根據(jù)RFC 6724中 規(guī)定 android 會優(yōu)先選擇IPv6 地址而不是 IPv4 地址闷盔，當(dāng)整個網(wǎng)絡(luò)中，同時支持IPv4和IPv6 地址時磕潮，設(shè)備中的應(yīng)用請求服務(wù)器DNS時吵取，會優(yōu)先返回IPv6地址嵌屎。

假如IPv6服務(wù)器支持內(nèi)容不夠完善赠制，則應(yīng)用顯示內(nèi)容會與IPv4服務(wù)器不一致浮定，甚至有問題征讲。

因此有需求是定制設(shè)備平臺扇苞，使得 IPV4優(yōu)先IPV6欺殿，主要修改2個地方：

1. 當(dāng)設(shè)備或平臺連接網(wǎng)絡(luò)時寄纵，原來是先請求ipv6地址，再請求ipv4地址祈餐，這樣會使用應(yīng)用會先拿到ipv6地址屏箍，所以需要調(diào)整順序仓坞，讓ipv4先請求dhcp地址货裹，再請求ipv6氨距。

2. DNS域名解析時，調(diào)整解析DNS的優(yōu)先順序蜒谤，即先解析IPv4地址山宾，再解析IPv6地址，注：android 12在DnsResolver代碼中鳍徽。

接下來對這2個修改點(diǎn)進(jìn)行逐一修改并說明资锰。

1. 當(dāng)設(shè)備或平臺連接網(wǎng)絡(luò)時，原來是先請求ipv6地址阶祭，再請求ipv4地址绷杜，這樣會使用應(yīng)用會先拿到ipv6地址，所以需要調(diào)整順序濒募，讓ipv4先請求dhcp地址鞭盟，再請求ipv6。

文件：packages/modules/NetworkStack/src/android/net/ip/IpClient.java

修改差異如下：

--- a/modules/NetworkStack/src/android/net/ip/IpClient.java
+++ b/modules/NetworkStack/src/android/net/ip/IpClient.java
@@ -161,6 +161,8 @@
     private final NetworkInformationShim mShim = NetworkInformationShimImpl.newInstance();
     private final IpProvisioningMetrics mIpProvisioningMetrics = new IpProvisioningMetrics();
     private final NetworkQuirkMetrics mNetworkQuirkMetrics;
+    //CN project let get ipv4 first and then ipv6, tiangui.tang @2023.9.7
//用于區(qū)別自定義code與AOSP
+    private final boolean bStartIPv6AfterIPv4 = true;
 
     /**
      * Dump all state machine and connectivity packet logs to the specified writer.
@@ -1734,7 +1736,21 @@
         recordMetric(failureType);
         mCallback.onProvisioningFailure(mLinkProperties);
     }
+    private void enqueueJumpToStoppingState(final DisconnectCode code) {
+        deferMessage(obtainMessage(CMD_JUMP_RUNNING_TO_STOPPING, code.getNumber()));
+    }
+    private void startIPv6AfterIPv4() {
+        if (bStartIPv6AfterIPv4 == false) {
+            return;
+        }
+        Log.d(mTag, "startIPv6AfterIPv4");
 
+        if (mConfiguration.mEnableIPv6 && !startIPv6()) {
+            doImmediateProvisioningFailure(IpManagerEvent.ERROR_STARTING_IPV6);
+            enqueueJumpToStoppingState(DisconnectCode.DC_ERROR_STARTING_IPV6);
+            return;
+        }
+    }
     private boolean startIPv4() {
         // If we have a StaticIpConfiguration attempt to apply it and
         // handle the result accordingly.
@@ -1744,6 +1760,7 @@
             } else {
                 return false;
             }
+            startIPv6AfterIPv4();
         } else {
             if (mDhcpClient != null) {
                 Log.wtf(mTag, "DhcpClient should never be non-null in startIPv4()");
@@ -2229,7 +2246,7 @@
             mPacketTracker = createPacketTracker();
             if (mPacketTracker != null) mPacketTracker.start(mConfiguration.mDisplayName);
 
-            if (mConfiguration.mEnableIPv6 && !startIPv6()) {
+            if ((bStartIPv6AfterIPv4 == false) && mConfiguration.mEnableIPv6 && !startIPv6()) {
                 doImmediateProvisioningFailure(IpManagerEvent.ERROR_STARTING_IPV6);
                 enqueueJumpToStoppingState(DisconnectCode.DC_ERROR_STARTING_IPV6);
                 return;
@@ -2414,6 +2431,7 @@
                 }
 
                 case EVENT_DHCPACTION_TIMEOUT:
+                    startIPv6AfterIPv4();
                     stopDhcpAction();
                     break;
 
@@ -2431,6 +2449,7 @@
 
                 case DhcpClient.CMD_CONFIGURE_LINKADDRESS: {
                     final LinkAddress ipAddress = (LinkAddress) msg.obj;
+                    startIPv6AfterIPv4();
                     if (mInterfaceCtrl.setIPv4Address(ipAddress)) {
                         mDhcpClient.sendMessage(DhcpClient.EVENT_LINKADDRESS_CONFIGURED);
                     } else {

2. DNS域名解析時瑰剃，調(diào)整解析DNS的優(yōu)先順序齿诉，即先解析IPv4地址，再解析IPv6地址晌姚，注：android 12在DnsResolver代碼中粤剧。

diff --git a/modules/DnsResolver/getaddrinfo.cpp b/modules/DnsResolver/getaddrinfo.cpp

--- a/modules/DnsResolver/getaddrinfo.cpp
+++ b/modules/DnsResolver/getaddrinfo.cpp
@@ -1147,7 +1147,8 @@
             return 1;
         } else {
             /* All other IPv6 addresses, including global unicast addresses. */
//DNS解析出來的地址進(jìn)行排序，IPv4（return 35) 比IPv6(改為return 34)更高優(yōu)先級
-            return 40;
+            LOG(DEBUG) << __func__ << " ttgctt force 34 for ipv6";
+            return 34;
         }
     } else {
         return 1;
@@ -1406,16 +1407,17 @@
                 query_ipv6 = have_ipv6(netcontext->app_mark, netcontext->uid);
                 query_ipv4 = have_ipv4(netcontext->app_mark, netcontext->uid);
             }
//調(diào)整順序挥唠，先請求IPv4對應(yīng)的DNS抵恋，再請求IPv6
-            if (query_ipv6) {
-                q.qtype = T_AAAA;
-                if (query_ipv4) {
+            //query_ipv6 = 0;
+            if (query_ipv4) {
+                q.qtype = T_A;
+                if (query_ipv6) {
                     q.next = &q2;
                     q2.name = name;
                     q2.qclass = C_IN;
-                    q2.qtype = T_A;
+                    q2.qtype = T_AAAA;
                 }
-            } else if (query_ipv4) {
-                q.qtype = T_A;
+            } else if (query_ipv6) {
+                q.qtype = T_AAAA;
             } else { 
                 return EAI_NODATA;
             }
@@ -1452,7 +1454,7 @@
         cur->ai_next = ai;
         while (cur && cur->ai_next) cur = cur->ai_next;
     }
     if (q.next) {
         ai = getanswer(q2.answer, q2.n, q2.name, q2.qtype, pai, &he);
         if (ai) cur->ai_next = ai;
     }