安卓通過DHCP協議的DORA Discovery發現 Offer提供 Request請求 Ack確認 獲取IP地址的過程
安卓N之前 5.0 6.0通過 android_net_utils_runDhcp 方法運行 /system/bin/dhcpcd 獲取ip地址
安卓N之後 N不要了runDhcpcd(),而是通過DhcpClient
DhcpClient是通過framework發送dhcpcd協議的UDP請求包直接去拿IP，不再使用開源的dhcpcd
google還用了一個狀態機 IpManager 來管理dhcpcd成功還是失敗等狀態，
將ip賦值給IpConfiguration和LinkProperties傳遞到上層的framework
/frameworks/opt/net/wifi/service/java/com/android/server/wifi/WifiStateMachine.java
// 當WifiStateMachine狀態機進入狀態ObtainingIpState時 獲取IP地址
class ObtainingIpState extends State {
@Override
public void enter() {
mIpManager.startProvisioning(IpManager.ProvisioningConfiguration prov); //啓動獲取IP地址
}
}
ObtainingIpState所在狀態機
/frameworks/base/services/net/java/android/net/ip/IpManager.java
class StartedState extends State {} IpManager中的三個狀態機
class StoppedState extends State {}
class StoppingState extends State {}
public void startProvisioning(ProvisioningConfiguration req) {
getNetworkInterface();
mCallback.setNeighborDiscoveryOffload(true);
// 給初始化的狀態機 StoppedState 發送消息CMD_START
sendMessage(CMD_START, new ProvisioningConfiguration(req));
}
========================================================================
class StoppedState extends State {
@Override
public boolean processMessage(Message msg) {
switch (msg.what) {
…..
case CMD_START:
mConfiguration = (ProvisioningConfiguration) msg.obj;
// 接收到 CMD_START 會進行狀態的切換，調用 StartedState的enter()方法
transitionTo(mStartedState);
break;
…..
}
==========================================
class StartedState extends State {
void enter(){
if(startIPv4()) // 狀態 StartedState 的enter 進入方法，調用startIPv4()函數
}
}
==========================================
private boolean startIPv4() {
// If we have a StaticIpConfiguration attempt to apply it and handle the result accordingly.
if (mConfiguration.mStaticIpConfig != null) { // 如果有靜態IP
if (setIPv4Address(mConfiguration.mStaticIpConfig.ipAddress)) {
handleIPv4Success(new DhcpResults(mConfiguration.mStaticIpConfig));
} else {
if (VDBG) { Log.d(mTag, "onProvisioningFailure()"); }
recordMetric(IpManagerEvent.PROVISIONING_FAIL);
mCallback.onProvisioningFailure(new LinkProperties(mLinkProperties));
return false;
}
} else {
// Start DHCPv4. 創建DhcpClient
mDhcpClient = DhcpClient.makeDhcpClient(mContext, IpManager.this, mInterfaceName);
mDhcpClient.registerForPreDhcpNotification(); // mRegisteredForPreDhcpNotification = true
//接收前面發過來的mDhcpClient.sendMessage(DhcpClient.CMD_START_DHCP);跟着跳轉到DhcpInitState:
mDhcpClient.sendMessage(DhcpClient.CMD_START_DHCP); // 發送CMD_START_DHCP消息
if (mConfiguration.mProvisioningTimeoutMs > 0) {
final long alarmTime = SystemClock.elapsedRealtime() +
mConfiguration.mProvisioningTimeoutMs;
mProvisioningTimeoutAlarm.schedule(alarmTime); // 在36秒後啓動timeout超時操作
}
}
return true;
}
private boolean setIPv4Address(LinkAddress address) {
final InterfaceConfiguration ifcg = new InterfaceConfiguration();
ifcg.setLinkAddress(address);
try {
final INetworkManagementService mNwService.setInterfaceConfig(mInterfaceName, ifcg);
if (VDBG) Log.d(mTag, "IPv4 configuration succeeded");
} catch (IllegalStateException | RemoteException e) {
Log.e(mTag, "IPv4 configuration failed: ", e);
return false;
}
return true;
}
==========================================
//接收前面發過來的mDhcpClient.sendMessage(DhcpClient.CMD_START_DHCP);跟着跳轉到 DhcpInitState:
mDhcpClient.sendMessage(DhcpClient.CMD_START_DHCP); // 發送CMD_START_DHCP消息
/frameworks/base/services/net/java/android/net/dhcp/DhcpClient.java
class StoppedState extends LoggingState {
@Override
public boolean processMessage(Message message) {
super.processMessage(message);
switch (message.what) {
case CMD_START_DHCP:
if (mRegisteredForPreDhcpNotification) {
transitionTo(mWaitBeforeStartState);
} else {
transitionTo(mDhcpInitState); // 狀態跳轉到 DhcpInitState
}
return HANDLED;
default:
return NOT_HANDLED;
}
}
}
class DhcpInitState extends PacketRetransmittingState {
public DhcpInitState() {
super();
}
//進入狀態時啓動一次startNewTransaction
//DORA Discover發現 Offer提供 Request請求 ACK確認 開始Discovery 發現?
