[gateway] Invoke PostRouteModify extension hook during xDS translation

The PostRouteModify RPC was defined in the extension proto but never
called by the translator. This adds processExtensionPostRouteHook in
extension.go and wires it into Translate() between the listener and
cluster hooks. The extension server can now inject per-route metadata
(e.g., project_id into filter_metadata) which is needed for OTEL
access log and tracing attribution.

Author: theRealWardo

pkg/gateway/xds/translator/extension.go

@@ -18,6 +18,7 @@ import (
 	"github.com/apoxy-dev/apoxy/pkg/log"
 	clusterv3 "github.com/envoyproxy/go-control-plane/envoy/config/cluster/v3"
 	listenerv3 "github.com/envoyproxy/go-control-plane/envoy/config/listener/v3"
+	routev3 "github.com/envoyproxy/go-control-plane/envoy/config/route/v3"
 	cachetypes "github.com/envoyproxy/go-control-plane/pkg/cache/types"
 	resourcev3 "github.com/envoyproxy/go-control-plane/pkg/resource/v3"
 	"github.com/envoyproxy/gateway/proto/extension"
@@ -150,6 +151,39 @@ func processExtensionPostListenerHook(
 	return nil
 }
 
+// processExtensionPostRouteHook calls PostRouteModify on the extension server
+// for each route in every RouteConfiguration, allowing the extension to inject
+// per-route metadata (e.g., project_id into filter_metadata).
+func processExtensionPostRouteHook(
+	ctx context.Context,
+	tCtx *types.ResourceVersionTable,
+	c extension.EnvoyGatewayExtensionClient,
+) error {
+	log := log.DefaultLogger
+
+	for _, r := range tCtx.XdsResources[resourcev3.RouteType] {
+		routeCfg := r.(*routev3.RouteConfiguration)
+		for _, vh := range routeCfg.GetVirtualHosts() {
+			for i, route := range vh.GetRoutes() {
+				log.Info("Processing extension post route hook", "route", route.GetName())
+				reqCtx, cancel := context.WithTimeout(ctx, 2*time.Second)
+				resp, err := c.PostRouteModify(reqCtx, &extension.PostRouteModifyRequest{
+					Route: route,
+				})
+				cancel()
+				if err != nil {
+					return err
+				}
+				if resp.GetRoute() != nil {
+					vh.Routes[i] = resp.GetRoute()
+				}
+			}
+		}
+	}
+
+	return nil
+}
+
 // processExtensionPostTranslateHook calls PostTranslateModify on the extension
 // server with all translated xDS clusters, allowing the extension to modify
 // or add clusters (e.g., to set per-project DNS resolver ports or inject an

pkg/gateway/xds/translator/translator.go

@@ -107,6 +107,10 @@ func (t *Translator) Translate(xdsIR *ir.Xds) (*types.ResourceVersionTable, erro
 		errs = errors.Join(errs, err)
 	}
 
+	if err := t.notifyExtensionServerAboutRoutes(tCtx); err != nil {
+		errs = errors.Join(errs, err)
+	}
+
 	if err := t.notifyExtensionServerAboutClusters(tCtx); err != nil {
 		errs = errors.Join(errs, err)
 	}
@@ -121,6 +125,24 @@ func (t *Translator) Translate(xdsIR *ir.Xds) (*types.ResourceVersionTable, erro
 	return tCtx, errs
 }
 
+// notifyExtensionServerAboutRoutes calls the extension server's PostRouteModify
+// hook for each route in every RouteConfiguration. This allows the extension to
+// inject per-route metadata (e.g., project_id into filter_metadata).
+func (t *Translator) notifyExtensionServerAboutRoutes(tCtx *types.ResourceVersionTable) error {
+	if t.ExtensionServer == nil {
+		return nil
+	}
+
+	if err := processExtensionPostRouteHook(t.Ctx, tCtx, t.ExtensionServer.EnvoyGatewayExtensionClient); err != nil {
+		if !t.ExtensionServer.FailOpen {
+			return err
+		}
+		slog.Error("Extension Manager PostRoute failure", "error", err)
+	}
+
+	return nil
+}
+
 // notifyExtensionServerAboutClusters calls the extension server's
 // PostTranslateModify hook with all translated xDS clusters.
 func (t *Translator) notifyExtensionServerAboutClusters(tCtx *types.ResourceVersionTable) error {