diff --git a/build.gradle.kts b/build.gradle.kts
index 41260dc15..8e78ba4f2 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -19,7 +19,8 @@ buildscript {
         classpath("com.android.tools.build:gradle:3.5.3")
         classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion")
         classpath("com.github.jengelman.gradle.plugins:shadow:5.2.0")
-        classpath("org.jetbrains.kotlin:kotlin-serialization:$kotlinVersion")
+        @kotlin.Suppress("GradleDependency") // 1.3.70 有 bug, 无法编译添加 SerialInfo
+        classpath("org.jetbrains.kotlin:kotlin-serialization:1.3.61") // 不要用 $kotlinVersion
         classpath("org.jetbrains.kotlinx:atomicfu-gradle-plugin:$atomicFuVersion")
     }
 }
diff --git a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/IOFormat.kt b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/IOFormat.kt
index a59013888..8f3f2a359 100644
--- a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/IOFormat.kt
+++ b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/IOFormat.kt
@@ -8,7 +8,7 @@ import kotlinx.serialization.SerializationStrategy
 
 interface IOFormat : SerialFormat {
 
-    fun <T> dump(serializer: SerializationStrategy<T>, input: Input): ByteArray
+    fun <T> dump(serializer: SerializationStrategy<T>, output: Output): ByteArray
 
-    fun <T> load(deserializer: DeserializationStrategy<T>, output: Output): T
+    fun <T> load(deserializer: DeserializationStrategy<T>, input: Input): T
 }
diff --git a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/jce/JceDecoder.kt b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/jce/JceDecoder.kt
index ab84bc36d..05fd2529a 100644
--- a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/jce/JceDecoder.kt
+++ b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/jce/JceDecoder.kt
@@ -10,13 +10,14 @@
 package net.mamoe.mirai.qqandroid.io.serialization.jce
 
 import kotlinx.serialization.*
+import kotlinx.serialization.builtins.ByteArraySerializer
 import kotlinx.serialization.internal.TaggedDecoder
 import kotlinx.serialization.modules.SerialModule
-import kotlinx.serialization.protobuf.ProtoId
+import net.mamoe.mirai.qqandroid.io.serialization.Jce
 
 
 @OptIn(InternalSerializationApi::class) // 将来 kotlinx 修改后再复制过来 mirai.
-private class JceDecoder(
+internal class JceDecoder(
     val jce: JceInput, override val context: SerialModule
 ) : TaggedDecoder<JceTag>() {
     override val updateMode: UpdateMode
@@ -25,23 +26,103 @@ private class JceDecoder(
     override fun SerialDescriptor.getTag(index: Int): JceTag {
         val annotations = this.getElementAnnotations(index)
 
-        val id = (annotations.asSequence().filterIsInstance<JceId>().firstOrNull()?.id
-            ?: annotations.asSequence().filterIsInstance<ProtoId>().firstOrNull()?.id) // 旧版本兼容
-            ?: error("cannot find @JceId or @ProtoId for ${this.getElementName(index)} in ${this.serialName}")
+        val id = annotations.filterIsInstance<JceId>().single().id
+        // ?: error("cannot find @JceId or @ProtoId for ${this.getElementName(index)} in ${this.serialName}")
+        println("getTag: ${this.getElementName(index)}=$id")
 
         return JceTag(
             id,
             this.getElementDescriptor(index).isNullable
         )
     }
-
-
-    override fun beginStructure(descriptor: SerialDescriptor, vararg typeParams: KSerializer<*>): CompositeDecoder {
-        TODO("Not yet implemented")
+    fun SerialDescriptor.getJceTagId(index: Int): Int {
+        return getElementAnnotations(index).filterIsInstance<JceId>().single().id
     }
 
