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57 lines
1.6 KiB
Go
57 lines
1.6 KiB
Go
// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package dns
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// This code is only used in Windows builds, but is in an
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// OS-independent file so tests can run all the time.
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import (
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"bytes"
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"encoding/binary"
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"unicode/utf16"
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)
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// maybeUnUTF16 tries to detect whether bs contains UTF-16, and if so
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// translates it to regular UTF-8.
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//
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// Some of wsl.exe's output get printed as UTF-16, which breaks a
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// bunch of things. Try to detect this by looking for a zero byte in
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// the first few bytes of output (which will appear if any of those
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// codepoints are basic ASCII - very likely). From that we can infer
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// that UTF-16 is being printed, and the byte order in use, and we
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// decode that back to UTF-8.
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//
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// https://github.com/microsoft/WSL/issues/4607
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func maybeUnUTF16(bs []byte) []byte {
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if len(bs)%2 != 0 {
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// Can't be complete UTF-16.
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return bs
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}
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checkLen := 20
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if len(bs) < checkLen {
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checkLen = len(bs)
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}
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zeroOff := bytes.IndexByte(bs[:checkLen], 0)
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if zeroOff == -1 {
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return bs
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}
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// We assume wsl.exe is trying to print an ASCII codepoint,
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// meaning the zero byte is in the upper 8 bits of the
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// codepoint. That means we can use the zero's byte offset to
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// work out if we're seeing little-endian or big-endian
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// UTF-16.
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var endian binary.ByteOrder = binary.LittleEndian
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if zeroOff%2 == 0 {
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endian = binary.BigEndian
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}
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var u16 []uint16
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for i := 0; i < len(bs); i += 2 {
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u16 = append(u16, endian.Uint16(bs[i:]))
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}
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return []byte(string(utf16.Decode(u16)))
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}
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