WNS: less agressive roaming

When connected, WNS no longer triggers network switching if the
current network didn't show up in the scan results.

While there, fixed the comments of
WifiNetworkSelectorTest#filterOutBlacklistedBssid.

Bug: 31707128
Test: Wifi Unit Tests
Change-Id: Ieebc71151396608cd63e0b834e3f1c572e4cb557

1 files changed, 21 insertions, 2 deletions

diff --git a/service/java/com/android/server/wifi/WifiNetworkSelector.java b/service/java/com/android/server/wifi/WifiNetworkSelector.java
index 753b4460e..38151eab4 100644
--- a/service/java/com/android/server/wifi/WifiNetworkSelector.java
+++ b/service/java/com/android/server/wifi/WifiNetworkSelector.java
@@ -253,12 +253,14 @@ public class WifiNetworkSelector {
         return (network.SSID + ":" + network.networkId);
     }
 
-    private List<ScanDetail> filterScanResults(List<ScanDetail> scanDetails) {
+    private List<ScanDetail> filterScanResults(List<ScanDetail> scanDetails, boolean isConnected,
+                    String currentBssid) {
         ArrayList<NetworkKey> unscoredNetworks = new ArrayList<NetworkKey>();
         List<ScanDetail> validScanDetails = new ArrayList<ScanDetail>();
         StringBuffer noValidSsid = new StringBuffer();
         StringBuffer blacklistedBssid = new StringBuffer();
         StringBuffer lowRssi = new StringBuffer();
+        boolean scanResultsHaveCurrentBssid = false;
 
         for (ScanDetail scanDetail : scanDetails) {
             ScanResult scanResult = scanDetail.getScanResult();
@@ -268,6 +270,11 @@ public class WifiNetworkSelector {
                 continue;
             }
 
+            // Check if the scan results contain the currently connected BSSID
+            if (scanResult.BSSID.equals(currentBssid)) {
+                scanResultsHaveCurrentBssid = true;
+            }
+
             final String scanId = toScanId(scanResult);
 
             if (isBssidDisabled(scanResult.BSSID)) {
@@ -289,6 +296,17 @@ public class WifiNetworkSelector {
             validScanDetails.add(scanDetail);
         }
 
+        // WNS listens to all single scan results. Some scan requests may not include
+        // the channel of the currently connected network, so the currently connected
+        // network won't show up in the scan results. We don't act on these scan results
+        // to avoid aggressive network switching which might trigger disconnection.
+        if (isConnected && !scanResultsHaveCurrentBssid) {
+            localLog("Current connected BSSID " + currentBssid + " is not in the scan results."
+                    + " Skip network selection.");
+            validScanDetails.clear();
+            return validScanDetails;
+        }
+
         if (noValidSsid.length() != 0) {
             localLog("Networks filtered out due to invalid SSID: " + noValidSsid);
         }
@@ -473,7 +491,8 @@ public class WifiNetworkSelector {
         updateBssidBlacklist();
 
         // Filter out unwanted networks.
-        List<ScanDetail> filteredScanDetails = filterScanResults(scanDetails);
+        List<ScanDetail> filteredScanDetails = filterScanResults(scanDetails, connected,
+                currentBssid);
         if (filteredScanDetails.size() == 0) {
             return null;
         }