+
+    private val ByteArraySerializer = ByteArraySerializer()
+
+    // TODO: 2020/3/6 can be object
+    private inner class SimpleByteArrayReader() : CompositeDecoder by this {
+        override fun decodeSequentially(): Boolean = true
+        override fun decodeByteElement(descriptor: SerialDescriptor, index: Int): Byte {
+            return jce.input.readByte()
+        }
+
+        override fun decodeElementIndex(descriptor: SerialDescriptor): Int {
+            return 0
+        }
+
+        override fun decodeCollectionSize(descriptor: SerialDescriptor): Int {
+            return jce.useHead { jce.readJceIntValue(it) }
+        }
+    }
+
+    // TODO: 2020/3/6 can be object
+    private inner class ListReader() : CompositeDecoder by this {
+        override fun decodeSequentially(): Boolean = false
+        override fun decodeElementIndex(descriptor: SerialDescriptor): Int {
+            return 0
+        }
+
+        override fun decodeCollectionSize(descriptor: SerialDescriptor): Int {
+            return jce.useHead { jce.readJceIntValue(it) }
+        }
+    }
+
+    override fun beginStructure(descriptor: SerialDescriptor, vararg typeParams: KSerializer<*>): CompositeDecoder {
+        if (descriptor == ByteArraySerializer.descriptor) {
+            return jce.skipToHeadAndUseIfPossibleOrFail(popTag().id) {
+                when (it.type) {
+                    Jce.SIMPLE_LIST -> SimpleByteArrayReader()
+                    Jce.LIST -> ListReader()
+                    else -> error("type mismatch. Expected SIMPLE_LIST or LIST, got ${it.type} instead")
+                }
+            }
+        }
+        return when (descriptor.kind) {
+            StructureKind.MAP -> {
+                error("map")
+            }
+            StructureKind.LIST -> ListReader()
+
+            else -> this
+        }
+    }
+
+    override fun <T> decodeSerializableValue(deserializer: DeserializationStrategy<T>): T {
+        println("decodeSerializableValue: ${deserializer.descriptor}")
+        return super.decodeSerializableValue(deserializer)
+    }
+
+    private var currentIndex = 0
+
+
+    override fun decodeSequentially(): Boolean = false
     override fun decodeElementIndex(descriptor: SerialDescriptor): Int {
-        TODO("Not yet implemented")
+        val jceHead = jce.currentHeadOrNull ?: return CompositeDecoder.READ_DONE
+        repeat(descriptor.elementsCount){
+            val tag = descriptor.getJceTagId(it)
+            if (tag == jceHead.tag) {
+                return it
+            }
+        }
+
+        return CompositeDecoder.READ_DONE // optional support
+    }
+
+    override fun decodeTaggedNull(tag: JceTag): Nothing? {
+        println("decodeTaggedNull")
+        return super.decodeTaggedNull(tag)
+    }
+
+    override fun <T : Any> decodeNullableSerializableValue(deserializer: DeserializationStrategy<T?>): T? {
+        return super.decodeNullableSerializableValue(deserializer)
+    }
+
+    override fun decodeTaggedValue(tag: JceTag): Any {
+        println("decodeTaggedValue")
+        return super.decodeTaggedValue(tag)
     }
 
     override fun decodeTaggedInt(tag: JceTag): Int =
@@ -77,7 +158,6 @@ private class JceDecoder(
     }
 
     override fun decodeTaggedNotNullMark(tag: JceTag): Boolean {
-        println("!! decodeTaggedNotNullMark: $tag")
-        return super.decodeTaggedNotNullMark(tag)
+        return jce.skipToHeadOrNull(tag.id) != null
     }
 }
diff --git a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/jce/JceInput.kt b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/jce/JceInput.kt
index 9e6edcc11..637551dac 100644
--- a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/jce/JceInput.kt
+++ b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/jce/JceInput.kt
@@ -18,7 +18,7 @@ import net.mamoe.mirai.utils.io.readString
 /**
  * Jce Input. 需要手动管理 head.
  */
-class JceInput(
+internal class JceInput(
     val input: Input, val charset: JceCharset
 ) {
     private var _head: JceHead? = null
@@ -95,7 +95,7 @@ class JceInput(
     }
 
     tailrec fun skipToHeadOrNull(tag: Int): JceHead? {
-        val current: JceHead = currentHead // no backing field
+        val current: JceHead = currentHeadOrNull ?: return null // no backing field
 
         return when {
             current.tag > tag -> null // tag 大了，即找不到
@@ -167,6 +167,7 @@ class JceInput(
 
