feat: full NFSv4.2 server and client in pure Go

Assisted-by: GLM 5.3 Flash

internal/nfsfs/xattr_linux_test.go

@@ -0,0 +1,64 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: MIT
+
+//go:build linux
+
+package nfsfs
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestLocalXattr(t *testing.T) {
+	root := t.TempDir()
+	if err := os.WriteFile(filepath.Join(root, "a.txt"), []byte("x"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	l, err := NewLocal(root)
+	if err != nil {
+		t.Fatal(err)
+	}
+	rootHandle, err := l.Root()
+	if err != nil {
+		t.Fatal(err)
+	}
+	fh, _, err := l.Lookup(rootHandle, "a.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := l.GetXattr(fh, "user.tag", 0); err != ErrNoXattr {
+		t.Fatalf("missing attribute: %v", err)
+	}
+	if err := l.SetXattr(fh, "user.tag", []byte("value"), XattrModeCreate); err != nil {
+		t.Fatalf("create: %v", err)
+	}
+	if err := l.SetXattr(fh, "user.tag", []byte("again"), XattrModeCreate); err == nil {
+		t.Fatal("create over a live attribute succeeded")
+	}
+	got, err := l.GetXattr(fh, "user.tag", 0)
+	if err != nil || string(got) != "value" {
+		t.Fatalf("value after the refused create %q: %v", got, err)
+	}
+	if err := l.SetXattr(fh, "user.tag", []byte("again"), XattrModeReplace); err != nil {
+		t.Fatalf("replace: %v", err)
+	}
+	got, err = l.GetXattr(fh, "user.tag", 0)
+	if err != nil || string(got) != "again" {
+		t.Fatalf("value after the replace %q: %v", got, err)
+	}
+	names, err := l.ListXattr(fh, 0)
+	if err != nil || len(names) != 1 || names[0] != "user.tag" {
+		t.Fatalf("names %v: %v", names, err)
+	}
+	if err := l.SetXattr(fh, "system.nfs", []byte("x"), XattrModeCreate); err == nil {
+		t.Fatal("a foreign namespace was accepted")
+	}
+	if err := l.RemoveXattr(fh, "user.tag"); err != nil {
+		t.Fatalf("remove: %v", err)
+	}
+	if err := l.RemoveXattr(fh, "user.tag"); err != ErrNoXattr {
+		t.Fatalf("remove again: %v", err)
+	}
+}