feat: support the JSON null type in tr_variant (#7255)

libtransmission/variant-benc.cc

@@ -277,6 +277,11 @@ namespace to_string_helpers
 {
 using OutBuf = libtransmission::StackBuffer<1024U * 8U, std::byte>;
 
+void saveNullFunc(tr_variant const& /*var*/, std::nullptr_t /*val*/, void* vout)
+{
+    static_cast<OutBuf*>(vout)->add("0:"sv);
+}
+
 void saveIntFunc(tr_variant const& /*var*/, int64_t const val, void* vout)
 {
     auto out = static_cast<OutBuf*>(vout);
@@ -338,6 +343,7 @@ std::string tr_variant_serde::to_benc_string(tr_variant const& var)
     using namespace to_string_helpers;
 
     static auto constexpr Funcs = WalkFuncs{
+        saveNullFunc, //
         saveIntFunc, //
         saveBoolFunc, //
         saveRealFunc, //

libtransmission/variant-json.cc

@@ -50,7 +50,7 @@ struct json_to_variant_handler : public rapidjson::BaseReaderHandler<>
 
     bool Null()
     {
-        *get_leaf() = tr_variant::unmanaged_string("");
+        *get_leaf() = nullptr;
         return true;
     }
 
@@ -311,6 +311,11 @@ private:
 
 using writer_var_t = std::variant<rapidjson::Writer<string_output_stream>, rapidjson::PrettyWriter<string_output_stream>>;
 
+void jsonNullFunc(tr_variant const& /*var*/, std::nullptr_t /*val*/, void* vdata)
+{
+    std::visit([](auto&& writer) { writer.Null(); }, *static_cast<writer_var_t*>(vdata));
+}
+
 void jsonIntFunc(tr_variant const& /*var*/, int64_t const val, void* vdata)
 {
     std::visit([val](auto&& writer) { writer.Int64(val); }, *static_cast<writer_var_t*>(vdata));
@@ -363,6 +368,7 @@ std::string tr_variant_serde::to_json_string(tr_variant const& var) const
     using namespace to_string_helpers;
 
     static auto constexpr Funcs = WalkFuncs{
+        jsonNullFunc, //
         jsonIntFunc, //
         jsonBoolFunc, //
         jsonRealFunc, //

libtransmission/variant.cc

@@ -208,6 +208,10 @@ void tr_variant::Merge::operator()(std::monostate const& src)
 {
     tgt_ = src;
 }
+void tr_variant::Merge::operator()(std::nullptr_t const& src)
+{
+    tgt_ = src;
+}
 void tr_variant::Merge::operator()(bool const& src)
 {
     tgt_ = src;
@@ -761,6 +765,10 @@ void tr_variant_serde::walk(tr_variant const& top, WalkFuncs const& walk_funcs,
 
         switch (variant_index(v))
         {
+        case tr_variant::NullIndex:
+            walk_funcs.null_func(*v, *v->get_if<tr_variant::NullIndex>(), user_data);
+            break;
+
         case tr_variant::BoolIndex:
             walk_funcs.bool_func(*v, *v->get_if<tr_variant::BoolIndex>(), user_data);
             break;

libtransmission/variant.h

@@ -30,15 +30,16 @@
 struct tr_variant
 {
 public:
-    enum Type : size_t
+    enum Type : uint8_t
     {
-        NoneIndex = 0,
-        BoolIndex = 1,
-        IntIndex = 2,
-        DoubleIndex = 3,
-        StringIndex = 4,
-        VectorIndex = 5,
-        MapIndex = 6
+        NoneIndex,
+        NullIndex,
+        BoolIndex,
+        IntIndex,
+        DoubleIndex,
+        StringIndex,
+        VectorIndex,
+        MapIndex
     };
 
     using Vector = std::vector<tr_variant>;
@@ -239,7 +240,11 @@ public:
     template<typename Val>
     tr_variant& operator=(Val value)
     {
-        if constexpr (std::is_same_v<Val, std::string_view>)
+        if constexpr (std::is_same_v<Val, std::nullptr_t>)
+        {
+            val_.emplace<std::nullptr_t>(value);
+        }
+        else if constexpr (std::is_same_v<Val, std::string_view>)
         {
             val_.emplace<StringHolder>(std::string{ value });
         }
@@ -392,6 +397,7 @@ private:
     public:
         explicit Merge(tr_variant& tgt);
         void operator()(std::monostate const& src);
+        void operator()(std::nullptr_t const& src);
         void operator()(bool const& src);
         void operator()(int64_t const& src);
         void operator()(double const& src);
@@ -403,7 +409,7 @@ private:
         tr_variant& tgt_;
     };
 
-    std::variant<std::monostate, bool, int64_t, double, StringHolder, Vector, Map> val_;
+    std::variant<std::monostate, std::nullptr_t, bool, int64_t, double, StringHolder, Vector, Map> val_;
 };
 
 template<>
@@ -567,6 +573,7 @@ private:
 
     struct WalkFuncs
     {
+        void (*null_func)(tr_variant const& var, std::nullptr_t val, void* user_data);
         void (*int_func)(tr_variant const& var, int64_t val, void* user_data);
         void (*bool_func)(tr_variant const& var, bool val, void* user_data);
         void (*double_func)(tr_variant const& var, double val, void* user_data);

tests/libtransmission/json-test.cc

@@ -61,7 +61,23 @@ TEST_P(JSONTest, testElements)
         "  \"null\": null }"
     };
 
-    auto const var = tr_variant_serde::json().inplace().parse(In).value_or(tr_variant{});
+    // Same as In, just formatted differently
+    static auto constexpr Out = std::string_view{
+        // clang-format off
+        "{"
+            "\"escaped\":\"bell \\b formfeed \\f linefeed \\n carriage return \\r tab \\t\","
+            "\"false\":false,"
+            "\"float\":6.5,"
+            "\"int\":5,"
+            "\"null\":null,"
+            "\"string\":\"hello world\","
+            "\"true\":true"
+        "}"
+        // clang-format on
+    };
+
+    auto serde = tr_variant_serde::json().inplace().compact();
+    auto var = serde.parse(In).value_or(tr_variant{});
     auto const* const map = var.get_if<tr_variant::Map>();
     ASSERT_NE(map, nullptr);
 
@@ -89,9 +105,10 @@ TEST_P(JSONTest, testElements)
     ASSERT_TRUE(b);
     EXPECT_FALSE(*b);
 
-    sv = map->value_if<std::string_view>(tr_quark_new("null"sv));
-    ASSERT_TRUE(sv);
-    EXPECT_EQ(""sv, *sv);
+    auto n = map->value_if<std::nullptr_t>(tr_quark_new("null"sv));
+    EXPECT_TRUE(n);
+
+    EXPECT_EQ(serde.to_string(var), Out);
 }
 
 TEST_P(JSONTest, testUtf8)