Comments from https://github.com/google/ExoPlayer/pull/2963#discussion_r122669328 applied

library/core/src/androidTest/java/com/google/android/exoplayer2/upstream/AndroidDataSourceConstants.java

+package com.google.android.exoplayer2.upstream;
+
+final class AndroidDataSourceConstants {
+  static final long SAMPLE_MP4_BYTES = 101597;
+  static final String SAMPLE_MP4_PATH = "/mp4/sample.mp4";
+
+  private AndroidDataSourceConstants() {}
+}

library/core/src/androidTest/java/com/google/android/exoplayer2/upstream/AndroidDataSourceTest.java → library/core/src/androidTest/java/com/google/android/exoplayer2/upstream/AssetDataSourceTest.java

@@ -4,10 +4,10 @@ import android.content.Context;
 import android.net.Uri;
 import android.test.InstrumentationTestCase;
 
-public class AndroidDataSourceTest extends InstrumentationTestCase {
+import static com.google.android.exoplayer2.upstream.AndroidDataSourceConstants.SAMPLE_MP4_BYTES;
+import static com.google.android.exoplayer2.upstream.AndroidDataSourceConstants.SAMPLE_MP4_PATH;
 
-  private static final long SAMPLE_MP4_BYTES = 101597;
-  private static final String SAMPLE_MP4_PATH = "/mp4/sample.mp4";
+public class AssetDataSourceTest extends InstrumentationTestCase {
 
   public void testAssetDataSource() throws Exception {
     final Context context = getInstrumentation().getContext();
@@ -18,14 +18,4 @@ public class AndroidDataSourceTest extends InstrumentationTestCase {
 
     assertEquals(SAMPLE_MP4_BYTES, sourceLengthBytes);
   }
-
-  public void testContentDataSource() throws Exception {
-    Context context = getInstrumentation().getContext();
-    ContentDataSource dataSource = new ContentDataSource(context);
-    Uri contentUri = Uri.parse("content://exoplayer" + SAMPLE_MP4_PATH);
-    DataSpec dataSpec = new DataSpec(contentUri);
-    long sourceLengthBytes = dataSource.open(dataSpec);
-
-    assertEquals(SAMPLE_MP4_BYTES, sourceLengthBytes);
-  }
 }

library/core/src/androidTest/java/com/google/android/exoplayer2/upstream/ContentDataSourceTest.java

+package com.google.android.exoplayer2.upstream;
+
+import android.content.Context;
+import android.net.Uri;
+import android.test.InstrumentationTestCase;
+
+import static com.google.android.exoplayer2.upstream.AndroidDataSourceConstants.SAMPLE_MP4_BYTES;
+import static com.google.android.exoplayer2.upstream.AndroidDataSourceConstants.SAMPLE_MP4_PATH;
+
+public class ContentDataSourceTest extends InstrumentationTestCase {
+
+  public void testContentDataSource() throws Exception {
+    Context context = getInstrumentation().getContext();
+    ContentDataSource dataSource = new ContentDataSource(context);
+    Uri contentUri = Uri.parse("content://exoplayer" + SAMPLE_MP4_PATH);
+    DataSpec dataSpec = new DataSpec(contentUri);
+    long sourceLengthBytes = dataSource.open(dataSpec);
+
+    assertEquals(SAMPLE_MP4_BYTES, sourceLengthBytes);
+  }
+}

library/core/src/main/java/com/google/android/exoplayer2/upstream/ContentDataSource.java

@@ -71,7 +71,7 @@ public final class ContentDataSource implements DataSource {
     try {
       uri = dataSpec.uri;
       assetFileDescriptor = resolver.openAssetFileDescriptor(uri, "r");
-      inputStream = assetFileDescriptor.createInputStream();
+      inputStream = new FileInputStream(assetFileDescriptor.getFileDescriptor());
       long skipped = inputStream.skip(dataSpec.position);
       if (skipped < dataSpec.position) {
         // We expect the skip to be satisfied in full. If it isn't then we're probably trying to
@@ -81,12 +81,16 @@ public final class ContentDataSource implements DataSource {
       if (dataSpec.length != C.LENGTH_UNSET) {
         bytesRemaining = dataSpec.length;
       } else {
-        bytesRemaining = inputStream.available();
-        if (bytesRemaining == 0) {
-          // FileInputStream.available() returns 0 if the remaining length cannot be determined, or
-          // if it's greater than Integer.MAX_VALUE. We don't know the true length in either case,
-          // so treat as unbounded.
-          bytesRemaining = C.LENGTH_UNSET;
+        bytesRemaining = assetFileDescriptor.getLength();
+        if (bytesRemaining == AssetFileDescriptor.UNKNOWN_LENGTH) {
+          // The asset must extend to the end of the file.
+          bytesRemaining = inputStream.available();
+          if (bytesRemaining == 0) {
+            // FileInputStream.available() returns 0 if the remaining length cannot be determined, or
+            // if it's greater than Integer.MAX_VALUE. We don't know the true length in either case,
+            // so treat as unbounded.
+            bytesRemaining = C.LENGTH_UNSET;
+          }
         }
       }
     } catch (IOException e) {