Don't setContentLength() in CacheDataSource if the current request ignores cache.

Otherwise an empty cache span is created.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=146014081

library/src/androidTest/java/com/google/android/exoplayer2/upstream/cache/CacheDataSourceTest.java

@@ -119,6 +119,13 @@ public class CacheDataSourceTest extends InstrumentationTestCase {
         C.LENGTH_UNSET, KEY_2)));
   }
 
+  public void testIgnoreCacheForUnsetLengthRequests() throws Exception {
+    CacheDataSource cacheDataSource = createCacheDataSource(false, true,
+        CacheDataSource.FLAG_IGNORE_CACHE_FOR_UNSET_LENGTH_REQUESTS);
+    assertReadData(cacheDataSource, true, 0, C.LENGTH_UNSET);
+    MoreAsserts.assertEmpty(simpleCache.getKeys());
+  }
+
   private void assertCacheAndRead(boolean unboundedRequest, boolean simulateUnknownLength)
       throws IOException {
     // Read all data from upstream and cache
@@ -171,6 +178,12 @@ public class CacheDataSourceTest extends InstrumentationTestCase {
 
   private CacheDataSource createCacheDataSource(boolean setReadException,
       boolean simulateUnknownLength) {
+    return createCacheDataSource(setReadException, simulateUnknownLength,
+        CacheDataSource.FLAG_BLOCK_ON_CACHE);
+  }
+
+  private CacheDataSource createCacheDataSource(boolean setReadException,
+      boolean simulateUnknownLength, @CacheDataSource.Flags int flags) {
     Builder builder = new Builder();
     if (setReadException) {
       builder.appendReadError(new IOException("Shouldn't read from upstream"));
@@ -178,8 +191,7 @@ public class CacheDataSourceTest extends InstrumentationTestCase {
     builder.setSimulateUnknownLength(simulateUnknownLength);
     builder.appendReadData(TEST_DATA);
     FakeDataSource upstream = builder.build();
-    return new CacheDataSource(simpleCache, upstream, CacheDataSource.FLAG_BLOCK_ON_CACHE,
-        MAX_CACHE_FILE_SIZE);
+    return new CacheDataSource(simpleCache, upstream, flags, MAX_CACHE_FILE_SIZE);
   }
 
 }

library/src/main/java/com/google/android/exoplayer2/upstream/cache/CacheDataSource.java

@@ -330,16 +330,16 @@ public final class CacheDataSource implements DataSource {
     // bytesRemaining == C.LENGTH_UNSET) and got a resolved length from open() request
     if (currentRequestUnbounded && currentBytesRemaining != C.LENGTH_UNSET) {
       bytesRemaining = currentBytesRemaining;
-      // If writing into cache
-      if (lockedSpan != null) {
-        setContentLength(dataSpec.position + bytesRemaining);
-      }
+      setContentLength(dataSpec.position + bytesRemaining);
     }
     return successful;
   }
 
   private void setContentLength(long length) throws IOException {
-    cache.setContentLength(key, length);
+    // If writing into cache
+    if (currentDataSource == cacheWriteDataSource) {
+      cache.setContentLength(key, length);
+    }
   }
 
   private void closeCurrentSource() throws IOException {