Android下实现非启动界面Wifi连接.doc

Android下实现非启动界面Wifi连接Android的网络功能和一般的linux并无太大的区别，我原来以为在Android上连接网络和普通的linux连接网络没有很大区别，事实上区别还是有一些的。由于项目的需要，我的目标是在Android的界面没有启动之前连接wifi，于是本来的期待是直接在init.rc中加入一些脚本调用即可，但研究了一会儿发现没有那么简单。首先要感谢anly_junbaidu贴吧的几篇博文，从/anly_jun/blog/item/8ecb92d593d144cf50da4b6e.html开始，一共有七篇关于Android Wifi模块分析，其中有大量博主自己使用UML工具画的调用讲解，对于理解Android Wifi工作机制还是有很用的。其中最重要的是下面这几幅图。（转自/anly_jun/blog/item/65e26e117e09ebcda6ef3f56.html）在想要对wifi硬件动作之前，需要做两件事情，一是要load wifi的driver，而是要打开wpa_supplicant，其实如果是连接没有加密的wifi，没有必要打开wpa_supplicant，但是为了讲问题化为熟知的问题，此处还是先按照提示调用wifi_load_driver()和wifi_start_supplicant()按照上面的提示写出来的初始化代码如下：int init_stage() / load the wifi driver: insmod .ko int ret = wifi_load_driver(); if(ret 0) LOGE(Failed to load Wi-Fi driver. %s,strerror(errno); return -1; / start wpa_supplicant ret = wifi_start_supplicant(); if(ret 0) LOGE(Failed to start supplicant daemon. %s,strerror(errno); return -1; return 0; 接下来，便是连接的过程了，经过上面的步骤，wifi的driver已经载入，wpa_supplicant也已经打开，那咱们就可以开始连接无线了吧。后来证实这是错误的，因为anly_jun的这篇Android wifi分析的粒度只在Java层面的函数级别，因此有一些细节并没有提到。在下面我会提到这些细节。按照一般的linux中连接wifi的步骤，这时候就可以直接调用一个程序来连接某个ssid的无线网络，然后调用dhcpd来分配ip了，我之前在eeepc上连接wifi就非常简单，调用iwconfig ssid，再调用dhcpd就可以了。但很遗憾，Android上并没有iwconfig这样方便的工具。这下线索似乎就断了，天无绝人之路，既然在Android的Java code中都可以添加一个无线网络并且连接，那我们就去Android的Java源代码中找一找。在Android中，程序员是使用WifiManager这个类来进行Wifi操作的，其中关于添加一个网络的代码如下：/* * Add a new network description to the set of configured networks. * The code networkId field of the supplied configuration object * is ignored. * * The new network will be marked DISABLED by default. To enable it, * called link #enableNetwork. * * param config the set of variables that describe the configuration, * contained in a link WifiConfiguration object. * return the ID of the newly created network description. This is used in * other operations to specified the network to be acted upon. * Returns code -1 on failure. */ public int addNetwork(WifiConfiguration config) if (config = null) return -1; workId = -1; return addOrUpdateNetwork(config); /* * Internal method for doing the RPC that creates a new network description * or updates an existing one. * * param config The possibly sparse object containing the variables that * are to set or updated in the network description. * return the ID of the network on success, code -1 on failure. */ private int addOrUpdateNetwork(WifiConfiguration config) try return mService.addOrUpdateNetwork(config); catch (RemoteException e) return -1; 看其中确实是调用了service的函数，于是又在frameworks/base/services/java/com/android/server/WifiService.java中找到了有关增加一个网络配置的相关代码/* * see link .wifi.WifiManager#addOrUpdateNetwork(WifiConfiguration) * return the supplicant-assigned identifier for the new or updated * network if the operation succeeds, or code -1 if it fails */ public int addOrUpdateNetwork(WifiConfiguration config) enforceChangePermission(); /* * If the supplied networkId is -1, we create