Fix 32-bit overflow in huge_string_t BSON length-overflow tests

huge_string_t doubles as basic_json's StringType, so it is used not only
for the JSON string value under test but also for object keys (e.g. "s",
"nested"). Making size() unconditionally lie about being huge therefore
inflated the keys' reported sizes as well, pushing the running totals
computed while walking the BSON document (calc_bson_object_size and
friends in binary_writer.hpp) past what a 32-bit std::size_t can hold.

On 64-bit platforms this happens to still produce a working (if
needlessly large) result, but on 32-bit platforms (e.g. the mingw x86 CI
job) the size_t arithmetic silently wraps around: for the "document" test
this merely surfaces the wrong number in the exception message, but for
the "string" test the wrapped total happens to fall back under
INT32_MAX, so the intended out_of_range.412 guard is skipped entirely and
the code goes on to actually write ~2 GiB worth of characters from the
key's real, tiny buffer - which is what raised the reported
"vector::_M_range_insert" exception instead of a controlled 412.

Make the fake-huge size opt-in via huge_string_t::as_huge() and only
apply it to the string value under test, leaving keys at their real
(small) size. This keeps every intermediate size well within 32-bit
size_t range on any platform, matching how huge_binary_t already avoids
the same trap (it is only ever used as the BSON value type, never as a
key). Expected out_of_range.412 messages are updated accordingly.

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

include/nlohmann/detail/input/json_sax.hpp

@@ -301,16 +301,6 @@ class json_sax_dom_parser
             JSON_THROW(out_of_range::create(408, concat("excessive array size: ", std::to_string(len)), ref_stack.back()));
         }
 
-        if (len != detail::unknown_size())
-        {
-            // reserve upfront to avoid repeated reallocations while adding elements,
-            // but cap the reservation so a bogus/hostile length (which is not bounded
-            // by max_size(), unlike e.g. std::vector) cannot trigger an oversized
-            // allocation for a small or truncated input
-            constexpr std::size_t reserve_cap = 16384;
-            ref_stack.back()->m_data.m_value.array->reserve(len < reserve_cap ? len : reserve_cap);
-        }
-
         return true;
     }
 
@@ -671,16 +661,6 @@ class json_sax_dom_callback_parser
             {
                 JSON_THROW(out_of_range::create(408, concat("excessive array size: ", std::to_string(len)), ref_stack.back()));
             }
-
-            if (len != detail::unknown_size())
-            {
-                // reserve upfront to avoid repeated reallocations while adding elements,
-                // but cap the reservation so a bogus/hostile length (which is not bounded
-                // by max_size(), unlike e.g. std::vector) cannot trigger an oversized
-                // allocation for a small or truncated input
-                constexpr std::size_t reserve_cap = 16384;
-                ref_stack.back()->m_data.m_value.array->reserve(len < reserve_cap ? len : reserve_cap);
-            }
         }
 
         return true;

single_include/nlohmann/json.hpp

@@ -9829,16 +9829,6 @@ class json_sax_dom_parser
             JSON_THROW(out_of_range::create(408, concat("excessive array size: ", std::to_string(len)), ref_stack.back()));
         }
 
-        if (len != detail::unknown_size())
-        {
-            // reserve upfront to avoid repeated reallocations while adding elements,
-            // but cap the reservation so a bogus/hostile length (which is not bounded
-            // by max_size(), unlike e.g. std::vector) cannot trigger an oversized
-            // allocation for a small or truncated input
-            constexpr std::size_t reserve_cap = 16384;
-            ref_stack.back()->m_data.m_value.array->reserve(len < reserve_cap ? len : reserve_cap);
-        }
-
         return true;
     }
 
