Android11 DHCP初识
先简单说一下DHCP过程，对于代码理解会有帮助。 1、客户端发起Discover，来寻找DHCP服务器 2、DHCPServer给Clinet发送offer 3、DHCPClient接受Offer以后发送DHCPRequest 4、DHCPServer发送packet ack表示可以用此IP，结束。
客户端代码主要在DhcpClient.java中。里面有一个状态机。 frameworks/base/packages/NetworkStack/src/android/net/dhcp/DhcpClient.java
在这里插入图片描述
DHCP客户端日志
09-07 11:17:32.758 1695 7348 D DhcpClient: Receive thread started
09-07 11:17:32.774 1695 3991 D DhcpClient: Broadcasting DHCPDISCOVER
09-07 11:17:32.783 1695 7348 D DhcpClient: Received packet: 78:8e:33:2a:57:9c OFFER, ip /192.168.1.171, mask /255.255.255.0, DNS servers: /218.2.135.1 /114.114.114.114 , gateways [/192.168.1.1] lease time 6912, domain null
09-07 11:17:32.784 1695 3991 D DhcpClient: Got pending lease: android.net.networkstack.DhcpResults@c1d00c7 DHCP server /192.168.1.1 Vendor info null lease 6912 seconds Servername
09-07 11:17:32.787 1695 3991 D DhcpClient: Broadcasting DHCPREQUEST ciaddr=0.0.0.0 request=192.168.1.171 serverid=192.168.1.1
09-07 11:17:32.799 1695 7348 D DhcpClient: Received packet: 78:8e:33:2a:57:9c ACK: your new IP /192.168.1.171, netmask /255.255.255.0, gateways [/192.168.1.1] DNS servers: /218.2.135.1 /114.114.114.114 , lease time 7200
09-07 11:17:32.801 1695 3991 D DhcpClient: Confirmed lease: android.net.networkstack.DhcpResults@a271e1d DHCP server /192.168.1.1 Vendor info null lease 7200 seconds Servername
09-07 11:17:32.819 1695 3991 D DhcpClient: Scheduling renewal in 3599s
09-07 11:17:32.820 1695 3991 D DhcpClient: Scheduling rebind in 6299s
09-07 11:17:32.820 1695 3991 D DhcpClient: Scheduling expiry in 7199s在DHCP客户端，有一个接收线程，用于接收DHCP的packet。
class ReceiveThread extends Thread {
private final byte[] mPacket = new byte[DhcpPacket.MAX_LENGTH];
private volatile boolean mStopped = false;
public void halt() {
mStopped = true;
closeSockets(); // Interrupts the read() call the thread is blocked in.
}
@Override
public void run() {
if (DBG) Log.d(TAG, "Receive thread started");
while (!mStopped) {
int length = 0; // Or compiler can't tell it's initialized if a parse error occurs.
