config

Station Manager: config package

Service responsible for loading and exposing application configuration.

Generated config.json

On first run, if no config.json is present in the working directory, the service writes a default, pretty-printed file with restrictive permissions (0640).

Selecting default datastore via environment

You can choose which datastore block gets written into a newly generated config.json using the environment variable SM_DEFAULT_DB.

Accepted values (case-insensitive):

• sqlite (default)
• postgres, postgresql, pg

Example:

# Use PostgreSQL defaults when generating a fresh config.json
export SM_DEFAULT_DB=pg

If the file already exists, the variable is ignored and the existing config is loaded.

Working directory resolution

The config service resolves its working directory via:

1. The injected WorkingDir field if provided
2. The SM_WORKING_DIR env var
3. The directory of the running executable

The resolved directory must exist.

Programmatic overrides (advanced)

If you pre-seed Service.AppConfig.LoggingConfig before calling Initialize(), the config service preserves that logging section instead of the one loaded from config.json. This is intentional to support:

• Unit/integration tests that need to inject invalid levels or specific writer options
• Programmatic bootstraps that want to override logging without modifying files

Notes:

• The sentinel for preserving is a non-empty LoggingConfig.Level.
• Only the logging section is preserved; other sections (e.g., datastore) still load from file.
• For typical usage, leave AppConfig empty and rely on the file.

Defaults and tuning guidance

The defaults aim for sensible behavior out of the box and should be tuned per environment and workload.

SQLite (modernc.org/sqlite)

• MaxOpenConns: 4 (readers benefit; writes are serialized)
• MaxIdleConns: 4
• ConnMaxLifetime: 0 (no forced recycle)
• ConnMaxIdleTime: 5m
• ContextTimeout: 5s
• TransactionContextTimeout: 10s
• Options:
  • _journal_mode=WAL
  • _busy_timeout=5000 (consider 10000 under heavier write contention)
  • _foreign_keys=on

Notes:

• WAL enables concurrent readers. Too many connections can increase lock contention; start small and measure.
• Transaction timeout should be longer than typical busy periods to avoid spurious cancellations.

PostgreSQL

• MaxOpenConns: 10 (consider 20+ for higher concurrency)
• MaxIdleConns: 5–10
• ConnMaxLifetime: 30–60m (keep below server rotation)
• ConnMaxIdleTime: 5–10m
• ContextTimeout: 5–10s
• TransactionContextTimeout: 15–30s
• SSLMode: disable for local dev; use require/verify-ca/verify-full in production

Notes:

• Tune pool sizes based on CPU, workload mix, and DB server capacity.
• Longer lifetimes reduce churn; align with server-side settings.

API

• Initialize() error — loads (or creates) config.json in the working directory; idempotent.
• DatastoreConfig() (types.DatastoreConfig, error) — returns the datastore settings.
• LoggingConfig() (types.LoggingConfig, error) — returns the logging settings.

Downstream services (database, logging) validate their respective sections when they initialize.