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_jun@baidu贴吧的几篇博文，从http://hi.baidu.com/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http://hi.baidu.com/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：

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：

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

我们来到frameworks/base/wifi/java/android/net/wifi/WifiStateTracker.java中，看看addNetwork和setNetworkVariable函数都是什么样的。

#define CONNECTED "CONNECTED" 
int connect_stage(int networkId) { 
    char cmdstr[256]; 
    // enable the network 
    snprintf(cmdstr, sizeof(cmdstr), "SELECT_NETWORK %d",networkId); 
    if(!doBooleanCommand(cmdstr,"OK")) { 
        LOGE("Failed to select network %d. %s", networkId, strerror(errno)); 
        return -1; 
    } 

    // wait for connect 
    char buf[256]; 
    while(1) { 
        int nread = wifi_wait_for_event(buf, sizeof(buf)); 
        if(nread > 0) { 
            LOGE("receive buf:\n %s\n",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

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 ifname[256]; 
    property_get("wifi.interface", 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

I/wpa_supplicant(  618): CTRL-EVENT-SCAN-RESULTS  Ready
I/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=3
E/        (  612): Finished init stage.
E/        (  612): Add a network 2
E/        (  612): Finished config stage.
I/wpa_supplicant(  618): CTRL-EVENT-STATE-CHANGE id=1 state=0
E/        (  612): receive buf:
E/        (  612):  CTRL-EVENT-STATE-CHANGE id=1 state=0
I/wpa_supplicant(  618): CTRL-EVENT-STATE-CHANGE id=-1 state=2
E/        (  612): receive buf:
E/        (  612):  CTRL-EVENT-STATE-CHANGE id=-1 state=2
I/wpa_supplicant(  618): CTRL-EVENT-SCAN-RESULTS  Ready
E/        (  612): receive buf:
E/        (  612):  CTRL-EVENT-SCAN-RESULTS  Ready
I/wpa_supplicant(  618): CTRL-EVENT-STATE-CHANGE id=-1 state=4
E/        (  612): receive buf:
E/        (  612):  CTRL-EVENT-STATE-CHANGE id=-1 state=4
I/wpa_supplicant(  618): Associated with 00:24:b2:c1:16:b6
E/        (  612): receive buf:
E/        (  612):  Associated with 00:24:b2:c1:16:b6
I/wpa_supplicant(  618): CTRL-EVENT-SCAN-RESULTS  Ready
E/        (  612): receive buf:
E/        (  612):  CTRL-EVENT-SCAN-RESULTS  Ready
D/NetworkLocationProvider(  127): onCellLocationChanged [4517,30785]
I/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.

# 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# wificonnect
I/wpa_supplicant(  871): CTRL-EVENT-SCAN-RESULTS  Ready
I/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=3
E/        (  865): Finished init stage.
E/        (  865): Add a network 2
E/        (  865): Finished config stage.
I/wpa_supplicant(  871): CTRL-EVENT-STATE-CHANGE id=1 state=0
E/        (  865): receive buf:
E/        (  865):  CTRL-EVENT-STATE-CHANGE id=1 state=0
I/wpa_supplicant(  871): CTRL-EVENT-STATE-CHANGE id=-1 state=2
E/        (  865): receive buf:
E/        (  865):  CTRL-EVENT-STATE-CHANGE id=-1 state=2
I/wpa_supplicant(  871): CTRL-EVENT-SCAN-RESULTS  Ready
E/        (  865): receive buf:
E/        (  865):  CTRL-EVENT-SCAN-RESULTS  Ready
I/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=3
E/        (  865): receive buf:
E/        (  865):  CTRL-EVENT-STATE-CHANGE id=-1 state=3
I/wpa_supplicant(  871): CTRL-EVENT-STATE-CHANGE id=2 state=4
E/        (  865): receive buf:
E/        (  865):  CTRL-EVENT-STATE-CHANGE id=2 state=4
I/wpa_supplicant(  871): Associated with 00:24:b2:c1:16:b6
I/wpa_supplicant(  871): CTRL-EVENT-STATE-CHANGE id=2 state=7
I/wpa_supplicant(  871): CTRL-EVENT-CONNECTED - Connection to 00:24:b2:c1:16:b6 completed (auth) [id=2 id_str=]
E/        (  865): receive buf:
E/        (  865):  Associated with 00:24:b2:c1:16:b6
E/        (  865): receive buf:
E/        (  865):  CTRL-EVENT-STATE-CHANGE id=2 state=7
E/        (  865): receive buf:
E/        (  865):  CTRL-EVENT-CONNECTED - Connection to 00:24:b2:c1:16:b6 completed (auth) [id=2 id_str=]
E/        (  865): Finished dhcp stage.

