Throw instead of writing MessagePack lengths beyond UINT32_MAX

MessagePack stores the length of a string, binary value, array, or
object in at most 32 bits. For a larger value, to_msgpack wrote no length
at all, so the output could not be read back. It now throws
out_of_range.412, which BSON already uses for its 32-bit length fields.

The check lives in one function, so each length is written by an
if/else chain that ends in a plain else, without a condition that can
never be false. It is tested with string and binary types that report a
size beyond UINT32_MAX without allocating it, like the BSON tests do.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/docs/api/basic_json/to_msgpack.md

@@ -30,6 +30,15 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 1. MessagePack serialization as a byte vector
 2. (none)
 
+## Exceptions
+
+- Throws [`out_of_range.412`](../../home/exceptions.md#jsonexceptionout_of_range412) if the length of a string, binary
+  value, array, or object exceeds 4294967295, the maximum MessagePack can store; example:
+  `"MessagePack length 4294967296 exceeds maximum of 4294967295"`
+- Throws [`out_of_range.415`](../../home/exceptions.md#jsonexceptionout_of_range415) if the subtype of a binary value
+  exceeds 255, the maximum of the MessagePack ext type; example:
+  `"subtype 70000 is too large for the MessagePack ext type (max 255)"`
+
 ## Exception safety
 
 Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
@@ -65,3 +74,4 @@ Linear in the size of the JSON value `j`.
 ## Version history
 
 - Added in version 2.0.9.
+- Throws `out_of_range.412` and `out_of_range.415` since version 3.13.0.

docs/mkdocs/docs/features/binary_formats/messagepack.md

@@ -65,6 +65,8 @@ specification:
       - arrays with more than 4294967295 elements
       - objects with more than 4294967295 elements
 
+    Serializing such a value throws [`out_of_range.412`](../../home/exceptions.md#jsonexceptionout_of_range412).
+
 !!! info "NaN/infinity handling"
 
     `NaN`, `Infinity`, and `-Infinity` are serialized as a MessagePack float 32 (type 0xCA, 5 bytes total),

docs/mkdocs/docs/home/exceptions.md

@@ -932,19 +932,25 @@ A JSON Patch `add` operation cannot be applied because the target location's par
 
 ### json.exception.out_of_range.412
 
-BSON stores the length of documents, arrays, strings, and binary values in a signed 32-bit integer. This exception is thrown when a value is too large to be described by such a length field.
+BSON stores the length of documents, arrays, strings, and binary values in a signed 32-bit integer, and MessagePack
+stores the length of strings, binary values, arrays, and objects in at most an unsigned 32-bit integer. This exception
+is thrown when a value is too large to be described by such a length field.
 
-!!! failure "Example message"
+!!! failure "Example messages"
 
     ```
     BSON length 2147483661 exceeds maximum of 2147483647
     ```
+    ```
+    MessagePack length 4294967296 exceeds maximum of 4294967295
+    ```
 
 !!! note
 
-    This exception was added in version 3.13.0. Before that, the length was silently truncated, and
+    This exception was added in version 3.13.0. Before that, the BSON length was silently truncated, and
     [`to_bson`](../api/basic_json/to_bson.md) produced documents with negative length prefixes that
-    [`from_bson`](../api/basic_json/from_bson.md) rejected.
+    [`from_bson`](../api/basic_json/from_bson.md) rejected; [`to_msgpack`](../api/basic_json/to_msgpack.md) wrote such
+    a value without any length, producing output that could not be read back.
 
 ### json.exception.out_of_range.413
 

include/nlohmann/detail/output/binary_writer.hpp

@@ -466,6 +466,22 @@ class binary_writer
         }
     }
 
+    /*!
+    @brief check that @a length fits into the 32 bits that MessagePack stores
+           the length of a string, binary value, array, or object in
+    @return the length as an unsigned 32-bit integer
+    @throw out_of_range.412 if @a length exceeds the range of std::uint32_t
+    */
+    static std::uint32_t to_msgpack_length(const std::size_t length, const BasicJsonType& j)
+    {
+        if (JSON_HEDLEY_UNLIKELY(!value_in_range_of<std::uint32_t>(length)))
+        {
+            JSON_THROW(out_of_range::create(412, concat("MessagePack length ", std::to_string(length), " exceeds maximum of ", std::to_string((std::numeric_limits<std::uint32_t>::max)())), &j));
+        }
+
+        return static_cast<std::uint32_t>(length);
+    }
+
     /*!
     @param[in] j  JSON value to serialize
     */
@@ -606,7 +622,7 @@ class binary_writer
             case value_t::string:
             {
                 // step 1: write control byte and the string length
-                const auto N = j.m_data.m_value.string->size();
+                const auto N = to_msgpack_length(j.m_data.m_value.string->size(), j);
                 if (N <= 31)
                 {
                     // fixstr
@@ -624,7 +640,7 @@ class binary_writer
                     oa.write_character(to_char_type(0xDA));
                     write_number(static_cast<std::uint16_t>(N));
                 }
-                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
+                else
                 {
                     // str 32
                     oa.write_character(to_char_type(0xDB));
@@ -641,7 +657,7 @@ class binary_writer
             case value_t::array:
             {
                 // step 1: write control byte and the array size
-                const auto N = j.m_data.m_value.array->size();
+                const auto N = to_msgpack_length(j.m_data.m_value.array->size(), j);
                 if (N <= 15)
                 {
                     // fixarray
@@ -653,7 +669,7 @@ class binary_writer
                     oa.write_character(to_char_type(0xDC));
                     write_number(static_cast<std::uint16_t>(N));
                 }
-                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
+                else
                 {
                     // array 32
                     oa.write_character(to_char_type(0xDD));
@@ -675,7 +691,7 @@ class binary_writer
                 const bool use_ext = j.m_data.m_value.binary->has_subtype();
 
