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Resolve the TODO(niels) in get_ubjson_string (#5355)

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The comment asked whether the no-op marker 'N' may be ignored when a
string is read. It may not: at that point the next byte must be a string
length type specification, and 'N' is not one. No-ops at positions where
a value may start are already consumed by the callers through
get_ignore_noop(), so nothing is lost by not skipping them here.

Replace the TODO with a comment stating that, and add regression tests
pinning both directions: a no-op is accepted at top level (also
repeated), before and after an array element, and before an object key,
between key and value, and before the closing brace of an object of
unknown size; it is rejected where a length type specification is
expected, i.e. after the 'S' marker of a string value and as the key
length of an object of known size.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-08-05 14:47:40 +02:00
committed by GitHub
parent 9a091d2b82
commit d5647e6a3b
3 changed files with 48 additions and 2 deletions
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tests/src/unit-ubjson.cpp
+38
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@@ -1713,6 +1713,44 @@ TEST_CASE("UBJSON")
CHECK(json::to_ubjson(json::from_ubjson(s_L)) == s_i);
}
SECTION("no-op markers")
{
// A no-op ('N') is valid wherever a value may start; it is consumed
// by get_ignore_noop() before the value is read. It is not valid
// where a string length type specification is expected.
SECTION("accepted where a value may start")
{
// at top level, also repeated
CHECK(json::from_ubjson(std::vector<uint8_t>({'N', 'i', 1})) == json(1));
CHECK(json::from_ubjson(std::vector<uint8_t>({'N', 'N', 'N', 'i', 1})) == json(1));
// inside an array of unknown size, before and after an element
CHECK(json::from_ubjson(std::vector<uint8_t>({'[', 'N', 'i', 1, ']'})) == json({1}));
CHECK(json::from_ubjson(std::vector<uint8_t>({'[', 'i', 1, 'N', ']'})) == json({1}));
// inside an object of unknown size: before a key, between key
// and value, and before the closing '}'
CHECK(json::from_ubjson(std::vector<uint8_t>({'{', 'N', 'U', 1, 'a', 'i', 1, '}'})) == json({{"a", 1}}));
CHECK(json::from_ubjson(std::vector<uint8_t>({'{', 'U', 1, 'a', 'N', 'i', 1, '}'})) == json({{"a", 1}}));
CHECK(json::from_ubjson(std::vector<uint8_t>({'{', 'U', 1, 'a', 'i', 1, 'N', '}'})) == json({{"a", 1}}));
}
SECTION("rejected where a length type specification is expected")
{
json _;
// after the 'S' marker of a string value
std::vector<uint8_t> const v_S = {'S', 'N', 'U', 1, 'a'};
CHECK_THROWS_WITH_AS(_ = json::from_ubjson(v_S), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing UBJSON string: expected length type specification (U, i, I, l, L); last byte: 0x4E", json::parse_error&);
// as the key length of an object with a known size, where
// no-ops are not permitted in the first place
std::vector<uint8_t> const v_key = {'{', '#', 'i', 1, 'N', 'U', 1, 'a', 'i', 1};
CHECK_THROWS_WITH_AS(_ = json::from_ubjson(v_key), "[json.exception.parse_error.113] parse error at byte 5: syntax error while parsing UBJSON string: expected length type specification (U, i, I, l, L); last byte: 0x4E", json::parse_error&);
}
}
SECTION("number")
{
SECTION("float")