pidfiles, graceful shutdown

main.go

@@ -1,31 +1,58 @@
 package main
 
 import (
+	"bytes"
+	"encoding/binary"
+	"flag"
 	"log"
 	"os"
+	"os/exec"
 	"sync"
 )
 
 var config Config
 
 const sockfile = "/tmp/gopaper.sock"
+const pidfilePath = "/tmp/gopaper.pid"
 
 func main() {
+	//SETUP FLAGS
+	var debugFlag = flag.Bool("debug", false, "help message for flag n")
+	flag.Parse()
 
-	//TODO:kill existing processes
+	//INITIALIZE CONFIG
-
-	log.SetFlags(log.LstdFlags | log.Lshortfile)
-
 	err := config.load()
-	logfile, err := openLogfile()
 	if err != nil {
-		log.Println("failed to load config", err)
+		log.Println("unable to initialize config", err)
-		cleanExit(1)
+	}
+
+	//SETUP LOGGER
+	log.SetFlags(log.LstdFlags | log.Lshortfile)
+	if *debugFlag {
+		logfile, err := openLogfile()
+		if err != nil {
+			log.Println("failed to load config", err)
+			cleanExit(1)
+		}
+		log.SetOutput(logfile)
 	}
-	log.SetOutput(logfile)
 	log.SetFlags(log.LstdFlags | log.Lshortfile | log.Lmicroseconds)
 	log.Println("Welcome to GoPaper!")
 
+	killPrevProc()
+	//create new pidfile
+	pid := os.Getpid()
+	pidfile, err := os.Create(pidfilePath)
+	if err != nil {
+		log.Println("error trying to create pidfile:", err)
+		cleanExit(1)
+	}
+	buf := new(bytes.Buffer)
+	err = binary.Write(buf, binary.LittleEndian, pid)
+	if err != nil {
+	}
+	pidfile.Write(buf.Bytes())
+
 	var waitGroup sync.WaitGroup
 	waitGroup.Add(1)
 	slideshowDir := make(chan string)
@@ -33,7 +60,7 @@ func main() {
 	func() {
 		defer func() {
 			if r := recover(); r != nil {
-				log.Println("Panic recovered at top level. Closing gracefully.", r)
+				log.Println("Panic recovered at top level", r)
 				cleanExit(1)
 			}
 		}()
@@ -63,6 +90,55 @@ func openLogfile() (*os.File, error) {
 }
 
 func cleanExit(code int) {
-	os.Remove(sockfile)
+	if code == 1 {
+		log.Println("shutting down gracefully after errors")
+	} else {
+		log.Println("shutting down gracefully")
+	}
+
+	err := os.Remove(sockfile)
+	if err != nil && !os.IsNotExist(err) {
+		log.Printf("unable to remove sockfile at %v. Error: %v\n", sockfile, err)
+	} else if !os.IsNotExist(err) {
+		log.Println("sockfile removed")
+	} else {
+		log.Println("no need to remove sockfile -- it doesn't exist")
+	}
+
+	err = os.Remove(pidfilePath)
+	if err != nil && !os.IsNotExist(err) {
+		log.Printf("unable to remove pidfile at %v. Error: %v\n", pidfilePath, err)
+	} else if !os.IsNotExist(err) {
+		log.Println("pidfile removed")
+	} else {
+		log.Println("no need to remove pidfile -- it doesn't exist")
+	}
 	os.Exit(code)
 }
+
+func killPrevProc() error {
+	//check if pidfile already exists
+	if _, err := os.Stat(pidfilePath); os.IsNotExist(err) {
+		return nil
+	}
+	//if it does, kill the process and delete the pidfile
+	prexPid, err := os.ReadFile(pidfilePath)
+	if err != nil {
+		log.Println("unable to read pre-existing pidfile", err)
+		return err
+	}
+	//kill process
+	//BUG: kill command doesn't work. prexPid == []
+	err = exec.Command("kill", "-9", string(prexPid)).Run()
+	if err != nil {
+		log.Printf("unable to kill process %v\n", string(prexPid))
+		return err
+	}
+	//remove pidfile
+	err = os.Remove(pidfilePath)
+	if err != nil {
+		log.Printf("unable to remove pidfile %v\n", pidfilePath)
+		return err
+	}
+	return nil
+}

server.go

@@ -25,8 +25,7 @@ func server(slideshowDir chan string) {
 	signal.Notify(c, os.Interrupt, syscall.SIGTERM)
 	go func() {
 		<-c
-		os.Remove(sockfile)
+		cleanExit(0)
-		os.Exit(1)
 	}()
 
 	for {