Experimental support for BSON (de)serialization

include/nlohmann/detail/exceptions.hpp

@@ -93,6 +93,7 @@ json.exception.parse_error.109 | parse error: array index 'one' is not a number
 json.exception.parse_error.110 | parse error at 1: cannot read 2 bytes from vector | When parsing CBOR or MessagePack, the byte vector ends before the complete value has been read.
 json.exception.parse_error.112 | parse error at 1: error reading CBOR; last byte: 0xF8 | Not all types of CBOR or MessagePack are supported. This exception occurs if an unsupported byte was read.
 json.exception.parse_error.113 | parse error at 2: expected a CBOR string; last byte: 0x98 | While parsing a map key, a value that is not a string has been read.
+json.exception.parse_error.114 | parse error: Unsupported BSON record type 0x0F | The parsing of the corresponding BSON record type is not implemented (yet).
 
 @note For an input with n bytes, 1 is the index of the first character and n+1
       is the index of the terminating null byte or the end of file. This also
@@ -236,6 +237,7 @@ json.exception.type_error.313 | invalid value to unflatten | The @ref unflatten
 json.exception.type_error.314 | only objects can be unflattened | The @ref unflatten function only works for an object whose keys are JSON Pointers.
 json.exception.type_error.315 | values in object must be primitive | The @ref unflatten function only works for an object whose keys are JSON Pointers and whose values are primitive.
 json.exception.type_error.316 | invalid UTF-8 byte at index 10: 0x7E | The @ref dump function only works with UTF-8 encoded strings; that is, if you assign a `std::string` to a JSON value, make sure it is UTF-8 encoded. |
+json.exception.type_error.317 | JSON value cannot be serialized to requested format | The dynamic type of the object cannot be represented in the requested serialization format (e.g. a raw `true` or `null` JSON object cannot be serialized to BSON) |
 
 @liveexample{The following code shows how a `type_error` exception can be
 caught.,type_error}
@@ -278,8 +280,9 @@ json.exception.out_of_range.403 | key 'foo' not found | The provided key was not
 json.exception.out_of_range.404 | unresolved reference token 'foo' | A reference token in a JSON Pointer could not be resolved.
 json.exception.out_of_range.405 | JSON pointer has no parent | The JSON Patch operations 'remove' and 'add' can not be applied to the root element of the JSON value.
 json.exception.out_of_range.406 | number overflow parsing '10E1000' | A parsed number could not be stored as without changing it to NaN or INF.
-json.exception.out_of_range.407 | number overflow serializing '9223372036854775808' | UBJSON only supports integers numbers up to 9223372036854775807. |
+json.exception.out_of_range.407 | number overflow serializing '9223372036854775808' | UBJSON and BSON only support integer numbers up to 9223372036854775807. |
 json.exception.out_of_range.408 | excessive array size: 8658170730974374167 | The size (following `#`) of an UBJSON array or object exceeds the maximal capacity. |
+json.exception.out_of_range.409 | BSON key cannot contain code point U+0000 (at byte 2) | Key identifiers to be serialized to BSON cannot contain code point U+0000, since the key is stored as zero-terminated c-string |
 
 @liveexample{The following code shows how an `out_of_range` exception can be
 caught.,out_of_range}

include/nlohmann/detail/input/binary_reader.hpp

@@ -80,6 +80,10 @@ class binary_reader
                 result = parse_ubjson_internal();
                 break;
 
+            case input_format_t::bson:
+                result = parse_bson_internal();
+                break;
+
             // LCOV_EXCL_START
             default:
                 assert(false);
@@ -121,6 +125,207 @@ class binary_reader
     }
 
