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Gateway lock

Last updated: 2025-12-11

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Why

  • Ensure only one gateway instance runs per host.
  • Survive crashes/SIGKILL without leaving stale lock files.
  • Fail fast with a clear error when the control port is already occupied.

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Mechanism

  • The gateway binds the WebSocket listener (default ws://127.0.0.1:18789) immediately on startup using an exclusive TCP listener.
  • If the bind fails with EADDRINUSE, startup throws GatewayLockError("another gateway instance is already listening on ws://127.0.0.1:<port>").
  • The OS releases the listener automatically on any process exit, including crashes and SIGKILL—no separate lock file or cleanup step is needed.
  • On shutdown the gateway closes the WebSocket server and underlying HTTP server to free the port promptly.

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Error surface

  • If another process holds the port, startup throws GatewayLockError("another gateway instance is already listening on ws://127.0.0.1:<port>").
  • Other bind failures surface as GatewayLockError("failed to bind gateway socket on ws://127.0.0.1:<port>: …").

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Operational notes

  • If the port is occupied by another process, the error is the same; free the port or choose another with clawdbot gateway --port <port>.
  • The macOS app still maintains its own lightweight PID guard before spawning the gateway; the runtime lock is enforced by the WebSocket bind.