sdk: expose manager options

This commit adds the possibility to configure the plugin manager with
custom options.

It will allow SDK users to override the options already provided by the
SDK and to futher customize it with configurations that were not
previously available. This is an advanced feature as it requires
some knowledge about the inner workings of OPA.

One use case for this is to provide a prometheus registerer and have the
status plugin metrics available for the client to use it in a
/metrics endpoint, for example.

resolves open-policy-agent#6662

Signed-off-by: Francisco Rodrigues <ednofco@gmail.com>

sdk/opa.go

@@ -48,6 +48,7 @@ type OPA struct {
 	hooks        hooks.Hooks
 	config       []byte
 	v1Compatible bool
+	managerOpts  []func(*plugins.Manager)
 }
 
 type state struct {
@@ -88,6 +89,7 @@ func New(ctx context.Context, opts Options) (*OPA, error) {
 	opa.console = opts.ConsoleLogger
 	opa.plugins = opts.Plugins
 	opa.v1Compatible = opts.V1Compatible
+	opa.managerOpts = opts.ManagerOpts
 
 	return opa, opa.configure(ctx, opa.config, opts.Ready, opts.block)
 }
@@ -141,6 +143,7 @@ func (opa *OPA) configure(ctx context.Context, bs []byte, ready chan struct{}, b
 	if opa.v1Compatible {
 		opts = append(opts, plugins.WithParserOptions(ast.ParserOptions{RegoVersion: ast.RegoV1}))
 	}
+	opts = append(opts, opa.managerOpts...)
 	manager, err := plugins.New(
 		bs,
 		opa.id,

sdk/opa_test.go

@@ -18,6 +18,9 @@ import (
 	"testing"
 	"time"
 
+	"github.com/prometheus/client_golang/prometheus"
+	promdto "github.com/prometheus/client_model/go"
+
 	"github.com/fortytw2/leaktest"
 	"github.com/google/go-cmp/cmp"
 	"github.com/google/go-cmp/cmp/cmpopts"
@@ -2772,3 +2775,72 @@ p { print("XXX") }
 		t.Fatal("expected print output but got:", e)
 	}
 }
+
+func TestConfigurableManagerOpts(t *testing.T) {
+	ctx := context.Background()
+
+	server := sdktest.MustNewServer(
+		sdktest.MockBundle("/bundles/bundle.tar.gz", map[string]string{
+			"main.rego": `
+package system
+
+main = true
+
+str = "foo"
+
+loopback = input
+`,
+		}),
+	)
+
+	defer server.Stop()
+
+	config := fmt.Sprintf(`{
+		"services": {
+			"test": {
+				"url": %q
+			}
+		},
+		"bundles": {
+			"test": {
+				"resource": "/bundles/bundle.tar.gz"
+			}
+		},
+		"status": {
+			"prometheus": true
+		}
+	}`, server.URL())
+
+	opa, err := sdk.New(ctx, sdk.Options{
+		ID:     "sdk-id-0",
+		Config: strings.NewReader(config),
+		ManagerOpts: []func(manager *plugins.Manager){
+			plugins.WithPrometheusRegister(prometheus.DefaultRegisterer),
+		},
+	})
+
+	defer opa.Stop(ctx)
+
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	m, err := prometheus.DefaultGatherer.Gather()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	registeredMetrics := toMetricMap(m)
+
+	if registeredMetrics["opa_info"] == false {
+		t.Errorf("expected metric 'opa_info' to be registered but it was not")
+	}
+}
+
+func toMetricMap(metrics []*promdto.MetricFamily) map[string]bool {
+	metricMap := make(map[string]bool, len(metrics))
+	for _, m := range metrics {
+		metricMap[m.GetName()] = true
+	}
+	return metricMap
+}

sdk/options.go

@@ -57,6 +57,11 @@ type Options struct {
 
 	V1Compatible bool
 
+	// ManagerOpts allows customization of the plugin manager.
+	// The given options get appended to the list of options already provided by the SDK and eventually
+	// overriding them.
+	ManagerOpts []func(manager *plugins.Manager)
+
 	config []byte
 	block  bool
 }