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

Assisted-by: GLM 5.3 Flash

internal/nfsfs/sparse_linux_test.go

@@ -0,0 +1,74 @@
+// 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 TestLocalSparse(t *testing.T) {
+	root := t.TempDir()
+	if err := os.WriteFile(filepath.Join(root, "s.bin"), make([]byte, 8192), 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, "s.bin")
+	if err != nil {
+		t.Fatal(err)
+	}
+	// The file is all data: the only hole is the virtual one every file
+	// carries at its end, so the seek answers the size with the eof flag,
+	// RFC 7862 section 15.11.
+	off, eof, err := l.SeekHole(fh, 0)
+	if err != nil || off != 8192 || !eof {
+		t.Fatalf("hole in a full file: %d %v %v", off, eof, err)
+	}
+	if off, eof, err := l.SeekData(fh, 0); err != nil || off != 0 || eof {
+		t.Fatalf("seek data: %d %v %v", off, eof, err)
+	}
+	// A seek past the end is NXIO, not an answer.
+	if _, _, err := l.SeekData(fh, 8193); err != ErrBeyondEOF {
+		t.Fatalf("seek past the end: %v", err)
+	}
+	// Punching a hole moves the first hole to the punched offset.
+	if err := l.Deallocate(fh, 4096, 4096); err != nil {
+		t.Fatalf("deallocate: %v", err)
+	}
+	off, eof, err = l.SeekHole(fh, 0)
+	if err != nil || off != 4096 || eof {
+		t.Fatalf("seek hole: %d %v %v", off, eof, err)
+	}
+	// No data follows inside the hole: the answer names the size with
+	// the eof flag.
+	if off, eof, err := l.SeekData(fh, 4096); err != nil || off != 8192 || !eof {
+		t.Fatalf("data in the hole: %d %v %v", off, eof, err)
+	}
+	// Allocate reserves the space without moving the hole back.
+	if err := l.Allocate(fh, 4096, 4096); err != nil {
+		t.Fatalf("allocate: %v", err)
+	}
+	if off, eof, err := l.SeekHole(fh, 0); err != nil || off != 4096 || eof {
+		t.Fatalf("seek hole after allocate: %d %v %v", off, eof, err)
+	}
+	// Allocate past the end grows the file to the end of the reserved
+	// range, which RFC 7862 section 15.1 requires.
+	if err := l.Allocate(fh, 8192, 4096); err != nil {
+		t.Fatalf("allocate past eof: %v", err)
+	}
+	info, err := l.Getattr(fh)
+	if err != nil || info.Size != 12288 {
+		t.Fatalf("size after the allocate past eof: %d, %v", info.Size, err)
+	}
+}