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Fix MSVC: avoid reserving by faked size in MessagePack size tests (#5604)

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The "Size above uint32" tests for arrays and objects fake a container
size of 2^32 and expect to_msgpack() to throw out_of_range.412. But
to_msgpack(j) first reserves binary_reserve_hint(j) bytes, which is
size + 1 for arrays and 2 * size + 1 for objects, i.e. 4 or 8 GiB.
Linux and macOS overcommit, so the reservation succeeds; on Windows it
throws std::bad_alloc before the size check is reached (seen with
msvc-vs2026 Debug x64 on the object test).

Write into a caller-owned vector instead, so nothing is reserved.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-27 20:57:16 +02:00
committed by GitHub
parent de6acd651e
commit 373005f7ac
1 changed files with 8 additions and 2 deletions
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tests/src/unit-msgpack.cpp
+8 -2
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@@ -2208,8 +2208,11 @@ TEST_CASE("MessagePack Size above uint32 for array")
auto& array = j.get_ref<huge_array_json::array_t&>();
array.fake_size = true;
// write into a caller-owned vector: to_msgpack(j) reserves space based on
// the (faked) element count, which fails with bad_alloc on Windows
std::vector<std::uint8_t> result;
CHECK_THROWS_WITH_AS(
huge_array_json::to_msgpack(j),
huge_array_json::to_msgpack(j, result),
"[json.exception.out_of_range.412] MessagePack length 4294967296 exceeds maximum of 4294967295",
json::out_of_range&);
@@ -2261,8 +2264,11 @@ TEST_CASE("MessagePack Size above uint32 for object")
auto& object = j.get_ref<huge_object_json::object_t&>();
object.fake_size = true;
// write into a caller-owned vector: to_msgpack(j) reserves space based on
// the (faked) element count, which fails with bad_alloc on Windows
std::vector<std::uint8_t> result;
CHECK_THROWS_WITH_AS(
huge_object_json::to_msgpack(j),
huge_object_json::to_msgpack(j, result),
"[json.exception.out_of_range.412] MessagePack length 4294967296 exceeds maximum of 4294967295",
json::out_of_range&);