tests/src/unit-user_defined_input.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

// cmake/test.cmake selects the C++ standard versions with which to build a
// unit test based on the presence of JSON_HAS_CPP_<VERSION> macros.
// When using macros that are only defined for particular versions of the standard
// (e.g., JSON_HAS_FILESYSTEM for C++17 and up), please mention the corresponding
// version macro in a comment close by, like this:
// JSON_HAS_CPP_<VERSION> (do not remove; see note at top of file)

#include "doctest_compatibility.h"

#include <nlohmann/json.hpp>
using nlohmann::json;

#include <array> // array
#include <cstddef> // size_t
#include <cstdint> // uint8_t
#include <list>
#include <string> // string
#include <vector> // vector

#if defined(__cpp_lib_concepts) && defined(JSON_HAS_CPP_20)
    #include <iterator>
#endif

namespace
{
TEST_CASE("Use arbitrary stdlib container")
{
    std::string raw_data = "[1,2,3,4]";
    std::list<char> data(raw_data.begin(), raw_data.end());

    json as_json = json::parse(data.begin(), data.end());
    CHECK(as_json.at(0) == 1);
    CHECK(as_json.at(1) == 2);
    CHECK(as_json.at(2) == 3);
    CHECK(as_json.at(3) == 4);
}

struct MyContainer
{
    const char* data;
};

const char* begin(const MyContainer& c)
{
    return c.data;
}

const char* end(const MyContainer& c)
{
    return c.data + strlen(c.data); // NOLINT(cppcoreguidelines-pro-bounds-pointer-arithmetic)
}

TEST_CASE("Custom container non-member begin/end")
{

    const MyContainer data{"[1,2,3,4]"};
    json as_json = json::parse(data);
    CHECK(as_json.at(0) == 1);
    CHECK(as_json.at(1) == 2);
    CHECK(as_json.at(2) == 3);
    CHECK(as_json.at(3) == 4);

}

struct MyContainerNonConstADL
{
    char* data;
    std::size_t size;
};

char* begin(MyContainerNonConstADL& c)
{
    return c.data;
}

char* end(MyContainerNonConstADL& c)
{
    return c.data + c.size; // NOLINT(cppcoreguidelines-pro-bounds-pointer-arithmetic)
}

TEST_CASE("Custom container non-member non-const begin/end")
{
    // Container with lvalue-only non-const ADL begin/end (bug reproduction)
    std::string raw_data = "[1,2,3,4]";
    MyContainerNonConstADL data{&raw_data[0], raw_data.size()}; // NOLINT(readability-container-data-pointer)
    const json as_json = json::parse(data);
    CHECK(as_json.at(0) == 1);
    CHECK(as_json.at(1) == 2);
    CHECK(as_json.at(2) == 3);
    CHECK(as_json.at(3) == 4);

    // Same container with accept()
    CHECK(json::accept(data));
}

TEST_CASE("Custom container non-member begin/end, rvalue")
{
    // Regression check: rvalue container parsing should still work
    const json as_json = json::parse(MyContainer{"[1,2,3,4]"});
    CHECK(as_json.at(0) == 1);
    CHECK(as_json.at(1) == 2);
    CHECK(as_json.at(2) == 3);
    CHECK(as_json.at(3) == 4);
}

TEST_CASE("Custom container member begin/end")
{
    struct MyContainer2
    {
        const char* data;

        const char* begin() const noexcept
        {
            return data;
        }

        const char* end() const noexcept
        {
            return data + strlen(data); // NOLINT(cppcoreguidelines-pro-bounds-pointer-arithmetic)
        }
    };

    const MyContainer2 data{"[1,2,3,4]"};
    json as_json = json::parse(data);
    CHECK(as_json.at(0) == 1);
    CHECK(as_json.at(1) == 2);
    CHECK(as_json.at(2) == 3);
    CHECK(as_json.at(3) == 4);
}

TEST_CASE("Custom iterator")
{
    const char* raw_data = "[1,2,3,4]";

    struct MyIterator
    {
        using difference_type = std::size_t;
        using value_type = char;
        using pointer = const char*;
        using reference = const char&;
        using iterator_category = std::input_iterator_tag;

