Android WiFi 扫描和连接热点

桃扇骨 2022-05-13 05:58 713阅读 0赞

本章主要介绍用户手动的在Settings中点击Scan和Connect按钮，输入密码后的连接过程，先看整体流程图：

![SouthEast][]

## WiFi Scan过程分析 ##

当用户进入Settings点击Scan后，就会调用到WifiManager的startScan()方法，当然在Settings里面有设置Scan的定时器，每隔一段时间就会去scan，在Wifi Framework中也有scan的定时器。对照上面的流程图，来看一下WifiManager的startScan()方法：

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1.  **public****boolean**startScan(WorkSourceworkSource)\{ 
2.  **try**\{ 
3.  mService.startScan(workSource);
4.  **return****true**;
5.  \}**catch**(RemoteExceptione)\{ 
6.  **return****false**;
7.  \}
8.  \}

**\[java\]** [view plain][] [copy][view plain] [![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  WifiService.java
2.  **public****void**startScan(WorkSourceworkSource)\{ 
3.  enforceChangePermission();
4.  **if**(workSource!=**null**)\{ 
5.  enforceWorkSourcePermission();
6.  //WifiManagercurrentlydoesn'tusenames,soneedtoclearnamesoutofthe
7.  //suppliedWorkSourcetoallowfutureWorkSourcecombining.
8.  workSource.clearNames();
9.  \}
10. mWifiStateMachine.startScan(Binder.getCallingUid(),workSource);
11. \}

WiFiStateMachine的startScan方法会给自己发送一个CMD\_START\_SCAN的message，由前面toggle on wifi的知识，这个消息将由DisconnectedState及其父State来处理，从代码中可以很容易的分析到，CMD\_START\_SCAN将会被DriverStartedState 来处理，进入到处理的代码中：

**\[java\]** [view plain][] [copy][view plain] [![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **public****boolean**processMessage(Messagemessage)\{ 
2.  **switch**(message.what)\{ 
3.  **case**CMD\_START\_SCAN:
4.  noteScanStart(message.arg1,(WorkSource)message.obj);
5.  startScanNative(WifiNative.SCAN\_WITH\_CONNECTION\_SETUP);
6.  **break**;

noteScanStart是用于通知电量统计用；startScanNative会向wpa\_supplicant发送SCAN的命令，当wpa\_suppliant执行完SCAN并成功找到一些AP后，就会给WifiMonitor发送CTRL-EVENT-SCAN-RESULTS的event，WifiMonitor会parse出这个event，并向WifiStateMachine发送SCAN\_RESULTS\_EVENT消息，WifiStateMachine的SupplicantStartedState会处理这个消息，如下：

**\[java\]** [view plain][] [copy][view plain] [![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **case**WifiMonitor.SCAN\_RESULTS\_EVENT:
2.  setScanResults();
3.  sendScanResultsAvailableBroadcast();
4.  mScanResultIsPending=**false**;
5.  **break**;

这里主要做了两件事，一是去获取scanResults，另外会发送一个广播信息出去，如果有检测这个广播的receive收到这个广播后，就可以调用函数去获取到scanResults并显示到listview上面，例如WifiSettings。进入到setScanResults里面来分析：

