DO NOT MERGE IpConnectivityMetrics: rate limit ApfProgramEvents

This patch uses the previously introduced TokenBucket to rate limit
ApfProgramEvents, still allowing for burst of ApfProgramEvents when a
new interface is set up (due to ipv4 provisioning, multicast lock, ipv6 RAs
triggering new APF program events in short amounts of time).

Test: new test in IpConnectivityMetricsTest
Bug: 1550402

(cherry picked from commit e1c173d224)

Change-Id: Ibe41e9a76db36ea502697a5f19fc0d91c40a3087

core/java/android/net/IIpConnectivityMetrics.aidl

@@ -23,7 +23,8 @@ import android.net.ConnectivityMetricsEvent;
 interface IIpConnectivityMetrics {
 
     /**
-     * @return number of remaining available slots in buffer.
+     * @return the number of remaining available slots in buffer,
+     * or -1 if the event was dropped due to rate limiting.
      */
     int logEvent(in ConnectivityMetricsEvent event);
 }

core/tests/coretests/src/android/util/TokenBucketTest.java

@@ -177,4 +177,3 @@ public class TokenBucketTest extends TestCase {
 
     interface Fn { void call(); }
 }
-

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

@@ -19,15 +19,19 @@ package com.android.server.connectivity;
 import android.content.Context;
 import android.net.ConnectivityMetricsEvent;
 import android.net.IIpConnectivityMetrics;
+import android.net.metrics.ApfProgramEvent;
 import android.net.metrics.IpConnectivityLog;
 import android.os.IBinder;
 import android.os.Parcelable;
 import android.provider.Settings;
 import android.text.TextUtils;
+import android.text.format.DateUtils;
+import android.util.ArrayMap;
 import android.util.Base64;
 import android.util.Log;
 import com.android.internal.annotations.GuardedBy;
 import com.android.internal.annotations.VisibleForTesting;
+import com.android.internal.util.TokenBucket;
 import com.android.server.SystemService;
 import java.io.FileDescriptor;
 import java.io.IOException;
@@ -49,6 +53,8 @@ final public class IpConnectivityMetrics extends SystemService {
     // Maximum size of the event buffer.
     private static final int MAXIMUM_BUFFER_SIZE = DEFAULT_BUFFER_SIZE * 10;
 
+    private static final int ERROR_RATE_LIMITED = -1;
+
     // Lock ensuring that concurrent manipulations of the event buffer are correct.
     // There are three concurrent operations to synchronize:
     //  - appending events to the buffer.
@@ -66,6 +72,8 @@ final public class IpConnectivityMetrics extends SystemService {
     private int mDropped;
     @GuardedBy("mLock")
     private int mCapacity;
+    @GuardedBy("mLock")
+    private final ArrayMap<Class<?>, TokenBucket> mBuckets = makeRateLimitingBuckets();
 
     private final ToIntFunction<Context> mCapacityGetter;
 
@@ -115,6 +123,10 @@ final public class IpConnectivityMetrics extends SystemService {
             if (event == null) {
                 return left;
             }
+            if (isRateLimited(event)) {
+                // Do not count as a dropped event. TODO: consider adding separate counter
+                return ERROR_RATE_LIMITED;
+            }
             if (left == 0) {
                 mDropped++;
                 return 0;
@@ -124,6 +136,11 @@ final public class IpConnectivityMetrics extends SystemService {
         }
     }
 
+    private boolean isRateLimited(ConnectivityMetricsEvent event) {
+        TokenBucket tb = mBuckets.get(event.data.getClass());
+        return (tb != null) && !tb.get();
+    }
+
     private String flushEncodedOutput() {
         final ArrayList<ConnectivityMetricsEvent> events;
         final int dropped;
@@ -246,4 +263,11 @@ final public class IpConnectivityMetrics extends SystemService {
         }
         return Math.min(size, MAXIMUM_BUFFER_SIZE);
     };
+
+    private static ArrayMap<Class<?>, TokenBucket> makeRateLimitingBuckets() {
+        ArrayMap<Class<?>, TokenBucket> map = new ArrayMap<>();
+        // one token every minute, 50 tokens max: burst of ~50 events every hour.
+        map.put(ApfProgramEvent.class, new TokenBucket((int)DateUtils.MINUTE_IN_MILLIS, 50));
+        return map;
+    }
 }

services/tests/servicestests/src/com/android/server/connectivity/IpConnectivityMetricsTest.java

@@ -19,6 +19,7 @@ package com.android.server.connectivity;
 import android.content.Context;
 import android.net.ConnectivityMetricsEvent;
 import android.net.IIpConnectivityMetrics;
+import android.net.metrics.ApfProgramEvent;
 import android.net.metrics.ApfStats;
 import android.net.metrics.DefaultNetworkEvent;
 import android.net.metrics.DhcpClientEvent;
@@ -112,6 +113,27 @@ public class IpConnectivityMetricsTest extends TestCase {
         assertEquals("", output3);
     }
 
+    public void testRateLimiting() {
+        final IpConnectivityLog logger = new IpConnectivityLog(mService.impl);
+        final ApfProgramEvent ev = new ApfProgramEvent(0, 0, 0, 0, 0);
+        final long fakeTimestamp = 1;
+
+        int attempt = 100; // More than burst quota, but less than buffer size.
+        for (int i = 0; i < attempt; i++) {
+            logger.log(ev);
+        }
+
+        String output1 = getdump("flush");
+        assertFalse("".equals(output1));
+
+        for (int i = 0; i < attempt; i++) {
+            assertFalse("expected event to be dropped", logger.log(fakeTimestamp, ev));
+        }
+
+        String output2 = getdump("flush");
+        assertEquals("", output2);
+    }
+
     public void testEndToEndLogging() {
         IpConnectivityLog logger = new IpConnectivityLog(mService.impl);