From 521a9af4dda24087e4ebe1f814980d9a4ab9dbb6 Mon Sep 17 00:00:00 2001
From: "Francisco A. Lozano" <flozano@gmail.com>
Date: Tue, 7 Jul 2015 06:33:41 +0900
Subject: [PATCH 1/2] Ongoing impl of select'able file descriptor

---
 starter.go | 38 ++++++++++++++++++++++++++++++++++----
 1 file changed, 34 insertions(+), 4 deletions(-)

diff --git a/starter.go b/starter.go
index 2b89842..7c1d241 100644
--- a/starter.go
+++ b/starter.go
@@ -188,9 +188,11 @@ func setEnv() {
 	}
 }
 
-func parsePortSpec(addr string) (string, int, error) {
+func parsePortSpec(addr string) (string, int, int, error) {
 	i := strings.IndexByte(addr, ':')
 	portPart := ""
+	fdPart := ""
+
 	if i < 0 {
 		portPart = addr
 		addr = ""
@@ -199,12 +201,26 @@ func parsePortSpec(addr string) (string, int, error) {
 		addr = addr[:i]
 	}
 
+	j := strings.IndexByte(portPart, '=')
+	if j > 0 {
+		fdPart = portPart[j+1:]
+		portPart = portPart[:j]
+	}
+
 	port, err := strconv.ParseInt(portPart, 10, 64)
 	if err != nil {
-		return "", -1, err
+		return "", -1, -1, err
 	}
 
-	return addr, int(port), nil
+	if fdPart == "" {
+		return addr, int(port), -1, nil
+	} else {
+		fd, err := strconv.ParseInt(fdPart, 10, 64)
+		if err != nil {
+			return addr, int(port), -1, err
+		}
+		return addr, int(port), int(fd), nil
+	}
 }
 
 func (s *Starter) Run() error {
@@ -223,7 +239,7 @@ func (s *Starter) Run() error {
 	for _, addr := range s.ports {
 		var l net.Listener
 
-		host, port, err := parsePortSpec(addr)
+		host, port, fd, err := parsePortSpec(addr)
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "failed to parse addr spec '%s': %s", addr, err)
 			return err
@@ -235,6 +251,20 @@ func (s *Starter) Run() error {
 			fmt.Fprintf(os.Stderr, "failed to listen to %s:%s\n", hostport, err)
 			return err
 		}
+		if fd != -1 {
+			file, err := l.(*net.TCPListener).File()
+			if err == nil {
+				oldFD := file.Fd()
+				err = syscall.Dup2 ( int(oldFD), fd)
+				if err == nil {
+					err = syscall.Close( int(oldFD) )
+				}
+			}
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "failed to duplicate fd: %s", err)
+				return err
+			}
+		}
 
 		spec := ""
 		if host == "" {

From 99b51ef6f120bd5dbe4093febb57c0cebd560983 Mon Sep 17 00:00:00 2001
From: "Francisco A. Lozano" <flozano@gmail.com>
Date: Tue, 7 Jul 2015 06:52:31 +0900
Subject: [PATCH 2/2] Replace listener with new listener from dup'ed FD

---
 starter.go | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/starter.go b/starter.go
index 7c1d241..1da9428 100644
--- a/starter.go
+++ b/starter.go
@@ -255,9 +255,12 @@ func (s *Starter) Run() error {
 			file, err := l.(*net.TCPListener).File()
 			if err == nil {
 				oldFD := file.Fd()
-				err = syscall.Dup2 ( int(oldFD), fd)
+				err = syscall.Dup2 (int(oldFD), fd)
 				if err == nil {
-					err = syscall.Close( int(oldFD) )
+					l, err = net.FileListener(os.NewFile(uintptr(fd), ""))
+					if err == nil {
+						err = syscall.Close(int(oldFD))
+					}
 				}
 			}
 			if err != nil {