                 // step 1: write control byte and the byte string length
-                const auto N = j.m_data.m_value.binary->size();
+                const auto N = to_msgpack_length(j.m_data.m_value.binary->size(), j);
                 if (N <= (std::numeric_limits<std::uint8_t>::max)())
                 {
                     std::uint8_t output_type{};
@@ -727,7 +743,7 @@ class binary_writer
                     oa.write_character(to_char_type(output_type));
                     write_number(static_cast<std::uint16_t>(N));
                 }
-                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
+                else
                 {
                     const std::uint8_t output_type = use_ext
                                                      ? 0xC9 // ext 32
@@ -759,7 +775,7 @@ class binary_writer
             case value_t::object:
             {
                 // step 1: write control byte and the object size
-                const auto N = j.m_data.m_value.object->size();
+                const auto N = to_msgpack_length(j.m_data.m_value.object->size(), j);
                 if (N <= 15)
                 {
                     // fixmap
@@ -771,7 +787,7 @@ class binary_writer
                     oa.write_character(to_char_type(0xDE));
                     write_number(static_cast<std::uint16_t>(N));
                 }
-                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
+                else
                 {
                     // map 32
                     oa.write_character(to_char_type(0xDF));

include/nlohmann/json.hpp

@@ -5993,56 +5993,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json diff(const basic_json& source, const basic_json& target,
                            const string_t& path = "")
-    {
-        return diff_recursively(source, target, path, 0);
-    }
-
-  private:
-    /// @brief two arrays or two objects @ref diff_iteratively is diffing
-    struct diff_frame
-    {
-        diff_frame(const basic_json* source_, const basic_json* target_, const std::size_t path_length_) noexcept
-            : source(source_), target(target_), path_length(path_length_)
-        {}
-
-        // declared for GCC's -Weffc++, which asks for them in a class with
-        // pointer members and a non-trivial destructor; the exception
-        // specifications are left implicit, as GCC 4.8 rejects explicit ones
-        // that differ from them
-        diff_frame(const diff_frame&) = default;
-        diff_frame(diff_frame&&) = default;
-        diff_frame& operator=(const diff_frame&) = default;
-        diff_frame& operator=(diff_frame&&) = default;
-        ~diff_frame() = default;
-
-        /// the values being diffed, both arrays or both objects
-        const basic_json* source;
-        const basic_json* target;
-        /// the length of their path in `current_path`
-        std::size_t path_length;
-        /// arrays: the next index to diff
-        std::size_t index = 0;
-        /// objects: the next member of source to look at
-        const_iterator member{}; // NOLINT(readability-redundant-member-init)
-        /// objects: the keys common to both, in source's order
-        std::vector<typename object_t::key_type> common_keys{}; // NOLINT(readability-redundant-member-init)
-        /// objects: the next entry of common_keys
-        std::size_t next_common = 0;
-        /// objects: the "add" operations for keys only target has
-        basic_json added_ops{}; // NOLINT(readability-redundant-member-init)
-    };
-
-    /*!
-    @brief @ref diff, for values at nesting level @a depth
-
-    Diffing two arrays or objects calls this function again, once per nesting
-    level, so values nested deeply enough used to exhaust the call stack and
-    terminate the process. The descent is bounded here: once @ref
-    detail::recursion_depth_limit levels have been entered, @ref
-    diff_iteratively diffs what is left without the call stack.
-    */
-    static basic_json diff_recursively(const basic_json& source, const basic_json& target,
-                                       const string_t& path, const std::size_t depth)
     {
         // the patch
         basic_json result(value_t::array);
@@ -6053,11 +6003,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             return result;
         }
 
