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Round-trip BJData ND-array annotations exactly (single precision, key order)

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to_bjdata() encoded a JData-annotated object as a BJData ND-array in two
cases where from_bjdata() then returned a different value, breaking the
documented round-trip guarantee:

1. A "single" element that is finite and in range but not exactly
   representable as float (e.g. 0.1) or that underflows to 0 (e.g. 1e-300)
   was silently narrowed instead of falling back to a plain object, unlike
   out-of-range integer elements. write_bjdata_ndarray() now only accepts a
   "single" element if it survives the narrowing to float and back, the
   same criterion write_compact_float() already uses for CBOR/MessagePack.

2. from_bjdata() emitted the annotation keys as _ArraySize_, _ArrayType_,
   _ArrayData_ instead of the documented _ArrayType_, _ArraySize_,
   _ArrayData_, because the size key is written while the dimension vector
   is read, before the type key. For ordered_json, whose comparison takes
   key order into account, this made a round trip of the documented example
   compare unequal. The element type marker is known before the dimension
   vector is read (it precedes '#'), so it is now passed down and the
   "_ArrayType_" key is emitted first.

Fixes #5661.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-09-29 23:52:34 +02:00
parent 633de8e44b
commit b98aef8a07
5 changed files with 162 additions and 52 deletions
Download Patch File Download Diff File Expand all files Collapse all files

79
single_include/nlohmann/json.hpp
View File

@@ -15495,10 +15495,15 @@ class binary_reader
is_ndarray can only return `true` when its initial value
is `false`
@param[in] prefix type marker if already read, otherwise set to 0
@param[in] ndarray_dtype the element type marker of the enclosing bjdata ndarray if
already known (it precedes the dimension vector read here),
otherwise 0; used to emit the "_ArrayType_" annotation key
before "_ArraySize_" if a dimension vector turns out to
describe an ndarray
@return whether size determination completed
*/
bool get_ubjson_size_value(std::size_t& result, bool& is_ndarray, char_int_type prefix = 0)
bool get_ubjson_size_value(std::size_t& result, bool& is_ndarray, char_int_type prefix = 0, char_int_type ndarray_dtype = 0)
{
if (prefix == 0)
{
@@ -15668,8 +15673,37 @@ class binary_reader
}
}
if (JSON_HEDLEY_UNLIKELY(!sax->start_object(3)))
{
return false;
}
// the element type precedes the dimension vector (see get_ubjson_size_type)
// and is passed down as ndarray_dtype; emit it here so the annotation keys
// follow the documented _ArrayType_, _ArraySize_, _ArrayData_ order
if (ndarray_dtype != 0)
{
auto it = std::lower_bound(bjd_types_map.begin(), bjd_types_map.end(), ndarray_dtype, [](const bjd_type & p, char_int_type t)
{
return p.first < t;
});
if (JSON_HEDLEY_UNLIKELY(it == bjd_types_map.end() || it->first != ndarray_dtype))
{
auto last_token = get_token_string();
return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read,
exception_message(input_format, "invalid byte: 0x" + last_token, "type"), nullptr));
}
string_t type_key = "_ArrayType_";
string_t type = it->second; // sax->string() takes a reference
if (JSON_HEDLEY_UNLIKELY(!sax->key(type_key) || !sax->string(type)))
{
return false;
}
}
string_t key = "_ArraySize_";
if (JSON_HEDLEY_UNLIKELY(!sax->start_object(3) || !sax->key(key) || !sax->start_array(dim.size())))
if (JSON_HEDLEY_UNLIKELY(!sax->key(key) || !sax->start_array(dim.size())))
{
return false;
}
@@ -15770,7 +15804,7 @@ class binary_reader
exception_message(input_format, concat("expected '#' after type information; last byte: 0x", last_token), "size"), nullptr));
}
const bool is_error = get_ubjson_size_value(result.first, is_ndarray);
const bool is_error = get_ubjson_size_value(result.first, is_ndarray, 0, result.second);
// an ndarray was read here only if the flag flipped; when it was
// seeded true, get_ubjson_size_value() already rejected the nested
// dimension vector
@@ -16006,30 +16040,17 @@ class binary_reader
if (input_format == input_format_t::bjdata && size_and_type.first != npos && (size_and_type.second & (1 << 8)) != 0)
{
size_and_type.second &= ~(static_cast<char_int_type>(1) << 8); // use bit 8 to indicate ndarray, here we remove the bit to restore the type marker
auto it = std::lower_bound(bjd_types_map.begin(), bjd_types_map.end(), size_and_type.second, [](const bjd_type & p, char_int_type t)
{
return p.first < t;
});
string_t key = "_ArrayType_";
if (JSON_HEDLEY_UNLIKELY(it == bjd_types_map.end() || it->first != size_and_type.second))
{
auto last_token = get_token_string();
return sax->parse_error(chars_read, last_token, parse_error::create(112, chars_read,
exception_message(input_format, "invalid byte: 0x" + last_token, "type"), nullptr));
}
string_t type = it->second; // sax->string() takes a reference
if (JSON_HEDLEY_UNLIKELY(!sax->key(key) || !sax->string(type)))
{
return false;
}
// the "_ArrayType_" and "_ArraySize_" annotation keys were already emitted by
// get_ubjson_size_value() (the type marker is known before the dimension vector
// that determines size_and_type.first is read, so it is emitted first there to
// match the documented _ArrayType_, _ArraySize_, _ArrayData_ key order)
if (size_and_type.second == 'C' || size_and_type.second == 'B')
{
size_and_type.second = 'U';
}
key = "_ArrayData_";
string_t key = "_ArrayData_";
if (JSON_HEDLEY_UNLIKELY(!sax->key(key) || !sax->start_array(size_and_type.first) ))
{
return false;
@@ -22321,9 +22342,21 @@ class binary_writer
case 'd':
{
const auto dval = el.template get<double>();
in_range = !std::isfinite(dval) ||
#ifdef __GNUC__
JSON_HEDLEY_DIAGNOSTIC_PUSH
JSON_HEDLEY_PRAGMA(GCC diagnostic ignored "-Wfloat-equal")
#endif
// a value that would be rounded (rather than exactly represented) by the
// narrowing to float is treated like an out-of-range integer element above;
// this is the same criterion write_compact_float() uses for CBOR/MessagePack
in_range = std::isnan(dval) ||
(dval >= static_cast<double>(std::numeric_limits<float>::lowest()) &&
dval <= static_cast<double>((std::numeric_limits<float>::max)()));
dval <= static_cast<double>((std::numeric_limits<float>::max)()) &&
static_cast<double>(static_cast<float>(dval)) == dval) ||
std::isinf(dval);
#ifdef __GNUC__
JSON_HEDLEY_DIAGNOSTIC_POP
#endif
break;
}
default: