fix json parser polymorphic support

mirai-api-http/src/main/kotlin/net/mamoe/mirai/api/http/Session.kt

@@ -87,9 +87,7 @@ abstract class Session internal constructor(
  *
  * TempSession在建立180s内没有转变为[AuthedSession]应被清除
  */
-class TempSession internal constructor(coroutineContext: CoroutineContext) : Session(coroutineContext) {
-
-}
+class TempSession internal constructor(coroutineContext: CoroutineContext) : Session(coroutineContext)
 
 /**
  * 任何[TempSession]认证后转化为一个[AuthedSession]

mirai-api-http/src/main/kotlin/net/mamoe/mirai/api/http/dto/DTO.kt

@@ -2,19 +2,10 @@ package net.mamoe.mirai.api.http.dto
 
 import kotlinx.serialization.*
 import kotlinx.serialization.json.Json
+import kotlinx.serialization.modules.SerializersModule
 
 interface DTO
 
-object MiraiJson {
-//    val json = Json(context = SerializersModule {
-//        polymorphic(MessagePacketDTO.serializer()) {
-//            GroupMessagePacketDTO::class with GroupMessagePacketDTO.serializer()
-//            FriendMessagePacketDTO::class with FriendMessagePacketDTO.serializer()
-//        }
-//    })
-    val json = Json
-}
-
 // 解析失败时直接返回null，由路由判断响应400状态
 @UseExperimental(ImplicitReflectionSerializer::class)
 inline fun <reified T : Any> String.jsonParseOrNull(
@@ -32,7 +23,6 @@ inline fun <reified T : Any> T.toJson(
             else MiraiJson.json.stringify(serializer, this)
 
 
-
 // 序列化列表时，stringify需要使用的泛型是T，而非List<T>
 // 因为使用的stringify的stringify(objs: List<T>)重载
 @UseExperimental(ImplicitReflectionSerializer::class, UnstableDefault::class)
@@ -40,3 +30,25 @@ inline fun <reified T : Any> List<T>.toJson(
     serializer: SerializationStrategy<List<T>>? = null
 ): String = if (serializer == null) MiraiJson.json.stringify(this)
 else MiraiJson.json.stringify(serializer, this)
+
+
+/**
+ * Json解析规则，需要注册支持的多态的类
+ */
+object MiraiJson {
+    val json = Json(context = SerializersModule {
+        polymorphic(MessagePacketDTO.serializer()) {
+            GroupMessagePacketDTO::class with GroupMessagePacketDTO.serializer()
+            FriendMessagePacketDTO::class with FriendMessagePacketDTO.serializer()
+            UnKnownMessagePacketDTO::class with UnKnownMessagePacketDTO.serializer()
+        }
+        polymorphic(MessageDTO.serializer()) {
+            AtDTO::class with AtDTO.serializer()
+            FaceDTO::class with FaceDTO.serializer()
+            PlainDTO::class with PlainDTO.serializer()
+            ImageDTO::class with ImageDTO.serializer()
+            XmlDTO::class with XmlDTO.serializer()
+            UnknownMessageDTO::class with UnknownMessageDTO.serializer()
+        }
+    })
+}
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