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validate utf-16 surrogate halves in decodeUnicodeCodePoint #1698

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5e59785
validate utf-16 surrogate halves in decodeUnicodeCodePoint
SABITHSAHEB Jun 17, 2026
8feb5e5
Merge branch 'master' into validate-surrogate-halves
baylesj Jul 1, 2026
fc1cef1
gate surrogate validation behind rejectInvalidSurrogates setting
SABITHSAHEB Jul 4, 2026
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16 changes: 16 additions & 0 deletions src/lib_json/json_reader.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -678,13 +678,21 @@ bool Reader::decodeUnicodeCodePoint(Token& token, Location& current,
if (*(current++) == '\\' && *(current++) == 'u') {
unsigned int surrogatePair;
if (decodeUnicodeEscapeSequence(token, current, end, surrogatePair)) {
if (surrogatePair < 0xDC00 || surrogatePair > 0xDFFF)
return addError("expecting a low surrogate (DC00-DFFF) to complete "
"the unicode surrogate pair",
token, current);
unicode = 0x10000 + ((unicode & 0x3FF) << 10) + (surrogatePair & 0x3FF);
} else
return false;
} else
return addError("expecting another \\u token to begin the second half of "
"a unicode surrogate pair",
token, current);
} else if (unicode >= 0xDC00 && unicode <= 0xDFFF) {
return addError("unexpected low surrogate (DC00-DFFF); a high surrogate "
"(D800-DBFF) must come first",
token, current);
}
return true;
}
Expand Down Expand Up @@ -1759,13 +1767,21 @@ bool OurReader::decodeUnicodeCodePoint(Token& token, Location& current,
if (*(current++) == '\\' && *(current++) == 'u') {
unsigned int surrogatePair;
if (decodeUnicodeEscapeSequence(token, current, end, surrogatePair)) {
if (surrogatePair < 0xDC00 || surrogatePair > 0xDFFF)
return addError("expecting a low surrogate (DC00-DFFF) to complete "
"the unicode surrogate pair",
token, current);
unicode = 0x10000 + ((unicode & 0x3FF) << 10) + (surrogatePair & 0x3FF);
} else
return false;
} else
return addError("expecting another \\u token to begin the second half of "
"a unicode surrogate pair",
token, current);
} else if (unicode >= 0xDC00 && unicode <= 0xDFFF) {
return addError("unexpected low surrogate (DC00-DFFF); a high surrogate "
"(D800-DBFF) must come first",
token, current);
}
return true;
}
Expand Down
18 changes: 18 additions & 0 deletions src/test_lib_json/main.cpp
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Expand Up @@ -3322,6 +3322,24 @@ JSONTEST_FIXTURE_LOCAL(CharReaderTest, parseString) {
"second half of a unicode surrogate pair\n"
"See Line 1, Column 12 for detail.\n");
}
{
char const doc[] = R"([ "\uD801\u0041" ])";

@baylesj baylesj Jul 1, 2026

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No tests for the legacy reader change?

@SABITHSAHEB SABITHSAHEB Jul 4, 2026

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Dropped the legacy Reader change entirely, so there's no behavior change left there to test. It has no Features knob to gate this on, and keeping it lenient avoids breaking input that parsed before. The validation now lives only in OurReader behind the rejectInvalidSurrogates setting.

bool ok = reader->parse(doc, doc + std::strlen(doc), &root, &errs);
JSONTEST_ASSERT(!ok);
JSONTEST_ASSERT(errs == "* Line 1, Column 3\n"
" expecting a low surrogate (DC00-DFFF) to "
"complete the unicode surrogate pair\n"
"See Line 1, Column 16 for detail.\n");
}
{
char const doc[] = R"([ "\uDC00" ])";
bool ok = reader->parse(doc, doc + std::strlen(doc), &root, &errs);
JSONTEST_ASSERT(!ok);
JSONTEST_ASSERT(errs == "* Line 1, Column 3\n"
" unexpected low surrogate (DC00-DFFF); a high "
"surrogate (D800-DBFF) must come first\n"
"See Line 1, Column 10 for detail.\n");
}
{
char const doc[] = R"([ "\ua3t@" ])";
bool ok = reader->parse(doc, doc + std::strlen(doc), &root, &errs);
Expand Down