**\[java\]** [view plain][] [copy][view plain] [![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **private****void**setScanResults()\{ 
2.  
3.  **while**(**true**)\{ 
4.  tmpResults=mWifiNative.scanResults(sid);
5.  **if**(TextUtils.isEmpty(tmpResults))**break**;
6.  scanResultsBuf.append(tmpResults);
7.  scanResultsBuf.append("\\n");
8.  String\[\]lines=tmpResults.split("\\n");
9.  sid=-1;
10. **for**(**int**i=lines.length-1;i>=0;i--)\{ 
11. **if**(lines\[i\].startsWith(END\_STR))\{ 
12. **break**;
13. \}**else****if**(lines\[i\].startsWith(ID\_STR))\{ 
14. **try**\{ 
15. sid=Integer.parseInt(lines\[i\].substring(ID\_STR.length()))+1;
16. \}**catch**(NumberFormatExceptione)\{ 
17. //Nothingtodo
18. \}
19. **break**;
20. \}
21. \}
22. **if**(sid==-1)**break**;
23. \}
24. 
25. scanResults=scanResultsBuf.toString();
26. **if**(TextUtils.isEmpty(scanResults))\{ 
27. **return**;
28. \}
29. 
30. **synchronized**(mScanResultCache)\{ 
31. 
32. **for**(Stringline:lines)\{ 
33. **if**(line.startsWith(BSSID\_STR))\{ 
34. bssid=**new**String(line.getBytes(),bssidStrLen,line.length()-bssidStrLen);
35. \}**else****if**(line.startsWith(FREQ\_STR))\{ 
36. **try**\{ 
37. freq=Integer.parseInt(line.substring(FREQ\_STR.length()));
38. \}**catch**(NumberFormatExceptione)\{ 
39. freq=0;
40. \}
41. \}
42. **else****if**(line.startsWith(SSID\_STR))\{ 
43. wifiSsid=WifiSsid.createFromAsciiEncoded(
44. line.substring(SSID\_STR.length()));
45. \}**else****if**(line.startsWith(DELIMITER\_STR)||line.startsWith(END\_STR))\{ 
46. **if**(bssid!=**null**)\{ 
47. Stringssid=(wifiSsid!=**null**)?wifiSsid.toString():WifiSsid.NONE;
48. Stringkey=bssid+ssid;
49. ScanResultscanResult=mScanResultCache.get(key);
50. **if**(scanResult!=**null**)\{ 
51. scanResult.level=level;
52. scanResult.wifiSsid=wifiSsid;
53. //KeepexistingAPI
54. scanResult.SSID=(wifiSsid!=**null**)?wifiSsid.toString():
55. WifiSsid.NONE;
56. scanResult.capabilities=flags;
57. scanResult.frequency=freq;
58. scanResult.timestamp=tsf;
59. \}**else**\{ 
60. scanResult=
61. **new**ScanResult(
62. wifiSsid,bssid,flags,level,freq,tsf);
63. mScanResultCache.put(key,scanResult);
64. \}
65. mScanResults.add(scanResult);
66. \}

这个函数看起来比较复杂，其实仔细分析，它只是循环的parse从WifiNative获取到AP列表信息，WifiNative.scanResut的返回结果如下，每个AP之间用"===="分割，末尾以“\#\#\#\#”来表示结束。

id=1  
bssid=68:7f:76:d7:1a:6e  
freq=2412  
level=-44  
tsf=1344626243700342  
flags=\[WPA2-PSK-CCMP\]\[WPS\]\[ESS\]  
ssid=zfdy  
====  
id=2  
bssid=68:5f:74:d7:1a:6f  
req=5180  
level=-73  
tsf=1344626243700373  
flags=\[WPA2-PSK-CCMP\]\[WPS\]\[ESS\]  
ssid=zuby  
\#\#\#\#

当所有的结果都被parse出来后，会被存到mScanResults这个ArrayList当中，另外会用bssid+ssid做key值，将这个scanResult存到mScanResultCache这个LRU（最近最少使用） cache当中。当然随着wifi driver不断的scan，发现新的AP，mScanResults和mScanResultCache中的数据也在不断的变化。

当应用程序收到sendScanResultsAvailableBroadcast发送的WifiManager.SCAN\_RESULTS\_AVAILABLE\_ACTION这个broadcast后，就可以去获取上面提供的mScanResults信息了，获取过程很简单，直接复制mScanResults这个ArrayList里面的成员，然后返回。，值得注意的是，sendScanResultsAvailableBroadcast设置了Intent.FLAG\_RECEIVER\_REGISTERED\_ONLY\_BEFORE\_BOOT这个属性，所以只有动态注册的broadcastReceive才会收到这个broadcast。

