fix(replay): Measure gesture batch durations on a monotonic clock (JAVA-830)

CHANGELOG.md

@@ -34,6 +34,7 @@
 - Stop blocking the main thread while the frame metrics thread starts when the first activity transaction begins ([#6500](https://github.com/getsentry/sentry-java/pull/6500))
   - On a busy device during cold start this could stall the launcher activity's `onCreate` for hundreds of milliseconds.
 - Do not inspect the response body of streaming Apollo 3 and 4 responses (`multipart/mixed`, `text/event-stream`) for failed requests, which blocked `@defer` and `@stream` ([#6432](https://github.com/getsentry/sentry-java/pull/6432))
+- Session Replay: Measure how long touch moves are batched on a monotonic clock, so a device time change during a swipe no longer drops its positions, delays them, or stretches their timing ([#6538](https://github.com/getsentry/sentry-java/pull/6538))
 
 ### Dependencies
 

sentry-android-replay/src/main/java/io/sentry/android/replay/gestures/ReplayGestureConverter.kt

@@ -9,6 +9,7 @@ import io.sentry.rrweb.RRWebInteractionMoveEvent
 import io.sentry.rrweb.RRWebInteractionMoveEvent.Position
 import io.sentry.time.Deadline
 import io.sentry.time.MonotonicTicker
+import io.sentry.time.Stopwatch
 import io.sentry.transport.ICurrentDateProvider
 import java.util.concurrent.TimeUnit.MILLISECONDS
 
@@ -24,7 +25,9 @@ internal class ReplayGestureConverter(
   }
 
   private val currentPositions = LinkedHashMap<Int, ArrayList<Position>>(10)
-  private var touchMoveBaseline = 0L
+
+  /** Started with the first position in [currentPositions], or `null` while none is batched. */
+  private var moveBatch: Stopwatch? = null
 
   /** When the next move event may be captured, or `null` before the first one. */
   private var moveDebounce: Deadline? = null
@@ -42,6 +45,9 @@ internal class ReplayGestureConverter(
         }
         moveDebounce = Deadline.after(ticker, TOUCH_MOVE_DEBOUNCE_THRESHOLD, MILLISECONDS)
 
+        // read once, so all pointers of this event share one offset
+        val totalOffset = moveBatch?.elapsed(MILLISECONDS) ?: 0L
+
         currentPositions.keys.forEach { pId ->
           val pIndex = event.findPointerIndex(pId)
 
@@ -51,21 +57,21 @@ internal class ReplayGestureConverter(
           }
 
           // idk why but rrweb does it like dis
-          if (touchMoveBaseline == 0L) {
-            touchMoveBaseline = now
+          if (moveBatch == null) {
+            moveBatch = Stopwatch.started(ticker)
           }
 
           currentPositions[pId]!! +=
             Position().apply {
               x = event.getX(pIndex) * recorderConfig.scaleFactorX
               y = event.getY(pIndex) * recorderConfig.scaleFactorY
               id = 0 // html node id, but we don't have it, so hardcode to 0 to align with FE
-              timeOffset = now - touchMoveBaseline
+              timeOffset = totalOffset
             }
         }
 
-        val totalOffset = now - touchMoveBaseline
-        return if (totalOffset > CAPTURE_MOVE_EVENT_THRESHOLD) {
+        // with nothing batched there is nothing to wait for
+        return if (moveBatch == null || totalOffset > CAPTURE_MOVE_EVENT_THRESHOLD) {
           val moveEvents = ArrayList<RRWebInteractionMoveEvent>(currentPositions.size)
           for ((pointerId, positions) in currentPositions) {
             if (positions.isNotEmpty()) {
@@ -81,7 +87,7 @@ internal class ReplayGestureConverter(
               currentPositions[pointerId]!!.clear()
             }
           }
-          touchMoveBaseline = 0L
+          moveBatch = null
           moveEvents
         } else {
           null

sentry-android-replay/src/test/java/io/sentry/android/replay/gestures/ReplayGestureConverterTest.kt

@@ -2,6 +2,7 @@ package io.sentry.android.replay.gestures
 
 import android.view.MotionEvent
 import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.google.common.truth.Truth.assertThat
 import io.sentry.android.replay.ScreenshotRecorderConfig
 import io.sentry.rrweb.RRWebInteractionEvent
 import io.sentry.rrweb.RRWebInteractionMoveEvent
@@ -141,6 +142,55 @@ class ReplayGestureConverterTest {
     moveEvent.recycle()
   }
 
+  @Test
+  fun `wall clock stepping backwards during a swipe does not hold back the batch`() {
+    val sut = fixture.getSut()
+    val recorderConfig = ScreenshotRecorderConfig(scaleFactorX = 1f, scaleFactorY = 1f)
+    val downEvent = MotionEvent.obtain(0, 0, MotionEvent.ACTION_DOWN, 100f, 200f, 0)
+    val moveEvent = MotionEvent.obtain(0, 0, MotionEvent.ACTION_MOVE, 110f, 210f, 0)
+    sut.convert(downEvent, recorderConfig)
+    assertThat(sut.convert(moveEvent, recorderConfig)).isNull()
+
+    // an NTP correction drags the wall clock back mid-swipe
+    fixture.now -= 1_000
+    fixture.advance(300)
+    assertThat(sut.convert(moveEvent, recorderConfig)).isNull()
+
+    fixture.advance(300)
+    val result = sut.convert(moveEvent, recorderConfig)
+
+    assertThat(result).hasSize(1)
+    val batch = result!!.single() as RRWebInteractionMoveEvent
+    assertThat(batch.positions!!.map { it.timeOffset }).containsExactly(-600L, -300L, 0L).inOrder()
+
+    downEvent.recycle()
+    moveEvent.recycle()
+  }
+
+  @Test
+  fun `wall clock stepping forwards during a swipe does not send the batch early`() {
+    val sut = fixture.getSut()
+    val recorderConfig = ScreenshotRecorderConfig(scaleFactorX = 1f, scaleFactorY = 1f)
+    val downEvent = MotionEvent.obtain(0, 0, MotionEvent.ACTION_DOWN, 100f, 200f, 0)
+    val moveEvent = MotionEvent.obtain(0, 0, MotionEvent.ACTION_MOVE, 110f, 210f, 0)
+    sut.convert(downEvent, recorderConfig)
+    assertThat(sut.convert(moveEvent, recorderConfig)).isNull()
+
+    fixture.now += 60_000
+    fixture.advance(300)
+    assertThat(sut.convert(moveEvent, recorderConfig)).isNull()
+
+    fixture.advance(300)
+    val result = sut.convert(moveEvent, recorderConfig)
+
+    assertThat(result).hasSize(1)
+    val batch = result!!.single() as RRWebInteractionMoveEvent
+    assertThat(batch.positions!!.map { it.timeOffset }).containsExactly(-600L, -300L, 0L).inOrder()
+
+    downEvent.recycle()
+    moveEvent.recycle()
+  }
+
   @Test
   fun `convert ACTION_UP event`() {
     val sut = fixture.getSut()