-        if (JSON_HEDLEY_UNLIKELY(depth >= detail::recursion_depth_limit()))
-        {
-            return diff_iteratively(source, target, path);
-        }
-
         if (source.type() != target.type())
         {
             // different types: replace value
@@ -6077,7 +6022,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                 while (i < source.size() && i < target.size())
                 {
                     // recursive call to compare array values at index i
-                    auto temp_diff = diff_recursively(source[i], target[i], detail::concat<string_t>(path, '/', detail::to_string<string_t>(i)), depth + 1);
+                    auto temp_diff = diff(source[i], target[i], detail::concat<string_t>(path, '/', detail::to_string<string_t>(i)));
                     result.insert(result.end(), temp_diff.begin(), temp_diff.end());
                     ++i;
                 }
@@ -6196,7 +6141,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                         if (common_it != common_keys_source_order.cend() && it.key() == *common_it)
                         {
                             const auto path_key = detail::concat<string_t>(path, '/', detail::escape(it.key()));
-                            auto temp_diff = diff_recursively(it.value(), target[it.key()], path_key, depth + 1);
+                            auto temp_diff = diff(it.value(), target[it.key()], path_key);
                             result.insert(result.end(), temp_diff.begin(), temp_diff.end());
                             ++common_it;
                         }
@@ -6280,301 +6225,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
         return result;
     }
-
-    /*!
-    @brief @ref diff without the call stack
-
-    Produces the same patch as @ref diff_recursively. Only reached for values
-    nested more deeply than @ref detail::recursion_depth_limit.
-    */
-    static basic_json diff_iteratively(const basic_json& source, const basic_json& target,
-                                       const string_t& path)
-    {
-        // the patch
-        basic_json result(value_t::array);
-
-        // The arrays and objects being diffed are kept on an explicit stack,
-        // and every pair of elements is still diffed completely before the
-        // next one, so the operations come out in the same order as in
-        // diff_recursively. The path of the values being diffed is kept in
-        // one buffer that grows and shrinks with the stack, rather than in a
-        // new string per level.
-        std::vector<diff_frame> stack;
-        string_t current_path = path;
-
-        // diff `s` against `t`, whose path is current_path: primitives,
-        // values of different types, and objects whose members were reordered
-        // are handled right away; arrays and other objects get a frame
-        const auto enter = [&result, &stack, &current_path](const basic_json & s, const basic_json & t)
-        {
-            // if the values are the same, there is nothing to do. Arrays and
-            // objects are not compared up front: comparing them visits
-            // everything below them, so doing that at every level would take
-            // quadratic time in the nesting depth - equal ones yield no
-            // operations anyway.
-            if ((!s.is_structured() || !t.is_structured()) && s == t)
-            {
-                return;
-            }
-
-            if (s.type() != t.type())
-            {
-                // different types: replace value
-                result.push_back(
-                {
-                    {"op", "replace"}, {"path", current_path}, {"value", t}
-                });
-                return;
-            }
-
-            switch (s.type())
-            {
-                case value_t::array:
-                {
-                    stack.emplace_back(&s, &t, current_path.size());
-                    return;
-                }
-
-                case value_t::object:
-                {
-                    // first pass: record, for every source key, whether it is
-                    // common to both objects (in source's iteration order) or
-                    // was deleted (i.e., in source but not in target) -- this is
-                    // a by-product of the t.find() call already needed to
-                    // tell the two cases apart, so it adds no extra lookups. The
-                    // "remove" ops themselves are emitted later, interleaved
-                    // with the per-key diffs in the fast path below, to match
-                    // source's original iteration order (as the original,
-                    // pre-reordering-aware implementation did) instead of
-                    // grouping all removes before all per-key diffs.
-                    std::vector<typename object_t::key_type> common_keys_source_order;
-                    for (auto it = s.cbegin(); it != s.cend(); ++it)
-                    {
-                        if (t.find(it.key()) != t.end())
-                        {
-                            common_keys_source_order.push_back(it.key());
-                        }
-                    }
-
-                    // second pass: find keys that were added (i.e., in target but
-                    // not in source), and record the keys common to both, in
-                    // target's iteration order -- again a by-product of the
-                    // s.find() call already needed to detect added keys. At
-                    // the same time, determine whether every added key comes
-                    // after every common key in target's order (a precondition
-                    // for the fast path below, which only ever appends new keys
-                    // at the very end): for an object_t whose iteration order is
-                    // a pure function of the key set (e.g. the default std::map,
-                    // which always iterates in sorted key order), the order
-                    // check further below is always true and this whole
-                    // mechanism is effectively a no-op; it only matters for a
-                    // reorderable object_t such as the one backing `ordered_json`.
-                    // patch ops for keys that were added (i.e., in target but not
-                    // in source); built here so the fast path below can reuse
-                    // them without a second s.find() per target key. Only
-                    // used by the fast path -- the slow (reordering) path
-                    // rebuilds "add" ops for every key itself.
-                    std::vector<typename object_t::key_type> common_keys_target_order;
-                    basic_json added_ops(value_t::array);
-                    bool new_keys_form_suffix = true;
-                    bool seen_new_key = false;
-                    for (auto it = t.cbegin(); it != t.cend(); ++it)
-                    {
-                        if (s.find(it.key()) == s.end())
-                        {
-                            seen_new_key = true;
-                            const auto path_key = detail::concat<string_t>(current_path, '/', detail::escape(it.key()));
-                            added_ops.push_back(
-                            {
-                                {"op", "add"}, {"path", path_key},
-                                {"value", it.value()}
-                            });
-                        }
-                        else
-                        {
-                            common_keys_target_order.push_back(it.key());
-                            if (seen_new_key)
-                            {
-                                new_keys_form_suffix = false;
-                            }
-                        }
-                    }
-
-                    if (common_keys_source_order == common_keys_target_order && new_keys_form_suffix)
-                    {
-                        // fast path: order of common keys already matches (or the
-                        // object_t's iteration order does not depend on
-                        // insertion history), so a plain per-key diff is correct
-                        // and minimal, as before. The frame walks source in
-                        // lockstep with common_keys_source_order, which is, by
-                        // construction, the subsequence of source's keys that
-                        // are common to both objects, in source's iteration
-                        // order -- so a cheap key comparison replaces another
-                        // lookup. Deleted keys are interleaved there too, in
-                        // source's original order, and the "add" ops collected
-                        // above are appended once all members are done.
-                        stack.emplace_back(&s, &t, current_path.size());
-                        stack.back().member = s.cbegin();
-                        stack.back().common_keys = std::move(common_keys_source_order);
-                        stack.back().added_ops = std::move(added_ops);
-                        return;
-                    }
-
-                    // slow path: the common keys are in a different relative
-                    // order in source and target (only possible for a
-                    // reorderable object_t like ordered_map). Building a
-                    // minimal reordering patch is a nontrivial (LCS-like)
-                    // problem; instead, remove every source key -- both
-                    // deleted keys (which must be removed regardless) and
-                    // common keys (removed so they can be re-added in
-                    // target's order) -- and re-add every key that should
-                    // remain, with its final target value, in target's
-                    // order. basic_json::patch()'s "add" operation on an
-                    // object uses operator[], which appends at the end for a
-                    // vector-backed insertion-ordered map when the key does
-                    // not already exist -- so removing a key and then adding
-                    // it moves it to the end, fixing its position.
-                    for (auto it = s.cbegin(); it != s.cend(); ++it)
-                    {
-                        const auto path_key = detail::concat<string_t>(current_path, '/', detail::escape(it.key()));
-                        result.push_back(object(
-                        {
-                            {"op", "remove"}, {"path", path_key}
-                        }));
-                    }
-
-                    // add every key that is either common (just removed
-                    // above) or brand new, in target's iteration order, so
-                    // that the final order after applying the patch matches
-                    // target exactly
-                    for (auto it = t.cbegin(); it != t.cend(); ++it)
-                    {
-                        const auto path_key = detail::concat<string_t>(current_path, '/', detail::escape(it.key()));
-                        result.push_back(
-                        {
-                            {"op", "add"}, {"path", path_key},
-                            {"value", it.value()}
-                        });
-                    }
-                    return;
-                }
-
-                case value_t::null:
-                case value_t::string:
-                case value_t::boolean:
-                case value_t::number_integer:
-                case value_t::number_unsigned:
-                case value_t::number_float:
-                case value_t::binary:
-                case value_t::discarded:
-                default:
-                {
-                    // both primitive types: replace value
-                    result.push_back(
-                    {
-                        {"op", "replace"}, {"path", current_path}, {"value", t}
-                    });
-                    return;
-                }
-            }
-        };
-
-        enter(source, target);
-        while (!stack.empty())
-        {
-            diff_frame& frame = stack.back();
-            const std::size_t path_length = frame.path_length;
-            const std::size_t depth = stack.size();
-
-            if (frame.source->is_array())
-            {
-                const auto& source_array = *frame.source->m_data.m_value.array;
-                const auto& target_array = *frame.target->m_data.m_value.array;
-
-                // first pass: traverse common elements
-                if (frame.index < source_array.size() && frame.index < target_array.size())
-                {
-                    const std::size_t i = frame.index++;
-                    detail::concat_into(current_path, '/', detail::to_string<string_t>(i));
-                    enter(source_array[i], target_array[i]); // may push, which invalidates `frame`
-                    if (stack.size() == depth)
-                    {
-                        current_path.resize(path_length);
-                    }
-                    continue;
-                }
-
-                // We now reached the end of at least one array
-                // in a second pass, traverse the remaining elements
-
-                // remove my remaining elements, highest index first; appending
-                // in that order avoids the quadratic reinsertion done before
-                for (std::size_t j = source_array.size(); j > frame.index; --j)
-                {
-                    result.push_back(object(
-                    {
-                        {"op", "remove"},
-                        {"path", detail::concat<string_t>(current_path, '/', detail::to_string<string_t>(j - 1))}
-                    }));
-                }
-
-                // add other remaining elements
-                for (std::size_t i = source_array.size(); i < target_array.size(); ++i)
-                {
-                    result.push_back(
-                    {
-                        {"op", "add"},
-                        {"path", detail::concat<string_t>(current_path, "/-")},
-                        {"value", target_array[i]}
-                    });
-                }
-            }
-            else
-            {
-                if (frame.member != frame.source->cend())
-                {
-                    const const_iterator it = frame.member;
-                    ++frame.member;
-                    if (frame.next_common < frame.common_keys.size() && it.key() == frame.common_keys[frame.next_common])
-                    {
-                        ++frame.next_common;
-                        const basic_json& target_value = (*frame.target)[it.key()];
-                        detail::concat_into(current_path, '/', detail::escape(it.key()));
-                        enter(it.value(), target_value); // may push, which invalidates `frame`
-                        if (stack.size() == depth)
-                        {
-                            current_path.resize(path_length);
-                        }
-                    }
-                    else
-                    {
-                        // found a key that is not in target -> remove it
-                        const auto path_key = detail::concat<string_t>(current_path, '/', detail::escape(it.key()));
-                        result.push_back(object(
-                        {
-                            {"op", "remove"}, {"path", path_key}
-                        }));
-                    }
-                    continue;
-                }
-
-                // append the "add" ops for brand-new keys collected when the
-                // object was entered
-                result.insert(result.end(), frame.added_ops.begin(), frame.added_ops.end());
-            }
-
-            // this array or object is done: continue with the one it is in
-            stack.pop_back();
-            if (!stack.empty())
-            {
-                current_path.resize(stack.back().path_length);
-            }
-        }
-
-        return result;
-    }
-
-  public:
     /// @}
 
