Fix incorrect interpolation of active bucket for partial requests.

Just because the bucket is active (ie. overlaps with 'now') doesn't
mean the request necessarily covers the entire bucket.

For example a bucketDuration=5 with a bucket from curStart=1 to
curEnd=6 with now=4 and requests:
- from start=0 to end=3 --> overlap=[1,3] --> bucketSpan=2
- from start=2 to end=3 --> overlap=[2,3] --> bucketSpan=1
- from start=2 to end=5 --> overlap=[2,4] --> bucketSpan=2
- from start=2 to end=7 --> overlap=[2,4] --> bucketSpan=2
and the previously correctly handled cases:
- from start=0 to end=5 --> overlap=[1,4] --> bucketSpan=3
- from start=0 to end=7 --> overlap=[1,4] --> bucketSpan=3

We fix this by bounding the end of buckets to now, this means
that bucketDuration is no longer a constant, but it simplifies
all the rest of the logic.

Test: builds, atest
Bug: 143338233
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I642b57f7b8486071ad7808fd9b901859923b6d25

1 files changed, 17 insertions, 17 deletions

diff --git a/core/java/android/net/NetworkStatsHistory.java b/core/java/android/net/NetworkStatsHistory.java
index 7b799e262419..c82c28822232 100644
--- a/core/java/android/net/NetworkStatsHistory.java
+++ b/core/java/android/net/NetworkStatsHistory.java
@@ -548,32 +548,32 @@ public class NetworkStatsHistory implements Parcelable {
         final int startIndex = getIndexAfter(end);
         for (int i = startIndex; i >= 0; i--) {
             final long curStart = bucketStart[i];
-            final long curEnd = curStart + bucketDuration;
+            long curEnd = curStart + bucketDuration;
 
             // bucket is older than request; we're finished
             if (curEnd <= start) break;
             // bucket is newer than request; keep looking
             if (curStart >= end) continue;
 
-            // include full value for active buckets, otherwise only fractional
-            final boolean activeBucket = curStart < now && curEnd > now;
-            final long overlap;
-            if (activeBucket) {
-                overlap = bucketDuration;
-            } else {
-                final long overlapEnd = curEnd < end ? curEnd : end;
-                final long overlapStart = curStart > start ? curStart : start;
-                overlap = overlapEnd - overlapStart;
-            }
+            // the active bucket is shorter then a normal completed bucket
+            if (curEnd > now) curEnd = now;
+            // usually this is simply bucketDuration
+            final long bucketSpan = curEnd - curStart;
+            // prevent division by zero
+            if (bucketSpan <= 0) continue;
+
+            final long overlapEnd = curEnd < end ? curEnd : end;
+            final long overlapStart = curStart > start ? curStart : start;
+            final long overlap = overlapEnd - overlapStart;
             if (overlap <= 0) continue;
 
             // integer math each time is faster than floating point
-            if (activeTime != null) entry.activeTime += activeTime[i] * overlap / bucketDuration;
-            if (rxBytes != null) entry.rxBytes += rxBytes[i] * overlap / bucketDuration;
-            if (rxPackets != null) entry.rxPackets += rxPackets[i] * overlap / bucketDuration;
-            if (txBytes != null) entry.txBytes += txBytes[i] * overlap / bucketDuration;
-            if (txPackets != null) entry.txPackets += txPackets[i] * overlap / bucketDuration;
-            if (operations != null) entry.operations += operations[i] * overlap / bucketDuration;
+            if (activeTime != null) entry.activeTime += activeTime[i] * overlap / bucketSpan;
+            if (rxBytes != null) entry.rxBytes += rxBytes[i] * overlap / bucketSpan;
+            if (rxPackets != null) entry.rxPackets += rxPackets[i] * overlap / bucketSpan;
+            if (txBytes != null) entry.txBytes += txBytes[i] * overlap / bucketSpan;
+            if (txPackets != null) entry.txPackets += txPackets[i] * overlap / bucketSpan;
+            if (operations != null) entry.operations += operations[i] * overlap / bucketSpan;
         }
         return entry;
     }