深海游弋的鱼 – 第 11 页

Clang的线程安全分析模块Thread Safety Analysis

背景

最近在浏览 Android 11 源代码的时候，发现在ART虚拟机头文件 art_method.h 中，存在大量的类似REQUIRES_SHARED(Locks::mutator_lock_); 的代码。

继续阅读Clang的线程安全分析模块Thread Safety Analysis

Android SSL证书设置和锁定(SSL/TLS Pinning)

我们认识到在移动端开发中安全性设置非常重要，尤其是目前非常流程H5混合式开发APP，在Android开发中，我们可以通过证书锁定的方式来增加客户端与服务端的安全保障《证书锁定SSL Pinning简介及用途》，本文主要介绍 SSL数字证书在Android开发中的证书锁定(SSL/TLS Pinning)

1. 常规SSL证书设置

通常由CA权威机构签发的证书，其根证书都内置在最新的Android操作系统中，因此默认情况下可不进行SSL证书锁定，开发APP时也就变得非常简单，以infinisign.com为例，摘自App security best practices

1.1 JAVA方法

URL url = new URL("https://infinisign.com");
HttpsURLConnection urlConnection = (HttpsURLConnection) url.openConnection();
urlConnection.connect();
InputStream in = urlConnection.getInputStream();

URL url = new URL("https://infinisign.com");

HttpsURLConnection urlConnection = (HttpsURLConnection) url.openConnection();

urlConnection.connect();

InputStream in = urlConnection.getInputStream();

1.2 KOTLIN方法

val url = URL("https://infinisign.com")
val urlConnection = url.openConnection() as HttpsURLConnection
urlConnection.connect()
urlConnection.inputStream.use {
    ...
}

val url = URL("https://infinisign.com")

val urlConnection = url.openConnection() as HttpsURLConnection

urlConnection.connect()

urlConnection.inputStream.use {

...

}

2. 网络安全性设置

本方案是官方提供，但需要依赖Android N（Android 7.0 API 24）及以后版本，可在APP开发阶段在APP中内置安全性设置，以达到防止中间人攻击（MITM）的目的，此方法只限制在Android 7.0 API 24以后版本，因此该版本之前的安全性设置仍然需要使用证书锁定方法，本文以infinisign.com为例。

2.1 创建配置文件

创建文件res/xml/network_security_config.xml，需要注意的是，使用证书锁定，需要配置一个备份密钥，假如证书到期或更换了CA品牌后，不至于重新发行APP，这个备份密码可以是中级证书或根证书。

通俗的说，如果系统检测到签发证书过期了，则自动使用其中级或才根级证书作为验证，因为通常中级机构、根机构的证书到期时间非常长。

但实际情况是，infinisign.com所售的CA签发证书有效期都是一年，而现在发行APP或更新APP通常在一年都会有更新重新上架操作。

<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
    <domain-config>
        <domain includeSubdomains="true">infinisign.com</domain>
        <pin digest="SHA-256">wLgBEAGmLltnXbK6pzpvPMeOCTKZ0QwrWGem6DkNf6o</pin>
        <!-- 备份密钥，比如infinisign.com的中级机构是geotrust -->
        <pin digest="SHA-256">wLgBEAGmLltnXbK6pzpvPMeOCTKZ0QwrWGem6DkNf6o</pin>
    </domain-config>
</network-security-config>

<?xml version="1.0" encoding="utf-8"?>

<network-security-config>

<domain-config>

<domain includeSubdomains="true">infinisign.com</domain>

<pin digest="SHA-256">wLgBEAGmLltnXbK6pzpvPMeOCTKZ0QwrWGem6DkNf6o</pin>

<pin digest="SHA-256">wLgBEAGmLltnXbK6pzpvPMeOCTKZ0QwrWGem6DkNf6o</pin>

</domain-config>

</network-security-config>

2.2 引入配置文件

在Androidmanifest.xml引入配置文件android:networkSecurityConfig="@xml/network_security_config"

<?xml version="1.0" encoding="utf-8"?>
<manifest ... >
    <application
        android:networkSecurityConfig="@xml/network_security_config">
        <!-- application 其它子元素 -->
    </application>
</manifest>

<?xml version="1.0" encoding="utf-8"?>

<application

android:networkSecurityConfig="@xml/network_security_config">

</application>

</manifest>

3. okHttp锁定

okHttp是一个用于Android处理网络请求的开源项目，是安卓端最流行的轻量级的网络框架，其主要用来替代HttpUrlConnection处理方式

client = new OkHttpClient.Builder()
    .certificatePinner(new CertificatePinner.Builder()
    .add("infinisign.com", "sha256/S8Ff3JCaO4V...")
    .build())
    .build();

client = new OkHttpClient.Builder()

.certificatePinner(new CertificatePinner.Builder()

.add("infinisign.com", "sha256/S8Ff3JCaO4V...")

