devctl-plugin-authoring

Devctl Plugin Authoring

Overview

Build repo-specific dev environment logic as a devctl plugin while devctl handles orchestration, supervision, and logs.

Workflow

1. Collect repo context

• Identify services to run and their commands, env vars, ports, and health checks.
• Identify prerequisites (node, docker, db migrations) and build/prepare steps.
• Decide which devctl ops you will implement.

2. Choose ops and config keys

• Start small: config.mutate, validate.run, and launch.plan are usually enough.
• Add build.run and prepare.run when you need ordered steps with artifacts.
• Add command.run only for dynamic helper commands (db reset, seed, etc.).
• Keep config keys stable and descriptive: env.*, services.<name>.port, services.<name>.url, artifacts.*.

3. Implement the protocol skeleton

• Emit a handshake as the very first stdout line.
• After the handshake, stdout must be only NDJSON frames (one JSON object per line).
• Send all logs to stderr; flush after every stdout write.
• Return E_UNSUPPORTED for unhandled ops to keep behavior explicit.

See references/protocol-quickref.md for minimal Python and bash skeletons.

4. Implement ops

• config.mutate: return a config patch with dotted keys; avoid side effects.
• build.run / prepare.run: run named steps and return step results; respect ctx.deadline_ms.
• validate.run: return actionable errors/warnings; do not hide failures.
• launch.plan: return services for devctl to supervise; do not start processes yourself.
• command.run: execute a named command from capabilities.commands; return exit_code.

Always honor:

• ctx.repo_root for relative paths.
• ctx.dry_run by avoiding side effects.
• ctx.deadline_ms by enforcing timeouts in subprocesses.

5. Wire the repo config

Add .devctl.yaml at repo root, e.g.:

• id: stable plugin identifier.
• path + args: how to run the plugin.
• env: optional plugin env vars.
• priority: merge precedence.

6. Test the loop

Use the tight feedback loop:

1. devctl plugins list
2. devctl plan
3. devctl up
4. devctl status
5. devctl logs --service <name> --follow
6. devctl down

If protocol issues appear, retry with devctl --log-level debug plugins list.

7. Troubleshoot common failures

• stdout contamination: non-JSON output on stdout; move logs to stderr.
• missing handshake: first stdout frame not a handshake; emit immediately.
• timeouts: enforce per-command timeouts using ctx.deadline_ms.
• health failures: check ports/URLs and health config in launch.plan.

References

• Use devctl help devctl-user-guide for the user workflow.
• Use devctl help devctl-scripting-guide for practical plugin patterns.
• Use devctl help devctl-plugin-authoring for full protocol schemas.