fix missing definition for group flag

cmd/cubby/main.go

@@ -8,6 +8,7 @@ import (
 	"net"
 	"os"
 	"os/signal"
+	"os/user"
 	"strconv"
 	"strings"
 	"sync"
@@ -257,20 +258,58 @@ func tokenize(line string) ([]string, error) {
 	return args, nil
 }
 
+// lookupGID resolves a group name or numeric GID string to a GID.
+func lookupGID(s string) (int, error) {
+	if n, err := strconv.Atoi(s); err == nil {
+		return n, nil
+	}
+	g, err := user.LookupGroup(s)
+	if err != nil {
+		return 0, fmt.Errorf("lookup group %q: %w", s, err)
+	}
+	n, err := strconv.Atoi(g.Gid)
+	if err != nil {
+		return 0, fmt.Errorf("parse gid %q: %w", g.Gid, err)
+	}
+	return n, nil
+}
+
 func main() {
 	sock := flag.String("socket", "/tmp/cubby.sock", "unix socket path")
+	group := flag.String("group", "", "group name or GID to share the socket with (mode 0660); default is owner-only (0600)")
 	flag.Parse()
 
+	mode := os.FileMode(0600)
+	gid := -1
+	if *group != "" {
+		g, err := lookupGID(*group)
+		if err != nil {
+			log.Fatalf("group: %v", err)
+		}
+		gid = g
+		mode = 0660
+	}
+
 	// Clean up any stale socket file from a previous run.
 	if _, err := os.Stat(*sock); err == nil {
 		_ = os.Remove(*sock)
 	}
 
+	// Set umask before Listen so the socket is created with the desired
+	// permissions immediately, with no window where it's world-accessible.
+	oldMask := syscall.Umask(int(^mode & 0777))
 	ln, err := net.Listen("unix", *sock)
+	syscall.Umask(oldMask)
 	if err != nil {
 		log.Fatalf("listen: %v", err)
 	}
-	_ = os.Chmod(*sock, 0600) // current user only
+	if gid != -1 {
+		if err := os.Chown(*sock, os.Getuid(), gid); err != nil {
+			log.Fatalf("chown socket: %v", err)
+		}
+	}
+	// Belt-and-suspenders: ensure the final mode regardless of umask quirks.
+	_ = os.Chmod(*sock, mode)
 
 	store := NewStore()