Fix UBSan implicit-conversion in BSON stream tests

std::string(first, last) over std::uint8_t iterators converts each byte
to char implicitly, which -fsanitize=implicit-conversion reports as soon
as a byte is >= 0x80 (the document size byte of the enlarged test input,
and 0xFF in the new array element name test). Build the string from a
const char* and a size instead.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N5NasCxh8jKXBaa6HBx9Xk
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/docs/features/json_view.md

@@ -253,34 +253,6 @@ Two conversions never copy at all:
 
 Both results are only valid as long as the view — and, for a string with no escapes, the borrowed source text — is.
 
-### `string_view` members
-
-A struct whose member is a `#!cpp std::string_view` (C++17) can be decoded from a view with the
-`NLOHMANN_DEFINE_TYPE_*` macros, and the member is not copied either: for a string without escape sequences it points
-into the document's source text, and for a string with escape sequences into the document's buffer of decoded strings.
-The member is valid as long as the document is alive and, for a document that
-[borrows its source text](#ownership-and-lifetime) (as [`parse()`](../api/basic_json_document/parse.md) does for
-an lvalue `#!cpp std::string`, a `#!cpp std::string_view`, or a C string), as long as that text is.
-
-```cpp
-struct record
-{
-    std::string_view name;
-    int count;
-    NLOHMANN_DEFINE_TYPE_INTRUSIVE(record, name, count)
-};
-
-const std::string text = R"({"name": "widget", "count": 3})";
-const json_document doc = json_document::parse(text);  // borrows text
-const record r = doc.root().get<record>();             // r.name points into text, valid while text and doc are
-```
-
-!!! warning "Decoding into a `string_view` from a `json` value dangles at once"
-
-    The same struct also compiles with `#!cpp json::parse(text).get<record>()`, but there `name` points into the
-    temporary `json` value, which is destroyed at the end of the statement. Use a named
-    [`json_document`](../api/json_document.md), as above, to decode such a struct.
-
 ## Writing generic code
 
 A view's type names its `BasicJsonType` and its [`view_mode`](../api/view_mode.md):

include/nlohmann/detail/input/binary_reader.hpp

@@ -465,15 +465,17 @@ class binary_reader
             }
 
             const std::size_t element_type_parse_position = chars_read;
+            // an array's elements are named "0", "1", ... in the wire format,
+            // and those names are not passed on: they are skipped unless
+            // error_handler_t::strict must reject ill-formed UTF-8 in them
+            const bool is_object = container_stack.back().is_object;
             key.clear();
-            if (JSON_HEDLEY_UNLIKELY(!get_bson_cstr(key)))
+            if (JSON_HEDLEY_UNLIKELY(!get_bson_cstr(key, is_object || error_handler == error_handler_t::strict)))
             {
                 return false;
             }
 
-            // an array's elements are named "0", "1", ... in the wire format,
-            // and those names are not passed on
-            if (container_stack.back().is_object && !sax->key(key))
+            if (is_object && !sax->key(key))
             {
                 return false;
             }
@@ -489,14 +491,18 @@ class binary_reader
     @brief Parses a C-style string from the BSON input.
     @param[in,out] result  A reference to the string variable where the read
                             string is to be stored.
+    @param[in] store  whether the characters are needed; if not (the names of
+                      an array's elements), they are skipped and @a result may
+                      be left unchanged, and they are not checked against
+                      @ref error_handler
     @return `true` if the \\x00-byte indicating the end of the string was
              encountered before the EOF; false` indicates an unexpected EOF.
     */
-    bool get_bson_cstr(string_t& result)
+    bool get_bson_cstr(string_t& result, const bool store = true)
     {
-        if (get_bson_cstr_bulk(result, std::integral_constant<bool, bulk_scan> {}))
+        if (get_bson_cstr_bulk(result, store, std::integral_constant<bool, bulk_scan> {}))
         {
-            return check_string_utf8(result, "key");
+            return !store || check_string_utf8(result, "key");
         }
 
         auto out = std::back_inserter(result);
@@ -509,7 +515,7 @@ class binary_reader
             }
             if (current == 0x00)
             {
-                return check_string_utf8(result, "key");
+                return !store || check_string_utf8(result, "key");
             }
             *out++ = static_cast<typename string_t::value_type>(current);
         }
@@ -519,10 +525,11 @@ class binary_reader
     @brief read a C-style string from contiguous input in one step
 