     ////////////////////////////////

single_include/nlohmann/json.hpp

@@ -19931,6 +19931,22 @@ class binary_writer
         }
     }
 
+    /*!
+    @brief check that @a length fits into the 32 bits that MessagePack stores
+           the length of a string, binary value, array, or object in
+    @return the length as an unsigned 32-bit integer
+    @throw out_of_range.412 if @a length exceeds the range of std::uint32_t
+    */
+    static std::uint32_t to_msgpack_length(const std::size_t length, const BasicJsonType& j)
+    {
+        if (JSON_HEDLEY_UNLIKELY(!value_in_range_of<std::uint32_t>(length)))
+        {
+            JSON_THROW(out_of_range::create(412, concat("MessagePack length ", std::to_string(length), " exceeds maximum of ", std::to_string((std::numeric_limits<std::uint32_t>::max)())), &j));
+        }
+
+        return static_cast<std::uint32_t>(length);
+    }
+
     /*!
     @param[in] j  JSON value to serialize
     */
@@ -20071,7 +20087,7 @@ class binary_writer
             case value_t::string:
             {
                 // step 1: write control byte and the string length
-                const auto N = j.m_data.m_value.string->size();
+                const auto N = to_msgpack_length(j.m_data.m_value.string->size(), j);
                 if (N <= 31)
                 {
                     // fixstr
@@ -20089,7 +20105,7 @@ class binary_writer
                     oa.write_character(to_char_type(0xDA));
                     write_number(static_cast<std::uint16_t>(N));
                 }
-                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
+                else
                 {
                     // str 32
                     oa.write_character(to_char_type(0xDB));
@@ -20106,7 +20122,7 @@ class binary_writer
             case value_t::array:
             {
                 // step 1: write control byte and the array size
-                const auto N = j.m_data.m_value.array->size();
+                const auto N = to_msgpack_length(j.m_data.m_value.array->size(), j);
                 if (N <= 15)
                 {
                     // fixarray
@@ -20118,7 +20134,7 @@ class binary_writer
                     oa.write_character(to_char_type(0xDC));
                     write_number(static_cast<std::uint16_t>(N));
                 }
-                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
+                else
                 {
                     // array 32
                     oa.write_character(to_char_type(0xDD));
@@ -20140,7 +20156,7 @@ class binary_writer
                 const bool use_ext = j.m_data.m_value.binary->has_subtype();
 