.build())

.build();

不过需要注意的是，okHttp锁定证书方式不适用于公钥锁定方式，必须以证书锁定方式内置SSL数字证书。

4. TrustManager锁定

TrustManager是一个比较老的证书锁定方法，主要用于早期的Android版本或者用于一些CA根机构在Android系统中缺失根证书的情形下，当然也适用于自签名证书的锁定，通常我们不建议这样做，因为TrustManager的缺点是中间人仍然可以使用成熟的绕过方案来实现截持。

在SSL普及的今天，let's encrypt的开源免费解决方案，和一些入门的便宜DV域名型SSL证书（见PositiveSSL ￥39/年）足以媲美自签名方案。

详细请参考javax.net.ssl.TrustManager接口实现，简单步骤如下

在APP源码中内置证书

/res/raw

1

/res/raw

使用KeyStore加载证书

val resourceStream = resources.openRawResource(R.raw.infinisign_cert)
val keyStoreType = KeyStore.getDefaultType()
val keyStore = KeyStore.getInstance(keyStoreType)
keyStore.load(resourceStream, null)

val resourceStream = resources.openRawResource(R.raw.infinisign_cert)

val keyStoreType = KeyStore.getDefaultType()

val keyStore = KeyStore.getInstance(keyStoreType)

keyStore.load(resourceStream, null)

TrustManagerFactory实例化证书

val trustManagerAlgorithm = TrustManagerFactory.getDefaultAlgorithm()
val trustManagerFactory = TrustManagerFactory.getInstance(trustManagerAlgorithm)
trustManagerFactory.init(keyStore)

val trustManagerAlgorithm = TrustManagerFactory.getDefaultAlgorithm()

val trustManagerFactory = TrustManagerFactory.getInstance(trustManagerAlgorithm)

trustManagerFactory.init(keyStore)

创建SSLContext实例，与TrustManager进行绑定。

val sslContext = SSLContext.getInstance("TLS")
sslContext.init(null, trustManagerFactory.trustManagers, null)
val url = URL("http://infinisign.com/")
val urlConnection = url.openConnection() as HttpsURLConnection
urlConnection.sslSocketFactory = sslContext.socketFactory

val sslContext = SSLContext.getInstance("TLS")

sslContext.init(null, trustManagerFactory.trustManagers, null)

val url = URL("http://infinisign.com/")

val urlConnection = url.openConnection() as HttpsURLConnection

urlConnection.sslSocketFactory = sslContext.socketFactory

总结

在多数移动操作系统中有大大小小几十个CA机构内置的根证书，但也不排除已经不被信任的CA机构存在的旧根证书，还有一些例如国内的一些基于Android老版本的操作系统仍然面临着安全风险，所以使用SSL数字证书锁定（SSL/TLS Pinning）的目标是缩小可信CA的范围，让APP客户端传送数据更安全，更切实地保障用户数据。

参考链接

安卓抓包测试-之tPacketcapture

一. tPacketcapture工具

1.什么是Packetcapture？

tPacketCapture数据包捕获，而无需使用任何root权限，原理是构建了一个本地VPN服务，引导网络请求流经VPN服务，从而实现抓包。 tPacketCapture使用了Android OS VpnService提供。捕获的数据保存在外部存储为PCAP文件格式。

2.操作步骤

1）安装tPacketCapture.apk

2）打开该APP，点击"Capture"按钮

3）触发需要抓包的操作

4）用以下命令，adb pull /mnt/shell/emulated/0/Android/data/jp.co.taosoftware.android.packetcapture/files/，把文件拷贝出来了

5）.pcap会保存在adb的相同路径下

6）将.pcap取出后，用wireshark打开就能看到了相关信息

参考链接

Guava Cache用法

背景

缓存的主要作用是暂时在内存中保存业务系统的数据处理结果，并且等待下次访问使用。在日长开发有很多场合，有一些数据量不是很大，不会经常改动，并且访问非常频繁。但是由于受限于硬盘IO的性能或者远程网络等原因获取可能非常的费时。会导致我们的程序非常缓慢，这在某些业务上是不能忍的！而缓存正是解决这类问题的神器！

继续阅读Guava Cache用法

解决okHttp不能自动缓存header cookies里的sessionid

由于app要实现登录缓存功能,但惊讶的发现不经过设置okHttp是不会自动管理header的.

官网的文档也是醉了,找了半天没看懂怎么搞.