Android下实现非启动界面Wifi连接就算是完成了，以上工作是在界面启动并且Wifi设置关闭的情况下进行的，但和在没有界面的时候应该差别不大，下面是程序的源代码

/* 
** 
** Copyright 2006, The Android Open Source Project 
** 
** Licensed under the Apache License, Version 2.0 (the "License"); 
** you may not use this file except in compliance with the License. 
** You may obtain a copy of the License at 
** 
**     http://www.apache.org/licenses/LICENSE-2.0 
** 
** Unless required by applicable law or agreed to in writing, software 
** distributed under the License is distributed on an "AS IS" BASIS, 
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
** See the License for the specific language governing permissions and 
** limitations under the License. 
*/ 

#include <stdio.h> 
#include <stdlib.h> 
#include <unistd.h> 
#include <errno.h> 
#include "string.h" 
#include "hardware_legacy/wifi.h" 
#include "cutils/log.h" 
#include "cutils/properties.h" 
#include <arpa/inet.h> 
#include <netutils/ifc.h> 
#include <netutils/dhcp.h> 

static int doCommand(const char *cmd, char *replybuf, int replybuflen) 
{ 
    size_t reply_len = replybuflen - 1; 

    if (wifi_command(cmd, replybuf, &reply_len) != 0) 
        return -1; 
    else { 
        // Strip off trailing newline 
        if (reply_len > 0 && replybuf[reply_len-1] == '\n') 
            replybuf[reply_len-1] = '\0'; 
        else 
            replybuf[reply_len] = '\0'; 
        return 0; 
    } 
} 

static int doIntCommand(const char *cmd) 
{ 
    char reply[256]; 

    if (doCommand(cmd, reply, sizeof(reply)) != 0) { 
        return -1; 
    } else { 
        return atoi(reply); 
    } 
} 

static int doBooleanCommand(const char *cmd, const char *expect) 
{ 
    char reply[256]; 

    if (doCommand(cmd, reply, sizeof(reply)) != 0) { 
        return 0; 
    } else { 
        return (strcmp(reply, expect) == 0); 
    } 
} 

// Send a command to the supplicant, and return the reply as a String 
static char* doStringCommand(const char *cmd) 
{ 
    char reply[4096]; 

    if (doCommand(cmd, reply, sizeof(reply)) != 0) { 
        return NULL; 
    } else { 
        return reply; 
    } 
} 

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; 
    } 

    ret = wifi_connect_to_supplicant(); 
    if(ret < 0) { 
        LOGE("Failed to connect supplicant daemon. %s",strerror(errno)); 
        return -1; 
    } 

    char ifname[256]; 
    property_get("wifi.interface", ifname ,"eth0"); 
    ret = ifc_enable(ifname); 
    if(ret < 0) { 
        LOGE("Failed to enable wifi interface %s. %s", ifname ,strerror(errno)); 
        return -1; 
    } 

    return 0; 
} 

int scan_stage(){ 
    // XXX we don't need to really scan the wifi 
    return 0; 
} 

#define SSID_NAME "ssid" 
#define KEY_MGMT "key_mgmt" 
#define SSID "\"xxxxx\"" 
#define PASS "NONE" 

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 cmdstr[256]; 
    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; 
    }