mirror of
https://github.com/nlohmann/json.git
synced 2026-10-04 13:40:33 +00:00
Niels Lohmann
50d8e71b9f
The class documentation called the parser a recursive descent parser, but sax_parse_internal() is a loop that keeps the open containers on an explicit stack. The comment at the end of an array and of an object said the flag is set to false while the code below it sets it to true. Describe what the code does instead. Comments only; behavior, the public API and the ABI are unchanged. Part of #5712 Signed-off-by: Niels Lohmann <mail@nlohmann.me>
570 lines
21 KiB
C++
570 lines
21 KiB
C++
// __ _____ _____ _____
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// __| | __| | | | JSON for Modern C++
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// | | |__ | | | | | | version 3.12.0
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// |_____|_____|_____|_|___| https://github.com/nlohmann/json
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//
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// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
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// SPDX-License-Identifier: MIT
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#pragma once
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#include <cmath> // isfinite
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#include <cstdint> // uint8_t
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#include <functional> // function
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#include <string> // string
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#include <utility> // move
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#include <vector> // vector
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#include <nlohmann/detail/exceptions.hpp>
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#include <nlohmann/detail/input/input_adapters.hpp>
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#include <nlohmann/detail/input/json_sax.hpp>
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#include <nlohmann/detail/input/lexer.hpp>
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#include <nlohmann/detail/macro_scope.hpp>
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#include <nlohmann/detail/meta/is_sax.hpp>
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#include <nlohmann/detail/string_concat.hpp>
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#include <nlohmann/detail/value_t.hpp>
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NLOHMANN_JSON_NAMESPACE_BEGIN
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namespace detail
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{
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////////////
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// parser //
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////////////
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enum class parse_event_t : std::uint8_t
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{
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/// the parser read `{` and started to process a JSON object
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object_start,
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/// the parser read `}` and finished processing a JSON object
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object_end,
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/// the parser read `[` and started to process a JSON array
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array_start,
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/// the parser read `]` and finished processing a JSON array
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array_end,
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/// the parser read a key of a value in an object
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key,
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/// the parser finished reading a JSON value
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value
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};
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template<typename BasicJsonType>
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using parser_callback_t =
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std::function<bool(int /*depth*/, parse_event_t /*event*/, BasicJsonType& /*parsed*/)>;
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/*!
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@brief syntax analysis
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This class implements an iterative parser that keeps the open containers on
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an explicit stack and reports what it reads as SAX events.
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*/
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template<typename BasicJsonType, typename InputAdapterType>
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class parser
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{
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using number_integer_t = typename BasicJsonType::number_integer_t;
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using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
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using number_float_t = typename BasicJsonType::number_float_t;
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using string_t = typename BasicJsonType::string_t;
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using lexer_t = lexer<BasicJsonType, InputAdapterType>;
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using token_type = typename lexer_t::token_type;
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public:
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/// a parser reading from an input adapter
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explicit parser(InputAdapterType&& adapter,
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parser_callback_t<BasicJsonType> cb = nullptr,
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const bool allow_exceptions_ = true,
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const bool ignore_comments = false,
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const bool ignore_trailing_commas_ = false,
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const bool discard_number_values_ = false)
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: callback(std::move(cb))
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, m_lexer(std::move(adapter), ignore_comments, discard_number_values_)
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, allow_exceptions(allow_exceptions_)
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, ignore_trailing_commas(ignore_trailing_commas_)
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{
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// read first token
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get_token();
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}
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/*!
