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

Platform: Rockchip
OS: Android 6.0
Kernel: 3.10.92


之前分析了WiFi的连接，连接上之后会获取ip地址.
自从Android6.0之后，Google引入了一个new DHCP client,它的代码都是融入在JAVA  Framework中，而旧的则是以service:  /system/bin/dhcpcd的形式存在，代码用C实现.

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

参考：

The new DHCP Client?
How to Fix Wifi Stuck "Obtaining IP Address"
Fix: Cannot connect to Wi-Fi after Marshmallow Update