json/tests/benchmarks/json_view/bench_decode.cpp

//     __ _____ _____ _____
//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
// |  |  |__   |  |  | | | |  version 3.12.0
// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
//
// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
// SPDX-License-Identifier: MIT

// Decoding into structs: the same types, with from_json() generated by the
// NLOHMANN_DEFINE_TYPE_* macros, read three ways. Only nlohmann/json takes
// part; the other libraries have no comparable mapping.
//
//   view           json_document::parse, then get<T>() on the view (from_json reads the view)
//   materialize    json_document::parse, then materialize().get<T>() (a json value first)
//   json::parse    json::parse, then get<T>()
//   json::get      get<T>() on an already parsed json value (the decoding alone)
//
// Documents: twitter (the statuses with their users and hashtags), citm_catalog
// (the performances with their seat categories), and a synthetic document of
// 20,000 nested records.
//
// Build: see README.md (same flags as bench_view.cpp).
#include <nlohmann/json_view.hpp>

#include <algorithm>
#include <chrono>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <fstream>
#include <functional>
#include <sstream>
#include <string>
#include <utility>
#include <vector>

using nlohmann::json;
using nlohmann::json_document;

static volatile std::size_t g_sink;

namespace twitter
{
struct hashtag
{
    std::string text;
    std::vector<int> indices;
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(hashtag, text, indices)

struct entities
{
    std::vector<hashtag> hashtags;
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(entities, hashtags)

struct user
{
    std::uint64_t id = 0;
    std::string screen_name;
    std::string description;
    std::int64_t followers_count = 0;
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(user, id, screen_name, description, followers_count)

struct status
{
    std::uint64_t id = 0;
    std::string text;
    user user;
    entities entities;
    std::int64_t retweet_count = 0;
    std::int64_t favorite_count = 0;
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(status, id, text, user, entities, retweet_count, favorite_count)

struct document
{
    std::vector<status> statuses;
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(document, statuses)

std::size_t digest(const document& d)
{
    std::size_t n = 0;
    for (const auto& s : d.statuses)
    {
        n += s.text.size() + s.user.screen_name.size() + s.entities.hashtags.size() + static_cast<std::size_t>(s.retweet_count);
    }
    return n;
}
}  // namespace twitter

namespace citm
{
struct area
{
    std::int64_t areaId = 0;
    std::vector<std::int64_t> blockIds;
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(area, areaId, blockIds)

struct seat_category
{
    std::vector<area> areas;
    std::int64_t seatCategoryId = 0;
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(seat_category, areas, seatCategoryId)

struct performance
{
    std::int64_t id = 0;
    std::int64_t eventId = 0;
    std::vector<seat_category> seatCategories;
    std::int64_t start = 0;
    std::string venueCode;
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(performance, id, eventId, seatCategories, start, venueCode)

struct document
{
    std::vector<performance> performances;
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(document, performances)

std::size_t digest(const document& d)
{
    std::size_t n = 0;
    for (const auto& p : d.performances)
    {
        n += p.seatCategories.size() + p.venueCode.size() + static_cast<std::size_t>(p.start % 1000);
        for (const auto& c : p.seatCategories)
        {
            n += c.areas.size();
        }
    }
    return n;
}
}  // namespace citm

namespace synthetic
{
struct position
{
    double x = 0;
    double y = 0;
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(position, x, y)

struct child
{
    std::int64_t id = 0;
    std::string label;
    bool active = false;
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(child, id, label, active)

struct record
{
    std::int64_t id = 0;
    std::string name;
    std::vector<std::string> tags;
    position pos;
    std::vector<child> children;
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(record, id, name, tags, pos, children)

struct document
{
    std::vector<record> records;
};
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(document, records)

std::string make_text(std::size_t n)
{
    std::string s = "{\"records\":[";
    for (std::size_t i = 0; i < n; ++i)
    {
        const std::string id = std::to_string(i);
        s += (i == 0 ? "" : ",");
        s += "{\"id\":" + id + ",\"name\":\"record number " + id + "\",\"tags\":[\"alpha\",\"beta\",\"gamma\"],";
        s += "\"pos\":{\"x\":" + id + ".25,\"y\":-" + id + ".5},\"children\":[";
        for (std::size_t k = 0; k < 3; ++k)
        {
            s += (k == 0 ? "" : ",");
            s += "{\"id\":" + std::to_string(i * 3 + k) + ",\"label\":\"child " + std::to_string(k) + "\",\"active\":" + (k % 2 == 0 ? "true" : "false") + "}";
        }
        s += "]}";
    }
    s += "]}";
    return s;
}

