[RK3288][Android6.0] WiFi之DHCP获取IP address流程

不知道引入new dchp client带来了什么好处，但是发现部分网友有遇到获取IP address失败的情况。

而是否用new DHCP client可以在Settings中的开发者选项里做切换：

下面是New DHCP Client的代码调用过程：

enter -> WifiStateMachine.java //ObtainingIpState   startDhcp -> //动态获取ip     maybeInitDhcpStateMachine -> //创建dhcp状态机       DhcpClient.makeDhcpStateMachine ->         new DhcpClient ->           createStateMachineCommandIntent //创建“KICK”intent后面用来处理packet           setInitialState(mStoppedState); //默认是mStoppedState状态         client.start ->            smh.completeConstruction    //开始DhcpClient的状态运行     mDhcpStateMachine.sendMessage -> //DhcpStateMachine.CMD_START_DHCP       processMessage -> DhcpClient.java //StoppedState       transitionTo(mWaitBeforeStartState) ->         enter -> WaitBeforeStartState没有enter,调用父类DhcpState           initInterface ->             mIface.getHardwareAddress //获得Mac地址           initSockets //ReceiveThread用来读取ipaddress           new ReceiveThread           mReceiveThread.start ->             run //ReceiveThread开始运行           mController.sendMessage(DhcpStateMachine.CMD_PRE_DHCP_ACTION) ->             processMessage -> L2ConnectedState               handlePreDhcpSetup ->                 mWifiP2pChannel.sendMessage -> //DhcpStateMachine.CMD_PRE_DHCP_ACTION_COMPLETE                   processMessage -> //WaitBeforeStartState的父类WaitBeforeOtherState                     transitionTo(mOtherState) -> //mOtherState在WaitBeforeStartState初始化的时候赋值，是DhcpInitState                       super.enter ->                         enter -> //PacketRetransmittingState                           sendMessage(CMD_KICK) ->                             processMessage ->                               sendPacket ->                                 sendDiscoverPacket ->                                   DhcpPacket.buildDiscoverPacket  -> //制作一个packet                                     buildDiscoverPacket ->                                       new DhcpDiscoverPacket ->                                         super ->    //调用父类构造函数                                           DhcpPacket                                       pkt.buildPacket ->                                         buildPacket -> DhcpDiscoverPacket.java                                           fillInPacket ->    //这个函数没看太明白是如何具体ip address的，貌似和upd协议有关                                             mClientIp.getAddress                                   transmitPacket ->                                     Os.sendto -> //发送给前面一直等待的ReceiveThread                                       Os.read -> //读取packet                                         DhcpPacket.decodeFullPacket //解包                                         sendMessage -> //CMD_RECEIVED_PACKET                                           processMessage -> //PacketRetransmittingState                                             receivePacket -> //DhcpInitState                                               packet.toDhcpResults //获得ipaddress                                               transitionTo(mDhcpRequestingState) ->                                                 enter -> //又调用了DhcpRequestingState的父类PacketRetransmittingState再发一次CMD_KICK                                                   sendRequestPacket -> 申请此IP                                                     DhcpPacket.buildRequestPacket ->                                                      transmitPacket -> //DhcpRequestingState                                                      ...... //中间步骤和上面一样                                                      receivePacket -> //DhcpRequestingState， 确认租用此IP                                                        packet.toDhcpResults                                                        transitionTo(mDhcpBoundState) ->                                                          enter -> //DhcpBoundState                                                            notifySuccess ->    //通知wifi状态机完成                                                              mController.sendMessage -> //DhcpStateMachine.CMD_POST_DHCP_ACTION                                                                handlePostDhcpSetup                                                                handleIPv4Success

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