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

Assisted-by: GLM 5.3 Flash

internal/nfs4server/xattr.go

@@ -0,0 +1,141 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: MIT
+
+// The handlers of the extended attribute family, RFC 8276. A backend
+// without the XattrFS half answers NOT_SUPP to all of them.
+
+package nfs4server
+
+import (
+	"sourcedock.dev/petrbalvin/nfs/internal/nfs4"
+	"sourcedock.dev/petrbalvin/nfs/internal/nfsfs"
+	"sourcedock.dev/petrbalvin/nfs/internal/xdr"
+)
+
+// xattrFS resolves the backend's xattr half, or nil when it has none.
+func (h *Handler) xattrFS() nfsfs.XattrFS {
+	x, _ := h.FS.(nfsfs.XattrFS)
+	return x
+}
+
+// getXattrOp serves GETXATTR: one named value of the current object.
+// The argument is the name alone, RFC 8276.
+func (h *Handler) getXattrOp(d *xdr.Decoder, reg *fhreg) ([]byte, uint32, error) {
+	name, err := d.String()
+	if err != nil {
+		return nil, 0, err
+	}
+	if !reg.haveCur {
+		return nil, nfs4.ErrNoFileHandle, nil
+	}
+	x := h.xattrFS()
+	if x == nil {
+		return nil, nfs4.ErrNotSupp, nil
+	}
+	value, xerr := x.GetXattr(reg.cur, name, 0)
+	if xerr == nfsfs.ErrNoXattr {
+		return nil, nfs4.ErrNoXattr, nil
+	}
+	if xerr == nfsfs.ErrXattrNotSupp {
+		return nil, nfs4.ErrNotSupp, nil
+	}
+	if xerr != nil {
+		return nil, mapErr(xerr), nil
+	}
+	return nfs4.AppendGetXattrRes(nil, value), nfs4.ErrOK, nil
+}
+
+// setXattrOp serves SETXATTR: it writes or creates or replaces one named
+// value of the current object. The argument order is the mode, the key
+// and the value, RFC 8276.
+func (h *Handler) setXattrOp(d *xdr.Decoder, reg *fhreg) ([]byte, uint32, error) {
+	mode, err := d.Uint32()
+	if err != nil {
+		return nil, 0, err
+	}
+	name, err := d.String()
+	if err != nil {
+		return nil, 0, err
+	}
+	value, err := d.VarOpaque()
+	if err != nil {
+		return nil, 0, err
+	}
+	if !reg.haveCur {
+		return nil, nfs4.ErrNoFileHandle, nil
+	}
+	x := h.xattrFS()
+	if x == nil {
+		return nil, nfs4.ErrNotSupp, nil
+	}
+	if err := x.SetXattr(reg.cur, name, value, mode); err != nil {
+		if err == nfsfs.ErrXattrNotSupp {
+			return nil, nfs4.ErrNotSupp, nil
+		}
+		return nil, mapErr(err), nil
+	}
+	return nil, nfs4.ErrOK, nil
+}
+
+// listXattrOp serves LISTXATTR: the names of the current object's
+// attributes, one page bounded by the budget. The whole list answers in
+// one page with the end of list flag set, so a resume cookie never
+// names a remaining entry: cookie zero answers everything and any other
+// cookie answers an empty final page, RFC 8276 section 5.
+func (h *Handler) listXattrOp(d *xdr.Decoder, reg *fhreg) ([]byte, uint32, error) {
+	cookie, err := d.Uint64()
+	if err != nil {
+		return nil, 0, err
+	}
+	maxcount, err := d.Uint32()
+	if err != nil {
+		return nil, 0, err
+	}
+	if maxcount > 1<<20 {
+		maxcount = 1 << 20
+	}
+	if !reg.haveCur {
+		return nil, nfs4.ErrNoFileHandle, nil
+	}
+	x := h.xattrFS()
+	if x == nil {
+		return nil, nfs4.ErrNotSupp, nil
+	}
+	names := []string{}
+	if cookie == 0 {
+		names, err = x.ListXattr(reg.cur, int(maxcount))
+		if err == nfsfs.ErrXattrNotSupp {
+			return nil, nfs4.ErrNotSupp, nil
+		}
+		if err != nil {
+			return nil, mapErr(err), nil
+		}
+	}
+	return nfs4.AppendListXattrRes(nil, cookie, names, true), nfs4.ErrOK, nil
+}
+
+// removeXattrOp serves REMOVEXATTR: it deletes one named value of the
+// current object.
+func (h *Handler) removeXattrOp(d *xdr.Decoder, reg *fhreg) ([]byte, uint32, error) {
+	name, err := d.String()
+	if err != nil {
+		return nil, 0, err
+	}
+	if !reg.haveCur {
+		return nil, nfs4.ErrNoFileHandle, nil
+	}
+	x := h.xattrFS()
+	if x == nil {
+		return nil, nfs4.ErrNotSupp, nil
+	}
+	if err := x.RemoveXattr(reg.cur, name); err != nil {
+		if err == nfsfs.ErrNoXattr {
+			return nil, nfs4.ErrNoXattr, nil
+		}
+		if err == nfsfs.ErrXattrNotSupp {
+			return nil, nfs4.ErrNotSupp, nil
+		}
+		return nil, mapErr(err), nil
+	}
+	return nil, nfs4.ErrOK, nil
+}