                 // step 1: write control byte and the byte string length
-                const auto N = j.m_data.m_value.binary->size();
+                const auto N = to_msgpack_length(j.m_data.m_value.binary->size(), j);
                 if (N <= (std::numeric_limits<std::uint8_t>::max)())
                 {
                     std::uint8_t output_type{};
@@ -20192,7 +20208,7 @@ class binary_writer
                     oa.write_character(to_char_type(output_type));
                     write_number(static_cast<std::uint16_t>(N));
                 }
-                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
+                else
                 {
                     const std::uint8_t output_type = use_ext
                                                      ? 0xC9 // ext 32
@@ -20224,7 +20240,7 @@ class binary_writer
             case value_t::object:
             {
                 // step 1: write control byte and the object size
-                const auto N = j.m_data.m_value.object->size();
+                const auto N = to_msgpack_length(j.m_data.m_value.object->size(), j);
                 if (N <= 15)
                 {
                     // fixmap
@@ -20236,7 +20252,7 @@ class binary_writer
                     oa.write_character(to_char_type(0xDE));
                     write_number(static_cast<std::uint16_t>(N));
                 }
-                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
+                else
                 {
                     // map 32
                     oa.write_character(to_char_type(0xDF));
@@ -30951,56 +30967,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json diff(const basic_json& source, const basic_json& target,
                            const string_t& path = "")
-    {
-        return diff_recursively(source, target, path, 0);
-    }
-
-  private:
-    /// @brief two arrays or two objects @ref diff_iteratively is diffing
-    struct diff_frame
-    {
-        diff_frame(const basic_json* source_, const basic_json* target_, const std::size_t path_length_) noexcept
-            : source(source_), target(target_), path_length(path_length_)
-        {}
-
-        // declared for GCC's -Weffc++, which asks for them in a class with
-        // pointer members and a non-trivial destructor; the exception
-        // specifications are left implicit, as GCC 4.8 rejects explicit ones
-        // that differ from them
-        diff_frame(const diff_frame&) = default;
-        diff_frame(diff_frame&&) = default;
-        diff_frame& operator=(const diff_frame&) = default;
-        diff_frame& operator=(diff_frame&&) = default;
-        ~diff_frame() = default;
-
-        /// the values being diffed, both arrays or both objects
-        const basic_json* source;
-        const basic_json* target;
-        /// the length of their path in `current_path`
-        std::size_t path_length;
-        /// arrays: the next index to diff
-        std::size_t index = 0;
-        /// objects: the next member of source to look at
-        const_iterator member{}; // NOLINT(readability-redundant-member-init)
-        /// objects: the keys common to both, in source's order
-        std::vector<typename object_t::key_type> common_keys{}; // NOLINT(readability-redundant-member-init)
-        /// objects: the next entry of common_keys
-        std::size_t next_common = 0;
-        /// objects: the "add" operations for keys only target has
-        basic_json added_ops{}; // NOLINT(readability-redundant-member-init)
-    };
-
-    /*!
-    @brief @ref diff, for values at nesting level @a depth
-
-    Diffing two arrays or objects calls this function again, once per nesting
-    level, so values nested deeply enough used to exhaust the call stack and
-    terminate the process. The descent is bounded here: once @ref
-    detail::recursion_depth_limit levels have been entered, @ref
-    diff_iteratively diffs what is left without the call stack.
-    */
-    static basic_json diff_recursively(const basic_json& source, const basic_json& target,
-                                       const string_t& path, const std::size_t depth)
     {
         // the patch
         basic_json result(value_t::array);
@@ -31011,11 +30977,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             return result;
         }
 