     @param[in,out] result  the string to append to
+    @param[in] store  whether to append the characters to @a result
     @return whether the string was read; if the input has no \\x00-byte, nothing
             is read, and @ref get_bson_cstr reports the end of the input
     */
-    bool get_bson_cstr_bulk(string_t& result, std::true_type /*bulk*/)
+    bool get_bson_cstr_bulk(string_t& result, const bool store, std::true_type /*bulk*/)
     {
         const std::size_t remaining = ia.bulk_remaining();
         if (remaining == 0)
@@ -530,18 +537,15 @@ class binary_reader
             return false;
         }
         const auto* const data = reinterpret_cast<const unsigned char*>(ia.bulk_data());
-        // a plain loop rather than std::memchr: most keys are short (array
-        // indices are keys, too), and the call would cost more than it saves
-        std::size_t length = 0;
-        while (length < remaining && data[length] != 0x00)
-        {
-            ++length;
-        }
+        const std::size_t length = find_zero_byte(data, remaining);
         if (length == remaining)
         {
             return false;
         }
-        result.append(reinterpret_cast<const typename string_t::value_type*>(data), length);
+        if (store)
+        {
+            result.append(reinterpret_cast<const typename string_t::value_type*>(data), length);
+        }
         // consume the string and its \x00-byte, as the byte-wise path does
         ia.bulk_skip(length + 1);
         chars_read += length + 1;
@@ -550,7 +554,7 @@ class binary_reader
     }
 
     /// input that is not contiguous: C-style strings are read byte by byte
-    bool get_bson_cstr_bulk(string_t& /*result*/, std::false_type /*bulk*/) const noexcept
+    bool get_bson_cstr_bulk(string_t& /*result*/, const bool /*store*/, std::false_type /*bulk*/) const noexcept
     {
         return false;
     }

include/nlohmann/detail/input/string_scan.hpp

@@ -90,6 +90,34 @@ JSON_HEDLEY_ALWAYS_INLINE std::size_t find_string_special(const unsigned char* d
     return n;
 }
 
+// return the index of the first 0x00 byte in [data, data+n), or n if there is
+// none; scans 8 bytes at a time (BSON's C-style strings)
+JSON_HEDLEY_ALWAYS_INLINE std::size_t find_zero_byte(const unsigned char* data, std::size_t n) noexcept
+{
+    constexpr std::uint64_t ones = 0x0101010101010101ull;
+    constexpr std::uint64_t high = 0x8080808080808080ull;
+    std::size_t i = 0;
+    for (; i + 8 <= n; i += 8)
+    {
+        const std::uint64_t v = read_eight_bytes(data + i);
+        const std::uint64_t zero = (v - ones) & ~v & high;
+        if (zero != 0)
+        {
+            // the lowest flagged byte is the first zero byte (see
+            // find_string_special())
+            return i + (static_cast<std::size_t>(count_trailing_zeros(zero)) / 8);
+        }
+    }
+    for (; i < n; ++i)
+    {
+        if (data[i] == 0x00)
+        {
+            return i;
+        }
+    }
+    return n;
+}
+
 // classify a byte as one the serializer must NOT copy verbatim when
 // ensure_ascii is requested: the closing quote, an escape, a control character
 // (< 0x20), DEL (0x7F), or any non-ASCII byte (>= 0x80). Everything else -

single_include/nlohmann/json.hpp

@@ -12458,6 +12458,34 @@ JSON_HEDLEY_ALWAYS_INLINE std::size_t find_string_special(const unsigned char* d
     return n;
 }
 