## 连接AP的流程 ##

当用户点击AP列表中一项并输入正确的密码后，就可以开始AP的连接过程了，主要调用的是WifiManager的connect函数，如下：

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1.  **public****void**connect(WifiConfigurationconfig,ActionListenerlistener)\{ 
2.  **if**(config==**null**)**throw****new**IllegalArgumentException("configcannotbenull");
3.  validateChannel();
4.  //UseINVALID\_NETWORK\_IDforarg1whenpassingaconfigobject
5.  //arg1isusedtopassnetworkidwhenthenetworkalreadyexists
6.  sAsyncChannel.sendMessage(CONNECT\_NETWORK,WifiConfiguration.INVALID\_NETWORK\_ID,
7.  putListener(listener),config);
8.  \}

其中第一个参数WifiConfiguration是当前需要连接的AP的配置信息，包括SSID、BSSID、密码以及加密方式等信息；ActionListern作为callback来通知客户程序connect方法是否调用成功，这里的调用成功只是指参数是否正确，并不表示AP是否连接成功。由前面介绍的AsyncChannel的知识，到WifiService中去看看如果处理CONNECT\_NETWORK这个消息：

**\[java\]** [view plain][] [copy][view plain] [![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **case**WifiManager.CONNECT\_NETWORK:
2.  **case**WifiManager.SAVE\_NETWORK:\{ 
3.  WifiConfigurationconfig=(WifiConfiguration)msg.obj;
4.  **int**networkId=msg.arg1;
5.  **if**(config!=**null**&&config.isValid())\{ 
6.  //ThisisrestrictedbecausethereisnoUIfortheuserto
7.  //monitor/controlPAC.
8.  **if**(config.proxySettings!=ProxySettings.PAC)\{ 
9.  **if**(DBG)Slog.d(TAG,"Connectwithconfig"\+config);
10. mWifiStateMachine.sendMessage(Message.obtain(msg));
11. \}reak;
12. \}

WifiService将这个消息传递给WifiStateMachine处理，由前面介绍的Scan的知识，这时候WifiStateMachine的ConnectModeState将处理CONNECT\_NETWORK这个消息，代码如下：

**\[java\]** [view plain][] [copy][view plain] [![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **case**WifiManager.CONNECT\_NETWORK:
2.  
3.  **int**netId=message.arg1;
4.  config=(WifiConfiguration)message.obj;
5.  
6.  /\*Savethenetworkconfig\*/
7.  **if**(config!=**null**)\{ 
8.  NetworkUpdateResultresult=mWifiConfigStore.saveNetwork(config);
9.  netId=result.getNetworkId();
10. \}
11. 
12. **if**(mWifiConfigStore.selectNetwork(netId)&&
13. mWifiNative.reconnect())\{ 
14. /\*Thestatetrackerhandlesenablingnetworksuponcompletion/failure\*/
15. mSupplicantStateTracker.sendMessage(WifiManager.CONNECT\_NETWORK);
16. replyToMessage(message,WifiManager.CONNECT\_NETWORK\_SUCCEEDED);
17. /\*Expectadisconnectionfromtheoldconnection\*/
18. transitionTo(mDisconnectingState);
19. \}
20. **break**;

这里主要调用了下面几个函数来进行AP的连接：WifiConfigStore.saveNetwok(config)将AP的配置信息写入到wpa\_supplicant.conf中；WifiConfigStore.selectNetwork(netId)用于enable即将要连接的AP，而disable掉其它的AP；WifiNative.reconnect()发起重新连接的请求给wpa\_supplicant。接着transition到DisconnectingState中，来看看DisconnectingState，这个状态code比较少：