其实实现自动管理cookie很简单很简单,在OkHttp的builder中加上个.cookiejar()就能实现自动缓存,代码如下:

        OkHttpClient.Builder b = new OkHttpClient.Builder();
        b.cookieJar(new CookieJar() {
            //这里一定一定一定是HashMap<String, List<Cookie>>,是String,不是url.
            private final HashMap<String, List<Cookie>> cookieStore = new HashMap<>();

            @Override
            public void saveFromResponse(HttpUrl url, List<Cookie> cookies) {
                cookieStore.put(url.host(), cookies);
            }

            @Override
            public List<Cookie> loadForRequest(HttpUrl url) {
                List<Cookie> cookies = cookieStore.get(url.host());
                return cookies != null ? cookies : new ArrayList<Cookie>();
            }
        });

OkHttpClient.Builder b = new OkHttpClient.Builder();

b.cookieJar(new CookieJar() {

//这里一定一定一定是HashMap<String, List<Cookie>>,是String,不是url.

private final HashMap<String, List<Cookie>> cookieStore = new HashMap<>();

@Override

public void saveFromResponse(HttpUrl url, List<Cookie> cookies) {

cookieStore.put(url.host(), cookies);

}

@Override

public List<Cookie> loadForRequest(HttpUrl url) {

List<Cookie> cookies = cookieStore.get(url.host());

return cookies != null ? cookies : new ArrayList<Cookie>();

}

});

!!!!!注意注意注意!!!!!!

HashMap的key是String!!!!直接传进去url,是没有效果的!!!!!

参考链接

解决OKHttp不能自动缓存header cookies 里的 sessionid

Android获取设备DNS服务器列表

import android.annotation.TargetApi;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.LinkProperties;
import android.net.Network;
import android.net.NetworkInfo;
import android.net.RouteInfo;
import android.os.Build;
import android.util.Log;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.LineNumberReader;
import java.lang.reflect.Method;
import java.net.InetAddress;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * DNS servers detector
 * <p>
 * IMPORTANT: don't cache the result.
 * <p>
 * Or if you want to cache the result make sure you invalidate the cache
 * on any network change.
 * <p>
 * It is always better to use a new instance of the detector when you need
 * current DNS servers otherwise you may get into troubles because of invalid/changed
 * DNS servers.
 * <p>
 * This class combines various methods and solutions from:
 * Dnsjava http://www.xbill.org/dnsjava/
 * Minidns https://github.com/MiniDNS/minidns
 * <p>
 * Unfortunately both libraries are not aware of Orero changes so new method was added to fix this.
 * <p>
 * Created by Madalin Grigore-Enescu on 2/24/18.
 */

public class DnsServersDetector {

    private static final String TAG = "DnsServersDetector";

    /**
     * Holds some default DNS servers used in case all DNS servers detection methods fail.
     * Can be set to null if you want caller to fail in this situation.
     */
    private static final String[] FACTORY_DNS_SERVERS = {
            "8.8.8.8",
            "8.8.4.4"
    };

    /**
     * Properties delimiter used in exec method of DNS servers detection
     */
    private static final String METHOD_EXEC_PROP_DELIM = "]: [";

    /**
     * Holds context this was created under
     */
    private Context context;

    //region - public //////////////////////////////////////////////////////////////////////////////
    ////////////////////////////////////////////////////////////////////////////////////////////////

    /**
     * Constructor
     */
    public DnsServersDetector(Context context) {
        this.context = context;
    }

    /**
     * Returns android DNS servers used for current connected network
     *
     * @return Dns servers array
     */
    public String[] getServers() {
        // METHOD 1: old deprecated system properties
        String[] result = getServersMethodSystemProperties();
        if (result != null && result.length > 0) {
            return result;
        }
        // METHOD 2 - use connectivity manager
        result = getServersMethodConnectivityManager();
        if (result != null && result.length > 0) {
            return result;
        }
        // LAST METHOD: detect android DNS servers by executing getprop string command in a separate process
        // This method fortunately works in Oreo too but many people may want to avoid exec
        // so it's used only as a failsafe scenario
        result = getServersMethodExec();
        if (result != null && result.length > 0) {
            return result;
        }
        // Fall back on factory DNS servers
        return FACTORY_DNS_SERVERS;
    }

    //endregion

    //region - private /////////////////////////////////////////////////////////////////////////////
    ////////////////////////////////////////////////////////////////////////////////////////////////

    /**
     * Detect android DNS servers by using connectivity manager
     * <p>
     * This method is working in android LOLLIPOP or later
     *
     * @return Dns servers array
     */
    private String[] getServersMethodConnectivityManager() {

        // This code only works on LOLLIPOP and higher
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            try {
                final ArrayList<String> priorityServersArrayList = new ArrayList<>();
                final ArrayList<String> serversArrayList = new ArrayList<>();
                final ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(android.content.Context.CONNECTIVITY_SERVICE);
                if (connectivityManager != null) {
                    // Iterate all networks
                    // Notice that android LOLLIPOP or higher allow iterating multiple connected networks of SAME type
                    for (Network network : connectivityManager.getAllNetworks()) {
                        final NetworkInfo networkInfo = connectivityManager.getNetworkInfo(network);
                        if (networkInfo.isConnected()) {
                            final LinkProperties linkProperties = connectivityManager.getLinkProperties(network);
                            final List<InetAddress> dnsServersList = linkProperties.getDnsServers();
                            // Prioritize the DNS servers for link which have a default route
                            if (linkPropertiesHasDefaultRoute(linkProperties)) {
                                for (InetAddress element : dnsServersList) {
                                    final String dnsHost = element.getHostAddress();
                                    priorityServersArrayList.add(dnsHost);
                                }
                            } else {
                                for (InetAddress element : dnsServersList) {
                                    final String dnsHost = element.getHostAddress();
                                    serversArrayList.add(dnsHost);
                                }
                            }
                        }
                    }
                }