a new empty * network configuration. Otherwise, the networkId should * refer to an existing configuration. */ int netId = workId; boolean newNetwork = netId = -1; boolean doReconfig = false; / networkId of -1 means we want to create a new network synchronized (mWifiStateTracker) if (newNetwork) netId = mWifiStateTracker.addNetwork(); if (netId 0 & replybufreply_len-1 = n) replybufreply_len-1 = message; else replybufreply_len = message; return 0; static jint doIntCommand(const char *cmd) char reply256; if (doCommand(cmd, reply, sizeof(reply) != 0) return (jint)-1; else return (jint)atoi(reply); static jboolean doBooleanCommand(const char *cmd, const char *expect) char reply256; if (doCommand(cmd, reply, sizeof(reply) != 0) return (jboolean)JNI_FALSE; else return (jboolean)(strcmp(reply, expect) = 0); static jint android_net_wifi_addNetworkCommand(JNIEnv* env, jobject clazz) return doIntCommand(ADD_NETWORK); static jboolean android_net_wifi_setNetworkVariableCommand(JNIEnv* env, jobject clazz, jint netId, jstring name, jstring value) char cmdstr256; jboolean isCopy; const char *nameStr = env-GetStringUTFChars(name, &isCopy); const char *valueStr = env-GetStringUTFChars(value, &isCopy); if (nameStr = NULL | valueStr = NULL) return JNI_FALSE; int cmdTooLong = snprintf(cmdstr, sizeof(cmdstr), SET_NETWORK %d %s %s, netId, nameStr, valueStr) = (int)sizeof(cmdstr); env-ReleaseStringUTFChars(name, nameStr); env-ReleaseStringUTFChars(value, valueStr); return (jboolean)!cmdTooLong & doBooleanCommand(cmdstr, OK); / - /* * JNI registration. */ static JNINativeMethod gWifiMethods = /* name, signature, funcPtr */ loadDriver, ()Z, (void *)android_net_wifi_loadDriver , unloadDriver, ()Z, (void *)android_net_wifi_unloadDriver , startSupplicant, ()Z, (void *)android_net_wifi_startSupplicant , stopSupplicant, ()Z, (void *)android_net_wifi_stopSupplicant , connectToSupplicant, ()Z, (void *)android_net_wifi_connectToSupplicant , closeSupplicantConnection, ()V, (void *)android_net_wifi_closeSupplicantConnection , listNetworksCommand, ()Ljava/lang/String;, (void*) android_net_wifi_listNetworksCommand , addNetworkCommand, ()I, (void*) android_net_wifi_addNetworkCommand , setNetworkVariableCommand, (ILjava/lang/String;Ljava/lang/String;)Z, (void*) android_net_wifi_setNetworkVariableCommand , getNetworkVariableCommand, (ILjava/lang/String;)Ljava/lang/String;, (void*) android_net_wifi_getNetworkVariableCommand , 看来这下终于找到干活儿的函数了，可喜可贺，于是我们得出结论：在Android中，要连上一个无线网络，首先需要添加一个网络，然后设置这个网络的配置，而这些步骤实际上都是通过向wpa_supplicant发送命令实现的。命令的格式例外的很简单，比如添加一个网络配置是ADD_NETWORK，设置一个网络配置是SET_NETWORK netId varName var。于是根据Java代码我写出了配置环节的代码。