Support systemd socket activation

hack/integration-systemd-socket.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+set -e
+if [ -z "$EXECED" ]
+then
+	systemd-socket-activate -E EXECED=1 -l /tmp/activate.sock socat ACCEPT-FD:3 EXEC:"rootlesskit $0",nofork 2>/dev/null &
+	OUTPUT="$(curl --unix-socket /tmp/activate.sock http://localhost/hello 2>/dev/null)"
+	[ "$(printf 'Hello\n' )" = "$OUTPUT" ] || exit 1
+else
+	[ "$LISTEN_FDS" = "1" ] || exit 1
+	read -r REQUEST
+	if [ "$(printf 'GET /hello HTTP/1.1\r\n')" = "$REQUEST" ]
+	then
+	    printf 'HTTP/1.1 200 OK\r\nContent-Length: 6\r\n\r\nHello\n'
+	else
+	    printf 'HTTP/1.1 400 Bad Request\r\nContent-Length: 5\r\n\r\nBad!\n'
+	fi
+fi

pkg/child/child.go

@@ -34,6 +34,23 @@ var propagationStates = map[string]uintptr{
 	"rslave":   uintptr(unix.MS_REC | unix.MS_SLAVE),
 }
 
+func setupFiles(cmd *exec.Cmd) {
+	// 0 1 and 2  are used for stdin. stdout, and stderr
+	const firstExtraFD = 3
+	systemdActivationFDs := 0
+	// check for systemd socket activation sockets
+	if v := os.Getenv("LISTEN_FDS"); v != "" {
+		if num, err := strconv.Atoi(v); err == nil {
+			systemdActivationFDs = num
+			cmd.ExtraFiles = make([]*os.File, systemdActivationFDs)
+		}
+	}
+	for fd := 0; fd < systemdActivationFDs; fd++ {
+		cmd.ExtraFiles[fd] = os.NewFile(uintptr(firstExtraFD + fd), "")
+	}
+}
+
+
 func createCmd(targetCmd []string) (*exec.Cmd, error) {
 	var args []string
 	if len(targetCmd) > 1 {
@@ -47,6 +64,7 @@ func createCmd(targetCmd []string) (*exec.Cmd, error) {
 	cmd.SysProcAttr = &syscall.SysProcAttr{
 		Pdeathsig: syscall.SIGKILL,
 	}
+	setupFiles(cmd)
 	return cmd, nil
 }
 

pkg/parent/parent.go

@@ -125,6 +125,27 @@ func LockStateDir(stateDir string) (*flock.Flock, error) {
 	return lock, nil
 }
 
+func setupFilesAndEnv(cmd *exec.Cmd, readPipe *os.File, writePipe *os.File, envKey string) {
+	// 0 1 and 2  are used for stdin. stdout, and stderr
+	const firstExtraFD = 3
+	systemdActivationFDs := 0
+	// check for systemd socket activation sockets
+	if v := os.Getenv("LISTEN_FDS"); v != "" {
+		if num, err := strconv.Atoi(v); err == nil {
+			systemdActivationFDs = num
+		}
+	}
+	cmd.ExtraFiles = make([]*os.File, systemdActivationFDs + 2)
+	for fd := 0; fd < systemdActivationFDs; fd++ {
+		cmd.ExtraFiles[fd] = os.NewFile(uintptr(firstExtraFD + fd), "")
+	}
+	readIndex := systemdActivationFDs
+	writeIndex := readIndex + 1
+	cmd.ExtraFiles[readIndex] = readPipe
+	cmd.ExtraFiles[writeIndex] = writePipe
+	cmd.Env = append(os.Environ(), envKey+"="+strconv.Itoa(firstExtraFD+readIndex)+","+strconv.Itoa(firstExtraFD+writeIndex))
+}
+
 func Parent(opt Opt) error {
 	if err := checkPreflight(opt); err != nil {
 		return err
@@ -178,8 +199,7 @@ func Parent(opt Opt) error {
 	cmd.Stdin = os.Stdin
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr
-	cmd.ExtraFiles = []*os.File{pipeR, pipe2W}
-	cmd.Env = append(os.Environ(), opt.PipeFDEnvKey+"=3,4")
+	setupFilesAndEnv(cmd, pipeR, pipe2W, opt.PipeFDEnvKey)
 	if opt.StateDirEnvKey != "" {
 		cmd.Env = append(cmd.Env, opt.StateDirEnvKey+"="+opt.StateDir)
 	}