@Override
public void enter() {
super.enter(); // 調用父類的 enter 方法中
startNewTransaction();
}
protected boolean sendPacket() {
return sendDiscoverPacket(); // 發送 DiscoverPacket 發現包
}
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); // 接收到了 Offer包 接下來發送 Request 請求包
}
}
}
private void startNewTransaction() {
mTransactionId = mRandom.nextInt(); // 傳輸包的id號?
mTransactionStartMillis = SystemClock.elapsedRealtime();
}
==================================================
PacketRetransmittingState
abstract class PacketRetransmittingState extends LoggingState {
private int mTimer;
protected int mTimeout = 0;
@Override
public void enter() {
super.enter();
initTimer();
maybeInitTimeout();
sendMessage(CMD_KICK); // 發送消息 CMD_KICK
}
@Override
public boolean processMessage(Message message) {
super.processMessage(message);
switch (message.what) {
case CMD_KICK:
// 調用了 sendPacket()抽象方法 所以就是之前的DhcpInitState的具體的實現 sendPacket()
sendPacket();
scheduleKick();
return HANDLED;
case CMD_RECEIVED_PACKET:
receivePacket((DhcpPacket) message.obj);
return HANDLED;
case CMD_TIMEOUT:
timeout();
return HANDLED;
default:
return NOT_HANDLED;
}
}
public void exit() {
mKickAlarm.cancel();
mTimeoutAlarm.cancel();
}
}
abstract protected boolean sendPacket();
abstract protected void receivePacket(DhcpPacket packet);
class DhcpInitState extends PacketRetransmittingState {
protected boolean sendPacket() {
return sendDiscoverPacket(); // 發送 DiscoverPacket 發現包
}
private boolean sendDiscoverPacket() {
ByteBuffer packet = DhcpPacket.buildDiscoverPacket(
DhcpPacket.ENCAP_L2, mTransactionId, getSecs(), mHwAddr,
DO_UNICAST, REQUESTED_PARAMS); // 創建 ByteBuffer的UDP包
return transmitPacket(packet, “DHCPDISCOVER”, DhcpPacket.ENCAP_L2, INADDR_BROADCAST); // 發送
}
}
private boolean transmitPacket(ByteBuffer buf, String description, int encap, Inet4Address to) {
try {
if (encap == DhcpPacket.ENCAP_L2) {
if (DBG) Log.d(TAG, "Broadcasting " + description);
// 送這裏發送出去
Os.sendto(mPacketSock, buf.array(), 0, buf.limit(), 0, mInterfaceBroadcastAddr);
} else if (encap == DhcpPacket.ENCAP_BOOTP && to.equals(INADDR_BROADCAST)) {
if (DBG) Log.d(TAG, "Broadcasting " + description);
// N.B.: We only need this codepath because DhcpRequestPacket
// hardcodes the source IP address to 0.0.0.0. We could reuse
// the packet socket if this ever changes.