int config_stage() / Add a network config to supplicant mode int networkId = doIntCommand(ADD_NETWORK); / Add a new network id if(networkId 0) LOGE(Failed to add a network configuration. %s,strerror(errno); return -1; LOGE(Add a network %d,networkId); / set the ssid of the destination wifi adhoc char cmdstr256; snprintf(cmdstr, sizeof(cmdstr), SET_NETWORK %d %s %s,networkId, SSID_NAME, SSID); if(!doBooleanCommand(cmdstr,OK) LOGE(Failed to set network %d configuration ssid. %s, networkId, strerror(errno); return -1; return networkId; 添加了一个配置的网络之后，选择某个网络配置的命令是SELECT_NETWORK netId。在SELECT_NETWORK之后，wpa_supplicant就尝试和该ssid的AP进行associate操作，在associate之后便调用dhcpd获取ip。SELECT_NETWORK是立即返回的函数，那么何以得知已经和无线AP连接上了呢？Android的界面里面连接/断开Wifi都是可以被接受到的事件，在WifiStateTracker中我们看到是由WifiMonitor来监听由wpa_supplicant发过来的消息的，于是我们来到framework/base/wifi/java/android/net/wifi/WifiMonitor.java，看到其中接受消息的Monitor线程class MonitorThread extends Thread public MonitorThread() super(WifiMonitor); public void run() if (connectToSupplicant() / Send a message indicating that it is now possible to send commands / to the supplicant mWifiStateTracker.notifySupplicantConnection(); else mWifiStateTracker.notifySupplicantLost(); return; /noinspection InfiniteLoopStatement for (;) String eventStr = WifiNative.waitForEvent(); / Skip logging the common but mostly uninteresting scan-results event if (Config.LOGD & eventStr.indexOf(scanResultsEvent) = -1) Log.v(TAG, Event + eventStr + ); if (!eventStr.startsWith(eventPrefix) if (eventStr.startsWith(wpaEventPrefix) & 0 0) LOGE(receive buf:n %sn,buf); if(strstr(buf,CONNECTED) 0) break; / XXX danger of not going out of the loop! continue; return 0; 在WifiStateTracer中我还找到了负责dhcp的DhcpHandler，按照其中的函数写了dhcp阶段的代码int dhcp_stage() int result; in_addr_t ipaddr, gateway, mask, dns1, dns2, server; uint32_t lease; char ifname256; char mDns1Name256; char mDns2Name256; property_get(erface, ifname ,eth0); snprintf(mDns1Name, sizeof(mDns1Name), net.%s.dns1,ifname); snprintf(mDns2Name, sizeof(mDns2Name), net.%s.dns2,ifname); result = dhcp_do_request(ifname, &ipaddr, &gateway, &mask, &dns1, &dns2, &server, &lease); if(result != 0) LOGE(Failed to dhcp on interface %s. %s, ifname, strerror(errno); return -1; struct in_addr dns_struct1, dns_struct2; dns_struct1.s_addr = dns1; dns_struct2.s_addr = dns2; property_set(mDns1Name,inet_ntoa(dns_struct1); property_set(mDns2Name,inet_ntoa(dns_struct2); return 0; 于是我用无线路由器建立了一个最简单的无线网络，ssid=TSever，没有密码，按照上面步骤进行联网。结果在ADD_NETWORK的步骤就出错了，无法获得网络id，这是怎么一回事呢？看到dhcp时的代码要对特定的Network Interface做操作，突然想起来之前在代码中似乎看到有对Interface做使能操作的代码WifiService在调用mWifiStateTracker.enableNetwork之前，还调用了String ifname = mWifiStateTracker.getInterfaceName(); NetworkUtils.enableInterface(ifname);这两句。于是在init阶段，加上了下面这段。 char ifname256; property_get(erface, ifname ,eth0); ret = ifc_enable(ifname); if(ret 0) LOGE(Failed to enable wifi interface %s. %s, ifname ,strerror(errno); return -1; 但是运行起来还是出同样的错误，不过这次busybox ifconfig之后可以发现eth0的端口了 ，至少没有做无用功。倒回去看在WifiMonitor的MonitorThread中有connectToSupplicant()的调用，本以为此调用不是非常关键，然后去hardware/libhardware_legacy/wifi/wifi.c文件里面看到全局有一个static struct wpa_ctrl *ctrl_conn;并且在wifi_command中需要用到这个ctrl_conn，那么如果这个ctrl_conn是NULL的话，所有的wifi_command命令自然都无法完成了，于是又加上了ret = wifi_connect_to_supplicant(); if(ret 0) LOGE(Failed to connect supplicant daemon. %s,strerror(errno); return -1; 这样编译完运行之后，果然顺利的分配到id了。