Add handling of SIGINT and SIGTERM

Handle exit signals so that deferred calls are executed. It's mainly
to unlink the socket before exiting.

cmd/tokidoki/main.go

@@ -8,7 +8,9 @@ import (
 	"net"
 	"net/http"
 	"os"
+	"os/signal"
 	"strings"
+	"syscall"
 
 	"github.com/emersion/go-webdav"
 	"github.com/emersion/go-webdav/caldav"
@@ -189,6 +191,7 @@ func main() {
 	log.Info().Str("address", addr).Msg("starting server")
 	log.Debug().Msg("debug output enabled")
 
+	go func() {
 		if (cert != "") && (key != "") {
 			err = server.ServeTLS(ln, cert, key)
 		} else {
@@ -197,4 +200,15 @@ func main() {
 		if err != http.ErrServerClosed {
 			log.Fatal().Err(err).Msg("ListenAndServe() error")
 		}
+	}()
+
+	sigCh := make(chan os.Signal, 1)
+	signal.Notify(sigCh, syscall.SIGINT, syscall.SIGTERM)
+	for sig := range sigCh {
+		switch sig {
+		case syscall.SIGINT, syscall.SIGTERM:
+			server.Shutdown(context.Background())
+			return
+		}
+	}
 }