        MyIterator& operator++()
        {
            ++ptr; // NOLINT(cppcoreguidelines-pro-bounds-pointer-arithmetic)
            return *this;
        }

        reference operator*() const
        {
            return *ptr;
        }

        bool operator!=(const MyIterator& rhs) const
        {
            return ptr != rhs.ptr;
        }

        const char* ptr;
    };

    // avoid -Wunused-local-typedefs
    CHECK(std::is_same<MyIterator::difference_type, std::size_t>::value);
    CHECK(std::is_same<MyIterator::value_type, char>::value);
    CHECK(std::is_same<MyIterator::pointer, const char*>::value);
    CHECK(std::is_same<MyIterator::reference, const char&>::value);
    CHECK(std::is_same<MyIterator::iterator_category, std::input_iterator_tag>::value);

    const MyIterator begin{raw_data};
    const MyIterator end{raw_data + strlen(raw_data)}; // NOLINT(cppcoreguidelines-pro-bounds-pointer-arithmetic)

    json as_json = json::parse(begin, end);
    CHECK(as_json.at(0) == 1);
    CHECK(as_json.at(1) == 2);
    CHECK(as_json.at(2) == 3);
    CHECK(as_json.at(3) == 4);
}

// Custom sentinel type for testing heterogeneous iterator+sentinel support
struct CustomSentinel
{
    const char* end_ptr;

    // only the iterator-first direction (it != sentinel) is ever evaluated by
    // the library's parse loop; a reversed-order overload would go unused and
    // trip -Wunneeded-internal-declaration under -Weverything
    friend bool operator!=(const char* it, const CustomSentinel& sentinel)
    {
        return it != sentinel.end_ptr;
    }
};

TEST_CASE("Parse with heterogeneous iterator and sentinel types")
{
    const std::string json_str = R"({"key":"value"})";
    const char* end_ptr = json_str.data() + json_str.size();

    // Parse using pointer and sentinel (different types)
    json j = json::parse(json_str.data(), CustomSentinel{end_ptr});
    CHECK(j["key"] == "value");

    // Accept using pointer and sentinel
    CHECK(json::accept(json_str.data(), CustomSentinel{end_ptr}));

    // Test that the same-type case still works
    std::string raw_data = R"([1,2,3])";
    std::list<char> data(raw_data.begin(), raw_data.end());
    json j2 = json::parse(data.begin(), data.end());
    CHECK(j2.at(0) == 1);
}

// A type whose data() hands out raw bytes but whose size() counts something
// else - here fixed-size records. Reading [data(), data() + size()) as bytes
// would silently truncate the input, so data() and size() alone must not be
// taken as evidence of contiguous byte storage.
struct record_buffer
{
    using value_type = std::array<char, 4>;

    std::string bytes;

    const char* data() const noexcept
    {
        return bytes.data();
    }
    std::size_t size() const noexcept
    {
        return bytes.size() / sizeof(value_type);
    }
    const char* begin() const noexcept
    {
        return bytes.data();
    }
    const char* end() const noexcept
    {
        return bytes.data() + bytes.size();
    }
};

TEST_CASE("Contiguous byte containers take the pointer adapter")
{
    // Containers with contiguous single-byte storage are routed through the
    // pointer-based adapter so the bulk fast paths apply in every standard, not
    // only in C++20 where the library iterators model std::contiguous_iterator.
    CHECK(nlohmann::detail::is_contiguous_byte_container<std::string>::value);
    CHECK(nlohmann::detail::is_contiguous_byte_container<std::vector<char>>::value);
    CHECK(nlohmann::detail::is_contiguous_byte_container<std::vector<std::uint8_t>>::value);
    CHECK(nlohmann::detail::is_contiguous_byte_container<std::array<char, 4>>::value);

    // input_adapter() takes its container by forwarding reference, so the trait
    // is also asked about reference types
    CHECK(nlohmann::detail::is_contiguous_byte_container<std::string&>::value);
    CHECK(nlohmann::detail::is_contiguous_byte_container<const std::string&>::value);

