Average scan results for AccessPoints.

This reduces jitter in the WifiTracker and is modeled after a prior
broken implementation which attempted to half-life the rssi each time
AccessPoint.update(ScanResult) is called.

Bug: 34774783
Test: runtest --path
frameworks/base/packages/SettingsLib/tests/integ/src/com/android/settingslib/wifi/AccessPointTest.java

Change-Id: Iab3f9914af40f2fd56e8ae7b45dcbd62176c8a67

packages/SettingsLib/src/com/android/settingslib/wifi/AccessPoint.java

@@ -394,8 +394,9 @@ public class AccessPoint implements Comparable<AccessPoint> {
      *
      * <p>If the given connection is active, the existing value of {@link #mRssi} will be returned.
      * If the given AccessPoint is not active, a value will be calculated from previous scan
-     * results, returning the best RSSI for all matching AccessPoints. If the access point is not
-     * connected and there are no scan results, the rssi will be set to {@link #UNREACHABLE_RSSI}.
+     * results, returning the best RSSI for all matching AccessPoints averaged with the previous
+     * value. If the access point is not connected and there are no scan results, the rssi will be
+     * set to {@link #UNREACHABLE_RSSI}.
      *
      * <p>Old scan results will be evicted from the cache when this method is invoked.
      */
@@ -413,7 +414,11 @@ public class AccessPoint implements Comparable<AccessPoint> {
             }
         }
 
-        mRssi = rssi;
+        if (rssi != UNREACHABLE_RSSI && mRssi != UNREACHABLE_RSSI) {
+            mRssi = (mRssi + rssi) / 2; // half-life previous value
+        } else {
+            mRssi = rssi;
+        }
     }
 
     /**

packages/SettingsLib/tests/integ/src/com/android/settingslib/wifi/AccessPointTest.java

@@ -195,6 +195,26 @@ public class AccessPointTest {
         assertThat(ap.getRssi()).isEqualTo(newRssi);
     }
 
+    @Test
+    public void testUpdateWithScanResultShouldAverageRssi() {
+        String ssid = "ssid";
+        int originalRssi = -65;
+        int newRssi = -80;
+        int expectedRssi = (originalRssi + newRssi) / 2;
+        AccessPoint ap =
+                new TestAccessPointBuilder(mContext).setSsid(ssid).setRssi(originalRssi).build();
+
+        ScanResult scanResult = new ScanResult();
+        scanResult.SSID = ssid;
+        scanResult.level = newRssi;
+        scanResult.BSSID = "bssid";
+        scanResult.timestamp = SystemClock.elapsedRealtime() * 1000;
+        scanResult.capabilities = "";
+        assertThat(ap.update(scanResult)).isTrue();
+
+        assertThat(ap.getRssi()).isEqualTo(expectedRssi);
+    }
+
     private AccessPoint createAccessPointWithScanResultCache() {
         Bundle bundle = new Bundle();
         ArrayList<ScanResult> scanResults = new ArrayList<>();
@@ -203,6 +223,7 @@ public class AccessPointTest {
             scanResult.level = i;
             scanResult.BSSID = "bssid-" + i;
             scanResult.timestamp = SystemClock.elapsedRealtime() * 1000;
+            scanResult.capabilities = "";
             scanResults.add(scanResult);
         }
 

packages/SettingsLib/tests/integ/src/com/android/settingslib/wifi/TestAccessPointBuilder.java

@@ -73,9 +73,15 @@ public class TestAccessPointBuilder {
         return this;
     }
 
+    public TestAccessPointBuilder setRssi(int rssi) {
+        mRssi = rssi;
+        return this;
+    }
+
     /**
-    * Set the signal level.
-    * Side effect: if this AccessPoint was previously unreachable,
+    * Set the rssi based upon the desired signal level.
+     *
+    * <p>Side effect: if this AccessPoint was previously unreachable,
     * setting the level will also make it reachable.
     */
     public TestAccessPointBuilder setLevel(int level) {