-        if (JSON_HEDLEY_UNLIKELY(depth >= detail::recursion_depth_limit()))
-        {
-            return diff_iteratively(source, target, path);
-        }
-
         if (source.type() != target.type())
         {
             // different types: replace value
@@ -31035,7 +30996,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                 while (i < source.size() && i < target.size())
                 {
                     // recursive call to compare array values at index i
-                    auto temp_diff = diff_recursively(source[i], target[i], detail::concat<string_t>(path, '/', detail::to_string<string_t>(i)), depth + 1);
+                    auto temp_diff = diff(source[i], target[i], detail::concat<string_t>(path, '/', detail::to_string<string_t>(i)));
                     result.insert(result.end(), temp_diff.begin(), temp_diff.end());
                     ++i;
                 }
@@ -31154,7 +31115,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                         if (common_it != common_keys_source_order.cend() && it.key() == *common_it)
                         {
                             const auto path_key = detail::concat<string_t>(path, '/', detail::escape(it.key()));
-                            auto temp_diff = diff_recursively(it.value(), target[it.key()], path_key, depth + 1);
+                            auto temp_diff = diff(it.value(), target[it.key()], path_key);
                             result.insert(result.end(), temp_diff.begin(), temp_diff.end());
                             ++common_it;
                         }
@@ -31238,301 +31199,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
         return result;
     }
-
-    /*!
-    @brief @ref diff without the call stack
-
-    Produces the same patch as @ref diff_recursively. Only reached for values
-    nested more deeply than @ref detail::recursion_depth_limit.
-    */
-    static basic_json diff_iteratively(const basic_json& source, const basic_json& target,
-                                       const string_t& path)
-    {
-        // the patch
-        basic_json result(value_t::array);
-
-        // The arrays and objects being diffed are kept on an explicit stack,
-        // and every pair of elements is still diffed completely before the
-        // next one, so the operations come out in the same order as in
-        // diff_recursively. The path of the values being diffed is kept in
-        // one buffer that grows and shrinks with the stack, rather than in a
-        // new string per level.
-        std::vector<diff_frame> stack;
-        string_t current_path = path;
-
-        // diff `s` against `t`, whose path is current_path: primitives,
-        // values of different types, and objects whose members were reordered
-        // are handled right away; arrays and other objects get a frame
-        const auto enter = [&result, &stack, &current_path](const basic_json & s, const basic_json & t)
-        {
-            // if the values are the same, there is nothing to do. Arrays and
-            // objects are not compared up front: comparing them visits
-            // everything below them, so doing that at every level would take
-            // quadratic time in the nesting depth - equal ones yield no
-            // operations anyway.
-            if ((!s.is_structured() || !t.is_structured()) && s == t)
-            {
-                return;
-            }
-
-            if (s.type() != t.type())
-            {
-                // different types: replace value
-                result.push_back(
-                {
-                    {"op", "replace"}, {"path", current_path}, {"value", t}
-                });
-                return;
-            }
-
-            switch (s.type())
-            {
-                case value_t::array:
-                {
-                    stack.emplace_back(&s, &t, current_path.size());
-                    return;
-                }
-
-                case value_t::object:
-                {
-                    // first pass: record, for every source key, whether it is
-                    // common to both objects (in source's iteration order) or
-                    // was deleted (i.e., in source but not in target) -- this is
-                    // a by-product of the t.find() call already needed to
-                    // tell the two cases apart, so it adds no extra lookups. The
-                    // "remove" ops themselves are emitted later, interleaved
-                    // with the per-key diffs in the fast path below, to match
-                    // source's original iteration order (as the original,
-                    // pre-reordering-aware implementation did) instead of
-                    // grouping all removes before all per-key diffs.
-                    std::vector<typename object_t::key_type> common_keys_source_order;
-                    for (auto it = s.cbegin(); it != s.cend(); ++it)
-                    {
-                        if (t.find(it.key()) != t.end())
-                        {
-                            common_keys_source_order.push_back(it.key());
-                        }
-                    }
-
-                    // second pass: find keys that were added (i.e., in target but
-                    // not in source), and record the keys common to both, in
-                    // target's iteration order -- again a by-product of the
-                    // s.find() call already needed to detect added keys. At
-                    // the same time, determine whether every added key comes
-                    // after every common key in target's order (a precondition
-                    // for the fast path below, which only ever appends new keys
-                    // at the very end): for an object_t whose iteration order is
-                    // a pure function of the key set (e.g. the default std::map,
-                    // which always iterates in sorted key order), the order
-                    // check further below is always true and this whole
-                    // mechanism is effectively a no-op; it only matters for a
-                    // reorderable object_t such as the one backing `ordered_json`.
-                    // patch ops for keys that were added (i.e., in target but not
-                    // in source); built here so the fast path below can reuse
-                    // them without a second s.find() per target key. Only
-                    // used by the fast path -- the slow (reordering) path
-                    // rebuilds "add" ops for every key itself.
-                    std::vector<typename object_t::key_type> common_keys_target_order;
-                    basic_json added_ops(value_t::array);
-                    bool new_keys_form_suffix = true;
-                    bool seen_new_key = false;
-                    for (auto it = t.cbegin(); it != t.cend(); ++it)
-                    {
-                        if (s.find(it.key()) == s.end())
-                        {
-                            seen_new_key = true;
-                            const auto path_key = detail::concat<string_t>(current_path, '/', detail::escape(it.key()));
-                            added_ops.push_back(
-                            {
-                                {"op", "add"}, {"path", path_key},
-                                {"value", it.value()}
-                            });
-                        }
-                        else
-                        {
-                            common_keys_target_order.push_back(it.key());
-                            if (seen_new_key)
-                            {
-                                new_keys_form_suffix = false;
-                            }
-                        }
-                    }
-
-                    if (common_keys_source_order == common_keys_target_order && new_keys_form_suffix)
-                    {
-                        // fast path: order of common keys already matches (or the
-                        // object_t's iteration order does not depend on