    // everything else keeps the iterator-based adapter
    CHECK_FALSE(nlohmann::detail::is_contiguous_byte_container<std::list<char>>::value);
    CHECK_FALSE(nlohmann::detail::is_contiguous_byte_container<std::vector<int>>::value);
    CHECK_FALSE(nlohmann::detail::is_contiguous_byte_container<const char*>::value);

    // including a type that has data() and size() but whose size() does not
    // count the units data() points at: its value_type says so
    CHECK_FALSE(nlohmann::detail::is_contiguous_byte_container<record_buffer>::value);

    // and such a container still parses through its iterators, in full - taking
    // it for a byte container would stop after data() + size() bytes
    const record_buffer buffer{"[1,2,3,4,5]"};
    CHECK(buffer.data() == buffer.bytes.data());
    CHECK(buffer.size() * sizeof(record_buffer::value_type) < buffer.bytes.size());
    CHECK(json::parse(buffer) == json({1, 2, 3, 4, 5}));
}

#if defined(__cpp_lib_concepts) && defined(JSON_HAS_CPP_20)
// JSON_HAS_CPP_20 (do not remove; see note at top of file)
TEST_CASE("Parse with std::counted_iterator and std::default_sentinel_t")
{
    using iterator_type = std::string::const_iterator;
    const std::string json_str = R"({"key":"value","array":[1,2,3]})";
    const auto len = static_cast<std::iter_difference_t<iterator_type>>(json_str.size());

    const std::counted_iterator<iterator_type> first(json_str.begin(), len);
    const json j = json::parse(first, std::default_sentinel);
    CHECK(j["key"] == "value");
    CHECK(j["array"].size() == 3);

    const std::counted_iterator<iterator_type> first2(json_str.begin(), len);
    CHECK(json::accept(first2, std::default_sentinel));
}

TEST_CASE("std::counted_iterator reaches the contiguous fast paths")
{
    // A sized sentinel makes the remaining element count computable in O(1), so
    // std::counted_iterator over a contiguous iterator must reach the same bulk
    // string/number scanners as a plain pointer - not just the byte-at-a-time
    // fallback (see #5268 for the equivalent memcpy fast path).
#if JSON_HAS_RANGES
    // JSON_HAS_RANGES is 0 on standard libraries with an incomplete <ranges>
    // (libstdc++ < 11, libc++ < 16), where the adapter deliberately falls back
    // to the byte-at-a-time scanner; everything below still has to work there.
    using adapter_type = nlohmann::detail::iterator_input_adapter<std::counted_iterator<const char*>, std::default_sentinel_t>;
    CHECK(adapter_type::supports_bulk_scan);
    CHECK(adapter_type::supports_seek);
#endif

    // exercise every fast path: long ASCII run, multibyte UTF-8, escapes, and
    // integer/floating-point numbers
    const std::string json_str =
        R"({"ascii":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",)"
        "\"utf8\":\"\xe4\xb8\xad\xe6\x96\x87\xf0\x9f\x98\x80\xc3\xa9\","
        R"("escaped":"aéb\n\\","ints":[0,-1,18446744073709551615,-9223372036854775808],)"
        R"("floats":[1.5,-2.25e3,0.30000000000000004]})";
    const auto len = static_cast<std::iter_difference_t<const char*>>(json_str.size());

    const std::counted_iterator<const char*> first(json_str.data(), len);
    const json j = json::parse(first, std::default_sentinel);

    // parsing through the pointer adapter must give exactly the same result
    CHECK(j == json::parse(json_str));

#if !defined(JSON_NOEXCEPTION)
    // Diagnostics that quote the offending token are reconstructed from the
    // already-consumed input (supports_seek), a path a sized sentinel only
    // reaches now; check a few that include the "last read" text. Parsing
    // invalid input aborts when exceptions are off, hence the guard.
    // Raw strings and explicit bytes: an escaped literal and two literals
    // written next to each other both read as mistakes to static analysis.
    const auto byte = [](int value)
    {
        return std::string(1, static_cast<char>(value));
    };
    const std::vector<std::string> diagnostic_docs =
    {
        "1\nx",
        "truX",
        "[tru]",
        R"("abc)",
        R"(["\ud834"])",
        R"(["a)" + byte(0x01) + R"(b"])",
        R"([")" + byte(0xC3) + byte(0x28) + R"("])",
        "[1e]",
        R"(["aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaX)"
    };

