Fix flaky UdpEncapsulationSocket test

This commit reduces the flakiness of the
testOpenAndCloseUdpEncapsulationSocket by retrying up to three times.
Unfortunately, testing port-selected socket creation is racy against
other applications. This helps to handle the same race condition as done
in IpSecService#bindToRandomPort

Bug: 128024100
Test: 200x runs of testOpenAndCloseUdpEncapsulationSocket
Change-Id: I7e036ce821019dbac6c50899bd0894e89d2fe82a
Merged-In: Idf040a67e53d9b9ec6e6c647ce24f8ada501d355
Merged-In: Iad9aea4b42cd8b31a5a2659bb9cb54dd1c64e8b7
(cherry picked from commit 614ab3dd4e49e9b664f5065983fb9067148fef12)

tests/net/java/com/android/server/IpSecServiceTest.java

@@ -156,10 +156,21 @@ public class IpSecServiceTest {
 
     @Test
     public void testOpenAndCloseUdpEncapsulationSocket() throws Exception {
-        int localport = findUnusedPort();
+        int localport = -1;
+        IpSecUdpEncapResponse udpEncapResp = null;
+
+        for (int i = 0; i < IpSecService.MAX_PORT_BIND_ATTEMPTS; i++) {
+            localport = findUnusedPort();
+
+            udpEncapResp = mIpSecService.openUdpEncapsulationSocket(localport, new Binder());
+            assertNotNull(udpEncapResp);
+            if (udpEncapResp.status == IpSecManager.Status.OK) {
+                break;
+            }
+
+            // Else retry to reduce possibility for port-bind failures.
+        }
 
-        IpSecUdpEncapResponse udpEncapResp =
-                mIpSecService.openUdpEncapsulationSocket(localport, new Binder());
         assertNotNull(udpEncapResp);
         assertEquals(IpSecManager.Status.OK, udpEncapResp.status);
         assertEquals(localport, udpEncapResp.port);
@@ -204,12 +215,11 @@ public class IpSecServiceTest {
 
     @Test
     public void testOpenUdpEncapsulationSocketAfterClose() throws Exception {
-        int localport = findUnusedPort();
         IpSecUdpEncapResponse udpEncapResp =
-                mIpSecService.openUdpEncapsulationSocket(localport, new Binder());
+                mIpSecService.openUdpEncapsulationSocket(0, new Binder());
         assertNotNull(udpEncapResp);
         assertEquals(IpSecManager.Status.OK, udpEncapResp.status);
-        assertEquals(localport, udpEncapResp.port);
+        int localport = udpEncapResp.port;
 
         mIpSecService.closeUdpEncapsulationSocket(udpEncapResp.resourceId);
         udpEncapResp.fileDescriptor.close();
@@ -226,12 +236,11 @@ public class IpSecServiceTest {
      */
     @Test
     public void testUdpEncapPortNotReleased() throws Exception {
-        int localport = findUnusedPort();
         IpSecUdpEncapResponse udpEncapResp =
-                mIpSecService.openUdpEncapsulationSocket(localport, new Binder());
+                mIpSecService.openUdpEncapsulationSocket(0, new Binder());
         assertNotNull(udpEncapResp);
         assertEquals(IpSecManager.Status.OK, udpEncapResp.status);
-        assertEquals(localport, udpEncapResp.port);
+        int localport = udpEncapResp.port;
 
         udpEncapResp.fileDescriptor.close();
 
@@ -273,14 +282,11 @@ public class IpSecServiceTest {
 
     @Test
     public void testOpenUdpEncapsulationSocketTwice() throws Exception {
-        int localport = findUnusedPort();
-
         IpSecUdpEncapResponse udpEncapResp =
-                mIpSecService.openUdpEncapsulationSocket(localport, new Binder());
+                mIpSecService.openUdpEncapsulationSocket(0, new Binder());
         assertNotNull(udpEncapResp);
         assertEquals(IpSecManager.Status.OK, udpEncapResp.status);
-        assertEquals(localport, udpEncapResp.port);
+        int localport = udpEncapResp.port;
-        mIpSecService.openUdpEncapsulationSocket(localport, new Binder());
 
         IpSecUdpEncapResponse testUdpEncapResp =
                 mIpSecService.openUdpEncapsulationSocket(localport, new Binder());