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2.5.7: share parse_array_index between json_pointer and json_view (#5891)

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Move json_pointer::parse_array_index() and its status enum to namespace detail
(json_pointer keeps a forwarding member), and let the json_view pointer
resolution use it instead of its own copy of the RFC 6901 index grammar. Both
accepted the same tokens with the same outcome. Also update the comment on
detail::decode(), which listed four of the five UTF-8 validators and now points
to the test that keeps them in sync.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann committed 2026-10-23 10:33:52 +02:00
1 parent ae59fbb5a4
commit 7506a1b0bf
3 files changed
+112 -130
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include/nlohmann/detail/json_pointer.hpp
+97 -84
View File
@@ -38,6 +38,100 @@ NLOHMANN_JSON_NAMESPACE_BEGIN
namespace detail
{
struct json_pointer_access;
/*!
@brief result of parse_array_index()
json_pointer::array_index() maps each value to the corresponding
parse_error/out_of_range exception; json_pointer::contains() and
get_checked_or_null(), which must not throw for an out-of-range or
unrepresentable index, and the json_view pointer resolution switch on it
directly instead.
*/
enum class array_index_status
{
ok, ///< @a s is a valid, representable array index
leading_zero, ///< @a s begins with '0' but has more than one character
not_a_number, ///< @a s is neither empty nor "-" and does not begin with a digit
unresolved, ///< @a s could not be converted to an integer
exceeds_size_type ///< @a s converts to an integer that exceeds SizeType
};
/*!
@brief convert a JSON Pointer reference token into an array index (RFC 6901, Sect. 4)
@param[in] s reference token to be converted into an array index; its data()
must be NUL-terminated
@param[out] idx the integer representation of @a s if array_index_status::ok
is returned; left unchanged otherwise
@return whether @a s is a valid array index, and if not, why
@note this function never throws; json_pointer::array_index(), the callers that
must not throw, and the json_view pointer resolution build on it instead
of each re-implementing the RFC 6901 digit rules and the range check
*/
template<typename SizeType, typename StringType>
array_index_status parse_array_index(const StringType& s, SizeType& idx) noexcept
{
// error condition (cf. RFC 6901, Sect. 4)
if (JSON_HEDLEY_UNLIKELY(s.size() > 1 && s[0] == '0'))
{
return array_index_status::leading_zero;
}
// error condition (cf. RFC 6901, Sect. 4); this also covers single-
// character tokens, so "/x" and "/xy" fail alike; "-" and the empty
// token are left to the conversion below and are reported as unresolved
if (JSON_HEDLEY_UNLIKELY(!s.empty() && !(s.size() == 1 && s[0] == '-') && !(s[0] >= '0' && s[0] <= '9')))
{
return array_index_status::not_a_number;
}
// fast path: up to 18 decimal digits cannot overflow unsigned long long or
// SizeType (9 digits for a 32-bit SizeType), so strtoull and errno are not needed
constexpr std::size_t max_fast_digits = sizeof(SizeType) >= 8 ? 18 : 9;
if (!s.empty() && s.size() <= max_fast_digits)
{
SizeType acc = 0;
for (std::size_t i = 0; i < s.size(); ++i)
{
const char c = s[i];
if (JSON_HEDLEY_UNLIKELY(c < '0' || c > '9'))
{
break; // not a plain number: let strtoull decide
}
acc = static_cast<SizeType>((acc * 10) + static_cast<SizeType>(c - '0'));
if (JSON_HEDLEY_UNLIKELY(i == s.size() - 1))
{
idx = acc;
return array_index_status::ok;
}
}
}
const char* p = s.data();
char* p_end = nullptr; // NOLINT(misc-const-correctness)
errno = 0; // strtoull doesn't reset errno
const unsigned long long res = std::strtoull(p, &p_end, 10); // NOLINT(runtime/int)
if (p == p_end // invalid input or empty string
|| errno == ERANGE // out of range
|| JSON_HEDLEY_UNLIKELY(static_cast<std::size_t>(p_end - p) != s.size())) // incomplete read
{
return array_index_status::unresolved;
}
// the index does not fit into SizeType; on 64-bit platforms this is
// only SIZE_MAX itself (see #2203 and #5395)
if (res >= static_cast<unsigned long long>((std::numeric_limits<SizeType>::max)())) // NOLINT(runtime/int)
{
return array_index_status::exceeds_size_type;
}
idx = static_cast<SizeType>(res);
return array_index_status::ok;
}
} // namespace detail
/// @brief JSON Pointer defines a string syntax for identifying a specific value within a JSON document
@@ -333,21 +427,7 @@ class json_pointer
JSON_THROW(detail::out_of_range::create(detail::exception_id::pointer_unresolved, detail::concat("unresolved reference token '", reference_token, "'"), context));
}
/*!