    for (const auto& text : diagnostic_docs)
    {
        CAPTURE(text)
        const std::counted_iterator<const char*> it(text.data(), static_cast<std::iter_difference_t<const char*>>(text.size()));
        std::string counted_message;
        std::string string_message;
        try
        {
            const json counted_result = json::parse(it, std::default_sentinel);
            static_cast<void>(counted_result);
        }
        catch (const json::parse_error& e)
        {
            counted_message = e.what();
        }
        try
        {
            const json string_result = json::parse(text);
            static_cast<void>(string_result);
        }
        catch (const json::parse_error& e)
        {
            string_message = e.what();
        }
        CHECK_FALSE(counted_message.empty());
        CHECK(counted_message == string_message);
    }

    // and errors must still be reported identically
    const std::string bad = "[01\n]";
    const std::counted_iterator<const char*> bad_first(bad.data(), static_cast<std::iter_difference_t<const char*>>(bad.size()));
    std::string counted_what;
    std::string string_what;
    try
    {
        const json counted_result = json::parse(bad_first, std::default_sentinel);
        static_cast<void>(counted_result);
    }
    catch (const json::parse_error& e)
    {
        counted_what = e.what();
    }
    try
    {
        const json string_result = json::parse(bad);
        static_cast<void>(string_result);
    }
    catch (const json::parse_error& e)
    {
        string_what = e.what();
    }
    CHECK_FALSE(counted_what.empty());
    CHECK(counted_what == string_what);
#endif
}

#if !defined(JSON_NOEXCEPTION)
// several cases below are truncated on purpose, and parsing invalid input
// aborts when exceptions are off
TEST_CASE("std::counted_iterator bulk scanning stops at the counted end")
{
    // The count, not the size of the underlying buffer, is the end of the
    // input: the bulk scanners must never look at the bytes behind it, even
    // though they are readable. Each case is compared against parsing the
    // equivalent prefix as a std::string.
    const auto via_counted = [](const std::string & buf, std::size_t n) -> std::string
    {
        const std::counted_iterator<const char*> first(buf.data(), static_cast<std::iter_difference_t<const char*>>(n));
        try
        {
            const json j = json::parse(first, std::default_sentinel);
            return "OK|" + j.dump();
        }
        catch (const json::parse_error& e)
        {
            return {e.what()};
        }
    };
    const auto via_prefix = [](const std::string & buf, std::size_t n) -> std::string
    {
        try
        {
            const json j = json::parse(buf.substr(0, n));
            return "OK|" + j.dump();
        }
        catch (const json::parse_error& e)
        {
            return {e.what()};
        }
    };

    struct testcase // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init)
    {
        const char* buffer;
        std::size_t count;
    };
    const std::vector<testcase> cases =
    {
        {"[\"abc\"]____TRAILING____", 7},                    // exact fit, tail hidden
        {"[\"abcdefghijklmnop\"]____", 8},                   // cut inside a string
        {"[\"abc\"]____", 6},                                // cut just before the closing quote
        {"[12345]xxxxx", 4},                                 // cut inside a number
        {"[123]999999", 5},                                  // number ends exactly at the count
        {"[\"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\"]", 12},        // closing quote only behind the count
        {"[\"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\"]", 19},      // cut inside an 8-byte SWAR stride
        {"[\"\xe4\xb8\xad\xe6\x96\x87\"]", 5},               // cut inside a UTF-8 sequence
        {"[\"\xe4\xb8\xad\xe6\x96\x87\"]____", 10},          // complete UTF-8, tail hidden
        {"[1.25e3]TRAILINGDIGITS999", 7},                    // number token reaches the count
    };

    for (const auto& tc : cases)
    {
        CAPTURE(tc.buffer)
        CAPTURE(tc.count)
        const std::string buffer = tc.buffer;
        CHECK(via_counted(buffer, tc.count) == via_prefix(buffer, tc.count));
    }
}
#endif
#endif

} // namespace