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@brief public parser interface
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@param[in] strict whether to expect the last token to be EOF
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@param[in,out] result parsed JSON value
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@throw parse_error.101 in case of an unexpected token (including invalid
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unicode escapes and surrogate errors, which are reported with a
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detailed message)
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*/
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void parse(const bool strict, BasicJsonType& result)
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{
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if (callback)
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{
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json_sax_dom_callback_parser<BasicJsonType, InputAdapterType> sdp(result, callback, allow_exceptions, &m_lexer);
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sax_parse_internal(&sdp);
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if (strict)
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{
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// in strict mode, input must be completely read
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if (get_token() != token_type::end_of_input)
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{
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sdp.parse_error(m_lexer.get_position(),
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m_lexer.get_token_string(),
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parse_error::create(101, m_lexer.get_position(),
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exception_message(token_type::end_of_input, "value"), nullptr));
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}
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}
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else
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{
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// the caller keeps using the input: position it right after
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// the value by leaving the character that terminated it
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m_lexer.release_lookahead();
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}
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// in case of an error, return a discarded value
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if (sdp.is_errored())
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{
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result = value_t::discarded;
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return;
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}
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// set top-level value to null if it was discarded by the callback
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// function
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if (result.is_discarded())
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{
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result = nullptr;
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}
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}
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else
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{
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json_sax_dom_parser<BasicJsonType, InputAdapterType> sdp(result, allow_exceptions, &m_lexer);
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sax_parse_internal(&sdp);
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if (strict)
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{
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// in strict mode, input must be completely read
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if (get_token() != token_type::end_of_input)
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{
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sdp.parse_error(m_lexer.get_position(),
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m_lexer.get_token_string(),
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parse_error::create(101, m_lexer.get_position(), exception_message(token_type::end_of_input, "value"), nullptr));
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}
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}
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else
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{
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// see above
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m_lexer.release_lookahead();
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}
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// in case of an error, return a discarded value
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if (sdp.is_errored())
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{
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result = value_t::discarded;
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return;
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}
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}
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result.assert_invariant();
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}
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/*!
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@brief public accept interface
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@param[in] strict whether to expect the last token to be EOF
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@return whether the input is a proper JSON text
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*/
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bool accept(const bool strict = true)
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{
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json_sax_acceptor<BasicJsonType> sax_acceptor;
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return sax_parse(&sax_acceptor, strict);
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}
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template<typename SAX>
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JSON_HEDLEY_NON_NULL(2)
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bool sax_parse(SAX* sax, const bool strict = true)
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{
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(void)detail::is_sax_static_asserts<SAX, BasicJsonType> {};
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const bool result = sax_parse_internal(sax);
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if (result)
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{
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if (strict)
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{
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// strict mode: next byte must be EOF
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if (get_token() != token_type::end_of_input)
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{
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return sax->parse_error(m_lexer.get_position(),
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m_lexer.get_token_string(),
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parse_error::create(101, m_lexer.get_position(), exception_message(token_type::end_of_input, "value"), nullptr));
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}
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}
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else
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{
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// the caller keeps using the input: position it right after
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// the value by leaving the character that terminated it
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m_lexer.release_lookahead();
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}
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}
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return result;
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}
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private:
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template<typename SAX>
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JSON_HEDLEY_NON_NULL(2)
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bool sax_parse_internal(SAX* sax)
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{
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// stack to remember the hierarchy of structured values we are parsing
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// true = array; false = object
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std::vector<bool> states;
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// value to avoid a goto (see comment where set to true)
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bool skip_to_state_evaluation = false;
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while (true)
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{
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if (!skip_to_state_evaluation)
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{
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// invariant: get_token() was called before each iteration
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switch (last_token)
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{
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case token_type::begin_object:
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{
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if (JSON_HEDLEY_UNLIKELY(!sax->start_object(detail::unknown_size())))
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{
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return false;
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}
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// closing } -> we are done
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if (get_token() == token_type::end_object)
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{
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if (JSON_HEDLEY_UNLIKELY(!sax->end_object()))
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{
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return false;
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}
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break;
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}
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// parse key
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if (JSON_HEDLEY_UNLIKELY(last_token != token_type::value_string))
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{
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return sax->parse_error(m_lexer.get_position(),
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m_lexer.get_token_string(),
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parse_error::create(101, m_lexer.get_position(), exception_message(token_type::value_string, "object key"), nullptr));
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}
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if (JSON_HEDLEY_UNLIKELY(!sax->key(m_lexer.get_string())))
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{
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return false;
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}
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// parse separator (:)
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if (JSON_HEDLEY_UNLIKELY(get_token() != token_type::name_separator))
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{
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return sax->parse_error(m_lexer.get_position(),
