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0ec4bdb8fa6e921f2ca45365c3eed42a2592f0b2
json/include/nlohmann/detail/input/json_sax.hpp
T
Niels Lohmann 0ec4bdb8fa Restore a duplicate key's prior value when the callback rejects its new value 
json_sax_dom_callback_parser::key() unconditionally overwrote the object
slot for a key with a `discarded` placeholder as soon as the key was
accepted by the parser callback. For a duplicate key (legal JSON), this
destroyed the pre-existing value from an earlier occurrence of the same
key before the new value was even parsed. If the new value was then
rejected by the callback, remove_discarded_value() erased the member
entirely instead of leaving the original value in place, contradicting
the documented behavior that a discarded value behaves as if it was
never read.

Add a small stash of (slot pointer, previous value) pairs so that when
key() overwrites an existing member with the discarded placeholder, the
previous value can be restored later if the corresponding value (scalar,
object, or array) is rejected, instead of being erased. The stash entry
is dropped without restoring once the new value is definitively
accepted (in handle_value() for scalars, end_object()/end_array() for
containers), so a duplicate key whose new value is accepted still keeps
the last value as before. Non-duplicate keys are unaffected: rejecting
their value still removes the member entirely, since there is nothing
to restore.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-05 17:05:55 +02:00

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// __ _____ _____ _____
// __| | __| | | | JSON for Modern C++
// | | |__ | | | | | | version 3.12.0
// |_____|_____|_____|_|___| https://github.com/nlohmann/json
//
// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
// SPDX-License-Identifier: MIT
#pragma once
#include <algorithm> // find_if
#include <cstddef>
#include <string> // string
#include <type_traits> // enable_if_t
#include <utility> // move, pair
#include <vector> // vector
#include <nlohmann/detail/exceptions.hpp>
#include <nlohmann/detail/input/lexer.hpp>
#include <nlohmann/detail/macro_scope.hpp>
#include <nlohmann/detail/string_concat.hpp>
NLOHMANN_JSON_NAMESPACE_BEGIN
/*!
@brief SAX interface
This class describes the SAX interface used by @ref nlohmann::json::sax_parse.
Each function is called in different situations while the input is parsed. The
boolean return value informs the parser whether to continue processing the
input.
*/
template<typename BasicJsonType>
struct json_sax
{
using number_integer_t = typename BasicJsonType::number_integer_t;
using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
using number_float_t = typename BasicJsonType::number_float_t;
using string_t = typename BasicJsonType::string_t;
using binary_t = typename BasicJsonType::binary_t;
/*!
@brief a null value was read
@return whether parsing should proceed
*/
virtual bool null() = 0;
/*!
@brief a boolean value was read
@param[in] val boolean value
@return whether parsing should proceed
*/
virtual bool boolean(bool val) = 0;
/*!
@brief an integer number was read
@param[in] val integer value
@return whether parsing should proceed
*/
virtual bool number_integer(number_integer_t val) = 0;
/*!
@brief an unsigned integer number was read
@param[in] val unsigned integer value
@return whether parsing should proceed
*/
virtual bool number_unsigned(number_unsigned_t val) = 0;
/*!
@brief a floating-point number was read
@param[in] val floating-point value
@param[in] s raw token value
@return whether parsing should proceed
*/
virtual bool number_float(number_float_t val, const string_t& s) = 0;
/*!
@brief a string value was read
@param[in] val string value
@return whether parsing should proceed
@note It is safe to move the passed string value.
*/
virtual bool string(string_t& val) = 0;
/*!
@brief a binary value was read
@param[in] val binary value
@return whether parsing should proceed
@note It is safe to move the passed binary value.
*/
virtual bool binary(binary_t& val) = 0;
/*!
@brief the beginning of an object was read
@param[in] elements number of object elements or -1 if unknown
@return whether parsing should proceed
@note binary formats may report the number of elements
*/
virtual bool start_object(std::size_t elements) = 0;
/*!
@brief an object key was read
@param[in] val object key
@return whether parsing should proceed
@note It is safe to move the passed string.
*/
virtual bool key(string_t& val) = 0;
/*!
@brief the end of an object was read
@return whether parsing should proceed
*/
virtual bool end_object() = 0;
/*!
@brief the beginning of an array was read
@param[in] elements number of array elements or -1 if unknown
@return whether parsing should proceed
@note binary formats may report the number of elements
*/
virtual bool start_array(std::size_t elements) = 0;
/*!