**\[java\]** [view plain][] [copy][view plain] [![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **class**DisconnectingState**extends**State\{ 
2.  @Override
3.  **public****boolean**processMessage(Messagemessage)\{ 
4.  **switch**(message.what)\{ 
5.  **case**CMD\_SET\_OPERATIONAL\_MODE:
6.  **if**(message.arg1!=CONNECT\_MODE)\{ 
7.  deferMessage(message);
8.  \}
9.  **break**;
10. **case**WifiMonitor.SUPPLICANT\_STATE\_CHANGE\_EVENT:
11. /\*IfwegetaSUPPLICANT\_STATE\_CHANGE\_EVENTbeforeNETWORK\_DISCONNECTION\_EVENT
12. \*wehavemissedthenetworkdisconnection,transitiontomDisconnectedState
13. \*andhandletherestoftheeventsthere
14. \*/
15. deferMessage(message);
16. handleNetworkDisconnect();
17. transitionTo(mDisconnectedState);
18. **break**;
19. **default**:
20. **return**NOT\_HANDLED;
21. \}
22. **return**HANDLED;
23. \}
24. \}

当执行完WifiNative.reconnect()，wpa\_supplicant会不断的往WifiMonitor发送包括CTRL-EVENT-STATE-CHANGE、ASSOCIATING、ASSOCIATED、FOUR\_WAY\_HANDSHARK、GROUP\_HANDSHARK等event，WifiMonitor会不断的去parse这些event并向WifiStatemachine发送消息，其中一个比较重要的消息就是当wpa\_supplicant的状态改变是会发送WifiMonitor.SUPPLICANT\_STATE\_CHANGE\_EVENT，上面的DisconnectiongState 收到这个消息后，会transition到DisconnectedState。

当Wifi和AP之间已经连接成功后，就会收到wpa\_supplicant发送上来的CTRL-EVENT-CONNECTED这个event，WifiMonitor收到这个消息后，会向WifiStateMachine发送NETWORK\_CONNECTION\_EVENT表示已经和AP之间成功的连线，WifiStateMachine的ConnectModeState会来处理这个消息，代码如下：

**\[java\]** [view plain][] [copy][view plain] [![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **case**WifiMonitor.NETWORK\_CONNECTION\_EVENT:
2.  **if**(DBG)log("Networkconnectionestablished");
3.  mLastNetworkId=message.arg1;
4.  mLastBssid=(String)message.obj;
5.  
6.  mWifiInfo.setBSSID(mLastBssid);
7.  mWifiInfo.setNetworkId(mLastNetworkId);
8.  /\*sendeventtoCM&networkchangebroadcast\*/
9.  setNetworkDetailedState(DetailedState.OBTAINING\_IPADDR);
10. sendNetworkStateChangeBroadcast(mLastBssid);
11. transitionTo(mObtainingIpState);
12. **break**;

WifiStateMachine处理完这个消息后，会跳转到ObtainingIpState，进到到ObtainingIpState的enter函数看看：

**\[java\]** [view plain][] [copy][view plain] [![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **class**ObtainingIpState**extends**State\{ 
2.  @Override
3.  **public****void**enter()\{ 
4.  **if**(!mWifiConfigStore.isUsingStaticIp(mLastNetworkId))\{ 
5.  //TODO:Ifwe'reswitchingbetweenstaticIPconfigurationandDHCP,removethe
6.  //staticconfigurationfirst.
7.  startDhcp();
8.  \}**else**\{ 
9.  //stopanyrunningdhcpbeforeassigningstaticIP
10. stopDhcp();
11. DhcpResultsdhcpResults=**new**DhcpResults(
12. mWifiConfigStore.getLinkProperties(mLastNetworkId));
13. InterfaceConfigurationifcg=**new**InterfaceConfiguration();
14. Iterator<LinkAddress>addrs=
15. dhcpResults.linkProperties.getLinkAddresses().iterator();
16. **if**(!addrs.hasNext())\{ 
17. loge("StaticIPlacksaddress");
18. sendMessage(CMD\_STATIC\_IP\_FAILURE);
19. \}**else**\{ 
20. ifcg.setLinkAddress(addrs.next());
21. ifcg.setInterfaceUp();
22. **try**\{ 
23. mNwService.setInterfaceConfig(mInterfaceName,ifcg);
24. **if**(DBG)log("StaticIPconfigurationsucceeded");
25. sendMessage(CMD\_STATIC\_IP\_SUCCESS,dhcpResults);
26. \}**catch**(RemoteExceptionre)\{ 
27. loge("StaticIPconfigurationfailed:"\+re);
28. sendMessage(CMD\_STATIC\_IP\_FAILURE);
29. \}**catch**(IllegalStateExceptione)\{ 
30. loge("StaticIPconfigurationfailed:"\+e);
31. sendMessage(CMD\_STATIC\_IP\_FAILURE);
32. \}
33. \}
34. \}
35. \}