Os.sendto(mUdpSock, buf, 0, to, DhcpPacket.DHCP_SERVER);
} else {
if (DBG) Log.d(TAG, String.format("Unicasting %s to %s",description, Os.getpeername(mUdpSock)));
Os.write(mUdpSock, buf);
}
} catch(ErrnoException|IOException e) {
Log.e(TAG, "Can't send packet: ", e);
return false;
}
return true;
}
==================================================================
另外一邊有一個接收線程ReceiveThread run()，一直在收dhcp server的的數據包。
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 {
//讀取DHCP服務發出的OFFER提交包
length = Os.read(mPacketSock 【FileDescriptor】, 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); // 發送接收到消息 CMD_RECEIVED_PACKET
} catch (IOException|ErrnoException e) {
if (!mStopped) {
Log.e(TAG, "Read error", e);
DhcpErrorEvent.logReceiveError(mIfaceName);
}
} catch (DhcpPacket.ParseException e) {
Log.e(TAG, "Can't parse packet: " + e.getMessage());
if (PACKET_DBG) {
Log.d(TAG, HexDump.dumpHexString(mPacket, 0, length));
}
DhcpErrorEvent.logParseError(mIfaceName, e.errorCode);
}
}
if (DBG) Log.d(TAG, "Receive thread stopped");
}
}
abstract class PacketRetransmittingState extends LoggingState {
@Override
public boolean processMessage(Message message) {
super.processMessage(message);
switch (message.what) {
case CMD_RECEIVED_PACKET:
receivePacket((DhcpPacket) message.obj); // 調用子類具體實現的receivePacket 方法
return HANDLED;
default:
return NOT_HANDLED;
}
}
}
class DhcpInitState extends PacketRetransmittingState {
class DhcpInitState extends PacketRetransmittingState {
protected void receivePacket(DhcpPacket packet) { // 完成 DORA 中的 Offer的階段
if (!isValidPacket(packet)) return;
if (!(packet instanceof DhcpOfferPacket)) return;
mOffer = packet.toDhcpResults();
if (mOffer != null) {
Log.d(TAG, "Got pending lease: " + mOffer);
// 接收到了來自DHCP服務器的OFFER包，切換狀態到 DhcpRequestingState 並進入到 enter() 方法
transitionTo(mDhcpRequestingState);
}
}
}
}
===================================================================
class DhcpRequestingState extends PacketRetransmittingState { // 進入到父類的enter 方法
public DhcpRequestingState() {
mTimeout = DHCP_TIMEOUT_MS / 2;
}
public void enter() {// 進入到父類的enter 方法
super.enter();
initTimer();
maybeInitTimeout();
sendMessage(CMD_KICK); // 再次發送 CMD_KICK 消息
}
public boolean processMessage(Message message) {
super.processMessage(message);
switch (message.what) {
case CMD_KICK: // 收到 CMD_KICK 消息
sendPacket(); // 發送包方法，此時調用的是具體子類 DhcpRequestingState的發送方法
scheduleKick();
return HANDLED;
default:
return NOT_HANDLED;
}
}
// 發送請求 完成 DORA中的 Request的階段
// 此時 繼續在接收線程中等待接收來自服務器的ACK DHCP數據包
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);
}
}
private boolean sendRequestPacket(
Inet4Address clientAddress, Inet4Address requestedAddress,
Inet4Address serverAddress, Inet4Address to) {
// TODO: should we use the transaction ID from the server?
final int encap = INADDR_ANY.equals(clientAddress)
? DhcpPacket.ENCAP_L2 : DhcpPacket.ENCAP_BOOTP;
ByteBuffer packet = DhcpPacket.buildRequestPacket(
encap, mTransactionId, getSecs(), clientAddress,
DO_UNICAST, mHwAddr, requestedAddress,
serverAddress, REQUESTED_PARAMS, null);
String serverStr = (serverAddress != null) ? serverAddress.getHostAddress() : null;
String description = "DHCPREQUEST ciaddr=" + clientAddress.getHostAddress() +
" request=" + requestedAddress.getHostAddress() +
" serverid=" + serverStr;
return transmitPacket(packet, description, encap, to); // 發送數據包
}
return transmitPacket(packet, "DHCPDISCOVER", DhcpPacket.ENCAP_L2, INADDR_BROADCAST); // 發送
}
}
private boolean transmitPacket(ByteBuffer buf, String description, int encap, Inet4Address to) {
try {
if (encap == DhcpPacket.ENCAP_L2) {
if (DBG) Log.d(TAG, "Broadcasting " + description);
// 送這裏發送出去 真正發送
Os.sendto(mPacketSock, buf.array(), 0, buf.limit(), 0, mInterfaceBroadcastAddr);
} else if (encap == DhcpPacket.ENCAP_BOOTP && to.equals(INADDR_BROADCAST)) {
if (DBG) Log.d(TAG, "Broadcasting " + description);
// N.B.: We only need this codepath because DhcpRequestPacket
// hardcodes the source IP address to 0.0.0.0. We could reuse
// the packet socket if this ever changes.
