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[JSC] The streaming JSON parser finds the end of a value that , ] or } follows #799

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Merged
Jarred-Sumner merged 1 commit into from
Oct 13, 2026
Merged

[JSC] The streaming JSON parser finds the end of a value that , ] or } follows #799

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14 changes: 12 additions & 2 deletions Source/JavaScriptCore/runtime/LiteralParser.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2345,12 +2345,22 @@ StreamingJSONParseResult LiteralParser<CharType, reviverMode>::tryStreamingParse
}

results.appendWithCrashOnOverflow(value);
lastGoodPosition = static_cast<size_t>(m_lexer.positionAfterLastToken() - m_lexer.start());

// The token after the value is already lexed. lex() records where the value ended, but
// nextAfterValue() lexes `,` `}` and `]` without lex(), so walk back from the token.
const CharType* valueEnd = m_lexer.positionAfterLastToken();
TokenType nextType = m_lexer.currentToken()->type;
if (nextType == TokComma || nextType == TokRBrace || nextType == TokRBracket) {
valueEnd = m_lexer.ptr() - 1;
while (isJSONWhiteSpace(valueEnd[-1]))
--valueEnd;
}
lastGoodPosition = static_cast<size_t>(valueEnd - m_lexer.start());

// Find the next newline and skip directly to it — one WTF::find,
// which uses memchr for 8-bit. This is both the delimiter check
// and the advance.
auto remaining = std::span { m_lexer.positionAfterLastToken(), m_lexer.end() };
auto remaining = std::span { valueEnd, m_lexer.end() };
size_t nlIndex = WTF::find(remaining, static_cast<CharType>('\n'));
if (nlIndex != notFound) {
// JSONL/NDJSON: exactly one value per line. Anything other than
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