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Name the key type when rejecting non-string CBOR/MessagePack map keys (#5594)

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

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>

* Point the MessagePack key note to the spec's profile section

The note linked to "Serialization: type to format conversion", which says nothing about key types. Restricting map keys to strings is only mentioned in the "Profile" section (under "Future discussion") as an example of a JSON-compatible profile, so link there and describe it as such instead of as a permission.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-28 17:51:07 +02:00
committed by GitHub
parent 373005f7ac
commit 9e1a09eec0
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