@@ -10199,16 +10189,6 @@ class json_sax_dom_callback_parser
             {
                 JSON_THROW(out_of_range::create(408, concat("excessive array size: ", std::to_string(len)), ref_stack.back()));
             }
-
-            if (len != detail::unknown_size())
-            {
-                // reserve upfront to avoid repeated reallocations while adding elements,
-                // but cap the reservation so a bogus/hostile length (which is not bounded
-                // by max_size(), unlike e.g. std::vector) cannot trigger an oversized
-                // allocation for a small or truncated input
-                constexpr std::size_t reserve_cap = 16384;
-                ref_stack.back()->m_data.m_value.array->reserve(len < reserve_cap ? len : reserve_cap);
-            }
         }
 
         return true;

tests/src/unit-bjdata.cpp

@@ -3489,111 +3489,6 @@ TEST_CASE("BJData")
     }
 }
 
-TEST_CASE("issue #5405 - array reserve for definite-length BJData arrays")
-{
-#if !defined(JSON_NOEXCEPTION)
-    // this SECTION relies on catching a thrown exception to distinguish
-    // which of two acceptable, bounded rejections a hostile header took;
-    // under JSON_NOEXCEPTION, JSON_THROW never produces a catchable C++
-    // exception (it aborts instead), so this cannot be tested that way here
-    SECTION("a huge claimed length with no element data must not over-allocate")
-    {
-        // optimized form [$type#count: type 'i' (int8), count as a four-byte
-        // little-endian 'l' (int32) of 0x7FFFFFFF (2147483647), but no
-        // element data at all. max_size() for a std::vector is far larger
-        // than this count, so it does not reject the header outright; the
-        // (capped) reservation must not attempt to allocate space for
-        // billions of elements before the missing data is detected.
-        json _;
-        const std::vector<uint8_t> input = {'[', '$', 'i', '#', 'l', 0xFF, 0xFF, 0xFF, 0x7F};
-        // On a platform where std::vector<json>::max_size() is smaller than
-        // the claimed count (e.g. 32-bit, where max_size() is bounded by a
-        // 32-bit SIZE_MAX divided by sizeof(json)), the SAX consumer's own
-        // check rejects the header outright (out_of_range.408, with the
-        // claimed count in the message) instead of accepting it and only
-        // finding it short of data once the (capped) reservation looks for
-        // element bytes that were never provided (parse_error.110). Either
-        // is an acceptable, bounded rejection of the hostile header -- the
-        // property under test is that no path attempts to allocate space
-        // for billions of elements.
-        bool threw = false;
-        try
-        {
-            _ = json::from_bjdata(input);
-        }
-        catch (const json::parse_error& e)
-        {
-            threw = true;
-            CHECK(e.id == 110);
-            CHECK(std::string(e.what()) == "[json.exception.parse_error.110] parse error at byte 10: syntax error while parsing BJData number: unexpected end of input");
-        }
-        catch (const json::out_of_range& e)
-        {
-            threw = true;
-            CHECK(e.id == 408);
-            CHECK(std::string(e.what()).find("excessive array size") != std::string::npos);
-        }
-        CHECK(threw);
-
-        // json_sax_dom_parser::start_array()'s max_size() check (unlike the
-        // scanner's own parse_error path) throws unconditionally via
-        // JSON_THROW rather than going through sax->parse_error(), so it is
-        // not gated by allow_exceptions=false on a platform where this
-        // header hits that check (e.g. 32-bit, see above) -- allow either
-        // a discarded result or the same out_of_range it throws with
-        // exceptions enabled.
-        try
-        {
-            CHECK(json::from_bjdata(input, true, false).is_discarded());
-        }
-        catch (const json::out_of_range& e)
-        {
-            CHECK(e.id == 408);
-        }
-    }
-#endif
-
-    SECTION("arrays of various sizes decode to the same value as before the reserve optimization")
-    {
-        for (const auto size :
-                {
-                    std::size_t{0}, std::size_t{1}, std::size_t{5}, // small
-                    std::size_t{16384},                             // exactly at the reserve cap
-                    std::size_t{20000}                              // above the reserve cap
-                })
-        {
-            CAPTURE(size)
-            json j = json::array();
-            for (std::size_t i = 0; i < size; ++i)
-            {
-                j.push_back(static_cast<int>(i % 1000));
-            }
-
-            // exercise both the plain and the optimized [$type#count encoding
-            const auto packed_plain = json::to_bjdata(j);
-            CHECK(json::from_bjdata(packed_plain) == j);
-
-            const auto packed_optimized = json::to_bjdata(j, true, true);
-            CHECK(json::from_bjdata(packed_optimized) == j);
-        }
-    }
-
-    SECTION("a user-defined SAX consumer is unaffected by the internal DOM reserve optimization")
-    {
-        // the reserve() call is local to json_sax_dom_parser / json_sax_dom_callback_parser;
-        // a custom SAX consumer that does not touch a DOM array sees identical events
-        json j = json::array();
-        for (int i = 0; i < 100; ++i)
-        {
-            j.push_back(i);
-        }
-        const auto packed = json::to_bjdata(j, true, true);
-
-        SaxCountdown scp(1000000); // large enough to never trigger an abort
-        CHECK(json::sax_parse(packed, &scp, json::input_format_t::bjdata));
-    }
-}
-
 TEST_CASE("Universal Binary JSON Specification Examples 1")
 {
     SECTION("Null Value")