@brief result of @ref parse_array_index
@ref array_index maps each value to the corresponding parse_error/out_of_range
exception; @ref contains and @ref get_checked_or_null, which must not throw for
an out-of-range or unrepresentable index, switch on it directly instead.
*/
enum class array_index_status
{
ok, ///< @a s is a valid, representable array index
leading_zero, ///< @a s begins with '0' but has more than one character
not_a_number, ///< @a s is neither empty nor "-" and does not begin with a digit
unresolved, ///< @a s could not be converted to an integer
exceeds_size_type ///< @a s converts to an integer that exceeds size_type
};
using array_index_status = detail::array_index_status;
/// whether a reference token is "-" (a plain comparison with a string literal is not always inlined)
static bool is_dash(const string_t& s) noexcept
@@ -355,78 +435,11 @@ class json_pointer
return s.size() == 1 && s[0] == '-';
}
/*!
@param[in] s reference token to be converted into an array index
@param[out] idx the integer representation of @a s if @ref array_index_status::ok
is returned; left unchanged otherwise
@return whether @a s is a valid array index, and if not, why
@note this function never throws; @ref array_index and the callers that must not
throw (@ref contains, @ref get_checked_or_null) build on it instead of each
re-implementing the RFC 6901 digit rules and the @a size_type range check
*/
/// detail::parse_array_index() for the size_type of @a BasicJsonType
template<typename BasicJsonType>
static array_index_status parse_array_index(const string_t& s, typename BasicJsonType::size_type& idx) noexcept
{
using size_type = typename BasicJsonType::size_type;
// error condition (cf. RFC 6901, Sect. 4)
if (JSON_HEDLEY_UNLIKELY(s.size() > 1 && s[0] == '0'))
{
return array_index_status::leading_zero;
}
// error condition (cf. RFC 6901, Sect. 4); this also covers single-
// character tokens, so "/x" and "/xy" fail alike; "-" and the empty
// token are left to the conversion below and are reported as unresolved
if (JSON_HEDLEY_UNLIKELY(!s.empty() && !is_dash(s) && !(s[0] >= '0' && s[0] <= '9')))
{
return array_index_status::not_a_number;
}
// fast path: up to 18 decimal digits cannot overflow unsigned long long or
// size_type (9 digits for a 32-bit size_type), so strtoull and errno are not needed
constexpr std::size_t max_fast_digits = sizeof(size_type) >= 8 ? 18 : 9;
if (!s.empty() && s.size() <= max_fast_digits)
{
size_type acc = 0;
for (std::size_t i = 0; i < s.size(); ++i)
{
const char c = s[i];
if (JSON_HEDLEY_UNLIKELY(c < '0' || c > '9'))
{
break; // not a plain number: let strtoull decide
}
acc = static_cast<size_type>((acc * 10) + static_cast<size_type>(c - '0'));
if (JSON_HEDLEY_UNLIKELY(i == s.size() - 1))
{
idx = acc;
return array_index_status::ok;
}
}
}
const char* p = s.data();
char* p_end = nullptr; // NOLINT(misc-const-correctness)
errno = 0; // strtoull doesn't reset errno
const unsigned long long res = std::strtoull(p, &p_end, 10); // NOLINT(runtime/int)
if (p == p_end // invalid input or empty string
|| errno == ERANGE // out of range
|| JSON_HEDLEY_UNLIKELY(static_cast<std::size_t>(p_end - p) != s.size())) // incomplete read
{
return array_index_status::unresolved;
}
// the index does not fit into size_type; on 64-bit platforms this is
// only SIZE_MAX itself (see #2203 and #5395)
if (res >= static_cast<unsigned long long>((std::numeric_limits<size_type>::max)())) // NOLINT(runtime/int)
{
return array_index_status::exceeds_size_type;
}
idx = static_cast<size_type>(res);
return array_index_status::ok;
return detail::parse_array_index(s, idx);
}
/*!
include/nlohmann/detail/string_utils.hpp
+9 -4
View File
@@ -196,7 +196,7 @@ This is a single-byte step of a "shift-based" UTF-8 decoder originally
written by Björn Hoehrmann. See
http://bjoern.hoehrmann.de/utf-8/decoder/dfa/ for details.
