29 lines
1.6 KiB
Markdown
29 lines
1.6 KiB
Markdown
---
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summary: "Gateway singleton guard using the WebSocket listener bind"
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read_when:
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- Running or debugging the gateway process
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- Investigating single-instance enforcement
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---
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# Gateway lock
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Last updated: 2025-12-11
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## Why
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- Ensure only one gateway instance runs per base port on the same host; additional gateways must use isolated profiles and unique ports.
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- Survive crashes/SIGKILL without leaving stale lock files.
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- Fail fast with a clear error when the control port is already occupied.
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## Mechanism
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- The gateway binds the WebSocket listener (default `ws://127.0.0.1:18789`) immediately on startup using an exclusive TCP listener.
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- If the bind fails with `EADDRINUSE`, startup throws `GatewayLockError("another gateway instance is already listening on ws://127.0.0.1:<port>")`.
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- The OS releases the listener automatically on any process exit, including crashes and SIGKILL—no separate lock file or cleanup step is needed.
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- On shutdown the gateway closes the WebSocket server and underlying HTTP server to free the port promptly.
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## Error surface
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- If another process holds the port, startup throws `GatewayLockError("another gateway instance is already listening on ws://127.0.0.1:<port>")`.
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- Other bind failures surface as `GatewayLockError("failed to bind gateway socket on ws://127.0.0.1:<port>: …")`.
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## Operational notes
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- If the port is occupied by *another* process, the error is the same; free the port or choose another with `clawdbot gateway --port <port>`.
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- The macOS app still maintains its own lightweight PID guard before spawning the gateway; the runtime lock is enforced by the WebSocket bind.
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