                // Append secondary arrays only if priority is empty
                if (priorityServersArrayList.isEmpty()) {
                    priorityServersArrayList.addAll(serversArrayList);
                }

                // Stop here if we have at least one DNS server
                if (priorityServersArrayList.size() > 0) {
                    return priorityServersArrayList.toArray(new String[0]);
                }
            } catch (Exception ex) {
                Log.d(TAG, "Exception detecting DNS servers using ConnectivityManager method", ex);
            }
        }
        // Failure
        return null;
    }

    /**
     * Detect android DNS servers by using old deprecated system properties
     * <p>
     * This method is NOT working anymore in Android 8.0
     * Official Android documentation state this in the article Android 8.0 Behavior Changes.
     * The system properties net.dns1, net.dns2, net.dns3, and net.dns4 are no longer available,
     * a change that improves privacy on the platform.
     * <p>
     * https://developer.android.com/about/versions/oreo/android-8.0-changes.html#o-pri
     *
     * @return Dns servers array
     */
    private String[] getServersMethodSystemProperties() {
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O) {
            // This originally looked for all lines containing .dns; but
            // http://code.google.com/p/android/issues/detail?id=2207#c73
            // indicates that net.dns* should always be the active nameservers, so
            // we use those.
            final String re1 = "^\\d+(\\.\\d+){3}$";
            final String re2 = "^[0-9a-f]+(:[0-9a-f]*)+:[0-9a-f]+$";
            ArrayList<String> serversArrayList = new ArrayList<>();
            try {
                Class<?> SystemProperties = Class.forName("android.os.SystemProperties");
                Method method = SystemProperties.getMethod("get", new Class[]{String.class});
                final String[] netdns = new String[]{"net.dns1", "net.dns2", "net.dns3", "net.dns4"};
                for (String netdn : netdns) {
                    Object[] args = new Object[]{netdn};
                    String v = (String) method.invoke(null, args);
                    if (v != null && (v.matches(re1) || v.matches(re2)) && !serversArrayList.contains(v)) {
                        serversArrayList.add(v);
                    }
                }

                // Stop here if we have at least one DNS server
                if (serversArrayList.size() > 0) {
                    return serversArrayList.toArray(new String[0]);
                }
            } catch (Exception e) {
                Log.d(TAG, "Exception detecting DNS servers using SystemProperties method", e);
            }
        }
        // Failed
        return null;
    }

    /**
     * Detect android DNS servers by executing getprop string command in a separate process
     * <p>
     * Notice there is an android bug when Runtime.exec() hangs without providing a Process object.
     * This problem is fixed in Jelly Bean (Android 4.1) but not in ICS (4.0.4) and probably it will never be fixed in ICS.
     * https://stackoverflow.com/questions/8688382/runtime-exec-bug-hangs-without-providing-a-process-object/11362081
     *
     * @return Dns servers array
     */
    private String[] getServersMethodExec() {
        // We are on the safe side and avoid any bug
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
            try {
                Process process = Runtime.getRuntime().exec("getprop");
                InputStream inputStream = process.getInputStream();
                LineNumberReader lineNumberReader = new LineNumberReader(new InputStreamReader(inputStream));
                Set<String> serversSet = methodExecParseProps(lineNumberReader);
                if (serversSet != null && serversSet.size() > 0) {
                    return serversSet.toArray(new String[0]);
                }
            } catch (Exception e) {
                Log.d(TAG, "Exception in getServersMethodExec", e);
            }
        }
        // Failed
        return null;
    }

    /**
     * Parse properties produced by executing getprop command
     *
     * @param lineNumberReader lineNumberReader
     * @return Set of parsed properties
     * @throws Exception Exception
     */
    private Set<String> methodExecParseProps(BufferedReader lineNumberReader) throws Exception {
        String line;
        Set<String> serversSet = new HashSet<String>(10);
        while ((line = lineNumberReader.readLine()) != null) {
            int split = line.indexOf(METHOD_EXEC_PROP_DELIM);
            if (split == -1) {
                continue;
            }
            String property = line.substring(1, split);

            int valueStart = split + METHOD_EXEC_PROP_DELIM.length();
            int valueEnd = line.length() - 1;
            if (valueEnd < valueStart) {
                // This can happen if a newline sneaks in as the first character of the property value. For example
                // "[propName]: [\n…]".
                Log.d(TAG, "Malformed property detected: \"" + line + '"');
                continue;
            }

            String value = line.substring(valueStart, valueEnd);

            if (value.isEmpty()) {
                continue;
            }

            if (property.endsWith(".dns") || property.endsWith(".dns1") ||
                property.endsWith(".dns2") || property.endsWith(".dns3") ||
                property.endsWith(".dns4")) {

