Add --port

main.go

@@ -8,6 +8,7 @@ import (
 	"flag"
 	"fmt"
 	"log/slog"
+	"net"
 	"net/http"
 	"os"
 	"os/signal"
@@ -99,6 +100,13 @@ func serve(args []string) error {
 		ErrorLog:          slog.NewLogLogger(log.Handler(), slog.LevelWarn),
 	}
 
+	// Bind before announcing anything: logging "listening" and only then
+	// failing to bind reads as a server that started and then died.
+	ln, err := net.Listen("tcp", cfg.Listen)
+	if err != nil {
+		return err
+	}
+
 	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
 	defer stop()
 
@@ -106,14 +114,14 @@ func serve(args []string) error {
 	go reloadOnHUP(ctx, tokens, log)
 
 	log.Info("listening",
-		"addr", cfg.Listen, "data", cfg.DataDir, "base", cfg.BasePath,
+		"addr", ln.Addr().String(), "data", cfg.DataDir, "base", cfg.BasePath,
 		"objects", st.Count(), "stored", config.FormatBytes(st.Total()),
 		"max_size", config.FormatSize(cfg.MaxSize),
 		"max_expiry", config.FormatDuration(cfg.MaxExpiry))
 
 	errc := make(chan error, 1)
 	go func() {
-		err := httpSrv.ListenAndServe()
+		err := httpSrv.Serve(ln)
 		if errors.Is(err, http.ErrServerClosed) {
 			err = nil
 		}