activation: allocate slice if we know the size

Use for range, and use the knowledge the everything is zeroed on
allocation, so gaps will be nil in the slice.

Author: Tamás Gulácsi

activation/files.go

@@ -42,7 +42,7 @@ func Files(unsetEnv bool) []*os.File {
 		return nil
 	}
 
-	var files []*os.File
+	files := make([]*os.File, 0, nfds)
 	for fd := listenFdsStart; fd < listenFdsStart+nfds; fd++ {
 		syscall.CloseOnExec(fd)
 		files = append(files, os.NewFile(uintptr(fd), "LISTEN_FD_"+strconv.Itoa(fd)))

activation/listeners.go

@@ -26,14 +26,11 @@ import (
 // corresponding with "udp, tcp, tcp", then the slice would contain {nil, net.Listener, net.Listener}
 func Listeners(unsetEnv bool) ([]net.Listener, error) {
 	files := Files(unsetEnv)
-	listeners := make([]net.Listener, 0)
+	listeners := make([]net.Listener, len(files))
 
-	for i := 0; i < len(files); i++ {
-		if pc, err := net.FileListener(files[i]); err == nil {
-			listeners = append(listeners, pc)
-			continue
-		} else {
-			listeners = append(listeners, nil)
+	for i, f := range files {
+		if pc, err := net.FileListener(f); err == nil {
+			listeners[i] = pc
 		}
 	}
 	return listeners, nil

activation/packetconns.go

@@ -26,13 +26,11 @@ import (
 // corresponding with "udp, tcp, udp", then the slice would contain {net.PacketConn, nil, net.PacketConn}
 func PacketConns(unsetEnv bool) ([]net.PacketConn, error) {
 	files := Files(unsetEnv)
-	conns := make([]net.PacketConn, 0)
-	for i := 0; i < len(files); i++ {
-		if pc, err := net.FilePacketConn(files[i]); err == nil {
-			conns = append(conns, pc)
-			continue
-		} else {
-			conns = append(conns, nil)
+	conns := make([]net.PacketConn, len(files))
+
+	for i, f := range files {
+		if pc, err := net.FilePacketConn(f); err == nil {
+			conns[i] = pc
 		}
 	}
 	return conns, nil