+// return the index of the first 0x00 byte in [data, data+n), or n if there is
+// none; scans 8 bytes at a time (BSON's C-style strings)
+JSON_HEDLEY_ALWAYS_INLINE std::size_t find_zero_byte(const unsigned char* data, std::size_t n) noexcept
+{
+    constexpr std::uint64_t ones = 0x0101010101010101ull;
+    constexpr std::uint64_t high = 0x8080808080808080ull;
+    std::size_t i = 0;
+    for (; i + 8 <= n; i += 8)
+    {
+        const std::uint64_t v = read_eight_bytes(data + i);
+        const std::uint64_t zero = (v - ones) & ~v & high;
+        if (zero != 0)
+        {
+            // the lowest flagged byte is the first zero byte (see
+            // find_string_special())
+            return i + (static_cast<std::size_t>(count_trailing_zeros(zero)) / 8);
+        }
+    }
+    for (; i < n; ++i)
+    {
+        if (data[i] == 0x00)
+        {
+            return i;
+        }
+    }
+    return n;
+}
+
 // classify a byte as one the serializer must NOT copy verbatim when
 // ensure_ascii is requested: the closing quote, an escape, a control character
 // (< 0x20), DEL (0x7F), or any non-ASCII byte (>= 0x80). Everything else -
@@ -18241,15 +18269,17 @@ class binary_reader
             }
 
             const std::size_t element_type_parse_position = chars_read;
+            // an array's elements are named "0", "1", ... in the wire format,
+            // and those names are not passed on: they are skipped unless
+            // error_handler_t::strict must reject ill-formed UTF-8 in them
+            const bool is_object = container_stack.back().is_object;
             key.clear();
-            if (JSON_HEDLEY_UNLIKELY(!get_bson_cstr(key)))
+            if (JSON_HEDLEY_UNLIKELY(!get_bson_cstr(key, is_object || error_handler == error_handler_t::strict)))
             {
                 return false;
             }
 
-            // an array's elements are named "0", "1", ... in the wire format,
-            // and those names are not passed on
-            if (container_stack.back().is_object && !sax->key(key))
+            if (is_object && !sax->key(key))
             {
                 return false;
             }
@@ -18265,14 +18295,18 @@ class binary_reader
     @brief Parses a C-style string from the BSON input.
     @param[in,out] result  A reference to the string variable where the read
                             string is to be stored.
+    @param[in] store  whether the characters are needed; if not (the names of
+                      an array's elements), they are skipped and @a result may
+                      be left unchanged, and they are not checked against
+                      @ref error_handler
     @return `true` if the \\x00-byte indicating the end of the string was
              encountered before the EOF; false` indicates an unexpected EOF.
     */
-    bool get_bson_cstr(string_t& result)
+    bool get_bson_cstr(string_t& result, const bool store = true)
     {
-        if (get_bson_cstr_bulk(result, std::integral_constant<bool, bulk_scan> {}))
+        if (get_bson_cstr_bulk(result, store, std::integral_constant<bool, bulk_scan> {}))
         {
-            return check_string_utf8(result, "key");
+            return !store || check_string_utf8(result, "key");
         }
 
         auto out = std::back_inserter(result);
@@ -18285,7 +18319,7 @@ class binary_reader
             }
             if (current == 0x00)
             {
-                return check_string_utf8(result, "key");
+                return !store || check_string_utf8(result, "key");
             }
             *out++ = static_cast<typename string_t::value_type>(current);
         }
@@ -18295,10 +18329,11 @@ class binary_reader
     @brief read a C-style string from contiguous input in one step
 
