Merge pull request #441 from thaJeztah/19.03_backport_fix_double_host

[19.03 backport] daemon: don't listen on the same address multiple times
Upstream-commit: c3936abb675e88a62215d7fac9f52b365f273ca6
Component: engine

Author: thaJeztah

components/engine/cmd/dockerd/daemon.go

@@ -608,11 +608,17 @@ func newAPIServerConfig(cli *DaemonCli) (*apiserver.Config, error) {
 
 func loadListeners(cli *DaemonCli, serverConfig *apiserver.Config) ([]string, error) {
 	var hosts []string
+	seen := make(map[string]struct{}, len(cli.Config.Hosts))
+
 	for i := 0; i < len(cli.Config.Hosts); i++ {
 		var err error
 		if cli.Config.Hosts[i], err = dopts.ParseHost(cli.Config.TLS, honorXDG, cli.Config.Hosts[i]); err != nil {
 			return nil, errors.Wrapf(err, "error parsing -H %s", cli.Config.Hosts[i])
 		}
+		if _, ok := seen[cli.Config.Hosts[i]]; ok {
+			continue
+		}
+		seen[cli.Config.Hosts[i]] = struct{}{}
 
 		protoAddr := cli.Config.Hosts[i]
 		protoAddrParts := strings.SplitN(protoAddr, "://", 2)