std::size_t digest(const document& d)
{
    std::size_t n = 0;
    for (const auto& r : d.records)
    {
        n += r.name.size() + r.tags.size() + r.children.size() + static_cast<std::size_t>(r.pos.x);
    }
    return n;
}
}  // namespace synthetic

namespace
{
std::string read_file(const std::string& p)
{
    std::ifstream f(p, std::ios::binary);
    if (!f)
    {
        std::fprintf(stderr, "cannot open %s\n", p.c_str());
        std::exit(1);
    }
    std::stringstream ss;
    ss << f.rdbuf();
    return ss.str();
}

double time_ns(const std::function<void()>& f)
{
    const auto t0 = std::chrono::steady_clock::now();
    f();
    const auto t1 = std::chrono::steady_clock::now();
    return static_cast<double>(std::chrono::duration_cast<std::chrono::nanoseconds>(t1 - t0).count());
}

struct engine
{
    std::string name;
    std::function<std::size_t()> run;
};

template<typename Document>
std::vector<engine> engines(const std::string& text, const json& parsed)
{
    return
    {
        {"view", [&text] { const json_document d = json_document::parse(text); return digest(d.root().get<Document>()); }},
        {"materialize", [&text] { const json_document d = json_document::parse(text); return digest(d.root().materialize().get<Document>()); }},
        {"json::parse", [&text] { return digest(json::parse(text).get<Document>()); }},
        {"json::get", [&parsed] { return digest(parsed.get<Document>()); }},
    };
}
}  // namespace

int main(int argc, char** argv)
{
    if (argc < 2)
    {
        std::fprintf(stderr, "usage: %s <json_test_data directory> [rounds]\n", argv[0]);
        return 1;
    }
    const std::string dir = argv[1];
    const int rounds = argc > 2 ? std::max(1, std::atoi(argv[2])) : 30;

    struct document_case
    {
        std::string name;
        std::string text;
        json parsed;
        std::vector<engine> engines;
    };
    std::vector<document_case> cases;
    cases.push_back({"twitter", read_file(dir + "/nativejson-benchmark/twitter.json"), json(), {}});
    cases.push_back({"citm_catalog", read_file(dir + "/nativejson-benchmark/citm_catalog.json"), json(), {}});
    cases.push_back({"synthetic", synthetic::make_text(20000), json(), {}});
    for (auto& c : cases)
    {
        c.parsed = json::parse(c.text);
    }
    cases[0].engines = engines<twitter::document>(cases[0].text, cases[0].parsed);
    cases[1].engines = engines<citm::document>(cases[1].text, cases[1].parsed);
    cases[2].engines = engines<synthetic::document>(cases[2].text, cases[2].parsed);

    std::FILE* csv = std::fopen("bench_decode.csv", "w");
    if (csv == nullptr)
    {
        std::perror("bench_decode.csv");
        return 1;
    }
    std::fprintf(csv, "doc,bytes,engine,ns\n");
    for (const auto& c : cases)
    {
        // all engines must decode the same values
        const std::size_t expected = c.engines[0].run();
        bool ok = true;
        for (const auto& e : c.engines)
        {
            ok = ok && e.run() == expected;
        }
        std::vector<double> best(c.engines.size(), 1e300);
        for (int r = 0; r < rounds; ++r)
        {
            for (std::size_t k = 0; k < c.engines.size(); ++k)
            {
                g_sink = c.engines[k].run(); // untimed: see bench_view.cpp
                best[k] = std::min(best[k], time_ns([&] { g_sink = c.engines[k].run(); }));
            }
        }
        std::printf("%-13s %-7s %s", c.name.c_str(), "decode", ok ? "" : "[MISMATCH] ");
        for (std::size_t k = 0; k < c.engines.size(); ++k)
        {
            const double us = best[k] / 1000.0;
            std::printf("  %s %.*fus (%.2fx)", c.engines[k].name.c_str(), us < 10 ? 3 : (us < 1000 ? 1 : 0), us, best[k] / best[0]);
            std::fprintf(csv, "%s,%zu,%s,%.1f\n", c.name.c_str(), c.text.size(), c.engines[k].name.c_str(), best[k]);
        }
        std::printf("\n");
    }
    std::fclose(csv);
    return 0;
}