diff --git a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/ContactImpl.kt b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/ContactImpl.kt
index bd6b5750c..e5e7bd4a4 100644
--- a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/ContactImpl.kt
+++ b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/ContactImpl.kt
@@ -44,9 +44,6 @@ internal class QQImpl(bot: QQAndroidBot, override val coroutineContext: Coroutin
         TODO("not implemented")
     }
 
-    override val isOnline: Boolean
-        get() = true
-
     override suspend fun queryProfile(): Profile {
         TODO("not implemented")
     }
diff --git a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/network/protocol/packet/PacketFactory.kt b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/network/protocol/packet/PacketFactory.kt
index b5c5f7b3c..f44f87ee6 100644
--- a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/network/protocol/packet/PacketFactory.kt
+++ b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/network/protocol/packet/PacketFactory.kt
@@ -169,7 +169,7 @@ internal object KnownPacketFactories {
         PacketLogger.verbose("包类型(flag2) = $flag2. (可能是 ${if (flag2 == 2) "OicqRequest" else "Uni"})")
 
         val flag3 = readByte().toInt()
-        check(flag3 == 0) { "Illegal flag3. Expected 0, whereas got $flag3. flag1=$flag1, flag2=$flag2" }
+        check(flag3 == 0) { "Illegal flag3. Expected 0, whereas got $flag3. flag1=$flag1, flag2=$flag2. Remaining=${this.readBytes().toUHexString()}" }
 
         readString(readInt() - 4)// uinAccount
 
diff --git a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/network/protocol/packet/list/FriendListPacket.kt b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/network/protocol/packet/list/FriendListPacket.kt
index 677bd3b2b..60da217db 100644
--- a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/network/protocol/packet/list/FriendListPacket.kt
+++ b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/network/protocol/packet/list/FriendListPacket.kt
@@ -14,7 +14,6 @@ import net.mamoe.mirai.qqandroid.network.protocol.packet.EMPTY_BYTE_ARRAY
 import net.mamoe.mirai.qqandroid.network.protocol.packet.OutgoingPacket
 import net.mamoe.mirai.qqandroid.network.protocol.packet.OutgoingPacketFactory
 import net.mamoe.mirai.qqandroid.network.protocol.packet.buildOutgoingUniPacket
-import net.mamoe.mirai.utils.io.debugIfFail
 
 
 internal class FriendList {
@@ -22,7 +21,7 @@ internal class FriendList {
     internal object GetTroopMemberList :
         OutgoingPacketFactory<GetTroopMemberList.Response>("friendlist.GetTroopMemberListReq") {
         override suspend fun ByteReadPacket.decode(bot: QQAndroidBot): Response {
-            val res = this.debugIfFail { this.decodeUniPacket(GetTroopMemberListResp.serializer()) }
+            val res = this.decodeUniPacket(GetTroopMemberListResp.serializer())
             return Response(
                 res.vecTroopMember,
                 res.nextUin
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/contact/ContactList.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/contact/ContactList.kt
index 3e96f57eb..ae59a5f2c 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/contact/ContactList.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/contact/ContactList.kt
@@ -2,9 +2,7 @@
 
 package net.mamoe.mirai.contact
 
-import net.mamoe.mirai.utils.LockFreeLinkedList
-import net.mamoe.mirai.utils.MiraiInternalAPI
-import net.mamoe.mirai.utils.joinToString
+import net.mamoe.mirai.utils.*
 
 
 /**
@@ -24,10 +22,12 @@ class ContactList<C : Contact>(@MiraiInternalAPI val delegate: LockFreeLinkedLis
 
     operator fun get(id: Long): C = delegate[id]
     fun getOrNull(id: Long): C? = delegate.getOrNull(id)
-    fun containsId(id: Long): Boolean = delegate.getOrNull(id) != null
+    @Deprecated("Use contains instead", ReplaceWith("contains(id)"))
+    fun containsId(id: Long): Boolean = contains(id)
 
     val size: Int get() = delegate.size
     operator fun contains(element: C): Boolean = delegate.contains(element)
+    operator fun contains(id: Long): Boolean = delegate.getOrNull(id) != null
     fun containsAll(elements: Collection<C>): Boolean = elements.all { contains(it) }
     fun isEmpty(): Boolean = delegate.isEmpty()
     inline fun forEach(block: (C) -> Unit) = delegate.forEach(block)
@@ -50,5 +50,35 @@ inline fun <C : Contact> LockFreeLinkedList<C>.filteringGetOrNull(filter: (C) ->
     return null
 }
 
