Two-field DB config: Driver + DSN, not a fused URL

byob-storage.2 configstorage

Problem: a single fused URL like DATABASE_URL=sqlite:///path.db or postgres://user:pass@host/db seems tidy but re-invents URL parsing in user code. sqlite file paths have hairy edge cases (:memory:, file:...?mode=memory&cache=shared, relative vs absolute). Postgres DSNs can be URL-form or libpq keyword-form. MySQL uses its own user:pass@tcp(...) format. Scheme-dispatch code drifts into a full parser as users hit edge cases.

Idea: match stdlib sql.Open(driver, dsn) directly. Config exposes two fields — Driver string and DSN string — populated from env vars (DB_DRIVER, DB_DSN) or TOML keys. The storage factory reads them, calls sql.Open, and dispatches to the per-backend constructor. Each driver parses its own DSN in whatever format it prefers; byob code never touches string-level parsing.

Tradeoffs: users set two env vars / TOML keys instead of one URL. In return: no scheme bikeshedding, no re-parsing edge cases, and the factory code is five lines. If a user really wants URL convenience later, a tiny ParseURL(s) (driver, dsn string, error) helper can be added on top without changing the core config shape.

Design

// internal/config/config.go
type DB struct {
    Driver string `toml:"driver"` // "sqlite" | "pgx"
    DSN    string `toml:"dsn"`    // driver-specific
}

// internal/storage/open.go
type Store interface { /* ... consumer-narrow methods ... */ }

func Open(ctx context.Context, cfg config.DB) (Store, error) {
    switch cfg.Driver {
    case "sqlite":
        return sqlite.Open(ctx, cfg.DSN)
    case "pgx":
        return postgres.Open(ctx, cfg.DSN)
    default:
        return nil, fmt.Errorf("unknown db driver: %q", cfg.Driver)
    }
}

Sample DSNs:

# sqlite on disk
DB_DRIVER=sqlite
DB_DSN=file:state.db?_pragma=journal_mode(WAL)

# postgres
DB_DRIVER=pgx
DB_DSN=postgres://user:pass@host:5432/appdb?sslmode=require

# cockroachdb (postgres wire, different port + params)
DB_DRIVER=pgx
DB_DSN=postgres://user:pass@cockroach.host:26257/appdb?sslmode=require

Factory exposes the Store via a lazy sync.OnceValues closure (see byob-factory-di.1) so mytool --help doesn't pay the cost of opening a connection.