                // normalize the address
                InetAddress ip = InetAddress.getByName(value);
                if (ip == null) continue;
                value = ip.getHostAddress();

                if (value == null) continue;
                if (value.length() == 0) continue;

                serversSet.add(value);
            }
        }
        return serversSet;
    }

    /**
     * Returns true if the specified link properties have any default route
     *
     * @param linkProperties linkProperties
     * @return true if the specified link properties have default route or false otherwise
     */
    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    private boolean linkPropertiesHasDefaultRoute(LinkProperties linkProperties) {
        for (RouteInfo route : linkProperties.getRoutes()) {
            if (route.isDefaultRoute()) {
                return true;
            }
        }
        return false;
    }
    //endregion
}

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import android.annotation.TargetApi;

import android.content.Context;

import android.net.ConnectivityManager;

import android.net.LinkProperties;

import android.net.Network;

import android.net.NetworkInfo;

import android.net.RouteInfo;

import android.os.Build;

import android.util.Log;

import java.io.BufferedReader;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.io.LineNumberReader;

import java.lang.reflect.Method;

import java.net.InetAddress;

import java.util.ArrayList;

import java.util.HashSet;

import java.util.List;

import java.util.Set;

/**

* DNS servers detector

*

* IMPORTANT: don't cache the result.

*

* Or if you want to cache the result make sure you invalidate the cache

* on any network change.

*

* It is always better to use a new instance of the detector when you need

* current DNS servers otherwise you may get into troubles because of invalid/changed

* DNS servers.

*

* This class combines various methods and solutions from:

* Dnsjava http://www.xbill.org/dnsjava/

* Minidns https://github.com/MiniDNS/minidns

*

* Unfortunately both libraries are not aware of Orero changes so new method was added to fix this.

*

* Created by Madalin Grigore-Enescu on 2/24/18.

public class DnsServersDetector {

private static final String TAG = "DnsServersDetector";

/**

* Holds some default DNS servers used in case all DNS servers detection methods fail.

* Can be set to null if you want caller to fail in this situation.

private static final String[] FACTORY_DNS_SERVERS = {

"8.8.8.8",

"8.8.4.4"

};

/**

* Properties delimiter used in exec method of DNS servers detection

private static final String METHOD_EXEC_PROP_DELIM = "]: [";

/**

* Holds context this was created under

private Context context;

//region - public //////////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////////////////////////////

/**

* Constructor

public DnsServersDetector(Context context) {

this.context = context;

}

/**

* Returns android DNS servers used for current connected network

* @return Dns servers array

public String[] getServers() {

// METHOD 1: old deprecated system properties

String[] result = getServersMethodSystemProperties();

if (result != null && result.length > 0) {

return result;

}

// METHOD 2 - use connectivity manager

result = getServersMethodConnectivityManager();

if (result != null && result.length > 0) {

return result;

}

// LAST METHOD: detect android DNS servers by executing getprop string command in a separate process

// This method fortunately works in Oreo too but many people may want to avoid exec

// so it's used only as a failsafe scenario

result = getServersMethodExec();

if (result != null && result.length > 0) {

return result;

}

// Fall back on factory DNS servers

return FACTORY_DNS_SERVERS;

}

//endregion

//region - private /////////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////////////////////////////

/**

* Detect android DNS servers by using connectivity manager

*

* This method is working in android LOLLIPOP or later

* @return Dns servers array

private String[] getServersMethodConnectivityManager() {

// This code only works on LOLLIPOP and higher

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {

try {

final ArrayList<String> priorityServersArrayList = new ArrayList<>();

final ArrayList<String> serversArrayList = new ArrayList<>();

final ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(android.content.Context.CONNECTIVITY_SERVICE);

if (connectivityManager != null) {

// Iterate all networks

// Notice that android LOLLIPOP or higher allow iterating multiple connected networks of SAME type

for (Network network : connectivityManager.getAllNetworks()) {

final NetworkInfo networkInfo = connectivityManager.getNetworkInfo(network);

if (networkInfo.isConnected()) {

final LinkProperties linkProperties = connectivityManager.getLinkProperties(network);

final List<InetAddress> dnsServersList = linkProperties.getDnsServers();

// Prioritize the DNS servers for link which have a default route

if (linkPropertiesHasDefaultRoute(linkProperties)) {

for (InetAddress element : dnsServersList) {

final String dnsHost = element.getHostAddress();

priorityServersArrayList.add(dnsHost);

}

} else {

for (InetAddress element : dnsServersList) {

final String dnsHost = element.getHostAddress();

serversArrayList.add(dnsHost);

}

// Append secondary arrays only if priority is empty

if (priorityServersArrayList.isEmpty()) {

priorityServersArrayList.addAll(serversArrayList);

}

// Stop here if we have at least one DNS server

if (priorityServersArrayList.size() > 0) {

return priorityServersArrayList.toArray(new String[0]);

}

} catch (Exception ex) {

Log.d(TAG, "Exception detecting DNS servers using ConnectivityManager method", ex);

}

// Failure

return null;

}

/**

* Detect android DNS servers by using old deprecated system properties

*

* This method is NOT working anymore in Android 8.0

* Official Android documentation state this in the article Android 8.0 Behavior Changes.

