pidfiles, graceful shutdown

main.go

@@ -1,22 +1,60 @@
 package main
 
 import (
+	"bytes"
+	"encoding/binary"
+	"errors"
 	"log"
 	"os"
+	"os/exec"
 	"sync"
 )
 
 var config Config
 
 const sockfile = "/tmp/gopaper.sock"
+const pidfilePath = "/var/run/gopaper.pid"
 
 func main() {
-
-	//TODO:kill existing processes
-
 	log.SetFlags(log.LstdFlags | log.Lshortfile)
 
-	err := config.load()
+	//MANAGE PIDFILES
+	//check if pidfile already exists
+	if _, err := os.Stat(pidfilePath); !errors.Is(err, os.ErrNotExist) {
+		//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)
+			cleanExit(1)
+		}
+		//kill process
+		err = exec.Command("kill", "-9", string(prexPid)).Run()
+		if err != nil {
+			log.Printf("unable to kill process %v\n", prexPid)
+			cleanExit(1)
+		}
+		//remove pidfile
+		err = os.Remove(pidfilePath)
+		if err != nil {
+			log.Printf("unable to remove pidfile %v\n", pidfilePath)
+			cleanExit(1)
+		}
+	}
+
+	//create new pidfile
+	pid := os.Getpid()
+	pidfile, err := os.Create(pidfilePath)
+	if err != nil {
+		log.Println("could not create pidfile", err)
+		cleanExit(1)
+	}
+	buf := new(bytes.Buffer)
+	err = binary.Write(buf, binary.LittleEndian, pid)
+	if err != nil {
+	}
+	pidfile.Write(buf.Bytes())
+
+	err = config.load()
 	logfile, err := openLogfile()
 	if err != nil {
 		log.Println("failed to load config", err)
@@ -33,7 +71,7 @@ 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 +101,24 @@ 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 {
+		log.Printf("unable to remove sockfile at %v. Error: %v\n", sockfile, err)
+	} else {
+		log.Println("sockfile removed")
+	}
+
+	err = os.Remove(pidfilePath)
+	if err != nil {
+		log.Printf("unable to remove pidfile at %v. Error: %v\n", pidfilePath, err)
+	} else {
+		log.Println("pidfile removed")
+	}
 	os.Exit(code)
 }

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 {