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132 lines
3.4 KiB
Go
132 lines
3.4 KiB
Go
//go:build windows
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// +build windows
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package winio
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import (
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"bytes"
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"encoding/binary"
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"fmt"
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"strings"
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"unicode/utf16"
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"unsafe"
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)
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const (
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reparseTagMountPoint = 0xA0000003
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reparseTagSymlink = 0xA000000C
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)
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type reparseDataBuffer struct {
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ReparseTag uint32
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ReparseDataLength uint16
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Reserved uint16
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SubstituteNameOffset uint16
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SubstituteNameLength uint16
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PrintNameOffset uint16
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PrintNameLength uint16
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}
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// ReparsePoint describes a Win32 symlink or mount point.
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type ReparsePoint struct {
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Target string
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IsMountPoint bool
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}
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// UnsupportedReparsePointError is returned when trying to decode a non-symlink or
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// mount point reparse point.
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type UnsupportedReparsePointError struct {
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Tag uint32
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}
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func (e *UnsupportedReparsePointError) Error() string {
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return fmt.Sprintf("unsupported reparse point %x", e.Tag)
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}
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// DecodeReparsePoint decodes a Win32 REPARSE_DATA_BUFFER structure containing either a symlink
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// or a mount point.
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func DecodeReparsePoint(b []byte) (*ReparsePoint, error) {
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tag := binary.LittleEndian.Uint32(b[0:4])
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return DecodeReparsePointData(tag, b[8:])
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}
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func DecodeReparsePointData(tag uint32, b []byte) (*ReparsePoint, error) {
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isMountPoint := false
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switch tag {
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case reparseTagMountPoint:
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isMountPoint = true
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case reparseTagSymlink:
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default:
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return nil, &UnsupportedReparsePointError{tag}
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}
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nameOffset := 8 + binary.LittleEndian.Uint16(b[4:6])
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if !isMountPoint {
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nameOffset += 4
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}
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nameLength := binary.LittleEndian.Uint16(b[6:8])
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name := make([]uint16, nameLength/2)
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err := binary.Read(bytes.NewReader(b[nameOffset:nameOffset+nameLength]), binary.LittleEndian, &name)
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if err != nil {
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return nil, err
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}
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return &ReparsePoint{string(utf16.Decode(name)), isMountPoint}, nil
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}
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func isDriveLetter(c byte) bool {
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return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
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}
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// EncodeReparsePoint encodes a Win32 REPARSE_DATA_BUFFER structure describing a symlink or
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// mount point.
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func EncodeReparsePoint(rp *ReparsePoint) []byte {
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// Generate an NT path and determine if this is a relative path.
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var ntTarget string
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relative := false
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if strings.HasPrefix(rp.Target, `\\?\`) {
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ntTarget = `\??\` + rp.Target[4:]
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} else if strings.HasPrefix(rp.Target, `\\`) {
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ntTarget = `\??\UNC\` + rp.Target[2:]
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} else if len(rp.Target) >= 2 && isDriveLetter(rp.Target[0]) && rp.Target[1] == ':' {
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ntTarget = `\??\` + rp.Target
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} else {
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ntTarget = rp.Target
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relative = true
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}
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// The paths must be NUL-terminated even though they are counted strings.
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target16 := utf16.Encode([]rune(rp.Target + "\x00"))
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ntTarget16 := utf16.Encode([]rune(ntTarget + "\x00"))
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size := int(unsafe.Sizeof(reparseDataBuffer{})) - 8
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size += len(ntTarget16)*2 + len(target16)*2
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tag := uint32(reparseTagMountPoint)
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if !rp.IsMountPoint {
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tag = reparseTagSymlink
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size += 4 // Add room for symlink flags
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}
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data := reparseDataBuffer{
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ReparseTag: tag,
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ReparseDataLength: uint16(size),
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SubstituteNameOffset: 0,
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SubstituteNameLength: uint16((len(ntTarget16) - 1) * 2),
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PrintNameOffset: uint16(len(ntTarget16) * 2),
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PrintNameLength: uint16((len(target16) - 1) * 2),
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}
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var b bytes.Buffer
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_ = binary.Write(&b, binary.LittleEndian, &data)
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if !rp.IsMountPoint {
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flags := uint32(0)
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if relative {
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flags |= 1
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}
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_ = binary.Write(&b, binary.LittleEndian, flags)
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}
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_ = binary.Write(&b, binary.LittleEndian, ntTarget16)
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_ = binary.Write(&b, binary.LittleEndian, target16)
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return b.Bytes()
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}
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