TEST_CASE("SECBUG-4103: from_json length truncated to negative int32", "[secbug_4103][!benchmark]") {
    // Smallest size whose int32 truncation is negative: 2^31 -> INT32_MIN.
    constexpr std::size_t size = std::size_t{1} << 31;

    REQUIRE(static_cast<std::int32_t>(size) < 0);

    // No NUL byte anywhere in the buffer, so libbson's strlen fallback runs off
    // the end. Leading '{' keeps it plausible JSON rather than an early reject
    // (the over-read happens before any parsing regardless).
    auto buf = std::unique_ptr<char[]>{new char[size]};
    std::memset(buf.get(), 'a', size);
    buf[0] = '{';

    stdx::string_view json{buf.get(), size};

    REQUIRE(json.size() == size);

    // strlen over-reads past the end of the 2 GiB allocation.
    REQUIRE_THROWS(from_json(json));
}