-                        // insertion history), so a plain per-key diff is correct
-                        // and minimal, as before. The frame walks source in
-                        // lockstep with common_keys_source_order, which is, by
-                        // construction, the subsequence of source's keys that
-                        // are common to both objects, in source's iteration
-                        // order -- so a cheap key comparison replaces another
-                        // lookup. Deleted keys are interleaved there too, in
-                        // source's original order, and the "add" ops collected
-                        // above are appended once all members are done.
-                        stack.emplace_back(&s, &t, current_path.size());
-                        stack.back().member = s.cbegin();
-                        stack.back().common_keys = std::move(common_keys_source_order);
-                        stack.back().added_ops = std::move(added_ops);
-                        return;
-                    }
-
-                    // slow path: the common keys are in a different relative
-                    // order in source and target (only possible for a
-                    // reorderable object_t like ordered_map). Building a
-                    // minimal reordering patch is a nontrivial (LCS-like)
-                    // problem; instead, remove every source key -- both
-                    // deleted keys (which must be removed regardless) and
-                    // common keys (removed so they can be re-added in
-                    // target's order) -- and re-add every key that should
-                    // remain, with its final target value, in target's
-                    // order. basic_json::patch()'s "add" operation on an
-                    // object uses operator[], which appends at the end for a
-                    // vector-backed insertion-ordered map when the key does
-                    // not already exist -- so removing a key and then adding
-                    // it moves it to the end, fixing its position.
-                    for (auto it = s.cbegin(); it != s.cend(); ++it)
-                    {
-                        const auto path_key = detail::concat<string_t>(current_path, '/', detail::escape(it.key()));
-                        result.push_back(object(
-                        {
-                            {"op", "remove"}, {"path", path_key}
-                        }));
-                    }
-
-                    // add every key that is either common (just removed
-                    // above) or brand new, in target's iteration order, so
-                    // that the final order after applying the patch matches
-                    // target exactly
-                    for (auto it = t.cbegin(); it != t.cend(); ++it)
-                    {
-                        const auto path_key = detail::concat<string_t>(current_path, '/', detail::escape(it.key()));
-                        result.push_back(
-                        {
-                            {"op", "add"}, {"path", path_key},
-                            {"value", it.value()}
-                        });
-                    }
-                    return;
-                }
-
-                case value_t::null:
-                case value_t::string:
-                case value_t::boolean:
-                case value_t::number_integer:
-                case value_t::number_unsigned:
-                case value_t::number_float:
-                case value_t::binary:
-                case value_t::discarded:
-                default:
-                {
-                    // both primitive types: replace value
-                    result.push_back(
-                    {
-                        {"op", "replace"}, {"path", current_path}, {"value", t}
-                    });
-                    return;
-                }
-            }
-        };
-
-        enter(source, target);
-        while (!stack.empty())
-        {
-            diff_frame& frame = stack.back();
-            const std::size_t path_length = frame.path_length;
-            const std::size_t depth = stack.size();
-
-            if (frame.source->is_array())
-            {
-                const auto& source_array = *frame.source->m_data.m_value.array;
-                const auto& target_array = *frame.target->m_data.m_value.array;
-
-                // first pass: traverse common elements
-                if (frame.index < source_array.size() && frame.index < target_array.size())
-                {
-                    const std::size_t i = frame.index++;
-                    detail::concat_into(current_path, '/', detail::to_string<string_t>(i));
-                    enter(source_array[i], target_array[i]); // may push, which invalidates `frame`
-                    if (stack.size() == depth)
-                    {
-                        current_path.resize(path_length);
-                    }
-                    continue;
-                }
-
-                // We now reached the end of at least one array
-                // in a second pass, traverse the remaining elements
-
-                // remove my remaining elements, highest index first; appending
-                // in that order avoids the quadratic reinsertion done before
-                for (std::size_t j = source_array.size(); j > frame.index; --j)
-                {
-                    result.push_back(object(
-                    {
-                        {"op", "remove"},
-                        {"path", detail::concat<string_t>(current_path, '/', detail::to_string<string_t>(j - 1))}
-                    }));
-                }
-
-                // add other remaining elements
-                for (std::size_t i = source_array.size(); i < target_array.size(); ++i)
-                {
-                    result.push_back(
-                    {
-                        {"op", "add"},
-                        {"path", detail::concat<string_t>(current_path, "/-")},
-                        {"value", target_array[i]}
-                    });
-                }
-            }
-            else
-            {
-                if (frame.member != frame.source->cend())
-                {
-                    const const_iterator it = frame.member;
-                    ++frame.member;
-                    if (frame.next_common < frame.common_keys.size() && it.key() == frame.common_keys[frame.next_common])
-                    {
-                        ++frame.next_common;
-                        const basic_json& target_value = (*frame.target)[it.key()];
-                        detail::concat_into(current_path, '/', detail::escape(it.key()));
-                        enter(it.value(), target_value); // may push, which invalidates `frame`
-                        if (stack.size() == depth)
-                        {
-                            current_path.resize(path_length);
-                        }
-                    }
-                    else
-                    {
-                        // found a key that is not in target -> remove it
-                        const auto path_key = detail::concat<string_t>(current_path, '/', detail::escape(it.key()));
-                        result.push_back(object(
-                        {
-                            {"op", "remove"}, {"path", path_key}
-                        }));
-                    }
-                    continue;
-                }
-
-                // append the "add" ops for brand-new keys collected when the
-                // object was entered
-                result.insert(result.end(), frame.added_ops.begin(), frame.added_ops.end());
-            }
-
-            // this array or object is done: continue with the one it is in
-            stack.pop_back();
-            if (!stack.empty())
-            {
-                current_path.resize(stack.back().path_length);
-            }
-        }
-
-        return result;
-    }
-
-  public:
     /// @}
 
