Allow socket activation from systemd.

cmd/circologd/main.go

@@ -31,9 +31,10 @@ func removeAtExit(socket string) {
 
 func main() {
 	var err error
+	var syslogSocket SyslogSocket
 	var logFmt formatter.SyslogRFC
 	logFmt.Format = syslog.Automatic
-	syslogSocketPath := flag.String("syslogd-socket", "", "The socket to listen to syslog addresses")
+	flag.Var(&syslogSocket, "syslogd-socket", "The socket to listen to syslog addresses")
 	// dumpSocketPath := flag.String("dump-socket", "/run/buffer.sock", "The socket that user will connect to in order to receive logs")
 	bufsize := flag.Int("buffer-size", 1000, "Number of messages to keep")
 	syslogAddr := flag.String("syslog-addr", "127.0.0.1:9514", "Address:port where to listen for syslog messages")
@@ -56,13 +57,18 @@ func main() {
 	server.SetFormat(logFmt.Format)
 	fmt.Printf("Syslog format set to: %s\n", logFmt.String())
 	server.SetHandler(handler)
-	if *syslogSocketPath != "" {
-		if err = server.ListenUnixgram(*syslogSocketPath); err != nil {
+	if syslogSocket.isSocketActivated {
+		fmt.Printf("Binding to socket `%s` [syslog]\n", syslogSocket.String())
+		server.Listen(syslogSocket.Listener)
+	} else {
+		syslogSocketPath := syslogSocket.Path
+		if syslogSocketPath != "" {
+			if err = server.ListenUnixgram(syslogSocketPath); err != nil {
 				fmt.Fprintln(os.Stderr, "argh", err)
 				os.Exit(1)
 			}
-		defer cleanSocket(*syslogSocketPath)
-		fmt.Printf("Binding socket `%s` [syslog]\n", *syslogSocketPath)
+			fmt.Printf("Binding socket `%s` [syslog]\n", syslogSocketPath)
+			removeAtExit(syslogSocketPath)
 		} else {
 			fmt.Printf("Binding address `%s` [syslog]\n", *syslogAddr)
 			if err = server.ListenUDP(*syslogAddr); err != nil {
@@ -70,6 +76,7 @@ func main() {
 				os.Exit(1)
 			}
 		}
+	}
 	if err = server.Boot(); err != nil {
 		fmt.Fprintln(os.Stderr, "argh", err)
 		os.Exit(1)

cmd/circologd/sockets.go

@@ -0,0 +1,48 @@
+package main
+
+import (
+	"net"
+
+	"github.com/coreos/go-systemd/activation"
+)
+
+// SyslogSocket is a struct eventually containing a net.Listener
+// ready with messages, and a Path in case the Listener is not present.
+type SyslogSocket struct {
+	Listener          net.Listener
+	Path              string
+	isSocketActivated bool
+}
+
+func (s *SyslogSocket) Set(v string) error {
+	sock, err := s.getActivationSocket()
+	if err != nil {
+		return err
+	}
+	s.isSocketActivated = false
+	if sock != nil {
+		s.Listener = sock
+		s.isSocketActivated = true
+		return nil
+	}
+	s.Path = v
+	return nil
+}
+
+func (s *SyslogSocket) String() string {
+	if s.isSocketActivated {
+		return "systemd-provided"
+	}
+	return s.Path
+}
+
+func (s *SyslogSocket) getActivationSocket() (net.Listener, error) {
+	listeners, err := activation.Listeners()
+	if err != nil {
+		return nil, err
+	}
+	if len(listeners) == 0 {
+		return nil, nil
+	}
+	return listeners[0], nil
+}