mirror of
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82cabbdc6b
basic_json_view::dump(indent, indent_char, ensure_ascii, number_format)
writes the text of a value as ordered_json::parse(text).dump() writes it
for the same arguments: members in document order (all of them, should a
key occur more than once), strings escaped by the same rules and with the
library's scanning kernels, floats with the library's conversion, and
integers copied from the source, where they are canonical except "-0".
With number_format::source, numbers are copied as they appear in the
source ("1.50", "1E2", "-0", all digits of long integers). operator<<
takes the indentation from the stream width, as for basic_json.
The writer (detail/view/serializer.hpp) writes through a raw pointer into
a string sized from the source extent of the value, and walks the index
iteratively, so the nesting depth is limited by memory only.
Tests compare the output of 2,000 generated documents with
ordered_json::dump() for several indentations and ensure_ascii, strings
with every kind of escape, numbers (5,000 random doubles, float as
number_float_t), duplicate keys, 100,000 levels of nesting, and streams.
ViewDump joins the benchmarks.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
405 lines
12 KiB
C++
405 lines
12 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 <algorithm> // max
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#include <array> // array
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#include <cmath> // isfinite
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#include <cstddef> // size_t
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#include <cstdint> // uint8_t, uint32_t
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#include <cstring> // memcpy, memset
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#include <limits> // numeric_limits
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#include <type_traits> // integral_constant
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#include <vector> // vector
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#include <nlohmann/json.hpp>
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#include <nlohmann/detail/view/document_data.hpp>
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#include <nlohmann/detail/view/macro_scope.hpp>
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#include <nlohmann/detail/view/node.hpp>
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#include <nlohmann/detail/view/number.hpp>
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NLOHMANN_JSON_NAMESPACE_BEGIN
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namespace detail
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{
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namespace view
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{
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/// append-only output buffer: writes through a raw pointer into a string that
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/// is resized ahead, and trimmed by finish()
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template<typename StringType>
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class output_buffer
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{
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public:
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output_buffer(StringType& out, std::size_t estimate)
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: m_out(out)
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{
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m_out.resize((std::max)(estimate, static_cast<std::size_t>(64)));
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m_pos = &m_out[0];
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m_end = m_pos + m_out.size();
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}
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void finish()
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{
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m_out.resize(static_cast<std::size_t>(m_pos - m_out.data()));
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}
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NLOHMANN_VIEW_ALWAYS_INLINE void reserve(std::size_t n)
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{
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if (NLOHMANN_VIEW_UNLIKELY(static_cast<std::size_t>(m_end - m_pos) < n))
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{
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grow(n);
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}
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}
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NLOHMANN_VIEW_ALWAYS_INLINE void put(char c)
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{
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reserve(1);
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*m_pos++ = c;
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}
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NLOHMANN_VIEW_ALWAYS_INLINE void put(const char* s, std::size_t n)
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{
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reserve(n);
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std::memcpy(m_pos, s, n);
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m_pos += n;
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}
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void put_repeated(char c, std::size_t n)
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{
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reserve(n);
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std::memset(m_pos, c, n);
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m_pos += n;
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}
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private:
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NLOHMANN_VIEW_NOINLINE void grow(std::size_t n)
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{
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const std::size_t used = static_cast<std::size_t>(m_pos - m_out.data());
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m_out.resize((std::max)(m_out.size() * 2, used + n + 256));
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m_pos = &m_out[0] + used;
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m_end = &m_out[0] + m_out.size();
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}
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StringType& m_out;
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char* m_pos = nullptr;
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char* m_end = nullptr;
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};
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/// how the view's dump() writes a value
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struct dump_style
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{
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bool pretty = false; ///< indent >= 0
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std::size_t indent = 0; ///< characters per level
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char indent_char = ' ';
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bool ensure_ascii = false;
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bool source_numbers = false; ///< copy number tokens from the source
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};
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/*!
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@brief write a view's subtree as basic_json::dump() writes the value
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The output of a subtree equals ordered_json::parse(text).dump() of it for
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the same arguments (members in document order): strings are escaped by the
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same rules, with the library's scanning kernels; floats are written with
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the library's conversion; integers are copied from the source, where they
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are canonical (except "-0", which parse() reads as 0). The walk is
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iterative, so the nesting depth is limited by memory only.