   private:
+
+    /*!
+    @brief Parses a C-style string from the BSON input.
+    @param [out] result A reference to the string variable where the read string
+                        is to be stored.
+    @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)
+    {
+        auto out = std::back_inserter(result);
+        while (true)
+        {
+            get();
+            if (JSON_UNLIKELY(not unexpect_eof(input_format_t::bson, "cstring")))
+            {
+                return false;
+            }
+            if (current == 0x00)
+            {
+                return true;
+            }
+            *out++ = static_cast<char>(current);
+        }
+
+        return true;
+    }
+
+    /*!
+    @brief Parses a zero-terminated string of length @a len from the BSON input.
+    @param [in]  len    The length (including the zero-byte at the end) of the string to be read.
+    @param [out] result A reference to the string variable where the read string
+                        is to be stored.
+    @tparam NumberType The type of the length @a len
+    @pre len > 0
+    @return `true` if the string was successfully parsed
+    */
+    template <typename NumberType>
+    bool get_bson_string(const NumberType len, string_t& result)
+    {
+        return get_string(input_format_t::bson, len - static_cast<NumberType>(1), result)
+               && get() != std::char_traits<char>::eof();
+    }
+
+    /*!
+    @return A hexadecimal string representation of the given @a byte
+    @param byte The byte to convert to a string
+    */
+    static std::string byte_hexstring(unsigned char byte)
+    {
+        char cr[3];
+        snprintf(cr, sizeof(cr), "%02hhX", byte);
+        return std::string{cr};
+    }
+
+    /*!
+    @brief Read a BSON document element of the given @a element_type.
+    @param element_type The BSON element type, c.f. http://bsonspec.org/spec.html
+    @param element_type_parse_position The position in the input stream, where the `element_type` was read.
+    @warning Not all BSON element types are supported yet. An unsupported @a element_type will
+             give rise to a parse_error.114: Unsupported BSON record type 0x...
+    @return whether a valid BSON-object/array was passed to the SAX parser
+    */
+    bool parse_bson_element_internal(int element_type, std::size_t element_type_parse_position)
+    {
+        switch (element_type)
+        {
+            case 0x01: // double
+            {
+                double number;
+                return get_number<double, true>(input_format_t::bson, number)
+                       && sax->number_float(static_cast<number_float_t>(number), "");
+            }
+            case 0x02: // string
+            {
+                std::int32_t len;
+                string_t value;
+                return get_number<std::int32_t, true>(input_format_t::bson, len)
+                       && get_bson_string(len, value)
+                       && sax->string(value);
+            }
+            case 0x08: // boolean
+            {
+                return sax->boolean(static_cast<bool>(get()));
+            }
+            case 0x10: // int32
+            {
+                std::int32_t value;
+                return get_number<std::int32_t, true>(input_format_t::bson, value)
+                       && sax->number_integer(static_cast<std::int32_t>(value));
+            }
+            case 0x12: // int64
+            {
+                std::int64_t value;
+                return get_number<std::int64_t, true>(input_format_t::bson, value)
+                       && sax->number_integer(static_cast<std::int64_t>(value));
+            }
+            case 0x0A: // null
+            {
+                return sax->null();
+            }
+            case 0x03: // object
+            {
+                return parse_bson_internal();
+            }
+            case 0x04: // array
+            {
+                return parse_bson_array();
+            }
+            default: // anything else not supported (yet)
+            {
+                auto element_type_str = byte_hexstring(element_type);
+                return sax->parse_error(element_type_parse_position, element_type_str, parse_error::create(114, element_type_parse_position, "Unsupported BSON record type 0x" + element_type_str));
+            }
+        }
+    }
+
+    /*!
+    @brief Read a BSON element list (as specified in the BSON-spec) from the input
+           and passes it to the SAX-parser.
+           The same binary layout is used for objects and arrays, hence it must
+           be indicated with the argument @a is_array which one is expected
+           (true --> array, false --> object).
+    @param is_array Determines if the element list being read is to be treated as
+           an object (@a is_array == false), or as an array (@a is_array == true).
+    @return whether a valid BSON-object/array was passed to the SAX parser
+    */
+    bool parse_bson_element_list(bool is_array)
+    {
+        while (auto element_type = get())
+        {
+            if (JSON_UNLIKELY(not unexpect_eof(input_format_t::bson, "element list")))
+            {
+                return false;
+            }
+
+            const std::size_t element_type_parse_position = chars_read;
+            string_t key;
+            if (JSON_UNLIKELY(not get_bson_cstr(key)))
+            {
+                return false;
+            }
+
+            if (!is_array)
+            {
+                sax->key(key);
+            }
+
+            if (JSON_UNLIKELY(not parse_bson_element_internal(element_type, element_type_parse_position)))
+            {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    /*!
+    @brief Reads an array from the BSON input and passes it to the SAX-parser.
+    @return whether a valid BSON-array was passed to the SAX parser
+    */
+    bool parse_bson_array()
+    {
+        std::int32_t documentSize;
+        get_number<std::int32_t, true>(input_format_t::bson, documentSize);
+
+        if (JSON_UNLIKELY(not sax->start_array(-1)))
+        {
+            return false;
+        }
+
+        if (JSON_UNLIKELY(not parse_bson_element_list(/*is_array*/true)))
+        {
+            return false;
+        }
+
+        return sax->end_array();
+    }
+
+    /*!
+    @brief Reads in a BSON-object and pass it to the SAX-parser.
+    @return whether a valid BSON-value was passed to the SAX parser
+    */
+    bool parse_bson_internal()
+    {
+        std::int32_t documentSize;
+        get_number<std::int32_t, true>(input_format_t::bson, documentSize);
+
+        if (JSON_UNLIKELY(not sax->start_object(-1)))
+        {
+            return false;
+        }
+
+        if (JSON_UNLIKELY(not parse_bson_element_list(/*is_array*/false)))
+        {
+            return false;
+        }
+
+        return sax->end_object();
+    }
+
     /*!
     @param[in] get_char  whether a new character should be retrieved from the
                          input (true, default) or whether the last read
@@ -875,7 +1080,7 @@ class binary_reader
           bytes in CBOR, MessagePack, and UBJSON are stored in network order
           (big endian) and therefore need reordering on little endian systems.
     */
-    template<typename NumberType>
+    template<typename NumberType, bool InputIsLittleEndian = false>
     bool get_number(const input_format_t format, NumberType& result)
     {
         // step 1: read input into array with system's byte order
@@ -889,7 +1094,7 @@ class binary_reader
             }
 
             // reverse byte order prior to conversion if necessary
-            if (is_little_endian)
+            if (is_little_endian && !InputIsLittleEndian)
             {
                 vec[sizeof(NumberType) - i - 1] = static_cast<uint8_t>(current);
             }
@@ -904,6 +1109,7 @@ class binary_reader
         return true;
     }
 
+
     /*!
     @brief create a string by reading characters from the input
 
@@ -1715,6 +1921,10 @@ class binary_reader
                 error_msg += "UBJSON";
                 break;
 
+            case input_format_t::bson:
+                error_msg += "BSON";
+                break;
+
             // LCOV_EXCL_START
             default:
                 assert(false);

include/nlohmann/detail/input/input_adapters.hpp

@@ -18,7 +18,7 @@ namespace nlohmann
 namespace detail
 {
 /// the supported input formats
-enum class input_format_t { json, cbor, msgpack, ubjson };
+enum class input_format_t { json, cbor, msgpack, ubjson, bson };
 
 ////////////////////
 // input adapters //