Move middleware context handler logic to service (#29605)

* middleware: Move context handler to own service

Signed-off-by: Arve Knudsen <arve.knudsen@gmail.com>

Co-authored-by: Emil Tullsted <sakjur@users.noreply.github.com>
Co-authored-by: Will Browne <wbrowne@users.noreply.github.com>

pkg/registry/di.go

@@ -0,0 +1,45 @@
+package registry
+
+import (
+	"fmt"
+
+	"github.com/facebookgo/inject"
+)
+
+// BuildServiceGraph builds a graph of services and their dependencies.
+// The services are initialized after the graph is built.
+func BuildServiceGraph(objs []interface{}, services []*Descriptor) error {
+	if services == nil {
+		services = GetServices()
+	}
+	for _, service := range services {
+		objs = append(objs, service.Instance)
+	}
+
+	serviceGraph := inject.Graph{}
+
+	// Provide services and their dependencies to the graph.
+	for _, obj := range objs {
+		if err := serviceGraph.Provide(&inject.Object{Value: obj}); err != nil {
+			return fmt.Errorf("failed to provide object to the graph: %w", err)
+		}
+	}
+
+	// Resolve services and their dependencies.
+	if err := serviceGraph.Populate(); err != nil {
+		return fmt.Errorf("failed to populate service dependencies: %w", err)
+	}
+
+	// Initialize services.
+	for _, service := range services {
+		if IsDisabled(service.Instance) {
+			continue
+		}
+
+		if err := service.Instance.Init(); err != nil {
+			return fmt.Errorf("service init failed: %w", err)
+		}
+	}
+
+	return nil
+}