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Throw instead of writing MessagePack lengths beyond UINT32_MAX (#5584)

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* Throw instead of writing MessagePack lengths beyond UINT32_MAX

MessagePack stores the length of a string, binary value, array, or
object in at most 32 bits. For a larger value, to_msgpack wrote no length
at all, so the output could not be read back. It now throws
out_of_range.412, which BSON already uses for its 32-bit length fields.

The check lives in one function, so each length is written by an
if/else chain that ends in a plain else, without a condition that can
never be false. It is tested with string and binary types that report a
size beyond UINT32_MAX without allocating it, like the BSON tests do.

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

* Fix the CI failures of the MessagePack length check

- mark to_msgpack_length's value as used when exceptions are disabled
  (-Wunused-parameter, misc-unused-parameters)
- put "Exception safety" before "Exceptions" in to_msgpack.md, as the
  documentation style check requires
- create the test's string value from its type: constructing it from a
  beyond_uint32_string_t considers the std::filesystem::path conversion,
  which libstdc++ 10 reports as ambiguous for a class derived from
  std::string (clang 13)

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

* Skip the MessagePack string length test for clang with libstdc++ 10

C++17 builds consider the std::filesystem::path conversion for the
string type, and with clang and libstdc++ 10 that conversion is
ambiguous for a class derived from std::string. Creating the value from
its type did not avoid it, since any basic_json with that string type
instantiates the check. The binary and ext cases are still tested there.

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

* Keep the MessagePack string test type and its alias in one block

astyle indented the alias oddly when it had an #ifdef of its own after
the binary alias; declare it right after the string type, in the same
block.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-27 14:28:16 +02:00
committed by GitHub
parent 6178982b8d
commit f7972970a4
6 changed files with 152 additions and 64 deletions
Download Patch File Download Diff File Expand all files Collapse all files
single_include/nlohmann/json.hpp
+25 -28
View File
@@ -19756,6 +19756,23 @@ class binary_writer
}
}
/*!
@brief check that @a length fits into the 32 bits that MessagePack stores
the length of a string, binary value, array, or object in
@return the length as an unsigned 32-bit integer
@throw out_of_range.412 if @a length exceeds the range of std::uint32_t
*/
static std::uint32_t to_msgpack_length(const std::size_t length, const BasicJsonType& j)
{
if (JSON_HEDLEY_UNLIKELY(!value_in_range_of<std::uint32_t>(length)))
{
JSON_THROW(out_of_range::create(412, concat("MessagePack length ", std::to_string(length), " exceeds maximum of ", std::to_string((std::numeric_limits<std::uint32_t>::max)())), &j));
}
static_cast<void>(j);
return static_cast<std::uint32_t>(length);
}
/*!
@param[in] j JSON value to serialize
*/
@@ -19895,7 +19912,7 @@ class binary_writer
case value_t::string:
{
// step 1: write control byte and the string length
const auto N = j.m_data.m_value.string->size();
const auto N = to_msgpack_length(j.m_data.m_value.string->size(), j);
if (N <= 31)
{
// fixstr
@@ -19913,17 +19930,12 @@ class binary_writer
oa.write_character(to_char_type(0xDA));
write_number(static_cast<std::uint16_t>(N));
}
else if (N <= (std::numeric_limits<std::uint32_t>::max)())
else
{
// str 32
oa.write_character(to_char_type(0xDB));
write_number(static_cast<std::uint32_t>(N));
}
else
{
JSON_THROW(out_of_range::create(412, concat("MessagePack size ", std::to_string(N), " exceeds maximum of ",
std::to_string((std::numeric_limits<std::uint32_t>::max)())), &j));
}
// step 2: write the string
oa.write_characters(
@@ -19935,7 +19947,7 @@ class binary_writer
case value_t::array:
{
// step 1: write control byte and the array size
const auto N = j.m_data.m_value.array->size();
const auto N = to_msgpack_length(j.m_data.m_value.array->size(), j);
if (N <= 15)
{
// fixarray
@@ -19947,17 +19959,12 @@ class binary_writer
oa.write_character(to_char_type(0xDC));
write_number(static_cast<std::uint16_t>(N));
}
else if (N <= (std::numeric_limits<std::uint32_t>::max)())
else
{
// array 32
oa.write_character(to_char_type(0xDD));
write_number(static_cast<std::uint32_t>(N));
}
else
{
JSON_THROW(out_of_range::create(412, concat("MessagePack size ", std::to_string(N), " exceeds maximum of ",
std::to_string((std::numeric_limits<std::uint32_t>::max)())), &j));
}
// step 2: write each element
for (const auto& el : *j.m_data.m_value.array)
@@ -19974,7 +19981,7 @@ class binary_writer
const bool use_ext = j.m_data.m_value.binary->has_subtype();
// step 1: write control byte and the byte string length
const auto N = j.m_data.m_value.binary->size();
const auto N = to_msgpack_length(j.m_data.m_value.binary->size(), j);
if (N <= (std::numeric_limits<std::uint8_t>::max)())
{
std::uint8_t output_type{};
@@ -20026,7 +20033,7 @@ class binary_writer
oa.write_character(to_char_type(output_type));
write_number(static_cast<std::uint16_t>(N));
}
else if (N <= (std::numeric_limits<std::uint32_t>::max)())
else
{
const std::uint8_t output_type = use_ext
? 0xC9 // ext 32
@@ -20035,11 +20042,6 @@ class binary_writer
oa.write_character(to_char_type(output_type));
write_number(static_cast<std::uint32_t>(N));
}
else
{
JSON_THROW(out_of_range::create(412, concat("MessagePack size ", std::to_string(N), " exceeds maximum of ",
std::to_string((std::numeric_limits<std::uint32_t>::max)())), &j));
}
// step 1.5: if this is an ext type, write the subtype
if (use_ext)
@@ -20063,7 +20065,7 @@ class binary_writer
case value_t::object:
{
// step 1: write control byte and the object size
const auto N = j.m_data.m_value.object->size();
const auto N = to_msgpack_length(j.m_data.m_value.object->size(), j);
if (N <= 15)
{
// fixmap
@@ -20075,17 +20077,12 @@ class binary_writer
oa.write_character(to_char_type(0xDE));
write_number(static_cast<std::uint16_t>(N));
}
else if (N <= (std::numeric_limits<std::uint32_t>::max)())
else
{
// map 32
oa.write_character(to_char_type(0xDF));
write_number(static_cast<std::uint32_t>(N));
}
else
{
JSON_THROW(out_of_range::create(412, concat("MessagePack size ", std::to_string(N), " exceeds maximum of ",
std::to_string((std::numeric_limits<std::uint32_t>::max)())), &j));
}
// step 2: write each element
for (const auto& el : *j.m_data.m_value.object)