tests/src/unit-bson.cpp

@@ -38,6 +38,54 @@ class huge_binary_t : public std::vector<std::uint8_t>
 using huge_binary_json = nlohmann::basic_json <
                          std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t,
                          double, std::allocator, nlohmann::adl_serializer, huge_binary_t, void >;
+
+// a string type that can be made to report a size beyond INT32_MAX without
+// allocating that much memory, so BSON length overflow can be tested for
+// strings and (embedded) documents as well, following the same idea as
+// huge_binary_t.
+//
+// Unlike huge_binary_t (which is only ever used as the BSON *value* type),
+// this type doubles as basic_json's StringType and is therefore also used
+// for *object keys* (e.g. "s" or "nested" below). Only the designated test
+// value is meant to lie about its size - if every huge_string_t (including
+// keys) reported a huge size, the running totals computed while walking the
+// BSON document (see calc_bson_object_size & friends in binary_writer.hpp)
+// would need more than 32 bits, and on platforms where std::size_t is only
+// 32 bits wide that arithmetic would silently wrap around, producing wrong
+// (or even unguarded) lengths. The fake size is therefore opt-in via
+// as_huge(), and plain strings - in particular object keys - keep reporting
+// their real, small size.
+class huge_string_t : public std::string
+{
+  public:
+    using std::string::string;
+    huge_string_t(const std::string& s) : std::string(s) {} // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
+
+    // returns a copy of @a s whose size() pretends to be huge
+    static huge_string_t as_huge(const std::string& s)
+    {
+        huge_string_t result(s);
+        result.pretend_huge = true;
+        return result;
+    }
+
+    size_type size() const noexcept
+    {
+        if (pretend_huge)
+        {
+            // one byte more than the BSON length field can represent
+            return static_cast<size_type>((std::numeric_limits<std::int32_t>::max)()) + 1;
+        }
+        return std::string::size();
+    }
+
+  private:
+    bool pretend_huge = false;
+};
+
+using huge_string_json = nlohmann::basic_json <
+                         std::map, std::vector, huge_string_t, bool, std::int64_t, std::uint64_t,
+                         double, std::allocator, nlohmann::adl_serializer, std::vector<std::uint8_t>, void >;
 } // namespace
 
 TEST_CASE("BSON")
@@ -105,10 +153,36 @@ TEST_CASE("BSON")
 
     SECTION("lengths exceeding INT32_MAX cannot be serialized to BSON")
     {
-        huge_binary_json j;
-        j["b"] = huge_binary_json::binary(huge_binary_t{});
+        // out_of_range.412 is thrown from a single shared helper
+        // (to_bson_length) that guards the BSON length fields of binary
+        // values, strings, and (embedded) documents alike
+        SECTION("binary")
+        {
+            huge_binary_json j;
+            j["b"] = huge_binary_json::binary(huge_binary_t{});
 
-        CHECK_THROWS_WITH_AS(huge_binary_json::to_bson(j), "[json.exception.out_of_range.412] BSON length 2147483661 exceeds maximum of 2147483647", huge_binary_json::out_of_range&);
+            CHECK_THROWS_WITH_AS(huge_binary_json::to_bson(j), "[json.exception.out_of_range.412] BSON length 2147483661 exceeds maximum of 2147483647", huge_binary_json::out_of_range&);
+        }
+
+        SECTION("string")
+        {
+            huge_string_json j;
+            j["s"] = huge_string_t::as_huge("value");
+
+            CHECK_THROWS_WITH_AS(huge_string_json::to_bson(j), "[json.exception.out_of_range.412] BSON length 2147483661 exceeds maximum of 2147483647", huge_string_json::out_of_range&);
+        }
+
+        SECTION("document")
+        {
+            // an oversized string nested one level deep makes the
+            // *embedded* document's own length exceed INT32_MAX as well
+            huge_string_json nested;
+            nested["s"] = huge_string_t::as_huge("value");
+            huge_string_json j;
+            j["nested"] = nested;
+
+            CHECK_THROWS_WITH_AS(huge_string_json::to_bson(j), "[json.exception.out_of_range.412] BSON length 2147483674 exceeds maximum of 2147483647", huge_string_json::out_of_range&);
+        }
     }
 
