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

Assisted-by: GLM 5.3 Flash

internal/nfs4/bitmap.go

@@ -0,0 +1,94 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: MIT
+
+package nfs4
+
+import (
+	"slices"
+
+	"sourcedock.dev/petrbalvin/nfs/internal/xdr"
+)
+
+// maxBitmapWords is the word count limit of a bitmap4. The protocol caps
+// the array at 100 words; the attribute table today ends far below that.
+const maxBitmapWords = 100
+
+// A Bitmap is a bitmap4: a compact set of attribute numbers.
+type Bitmap []uint32
+
+// OfBits returns a Bitmap carrying exactly the given attribute numbers.
+func OfBits(bits ...uint32) Bitmap {
+	if len(bits) == 0 {
+		return Bitmap{}
+	}
+	var words Bitmap
+	for _, n := range bits {
+		w := int(n / 32)
+		for len(words) <= w {
+			words = append(words, 0)
+		}
+		words[w] |= 1 << (n % 32)
+	}
+	return words
+}
+
+// Has reports whether the attribute number n is set.
+func (m Bitmap) Has(n uint32) bool {
+	w := int(n / 32)
+	return w < len(m) && m[w]&(1<<(n%32)) != 0
+}
+
+// With returns a bitmap carrying n in addition to what was already set.
+// Words the original bitmap already held are never dropped, even when the
+// new bit lands in a lower word.
+func (m Bitmap) With(n uint32) Bitmap {
+	w := int(n / 32)
+	out := make(Bitmap, max(w+1, len(m)))
+	copy(out, m)
+	out[w] |= 1 << (n % 32)
+	return out
+}
+
+// AppendTo appends the bitmap in wire form: a count of words followed by
+// the words, with trailing zero words trimmed.
+func (m Bitmap) AppendTo(b []byte) []byte {
+	trimmed := m
+	for len(trimmed) > 0 && trimmed[len(trimmed)-1] == 0 {
+		trimmed = trimmed[:len(trimmed)-1]
+	}
+	b = xdr.AppendUint32(b, uint32(len(trimmed)))
+	for _, w := range trimmed {
+		b = xdr.AppendUint32(b, w)
+	}
+	return b
+}
+
+// ReadBitmap reads a bitmap4. A bitmap beyond the word limit is refused
+// before any of it is buffered.
+func ReadBitmap(d *xdr.Decoder) (Bitmap, error) {
+	n, err := d.Uint32()
+	if err != nil {
+		return nil, err
+	}
+	if n > maxBitmapWords {
+		return nil, xdr.ErrBadLength
+	}
+	m := make(Bitmap, 0, n)
+	for range n {
+		w, err := d.Uint32()
+		if err != nil {
+			return nil, err
+		}
+		m = append(m, w)
+	}
+	return m, nil
+}
+
+// Words reports the words of the bitmap, without trailing zero words.
+func (m Bitmap) Words() []uint32 {
+	trimmed := slices.Clone(m)
+	for len(trimmed) > 0 && trimmed[len(trimmed)-1] == 0 {
+		trimmed = trimmed[:len(trimmed)-1]
+	}
+	return trimmed
+}