Don't open DataSink if resolved length is 0

- It's wasted effort
- DataSpec reconstruction fails because creating a DataSpec with 0
  length isn't allowed.
- Also better document DataSink open/close, to be like DataSource.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=194778132

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

@@ -37,6 +37,9 @@ public interface DataSink {
   /**
    * Opens the sink to consume the specified data.
    *
+   * <p>Note: If an {@link IOException} is thrown, callers must still call {@link #close()} to
+   * ensure that any partial effects of the invocation are cleaned up.
+   *
    * @param dataSpec Defines the data to be consumed.
    * @throws IOException If an error occurs opening the sink.
    */
@@ -55,8 +58,10 @@ public interface DataSink {
   /**
    * Closes the sink.
    *
+   * <p>Note: This method must be called even if the corresponding call to {@link #open(DataSpec)}
+   * threw an {@link IOException}. See {@link #open(DataSpec)} for more details.
+   *
    * @throws IOException If an error occurs closing the sink.
    */
   void close() throws IOException;
-
 }

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

@@ -28,6 +28,9 @@ public final class TeeDataSource implements DataSource {
   private final DataSource upstream;
   private final DataSink dataSink;
 
+  private boolean dataSinkNeedsClosing;
+  private long bytesRemaining;
+
   /**
    * @param upstream The upstream {@link DataSource}.
    * @param dataSink The {@link DataSink} into which data is written.
@@ -39,24 +42,40 @@ public final class TeeDataSource implements DataSource {
 
   @Override
   public long open(DataSpec dataSpec) throws IOException {
-    long dataLength = upstream.open(dataSpec);
-    if (dataSpec.length == C.LENGTH_UNSET && dataLength != C.LENGTH_UNSET) {
+    bytesRemaining = upstream.open(dataSpec);
+    if (bytesRemaining == 0) {
+      return 0;
+    }
+    if (dataSpec.length == C.LENGTH_UNSET && bytesRemaining != C.LENGTH_UNSET) {
       // Reconstruct dataSpec in order to provide the resolved length to the sink.
-      dataSpec = new DataSpec(dataSpec.uri, dataSpec.absoluteStreamPosition, dataSpec.position,
-          dataLength, dataSpec.key, dataSpec.flags);
+      dataSpec =
+          new DataSpec(
+              dataSpec.uri,
+              dataSpec.absoluteStreamPosition,
+              dataSpec.position,
+              bytesRemaining,
+              dataSpec.key,
+              dataSpec.flags);
     }
+    dataSinkNeedsClosing = true;
     dataSink.open(dataSpec);
-    return dataLength;
+    return bytesRemaining;
   }
 
   @Override
   public int read(byte[] buffer, int offset, int max) throws IOException {
-    int num = upstream.read(buffer, offset, max);
-    if (num > 0) {
-      // TODO: Consider continuing even if disk writes fail.
-      dataSink.write(buffer, offset, num);
+    if (bytesRemaining == 0) {
+      return C.RESULT_END_OF_INPUT;
+    }
+    int bytesRead = upstream.read(buffer, offset, max);
+    if (bytesRead > 0) {
+      // TODO: Consider continuing even if writes to the sink fail.
+      dataSink.write(buffer, offset, bytesRead);
+      if (bytesRemaining != C.LENGTH_UNSET) {
+        bytesRemaining -= bytesRead;
+      }
     }
-    return num;
+    return bytesRead;
   }
 
   @Override
@@ -69,7 +88,10 @@ public final class TeeDataSource implements DataSource {
     try {
       upstream.close();
     } finally {
-      dataSink.close();
+      if (dataSinkNeedsClosing) {
+        dataSinkNeedsClosing = false;
+        dataSink.close();
+      }
     }
   }