     @param[in,out] result  the string to append to
+    @param[in] store  whether to append the characters to @a result
     @return whether the string was read; if the input has no \\x00-byte, nothing
             is read, and @ref get_bson_cstr reports the end of the input
     */
-    bool get_bson_cstr_bulk(string_t& result, std::true_type /*bulk*/)
+    bool get_bson_cstr_bulk(string_t& result, const bool store, std::true_type /*bulk*/)
     {
         const std::size_t remaining = ia.bulk_remaining();
         if (remaining == 0)
@@ -18306,18 +18341,15 @@ class binary_reader
             return false;
         }
         const auto* const data = reinterpret_cast<const unsigned char*>(ia.bulk_data());
-        // a plain loop rather than std::memchr: most keys are short (array
-        // indices are keys, too), and the call would cost more than it saves
-        std::size_t length = 0;
-        while (length < remaining && data[length] != 0x00)
-        {
-            ++length;
-        }
+        const std::size_t length = find_zero_byte(data, remaining);
         if (length == remaining)
         {
             return false;
         }
-        result.append(reinterpret_cast<const typename string_t::value_type*>(data), length);
+        if (store)
+        {
+            result.append(reinterpret_cast<const typename string_t::value_type*>(data), length);
+        }
         // consume the string and its \x00-byte, as the byte-wise path does
         ia.bulk_skip(length + 1);
         chars_read += length + 1;
@@ -18326,7 +18358,7 @@ class binary_reader
     }
 
     /// input that is not contiguous: C-style strings are read byte by byte
-    bool get_bson_cstr_bulk(string_t& /*result*/, std::false_type /*bulk*/) const noexcept
+    bool get_bson_cstr_bulk(string_t& /*result*/, const bool /*store*/, std::false_type /*bulk*/) const noexcept
     {
         return false;
     }

tests/src/unit-bson.cpp

@@ -1164,7 +1164,13 @@ TEST_CASE("BSON keys from contiguous and stream input")
     // contiguous input reads a key up to its \x00-byte in one step, a stream
     // reads it byte by byte; both must give the same value or error for the
     // complete document and for every truncation of it
-    const json j = {{"", true}, {"k", {1, 2, 3}}, {std::string(40, 'x'), {{"nested key", "value"}}}};
+    json j = {{"", true}, {"k", {1, 2, 3}}, {std::string(40, 'x'), {{"nested key", "value"}}}};
+    // keys and array element names ("0" to "11") that end at every position of
+    // an 8-byte word, which contiguous input scans at a time
+    for (std::size_t length = 1; length <= 17; ++length)
+    {
+        j[std::string(length, static_cast<char>('a' + length))] = json::array({0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, {11}});
+    }
     const std::vector<std::uint8_t> bson = json::to_bson(j);
     CHECK(json::from_bson(bson) == j);
 
@@ -1184,7 +1190,7 @@ TEST_CASE("BSON keys from contiguous and stream input")
         }
         try
         {
-            std::istringstream stream(std::string(input.begin(), input.end()));
+            std::istringstream stream(std::string(reinterpret_cast<const char*>(input.data()), input.size()));
             from_stream = json::from_bson(stream).dump();
         }
         catch (const json::parse_error& e)
@@ -1194,6 +1200,33 @@ TEST_CASE("BSON keys from contiguous and stream input")
         CHECK(from_vector == from_stream);
     }
 }
+
+TEST_CASE("BSON array element names")
+{
+    // an array's element names are not part of the value, so they are not
+    // passed on; error_handler_t::strict still rejects ill-formed UTF-8 in them
+    const std::vector<std::uint8_t> bson =
+    {
+        0x1D, 0x00, 0x00, 0x00, // size (little endian)
+        0x04, 'a', 0x00,        // entry: array "a"
+        0x15, 0x00, 0x00, 0x00, // size (little endian)
+        0x08, 0xFF, 0x00, 0x01, // entry: boolean named "\xFF", true
+        0x08, '1', '2', '3', '4', '5', '6', '7', '8', '9', 0x00, 0x00, // entry: boolean named "123456789", false
+        0x00,                   // end of the array
+        0x00                    // end of the document
+    };
+    const json expected = {{"a", {true, false}}};
+
+    CHECK(json::from_bson(bson) == expected);
+    CHECK(json::from_bson(bson, true, true, json::error_handler_t::replace) == expected);
+    CHECK(json::from_bson(bson, true, true, json::error_handler_t::ignore) == expected);
+
+    json _;
+    CHECK_THROWS_WITH_AS(_ = json::from_bson(bson, true, true, json::error_handler_t::strict), "[json.exception.parse_error.113] parse error at byte 14: syntax error while parsing BSON key: invalid string: ill-formed UTF-8 byte", json::parse_error&);
+
+    std::istringstream stream(std::string(reinterpret_cast<const char*>(bson.data()), bson.size()));
+    CHECK(json::from_bson(stream) == expected);
+}
 #endif
 
