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Extract the move prefix check into a named helper lambda

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Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-06 18:52:20 +02:00
parent 95c1df59ef
commit 47bd3e67cb
2 changed files with 50 additions and 42 deletions
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include/nlohmann/json.hpp
+25 -21
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@@ -4947,6 +4947,30 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
}
};
// RFC 6902 (section 4.4) forbids "from" from being a proper prefix
// of "path" for a "move" operation: a location cannot be moved into
// one of its own children. Compares reference tokens (already
// unescaped by json_pointer's parser) rather than the raw pointer
// strings, since a token may itself contain an escaped '/' or '~'
// that would defeat a naive string-prefix comparison. "from" equal
// to "path" is *not* a proper prefix and must return false.
const auto is_proper_prefix = [](const json_pointer & from, const json_pointer & to)
{
const auto from_size = from.reference_tokens.size();
if (from_size >= to.reference_tokens.size())
{
return false;
}
for (std::size_t i = 0; i < from_size; ++i)
{
if (!(from.reference_tokens[i] == to.reference_tokens[i]))
{
return false;
}
}
return true;
};
// type check: top level value must be an array
if (JSON_HEDLEY_UNLIKELY(!json_patch.is_array()))
{
@@ -5022,27 +5046,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
const auto from_path = get_value("move", "from", true).template get<string_t>();
json_pointer from_ptr(from_path);
// RFC 6902 (section 4.4) forbids "from" from being a
// proper prefix of "path": a location cannot be moved
// into one of its own children. Compare the pointers'
// reference tokens (already unescaped by json_pointer's
// parser) rather than the raw pointer strings, since a
// token may itself contain an escaped '/' or '~' that
// would defeat a naive string-prefix comparison. This is
// written as an explicit, manually-bounded loop (rather
// than std::equal(first1, last1, first2), whose second
// range has no explicit end iterator) so every access to
// ptr.reference_tokens is visibly guarded by the same
// index the loop condition already bounds against
// from_size -- from_size < ptr.reference_tokens.size()
// is checked once, up front, before the loop runs at all.
const auto from_size = from_ptr.reference_tokens.size();
bool from_is_proper_prefix_of_path = from_size < ptr.reference_tokens.size();
for (std::size_t i = 0; from_is_proper_prefix_of_path && i < from_size; ++i)
{
from_is_proper_prefix_of_path = from_ptr.reference_tokens[i] == ptr.reference_tokens[i];
}
if (JSON_HEDLEY_UNLIKELY(from_is_proper_prefix_of_path))
if (JSON_HEDLEY_UNLIKELY(is_proper_prefix(from_ptr, ptr)))
{
JSON_THROW(out_of_range::create(414, detail::concat("cannot move value: 'from' path '", from_path, "' is a proper prefix of 'path' '", path, "'"), &result));
}