try {
length = Os.read(mPacketSock, mPacket, 0, mPacket.length);
DhcpPacket packet = null;
packet = DhcpPacket.decodeFullPacket(mPacket, length, DhcpPacket.ENCAP_L2);
if (DBG) Log.d(TAG, "Received packet: " + packet);
sendMessage(CMD_RECEIVED_PACKET, packet);
} catch (IOException|ErrnoException e) {
if (!mStopped) {
Log.e(TAG, "Read error", e);
logError(DhcpErrorEvent.RECEIVE_ERROR);
}
} catch (DhcpPacket.ParseException e) {
Log.e(TAG, "Can't parse packet: " + e.getMessage());
if (PACKET_DBG) {
Log.d(TAG, HexDump.dumpHexString(mPacket, 0, length));
}
if (e.errorCode == DhcpErrorEvent.DHCP_NO_COOKIE) {
int snetTagId = 0x534e4554;
String bugId = "31850211";
int uid = -1;
String data = DhcpPacket.ParseException.class.getName();
EventLog.writeEvent(snetTagId, bugId, uid, data);
}
logError(e.errorCode);
}
}
if (DBG) Log.d(TAG, "Receive thread stopped");
}
}初始状态是StoppedState
setInitialState(mStoppedState);IPClient会发送CMD_START_DHCP，然后DHCPClient接收到以后会开启DHCP，进入DhcpInitState
class StoppedState extends State {
@Override
public boolean processMessage(Message message) {
switch (message.what) {
case CMD_START_DHCP:
if (mRegisteredForPreDhcpNotification) {
transitionTo(mWaitBeforeStartState);
} else {
transitionTo(mDhcpInitState);
}
return HANDLED;DhcpInitState 会接收packet包，如果数据包合法，则发送请求数据包。
class DhcpInitState extends PacketRetransmittingState {
public DhcpInitState() {
super();
}
@Override
public void enter() {
super.enter();
startNewTransaction();
mLastInitEnterTime = SystemClock.elapsedRealtime();
}
protected boolean sendPacket() {
return sendDiscoverPacket();
}
protected void receivePacket(DhcpPacket packet) {
if (!isValidPacket(packet)) return;
if (!(packet instanceof DhcpOfferPacket)) return;
mOffer = packet.toDhcpResults();
if (mOffer != null) {
Log.d(TAG, "Got pending lease: " + mOffer);
transitionTo(mDhcpRequestingState);
}
}
}DhcpRequestingState 中可以看到，如果超时，会返回到DhcpInitState 。如果receive到DHCP结果，并且确认没问题，则进入ConfiguringInterfaceState
class DhcpRequestingState extends PacketRetransmittingState {
public DhcpRequestingState() {
mTimeout = DHCP_TIMEOUT_MS / 2;
}
protected boolean sendPacket() {
return sendRequestPacket(
INADDR_ANY, // ciaddr
(Inet4Address) mOffer.ipAddress.getAddress(), // DHCP_REQUESTED_IP
(Inet4Address) mOffer.serverAddress, // DHCP_SERVER_IDENTIFIER
INADDR_BROADCAST); // packet destination address
}
protected void receivePacket(DhcpPacket packet) {
if (!isValidPacket(packet)) return;
if ((packet instanceof DhcpAckPacket)) {
DhcpResults results = packet.toDhcpResults();
if (results != null) {
setDhcpLeaseExpiry(packet);
acceptDhcpResults(results, "Confirmed");
transitionTo(mConfiguringInterfaceState);
}
} else if (packet instanceof DhcpNakPacket) {
// TODO: Wait a while before returning into INIT state.
Log.d(TAG, "Received NAK, returning to INIT");
mOffer = null;
transitionTo(mDhcpInitState);
}
}
@Override
protected void timeout() {
// After sending REQUESTs unsuccessfully for a while, go back to init.
transitionTo(mDhcpInitState);
}
}ConfiguringInterfaceState 这里就很简单了，直接跳转到DhcpBoundState
class ConfiguringInterfaceState extends LoggingState {
@Override
public void enter() {
super.enter();
mController.sendMessage(CMD_CONFIGURE_LINKADDRESS, mDhcpLease.ipAddress);
}
@Override
public boolean processMessage(Message message) {
super.processMessage(message);
switch (message.what) {
case EVENT_LINKADDRESS_CONFIGURED:
transitionTo(mDhcpBoundState);
return HANDLED;
default:
return NOT_HANDLED;
}
}
}正常的一次DHCP流程就是这样，比较简单。 StoppedState->DhcpInitState ->DhcpRequestingState ->ConfiguringInterfaceState ->DhcpBoundState 但是DHCPClient实际比较复杂，有很多状态，以后慢慢再看。
本文参与 腾讯云自媒体分享计划，分享自作者个人站点/博客。
原始发表：2021-09-07 ，如有侵权请联系 cloudcommunity@tencent.com 删除
评论
登录后参与评论
推荐阅读