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*/
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template<typename BasicJsonType>
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class view_serializer
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{
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using string_t = typename BasicJsonType::string_t;
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using number_float_t = typename BasicJsonType::number_float_t;
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public:
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view_serializer(const document_data& d, string_t& out, std::size_t estimate, const dump_style& style)
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: m_doc(d), m_out(out, estimate), m_style(style)
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{}
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void dump(const node* root)
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{
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struct frame
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{
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const node* pos; ///< next element, or key of the next member
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const node* end;
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bool object;
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bool first; ///< nothing written yet
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};
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std::vector<frame> stack;
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const node* n = root;
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for (;;)
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{
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// write the value at n
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if (is_container(*n))
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{
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const bool object = n->kind == static_cast<std::uint8_t>(value_t::object);
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if (n->len == 0)
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{
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m_out.put(object ? "{}" : "[]", 2);
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}
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else
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{
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m_out.put(object ? '{' : '[');
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stack.push_back(frame{document_data::first_child(n), document_data::child_end(n), object, true});
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}
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}
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else
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{
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write_scalar(*n);
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}
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// go to the next value: close finished containers, then separate
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for (;;)
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{
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if (stack.empty())
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{
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m_out.finish();
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return;
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}
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frame& f = stack.back();
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if (f.pos == f.end)
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{
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const bool object = f.object;
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stack.pop_back();
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newline(stack.size());
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m_out.put(object ? '}' : ']');
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continue;
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}
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if (!f.first)
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{
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m_out.put(',');
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}
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f.first = false;
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newline(stack.size());
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if (f.object)
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{
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write_string(*f.pos);
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if (m_style.pretty)
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{
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m_out.put(": ", 2);
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}
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else
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{
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m_out.put(':');
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}
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n = f.pos + 1;
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}
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else
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{
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n = f.pos;
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}
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f.pos = document_data::after(n);
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break;
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}
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}
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}
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private:
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void newline(std::size_t level)
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{
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if (m_style.pretty)
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{
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m_out.put('\n');
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m_out.put_repeated(m_style.indent_char, level * m_style.indent);
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}
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}
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void write_scalar(const node& n)
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{
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switch (static_cast<value_t>(n.kind))
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{
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case value_t::null:
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m_out.put("null", 4);
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break;
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case value_t::boolean:
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if ((n.flags & node_flags::is_true) != 0)
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{
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m_out.put("true", 4);
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}
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else
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{
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m_out.put("false", 5);
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}
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break;
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case value_t::string:
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write_string(n);
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break;
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case value_t::number_integer:
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case value_t::number_unsigned:
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{
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const char* const token = m_doc.str(n);
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const std::uint32_t len = number_length(n);
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if (!m_style.source_numbers && len == 2 && token[0] == '-' && token[1] == '0')
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{
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m_out.put('0'); // parse() reads -0 as the integer 0
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}
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else
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{
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m_out.put(token, len);
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}
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break;
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}
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case value_t::number_float:
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if (m_style.source_numbers)
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{
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m_out.put(m_doc.str(n), n.len);
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}
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else
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{
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write_float(float_value<number_float_t>(m_doc.str(n), n));
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}
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break;
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case value_t::object:
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case value_t::array:
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case value_t::binary:
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case value_t::discarded:
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default:
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break;
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}
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}
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/// as serializer::dump_float()
