Prevent reading into preload parts.

This is to ensure we can still discard the data if needed.

Issue: #5011
PiperOrigin-RevId: 344977548

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/HlsSampleStreamWrapper.java

@@ -596,6 +596,11 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
       downstreamTrackFormat = trackFormat;
     }
 
+    if (!mediaChunks.isEmpty() && !mediaChunks.get(0).isPublished()) {
+      // Don't read into preload chunks until we can be sure they are permanently published.
+      return C.RESULT_NOTHING_READ;
+    }
+
     int result =
         sampleQueues[sampleQueueIndex].read(formatHolder, buffer, requireFormat, loadingFinished);
     if (result == C.RESULT_FORMAT_READ) {
@@ -625,6 +630,21 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
 
     SampleQueue sampleQueue = sampleQueues[sampleQueueIndex];
     int skipCount = sampleQueue.getSkipCount(positionUs, loadingFinished);
+
+    // Ensure we don't skip into preload chunks until we can be sure they are permanently published.
+    int readIndex = sampleQueue.getReadIndex();
+    for (int i = 0; i < mediaChunks.size(); i++) {
+      HlsMediaChunk mediaChunk = mediaChunks.get(i);
+      int firstSampleIndex = mediaChunks.get(i).getFirstSampleIndex(sampleQueueIndex);
+      if (readIndex + skipCount <= firstSampleIndex) {
+        break;
+      }
+      if (!mediaChunk.isPublished()) {
+        skipCount = firstSampleIndex - readIndex;
+        break;
+      }
+    }
+
     sampleQueue.skip(skipCount);
     return skipCount;
   }