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m_lexer.get_token_string(),
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parse_error::create(101, m_lexer.get_position(), exception_message(token_type::name_separator, "object separator"), nullptr));
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}
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// remember we are now inside an object
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states.push_back(false);
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// parse values
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get_token();
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continue;
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}
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case token_type::begin_array:
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{
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if (JSON_HEDLEY_UNLIKELY(!sax->start_array(detail::unknown_size())))
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{
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return false;
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}
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// closing ] -> we are done
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if (get_token() == token_type::end_array)
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{
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if (JSON_HEDLEY_UNLIKELY(!sax->end_array()))
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{
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return false;
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}
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break;
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}
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// remember we are now inside an array
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states.push_back(true);
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// parse values (no need to call get_token)
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continue;
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}
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case token_type::value_float:
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{
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const auto res = m_lexer.get_number_float();
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if (JSON_HEDLEY_UNLIKELY(!std::isfinite(res)))
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{
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return sax->parse_error(m_lexer.get_position(),
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m_lexer.get_token_string(),
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out_of_range::create(406, concat("number overflow parsing '", m_lexer.get_token_string(), '\''), nullptr));
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}
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if (JSON_HEDLEY_UNLIKELY(!sax->number_float(res, m_lexer.get_string())))
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{
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return false;
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}
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break;
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}
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case token_type::literal_false:
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{
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if (JSON_HEDLEY_UNLIKELY(!sax->boolean(false)))
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{
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return false;
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}
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break;
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}
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case token_type::literal_null:
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{
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if (JSON_HEDLEY_UNLIKELY(!sax->null()))
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{
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return false;
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}
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break;
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}
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case token_type::literal_true:
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{
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if (JSON_HEDLEY_UNLIKELY(!sax->boolean(true)))
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{
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return false;
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}
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break;
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}
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case token_type::value_integer:
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{
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if (JSON_HEDLEY_UNLIKELY(!sax->number_integer(m_lexer.get_number_integer())))
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{
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return false;
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}
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break;
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}
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case token_type::value_string:
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{
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if (JSON_HEDLEY_UNLIKELY(!sax->string(m_lexer.get_string())))
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{
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return false;
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}
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break;
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}
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case token_type::value_unsigned:
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{
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if (JSON_HEDLEY_UNLIKELY(!sax->number_unsigned(m_lexer.get_number_unsigned())))
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{
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return false;
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}
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break;
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}
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case token_type::parse_error:
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{
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// using "uninitialized" to avoid an "expected" message
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return sax->parse_error(m_lexer.get_position(),
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m_lexer.get_token_string(),
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parse_error::create(101, m_lexer.get_position(), exception_message(token_type::uninitialized, "value"), nullptr));
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}
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case token_type::end_of_input:
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{
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if (JSON_HEDLEY_UNLIKELY(m_lexer.get_position().chars_read_total == 1))
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{
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return sax->parse_error(m_lexer.get_position(),
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m_lexer.get_token_string(),
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parse_error::create(101, m_lexer.get_position(),
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"attempting to parse an empty input; check that your input string or stream contains the expected JSON", nullptr));
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}
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return sax->parse_error(m_lexer.get_position(),
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m_lexer.get_token_string(),
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parse_error::create(101, m_lexer.get_position(), exception_message(token_type::literal_or_value, "value"), nullptr));
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}
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case token_type::uninitialized:
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case token_type::end_array:
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case token_type::end_object:
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case token_type::name_separator:
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case token_type::value_separator:
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case token_type::literal_or_value:
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default: // the last token was unexpected
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{
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return sax->parse_error(m_lexer.get_position(),
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m_lexer.get_token_string(),
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parse_error::create(101, m_lexer.get_position(), exception_message(token_type::literal_or_value, "value"), nullptr));
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}
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}
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}
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else
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{
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skip_to_state_evaluation = false;
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}
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// we reached this line after we successfully parsed a value
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if (states.empty())
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{
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// empty stack: we reached the end of the hierarchy: done
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return true;
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}
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if (states.back()) // array
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{
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// comma -> next value
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// or end of array (ignore_trailing_commas = true)
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if (get_token() == token_type::value_separator)
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{
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// parse a new value
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get_token();
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// if ignore_trailing_commas and last_token is ], we can continue to "closing ]"
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if (!(ignore_trailing_commas && last_token == token_type::end_array))
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{
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continue;
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}
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}
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// closing ]
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if (JSON_HEDLEY_LIKELY(last_token == token_type::end_array))
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{
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if (JSON_HEDLEY_UNLIKELY(!sax->end_array()))
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{
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return false;
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}
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// We are done with this array. Before we can parse a
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// new value, we need to evaluate the new state first.