Os.sendto(mUdpSock, buf, 0, to, DhcpPacket.DHCP_SERVER);
} else {
if (DBG) Log.d(TAG, String.format("Unicasting %s to %s",description, Os.getpeername(mUdpSock)));
Os.write(mUdpSock, buf);
}
} catch(ErrnoException|IOException e) {
Log.e(TAG, "Can't send packet: ", e);
return false;
}
return true;
}
===========================================================
另外一邊有一個接收線程ReceiveThread run()，一直在收dhcp server的的數據包。
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 {
//讀取DHCP服務發出的ACK確認包
length = Os.read(mPacketSock 【FileDescriptor】, mPacket, 0, mPacket.length);
DhcpPacket packet = null;
packet = DhcpPacket.decodeFullPacket(mPacket, length, DhcpPacket.ENCAP_L2);
if (DBG) Log.d(TAG, "Received packet: " + packet);
// 發送接收到消息 CMD_RECEIVED_PACKET 此時處理的狀態是 DhcpRequestingState
sendMessage(CMD_RECEIVED_PACKET, packet);
} catch (IOException|ErrnoException e) {
if (!mStopped) {
Log.e(TAG, "Read error", e);
DhcpErrorEvent.logReceiveError(mIfaceName);
}
} catch (DhcpPacket.ParseException e) {
Log.e(TAG, "Can't parse packet: " + e.getMessage());
if (PACKET_DBG) {
Log.d(TAG, HexDump.dumpHexString(mPacket, 0, length));
}
DhcpErrorEvent.logParseError(mIfaceName, e.errorCode);
}
}
if (DBG) Log.d(TAG, "Receive thread stopped");
}
}
// 處理消息 CMD_RECEIVED_PACKET 對應的數據包是 ACK數據包 UDP
class DhcpRequestingState extends PacketRetransmittingState {
public boolean processMessage(Message message) {
super.processMessage(message);
switch (message.what) {
case CMD_RECEIVED_PACKET:
receivePacket((DhcpPacket) message.obj); //DhcpRequestingState處理接收到的數據包
return HANDLED;
default:
return NOT_HANDLED;
}
}
protected void receivePacket(DhcpPacket packet) {
if (!isValidPacket(packet)) return;
if ((packet instanceof DhcpAckPacket)) {
DhcpResults results = packet.toDhcpResults();
if (results != null) {
setDhcpLeaseExpiry(packet);
//這裏會調用notifySuccess，發送CMD去通知IpManager說，IP拿到了 分析 acceptDhcpResults
acceptDhcpResults(results, "Confirmed"); // 分叉
//進入新的狀態 ConfiguringInterfaceState enter方法
transitionTo(mConfiguringInterfaceState);
}
} else if (packet instanceof DhcpNakPacket) { // 收到的是NACK 解決數據包的話
// TODO: Wait a while before returning into INIT state.
