client layer.

Transport model

The in-process path uses typed channels:

  • client -> server: ClientRequest / ClientNotification
  • server -> client: InProcessServerEvent
    • ServerRequest
    • ServerNotification
    • LegacyNotification

JSON serialization is still used at external transport boundaries (stdio/websocket), but the in-process hot path is typed.

Typed requests still receive app-server responses through the JSON-RPC result envelope internally. That is intentional: the in-process path is meant to preserve app-server semantics while removing the process boundary, not to introduce a second response contract.

Bootstrap behavior

The client facade starts an already-initialized in-process runtime, but thread bootstrap still follows normal app-server flow:

  • caller sends thread/start or thread/resume
  • app-server returns the immediate typed response
  • richer session metadata may arrive later as a SessionConfigured legacy event

Surfaces such as TUI and exec may therefore need a short bootstrap phase where they reconcile startup response data with later events.

Backpressure and shutdown

  • Queues are bounded and use DEFAULT_IN_PROCESS_CHANNEL_CAPACITY by default.
  • Full queues return explicit overload behavior instead of unbounded growth.
  • shutdown() performs a bounded graceful shutdown and then aborts if timeout is exceeded.

If the client falls behind on event consumption, the worker emits InProcessServerEvent::Lagged and may reject pending server requests so approval flows do not hang indefinitely behind a saturated queue.