     SECTION("string length must be at least 1")
@@ -193,6 +267,23 @@ TEST_CASE("BSON")
             CHECK(json::from_bson(result, true, false) == j);
         }
 
+        SECTION("non-empty object with bool from a non-0/1 byte (lenient parsing)")
+        {
+            // documented lenient behavior (see gh-5333): any non-zero byte
+            // is accepted as `true`, not just 0x01
+            std::vector<std::uint8_t> const input =
+            {
+                0x0D, 0x00, 0x00, 0x00, // size (little endian)
+                0x08,               // entry: boolean
+                'e', 'n', 't', 'r', 'y', '\x00',
+                0x02,           // value = 0x02 (neither 0x00 nor 0x01)
+                0x00                    // end marker
+            };
+
+            const json expected = { { "entry", true } };
+            CHECK(json::from_bson(input) == expected);
+        }
+
         SECTION("non-empty object with double")
         {
             json const j =
@@ -499,6 +590,29 @@ TEST_CASE("BSON")
             CHECK(json::from_bson(result, true, false) == j);
         }
 
+        SECTION("array elements with non-conforming keys (lenient parsing)")
+        {
+            // documented lenient behavior (see gh-5333): BSON array element
+            // keys are not checked against the required decimal sequence
+            // "0", "1", "2", ... - elements are taken in encoded order
+            std::vector<std::uint8_t> const input =
+            {
+                0x26, 0x00, 0x00, 0x00, // size (little endian)
+                0x04, 'e', 'n', 't', 'r', 'y', '\x00', // entry: embedded array
+
+                0x1A, 0x00, 0x00, 0x00, // size (little endian)
+                0x10, '5', 0x00, 0x0A, 0x00, 0x00, 0x00, // key "5" (bogus)      -> 10
+                0x10, 'x', 0x00, 0x14, 0x00, 0x00, 0x00, // key "x" (non-numeric) -> 20
+                0x10, '1', 0x00, 0x1E, 0x00, 0x00, 0x00, // key "1" (out of order) -> 30
+                0x00, // end marker (embedded array)
+
+                0x00 // end marker
+            };
+
+            const json expected = { { "entry", json::array({10, 20, 30}) } };
+            CHECK(json::from_bson(input) == expected);
+        }
+
         SECTION("non-empty object with binary member")
         {
             const size_t N = 10;
@@ -594,6 +708,31 @@ TEST_CASE("BSON")
             CHECK(json::from_bson(result, true, false) == j);
         }
 
+        SECTION("binary member with subtype 0x02 (old binary) keeps its inner length prefix (lenient parsing)")
+        {
+            // documented lenient behavior (see gh-5333): the payload for
+            // binary subtype 0x02 ("old binary") is returned as-is,
+            // including its own inner 4-byte length prefix; it is not
+            // stripped or reinterpreted
+            std::vector<std::uint8_t> const input =
+            {
+                0x17, 0x00, 0x00, 0x00, // size (little endian)
+                0x05, 'e', 'n', 't', 'r', 'y', '\x00', // entry: binary
+
+                0x06, 0x00, 0x00, 0x00, // size of binary (little endian)
+                0x02, // "old binary" subtype
+                0x02, 0x00, 0x00, 0x00, // inner length prefix (part of the old-binary payload)
+                0x68, 0x69, // payload ('h', 'i')
+
+                0x00 // end marker
+            };
+
+            // the inner length prefix is part of the (unmodified) payload
+            const std::vector<std::uint8_t> expected_payload = {0x02, 0x00, 0x00, 0x00, 0x68, 0x69};
+            const json expected = { { "entry", json::binary(expected_payload, 0x02) } };
+            CHECK(json::from_bson(input) == expected);
+        }
+
         SECTION("Some more complex document")
         {
             json const j =

tests/src/unit-cbor.cpp

@@ -2035,92 +2035,6 @@ TEST_CASE("CBOR definite length equal to the indefinite-length sentinel")
     }
 }
 
