Add Promises for EME (Chromium side)

media/base/cdm_promise.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef MEDIA_BASE_CDM_PROMISE_H_
+#define MEDIA_BASE_CDM_PROMISE_H_
+
+#include <string>
+
+#include "base/basictypes.h"
+#include "base/callback.h"
+#include "media/base/media_export.h"
+#include "media/base/media_keys.h"
+
+namespace media {
+
+typedef base::Callback<void(MediaKeys::Exception exception_code,
+                            uint32 system_code,
+                            const std::string& error_message)>
+    PromiseRejectedCB;

[xhwang, 2014/05/22 16:44:14]

This seems to be only used in class CdmPromise. How about moving the typedef
into class CdmPromise?

[jrummell, 2014/05/29 00:54:40]

Done.

+
+// Interface for promises being resolved/rejected in response to various
+// session actions. These may be called synchronously or asynchronously.
+// Only one method may be called on any promise. It is expected that the
+// caller free the promise once it is resolved/rejected.
+template <typename T>
+class MEDIA_EXPORT CdmPromise {

[xhwang, 2014/05/23 06:01:23]

See above for the idea of having a base class for all CDM Promises.

[jrummell, 2014/05/29 00:54:40]

Done.

+ public:
+  CdmPromise(base::Callback<void(const T&)> resolve_cb,
+             PromiseRejectedCB rejected_cb);
+  virtual ~CdmPromise();
+
+  // Used to indicate that operation succeeded.
+  virtual void resolve(const T& result);
+
+  // Used to indicate that the operation failed. |exception_code| must be
+  // specified. |system_code| is a Key System-specific value for the error
+  // that occurred, or 0 if there is no associated status code or such status
+  // codes are not supported by the Key System. |error_message| is optional.
+  virtual void reject(MediaKeys::Exception exception_code,
+                      uint32 system_code,
+                      const std::string& error_message);
+
+ private:
+  base::Callback<void(const T&)> resolve_cb_;
+  PromiseRejectedCB rejected_cb_;

[xhwang, 2014/05/22 16:44:14]

we have |resolve_cb_| but |reject"ed"_cb_|. Shall we be consistent?  e.g.
resolve_cb & reject_cb?

[jrummell, 2014/05/29 00:54:40]

Done.

+  bool is_pending_;

[xhwang, 2014/05/22 16:44:14]

Add comment for |is_pending_|.

[jrummell, 2014/05/29 00:54:40]

Done.

+
+  DISALLOW_COPY_AND_ASSIGN(CdmPromise);
+};
+
+// Specialization for no parameter to resolve().
+template <>
+class MEDIA_EXPORT CdmPromise<void> {
+ public:
+  CdmPromise(base::Callback<void(void)> resolve_cb,
+             PromiseRejectedCB rejected_cb);
+  virtual ~CdmPromise();
+  virtual void resolve();
+  virtual void reject(MediaKeys::Exception exception_code,
+                      uint32 system_code,
+                      const std::string& error_message);
+
+ private:
+  base::Callback<void(void)> resolve_cb_;

[xhwang, 2014/05/22 16:44:14]

Actually base::Callback<void(void)> == base::Closure :)

https://code.google.com/p/chromium/codesearch#chromium/src/base/callback.h&l=766

[xhwang, 2014/05/22 16:44:14]

How about having a template class 

template <typename T> struct PromiseResolveCB {
  base::Callback<void(const T&)> cb;
};

template <> struct PromiseResolveCB<void> {
  base::Callback<void(void)> cb;
};

Then you can use PromiseResolveCB<T> resulve_cb_ in CdmPromise and you don't
have to specialize the full class, which will save a lot of duplicate code in
this class.

The downside of this is that you'll need to do something like
resolve_cb_.cb.Run()
But this seems fine to me since it's implementation detail of this class. WDYT?

[jrummell, 2014/05/29 00:54:40]

I put it this way so that it maps to the basic template (void(const T&) becomes
void(void)).

[jrummell, 2014/05/29 00:54:40]

With the refactoring to CdmPromiseTemplate, not much overriding is required.

+  PromiseRejectedCB rejected_cb_;
+  bool is_pending_;
+
+  DISALLOW_COPY_AND_ASSIGN(CdmPromise);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_CDM_PROMISE_H_