@brief the end of an array was read
@return whether parsing should proceed
*/
virtual bool end_array() = 0;
/*!
@brief a parse error occurred
@param[in] position the position in the input where the error occurs
@param[in] last_token the last read token
@param[in] ex an exception object describing the error
@return whether parsing should proceed (must return false)
*/
virtual bool parse_error(std::size_t position,
const std::string& last_token,
const detail::exception& ex) = 0;
json_sax() = default;
json_sax(const json_sax&) = default;
json_sax(json_sax&&) noexcept = default;
json_sax& operator=(const json_sax&) = default;
json_sax& operator=(json_sax&&) noexcept = default;
virtual ~json_sax() = default;
};
namespace detail
{
constexpr std::size_t unknown_size()
{
return (std::numeric_limits<std::size_t>::max)();
}
/*!
@brief SAX implementation to create a JSON value from SAX events
This class implements the @ref json_sax interface and processes the SAX events
to create a JSON value which makes it basically a DOM parser. The structure or
hierarchy of the JSON value is managed by the stack `ref_stack` which contains
a pointer to the respective array or object for each recursion depth.
After successful parsing, the value that is passed by reference to the
constructor contains the parsed value.
@tparam BasicJsonType the JSON type
*/
template<typename BasicJsonType, typename InputAdapterType>
class json_sax_dom_parser
{
public:
using number_integer_t = typename BasicJsonType::number_integer_t;
using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
using number_float_t = typename BasicJsonType::number_float_t;
using string_t = typename BasicJsonType::string_t;
using binary_t = typename BasicJsonType::binary_t;
using lexer_t = lexer<BasicJsonType, InputAdapterType>;
/*!
@param[in,out] r reference to a JSON value that is manipulated while
parsing
@param[in] allow_exceptions_ whether parse errors yield exceptions
*/
explicit json_sax_dom_parser(BasicJsonType& r, const bool allow_exceptions_ = true, lexer_t* lexer_ = nullptr)
: root(r), allow_exceptions(allow_exceptions_), m_lexer_ref(lexer_)
{}
// make class move-only
json_sax_dom_parser(const json_sax_dom_parser&) = delete;
json_sax_dom_parser(json_sax_dom_parser&&) = default; // NOLINT(hicpp-noexcept-move,performance-noexcept-move-constructor)
json_sax_dom_parser& operator=(const json_sax_dom_parser&) = delete;
json_sax_dom_parser& operator=(json_sax_dom_parser&&) = default; // NOLINT(hicpp-noexcept-move,performance-noexcept-move-constructor)
~json_sax_dom_parser() = default;
bool null()
{
handle_value(nullptr);
return true;
}
bool boolean(bool val)
{
handle_value(val);
return true;
}
bool number_integer(number_integer_t val)
{
handle_value(val);
return true;
}
bool number_unsigned(number_unsigned_t val)
{
handle_value(val);
return true;
}
bool number_float(number_float_t val, const string_t& /*unused*/)
{
handle_value(val);
return true;
}
bool string(string_t& val)
{
handle_value(val);
return true;
}
bool binary(binary_t& val)
{
handle_value(std::move(val));
return true;
}
bool start_object(std::size_t len)
{
ref_stack.push_back(handle_value(BasicJsonType::value_t::object));
#if JSON_DIAGNOSTIC_POSITIONS
// Manually set the start position of the object here.
// Ensure this is after the call to handle_value to ensure correct start position.
if (m_lexer_ref)
{
// Lexer has read the first character of the object, so
// subtract 1 from the position to get the correct start position.
ref_stack.back()->start_position = m_lexer_ref->get_position() - 1;
}
#endif
if (JSON_HEDLEY_UNLIKELY(len != detail::unknown_size() && len > ref_stack.back()->max_size()))
{
JSON_THROW(out_of_range::create(408, concat("excessive object size: ", std::to_string(len)), ref_stack.back()));
}
return true;
}
bool key(string_t& val)
{
JSON_ASSERT(!ref_stack.empty());
JSON_ASSERT(ref_stack.back()->is_object());
// add null at the given key and store the reference for later
object_element = &(ref_stack.back()->m_data.m_value.object->operator[](val));
return true;
}
bool end_object()
{
JSON_ASSERT(!ref_stack.empty());
JSON_ASSERT(ref_stack.back()->is_object());
#if JSON_DIAGNOSTIC_POSITIONS
if (m_lexer_ref)
{
// Lexer's position is past the closing brace, so set that as the end position.
ref_stack.back()->end_position = m_lexer_ref->get_position();
}
#endif
ref_stack.back()->set_parents();
ref_stack.pop_back();
return true;
}
bool start_array(std::size_t len)
{
ref_stack.push_back(handle_value(BasicJsonType::value_t::array));
#if JSON_DIAGNOSTIC_POSITIONS
// Manually set the start position of the array here.
