Support NetworkCallbacks based on signal strength.

Bug: 21405941
Change-Id: I2ed8a5aeb8dac464a4305671ed22abcacb485bc9

core/java/android/net/NetworkAgent.java

@@ -184,6 +184,14 @@ public abstract class NetworkAgent extends Handler {
      */
     public static final int EVENT_PACKET_KEEPALIVE = BASE + 13;
 
+    /**
+     * Sent by ConnectivityService to inform this network transport of signal strength thresholds
+     * that when crossed should trigger a system wakeup and a NetworkCapabilities update.
+     *
+     *   obj = int[] describing signal strength thresholds.
+     */
+    public static final int CMD_SET_SIGNAL_STRENGTH_THRESHOLDS = BASE + 14;
+
     public NetworkAgent(Looper looper, Context context, String logTag, NetworkInfo ni,
             NetworkCapabilities nc, LinkProperties lp, int score) {
         this(looper, context, logTag, ni, nc, lp, score, null);
@@ -286,6 +294,11 @@ public abstract class NetworkAgent extends Handler {
                 stopPacketKeepalive(msg);
                 break;
             }
+
+            case CMD_SET_SIGNAL_STRENGTH_THRESHOLDS: {
+                setSignalStrengthThresholds((int[]) msg.obj);
+                break;
+            }
         }
     }
 
@@ -445,6 +458,13 @@ public abstract class NetworkAgent extends Handler {
         queueOrSendMessage(EVENT_PACKET_KEEPALIVE, slot, reason);
     }
 
+    /**
+     * Called by ConnectivityService to inform this network transport of signal strength thresholds
+     * that when crossed should trigger a system wakeup and a NetworkCapabilities update.
+     */
+    protected void setSignalStrengthThresholds(int[] thresholds) {
+    }
+
     protected void log(String s) {
         Log.d(LOG_TAG, "NetworkAgent: " + s);
     }

core/java/android/net/NetworkCapabilities.java

@@ -48,6 +48,7 @@ public final class NetworkCapabilities implements Parcelable {
             mLinkUpBandwidthKbps = nc.mLinkUpBandwidthKbps;
             mLinkDownBandwidthKbps = nc.mLinkDownBandwidthKbps;
             mNetworkSpecifier = nc.mNetworkSpecifier;
+            mSignalStrength = nc.mSignalStrength;
         }
     }
 
@@ -60,6 +61,7 @@ public final class NetworkCapabilities implements Parcelable {
         mNetworkCapabilities = mTransportTypes = 0;
         mLinkUpBandwidthKbps = mLinkDownBandwidthKbps = 0;
         mNetworkSpecifier = null;
+        mSignalStrength = SIGNAL_STRENGTH_UNSPECIFIED;
     }
 
     /**
@@ -300,6 +302,7 @@ public final class NetworkCapabilities implements Parcelable {
             return "unknown non-requestable capabilities " + Long.toHexString(mNetworkCapabilities);
         }
         if (mLinkUpBandwidthKbps != 0 || mLinkDownBandwidthKbps != 0) return "link bandwidth";
+        if (hasSignalStrength()) return "signalStrength";
         return null;
     }
 
@@ -568,6 +571,68 @@ public final class NetworkCapabilities implements Parcelable {
         }
     }
 
+    /**
+     * Magic value that indicates no signal strength provided. A request specifying this value is
+     * always satisfied.
+     *
+     * @hide
+     */
+    public static final int SIGNAL_STRENGTH_UNSPECIFIED = Integer.MIN_VALUE;
+
+    /**
+     * Signal strength. This is a signed integer, and higher values indicate better signal.
+     * The exact units are bearer-dependent. For example, Wi-Fi uses RSSI.
+     */
+    private int mSignalStrength;
+
+    /**
+     * Sets the signal strength. This is a signed integer, with higher values indicating a stronger
+     * signal. The exact units are bearer-dependent. For example, Wi-Fi uses the same RSSI units
+     * reported by WifiManager.
+     * <p>
+     * Note that when used to register a network callback, this specifies the minimum acceptable
+     * signal strength. When received as the state of an existing network it specifies the current
+     * value. A value of code SIGNAL_STRENGTH_UNSPECIFIED} means no value when received and has no
+     * effect when requesting a callback.
+     *
+     * @param signalStrength the bearer-specific signal strength.
+     * @hide
+     */
+    public void setSignalStrength(int signalStrength) {
+        mSignalStrength = signalStrength;
+    }
+
+    /**
+     * Returns {@code true} if this object specifies a signal strength.
+     *
+     * @hide
+     */
+    public boolean hasSignalStrength() {
+        return mSignalStrength > SIGNAL_STRENGTH_UNSPECIFIED;
+    }
+
+    /**
+     * Retrieves the signal strength.
+     *
+     * @return The bearer-specific signal strength.
+     * @hide
+     */
+    public int getSignalStrength() {
+        return mSignalStrength;
+    }
+
+    private void combineSignalStrength(NetworkCapabilities nc) {
+        this.mSignalStrength = Math.max(this.mSignalStrength, nc.mSignalStrength);
+    }
+
+    private boolean satisfiedBySignalStrength(NetworkCapabilities nc) {
+        return this.mSignalStrength <= nc.mSignalStrength;
+    }
+
+    private boolean equalsSignalStrength(NetworkCapabilities nc) {
+        return this.mSignalStrength == nc.mSignalStrength;
+    }
+
     /**
      * Combine a set of Capabilities to this one.  Useful for coming up with the complete set
      * @hide
@@ -577,6 +642,7 @@ public final class NetworkCapabilities implements Parcelable {
         combineTransportTypes(nc);
         combineLinkBandwidths(nc);
         combineSpecifiers(nc);
+        combineSignalStrength(nc);
     }
 