ObtainingIpState就是获取IP的状态，这里分为两种获取IP的方式，一种是用户静态配置的，另一种是通过DHCP动态分配。这里只看动态分配的，进到到startDhcp去分析：

**\[java\]** [view plain][] [copy][view plain] [![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **void**startDhcp()\{ 
2.  **if**(mDhcpStateMachine==**null**)\{ 
3.  mDhcpStateMachine=DhcpStateMachine.makeDhcpStateMachine(
4.  mContext,WifiStateMachine.**this**,mInterfaceName);
5.  
6.  \}
7.  mDhcpStateMachine.registerForPreDhcpNotification();
8.  mDhcpStateMachine.sendMessage(DhcpStateMachine.CMD\_START\_DHCP);
9.  \}

首先去创建DhcpStateMachine的实例，然后向它发送一个CMD\_START\_DHCP的命令，DhcpStateMachine初始化完毕后，收到这个消息就会马上向WifiStateMachine发送CMD\_PRE\_DHCP\_ACTION表示DhcpStateMachine马上就要开始发送discovery或者renew的封包了，来看WifiStateMachine收到这个消息的处理：

**\[java\]** [view plain][] [copy][view plain] [![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **public****boolean**processMessage(Messagemessage)\{ 
2.  **switch**(message.what)\{ 
3.  **case**DhcpStateMachine.CMD\_PRE\_DHCP\_ACTION:
4.  handlePreDhcpSetup();
5.  **break**;
6.  **case**DhcpStateMachine.CMD\_POST\_DHCP\_ACTION:
7.  handlePostDhcpSetup();
8.  **if**(message.arg1==DhcpStateMachine.DHCP\_SUCCESS)\{ 
9.  **if**(DBG)log("DHCPsuccessful");
10. handleSuccessfulIpConfiguration((DhcpResults)message.obj);
11. transitionTo(mVerifyingLinkState);
12. \}**else****if**(message.arg1==DhcpStateMachine.DHCP\_FAILURE)\{ 
13. **if**(DBG)log("DHCPfailed");
14. handleFailedIpConfiguration();
15. transitionTo(mDisconnectingState);
16. \}
17. **break**;

在处理完CMD\_PRE\_DHCP\_ACTION后，WifiStateMachine会向DhcpStateMachine发送CMD\_PRE\_DHCP\_ACTION\_COMPLETE，用于指示前期准备工作已经做好了，这是就可以开始dhcp的discovery/reponse了，用于两端来获取IP，当IP成功获取后，DhcpStateMachine会给WifiStateMachine发送CMD\_POST\_DHCP\_ACTION消息，其中arg1表示是成功还是失败，如果成功，就会调用handleSuccessfulIpConfiguration来处理，并transition 到VerifyingLinkState中；如果失败则会transition到DisconectingState中。这里只看成功获取IP的情况，进入到VerifyingLinkState中：