// Ensure this is after the call to handle_value to ensure correct start position.
if (m_lexer_ref)
{
ref_stack.back()->start_position = m_lexer_ref->get_position() - 1;
}
#endif
if (JSON_HEDLEY_UNLIKELY(len != detail::unknown_size() && len > ref_stack.back()->max_size()))
{
JSON_THROW(out_of_range::create(408, concat("excessive array size: ", std::to_string(len)), ref_stack.back()));
}
return true;
}
bool end_array()
{
JSON_ASSERT(!ref_stack.empty());
JSON_ASSERT(ref_stack.back()->is_array());
#if JSON_DIAGNOSTIC_POSITIONS
if (m_lexer_ref)
{
// Lexer's position is past the closing bracket, so set that as the end position.
ref_stack.back()->end_position = m_lexer_ref->get_position();
}
#endif
ref_stack.back()->set_parents();
ref_stack.pop_back();
return true;
}
template<class Exception>
bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/,
const Exception& ex)
{
errored = true;
static_cast<void>(ex);
if (allow_exceptions)
{
JSON_THROW(ex);
}
return false;
}
constexpr bool is_errored() const
{
return errored;
}
private:
#if JSON_DIAGNOSTIC_POSITIONS
void handle_diagnostic_positions_for_json_value(BasicJsonType& v)
{
if (m_lexer_ref)
{
// Lexer has read past the current field value, so set the end position to the current position.
// The start position will be set below based on the length of the string representation
// of the value.
v.end_position = m_lexer_ref->get_position();
switch (v.type())
{
case value_t::boolean:
{
// 4 and 5 are the string length of "true" and "false"
v.start_position = v.end_position - (v.m_data.m_value.boolean ? 4 : 5);
break;
}
case value_t::null:
{
// 4 is the string length of "null"
v.start_position = v.end_position - 4;
break;
}
case value_t::string:
{
// escape sequences make the token longer than the value it
// parses to, so the start position cannot be derived from
// the value; use the offset the lexer recorded instead
v.start_position = m_lexer_ref->get_token_start_position();
break;
}
// As we handle the start and end positions for values created during parsing,
// we do not expect the following value type to be called. Regardless, set the positions
// in case this is created manually or through a different constructor. Exclude from lcov
// since the exact condition of this switch is esoteric.
// LCOV_EXCL_START
case value_t::discarded:
{
v.end_position = std::string::npos;
v.start_position = v.end_position;
break;
}
// LCOV_EXCL_STOP
case value_t::binary:
case value_t::number_integer:
case value_t::number_unsigned:
case value_t::number_float:
{
v.start_position = v.end_position - m_lexer_ref->get_string().size();
break;
}
case value_t::object:
case value_t::array:
{
// object and array are handled in start_object() and start_array() handlers
// skip setting the values here.
break;
}
default: // LCOV_EXCL_LINE
// Handle all possible types discretely, default handler should never be reached.
JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert,-warnings-as-errors) LCOV_EXCL_LINE
}
}
}
#endif
/*!
@invariant If the ref stack is empty, then the passed value will be the new
root.