     /**
@@ -593,7 +659,8 @@ public final class NetworkCapabilities implements Parcelable {
                 satisfiedByNetCapabilities(nc, onlyImmutable) &&
                 satisfiedByTransportTypes(nc) &&
                 (onlyImmutable || satisfiedByLinkBandwidths(nc)) &&
-                satisfiedBySpecifier(nc));
+                satisfiedBySpecifier(nc) &&
+                (onlyImmutable || satisfiedBySignalStrength(nc)));
     }
 
     /**
@@ -638,6 +705,7 @@ public final class NetworkCapabilities implements Parcelable {
         return (equalsNetCapabilities(that) &&
                 equalsTransportTypes(that) &&
                 equalsLinkBandwidths(that) &&
+                equalsSignalStrength(that) &&
                 equalsSpecifier(that));
     }
 
@@ -649,7 +717,8 @@ public final class NetworkCapabilities implements Parcelable {
                 ((int)(mTransportTypes >> 32) * 7) +
                 (mLinkUpBandwidthKbps * 11) +
                 (mLinkDownBandwidthKbps * 13) +
-                (TextUtils.isEmpty(mNetworkSpecifier) ? 0 : mNetworkSpecifier.hashCode() * 17));
+                (TextUtils.isEmpty(mNetworkSpecifier) ? 0 : mNetworkSpecifier.hashCode() * 17) +
+                (mSignalStrength * 19));
     }
 
     @Override
@@ -663,7 +732,9 @@ public final class NetworkCapabilities implements Parcelable {
         dest.writeInt(mLinkUpBandwidthKbps);
         dest.writeInt(mLinkDownBandwidthKbps);
         dest.writeString(mNetworkSpecifier);
+        dest.writeInt(mSignalStrength);
     }
+
     public static final Creator<NetworkCapabilities> CREATOR =
         new Creator<NetworkCapabilities>() {
             @Override
@@ -675,6 +746,7 @@ public final class NetworkCapabilities implements Parcelable {
                 netCap.mLinkUpBandwidthKbps = in.readInt();
                 netCap.mLinkDownBandwidthKbps = in.readInt();
                 netCap.mNetworkSpecifier = in.readString();
+                netCap.mSignalStrength = in.readInt();
                 return netCap;
             }
             @Override
@@ -731,6 +803,8 @@ public final class NetworkCapabilities implements Parcelable {
         String specifier = (mNetworkSpecifier == null ?
                 "" : " Specifier: <" + mNetworkSpecifier + ">");
 
-        return "[" + transports + capabilities + upBand + dnBand + specifier + "]";
+        String signalStrength = (hasSignalStrength() ? " SignalStrength: " + mSignalStrength : "");
+
+        return "[" + transports + capabilities + upBand + dnBand + specifier + signalStrength + "]";
     }
 }

core/java/android/net/NetworkRequest.java

@@ -185,6 +185,24 @@ public class NetworkRequest implements Parcelable {
             mNetworkCapabilities.setNetworkSpecifier(networkSpecifier);
             return this;
         }
+
+        /**
+         * Sets the signal strength. This is a signed integer, with higher values indicating a
+         * stronger signal. The exact units are bearer-dependent. For example, Wi-Fi uses the same
+         * RSSI units reported by WifiManager.
+         * <p>
+         * Note that when used to register a network callback, this specifies the minimum acceptable
+         * signal strength. When received as the state of an existing network it specifies the
+         * current value. A value of {@code SIGNAL_STRENGTH_UNSPECIFIED} means no value when
+         * received and has no effect when requesting a callback.
+         *
+         * @param signalStrength the bearer-specific signal strength.
+         * @hide
+         */
+        public Builder setSignalStrength(int signalStrength) {
+            mNetworkCapabilities.setSignalStrength(signalStrength);
+            return this;
+        }
     }
 