**\[java\]** [view plain][] [copy][view plain] [![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **class**VerifyingLinkState**extends**State\{ 
2.  @Override
3.  **public****void**enter()\{ 
4.  log(getName()+"enter");
5.  setNetworkDetailedState(DetailedState.VERIFYING\_POOR\_LINK);
6.  mWifiConfigStore.updateStatus(mLastNetworkId,DetailedState.VERIFYING\_POOR\_LINK);
7.  sendNetworkStateChangeBroadcast(mLastBssid);
8.  \}
9.  @Override
10. **public****boolean**processMessage(Messagemessage)\{ 
11. **switch**(message.what)\{ 
12. **case**WifiWatchdogStateMachine.POOR\_LINK\_DETECTED:
13. //stayhere
14. log(getName()+"POOR\_LINK\_DETECTED:notransition");
15. **break**;
16. **case**WifiWatchdogStateMachine.GOOD\_LINK\_DETECTED:
17. log(getName()+"GOOD\_LINK\_DETECTED:transitiontocaptiveportalcheck");
18. transitionTo(mCaptivePortalCheckState);
19. **break**;
20. **default**:
21. **if**(DBG)log(getName()+"what="\+message.what+"NOT\_HANDLED");
22. **return**NOT\_HANDLED;
23. \}
24. **return**HANDLED;
25. \}
26. \}

在VerifyingLinkState主要是来验证当前连接状况的，主要方式是通过统计信号强度以及丢包率，这些工作是交给WifiWatchdogStateMachine来做的，当WifiAP的信号强度增强或者变弱，会发送两种消息给WifiStateMachine，一种是WifiWatchdogStateMachine.GOOD\_LINK\_DETECTED，另一种是WifiWatchdogStateMachine.POOR\_LINK\_DETECTED。当收到GOOD\_LINK\_DETECTED消息后，就会跳转到CaptivePortalCheckState中；当收到的是POOR\_LINK\_DETECTED，则维持原来的状态不变。我们跳转到CaptivePortalCheckState去分析：

**\[java\]** [view plain][] [copy][view plain] [![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  **class**CaptivePortalCheckState**extends**State\{ 
2.  @Override
3.  **public****void**enter()\{ 
4.  log(getName()+"enter");
5.  setNetworkDetailedState(DetailedState.CAPTIVE\_PORTAL\_CHECK);
6.  mWifiConfigStore.updateStatus(mLastNetworkId,DetailedState.CAPTIVE\_PORTAL\_CHECK);
7.  sendNetworkStateChangeBroadcast(mLastBssid);
8.  \}
9.  @Override
10. **public****boolean**processMessage(Messagemessage)\{ 
11. **switch**(message.what)\{ 
12. **case**CMD\_CAPTIVE\_CHECK\_COMPLETE:
13. log(getName()+"CMD\_CAPTIVE\_CHECK\_COMPLETE");
14. **try**\{ 
15. mNwService.enableIpv6(mInterfaceName);
16. \}**catch**(RemoteExceptionre)\{ 
17. loge("FailedtoenableIPv6:"\+re);
18. \}**catch**(IllegalStateExceptione)\{ 
19. loge("FailedtoenableIPv6:"\+e);
20. \}
21. setNetworkDetailedState(DetailedState.CONNECTED);
22. mWifiConfigStore.updateStatus(mLastNetworkId,DetailedState.CONNECTED);
23. sendNetworkStateChangeBroadcast(mLastBssid);
24. transitionTo(mConnectedState);
25. **break**;
26. **default**:
27. **return**NOT\_HANDLED;
28. \}
29. **return**HANDLED;
30. \}
31. \}

首先会发送CAPTIVE\_PORTAL\_CHECK的broadcast，这个会被WifiStateTracker接收并处理，然后调用ConnectivityService的接口去处理captive portal相关的内容，与captive portal相关的只是可以参考：http://en.wikipedia.org/wiki/Captive\_portal

当ConnectivityService完成captive portal check后，就会给WifiStateMachine发送CMD\_CAPTIVE\_CHECK\_COMPLETE消息，就会跳转到ConnectedState表示连接过程的结束了

转自：http://blog.csdn.net/lilian0118/article/details/22408287

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