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

Assisted-by: GLM 5.3 Flash

internal/nfsfs/local_cache_linux_test.go

@@ -0,0 +1,73 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: MIT
+
+package nfsfs
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// openFDs counts the descriptors the process holds through /proc. The
+// count is a lower bound of live descriptors and good enough to prove a
+// cache does not leak: a thousand operations over one file must not add a
+// thousand descriptors.
+func openFDs(t *testing.T) int {
+	t.Helper()
+	entries, err := os.ReadDir("/proc/self/fd")
+	if err != nil {
+		t.Skipf("/proc/self/fd is unavailable: %v", err)
+	}
+	return len(entries)
+}
+
+// TestCacheNoDescriptorLeak drives more operations over one file than the
+// cache can hold and requires the process descriptor count to stay flat.
+func TestCacheNoDescriptorLeak(t *testing.T) {
+	l, h, _ := cacheTestRoot(t, "leak")
+	before := openFDs(t)
+	for range 1000 {
+		if _, err := l.Read(h, 0, 4); err != nil {
+			t.Fatalf("Read: %v", err)
+		}
+	}
+	after := openFDs(t)
+	if after-before > 8 {
+		t.Fatalf("descriptors grew from %d to %d over 1000 reads", before, after)
+	}
+}
+
+// TestCacheBound holds when many distinct files flow through: after
+// touching twice the bound, at most the bound of cache entries may remain.
+func TestCacheBound(t *testing.T) {
+	root := t.TempDir()
+	l, err := NewLocal(root)
+	if err != nil {
+		t.Fatalf("NewLocal: %v", err)
+	}
+	rh, err := l.Root()
+	if err != nil {
+		t.Fatalf("Root: %v", err)
+	}
+	for i := range 2 * fdCacheLimit {
+		name := fmt.Sprintf("f%d", i)
+		if err := os.WriteFile(filepath.Join(root, name), []byte("x"), 0o644); err != nil {
+			t.Fatalf("WriteFile: %v", err)
+		}
+		h, _, err := l.Lookup(rh, name)
+		if err != nil {
+			t.Fatalf("Lookup: %v", err)
+		}
+		if _, err := l.Read(h, 0, 1); err != nil {
+			t.Fatalf("Read %s: %v", name, err)
+		}
+	}
+	l.fdMu.Lock()
+	n := len(l.fds)
+	l.fdMu.Unlock()
+	if n > fdCacheLimit {
+		t.Fatalf("cache holds %d entries, bound is %d", n, fdCacheLimit)
+	}
+}