Implement log rotation

Closes #132.

config.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"path/filepath"
 
 	"github.com/foxcpp/maddy/config"
 	"github.com/foxcpp/maddy/log"
@@ -34,7 +35,7 @@ func logOutput(m *config.Map, node *config.Node) (interface{}, error) {
 
 func LogOutputOption(args []string) (log.Output, error) {
 	outs := make([]log.Output, 0, len(args))
-	for _, arg := range args {
+	for i, arg := range args {
 		switch arg {
 		case "stderr":
 			outs = append(outs, log.WriterOutput(os.Stderr, false))
@@ -52,7 +53,18 @@ func LogOutputOption(args []string) (log.Output, error) {
 			}
 			return nil, nil
 		default:
-			w, err := os.OpenFile(arg, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0666)
+			// Log file paths are converted to absolute to make sure
+			// we will be able to recreate them in right location
+			// after changing working directory to the state dir.
+			absPath, err := filepath.Abs(arg)
+			if err != nil {
+				return nil, err
+			}
+			// We change the actual argument, so logOut object will
+			// keep the absolute path for reinitialization.
+			args[i] = absPath
+
+			w, err := os.OpenFile(absPath, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0666)
 			if err != nil {
 				return nil, fmt.Errorf("failed to create log file: %v", err)
 			}
@@ -70,3 +82,19 @@ func LogOutputOption(args []string) (log.Output, error) {
 func defaultLogOutput() (interface{}, error) {
 	return log.DefaultLogger.Out, nil
 }
+
+func reinitLogging() {
+	out, ok := log.DefaultLogger.Out.(logOut)
+	if !ok {
+		log.Println("Can't reinitialize logger because it was replaced before, this is a bug")
+		return
+	}
+
+	newOut, err := LogOutputOption(out.args)
+	if err != nil {
+		log.Println("Can't reinitialize logger:", err)
+		return
+	}
+
+	log.DefaultLogger.Out = newOut
+}

maddy.go

@@ -100,10 +100,21 @@ func Start(cfg []config.Node) error {
 	}
 
 	sig := make(chan os.Signal, 5)
-	signal.Notify(sig, os.Interrupt, syscall.SIGTERM, syscall.SIGHUP, syscall.SIGINT)
+	signal.Notify(sig, os.Interrupt, syscall.SIGTERM, syscall.SIGHUP, syscall.SIGINT, syscall.SIGUSR1)
+
+	for {
+		switch s := <-sig; s {
+		case syscall.SIGUSR1:
+			log.Println("SIGUSR1 received, reinitializing logging")
+			reinitLogging()
+		default:
+			log.Printf("signal received (%v), next signal will force immediate shutdown.", s)
+			// break inside switch exits switch, not outer loop
+			goto exitsigloop
+		}
+	}
+exitsigloop:
 
-	s := <-sig
-	log.Printf("signal received (%v), next signal will force immediate shutdown.", s)
 	go func() {
 		s := <-sig
 		log.Printf("forced shutdown due to signal (%v)!", s)