* The system properties net.dns1, net.dns2, net.dns3, and net.dns4 are no longer available,

* a change that improves privacy on the platform.

*

* https://developer.android.com/about/versions/oreo/android-8.0-changes.html#o-pri

* @return Dns servers array

private String[] getServersMethodSystemProperties() {

if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O) {

// This originally looked for all lines containing .dns; but

// http://code.google.com/p/android/issues/detail?id=2207#c73

// indicates that net.dns* should always be the active nameservers, so

// we use those.

final String re1 = "^\\d+(\\.\\d+){3}$";

final String re2 = "^[0-9a-f]+(:[0-9a-f]*)+:[0-9a-f]+$";

ArrayList<String> serversArrayList = new ArrayList<>();

try {

Class<?> SystemProperties = Class.forName("android.os.SystemProperties");

Method method = SystemProperties.getMethod("get", new Class[]{String.class});

final String[] netdns = new String[]{"net.dns1", "net.dns2", "net.dns3", "net.dns4"};

for (String netdn : netdns) {

Object[] args = new Object[]{netdn};

String v = (String) method.invoke(null, args);

if (v != null && (v.matches(re1) || v.matches(re2)) && !serversArrayList.contains(v)) {

serversArrayList.add(v);

}

// Stop here if we have at least one DNS server

if (serversArrayList.size() > 0) {

return serversArrayList.toArray(new String[0]);

}

} catch (Exception e) {

Log.d(TAG, "Exception detecting DNS servers using SystemProperties method", e);

}

// Failed

return null;

}

/**

* Detect android DNS servers by executing getprop string command in a separate process

*

* Notice there is an android bug when Runtime.exec() hangs without providing a Process object.

* This problem is fixed in Jelly Bean (Android 4.1) but not in ICS (4.0.4) and probably it will never be fixed in ICS.

* https://stackoverflow.com/questions/8688382/runtime-exec-bug-hangs-without-providing-a-process-object/11362081

* @return Dns servers array

private String[] getServersMethodExec() {

// We are on the safe side and avoid any bug

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {

try {

Process process = Runtime.getRuntime().exec("getprop");

InputStream inputStream = process.getInputStream();

LineNumberReader lineNumberReader = new LineNumberReader(new InputStreamReader(inputStream));

Set<String> serversSet = methodExecParseProps(lineNumberReader);

if (serversSet != null && serversSet.size() > 0) {

return serversSet.toArray(new String[0]);

}

} catch (Exception e) {

Log.d(TAG, "Exception in getServersMethodExec", e);

}

// Failed

return null;

}

/**

* Parse properties produced by executing getprop command

* @param lineNumberReader lineNumberReader

* @return Set of parsed properties

* @throws Exception Exception

private Set<String> methodExecParseProps(BufferedReader lineNumberReader) throws Exception {

String line;

Set<String> serversSet = new HashSet<String>(10);

while ((line = lineNumberReader.readLine()) != null) {

int split = line.indexOf(METHOD_EXEC_PROP_DELIM);

if (split == -1) {

continue;

}

String property = line.substring(1, split);

int valueStart = split + METHOD_EXEC_PROP_DELIM.length();

int valueEnd = line.length() - 1;

if (valueEnd < valueStart) {

// This can happen if a newline sneaks in as the first character of the property value. For example

// "[propName]: [\n…]".

Log.d(TAG, "Malformed property detected: \"" + line + '"');

continue;

}

String value = line.substring(valueStart, valueEnd);

if (value.isEmpty()) {

continue;

}

if (property.endsWith(".dns") || property.endsWith(".dns1") ||

property.endsWith(".dns2") || property.endsWith(".dns3") ||

property.endsWith(".dns4")) {

// normalize the address

InetAddress ip = InetAddress.getByName(value);

if (ip == null) continue;

value = ip.getHostAddress();

if (value == null) continue;

if (value.length() == 0) continue;

serversSet.add(value);

}

return serversSet;

}

/**

* Returns true if the specified link properties have any default route

* @param linkProperties linkProperties

* @return true if the specified link properties have default route or false otherwise

@TargetApi(Build.VERSION_CODES.LOLLIPOP)

private boolean linkPropertiesHasDefaultRoute(LinkProperties linkProperties) {

for (RouteInfo route : linkProperties.getRoutes()) {

if (route.isDefaultRoute()) {

return true;

}

return false;

}

//endregion

}

参考链接

Android DNS更新与DNS-Prefetch

一、什么是DNS

DNS（Domain Name System，域名系统），dns用于将域名解析解析为ip地址。

例如：给你www.baidu.com的主机名，你给
我查出对应的ip地址：163.177.151.109。一些主机名还会有别名，如www.baidu.com就
有别名www.a.shifen.com，甚至不止一个别名，或一个别名有2个ip地址。在linux机子
上，运行nslookup（name service lookup）就是进行域名解析。如下面：

~$ nslookup www.baidu.com
Server:         127.0.0.1
Address:        127.0.0.1#53

Non-authoritative answer:
www.baidu.com   canonical name = www.a.shifen.com.
Name:   www.a.shifen.com
Address: 163.177.151.109
Name:   www.a.shifen.com
Address: 163.177.151.110

~$ nslookup www.baidu.com

Server: 127.0.0.1

Address: 127.0.0.1#53

Non-authoritative answer:

www.baidu.com canonical name = www.a.shifen.com.

