BSON: Support empty objects

include/nlohmann/detail/input/binary_reader.hpp

@@ -127,25 +127,18 @@ class binary_reader
 
     bool parse_bson_internal()
     {
-        int docLen = 0;
+        std::int32_t documentSize;
-        int byte;
+        get_number_little_endian(documentSize);
-        for (int i = 0; i < 4; ++i)
+
+        if (not JSON_UNLIKELY(sax->start_object(documentSize - 5)))
         {
-            byte = get();
-            if (JSON_UNLIKELY(current == std::char_traits<char>::eof()))
-            {
-                if (i == 1)
-                {
-                    return sax->boolean(docLen != 0x00);
-                }
             return false;
         }
-            docLen |= static_cast<std::int32_t>(byte) << 8 * i;
-        }
 
-        //sax->null();
+        const auto result = sax->end_object();
+
         get();
-        return true;
+        return result;
     }
 
     /*!
@@ -927,6 +920,35 @@ class binary_reader
         return true;
     }
 
+    template<typename NumberType>
+    bool get_number_little_endian(NumberType& result)
+    {
+        // step 1: read input into array with system's byte order
+        std::array<uint8_t, sizeof(NumberType)> vec;
+        for (std::size_t i = 0; i < sizeof(NumberType); ++i)
+        {
+            get();
+            if (JSON_UNLIKELY(not unexpect_eof()))
+            {
+                return false;
+            }
+
+            // reverse byte order prior to conversion if necessary
+            if (!is_little_endian)
+            {
+                vec[sizeof(NumberType) - i - 1] = static_cast<uint8_t>(current);
+            }
+            else
+            {
+                vec[i] = static_cast<uint8_t>(current); // LCOV_EXCL_LINE
+            }
+        }
+
+        // step 2: convert array into number of type T and return
+        std::memcpy(&result, vec.data(), sizeof(NumberType));
+        return true;
+    }
+
     /*!
     @brief create a string by reading characters from the input
 

include/nlohmann/detail/output/binary_writer.hpp

@@ -684,7 +684,8 @@ class binary_writer
     void write_bson_object(const BasicJsonType& j)
     {
         assert(j.type() == value_t::object);
-
+        write_number_little_endian(5);
+        oa->write_character(static_cast<CharType>(0x00));
     }
 
     /*!

single_include/nlohmann/json.hpp

@@ -6068,25 +6068,18 @@ class binary_reader
 
     bool parse_bson_internal()
     {
-        int docLen = 0;
+        std::int32_t documentSize;
-        int byte;
+        get_number_little_endian(documentSize);
-        for (int i = 0; i < 4; ++i)
+
+        if (not JSON_UNLIKELY(sax->start_object(documentSize - 5)))
         {
-            byte = get();
-            if (JSON_UNLIKELY(current == std::char_traits<char>::eof()))
-            {
-                if (i == 1)
-                {
-                    return sax->boolean(docLen != 0x00);
-                }
             return false;
         }
-            docLen |= static_cast<std::int32_t>(byte) << 8 * i;
-        }
 
-        //sax->null();
+        const auto result = sax->end_object();
+
         get();
-        return true;
+        return result;
     }
 
     /*!
@@ -6868,6 +6861,35 @@ class binary_reader
         return true;
     }
 
+    template<typename NumberType>
+    bool get_number_little_endian(NumberType& result)
+    {
+        // step 1: read input into array with system's byte order
+        std::array<uint8_t, sizeof(NumberType)> vec;
+        for (std::size_t i = 0; i < sizeof(NumberType); ++i)
+        {
+            get();
+            if (JSON_UNLIKELY(not unexpect_eof()))
+            {
+                return false;
+            }
+
+            // reverse byte order prior to conversion if necessary
+            if (!is_little_endian)
+            {
+                vec[sizeof(NumberType) - i - 1] = static_cast<uint8_t>(current);
+            }
+            else
+            {
+                vec[i] = static_cast<uint8_t>(current); // LCOV_EXCL_LINE
+            }
+        }
+
+        // step 2: convert array into number of type T and return
+        std::memcpy(&result, vec.data(), sizeof(NumberType));
+        return true;
+    }
+
     /*!
     @brief create a string by reading characters from the input
 
@@ -8354,7 +8376,8 @@ class binary_writer
     void write_bson_object(const BasicJsonType& j)
     {
         assert(j.type() == value_t::object);
-
+        write_number_little_endian(5);
+        oa->write_character(static_cast<CharType>(0x00));
     }
 
     /*!

test/src/unit-bson.cpp

@@ -36,7 +36,7 @@ using nlohmann::json;
 
 TEST_CASE("BSON")
 {
-    SECTION("individual values")
+    SECTION("individual values not supported")
     {
         SECTION("discarded")
         {
@@ -66,5 +66,50 @@ TEST_CASE("BSON")
                 REQUIRE_THROWS_AS(json::to_bson(j), json::type_error);
             }
         }
+
+        SECTION("number")
+        {
+            json j = 42;
+            REQUIRE_THROWS_AS(json::to_bson(j), json::type_error);
+        }
+
+        SECTION("float")
+        {
+            json j = 4.2;
+            REQUIRE_THROWS_AS(json::to_bson(j), json::type_error);
+        }
+
+        SECTION("string")
+        {
+            json j = "not supported";
+            REQUIRE_THROWS_AS(json::to_bson(j), json::type_error);
+        }
+
+        SECTION("array")
+        {
+            json j = std::vector<int> {1, 2, 3, 4, 5, 6, 7};
+            REQUIRE_THROWS_AS(json::to_bson(j), json::type_error);
+        }
+    }
+
+    SECTION("objects")
+    {
+        SECTION("empty object")
+        {
+            json j = json::object();
+            std::vector<uint8_t> expected =
+            {
+                0x05, 0x00, 0x00, 0x00, // size (little endian)
+                // no entries
+                0x00 // end marker
+            };
+
+            const auto result = json::to_bson(j);
+            CHECK(result == expected);
+
+            // roundtrip
+            CHECK(json::from_bson(result) == j);
+            CHECK(json::from_bson(result, true, false) == j);
+        }
     }
 }