The library checks UTF-8 well-formedness (RFC 3629, section 4) in three
The library checks UTF-8 well-formedness (RFC 3629, section 4) in five
places, which differ in speed, diagnostics, and how they read the input:
- decode() below: the serializer, to escape and, in strict mode, reject
@@ -210,10 +210,15 @@ places, which differ in speed, diagnostics, and how they read the input:
bulk string scan, the bulk path of the BON8 reader, and the BON8 writer.
They must accept exactly what the lexer's switch accepts.
- the byte path of binary_reader::get_bon8_string(): BON8 input without bulk
access, and the bytes the bulk path leaves to it.
access, and the bytes the bulk path leaves to it. It takes the valid range
of the second byte from utf8_shape().
- check_utf8() in detail/view/edit.hpp: strings stored in an editable
json_document, with the index of the offending byte. It also uses
utf8_shape().
All four must accept the same set of sequences, so a change to one needs a
matching change to the others.
All five must accept the same set of sequences, which the test "UTF-8
validators accept the same sequences" in unit-class_lexer.cpp checks
exhaustively against decode() and utf8_shape().
@param[in,out] state the current decoder state
@param[in,out] codep codepoint (valid only if resulting state is UTF8_ACCEPT)
include/nlohmann/detail/view/pointer.hpp
+6 -42
View File
@@ -32,51 +32,15 @@ enum class pointer_mode
contains, ///< as basic_json::contains(): no exceptions at all
};
/// the outcome of reading an array index from a reference token
enum class index_status
{
ok,
leading_zero, ///< parse_error.106
not_number, ///< parse_error.109
unresolved, ///< out_of_range.404
too_large, ///< out_of_range.410
};
/// the outcome of reading an array index: detail::parse_array_index(), shared with json_pointer
using index_status = detail::array_index_status;
/// reads an array index like json_pointer::array_index (RFC 6901, Sect. 4),
/// but reports errors instead of throwing them
template<typename StringType>
index_status array_index(const StringType& s, std::size_t& idx) noexcept
{
// as basic_json: the empty token and "-" (past the last element) are
// unresolved rather than not a number
if (s.empty() || (s.size() == 1 && s[0] == '-'))
{
return index_status::unresolved;
}
if (s[0] < '0' || s[0] > '9')
{
return index_status::not_number;
}
if (s.size() > 1 && s[0] == '0')
{
return index_status::leading_zero;
}
std::uint64_t v = 0;
for (const auto c : s)
{
const auto d = static_cast<unsigned>(static_cast<unsigned char>(c)) - '0';
if (d > 9 || v > ((std::numeric_limits<std::uint64_t>::max)() - d) / 10)
{
return index_status::unresolved; // not a number, or beyond unsigned long long
}
v = (v * 10) + d;
}
if (v >= (std::numeric_limits<std::size_t>::max)()) // (std::size_t converts to std::uint64_t implicitly)
{
return index_status::too_large;
}
idx = static_cast<std::size_t>(v);
return index_status::ok;
return detail::parse_array_index(s, idx);
}
/// throws the exception json_pointer::array_index throws for this status
@@ -87,9 +51,9 @@ template<typename StringType>
{
case index_status::leading_zero:
throw_parse_error(exception_id::pointer_index_leading_zero, concat("array index '", s, "' must not begin with '0'"));
case index_status::not_number:
case index_status::not_a_number:
throw_parse_error(exception_id::pointer_index_not_a_number, concat("array index '", s, "' is not a number"));
case index_status::too_large:
case index_status::exceeds_size_type:
throw_out_of_range(exception_id::value_out_of_range, concat("array index ", s, " exceeds size_type")); // LCOV_EXCL_LINE
case index_status::unresolved:
case index_status::ok:
@@ -139,7 +103,7 @@ View resolve_pointer(View cur, const Tokens& tokens, pointer_mode mode)
const index_status status = array_index(token, idx);
if (status != index_status::ok)
{
const bool parse_error = status == index_status::leading_zero || status == index_status::not_number;
const bool parse_error = status == index_status::leading_zero || status == index_status::not_a_number;
if (throwing || (mode == pointer_mode::value && parse_error))
{
throw_array_index_error(status, token);