1 files changed, 28 insertions, 8 deletions
diff --git a/net/dns/manager.go b/net/dns/manager.go
index ebf91811a..1e9eb7fe7 100644
--- a/net/dns/manager.go
+++ b/net/dns/manager.go
@@ -35,6 +35,9 @@ import (
 
 var (
 	errFullQueue = errors.New("request queue full")
+	// ErrNoDNSConfig is returned by RecompileDNSConfig when the Manager
+	// has no existing DNS configuration.
+	ErrNoDNSConfig = errors.New("no DNS configuration")
 )
 
 // maxActiveQueries returns the maximal number of DNS requests that can
@@ -91,21 +94,18 @@ func NewManager(logf logger.Logf, oscfg OSConfigurator, health *health.Tracker,
 	}
 
 	// Rate limit our attempts to correct our DNS configuration.
+	// This is done on incoming queries, we don't want to spam it.
 	limiter := rate.NewLimiter(1.0/5.0, 1)
 
 	// This will recompile the DNS config, which in turn will requery the system
 	// DNS settings. The recovery func should triggered only when we are missing
 	// upstream nameservers and require them to forward a query.
 	m.resolver.SetMissingUpstreamRecovery(func() {
-		m.mu.Lock()
-		defer m.mu.Unlock()
-		if m.config == nil {
-			return
-		}
-
 		if limiter.Allow() {
-			m.logf("DNS resolution failed due to missing upstream nameservers.  Recompiling DNS configuration.")
-			m.setLocked(*m.config)
+			m.logf("resolution failed due to missing upstream nameservers.  Recompiling DNS configuration.")
+			if err := m.RecompileDNSConfig(); err != nil {
+				m.logf("config recompilation failed: %v", err)
+			}
 		}
 	})
 
@@ -117,6 +117,26 @@ func NewManager(logf logger.Logf, oscfg OSConfigurator, health *health.Tracker,
 // Resolver returns the Manager's DNS Resolver.
 func (m *Manager) Resolver() *resolver.Resolver { return m.resolver }
 
+// RecompileDNSConfig sets the DNS config to the current value, which has
+// the side effect of re-querying the OS's interface nameservers.  This should be used
+// on platforms where the interface nameservers can change.  Darwin, for example,
+// where the nameservers aren't always available when we process a major interface
+// change event, or platforms where the nameservers may change while tunnel is up.
+//
+// This should be called if it is determined that [OSConfigurator.GetBaseConfig] may
+// give a better or different result than when [Manager.Set] was last called.  The
+// logic for making that determination is up to the caller.
+//
+// It returns [ErrNoDNSConfig] if the [Manager] has no existing DNS configuration.
+func (m *Manager) RecompileDNSConfig() error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if m.config == nil {
+		return ErrNoDNSConfig
+	}
+	return m.setLocked(*m.config)
+}
+
 func (m *Manager) Set(cfg Config) error {
 	m.mu.Lock()
 	defer m.mu.Unlock()