[eme] Handle multiple calls to MediaKeySession.close()

media/cdm/aes_decryptor.cc

Index: media/cdm/aes_decryptor.cc
diff --git a/media/cdm/aes_decryptor.cc b/media/cdm/aes_decryptor.cc
index d6a720d4bade09d52f11c148101e1f94b46e92c5..eccaec36b9800be4f660e9c8d379b95433e0b8d5 100644
--- a/media/cdm/aes_decryptor.cc
+++ b/media/cdm/aes_decryptor.cc
@@ -405,9 +405,20 @@ void AesDecryptor::UpdateSession(const std::string& session_id,
 // Runs the parallel steps from https://w3c.github.io/encrypted-media/#close.
 void AesDecryptor::CloseSession(const std::string& session_id,
                                 std::unique_ptr<SimpleCdmPromise> promise) {
-  // Validate that this is a reference to an active session and then forget it.
+  // Validate that this is a reference to an active session. close() shouldn't
+  // be called if the session is already closed. However, the operation is
+  // asynchronous, so there is a window where close() was called a second time
+  // just before the closed event arrives. As a result it is possible that the
+  // session is already closed, so assume that the session is closed if it
+  // doesn't exist.
+  //
+  // close() is called from a MediaKeySession object, so it is unlikely that
+  // this method will be called with a previously unseen |session_id|.
   std::set<std::string>::iterator it = valid_sessions_.find(session_id);
-  DCHECK(it != valid_sessions_.end());
+  if (it == valid_sessions_.end()) {

[xhwang, 2016/12/07 06:51:42]

Now we cannot detect an invalid sesion_id... Since the spec actually doesn't say
removing the session, shall we keep a list of closed_sessions_?

Also valid_sessions_ seems ambiguous. It really should be open_sessions_.

[jrummell, 2016/12/07 22:26:50]

I don't think there is any way to get a invalid session_id, unless due to a bug
somewhere. So it's not necessary to bother with closed session IDs. Worst case
is we indicate that the invalid session ID is closed, which I guess is
technically true as it doesn't exist.
Done.

+    promise->resolve();
+    return;
+  }
 
   // 5.1. Let cdm be the CDM instance represented by session's cdm instance
   //      value.