Allow reading of response headers from HttpDataSource implementations

library/src/main/java/com/google/android/exoplayer/upstream/DefaultHttpDataSource.java

@@ -152,6 +152,11 @@ public class DefaultHttpDataSource implements HttpDataSource {
     return connection == null ? null : connection.getURL().toString();
   }
 
+  @Override
+  public Map<String, List<String>> getResponseHeaders() {
+    return connection == null ? null : connection.getHeaderFields();
+  }
+
   @Override
   public void setRequestProperty(String name, String value) {
     Assertions.checkNotNull(name);

library/src/main/java/com/google/android/exoplayer/upstream/HttpDataSource.java

@@ -145,4 +145,11 @@ public interface HttpDataSource extends UriDataSource {
    */
   void clearAllRequestProperties();
 
+  /**
+   * Gets the headers provided in the response.
+   *
+   * @return The response headers, or {@code null} if response headers are unavailable.
+   */
+  Map<String, List<String>> getResponseHeaders();
+
 }