Name: www.a.shifen.com

Address: 163.177.151.109

Name: www.a.shifen.com

Address: 163.177.151.110

DNS工作方式分为递归查询和迭代查询，具体可参考下图

继续阅读Android DNS更新与DNS-Prefetch

【解决】Unable to locate adb

环境：Android Studio 4.0 打开虚拟设备时，弹出“Unable to locate adb”，如下图：

继续阅读【解决】Unable to locate adb

flutter动态申请权限

https://pub.flutter-io.cn/packages/permission_handler

https://www.jianshu.com/p/fa68876fbdfd

例

  Future requestPermission() async {
    // 申请权限
    Map<PermissionGroup, PermissionStatus> permissions =
        await PermissionHandler().requestPermissions([PermissionGroup.storage]);

    // 申请结果
    PermissionStatus permission = await PermissionHandler()
        .checkPermissionStatus(PermissionGroup.storage);

    if (permission == PermissionStatus.granted) {
      print("权限申请通过");
    } else {
      print("权限申请通过");
    }
  }
}

Future requestPermission() async {

// 申请权限

Map<PermissionGroup, PermissionStatus> permissions =

await PermissionHandler().requestPermissions([PermissionGroup.storage]);

// 申请结果

PermissionStatus permission = await PermissionHandler()

.checkPermissionStatus(PermissionGroup.storage);

if (permission == PermissionStatus.granted) {

print("权限申请通过");

} else {

print("权限申请通过");

}

参考链接

flutter 动态申请权限

AAPT: error: resource android:attr/fontVariationSettings not found

最近在编译Flutter项目的时候，报错如下：

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':app:processDebugResources'.
> Android resource linking failed
  Output:  /Users/xxxx/Source/developer_quest/build/app/intermediates/incremental/mergeDebugResources/merged.dir/values/values.xml:86: error: resource android:attr/fontVariationSettings not found.
  /Users/xxxx/Source/developer_quest/build/app/intermediates/incremental/mergeDebugResources/merged.dir/values/values.xml:87: error: resource android:attr/ttcIndex not found.
  error: failed linking references.

  Command: /Users/xxxx/.gradle/caches/transforms-1/files-1.1/aapt2-3.2.1-4818971-osx.jar/ace5a2b7765511437e6add51febae423/aapt2-3.2.1-4818971-osx/aapt2 link -I\
          /Users/xxxx/Library/Android/sdk/platforms/android-27/android.jar\
          --manifest\
          /Users/xxxx/Source/developer_quest/build/app/intermediates/merged_manifests/debug/processDebugManifest/merged/AndroidManifest.xml\
          -o\
          /Users/xxxx/Source/developer_quest/build/app/intermediates/processed_res/debug/processDebugResources/out/resources-debug.ap_\
          -R\
          @/Users/xxxx/Source/developer_quest/build/app/intermediates/incremental/processDebugResources/resources-list-for-resources-debug.ap_.txt\
          --auto-add-overlay\
          --java\
          /Users/xxxx/Source/developer_quest/build/app/generated/not_namespaced_r_class_sources/debug/processDebugResources/r\
          --custom-package\
          dev.flutter.devrpg\
          -0\
          apk\
          --output-text-symbols\
          /Users/xxxx/Source/developer_quest/build/app/intermediates/symbols/debug/R.txt\
          --no-version-vectors
  Daemon:  AAPT2 aapt2-3.2.1-4818971-osx Daemon #0
  Output:  /Users/xxxx/.gradle/caches/transforms-1/files-1.1/core-1.1.0.aar/becc1f5b1538f3fe61f1f959fb2bd672/res/values/values.xml:174:5-210:25: AAPT: error: resource android:attr/fontVariationSettings not found.

