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Reject ill-formed UTF-8 in CBOR/UBJSON/BJData/BSON writers, accept it in MessagePack reader

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to_cbor(), to_ubjson(), to_bjdata(), and to_bson() wrote a string or object
key with ill-formed UTF-8 byte for byte, but from_cbor()/from_ubjson()/
from_bjdata()/from_bson() reject such strings with parse_error.113 since
d19f7f5dc (#5185, not yet released): a value that serialized without error
could not be read back by the same library (#5651).

CBOR (RFC 8949 Section 5), UBJSON, BJData, and BSON all require text strings
and object keys/element names to be valid UTF-8, so their writers now
validate and throw type_error.316, like to_bon8() already does. For BSON,
the check runs in the size-computation pass, before any byte is written, the
same way the binary subtype check works. check_bon8_utf8() is renamed to
check_utf8() since it is now shared by all of these writers.

MessagePack's specification explicitly allows a str object to contain an
invalid byte sequence and expects a deserializer to hand the bytes back
unchanged, so its writer is unaffected and from_msgpack() (object keys
included) no longer validates UTF-8, restoring its pre-#5185 behavior.
dump() still rejects ill-formed UTF-8 with type_error.316 unless an error
handler is passed.

Docs: add the type_error.316 exception to to_cbor/to_ubjson/to_bjdata/to_bson,
document the writer-side check on the cbor/bson/ubjson/bjdata format pages,
and rewrite the MessagePack UTF-8 warning to describe the round-trip and
dump() behavior instead of a validation requirement the spec does not have.

Tests: add ill-formed value/key cases (invalid byte, truncated sequence,
encoded surrogate, overlong encoding) expecting type_error.316 to
unit-cbor.cpp, unit-ubjson.cpp, unit-bjdata.cpp, and unit-bson.cpp (which
also checks the output vector stays empty), and turn unit-msgpack.cpp's
former parse_error.113 ill-formed-UTF-8 tests into byte-for-byte round-trip
tests for both values and keys.

This text was written by Claude Code.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-30 22:19:11 +02:00
parent 7d7055ec50
commit 73d116547a
17 changed files with 297 additions and 41 deletions
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tests/src/unit-cbor.cpp
+19
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@@ -1896,6 +1896,25 @@ TEST_CASE("CBOR")
CHECK(json::from_cbor(json::to_cbor(j)) == j);
}
SECTION("to_cbor rejects ill-formed UTF-8 (see #5651)")
{
// to_cbor() must reject the same ill-formed strings from_cbor()
// rejects, so a value it accepts can always be read back
CHECK_THROWS_WITH_AS(json::to_cbor(json("\xFF")), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xFF", json::type_error&);
// a truncated multi-byte sequence
CHECK_THROWS_WITH_AS(json::to_cbor(json("\xC3")), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xC3", json::type_error&);
// an encoded surrogate half (U+D800)
CHECK_THROWS_WITH_AS(json::to_cbor(json("\xED\xA0\x80")), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xED", json::type_error&);
// an overlong encoding of '.'
CHECK_THROWS_WITH_AS(json::to_cbor(json("\xC0\xAF")), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xC0", json::type_error&);
// an object key with ill-formed UTF-8 is rejected the same way
CHECK_THROWS_WITH_AS(json::to_cbor(json{{"\xFF", 1}}), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xFF", json::type_error&);
// binary values are not text and are unaffected
CHECK_NOTHROW(json::to_cbor(json::binary(std::vector<std::uint8_t>({0xFF}))));
}
SECTION("invalid UTF-8 in indefinite-length string")
{
json _;