@invariant If the ref stack contains a value, then it is an array or an
object to which we can add elements
*/
template<typename Value>
JSON_HEDLEY_RETURNS_NON_NULL
BasicJsonType* handle_value(Value&& v)
{
if (ref_stack.empty())
{
root = BasicJsonType(std::forward<Value>(v));
#if JSON_DIAGNOSTIC_POSITIONS
handle_diagnostic_positions_for_json_value(root);
#endif
return &root;
}
JSON_ASSERT(ref_stack.back()->is_array() || ref_stack.back()->is_object());
if (ref_stack.back()->is_array())
{
ref_stack.back()->m_data.m_value.array->emplace_back(std::forward<Value>(v));
#if JSON_DIAGNOSTIC_POSITIONS
handle_diagnostic_positions_for_json_value(ref_stack.back()->m_data.m_value.array->back());
#endif
return &(ref_stack.back()->m_data.m_value.array->back());
}
JSON_ASSERT(ref_stack.back()->is_object());
JSON_ASSERT(object_element);
*object_element = BasicJsonType(std::forward<Value>(v));
#if JSON_DIAGNOSTIC_POSITIONS
handle_diagnostic_positions_for_json_value(*object_element);
#endif
return object_element;
}
/// the parsed JSON value
BasicJsonType& root;
/// stack to model hierarchy of values
std::vector<BasicJsonType*> ref_stack {};
/// helper to hold the reference for the next object element
BasicJsonType* object_element = nullptr;
/// whether a syntax error occurred
bool errored = false;
/// whether to throw exceptions in case of errors
const bool allow_exceptions = true;
/// the lexer reference to obtain the current position
lexer_t* m_lexer_ref = nullptr;
};
template<typename BasicJsonType, typename InputAdapterType>
class json_sax_dom_callback_parser
{
public:
using number_integer_t = typename BasicJsonType::number_integer_t;
using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
using number_float_t = typename BasicJsonType::number_float_t;
using string_t = typename BasicJsonType::string_t;
using binary_t = typename BasicJsonType::binary_t;
using parser_callback_t = typename BasicJsonType::parser_callback_t;
using parse_event_t = typename BasicJsonType::parse_event_t;
using lexer_t = lexer<BasicJsonType, InputAdapterType>;
json_sax_dom_callback_parser(BasicJsonType& r,
parser_callback_t cb,
const bool allow_exceptions_ = true,
lexer_t* lexer_ = nullptr)
: root(r), callback(std::move(cb)), allow_exceptions(allow_exceptions_), m_lexer_ref(lexer_)
{
keep_stack.push_back(true);
}
// make class move-only
json_sax_dom_callback_parser(const json_sax_dom_callback_parser&) = delete;
json_sax_dom_callback_parser(json_sax_dom_callback_parser&&) = default; // NOLINT(hicpp-noexcept-move,performance-noexcept-move-constructor)
json_sax_dom_callback_parser& operator=(const json_sax_dom_callback_parser&) = delete;
json_sax_dom_callback_parser& operator=(json_sax_dom_callback_parser&&) = default; // NOLINT(hicpp-noexcept-move,performance-noexcept-move-constructor)
~json_sax_dom_callback_parser() = default;
bool null()
{
handle_value(nullptr);
return true;
}
bool boolean(bool val)
{
handle_value(val);
return true;
}
bool number_integer(number_integer_t val)
{
handle_value(val);
return true;
}
bool number_unsigned(number_unsigned_t val)
{
handle_value(val);
return true;
}
bool number_float(number_float_t val, const string_t& /*unused*/)
{
handle_value(val);
return true;
}
bool string(string_t& val)
{
handle_value(val);
return true;
}
bool binary(binary_t& val)
{
handle_value(std::move(val));
return true;
}
bool start_object(std::size_t len)
{
// check callback for object start
const bool keep = callback(static_cast<int>(ref_stack.size()), parse_event_t::object_start, discarded);
keep_stack.push_back(keep);
auto val = handle_value(BasicJsonType::value_t::object, true);
ref_stack.push_back(val.second);
if (ref_stack.back())
{
#if JSON_DIAGNOSTIC_POSITIONS
// Manually set the start position of the object here.
// Ensure this is after the call to handle_value to ensure correct start position.
if (m_lexer_ref)
{
// Lexer has read the first character of the object, so
// subtract 1 from the position to get the correct start position.