     // implement the Parcelable interface

services/core/java/com/android/server/ConnectivityService.java

@@ -150,6 +150,8 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.SortedSet;
+import java.util.TreeSet;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
@@ -1914,7 +1916,7 @@ public class ConnectivityService extends IConnectivityManager.Stub
                                 (NetworkCapabilities)msg.obj;
                         if (networkCapabilities.hasCapability(NET_CAPABILITY_CAPTIVE_PORTAL) ||
                                 networkCapabilities.hasCapability(NET_CAPABILITY_VALIDATED)) {
-                            Slog.wtf(TAG, "BUG: " + nai + " has stateful capability.");
+                            Slog.wtf(TAG, "BUG: " + nai + " has CS-managed capability.");
                         }
                         if (nai.created && !nai.networkCapabilities.equalImmutableCapabilities(
                                 networkCapabilities)) {
@@ -2274,6 +2276,9 @@ public class ConnectivityService extends IConnectivityManager.Stub
                     bestNetwork = network;
                 }
             }
+            if (!nri.isRequest && network.satisfiesImmutableCapabilitiesOf(nri.request)) {
+                updateSignalStrengthThresholds(network);
+            }
         }
         if (bestNetwork != null) {
             if (DBG) log("using " + bestNetwork.name());
@@ -2419,6 +2424,9 @@ public class ConnectivityService extends IConnectivityManager.Stub
                 // if this listen request applies and remove it.
                 for (NetworkAgentInfo nai : mNetworkAgentInfos.values()) {
                     nai.networkRequests.remove(nri.request.requestId);
+                    if (nai.satisfiesImmutableCapabilitiesOf(nri.request)) {
+                        updateSignalStrengthThresholds(nai);
+                    }
                 }
             }
             callCallbackForRequest(nri, null, ConnectivityManager.CALLBACK_RELEASED);
@@ -3664,6 +3672,34 @@ public class ConnectivityService extends IConnectivityManager.Stub
         }
     }
 
+    private int[] getSignalStrengthThresholds(NetworkAgentInfo nai) {
+        final SortedSet<Integer> thresholds = new TreeSet();
+        synchronized (nai) {
+            for (NetworkRequestInfo nri : mNetworkRequests.values()) {
+                if (nri.request.networkCapabilities.hasSignalStrength() &&
+                        nai.satisfiesImmutableCapabilitiesOf(nri.request)) {
+                    thresholds.add(nri.request.networkCapabilities.getSignalStrength());
+                }
+            }
+        }
+        // We can't just do something like:
+        //     return thresholds.toArray(new int[thresholds.size()]);
+        // because autoboxing does not work for primitive arrays.
+        final int[] out = new int[thresholds.size()];
+        int pos = 0;
+        for (Integer threshold : thresholds) {
+            out[pos] = threshold;
+            pos++;
+        }
+        return out;
+    }
+
+    private void updateSignalStrengthThresholds(NetworkAgentInfo nai) {
+        nai.asyncChannel.sendMessage(
+                android.net.NetworkAgent.CMD_SET_SIGNAL_STRENGTH_THRESHOLDS,
+                0, 0, getSignalStrengthThresholds(nai));
+    }
+
     @Override
     public NetworkRequest requestNetwork(NetworkCapabilities networkCapabilities,
             Messenger messenger, int timeoutMs, IBinder binder, int legacyType) {
@@ -4132,6 +4168,9 @@ public class ConnectivityService extends IConnectivityManager.Stub
                 networkAgent.networkCapabilities = networkCapabilities;
             }
             rematchAllNetworksAndRequests(networkAgent, networkAgent.getCurrentScore(), nascent);
+            // TODO: reduce the number of callbacks where possible. For example, only send signal
+            // strength changes if the NetworkRequest used to register the callback specified a
+            // signalStrength.
             notifyNetworkCallbacks(networkAgent, ConnectivityManager.CALLBACK_CAP_CHANGED);
         }
     }
@@ -4594,6 +4633,15 @@ public class ConnectivityService extends IConnectivityManager.Stub
                 // TODO: support proxy per network.
             }
 
+            // Whether a particular NetworkRequest listen should cause signal strength thresholds to
+            // be communicated to a particular NetworkAgent depends only on the network's immutable,
+            // capabilities, so it only needs to be done once on initial connect, not every time the
+            // network's capabilities change. Note that we do this before rematching the network,
+            // so we could decide to tear it down immediately afterwards. That's fine though - on
+            // disconnection NetworkAgents should stop any signal strength monitoring they have been
+            // doing.
+            updateSignalStrengthThresholds(networkAgent);
+
             // Consider network even though it is not yet validated.
             rematchNetworkAndRequests(networkAgent, NascentState.NOT_JUST_VALIDATED,
                     ReapUnvalidatedNetworks.REAP);

services/core/java/com/android/server/connectivity/NetworkAgentInfo.java

@@ -128,6 +128,12 @@ public class NetworkAgentInfo {
                 request.networkCapabilities.satisfiedByNetworkCapabilities(networkCapabilities);
     }
 
+    public boolean satisfiesImmutableCapabilitiesOf(NetworkRequest request) {
+        return created &&
+                request.networkCapabilities.satisfiedByImmutableNetworkCapabilities(
+                        networkCapabilities);
+    }
+
     public boolean isVPN() {
         return networkCapabilities.hasTransport(NetworkCapabilities.TRANSPORT_VPN);
     }