Implement systemd socket activation

Makefile

@@ -42,7 +42,7 @@ dist: clean vendor build
 	(cd "$(TMP)" && tar -cvzf "$(BIN)-$(VERSION)-src.tar.gz" "$(BIN)-$(VERSION)")
 
 	mkdir "$(TMP)/$(BIN)-$(VERSION)-linux64"
-	cp "$(BIN)" "$(BIN).service" LICENSE README.md "$(TMP)/$(BIN)-$(VERSION)-linux64"
+	cp "$(BIN)" "$(BIN).service" "$(BIN).socket" LICENSE README.md "$(TMP)/$(BIN)-$(VERSION)-linux64"
 	(cd "$(TMP)" && tar -cvzf "$(BIN)-$(VERSION)-linux64.tar.gz" "$(BIN)-$(VERSION)-linux64")
 
 	mkdir -p dist
@@ -60,5 +60,6 @@ dist: clean vendor build
 install:
 	install -Dm755 -t "$(BIN_DIR)/" $(BIN)
 	install -Dm644 -t "$(LIB_DIR)/systemd/user" "$(BIN).service"
+	install -Dm644 -t "$(LIB_DIR)/systemd/user" "$(BIN).socket"
 	install -Dm644 -t "$(SHARE_DIR)/licenses/$(BIN)/" LICENSE
 	install -Dm644 -t "$(SHARE_DIR)/doc/$(BIN)/" README.md

README.md

@@ -14,13 +14,20 @@ _See also: [FAQ: Which UI components are already integrated with this app?](#faq
 
 On Arch Linux, you can install it with `pacman -S yubikey-touch-detector`
 
-The package also installs a systemd service, make sure to start and enable it:
+The package also installs a systemd service and socket. If you want the app to launch on startup, just enable the service like so:
 
 ```
 $ systemctl --user daemon-reload
 $ systemctl --user enable --now yubikey-touch-detector.service
 ```
 
+If you want the service to be started only when there is a listener on Unix socket, enable the socket instead like so:
+
+```
+$ systemctl --user daemon-reload
+$ systemctl --user enable --now yubikey-touch-detector.socket
+```
+
 Alternatively you can download the latest release from the [GitHub releases](https://github.com/maximbaz/yubikey-touch-detector/releases) page. All releases are signed with [my PGP key](https://keybase.io/maximbaz).
 
 Finally you can install the app with `go`:
@@ -69,7 +76,7 @@ YUBIKEY_TOUCH_DETECTOR_LIBNOTIFY=true
 
 #### Integrating with other UI components
 
-First of all, make sure the app is always running (e.g. start a provided systemd user service).
+First of all, make sure the app is always running (e.g. start a provided systemd user service or socket).
 
 Next, in order to integrate the app with other UI components to display a visible indicator, use any of the available notifiers in the `notifier` subpackage.
 

go.mod

@@ -3,6 +3,7 @@ module github.com/maximbaz/yubikey-touch-detector
 go 1.14
 
 require (
+	github.com/coreos/go-systemd/v22 v22.1.0
 	github.com/konsorten/go-windows-terminal-sequences v1.0.2 // indirect
 	github.com/menefotto/go-libnotify v0.0.0-20160821232856-351dc16572b9
 	github.com/rjeczalik/notify v0.9.2

go.sum

@@ -1,8 +1,11 @@
+github.com/coreos/go-systemd/v22 v22.1.0 h1:kq/SbG2BCKLkDKkjQf5OWwKWUKj1lgs3lFI4PxnR5lg=
+github.com/coreos/go-systemd/v22 v22.1.0/go.mod h1:xO0FLkIi5MaZafQlIrOotqXZ90ih+1atmu1JpKERPPk=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/fatih/set v0.2.1 h1:nn2CaJyknWE/6txyUDGwysr3G5QC6xWB/PtVjPBbeaA=
 github.com/fatih/set v0.2.1/go.mod h1:+RKtMCH+favT2+3YecHGxcc0b4KyVWA1QWWJUs4E0CI=
+github.com/godbus/dbus/v5 v5.0.3/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
 github.com/konsorten/go-windows-terminal-sequences v1.0.1/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=
 github.com/konsorten/go-windows-terminal-sequences v1.0.2 h1:DB17ag19krx9CFsz4o3enTrPXyIXCl+2iCXH/aMAp9s=
 github.com/konsorten/go-windows-terminal-sequences v1.0.2/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=

notifier/unix_socket.go

@@ -7,6 +7,7 @@ import (
 	"strings"
 	"sync"
 
+	"github.com/coreos/go-systemd/v22/activation"
 	log "github.com/sirupsen/logrus"
 )
 
@@ -23,19 +24,33 @@ func SetupUnixSocketNotifier(notifiers *sync.Map, exits *sync.Map) {
 		return
 	}
 
-	socketFile := path.Join(socketDir, "yubikey-touch-detector.socket")
-	if _, err := os.Stat(socketFile); err == nil {
-		log.Warnf("'%v' already exists, assuming it's an obsolete one and trying to recover", socketFile)
-		if err = os.Remove(socketFile); err != nil {
-			log.Errorf("Cannot remove '%v' in order to recover from possible previous crash", socketFile)
-			return
-		}
+	listeners, err := activation.Listeners()
+	if err != nil {
+		log.Errorf("Error receiving activation listeners from systemd, proceeding to create our own unix socket: %v", err)
 	}
 
-	socket, err := net.Listen("unix", socketFile)
-	if err != nil {
-		log.Error("Cannot establish a proxy SSH socket: ", err)
-		return
+	var socket net.Listener
+	if len(listeners) > 1 {
+		log.Warn("Received more than one listener from systemd which should not be possible, using the first one")
+		socket = listeners[0]
+	} else if len(listeners) == 1 {
+		socket = listeners[0]
+	} else {
+		socketFile := path.Join(socketDir, "yubikey-touch-detector.socket")
+
+		if _, err := os.Stat(socketFile); err == nil {
+			log.Warnf("'%v' already exists, assuming it's obsolete and trying to recover", socketFile)
+			if err = os.Remove(socketFile); err != nil {
+				log.Errorf("Cannot remove '%v' in order to recover from possible previous crash", socketFile)
+				return
+			}
+		}
+
+		socket, err = net.Listen("unix", socketFile)
+		if err != nil {
+			log.Error("Cannot establish a unix socket listener: ", err)
+			return
+		}
 	}
 
 	exit := make(chan bool)

yubikey-touch-detector.socket

@@ -0,0 +1,9 @@
+[Unit]
+Description=Unix socket activation for YubiKey touch detector service
+
+[Socket]
+ListenStream=%t/yubikey-touch-detector.socket
+RemoveOnStop=yes
+
+[Install]
+WantedBy=sockets.target