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encoding/unicode: fix surrogate pair handling in UTF-16 decoder #62

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encoding/unicode: fix surrogate pair handling in UTF-16 decoder #62

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16 changes: 12 additions & 4 deletions encoding/unicode/unicode.go
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Original file line number Diff line number Diff line change
Expand Up @@ -400,19 +400,23 @@ func (u *utf16Decoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, e
}
r, sSize = rune(x), 2
if utf16.IsSurrogate(r) {
if nSrc+3 < len(src) {
if isHighSurrogate(r) && nSrc+3 < len(src) {
x = uint16(src[nSrc+2])<<8 | uint16(src[nSrc+3])
if u.current.endianness == LittleEndian {
x = x>>8 | x<<8
}
// Save for next iteration if it is not a high surrogate.
if isHighSurrogate(rune(x)) {
// Combine into a surrogate pair only if the second
// code unit is a low surrogate (U+DC00..U+DFFF).
if isLowSurrogate(rune(x)) {
r, sSize = utf16.DecodeRune(r, rune(x)), 4
}
} else if !atEOF {
} else if isHighSurrogate(r) && !atEOF {
err = transform.ErrShortSrc
break
}
// Unpaired surrogates (low without preceding high, or
// high without following low) fall through and are
// replaced with U+FFFD by the RuneLen check below.
}
if dSize = utf8.RuneLen(r); dSize < 0 {
r, dSize = utf8.RuneError, 3
Expand All @@ -435,6 +439,10 @@ func (u *utf16Decoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, e
}

func isHighSurrogate(r rune) bool {
return 0xD800 <= r && r <= 0xDBFF
}

func isLowSurrogate(r rune) bool {
return 0xDC00 <= r && r <= 0xDFFF
}

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