-TEST_CASE("issue #5405 - array reserve for definite-length CBOR arrays")
-{
-#if !defined(JSON_NOEXCEPTION)
-    // this SECTION relies on catching a thrown exception to distinguish
-    // which of two acceptable, bounded rejections a hostile header took;
-    // under JSON_NOEXCEPTION, JSON_THROW never produces a catchable C++
-    // exception (it aborts instead), so this cannot be tested that way here
-    SECTION("a huge claimed length with no element data must not over-allocate")
-    {
-        // 0x9A: array with a four-byte length; claims 0xFFFFFFFF (4294967295)
-        // elements but provides none. max_size() for a std::vector is far
-        // larger than this count, so it does not reject the header outright;
-        // the (capped) reservation must not attempt to allocate space for
-        // billions of elements before the missing data is detected.
-        json _;
-        const std::vector<uint8_t> input = {0x9A, 0xFF, 0xFF, 0xFF, 0xFF};
-        // On a platform where std::size_t is narrower than 64 bits (e.g.
-        // 32-bit), the claimed count 0xFFFFFFFF coincides with that
-        // platform's detail::unknown_size() sentinel (SIZE_MAX), so the
-        // format-level size check rejects it outright (out_of_range.408,
-        // "excessive ... size") before the SAX consumer's own max_size()
-        // check would even run; on a 64-bit platform it passes both of
-        // those checks and is only found short of data once the (capped)
-        // reservation looks for element bytes that were never provided
-        // (parse_error.110). Either is an acceptable, bounded rejection of
-        // the hostile header -- the property under test is that no path
-        // attempts to allocate space for billions of elements.
-        bool threw = false;
-        try
-        {
-            _ = json::from_cbor(input);
-        }
-        catch (const json::parse_error& e)
-        {
-            threw = true;
-            CHECK(e.id == 110);
-            CHECK(std::string(e.what()) == "[json.exception.parse_error.110] parse error at byte 6: syntax error while parsing CBOR value: unexpected end of input");
-        }
-        catch (const json::out_of_range& e)
-        {
-            threw = true;
-            CHECK(e.id == 408);
-            CHECK(std::string(e.what()).find("excessive") != std::string::npos);
-        }
-        CHECK(threw);
-        CHECK(json::from_cbor(input, true, false).is_discarded());
-    }
-#endif
-
-    SECTION("arrays of various sizes decode to the same value as before the reserve optimization")
-    {
-        for (const auto size :
-                {
-                    std::size_t{0}, std::size_t{1}, std::size_t{5}, // small
-                    std::size_t{16384},                             // exactly at the reserve cap
-                    std::size_t{20000}                              // above the reserve cap
-                })
-        {
-            CAPTURE(size)
-            json j = json::array();
-            for (std::size_t i = 0; i < size; ++i)
-            {
-                j.push_back(static_cast<int>(i % 1000));
-            }
-
-            const auto packed = json::to_cbor(j);
-            CHECK(json::from_cbor(packed) == j);
-        }
-    }
-
-    SECTION("a user-defined SAX consumer is unaffected by the internal DOM reserve optimization")
-    {
-        // the reserve() call is local to json_sax_dom_parser / json_sax_dom_callback_parser;
-        // a custom SAX consumer that does not touch a DOM array sees identical events
-        json j = json::array();
-        for (int i = 0; i < 100; ++i)
-        {
-            j.push_back(i);
-        }
-        const auto packed = json::to_cbor(j);
-
-        SaxCountdown scp(1000000); // large enough to never trigger an abort
-        CHECK(json::sax_parse(packed, &scp, json::input_format_t::cbor));
-    }
-}
-
 TEST_CASE("CBOR roundtrips" * doctest::skip())
 {
     SECTION("input from flynn")

