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Name the key type when rejecting non-string CBOR/MessagePack map keys

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CBOR and MessagePack allow map keys of any type, but JSON object keys
are always strings, so such maps are rejected. The error so far was the
one for a malformed string (e.g. "expected length specification
(0xA0-0xBF, 0xD9-0xDB); last byte: 0xC0" for a nil key), which does not
tell the user what went wrong. Report the type of the key instead:

  syntax error while parsing MessagePack object key: only string keys
  are supported, but found nil; last byte: 0xC0

The exception id (parse_error.113) and type are unchanged. Malformed
string keys and a missing key keep their previous messages. Document
the restriction on the CBOR and MessagePack pages.

Refs #2766, #3381

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-27 16:40:40 +02:00
parent f682cd2ef1
commit df9a000e3a
10 changed files with 484 additions and 17 deletions
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tests/src/unit-msgpack.cpp
+60 -1
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@@ -1551,10 +1551,69 @@ TEST_CASE("MessagePack")
SECTION("invalid string in map")
{
json _;
CHECK_THROWS_WITH_AS(_ = json::from_msgpack(std::vector<uint8_t>({0x81, 0xff, 0x01})), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing MessagePack string: expected length specification (0xA0-0xBF, 0xD9-0xDB); last byte: 0xFF", json::parse_error&);
CHECK_THROWS_WITH_AS(_ = json::from_msgpack(std::vector<uint8_t>({0x81, 0xff, 0x01})), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing MessagePack object key: only string keys are supported, but found an integer; last byte: 0xFF", json::parse_error&);
CHECK(json::from_msgpack(std::vector<uint8_t>({0x81, 0xff, 0x01}), true, false).is_discarded());
}
SECTION("non-string key (see #3381)")
{
// only strings map to JSON object keys; any other key is rejected
// with a message naming its type
const std::vector<std::pair<std::vector<std::uint8_t>, std::string>> cases =
{
{{0x81, 0xC0, 0x01}, "nil; last byte: 0xC0"},
{{0x81, 0xC2, 0x01}, "a boolean; last byte: 0xC2"},
{{0x81, 0xC3, 0x01}, "a boolean; last byte: 0xC3"},
{{0x81, 0xCA, 0x3F, 0x80, 0x00, 0x00, 0x01}, "a float; last byte: 0xCA"},
{{0x81, 0xCB, 0x3F, 0xF0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01}, "a float; last byte: 0xCB"},
{{0x81, 0xC4, 0x00, 0x01}, "a bin; last byte: 0xC4"},
{{0x81, 0xC5, 0x00, 0x00, 0x01}, "a bin; last byte: 0xC5"},
{{0x81, 0xC6, 0x00, 0x00, 0x00, 0x00, 0x01}, "a bin; last byte: 0xC6"},
{{0x81, 0xC7, 0x00, 0x01, 0x01}, "an ext; last byte: 0xC7"},
{{0x81, 0xC8, 0x00, 0x00, 0x01, 0x01}, "an ext; last byte: 0xC8"},
{{0x81, 0xC9, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01}, "an ext; last byte: 0xC9"},
{{0x81, 0xD4, 0x01, 0x00, 0x01}, "an ext; last byte: 0xD4"},
{{0x81, 0xD5, 0x01, 0x00, 0x00, 0x01}, "an ext; last byte: 0xD5"},
{{0x81, 0xD6, 0x01, 0x00, 0x00, 0x00, 0x00, 0x01}, "an ext; last byte: 0xD6"},
{{0x81, 0xD7, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01}, "an ext; last byte: 0xD7"},
{{0x81, 0xD8, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01}, "an ext; last byte: 0xD8"},
{{0x81, 0xCC, 0x01, 0x01}, "an integer; last byte: 0xCC"},
{{0x81, 0xCD, 0x00, 0x01, 0x01}, "an integer; last byte: 0xCD"},
{{0x81, 0xCE, 0x00, 0x00, 0x00, 0x01, 0x01}, "an integer; last byte: 0xCE"},
{{0x81, 0xCF, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01}, "an integer; last byte: 0xCF"},
{{0x81, 0xD0, 0x01, 0x01}, "an integer; last byte: 0xD0"},
{{0x81, 0xD1, 0x00, 0x01, 0x01}, "an integer; last byte: 0xD1"},
{{0x81, 0xD2, 0x00, 0x00, 0x00, 0x01, 0x01}, "an integer; last byte: 0xD2"},
{{0x81, 0xD3, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01}, "an integer; last byte: 0xD3"},
{{0x81, 0x00, 0x01}, "an integer; last byte: 0x00"},
{{0x81, 0x7F, 0x01}, "an integer; last byte: 0x7F"},
{{0x81, 0xE0, 0x01}, "an integer; last byte: 0xE0"},
{{0x81, 0x80, 0x01}, "a map; last byte: 0x80"},
{{0x81, 0x8F, 0x01}, "a map; last byte: 0x8F"},
{{0x81, 0xDE, 0x00, 0x00, 0x01}, "a map; last byte: 0xDE"},
{{0x81, 0xDF, 0x00, 0x00, 0x00, 0x00, 0x01}, "a map; last byte: 0xDF"},
{{0x81, 0x90, 0x01}, "an array; last byte: 0x90"},
{{0x81, 0x9F, 0x01}, "an array; last byte: 0x9F"},
{{0x81, 0xDC, 0x00, 0x00, 0x01}, "an array; last byte: 0xDC"},
{{0x81, 0xDD, 0x00, 0x00, 0x00, 0x00, 0x01}, "an array; last byte: 0xDD"},
};
for (const auto& c : cases)
{
CAPTURE(c.first)
const std::string expected = "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing MessagePack object key: only string keys are supported, but found " + c.second;
json _;
CHECK_THROWS_WITH_AS(_ = json::from_msgpack(c.first), expected.c_str(), json::parse_error&);
CHECK(json::from_msgpack(c.first, true, false).is_discarded());
}
json _;
// the unused byte 0xC1 is still reported as a malformed string
CHECK_THROWS_WITH_AS(_ = json::from_msgpack(std::vector<uint8_t>({0x81, 0xC1, 0x01})), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing MessagePack string: expected length specification (0xA0-0xBF, 0xD9-0xDB); last byte: 0xC1", json::parse_error&);
// a missing key is still reported as the end of input
CHECK_THROWS_WITH_AS(_ = json::from_msgpack(std::vector<uint8_t>({0x81})), "[json.exception.parse_error.110] parse error at byte 2: syntax error while parsing MessagePack string: unexpected end of input", json::parse_error&);
}
SECTION("invalid UTF-8 in string (see #5529)")
{
// a fixstr of length 2 (0xA0 | 2) whose bytes are not valid UTF-8