     // region readers
     fun readJceIntValue(head: JceHead): Int {
+        println("readJceIntValue: $head")
         return when (head.type) {
             Jce.ZERO_TYPE -> 0
             Jce.BYTE -> input.readByte().toInt()
@@ -197,6 +198,7 @@ class JceInput(
     }
 
     fun readJceByteValue(head: JceHead): Byte {
+        println("readJceByteValue: $head")
         return when (head.type) {
             Jce.ZERO_TYPE -> 0
             Jce.BYTE -> input.readByte()
diff --git a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/jce/JceNew.kt b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/jce/JceNew.kt
index 44169bf37..410b23c3b 100644
--- a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/jce/JceNew.kt
+++ b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/jce/JceNew.kt
@@ -9,30 +9,15 @@
 
 package net.mamoe.mirai.qqandroid.io.serialization.jce
 
-import io.ktor.utils.io.core.*
-import kotlinx.serialization.*
-import kotlinx.serialization.internal.TaggedDecoder
+import io.ktor.utils.io.core.Input
+import io.ktor.utils.io.core.Output
+import kotlinx.serialization.DeserializationStrategy
+import kotlinx.serialization.SerialFormat
+import kotlinx.serialization.SerializationStrategy
 import kotlinx.serialization.modules.EmptyModule
 import kotlinx.serialization.modules.SerialModule
-import kotlinx.serialization.protobuf.ProtoId
 import net.mamoe.mirai.qqandroid.io.serialization.IOFormat
-import net.mamoe.mirai.qqandroid.io.serialization.Jce
-import net.mamoe.mirai.qqandroid.io.serialization.Jce.Companion.BYTE
-import net.mamoe.mirai.qqandroid.io.serialization.Jce.Companion.DOUBLE
-import net.mamoe.mirai.qqandroid.io.serialization.Jce.Companion.FLOAT
-import net.mamoe.mirai.qqandroid.io.serialization.Jce.Companion.INT
-import net.mamoe.mirai.qqandroid.io.serialization.Jce.Companion.LIST
-import net.mamoe.mirai.qqandroid.io.serialization.Jce.Companion.LONG
-import net.mamoe.mirai.qqandroid.io.serialization.Jce.Companion.MAP
-import net.mamoe.mirai.qqandroid.io.serialization.Jce.Companion.SHORT
-import net.mamoe.mirai.qqandroid.io.serialization.Jce.Companion.SIMPLE_LIST
-import net.mamoe.mirai.qqandroid.io.serialization.Jce.Companion.STRING1
-import net.mamoe.mirai.qqandroid.io.serialization.Jce.Companion.STRING4
-import net.mamoe.mirai.qqandroid.io.serialization.Jce.Companion.STRUCT_BEGIN
-import net.mamoe.mirai.qqandroid.io.serialization.Jce.Companion.STRUCT_END
-import net.mamoe.mirai.qqandroid.io.serialization.Jce.Companion.ZERO_TYPE
 import net.mamoe.mirai.qqandroid.io.serialization.JceCharset
-import net.mamoe.mirai.utils.io.readString
 
 /**
  * Jce 数据结构序列化和反序列化器.
@@ -40,18 +25,19 @@ import net.mamoe.mirai.utils.io.readString
  * @author Him188
  */
 class JceNew(
-    override val context: SerialModule
+    override val context: SerialModule,
+    val charset: JceCharset
 ) : SerialFormat, IOFormat {
-    companion object Default : IOFormat by JceNew(
-        EmptyModule
-    )
-
-    override fun <T> dump(serializer: SerializationStrategy<T>, input: Input): ByteArray {
+    override fun <T> dump(serializer: SerializationStrategy<T>, output: Output): ByteArray {
         TODO("Not yet implemented")
     }
 
-    override fun <T> load(deserializer: DeserializationStrategy<T>, output: Output): T {
-        TODO("Not yet implemented")
+    override fun <T> load(deserializer: DeserializationStrategy<T>, input: Input): T {
+        return JceDecoder(JceInput(input, charset), context).decodeSerializableValue(deserializer)
     }
 