  /Users/xxxx/.gradle/caches/transforms-1/files-1.1/core-1.1.0.aar/becc1f5b1538f3fe61f1f959fb2bd672/res/values/values.xml:174:5-210:25: AAPT: error: resource android:attr/ttcIndex not found.

  error: failed linking references.
  Command: /Users/xxxx/.gradle/caches/transforms-1/files-1.1/aapt2-3.2.1-4818971-osx.jar/ace5a2b7765511437e6add51febae423/aapt2-3.2.1-4818971-osx/aapt2 link -I\
          /Users/xxxx/Library/Android/sdk/platforms/android-27/android.jar\
          --manifest\
          /Users/xxxx/Source/developer_quest/build/app/intermediates/merged_manifests/debug/processDebugManifest/merged/AndroidManifest.xml\
          -o\
          /Users/xxxx/Source/developer_quest/build/app/intermediates/processed_res/debug/processDebugResources/out/resources-debug.ap_\
          -R\
          @/Users/xxxx/Source/developer_quest/build/app/intermediates/incremental/processDebugResources/resources-list-for-resources-debug.ap_.txt\
          --auto-add-overlay\
          --java\
          /Users/xxxx/Source/developer_quest/build/app/generated/not_namespaced_r_class_sources/debug/processDebugResources/r\
          --custom-package\
          dev.flutter.devrpg\
          -0\
          apk\
          --output-text-symbols\
          /Users/xxxx/Source/developer_quest/build/app/intermediates/symbols/debug/R.txt\
          --no-version-vectors
  Daemon:  AAPT2 aapt2-3.2.1-4818971-osx Daemon #0

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 13s
Exception: Gradle task assembleDebug failed with exit code 1

FAILURE: Build failed with an exception.

* What went wrong:

Execution failed for task ':app:processDebugResources'.

> Android resource linking failed

Output: /Users/xxxx/Source/developer_quest/build/app/intermediates/incremental/mergeDebugResources/merged.dir/values/values.xml:86: error: resource android:attr/fontVariationSettings not found.

/Users/xxxx/Source/developer_quest/build/app/intermediates/incremental/mergeDebugResources/merged.dir/values/values.xml:87: error: resource android:attr/ttcIndex not found.

error: failed linking references.

Command: /Users/xxxx/.gradle/caches/transforms-1/files-1.1/aapt2-3.2.1-4818971-osx.jar/ace5a2b7765511437e6add51febae423/aapt2-3.2.1-4818971-osx/aapt2 link -I\

/Users/xxxx/Library/Android/sdk/platforms/android-27/android.jar\

--manifest\

/Users/xxxx/Source/developer_quest/build/app/intermediates/merged_manifests/debug/processDebugManifest/merged/AndroidManifest.xml\

-o\

/Users/xxxx/Source/developer_quest/build/app/intermediates/processed_res/debug/processDebugResources/out/resources-debug.ap_\

-R\

@/Users/xxxx/Source/developer_quest/build/app/intermediates/incremental/processDebugResources/resources-list-for-resources-debug.ap_.txt\

--auto-add-overlay\

--java\

/Users/xxxx/Source/developer_quest/build/app/generated/not_namespaced_r_class_sources/debug/processDebugResources/r\

--custom-package\

dev.flutter.devrpg\

-0\

apk\

--output-text-symbols\

/Users/xxxx/Source/developer_quest/build/app/intermediates/symbols/debug/R.txt\

--no-version-vectors

Daemon: AAPT2 aapt2-3.2.1-4818971-osx Daemon #0

Output: /Users/xxxx/.gradle/caches/transforms-1/files-1.1/core-1.1.0.aar/becc1f5b1538f3fe61f1f959fb2bd672/res/values/values.xml:174:5-210:25: AAPT: error: resource android:attr/fontVariationSettings not found.

/Users/xxxx/.gradle/caches/transforms-1/files-1.1/core-1.1.0.aar/becc1f5b1538f3fe61f1f959fb2bd672/res/values/values.xml:174:5-210:25: AAPT: error: resource android:attr/ttcIndex not found.

error: failed linking references.

Command: /Users/xxxx/.gradle/caches/transforms-1/files-1.1/aapt2-3.2.1-4818971-osx.jar/ace5a2b7765511437e6add51febae423/aapt2-3.2.1-4818971-osx/aapt2 link -I\

/Users/xxxx/Library/Android/sdk/platforms/android-27/android.jar\

--manifest\

/Users/xxxx/Source/developer_quest/build/app/intermediates/merged_manifests/debug/processDebugManifest/merged/AndroidManifest.xml\

-o\

/Users/xxxx/Source/developer_quest/build/app/intermediates/processed_res/debug/processDebugResources/out/resources-debug.ap_\

-R\

@/Users/xxxx/Source/developer_quest/build/app/intermediates/incremental/processDebugResources/resources-list-for-resources-debug.ap_.txt\

--auto-add-overlay\

--java\

/Users/xxxx/Source/developer_quest/build/app/generated/not_namespaced_r_class_sources/debug/processDebugResources/r\

--custom-package\

dev.flutter.devrpg\

-0\

apk\

--output-text-symbols\

/Users/xxxx/Source/developer_quest/build/app/intermediates/symbols/debug/R.txt\

--no-version-vectors

Daemon: AAPT2 aapt2-3.2.1-4818971-osx Daemon #0

* Try:

Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 13s

Exception: Gradle task assembleDebug failed with exit code 1

解决方案：

try to change the compileSdkVersion above 27:

compileSdkVersion 28

参考链接

resource android:attr/fontVariationSettings not found

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