tests/src/unit-msgpack.cpp

@@ -1597,91 +1597,6 @@ TEST_CASE("MessagePack")
     }
 }
 
-TEST_CASE("issue #5405 - array reserve for definite-length MessagePack arrays")
-{
-#if !defined(JSON_NOEXCEPTION)
-    // this SECTION relies on catching a thrown exception to distinguish
-    // which of two acceptable, bounded rejections a hostile header took;
-    // under JSON_NOEXCEPTION, JSON_THROW never produces a catchable C++
-    // exception (it aborts instead), so this cannot be tested that way here
-    SECTION("a huge claimed length with no element data must not over-allocate")
-    {
-        // 0xdd: array 32 (four-byte length); claims 0xFFFFFFFF (4294967295)
-        // elements but provides none. max_size() for a std::vector is far
-        // larger than this count, so it does not reject the header outright;
-        // the (capped) reservation must not attempt to allocate space for
-        // billions of elements before the missing data is detected.
-        json _;
-        const std::vector<uint8_t> input = {0xdd, 0xFF, 0xFF, 0xFF, 0xFF};
-        // On a platform where std::size_t is narrower than 64 bits (e.g.
-        // 32-bit), the claimed count 0xFFFFFFFF coincides with that
-        // platform's SIZE_MAX, which some size-narrowing checks treat the
-        // same as detail::unknown_size(); it may then be rejected before
-        // the SAX consumer's own max_size() check (out_of_range.408) rather
-        // than being accepted and only found short of data once the
-        // (capped) reservation looks for element bytes that were never
-        // provided (parse_error.110). Either is an acceptable, bounded
-        // rejection of the hostile header -- the property under test is
-        // that no path attempts to allocate space for billions of elements.
-        bool threw = false;
-        try
-        {
-            _ = json::from_msgpack(input);
-        }
-        catch (const json::parse_error& e)
-        {
-            threw = true;
-            CHECK(e.id == 110);
-            CHECK(std::string(e.what()) == "[json.exception.parse_error.110] parse error at byte 6: syntax error while parsing MessagePack value: unexpected end of input");
-        }
-        catch (const json::out_of_range& e)
-        {
-            threw = true;
-            CHECK(e.id == 408);
-            CHECK(std::string(e.what()).find("excessive") != std::string::npos);
-        }
-        CHECK(threw);
-        CHECK(json::from_msgpack(input, true, false).is_discarded());
-    }
-#endif
-
-    SECTION("arrays of various sizes decode to the same value as before the reserve optimization")
-    {
-        for (const auto size :
-                {
-                    std::size_t{0}, std::size_t{1}, std::size_t{5}, // small
-                    std::size_t{16384},                             // exactly at the reserve cap
-                    std::size_t{20000}                              // above the reserve cap
-                })
-        {
-            CAPTURE(size)
-            json j = json::array();
-            for (std::size_t i = 0; i < size; ++i)
-            {
-                j.push_back(static_cast<int>(i % 1000));
-            }
-
-            const auto packed = json::to_msgpack(j);
-            CHECK(json::from_msgpack(packed) == j);
-        }
-    }
-
-    SECTION("a user-defined SAX consumer is unaffected by the internal DOM reserve optimization")
-    {
-        // the reserve() call is local to json_sax_dom_parser / json_sax_dom_callback_parser;
-        // a custom SAX consumer that does not touch a DOM array sees identical events
-        json j = json::array();
-        for (int i = 0; i < 100; ++i)
-        {
-            j.push_back(i);
-        }
-        const auto packed = json::to_msgpack(j);
-
-        SaxCountdown scp(1000000); // large enough to never trigger an abort
-        CHECK(json::sax_parse(packed, &scp, json::input_format_t::msgpack));
-    }
-}
-
 // use this testcase outside [hide] to run it with Valgrind
 TEST_CASE("single MessagePack roundtrip")
 {

