Silence connection errors by default

Often times the connection-level errors clutter the logs, for
instance with failed TLS handshakes or unknown hostname.

cmd/tlstunnel/main.go

@@ -17,6 +17,8 @@ import (
 var (
 	configPath   = "config"
 	certDataPath = ""
+
+	debug = false
 )
 
 func newServer() (*tlstunnel.Server, error) {
@@ -26,6 +28,7 @@ func newServer() (*tlstunnel.Server, error) {
 	}
 
 	srv := tlstunnel.NewServer()
+	srv.Debug = debug
 
 	loggerCfg := zap.Config{
 		Level:             zap.NewAtomicLevelAt(zap.InfoLevel),
@@ -68,6 +71,7 @@ func bumpOpenedFileLimit() error {
 
 func main() {
 	flag.StringVar(&configPath, "config", configPath, "path to configuration file")
+	flag.BoolVar(&debug, "debug", false, "enable debug logging")
 	flag.Parse()
 
 	if err := bumpOpenedFileLimit(); err != nil {

server.go

@@ -38,6 +38,7 @@ func newACMECache() *acmeCache {
 type Server struct {
 	Listeners map[string]*Listener // indexed by listening address
 	Frontends []*Frontend
+	Debug     bool
 
 	ManagedNames   []string
 	UnmanagedCerts []tls.Certificate
@@ -256,8 +257,10 @@ func (ln *Listener) serve() error {
 		}
 
 		go func() {
-			if err := ln.handle(conn); err != nil {
-				log.Printf("listener %q: %v", ln.Address, err)
+			err := ln.handle(conn)
+			srv := ln.atomic.Load().(*listenerHandles).Server
+			if err != nil && srv.Debug {
+				log.Printf("listener %q: connection %q: %v", ln.Address, conn.RemoteAddr(), err)
 			}
 		}()
 	}