Write a Driver

A driver block connects an external dependency to a capability package. The driver module should depend on the capability package; the capability package must not depend backward on the driver module.

Where to put a driver module

Using a cache driver as an example, the driver module path can be:

github.com/acme/runa-cache-driver

Drivers only implement interfaces defined by capability packages

The driver implements the interface defined by the capability package:

type Driver struct {
    client *Client
}

func NewDriver(client *Client) cache.Driver {
    return &Driver{client: client}
}

Official driver factories are named Driver(...):

func Driver(client *Client, options ...Option) cache.Driver {
    return &driver{client: client}
}

Register through the capability package

app.Install(cache.Provider(
    cache.RegisterDriver("acme", acme.Driver(client)),
    cache.RegisterPool("default", cache.Use("acme")),
))

Join shutdown when holding connections

If a driver holds a connection, it must implement the Close(ctx) required by the capability interface so DI shutdown can release resources.

func (d *driver) Close(ctx context.Context) error {
    return d.client.Close()
}

Acceptance checklist

• The driver package passes go test ./... independently.
• It can be registered without modifying the capability package source.
• When the driver is not used, its external dependencies do not enter the user’s go.sum.