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void write_float(number_float_t x)
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{
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if (!std::isfinite(x))
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{
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m_out.put("null", 4);
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return;
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}
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write_float(x, std::integral_constant < bool,
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(std::numeric_limits<number_float_t>::is_iec559 && std::numeric_limits<number_float_t>::digits == 24 && std::numeric_limits<number_float_t>::max_exponent == 128)
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|| (std::numeric_limits<number_float_t>::is_iec559 && std::numeric_limits<number_float_t>::digits == 53 && std::numeric_limits<number_float_t>::max_exponent == 1024) > {});
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}
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void write_float(number_float_t x, std::true_type /*is_ieee_single_or_double*/)
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{
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std::array<char, 64> buf{};
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const char* const end = ::nlohmann::detail::to_chars(buf.data(), buf.data() + buf.size(), x);
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m_out.put(buf.data(), static_cast<std::size_t>(end - buf.data()));
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}
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void write_float(number_float_t x, std::false_type /*is_ieee_single_or_double*/)
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{
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// other types (e.g. long double) are rare: the library writes them
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const string_t s = BasicJsonType(x).dump();
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m_out.put(s.data(), s.size());
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}
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void write_string(const node& n)
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{
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const char* const s = m_doc.str(n);
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m_out.put('"');
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if ((n.flags & node_flags::escaped) == 0 && !m_style.ensure_ascii)
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{
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// a string without escape sequences has nothing to escape
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m_out.put(s, n.len);
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}
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else if (m_style.ensure_ascii)
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{
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write_escaped<true>(reinterpret_cast<const unsigned char*>(s), n.len); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
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}
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else
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{
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write_escaped<false>(reinterpret_cast<const unsigned char*>(s), n.len); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
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}
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m_out.put('"');
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}
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/// as serializer::dump_escaped() for valid UTF-8 (the view has no other)
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template<bool EnsureAscii>
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void write_escaped(const unsigned char* s, std::size_t n)
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{
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std::size_t i = 0;
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while (i < n)
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{
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const std::size_t run = EnsureAscii ? (is_ascii_copyable(s[i]) ? find_ascii_copyable_run(s + i, n - i) : 0)
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: string_bulk_run(s + i, n - i);
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if (run != 0)
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{
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m_out.put(reinterpret_cast<const char*>(s + i), run); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
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i += run;
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continue;
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}
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std::uint32_t codepoint = s[i];
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std::size_t len = 1;
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if (codepoint >= 0xC0)
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{
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len = codepoint >= 0xF0 ? 4 : (codepoint >= 0xE0 ? 3 : 2);
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codepoint &= 0xFFu >> (len + 1);
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for (std::size_t k = 1; k < len; ++k)
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{
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codepoint = (codepoint << 6u) | (s[i + k] & 0x3Fu);
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}
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}
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write_codepoint<EnsureAscii>(codepoint, s + i, len);
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i += len;
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}
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}
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template<bool EnsureAscii>
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void write_codepoint(std::uint32_t codepoint, const unsigned char* bytes, std::size_t len)
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{
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switch (codepoint)
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{
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case 0x08:
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m_out.put("\\b", 2);
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return;
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case 0x09:
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m_out.put("\\t", 2);
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return;
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case 0x0A:
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m_out.put("\\n", 2);
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return;
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case 0x0C:
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m_out.put("\\f", 2);
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return;
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case 0x0D:
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m_out.put("\\r", 2);
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return;
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case 0x22:
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m_out.put("\\\"", 2);
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return;
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case 0x5C:
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m_out.put("\\\\", 2);
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return;
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default:
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break;
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}
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if (codepoint <= 0x1F || (EnsureAscii && codepoint >= 0x7F))
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{
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if (codepoint <= 0xFFFF)
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{
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write_u_escape(codepoint);
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}
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else
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{
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write_u_escape(0xD7C0u + (codepoint >> 10u));
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write_u_escape(0xDC00u + (codepoint & 0x3FFu));
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}
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return;
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}
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m_out.put(reinterpret_cast<const char*>(bytes), len); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
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}
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void write_u_escape(std::uint32_t u)
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{
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static constexpr const char* hex = "0123456789abcdef";
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const std::array<char, 6> e = {{'\\', 'u', hex[(u >> 12u) & 0xFu], hex[(u >> 8u) & 0xFu], hex[(u >> 4u) & 0xFu], hex[u & 0xFu]}};
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m_out.put(e.data(), e.size());
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}
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const document_data& m_doc;
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output_buffer<string_t> m_out;
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const dump_style m_style;
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};
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} // namespace view
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} // namespace detail
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NLOHMANN_JSON_NAMESPACE_END
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