ref_stack.back()->start_position = m_lexer_ref->get_position() - 1;
}
#endif
// check object limit
if (JSON_HEDLEY_UNLIKELY(len != detail::unknown_size() && len > ref_stack.back()->max_size()))
{
JSON_THROW(out_of_range::create(408, concat("excessive object size: ", std::to_string(len)), ref_stack.back()));
}
}
return true;
}
bool key(string_t& val)
{
BasicJsonType k = BasicJsonType(val);
// check callback for the key
const bool keep = callback(static_cast<int>(ref_stack.size()), parse_event_t::key, k);
key_keep_stack.push_back(keep);
// add discarded value at the given key and store the reference for later
if (keep && ref_stack.back())
{
auto& obj = *ref_stack.back()->m_data.m_value.object;
const auto it = obj.find(val);
if (it != obj.end())
{
// this is a duplicate key (legal in JSON); remember its
// current value so it can be restored later if the new
// value is rejected by the callback, instead of being
// erased together with the discarded placeholder
duplicate_key_stash.emplace_back(&(it->second), it->second);
}
object_element = &(obj[val] = discarded);
}
return true;
}
bool end_object()
{
if (ref_stack.back())
{
if (!callback(static_cast<int>(ref_stack.size()) - 1, parse_event_t::object_end, *ref_stack.back()))
{
// discard object, unless this slot holds a duplicate key's
// previous value pending restoration, in which case that
// value is restored instead of being discarded
if (!resolve_duplicate_key_stash(ref_stack.back(), true))
{
*ref_stack.back() = discarded;
#if JSON_DIAGNOSTIC_POSITIONS
// Set start/end positions for discarded object.
handle_diagnostic_positions_for_json_value(*ref_stack.back());
#endif
}
}
else
{
#if JSON_DIAGNOSTIC_POSITIONS
if (m_lexer_ref)
{
// Lexer's position is past the closing brace, so set that as the end position.
ref_stack.back()->end_position = m_lexer_ref->get_position();
}
#endif
ref_stack.back()->set_parents();
// this object is finally, definitively kept; drop any
// pending duplicate-key stash entry for its slot since it
// can no longer be restored
resolve_duplicate_key_stash(ref_stack.back(), false);
}
}
JSON_ASSERT(!ref_stack.empty());
JSON_ASSERT(!keep_stack.empty());
ref_stack.pop_back();
keep_stack.pop_back();
if (!ref_stack.empty() && ref_stack.back() && ref_stack.back()->is_structured())
{
// remove discarded value
remove_discarded_value(*ref_stack.back());
}
return true;
}
bool start_array(std::size_t len)
{
const bool keep = callback(static_cast<int>(ref_stack.size()), parse_event_t::array_start, discarded);
keep_stack.push_back(keep);
auto val = handle_value(BasicJsonType::value_t::array, true);
ref_stack.push_back(val.second);
if (ref_stack.back())
{
#if JSON_DIAGNOSTIC_POSITIONS
// Manually set the start position of the array here.
// Ensure this is after the call to handle_value to ensure correct start position.
if (m_lexer_ref)
{
// Lexer has read the first character of the array, so
// subtract 1 from the position to get the correct start position.
ref_stack.back()->start_position = m_lexer_ref->get_position() - 1;
}
#endif
// check array limit
if (JSON_HEDLEY_UNLIKELY(len != detail::unknown_size() && len > ref_stack.back()->max_size()))
{
JSON_THROW(out_of_range::create(408, concat("excessive array size: ", std::to_string(len)), ref_stack.back()));
}
}
return true;
}
bool end_array()
{
bool keep = true;
const bool stored = ref_stack.back() != nullptr;
if (stored)
{
keep = callback(static_cast<int>(ref_stack.size()) - 1, parse_event_t::array_end, *ref_stack.back());
if (keep)
{
#if JSON_DIAGNOSTIC_POSITIONS
if (m_lexer_ref)
{
// Lexer's position is past the closing bracket, so set that as the end position.
ref_stack.back()->end_position = m_lexer_ref->get_position();
}
#endif
ref_stack.back()->set_parents();
// this array is finally, definitively kept; drop any
// pending duplicate-key stash entry for its slot since it
// can no longer be restored
resolve_duplicate_key_stash(ref_stack.back(), false);
}
else
{
// discard array, unless this slot holds a duplicate key's
// previous value pending restoration, in which case that
// value is restored instead of being discarded
if (!resolve_duplicate_key_stash(ref_stack.back(), true))
{
*ref_stack.back() = discarded;
#if JSON_DIAGNOSTIC_POSITIONS
// Set start/end positions for discarded array.
