Android O : DNS列表获取及IPv4/IPv6优先级修改

一、Android应用获取有线网络DNS列表

    /**
     * 获取DNS列表
     */
    private List<String> getDnsList() {
        List<String> dnsList = new ArrayList();
        if (this.mIEthernetManager == null) {
            return dnsList;
        } else {
            try {
                IpConfiguration config = this.mIEthernetManager.getConfiguration();
                Iterator i$;
                InetAddress nameserver;
                if (config.getIpAssignment() == IpConfiguration.IpAssignment.STATIC) {
                    int state = this.mIEthernetManager.getState();
                    if (state != 3) {
                        return dnsList;
                    }

                    i$ = config.getStaticIpConfiguration().dnsServers.iterator();
                    while(i$.hasNext()) {
                        nameserver = (InetAddress)i$.next();
                        dnsList.add(nameserver.getHostAddress());
                    }
                } else {
                    if (this.mIConnectivityManager == null) {
                        return dnsList;
                    }

                    LinkProperties lp = this.mIConnectivityManager.getLinkPropertiesForType(9);
                    if (lp == null) {
                        return dnsList;
                    }

                    i$ = lp.getDnsServers().iterator();

                    while(i$.hasNext()) {
                        nameserver = (InetAddress)i$.next();
                        dnsList.add(nameserver.getHostAddress());
                    }
                }
                return dnsList;
            } catch (NullPointerException | RemoteException var6) {
                var6.printStackTrace();
                return dnsList;
            }
        }
    }

二、framework层修改DNS列表IPv4/IPv6的优先级

　　路由器同时支持IPv4和IPv6的情况下，Android系统会优先使用IPv6，DNS信息中可能会显示类似 "fe80:xx:xx"的格式，这就是IPv6的DNS格式。

　　修改DNS列表，把IPv4放在首位返回：

　　frameworksasecorejavaandroid etLinkProperties.java

    /**
     * Returns all the {@link InetAddress} for DNS servers on this link.
     *
     * @return An umodifiable {@link List} of {@link InetAddress} for DNS servers on
     *         this link.
     */
    public List<InetAddress> getDnsServers() {
        //Sheldon add patch begin
        //在列表中查找到有IPv4 DNS且不在首位时，将其交换到首位，应用层获取到的列表第一个便是IPv4的DNS
        int index = 0;
        boolean isSortDone = true;
        for (InetAddress addr : mDnses) {
            boolean isIpv4 = (addr instanceof Inet4Address);
            if(index==0 && !isIpv4){
                isSortDone = false;
            }
            //Log.v(TAG, "Get DNS : " + addr.getHostAddress() + ", isIpv4 : " + isIpv4 + ", index = " + index);

            if(!isSortDone && isIpv4){
                Collections.swap(mDnses,0,index);
                Log.d(TAG, "Put ipv4 dns first ~");
                isSortDone = true;
            }

            index++;
        }
        //Sheldon add patch end
        return Collections.unmodifiableList(mDnses);
    }

　　另外，如果想默认关闭IPv6只使用IPv4可以进行如下修改：

　　frameworksopt etethernetjavacomandroidserverethernetEthernetNetworkFactory.java

    public void startIpManager() {

        ......

        } else {
            provisioningConfiguration = mIpManager.buildProvisioningConfiguration()
                    .withProvisioningTimeoutMs(0)
                    .withoutIPv6() //默认配置去除IPv6
                    .build();
        }

        mIpManager.startProvisioning(provisioningConfiguration);
    }