 TEST_CASE("Negative size of binary value")

tests/src/unit-json_view_from_json.cpp

@@ -39,7 +39,6 @@ using nlohmann::ordered_json_document;
 
 #ifdef JSON_HAS_CPP_17
     #include <optional>
-    #include <string_view>
 #endif
 
 // NLOHMANN_JSON_SERIALIZE_ENUM uses a static std::pair; same() compares floating-point values on purpose
@@ -470,70 +469,5 @@ TEST_CASE("json_view from_json")
 #endif
 }
 
-#ifdef JSON_HAS_CPP_17
-namespace view_from_json
-{
-// a string_view member is not copied: it points into the source text or, for a
-// string with escape sequences, into the buffer of decoded strings of the document
-struct named_view
-{
-    // initialized for GCC -Weffc++
-    // NOLINTNEXTLINE(readability-redundant-member-init)
-    std::string_view name{};
-    int n = 0;
-    NLOHMANN_DEFINE_TYPE_INTRUSIVE(named_view, name, n)
-};
-}  // namespace view_from_json
-
-TEST_CASE("json_view from_json: string_view members borrow from the document")
-{
-    using view_from_json::named_view;
-
-    // whether all of s is inside the bytes of text
-    const auto within = [](std::string_view s, std::string_view text)
-    {
-        const auto first = reinterpret_cast<std::uintptr_t>(text.data());
-        const auto begin = reinterpret_cast<std::uintptr_t>(s.data());
-        return begin >= first && begin + s.size() <= first + text.size();
-    };
-
-    SECTION("a string without escapes points into the source text")
-    {
-        const std::string text = R"({"name": "hello", "n": 1})";
-        const json_document d = json_document::parse(text);
-        REQUIRE_FALSE(d.owns_source());
-        const auto r = d.root().get<named_view>();
-        CHECK(r.name == "hello");
-        CHECK(r.n == 1);
-        CHECK(within(r.name, text));
-        CHECK(within(r.name, d.source()));
-    }
-
-    SECTION("a string with escapes points into the document, not into the source text")
-    {
-        const std::string text = R"({"name": "a\nb", "n": 2})";
-        json_document d = json_document::parse(text);
-        REQUIRE_FALSE(d.owns_source());
-        const auto r = d.root().get<named_view>();
-        CHECK(r.name == "a\nb");
-        CHECK(r.n == 2);
-        CHECK_FALSE(within(r.name, text));
-        // valid as long as the document is alive, even if the document is moved
-        const json_document moved = std::move(d);
-        CHECK(r.name == "a\nb");
-        CHECK(moved.root().get<named_view>().name == r.name);
-    }
-
-    SECTION("a document that owns its text keeps the members readable while it is alive")
-    {
-        const json_document d = json_document::parse(std::string(R"({"name": "owned", "n": 3})"));
-        REQUIRE(d.owns_source());
-        const auto r = d.root().get<named_view>();
-        CHECK(r.name == "owned");
-        CHECK(within(r.name, d.source()));
-    }
-}
-#endif
-
 DOCTEST_CLANG_SUPPRESS_WARNING_POP
 DOCTEST_GCC_SUPPRESS_WARNING_POP