Log.d(TAG, "Received NAK, returning to INIT");
mOffer = null;
transitionTo(mDhcpInitState);
}
}
}
//這裏會調用notifySuccess，發送CMD去通知IpManager說，IP拿到了 分析 acceptDhcpResults
acceptDhcpResults(results, “Confirmed”);
private void acceptDhcpResults(DhcpResults results, String msg) {
mDhcpLease = results;
mOffer = null;
Log.d(TAG, msg + " lease: " + mDhcpLease);
notifySuccess(); // 通知成功拿到IP地址了
}
private void notifySuccess() {
mController【StateMachine】.sendMessage( CMD_POST_DHCP_ACTION, DHCP_SUCCESS, 0, new DhcpResults(mDhcpLease));
}
class StartedState extends State {
@Override
public boolean processMessage(Message msg) {
switch (msg.what) {
case DhcpClient.CMD_POST_DHCP_ACTION:
stopDhcpAction();
switch (msg.arg1) {
case DhcpClient.DHCP_SUCCESS:
handleIPv4Success((DhcpResults) msg.obj); // 處理 handleIPv4Success IPV4地址
break;
case DhcpClient.DHCP_FAILURE:
handleIPv4Failure();
break;
default:
Log.e(mTag, "Unknown CMD_POST_DHCP_ACTION status:" + msg.arg1);
}
break;
}
}
}
private void handleIPv4Success(DhcpResults dhcpResults) {
mDhcpResults = new DhcpResults(dhcpResults);
final LinkProperties newLp = assembleLinkProperties();
final ProvisioningChange delta = setLinkProperties(newLp);
if (VDBG) {
Log.d(mTag, "onNewDhcpResults(" + Objects.toString(dhcpResults) + ")");
}
mCallback.onNewDhcpResults(dhcpResults);
dispatchCallback(delta, newLp); //這裏分發dhcpResults 把IPv4地址發出去
}
private void dispatchCallback(ProvisioningChange delta, LinkProperties newLp) {
switch (delta) {
case GAINED_PROVISIONING:
if (VDBG) { Log.d(mTag, "onProvisioningSuccess()"); }
recordMetric(IpManagerEvent.PROVISIONING_OK);
mCallback.onProvisioningSuccess(newLp); // 回調
break;
}
}
dispatchCallback 的結果最後會作用到 WaitForProvisioningCallback
public static class WaitForProvisioningCallback extends Callback {
private LinkProperties mCallbackLinkProperties;
public LinkProperties waitForProvisioning() {
synchronized (this) {
try {
wait();
} catch (InterruptedException e) {}
return mCallbackLinkProperties;
}
}
@Override
public void onProvisioningSuccess(LinkProperties newLp) { // 回調
synchronized (this) {
mCallbackLinkProperties = newLp; // 把當前的IPv4保存起來
notify();
}
}
@Override
public void onProvisioningFailure(LinkProperties newLp) {
synchronized (this) {
mCallbackLinkProperties = null;
notify();
}
}
} acceptDhcpResults 分析到此爲止 開始分析新的狀態
//進入新的狀態 ConfiguringInterfaceState enter方法
ConfiguringInterfaceState
class ConfiguringInterfaceState extends LoggingState {
@Override
public void enter() {
super.enter();
// 發送消息 CMD_CONFIGURE_LINKADDRESS 被StartedState 處理
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;
}
}
}
========================
class StartedState extends State {
@Override
public boolean processMessage(Message msg) {
switch (msg.what) {
case DhcpClient.CMD_CONFIGURE_LINKADDRESS: {
final LinkAddress ipAddress = (LinkAddress) msg.obj;
if (setIPv4Address(ipAddress)) { // 設置 IPv4地址
mDhcpClient.sendMessage(DhcpClient.EVENT_LINKADDRESS_CONFIGURED);
} else {
Log.e(mTag, "Failed to set IPv4 address!");
dispatchCallback(ProvisioningChange.LOST_PROVISIONING,
new LinkProperties(mLinkProperties));
transitionTo(mStoppingState);
}
break;
}
}
=========================================
// 回到開頭的 setIPv4Address 至此獲得了IP地址
private boolean setIPv4Address(LinkAddress address) {
final InterfaceConfiguration ifcg = new InterfaceConfiguration();
ifcg.setLinkAddress(address);
try {
final INetworkManagementService mNwService.setInterfaceConfig(mInterfaceName, ifcg);
if (VDBG) Log.d(mTag, “IPv4 configuration succeeded”);
} catch (IllegalStateException | RemoteException e) {
Log.e(mTag, “IPv4 configuration failed: “, e);
return false;
}
return true;
}
NetworkManagementService.java
@Override
public void setInterfaceConfig(String iface, InterfaceConfiguration cfg) {
mContext.enforceCallingOrSelfPermission(CONNECTIVITY_INTERNAL, TAG);
LinkAddress linkAddr = cfg.getLinkAddress();
if (linkAddr == null || linkAddr.getAddress() == null) {
throw new IllegalStateException("Null LinkAddress given");
}
final Command cmd = new Command("interface", "setcfg", iface,
linkAddr.getAddress().getHostAddress(),
linkAddr.getPrefixLength());
for (String flag : cfg.getFlags()) {
cmd.appendArg(flag);
}
try {
mConnector.execute(cmd); // 執行命令
} catch (NativeDaemonConnectorException e) {
throw e.rethrowAsParcelableException();
}
}
http://m.blog.csdn.net/xiaoxiangyuhai/article/details/75219357