     ////////////////////////////////

tests/src/unit-json_patch.cpp

@@ -15,65 +15,8 @@ using nlohmann::json;
 #endif
 
 #include <fstream>
-#include <string>
-#include <vector>
 #include "make_test_data_available.hpp"
 
-namespace
-{
-// alternating objects and arrays nested `depth` levels deep, with members that
-// depend on `variant` at some levels, so diffing two variants yields
-// operations on many levels: replacing the innermost value, adding, removing,
-// and (for ordered_json) reordering members, and changing array lengths
-template<typename BasicJsonType>
-BasicJsonType nested(const std::size_t depth, const int variant)
-{
-    BasicJsonType value = variant;
-    for (std::size_t i = 0; i < depth; ++i)
-    {
-        if (i % 2 == 0)
-        {
-            BasicJsonType object = BasicJsonType::object();
-            if ((i + static_cast<std::size_t>(variant)) % 7 == 0)
-            {
-                object["x"] = i;
-            }
-            if (variant == 2 && i % 11 == 0)
-            {
-                object["z"] = "z";
-            }
-            object["a"] = std::move(value);
-            if (variant == 1 && i % 5 == 0)
-            {
-                object["y"] = 1;
-            }
-            value = std::move(object);
-        }
-        else
-        {
-            BasicJsonType array = BasicJsonType::array({std::move(value)});
-            if ((i + static_cast<std::size_t>(variant)) % 3 == 0)
-            {
-                array.push_back(i);
-            }
-            value = std::move(array);
-        }
-    }
-    return value;
-}
-
-// a path of `depth` reference tokens, as nested() nests its values
-std::string nested_path(const std::size_t depth)
-{
-    std::string path;
-    for (std::size_t i = depth; i > 0; --i)
-    {
-        path += (i - 1) % 2 == 0 ? "/a" : "/0";
-    }
-    return path;
-}
-} // namespace
-
 TEST_CASE("JSON patch")
 {
     SECTION("examples from RFC 6902")
@@ -1808,99 +1751,3 @@ TEST_CASE("JSON patch - diff emits array removals in descending index order")
         CHECK(source.patch(patch) == target);
     }
 }
-
-TEST_CASE("JSON patch: diff of deeply nested values")
-{
-    SECTION("the diff reproduces the target at every depth")
-    {
-        // depths on either side of the nesting depth up to which diff()
-        // recurses (detail::recursion_depth_limit(), 128); not every depth up
-        // to 300, as the test would then time out under Valgrind
-        std::vector<std::size_t> depths;
-        for (std::size_t depth = 0; depth <= 16; ++depth)
-        {
-            depths.push_back(depth);
-        }
-        for (std::size_t depth = 120; depth <= 136; ++depth)
-        {
-            depths.push_back(depth);
-        }
-        depths.push_back(300);
-
-        for (const auto depth : depths)
-        {
-            CAPTURE(depth);
-            for (int from = 0; from < 3; ++from)
-            {
-                for (int to = 0; to < 3; ++to)
-                {
-                    CAPTURE(from);
-                    CAPTURE(to);
-                    const auto source = nested<json>(depth, from);
-                    const auto target = nested<json>(depth, to);
-                    const auto patch = json::diff(source, target);
-                    CHECK(source.patch(patch) == target);
-                    CHECK(patch.empty() == (from == to));
-
-                    const auto ordered_source = nested<nlohmann::ordered_json>(depth, from);
-                    const auto ordered_target = nested<nlohmann::ordered_json>(depth, to);
-                    CHECK(ordered_source.patch(nlohmann::ordered_json::diff(ordered_source, ordered_target)) == ordered_target);
-                }
-            }
-        }
-    }
-
-    SECTION("a difference only in the innermost value is one replace operation")
-    {
-        for (std::size_t depth = 0; depth <= 300; ++depth)
-        {
-            CAPTURE(depth);
-            json source = 1;
-            json target = 2;
-            for (std::size_t i = 0; i < depth; ++i)
-            {
-                source = i % 2 == 0 ? json::object({{"a", std::move(source)}}) : json::array({std::move(source)});
-                target = i % 2 == 0 ? json::object({{"a", std::move(target)}}) : json::array({std::move(target)});
-            }
-            CHECK(json::diff(source, target, "/root") == json::array({{{"op", "replace"}, {"path", "/root" + nested_path(depth)}, {"value", 2}}}));
-        }
-    }
-
-    SECTION("values nested too deeply for the call stack (#5393)")
-    {
-        // diff() used to recurse once per nesting level, and compared the
-        // values with operator== on every level. The values are only
-        // parsed and diffed, never copied or compared, since those recurse
-        // too.
-        const std::size_t depth = 100000;
-        for (const bool objects :
-                {
-                    false, true
-                })
-        {
-            CAPTURE(objects);
-            std::string source_text;
-            std::string target_text;
-            std::string equal_text;
-            std::string path;
-            for (std::size_t i = 0; i < depth; ++i)
-            {
-                source_text += objects ? "{\"a\":" : "[";
-                path += objects ? "/a" : "/0";
-            }
-            target_text = source_text + "2";
-            equal_text = source_text + "1";
-            source_text += "1";
-            const std::string closing(depth, objects ? '}' : ']');
-            const auto source = json::parse(source_text + closing);
-
-            const auto patch = json::diff(source, json::parse(target_text + closing));
-            REQUIRE(patch.size() == 1);
-            CHECK(patch[0]["op"] == "replace");
-            CHECK(patch[0]["path"] == path);
-            CHECK(patch[0]["value"] == 2);
-
-            CHECK(json::diff(source, json::parse(equal_text + closing)).empty());
-        }
-    }
-}

tests/src/unit-msgpack.cpp

@@ -14,6 +14,7 @@ using nlohmann::json;
     using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
 #endif
 
+#include <cstdint> // SIZE_MAX, UINT32_MAX
 #include <fstream>
 #include <sstream>
 #include <iomanip>
@@ -2150,3 +2151,65 @@ TEST_CASE("MessagePack with std::byte")
     }
 }
 #endif
+
+namespace
+{
+// types that report a size beyond UINT32_MAX without allocating that much
+// memory, so the MessagePack length limit can be tested cheaply; see the
+// similar types in unit-bson.cpp
+std::size_t beyond_uint32_size()
+{
+    return static_cast<std::size_t>((std::numeric_limits<std::uint32_t>::max)()) + 1;
+}
+
+class beyond_uint32_binary_t : public std::vector<std::uint8_t>
+{
+  public:
+    using std::vector<std::uint8_t>::vector;
+
+    size_type size() const noexcept // NOLINT(readability-convert-member-functions-to-static)
+    {
+        return beyond_uint32_size();
+    }
+};
+
+class beyond_uint32_string_t : public std::string
+{
+  public:
+    using std::string::string;
+
+    size_type size() const noexcept // NOLINT(readability-convert-member-functions-to-static)
+    {
+        return beyond_uint32_size();
+    }
+};
+
+using beyond_uint32_binary_json = nlohmann::basic_json <
+                                  std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t,
+                                  double, std::allocator, nlohmann::adl_serializer, beyond_uint32_binary_t, void >;
+
+using beyond_uint32_string_json = nlohmann::basic_json <
+                                  std::map, std::vector, beyond_uint32_string_t, bool, std::int64_t, std::uint64_t,
+                                  double, std::allocator, nlohmann::adl_serializer, std::vector<std::uint8_t>, void >;
+} // namespace
+
+TEST_CASE("MessagePack lengths beyond UINT32_MAX cannot be serialized")
+{
+    // MessagePack stores the length of a string, binary value, array, or
+    // object in at most 32 bits; a larger one used to be written without any
+    // length at all
+#if SIZE_MAX > UINT32_MAX
+    {
+        const char* const expected = "[json.exception.out_of_range.412] MessagePack length 4294967296 exceeds maximum of 4294967295";
+
+        const beyond_uint32_binary_json binary = beyond_uint32_binary_json::binary(beyond_uint32_binary_t{});
+        CHECK_THROWS_WITH_AS(beyond_uint32_binary_json::to_msgpack(binary), expected, beyond_uint32_binary_json::out_of_range&);
+
+        const beyond_uint32_binary_json ext = beyond_uint32_binary_json::binary(beyond_uint32_binary_t{}, 42);
+        CHECK_THROWS_WITH_AS(beyond_uint32_binary_json::to_msgpack(ext), expected, beyond_uint32_binary_json::out_of_range&);
+
+        const beyond_uint32_string_json string = beyond_uint32_string_t("value");
+        CHECK_THROWS_WITH_AS(beyond_uint32_string_json::to_msgpack(string), expected, beyond_uint32_string_json::out_of_range&);
+    }
+#endif
+}