handle_diagnostic_positions_for_json_value(*ref_stack.back());
#endif
}
}
}
JSON_ASSERT(!ref_stack.empty());
JSON_ASSERT(!keep_stack.empty());
ref_stack.pop_back();
keep_stack.pop_back();
// remove discarded value
if (!ref_stack.empty() && ref_stack.back())
{
if (!keep && ref_stack.back()->is_array())
{
ref_stack.back()->m_data.m_value.array->pop_back();
}
else if ((!keep || !stored) && ref_stack.back()->is_object())
{
// the array is either still stored under its key or was never
// stored, leaving the placeholder key() wrote; both show up as
// a discarded member of the parent object
remove_discarded_value(*ref_stack.back());
}
}
return true;
}
template<class Exception>
bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/,
const Exception& ex)
{
errored = true;
static_cast<void>(ex);
if (allow_exceptions)
{
JSON_THROW(ex);
}
return false;
}
constexpr bool is_errored() const
{
return errored;
}
private:
#if JSON_DIAGNOSTIC_POSITIONS
void handle_diagnostic_positions_for_json_value(BasicJsonType& v)
{
if (m_lexer_ref)
{
// Lexer has read past the current field value, so set the end position to the current position.
// The start position will be set below based on the length of the string representation
// of the value.
v.end_position = m_lexer_ref->get_position();
switch (v.type())
{
case value_t::boolean:
{
// 4 and 5 are the string length of "true" and "false"
v.start_position = v.end_position - (v.m_data.m_value.boolean ? 4 : 5);
break;
}
case value_t::null:
{
// 4 is the string length of "null"
v.start_position = v.end_position - 4;
break;
}
case value_t::string:
{
// escape sequences make the token longer than the value it
// parses to, so the start position cannot be derived from
// the value; use the offset the lexer recorded instead
v.start_position = m_lexer_ref->get_token_start_position();
break;
}
case value_t::discarded:
{
v.end_position = std::string::npos;
v.start_position = v.end_position;
break;
}
case value_t::binary:
case value_t::number_integer:
case value_t::number_unsigned:
case value_t::number_float:
{
v.start_position = v.end_position - m_lexer_ref->get_string().size();
break;
}
case value_t::object:
case value_t::array:
{
// object and array are handled in start_object() and start_array() handlers
// skip setting the values here.
break;
}
default: // LCOV_EXCL_LINE
// Handle all possible types discretely, default handler should never be reached.
JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert,-warnings-as-errors) LCOV_EXCL_LINE
}
}
}
#endif
/// if there is a pending duplicate-key stash entry for this exact slot,
/// remove it from the stash; if restore_value is true, the stashed
/// previous value is moved back into the slot first (use this when the
/// new value at that slot was rejected); otherwise the stash entry is
/// simply dropped (use this when the new value was accepted, so it
/// correctly supersedes the old one and no restore should ever happen
/// for this slot again)
/// @return whether a matching stash entry was found (and processed)
bool resolve_duplicate_key_stash(BasicJsonType* slot, bool restore_value)
{
const auto it = std::find_if(duplicate_key_stash.begin(), duplicate_key_stash.end(),
[slot](const std::pair<BasicJsonType*, BasicJsonType>& entry)
{
return entry.first == slot;
});
if (it == duplicate_key_stash.end())
{
return false;
}
if (restore_value)
{
*slot = std::move(it->second);
}
duplicate_key_stash.erase(it);
return true;
}
/// remove the discarded value the callback rejected from its parent,
/// unless it is a duplicate key's slot with a stashed previous value,
/// in which case that previous value is restored instead
void remove_discarded_value(BasicJsonType& parent)
{
for (auto it = parent.begin(); it != parent.end(); ++it)
{
if (it->is_discarded())
{
if (!resolve_duplicate_key_stash(&(*it), true))
{
parent.erase(it);
}
break;
}
}
}
/*!
@param[in] v value to add to the JSON value we build during parsing
@param[in] skip_callback whether we should skip calling the callback
function; this is required after start_array() and
start_object() SAX events, because otherwise we would call the
callback function with an empty array or object, respectively.
@invariant If the ref stack is empty, then the passed value will be the new
root.
