Add observatory / latestPing balancing strategy

Co-authored-by: Shelikhoo <xiaokangwang@outlook.com>

common/session/context.go

@@ -11,6 +11,7 @@ const (
 	contentSessionKey
 	muxPreferedSessionKey
 	sockoptSessionKey
+	trackedConnectionErrorKey
 )
 
 // ContextWithID returns a new context with the given ID.
@@ -84,3 +85,33 @@ func SockoptFromContext(ctx context.Context) *Sockopt {
 	}
 	return nil
 }
+
+func GetForcedOutboundTagFromContext(ctx context.Context) string {
+	if ContentFromContext(ctx) == nil {
+		return ""
+	}
+	return ContentFromContext(ctx).Attribute("forcedOutboundTag")
+}
+
+func SetForcedOutboundTagToContext(ctx context.Context, tag string) context.Context {
+	if contentFromContext := ContentFromContext(ctx); contentFromContext == nil {
+		ctx = ContextWithContent(ctx, &Content{})
+	}
+	ContentFromContext(ctx).SetAttribute("forcedOutboundTag", tag)
+	return ctx
+}
+
+type TrackedRequestErrorFeedback interface {
+	SubmitError(err error)
+}
+
+func SubmitOutboundErrorToOriginator(ctx context.Context, err error) {
+	if errorTracker := ctx.Value(trackedConnectionErrorKey); errorTracker != nil {
+		errorTracker := errorTracker.(TrackedRequestErrorFeedback)
+		errorTracker.SubmitError(err)
+	}
+}
+
+func TrackedConnectionError(ctx context.Context, tracker TrackedRequestErrorFeedback) context.Context {
+	return context.WithValue(ctx, trackedConnectionErrorKey, tracker)
+}