json/include/nlohmann/detail/view/document_data.hpp

//     __ _____ _____ _____
//  __|  |   __|     |   | |  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 <array> // array
#include <cstddef> // size_t
#include <cstring> // memcmp, memcpy
#include <limits> // numeric_limits
#include <new> // bad_alloc, operator new, placement new
#include <string> // string
#include <vector> // vector

#include <nlohmann/json.hpp>
#include <nlohmann/detail/view/macro_scope.hpp>
#include <nlohmann/detail/view/node.hpp>

NLOHMANN_JSON_NAMESPACE_BEGIN
namespace detail
{
namespace view
{

/// storage of a parsed document; heap-allocated (header and an initial node
/// array in one block) so that views survive moves of the owning document
struct document_data
{
    const char* src = nullptr;
    std::size_t size = 0;
    node* nodes = nullptr; ///< the node index (see node.hpp)
    std::size_t node_count = 0;
    std::size_t node_capacity = 0;
    node* inline_nodes = nullptr; ///< node array allocated together with this header
    std::size_t inline_capacity = 0;
    std::size_t max_depth = 0; ///< deepest nesting of arrays and objects (the root container is depth 1)
    std::vector<char> arena; ///< decoded strings that contained escapes (no terminator: they are handed out with their length)
    std::string owned; ///< owned copy of the input, if any (a std::string, so that its NUL serves as the parser's sentinel)
    std::array<const char*, 4> base = {{nullptr, nullptr, nullptr, nullptr}}; ///< string bases: source, arena (indexed by flags & node_flags::storage)
    bool discarded = true;

    /// One allocation for the header and room for `count` nodes, so that a
    /// small document needs one allocation instead of two. Large documents get
    /// a separate node array instead (so it can be trimmed). When a document
    /// outgrows the inline array, that array stays unused: at most 256 nodes
    /// (4 KiB), and only for documents whose estimate was too small.
    static document_data* create(std::size_t count)
    {
        count = count <= 256 ? count : 0;
        void* mem = ::operator new (sizeof(document_data) + (count * sizeof(node)));
        auto* d = new (mem) document_data(); // NOLINT(cppcoreguidelines-owning-memory): owned by the returned pointer, freed by deleter
        // (aligned: sizeof is a multiple of the alignment; through void*, as GCC's -Wcast-align wants)
        // (null without inline nodes, not a pointer past the end of the allocation)
        d->inline_nodes = count == 0 ? nullptr : static_cast<node*>(static_cast<void*>(static_cast<char*>(mem) + sizeof(document_data))); // NOLINT(bugprone-casting-through-void)
        d->inline_capacity = count;
        d->nodes = d->inline_nodes;
        d->node_capacity = count;
        return d;
    }

    struct deleter
    {
        void operator()(document_data* d) const noexcept
        {
            d->~document_data();
            ::operator delete (d);
        }
    };

    /// user-provided so that the class-type members can be initialized in the
    /// member initialization list (-Weffc++ asks for it, and old GCC rejects a
    /// defaulted constructor whose exception specification differs from the
    /// implicit one); they cannot take default member initializers, which old
    /// Clang (3.4-3.6) rejects. The other members have default member
    /// initializers. noexcept: create() constructs into raw memory and could not
    /// release it if this threw (the std::vector and std::string default
    /// constructors do not allocate).
    document_data() noexcept
        : arena() // NOLINT(readability-redundant-member-init)
        , owned() // NOLINT(readability-redundant-member-init)
    {}
    document_data(const document_data&) = delete;
    document_data(document_data&&) = delete;
    document_data& operator=(const document_data&) = delete;
    document_data& operator=(document_data&&) = delete;
    ~document_data()
    {
        release();
    }

    void release() noexcept
    {
        if (nodes != inline_nodes)
        {
            ::operator delete (nodes);
        }
        nodes = inline_nodes;
        node_capacity = inline_capacity;
    }

    /// the largest node count whose size in bytes fits a std::size_t
    static constexpr std::size_t max_nodes() noexcept
    {
        return (std::numeric_limits<std::size_t>::max)() / sizeof(node);
    }

    [[noreturn]] NLOHMANN_VIEW_NOINLINE static void throw_bad_alloc()
    {
        NLOHMANN_VIEW_THROW(std::bad_alloc());
    }

    /// make room for n nodes; keeps the first node_count nodes (throws
    /// std::bad_alloc for a count that does not fit the address space,
    /// instead of wrapping around in n * sizeof(node))
    void reserve(std::size_t n)
    {
        if (n <= node_capacity)
        {
            return;
        }
        if (NLOHMANN_VIEW_UNLIKELY(n > max_nodes()))
        {
            throw_bad_alloc();
        }
        node* fresh = static_cast<node*>(::operator new (n * sizeof(node)));
        if (node_count != 0)
        {
            std::memcpy(fresh, nodes, node_count * sizeof(node));
        }
        release();
        nodes = fresh;
        node_capacity = n;
    }

    const char* str(const node& n) const noexcept
    {
        return base[n.flags & node_flags::storage] + n.off;
    }

    /// whether the string of node k (a key) is the n bytes at key
    bool key_equals(const node& k, const char* key, std::size_t n) const noexcept
    {
        return k.len == n && (n == 0 || std::memcmp(str(k), key, n) == 0);
    }

    /// the node after n's subtree (containers span `next` nodes, scalars one)
    static NLOHMANN_VIEW_ALWAYS_INLINE const node* after(const node* n) noexcept
    {
        return n + (is_container(*n) ? n->next : 1u);
    }

    /// first element (array) or first key (object) of a container
    static NLOHMANN_VIEW_ALWAYS_INLINE const node* first_child(const node* n) noexcept
    {
        return n + 1;
    }

    /// end of the elements of a container
    static NLOHMANN_VIEW_ALWAYS_INLINE const node* child_end(const node* n) noexcept
    {
        return n + n->next;
    }
};

}  // namespace view
}  // namespace detail
NLOHMANN_JSON_NAMESPACE_END