Allow to daemonize the app

1 files changed, 105 insertions, 19 deletions

diff --git a/daemon.go b/daemon.go
index 54592de8..5fc4b651 100644
--- a/daemon.go
+++ b/daemon.go
@@ -6,61 +6,147 @@ import (
 	"os/exec"
 	"os/user"
 
+	"encoding/json"
 	"fmt"
 	"github.com/kardianos/osext"
+	"os/signal"
 	"strconv"
 	"syscall"
 )
 
-func daemonize() {
-	if *pagesUser == "" {
+const daemonRunProgram = "daemon-run"
+
+func daemonMain() {
+	if os.Args[0] != daemonRunProgram {
 		return
 	}
 
+	fmt.Printf("Starting the daemon as unprivileged user...\n")
+
+	// read the configuration from the pipe "ExtraFiles"
+	var config appConfig
+	if err := json.NewDecoder(os.NewFile(3, "options")).Decode(&config); err != nil {
+		log.Fatalln(err)
+	}
+	runApp(config)
+	os.Exit(0)
+}
+
+func daemonReexec(cmdUser string, args ...string) (cmd *exec.Cmd, err error) {
 	path, err := osext.Executable()
 	if err != nil {
-		log.Fatalln(err)
+		return
 	}
 
-	u, err := user.Lookup(*pagesUser)
+	u, err := user.Lookup(cmdUser)
 	if err != nil {
-		log.Fatalln(err)
+		return
 	}
 
 	uid, err := strconv.Atoi(u.Uid)
 	if err != nil {
-		log.Fatalln(err)
+		return
 	}
 
 	gid, err := strconv.Atoi(u.Gid)
 	if err != nil {
-		log.Fatalln(err)
+		return
 	}
 
-	cmd := &exec.Cmd{
+	cmd = &exec.Cmd{
 		Path:   path,
-		Args:   append(os.Args, "-pages-user", "", "-pages-root", "/"),
+		Args:   args,
 		Stdin:  os.Stdin,
 		Stdout: os.Stdout,
 		Stderr: os.Stderr,
 		SysProcAttr: &syscall.SysProcAttr{
-			Chroot: *pagesRoot,
 			Credential: &syscall.Credential{
 				Uid: uint32(uid),
 				Gid: uint32(gid),
 			},
-			//Setsid:     true,
-			Setpgid: true,
+			Setsid: true,
 		},
 	}
-	//cmd.SysProcAttr = nil
+	return
+}
 
-	fmt.Println("Deamonizing as", uid, "and", gid, "...")
-	err = cmd.Run()
+func daemonUpdateFd(cmd *exec.Cmd, fd *uintptr) {
+	if *fd == 0 {
+		return
+	}
+
+	file := os.NewFile(*fd, "[socket]")
+	// we add 3 since, we have a 3 predefined FDs
+	*fd = uintptr(3 + len(cmd.ExtraFiles))
+	cmd.ExtraFiles = append(cmd.ExtraFiles, file)
+}
+
+func killProcess(cmd *exec.Cmd) {
+	if cmd.Process != nil {
+		cmd.Process.Kill()
+	}
+	cmd.Wait()
+	for _, file := range cmd.ExtraFiles {
+		file.Close()
+	}
+}
+
+func passSignals(cmd *exec.Cmd) {
+	s := make(chan os.Signal)
+	signal.Notify(s, syscall.SIGTERM)
+
+	go func() {
+		for {
+			<-s
+			if cmd.Process != nil {
+				cmd.Process.Kill()
+			}
+		}
+	}()
+}
+
+func daemonize(config appConfig, cmdUser string) {
+	var err error
+	defer func() {
+		if err != nil {
+			log.Fatalln(err)
+		}
+	}()
+	fmt.Printf("Running the daemon as unprivileged user: %v...\n", cmdUser)
+
+	cmd, err := daemonReexec(cmdUser, daemonRunProgram)
 	if err != nil {
-		log.Fatalln(err)
-		os.Exit(1)
-	} else {
-		os.Exit(0)
+		return
 	}
+	defer killProcess(cmd)
+
+	// Create a pipe to pass the configuration
+	configReader, configWriter, err := os.Pipe()
+	if err != nil {
+		return
+	}
+	defer configWriter.Close()
+	cmd.ExtraFiles = append(cmd.ExtraFiles, configReader)
+
+	// Create a new file and store the FD
+	daemonUpdateFd(cmd, &config.ListenHTTP)
+	daemonUpdateFd(cmd, &config.ListenHTTPS)
+	daemonUpdateFd(cmd, &config.listenProxy)
+
+	// Start the process
+	if err = cmd.Start(); err != nil {
+		return
+	}
+
+	// Write the configuration
+	if err = json.NewEncoder(configWriter).Encode(config); err != nil {
+		return
+	}
+	configWriter.Close()
+
+	// Pass through signals
+	passSignals(cmd)
+
+	// Wait for process to exit
+	err = cmd.Wait()
 }