-fun <C : Contact> LockFreeLinkedList<C>.getOrAdd(id: Long, supplier: () -> C): C =
-    filteringGetOrAdd({ it.id == id }, supplier)
+
+/**
+ * Collect all the elements into a [MutableList] then cast it as a [List]
+ */
+fun <E : Contact> ContactList<E>.toList(): List<E> = toMutableList()
+
+/**
+ * Collect all the elements into a [MutableList].
+ */
+@UseExperimental(MiraiInternalAPI::class)
+fun <E : Contact> ContactList<E>.toMutableList(): MutableList<E> = this.delegate.toMutableList()
+
+/**
+ * Collect all the elements into a [MutableSet] then cast it as a [Set]
+ */
+fun <E : Contact> ContactList<E>.toSet(): Set<E> = toMutableSet()
+
+/**
+ * Collect all the elements into a [MutableSet].
+ */
+@UseExperimental(MiraiInternalAPI::class)
+fun <E : Contact> ContactList<E>.toMutableSet(): MutableSet<E> = this.delegate.toMutableSet()
+
+/**
+ * Builds a [Sequence] containing all the elements in [this] in the same order.
+ *
+ * Note that the sequence is dynamic, that is, elements are yielded atomically only when it is required
+ */
+@UseExperimental(MiraiInternalAPI::class)
+fun <E : Contact> ContactList<E>.asSequence(): Sequence<E> {
+    return this.delegate.asSequence()
+}
\ No newline at end of file
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/contact/QQ.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/contact/QQ.kt
index 8bfd19824..fe380d5f8 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/contact/QQ.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/contact/QQ.kt
@@ -22,9 +22,9 @@ import net.mamoe.mirai.data.Profile
  */
 interface QQ : Contact, CoroutineScope {
     /**
-     * 是否在线. 这个属性的值将会与服务器同步更新.
+     * QQ 号码
      */
-    val isOnline: Boolean
+    override val id: Long
 
     /**
      * 请求头像下载链接
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/utils/LockFreeLinkedList.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/utils/LockFreeLinkedList.kt
index 80b6c29cc..711099469 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/utils/LockFreeLinkedList.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/utils/LockFreeLinkedList.kt
@@ -19,12 +19,12 @@ inline fun <E> LockFreeLinkedList<E>.joinToString(
 }.dropLast(separator.length) + postfix
 
 /**
- * Returns a [List] containing all the elements in [this] in the same order
+ * Collect all the elements into a [MutableList] then cast it as a [List]
  */
 fun <E> LockFreeLinkedList<E>.toList(): List<E> = toMutableList()
 
 /**
- * Returns a [MutableList] containing all the elements in [this] in the same order
+ * Collect all the elements into a [MutableList].
  */
 fun <E> LockFreeLinkedList<E>.toMutableList(): MutableList<E> {
     val list = mutableListOf<E>()
@@ -32,6 +32,33 @@ fun <E> LockFreeLinkedList<E>.toMutableList(): MutableList<E> {
     return list
 }
 
+/**
+ * Collect all the elements into a [MutableSet] then cast it as a [Set]
+ */
+fun <E> LockFreeLinkedList<E>.toSet(): Set<E> = toMutableSet()
+
+/**
+ * Collect all the elements into a [MutableSet].
+ */
+fun <E> LockFreeLinkedList<E>.toMutableSet(): MutableSet<E> {
+    val list = mutableSetOf<E>()
+    this.forEach { list.add(it) }
+    return list
+}
+
+/**
+ * Builds a [Sequence] containing all the elements in [this] in the same order.
+ *
+ * Note that the sequence is dynamic, that is, elements are yielded atomically only when it is required
+ */
+fun <E> LockFreeLinkedList<E>.asSequence(): Sequence<E> {
+    return sequence {
+        forEach {
+            yield(it)
+        }
+    }
+}
+
 /**
  * Implementation of lock-free LinkedList.
  *
@@ -87,6 +114,9 @@ open class LockFreeLinkedList<E> {
 
     open operator fun plusAssign(element: E) = this.addLast(element)
 
+    /**
+     * 过滤并获取, 获取不到则添加一个元素.
+     */
     inline fun filteringGetOrAdd(filter: (E) -> Boolean, noinline supplier: () -> E): E {
         val node = LazyNode(tail, supplier)
 
@@ -149,6 +179,9 @@ open class LockFreeLinkedList<E> {
         }
     }
 
+    /**
+     * 动态计算的大小
+     */
     val size: Int get() = head.countChildIterate<Node<E>>({ it.nextNode }, { it !is Tail }) - 1 // empty head is always included
 
     open operator fun contains(element: E): Boolean {