Network: change state initialization and update sequence:

- Do nothing in init block
- Start state after notifying  `beforeStateChanged`
- StateClosed: do close after being updated to public

close #1893

mirai-core/src/commonMain/kotlin/network/handler/NetworkHandlerSupport.kt

@@ -1,10 +1,10 @@
 /*
- * Copyright 2019-2021 Mamoe Technologies and contributors.
+ * Copyright 2019-2022 Mamoe Technologies and contributors.
  *
- *  此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
- *  Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
+ * 此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
+ * Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
  *
- *  https://github.com/mamoe/mirai/blob/master/LICENSE
+ * https://github.com/mamoe/mirai/blob/dev/LICENSE
  */
 
 package net.mamoe.mirai.internal.network.handler
@@ -159,6 +159,26 @@ internal abstract class NetworkHandlerSupport(
         final override val coroutineContext: CoroutineContext =
             this@NetworkHandlerSupport.coroutineContext + Job(this@NetworkHandlerSupport.coroutineContext.job)
 
+        // Do not use init blocks to launch anything. Do use [startState]
+
+        /**
+         * Starts things that should be done in this state.
+         *
+         * Called after this instance is initialized, and it is at suitable time for initialization.
+         *
+         * Note: must be fast.
+         */
+        open fun startState() {
+
+        }
+
+        /**
+         * Called after this instance is set to [_state]. (Visible publicly)
+         */
+        open fun afterUpdated() {
+
+        }
+
         open fun getCause(): Throwable? = null
 
         /**
@@ -248,7 +268,7 @@ internal abstract class NetworkHandlerSupport(
             val stateObserver = context.getOrNull(StateObserver)
 
             val impl = try {
-                new() // inline only once
+                new()
             } catch (e: Throwable) {
                 stateObserver?.exceptionOnCreatingNewState(this, old, e)
                 throw e
@@ -257,8 +277,14 @@ internal abstract class NetworkHandlerSupport(
             check(old !== impl) { "Old and new states cannot be the same." }
 
             stateObserver?.beforeStateChanged(this, old, impl)
+
+            // We should startState before expose it publicly because State.resumeConnection may wait for some jobs that are launched in startState.
+            // We cannot close old state before changing the 'public' _state to be the new one, otherwise every client will get some kind of exceptions (unspecified, maybe CancellationException).
+            impl.startState() // launch jobs
             _state = impl // update current state
             old.cancel(StateSwitchingException(old, impl)) // close old
+            impl.afterUpdated() // now do post-update things.
+
             stateObserver?.stateChanged(this, old, impl) // notify observer
             _stateChannel.trySend(impl.correspondingState) // notify selector
 

mirai-core/src/commonMain/kotlin/network/handler/state/StateObserver.kt

@@ -1,10 +1,10 @@
 /*
- * Copyright 2019-2021 Mamoe Technologies and contributors.
+ * Copyright 2019-2022 Mamoe Technologies and contributors.
  *
- *  此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
- *  Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
+ * 此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
+ * Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
  *
- *  https://github.com/mamoe/mirai/blob/master/LICENSE
+ * https://github.com/mamoe/mirai/blob/dev/LICENSE
  */
 
 package net.mamoe.mirai.internal.network.handler.state
@@ -22,7 +22,7 @@ import net.mamoe.mirai.internal.network.handler.NetworkHandlerSupport
 internal interface StateObserver {
 
     /**
-     * Called when _state is being changed_, where [NetworkHandlerSupport._state] is still [previous].
+     * Called when _state is being changed_, where [NetworkHandlerSupport._state] is still [previous], and new state is not yet started.
      */
     fun beforeStateChanged(
         networkHandler: NetworkHandlerSupport,

mirai-core/src/commonMain/kotlin/network/impl/netty/NettyNetworkHandler.kt

@@ -259,14 +259,16 @@ internal open class NettyNetworkHandler(
          */
         private val collectiveExceptions: ExceptionCollector,
     ) : NettyState(State.CONNECTING) {
-        private val connection = async {
-            createConnection()
-        }
+        private lateinit var connection: Deferred<io.netty.channel.Channel>
 
         @Suppress("JoinDeclarationAndAssignment")
-        private val connectResult: Deferred<Unit>
+        private lateinit var connectResult: Deferred<Unit>
+
+        override fun startState() {
+            connection = async {
+                createConnection()
+            }
 
-        init {
             connectResult = async {
                 connection.join()
                 context[SsoProcessor].login(this@NettyNetworkHandler)
@@ -318,7 +320,8 @@ internal open class NettyNetworkHandler(
     protected inner class StateLoading(
         private val connection: NettyChannel,
     ) : NettyState(State.LOADING) {
-        init {
+
+        override fun startState() {
             coroutineContext.job.invokeOnCompletion {
                 if (it != null) {
                     connection.close()
@@ -351,7 +354,7 @@ internal open class NettyNetworkHandler(
         private val connection: NettyChannel,
         private val configPush: Job,
     ) : NettyState(State.OK) {
-        init {
+        override fun startState() {
             coroutineContext.job.invokeOnCompletion { err ->
                 if (err is StateSwitchingException) {
                     if (err.new.correspondingState == State.CLOSED) {
@@ -396,7 +399,8 @@ internal open class NettyNetworkHandler(
     protected inner class StateClosed(
         val exception: Throwable?,
     ) : NettyState(State.CLOSED) {
-        init {
+
+        override fun afterUpdated() {
             close(exception)
         }