运行一下程序，还是出现了错误，输出的log如下。I/wpa_supplicant( 618): CTRL-EVENT-SCAN-RESULTS ReadyI/wpa_supplicant( 618): Trying to associate with 00:24:b2:c1:16:b6 (SSID=TServer freq=2462 MHz)I/wpa_supplicant( 618): CTRL-EVENT-STATE-CHANGE id=-1 state=3E/ ( 612): Finished init stage.E/ ( 612): Add a network 2E/ ( 612): Finished config stage.I/wpa_supplicant( 618): CTRL-EVENT-STATE-CHANGE id=1 state=0E/ ( 612): receive buf:E/ ( 612): CTRL-EVENT-STATE-CHANGE id=1 state=0I/wpa_supplicant( 618): CTRL-EVENT-STATE-CHANGE id=-1 state=2E/ ( 612): receive buf:E/ ( 612): CTRL-EVENT-STATE-CHANGE id=-1 state=2I/wpa_supplicant( 618): CTRL-EVENT-SCAN-RESULTS ReadyE/ ( 612): receive buf:E/ ( 612): CTRL-EVENT-SCAN-RESULTS ReadyI/wpa_supplicant( 618): CTRL-EVENT-STATE-CHANGE id=-1 state=4E/ ( 612): receive buf:E/ ( 612): CTRL-EVENT-STATE-CHANGE id=-1 state=4I/wpa_supplicant( 618): Associated with 00:24:b2:c1:16:b6E/ ( 612): receive buf:E/ ( 612): Associated with 00:24:b2:c1:16:b6I/wpa_supplicant( 618): CTRL-EVENT-SCAN-RESULTS ReadyE/ ( 612): receive buf:E/ ( 612): CTRL-EVENT-SCAN-RESULTS ReadyD/NetworkLocationProvider( 127): onCellLocationChanged 4517,30785I/wpa_supplicant( 618): Authentication with 00:24:b2:c1:16:b6 timed out.E/ ( 612): receive buf:E/ ( 612): Authentication with 00:24:b2:c1:16:b6 timed out.注意到红色的那句log，我的wifi并没有设置密码，为什么还需要Authentication呢？想一想是不是wpa_supplicant的限制，于是去网上搜了到了这篇wpa_supplicant 工具使用，发现没有密码的情况下应该是这样的配置# 明文连接方式（不使用WPA和IEEE802.1X）network= ssid=plaintext-test key_mgmt=NONE于是在config阶段加上了对key_mgmt的设置，这下就连上了Wifi了，正确的log如下bash-4.1# wificonnectI/wpa_supplicant( 871): CTRL-EVENT-SCAN-RESULTS ReadyI/wpa_supplicant( 871): Trying to associate with 00:24:b2:c1:16:b6 (SSID=TServer freq=2462 MHz)I/wpa_supplicant( 871): CTRL-EVENT-STATE-CHANGE id=-1 state=3E/ ( 865): Finished init stage.E/ ( 865): Add a network 2E/ ( 865): Finished config stage.I/wpa_supplicant( 871): CTRL-EVENT-STATE-CHANGE id=1 state=0E/ ( 865): receive buf:E/ ( 865): CTRL-EVENT-STATE-CHANGE id=1 state=0I/wpa_supplicant( 871): CTRL-EVENT-STATE-CHANGE id=-1 state=2E/ ( 865): receive buf:E/ ( 865): CTRL-EVENT-STATE-CHANGE id=-1 state=2I/wpa_supplicant( 871): CTRL-EVENT-SCAN-RESULTS ReadyE/ ( 865): receive buf:E/ ( 865): CTRL-EVENT-SCAN-RESULTS ReadyI/wpa_supplicant( 871): Trying to associate with 00:24:b2:c1:16:b6 (SSID=TServer freq=2462 MHz)E/ ( 865): receive buf:E/ ( 865): Trying to associate with 00:24:b2:c1:16:b6 (SSID=TServer freq=2462 MHz)I/wpa_supplicant( 871): CTRL-EVENT-STATE-CHANGE id=-1 state=3E/ ( 865): receive buf:E/ ( 865): CTRL-EVENT-STATE-CHANGE id=-1 state=3I/wpa_supplicant( 871): CTRL-EVENT-STATE-CHANGE id=2 state=4E/ ( 865): receive buf:E/ ( 865): CTRL-EVENT-STATE-CHANGE id=2 state=4I/wpa_supplicant(