+    companion object {
+        val UTF_8 = JceNew(EmptyModule, JceCharset.UTF8)
+        val GBK = JceNew(EmptyModule, JceCharset.GBK)
+    }
 }
\ No newline at end of file
diff --git a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/jce/common.kt b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/jce/common.kt
index eefd29041..a1f39126d 100644
--- a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/jce/common.kt
+++ b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/io/serialization/jce/common.kt
@@ -18,6 +18,7 @@ import net.mamoe.mirai.qqandroid.io.serialization.Jce
  * 标注 JCE 序列化时使用的 ID
  */
 @SerialInfo
+@Target(AnnotationTarget.PROPERTY)
 annotation class JceId(val id: Int)
 
 /**
@@ -31,6 +32,9 @@ internal data class JceTag(
     val isNullable: Boolean
 )
 
+fun JceHead.checkType(type: Byte) {
+    check(this.type == type) {"type mismatch. Expected $type, actual ${this.type}"}
+}
 
 @PublishedApi
 internal fun Output.writeJceHead(type: Byte, tag: Int) {
diff --git a/mirai-core-qqandroid/src/commonTest/kotlin/net.mamoe.mirai.qqandroid.io.serialization/JceInputTest.kt b/mirai-core-qqandroid/src/commonTest/kotlin/net.mamoe.mirai.qqandroid.io.serialization/JceInputTest.kt
index 6cc28b32c..54a438c73 100644
--- a/mirai-core-qqandroid/src/commonTest/kotlin/net.mamoe.mirai.qqandroid.io.serialization/JceInputTest.kt
+++ b/mirai-core-qqandroid/src/commonTest/kotlin/net.mamoe.mirai.qqandroid.io.serialization/JceInputTest.kt
@@ -1,9 +1,12 @@
-@file:Suppress("unused")
+@file:Suppress("unused", "DEPRECATION_ERROR")
 
 package net.mamoe.mirai.qqandroid.io.serialization
 
 import io.ktor.utils.io.core.*
+import kotlinx.serialization.Serializable
+import net.mamoe.mirai.qqandroid.io.serialization.jce.JceId
 import net.mamoe.mirai.qqandroid.io.serialization.jce.JceInput
+import net.mamoe.mirai.qqandroid.io.serialization.jce.JceNew
 import net.mamoe.mirai.qqandroid.io.serialization.jce.writeJceHead
 import kotlin.test.Test
 import kotlin.test.assertEquals
@@ -35,6 +38,39 @@ internal const val ZERO_TYPE: Byte = 12
  */
 @Suppress("INVISIBLE_MEMBER") // bug
 internal class JceInputTest {
+    @Serializable
+    data class TestSerializableClassA(
+        @JceId(0) val byte: Byte = 66,
+        @JceId(1) val short: Short = 123,
+        @JceId(3) val int: Int = 123456,
+        @JceId(8) val float: Float = 123f,
+        @JceId(15) val long: Long = 123456789123456789L,
+        @JceId(16) val double: Double = 123456.0,
+        @JceId(17) val boolean: Boolean = true,
+        @JceId(11111) val nullable: Int? = null
+    )
+
+    @Test
+    fun testSerializableClassA() {
+        val input = buildPacket {
+            writeJceHead(BYTE, 0)
+            writeByte(66)
+            writeJceHead(SHORT, 1)
+            writeShort(123)
+            writeJceHead(INT, 3)
+            writeInt(123456)
+            writeJceHead(FLOAT, 8)
+            writeFloat(123f)
+            writeJceHead(LONG, 15)
+            writeLong(123456789123456789L)
+            writeJceHead(DOUBLE, 16)
+            writeDouble(123456.0)
+            writeJceHead(BYTE, 17)
+            writeByte(1) // boolean
+        }
+
+        assertEquals(TestSerializableClassA(), JceNew.UTF_8.load(TestSerializableClassA.serializer(), input))
+    }
 
     @Test
     fun testHeadSkip() {