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// By setting skip_to_state_evaluation to true, the next
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// iteration skips parsing a value and evaluates the
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// enclosing state directly.
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JSON_ASSERT(!states.empty());
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states.pop_back();
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skip_to_state_evaluation = true;
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continue;
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}
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return sax->parse_error(m_lexer.get_position(),
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m_lexer.get_token_string(),
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parse_error::create(101, m_lexer.get_position(), exception_message(token_type::end_array, "array"), nullptr));
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}
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// states.back() is false -> object
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// comma -> next value
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// or end of object (ignore_trailing_commas = true)
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if (get_token() == token_type::value_separator)
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{
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get_token();
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// if ignore_trailing_commas and last_token is }, we can continue to "closing }"
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if (!(ignore_trailing_commas && last_token == token_type::end_object))
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{
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// parse key
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if (JSON_HEDLEY_UNLIKELY(last_token != token_type::value_string))
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{
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return sax->parse_error(m_lexer.get_position(),
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m_lexer.get_token_string(),
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parse_error::create(101, m_lexer.get_position(), exception_message(token_type::value_string, "object key"), nullptr));
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}
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if (JSON_HEDLEY_UNLIKELY(!sax->key(m_lexer.get_string())))
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{
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return false;
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}
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// parse separator (:)
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if (JSON_HEDLEY_UNLIKELY(get_token() != token_type::name_separator))
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{
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return sax->parse_error(m_lexer.get_position(),
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m_lexer.get_token_string(),
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parse_error::create(101, m_lexer.get_position(), exception_message(token_type::name_separator, "object separator"), nullptr));
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}
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// parse values
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get_token();
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continue;
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}
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}
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// closing }
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if (JSON_HEDLEY_LIKELY(last_token == token_type::end_object))
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{
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if (JSON_HEDLEY_UNLIKELY(!sax->end_object()))
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{
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return false;
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}
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// We are done with this object. Before we can parse a
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// new value, we need to evaluate the new state first.
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// By setting skip_to_state_evaluation to true, the next
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// iteration skips parsing a value and evaluates the
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// enclosing state directly.
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JSON_ASSERT(!states.empty());
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states.pop_back();
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skip_to_state_evaluation = true;
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continue;
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}
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return sax->parse_error(m_lexer.get_position(),
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m_lexer.get_token_string(),
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parse_error::create(101, m_lexer.get_position(), exception_message(token_type::end_object, "object"), nullptr));
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}
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}
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/// get next token from lexer
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token_type get_token()
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{
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return last_token = m_lexer.scan();
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}
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std::string exception_message(const token_type expected, const std::string& context)
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{
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std::string error_msg = "syntax error ";
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if (!context.empty())
|
|
{
|
|
error_msg += concat("while parsing ", context, ' ');
|
|
}
|
|
|
|
error_msg += "- ";
|
|
|
|
if (last_token == token_type::parse_error)
|
|
{
|
|
error_msg += concat(m_lexer.get_error_message(), "; last read: '",
|
|
m_lexer.get_token_string(), '\'');
|
|
}
|
|
else
|
|
{
|
|
error_msg += concat("unexpected ", lexer_t::token_type_name(last_token));
|
|
}
|
|
|
|
if (expected != token_type::uninitialized)
|
|
{
|
|
error_msg += concat("; expected ", lexer_t::token_type_name(expected));
|
|
}
|
|
|
|
return error_msg;
|
|
}
|
|
|
|
private:
|
|
/// callback function
|
|
const parser_callback_t<BasicJsonType> callback = nullptr;
|
|
/// the type of the last read token
|
|
token_type last_token = token_type::uninitialized;
|
|
/// the lexer
|
|
lexer_t m_lexer;
|
|
/// whether to throw exceptions in case of errors
|
|
const bool allow_exceptions = true;
|
|
/// whether trailing commas in objects and arrays should be ignored (true) or signaled as errors (false)
|
|
const bool ignore_trailing_commas = false;
|
|
};
|
|
|
|
} // namespace detail
|
|
NLOHMANN_JSON_NAMESPACE_END
|