nfs/internal/nfsfs/ro.go

// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: MIT

package nfsfs

import (
	"errors"
)

// ErrReadOnly marks an operation a read only export refuses, NFS4ERR_ROFS
// on the wire.
var ErrReadOnly = errors.New("nfsfs: the export is read only")

// A roFS wraps an export and hides its mutating halves. The Writer half
// is gone, so the dispatcher answers NFS4ERR_ROFS for every operation
// that would change anything through it. The optional halves keep their
// reads and refuse their writes with ErrReadOnly, so an export served
// read only still reports its extended attributes, its holes and its
// named attributes, and refuses to touch them.
type roFS struct{ FS }

// ReadOnly serves fs read only: the reads of every half pass through, the
// writes of the mutating halves answer ErrReadOnly, and the mutating
// Writer half disappears from the type.
func ReadOnly(fs FS) FS {
	return roFS{fs}
}

// GetXattr reads one named attribute of the object.
func (ro roFS) GetXattr(h Handle, name string, max int) ([]byte, error) {
	x, ok := ro.FS.(XattrFS)
	if !ok {
		return nil, ErrXattrNotSupp
	}
	return x.GetXattr(h, name, max)
}

// ListXattr names the attributes of the object.
func (ro roFS) ListXattr(h Handle, max int) ([]string, error) {
	x, ok := ro.FS.(XattrFS)
	if !ok {
		return nil, ErrXattrNotSupp
	}
	return x.ListXattr(h, max)
}

// SetXattr refuses a write on a read only export.
func (ro roFS) SetXattr(h Handle, name string, value []byte, mode uint32) error {
	return ErrReadOnly
}

// RemoveXattr refuses a write on a read only export.
func (ro roFS) RemoveXattr(h Handle, name string) error {
	return ErrReadOnly
}

// SeekHole reports the first hole at or after the offset.
func (ro roFS) SeekHole(h Handle, offset int64) (int64, bool, error) {
	s, ok := ro.FS.(interface {
		SeekHole(Handle, int64) (int64, bool, error)
		SeekData(Handle, int64) (int64, bool, error)
	})
	if !ok {
		return 0, false, ErrNoSparse
	}
	return s.SeekHole(h, offset)
}

// SeekData reports the first data byte at or after the offset.
func (ro roFS) SeekData(h Handle, offset int64) (int64, bool, error) {
	s, ok := ro.FS.(interface {
		SeekHole(Handle, int64) (int64, bool, error)
		SeekData(Handle, int64) (int64, bool, error)
	})
	if !ok {
		return 0, false, ErrNoSparse
	}
	return s.SeekData(h, offset)
}

// Allocate refuses a space reservation on a read only export.
func (ro roFS) Allocate(h Handle, offset, length int64) error {
	return ErrReadOnly
}

// Deallocate refuses a hole punch on a read only export.
func (ro roFS) Deallocate(h Handle, offset, length int64) error {
	return ErrReadOnly
}