138 lines
3.1 KiB
Go
138 lines
3.1 KiB
Go
package winio
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import (
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"bytes"
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"encoding/binary"
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"errors"
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)
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type fileFullEaInformation struct {
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NextEntryOffset uint32
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Flags uint8
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NameLength uint8
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ValueLength uint16
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}
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var (
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fileFullEaInformationSize = binary.Size(&fileFullEaInformation{})
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errInvalidEaBuffer = errors.New("invalid extended attribute buffer")
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errEaNameTooLarge = errors.New("extended attribute name too large")
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errEaValueTooLarge = errors.New("extended attribute value too large")
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)
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// ExtendedAttribute represents a single Windows EA.
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type ExtendedAttribute struct {
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Name string
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Value []byte
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Flags uint8
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}
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func parseEa(b []byte) (ea ExtendedAttribute, nb []byte, err error) {
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var info fileFullEaInformation
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err = binary.Read(bytes.NewReader(b), binary.LittleEndian, &info)
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if err != nil {
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err = errInvalidEaBuffer
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return
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}
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nameOffset := fileFullEaInformationSize
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nameLen := int(info.NameLength)
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valueOffset := nameOffset + int(info.NameLength) + 1
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valueLen := int(info.ValueLength)
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nextOffset := int(info.NextEntryOffset)
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if valueLen+valueOffset > len(b) || nextOffset < 0 || nextOffset > len(b) {
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err = errInvalidEaBuffer
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return
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}
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ea.Name = string(b[nameOffset : nameOffset+nameLen])
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ea.Value = b[valueOffset : valueOffset+valueLen]
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ea.Flags = info.Flags
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if info.NextEntryOffset != 0 {
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nb = b[info.NextEntryOffset:]
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}
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return
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}
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// DecodeExtendedAttributes decodes a list of EAs from a FILE_FULL_EA_INFORMATION
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// buffer retrieved from BackupRead, ZwQueryEaFile, etc.
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func DecodeExtendedAttributes(b []byte) (eas []ExtendedAttribute, err error) {
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for len(b) != 0 {
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ea, nb, err := parseEa(b)
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if err != nil {
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return nil, err
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}
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eas = append(eas, ea)
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b = nb
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}
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return
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}
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func writeEa(buf *bytes.Buffer, ea *ExtendedAttribute, last bool) error {
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if int(uint8(len(ea.Name))) != len(ea.Name) {
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return errEaNameTooLarge
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}
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if int(uint16(len(ea.Value))) != len(ea.Value) {
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return errEaValueTooLarge
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}
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entrySize := uint32(fileFullEaInformationSize + len(ea.Name) + 1 + len(ea.Value))
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withPadding := (entrySize + 3) &^ 3
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nextOffset := uint32(0)
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if !last {
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nextOffset = withPadding
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}
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info := fileFullEaInformation{
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NextEntryOffset: nextOffset,
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Flags: ea.Flags,
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NameLength: uint8(len(ea.Name)),
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ValueLength: uint16(len(ea.Value)),
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}
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err := binary.Write(buf, binary.LittleEndian, &info)
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if err != nil {
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return err
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}
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_, err = buf.Write([]byte(ea.Name))
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if err != nil {
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return err
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}
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err = buf.WriteByte(0)
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if err != nil {
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return err
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}
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_, err = buf.Write(ea.Value)
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if err != nil {
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return err
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}
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_, err = buf.Write([]byte{0, 0, 0}[0 : withPadding-entrySize])
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if err != nil {
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return err
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}
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return nil
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}
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// EncodeExtendedAttributes encodes a list of EAs into a FILE_FULL_EA_INFORMATION
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// buffer for use with BackupWrite, ZwSetEaFile, etc.
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func EncodeExtendedAttributes(eas []ExtendedAttribute) ([]byte, error) {
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var buf bytes.Buffer
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for i := range eas {
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last := false
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if i == len(eas)-1 {
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last = true
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}
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err := writeEa(&buf, &eas[i], last)
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if err != nil {
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return nil, err
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}
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}
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return buf.Bytes(), nil
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}
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