@invariant If the ref stack contains a value, then it is an array or an
object to which we can add elements
@return pair of boolean (whether value should be kept) and pointer (to the
passed value in the ref_stack hierarchy; nullptr if not kept)
*/
template<typename Value>
std::pair<bool, BasicJsonType*> handle_value(Value&& v, const bool skip_callback = false)
{
JSON_ASSERT(!keep_stack.empty());
// do not handle this value if we know it would be added to a discarded
// container
if (!keep_stack.back())
{
return {false, nullptr};
}
// create value
auto value = BasicJsonType(std::forward<Value>(v));
#if JSON_DIAGNOSTIC_POSITIONS
handle_diagnostic_positions_for_json_value(value);
#endif
// check callback
const bool keep = skip_callback || callback(static_cast<int>(ref_stack.size()), parse_event_t::value, value);
// do not handle this value if we just learnt it shall be discarded
if (!keep)
{
// if the value was to become an object member, key() already
// stored a placeholder for it that has to be removed again
if (!ref_stack.empty() && ref_stack.back() && ref_stack.back()->is_object())
{
JSON_ASSERT(!key_keep_stack.empty());
const bool placeholder_stored = key_keep_stack.back();
key_keep_stack.pop_back();
if (placeholder_stored)
{
remove_discarded_value(*ref_stack.back());
}
}
return {false, nullptr};
}
if (ref_stack.empty())
{
root = std::move(value);
return {true, & root};
}
// skip this value if we already decided to skip the parent
// (https://github.com/nlohmann/json/issues/971#issuecomment-413678360)
if (!ref_stack.back())
{
return {false, nullptr};
}
// we now only expect arrays and objects
JSON_ASSERT(ref_stack.back()->is_array() || ref_stack.back()->is_object());
// array
if (ref_stack.back()->is_array())
{
ref_stack.back()->m_data.m_value.array->emplace_back(std::move(value));
return {true, & (ref_stack.back()->m_data.m_value.array->back())};
}
// object
JSON_ASSERT(ref_stack.back()->is_object());
// check if we should store an element for the current key
JSON_ASSERT(!key_keep_stack.empty());
const bool store_element = key_keep_stack.back();
key_keep_stack.pop_back();
if (!store_element)
{
return {false, nullptr};
}
JSON_ASSERT(object_element);
*object_element = std::move(value);
if (!skip_callback)
{
// this scalar value finally, definitively replaces whatever was
// at this slot; drop any pending duplicate-key stash entry for
// it since it can no longer be restored (a container value at
// this slot is resolved later, in end_object()/end_array(),
// since skip_callback is true for the placeholder handling that
// happens here for those)
resolve_duplicate_key_stash(object_element, false);
}
return {true, object_element};
}
/// the parsed JSON value
BasicJsonType& root;
/// stack to model hierarchy of values
std::vector<BasicJsonType*> ref_stack {};
/// stack to manage which values to keep
std::vector<bool> keep_stack {}; // NOLINT(readability-redundant-member-init)
/// stack to manage which object keys to keep
std::vector<bool> key_keep_stack {}; // NOLINT(readability-redundant-member-init)
/// helper to hold the reference for the next object element
BasicJsonType* object_element = nullptr;
/// stash of (slot pointer, previous value) for object members that
/// already existed when key() was called again for the same key
/// (duplicate keys); used to restore the previous value if the new
/// value is later rejected by the callback, instead of erasing the
/// member entirely
std::vector<std::pair<BasicJsonType*, BasicJsonType>> duplicate_key_stash {};
/// whether a syntax error occurred
bool errored = false;
/// callback function
const parser_callback_t callback = nullptr;
/// whether to throw exceptions in case of errors
const bool allow_exceptions = true;
/// a discarded value for the callback
BasicJsonType discarded = BasicJsonType::value_t::discarded;
/// the lexer reference to obtain the current position
lexer_t* m_lexer_ref = nullptr;
};
template<typename BasicJsonType>
class json_sax_acceptor
{
public:
using number_integer_t = typename BasicJsonType::number_integer_t;
using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
using number_float_t = typename BasicJsonType::number_float_t;
using string_t = typename BasicJsonType::string_t;
using binary_t = typename BasicJsonType::binary_t;
bool null()
{
return true;
}
bool boolean(bool /*unused*/)
{
return true;
}
bool number_integer(number_integer_t /*unused*/)
{
return true;
}
bool number_unsigned(number_unsigned_t /*unused*/)
{
return true;
}
bool number_float(number_float_t /*unused*/, const string_t& /*unused*/)
{
return true;
}
bool string(string_t& /*unused*/)
{
return true;
}
bool binary(binary_t& /*unused*/)
{
return true;
}
bool start_object(std::size_t /*unused*/ = detail::unknown_size())
{
return true;
}
bool key(string_t& /*unused*/)
{
return true;
}
bool end_object()
{
return true;
}
bool start_array(std::size_t /*unused*/ = detail::unknown_size())
{
return true;
}
bool end_array()
{
return true;
}
bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/, const detail::exception& /*unused*/)
{
return false;
}
};
} // namespace detail
NLOHMANN_JSON_NAMESPACE_END
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