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Assert memcpy buffer bounds in the contiguous get_elements fast path

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Make the "buffers are large enough" reasoning explicit: before the copy,
assert that `copied` fits both the caller-provided destination (`wanted`
bytes) and the remaining input range (`available` bytes). These hold by
construction (`copied = min(wanted, available)`) but were previously only
implied; the asserts document the invariant and would catch a future
regression that breaks it.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Niels Lohmann
2026-07-04 11:02:30 +02:00
co-authored by Claude Opus 4.8
parent 5355190cff
commit 79a8c279c0
2 changed files with 10 additions and 0 deletions
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include/nlohmann/detail/input/input_adapters.hpp
+5
View File
@@ -206,6 +206,11 @@ class iterator_input_adapter
const std::size_t copied = (std::min)(wanted, available);
if (JSON_HEDLEY_LIKELY(copied != 0))
{
// the copy must stay within both buffers: the caller-provided
// destination holds `wanted` bytes and the remaining input range
// holds `available` bytes, and `copied` is the minimum of the two
JSON_ASSERT(copied <= wanted); // does not overrun the destination
JSON_ASSERT(copied <= available); // does not read past the input end
// &*current yields the raw address for both raw pointers and
// non-pointer contiguous iterators (e.g. std::vector's iterator)
std::memcpy(dest, &*current, copied);
single_include/nlohmann/json.hpp
+5
View File
@@ -7038,6 +7038,11 @@ class iterator_input_adapter
const std::size_t copied = (std::min)(wanted, available);
if (JSON_HEDLEY_LIKELY(copied != 0))
{
// the copy must stay within both buffers: the caller-provided
// destination holds `wanted` bytes and the remaining input range
// holds `available` bytes, and `copied` is the minimum of the two
JSON_ASSERT(copied <= wanted); // does not overrun the destination
JSON_ASSERT(copied <= available); // does not read past the input end
// &*current yields the raw address for both raw pointers and
// non-pointer contiguous iterators (e.g. std::vector's iterator)
std::memcpy(dest, &*current, copied);