From 3e27cad5b17f7285a92564c7625484a8711b8c3b Mon Sep 17 00:00:00 2001
From: Blallo <blallo@autistici.org>
Date: Fri, 3 May 2019 10:45:35 +0200
Subject: [PATCH] Allow socket activation from systemd.

---
 cmd/circologd/main.go    | 31 ++++++++++++++++----------
 cmd/circologd/sockets.go | 48 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+), 12 deletions(-)
 create mode 100644 cmd/circologd/sockets.go

diff --git a/cmd/circologd/main.go b/cmd/circologd/main.go
index 31821e7..4063d8b 100644
--- a/cmd/circologd/main.go
+++ b/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")
@@ -56,18 +57,24 @@ 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 {
-			fmt.Fprintln(os.Stderr, "argh", err)
-			os.Exit(1)
-		}
-		defer cleanSocket(*syslogSocketPath)
-		fmt.Printf("Binding socket `%s` [syslog]\n", *syslogSocketPath)
+	if syslogSocket.isSocketActivated {
+		fmt.Printf("Binding to socket `%s` [syslog]\n", syslogSocket.String())
+		server.Listen(syslogSocket.Listener)
 	} else {
-		fmt.Printf("Binding address `%s` [syslog]\n", *syslogAddr)
-		if err = server.ListenUDP(*syslogAddr); err != nil {
-			fmt.Fprintln(os.Stderr, "argh", err)
-			os.Exit(1)
+		syslogSocketPath := syslogSocket.Path
+		if syslogSocketPath != "" {
+			if err = server.ListenUnixgram(syslogSocketPath); err != nil {
+				fmt.Fprintln(os.Stderr, "argh", err)
+				os.Exit(1)
+			}
+			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 {
+				fmt.Fprintln(os.Stderr, "argh", err)
+				os.Exit(1)
+			}
 		}
 	}
 	if err = server.Boot(); err != nil {
diff --git a/cmd/circologd/sockets.go b/cmd/circologd/sockets.go
new file mode 100644
index 0000000..aa2919c
--- /dev/null
+++ b/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
+}