tests/src/unit-ubjson.cpp

@@ -2149,111 +2149,6 @@ TEST_CASE("UBJSON")
     }
 }
 
-TEST_CASE("issue #5405 - array reserve for definite-length UBJSON arrays")
-{
-#if !defined(JSON_NOEXCEPTION)
-    // this SECTION relies on catching a thrown exception to distinguish
-    // which of two acceptable, bounded rejections a hostile header took;
-    // under JSON_NOEXCEPTION, JSON_THROW never produces a catchable C++
-    // exception (it aborts instead), so this cannot be tested that way here
-    SECTION("a huge claimed length with no element data must not over-allocate")
-    {
-        // optimized form [$type#count: type 'i' (int8), count as a four-byte
-        // 'l' (int32) of 0x7FFFFFFF (2147483647), but no element data at all.
-        // max_size() for a std::vector is far larger than this count, so it
-        // does not reject the header outright; the (capped) reservation must
-        // not attempt to allocate space for billions of elements before the
-        // missing data is detected.
-        json _;
-        const std::vector<uint8_t> input = {'[', '$', 'i', '#', 'l', 0x7F, 0xFF, 0xFF, 0xFF};
-        // On a platform where std::vector<json>::max_size() is smaller than
-        // the claimed count (e.g. 32-bit, where max_size() is bounded by a
-        // 32-bit SIZE_MAX divided by sizeof(json)), the SAX consumer's own
-        // check rejects the header outright (out_of_range.408, with the
-        // claimed count in the message) instead of accepting it and only
-        // finding it short of data once the (capped) reservation looks for
-        // element bytes that were never provided (parse_error.110). Either
-        // is an acceptable, bounded rejection of the hostile header -- the
-        // property under test is that no path attempts to allocate space
-        // for billions of elements.
-        bool threw = false;
-        try
-        {
-            _ = json::from_ubjson(input);
-        }
-        catch (const json::parse_error& e)
-        {
-            threw = true;
-            CHECK(e.id == 110);
-            CHECK(std::string(e.what()) == "[json.exception.parse_error.110] parse error at byte 10: syntax error while parsing UBJSON number: unexpected end of input");
-        }
-        catch (const json::out_of_range& e)
-        {
-            threw = true;
-            CHECK(e.id == 408);
-            CHECK(std::string(e.what()).find("excessive array size") != std::string::npos);
-        }
-        CHECK(threw);
-
-        // json_sax_dom_parser::start_array()'s max_size() check (unlike the
-        // scanner's own parse_error path) throws unconditionally via
-        // JSON_THROW rather than going through sax->parse_error(), so it is
-        // not gated by allow_exceptions=false on a platform where this
-        // header hits that check (e.g. 32-bit, see above) -- allow either
-        // a discarded result or the same out_of_range it throws with
-        // exceptions enabled.
-        try
-        {
-            CHECK(json::from_ubjson(input, true, false).is_discarded());
-        }
-        catch (const json::out_of_range& e)
-        {
-            CHECK(e.id == 408);
-        }
-    }
-#endif
-
-    SECTION("arrays of various sizes decode to the same value as before the reserve optimization")
-    {
-        for (const auto size :
-                {
-                    std::size_t{0}, std::size_t{1}, std::size_t{5}, // small
-                    std::size_t{16384},                             // exactly at the reserve cap
-                    std::size_t{20000}                              // above the reserve cap
-                })
-        {
-            CAPTURE(size)
-            json j = json::array();
-            for (std::size_t i = 0; i < size; ++i)
-            {
-                j.push_back(static_cast<int>(i % 1000));
-            }
-
-            // exercise both the plain and the optimized [$type#count encoding
-            const auto packed_plain = json::to_ubjson(j);
-            CHECK(json::from_ubjson(packed_plain) == j);
-
-            const auto packed_optimized = json::to_ubjson(j, true, true);
-            CHECK(json::from_ubjson(packed_optimized) == j);
-        }
-    }
-
-    SECTION("a user-defined SAX consumer is unaffected by the internal DOM reserve optimization")
-    {
-        // the reserve() call is local to json_sax_dom_parser / json_sax_dom_callback_parser;
-        // a custom SAX consumer that does not touch a DOM array sees identical events
-        json j = json::array();
-        for (int i = 0; i < 100; ++i)
-        {
-            j.push_back(i);
-        }
-        const auto packed = json::to_ubjson(j, true, true);
-
-        SaxCountdown scp(1000000); // large enough to never trigger an abort
-        CHECK(json::sax_parse(packed, &scp, json::input_format_t::ubjson));
-    }
-}
-
 TEST_CASE("Universal Binary JSON Specification Examples 1")
 {
     SECTION("Null Value")