media/base/cdm_promise.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef MEDIA_BASE_CDM_PROMISE_H_
   6 #define MEDIA_BASE_CDM_PROMISE_H_
   7
   8 #include <string>
   9
  10 #include "base/basictypes.h"
  11 #include "base/logging.h"
  12 #include "media/base/media_export.h"
  13 #include "media/base/media_keys.h"
  14
  15 namespace media {
  16
  17 // Interface for promises being resolved/rejected in response to various
  18 // session actions. These may be called synchronously or asynchronously.
  19 // The promise must be resolved or rejected exactly once. It is expected that
  20 // the caller free the promise once it is resolved/rejected.
  21
  22 // These classes are almost generic, except for the parameters to reject(). If
  23 // a generic class for promises is available, this could be changed to use the
  24 // generic class as long as the parameters to reject() can be set appropriately.
  25
  26 // The base class only has a reject() method and GetResolveParameterType() that
  27 // indicates the type of CdmPromiseTemplate. CdmPromiseTemplate<T> adds the
  28 // resolve(T) method that is dependent on the type of promise. This base class
  29 // is specified so that the promises can be easily saved before passing across
  30 // the pepper interface.
  31 class MEDIA_EXPORT CdmPromise {
  32  public:
  33   enum ResolveParameterType {
  34     VOID_TYPE,
  35     STRING_TYPE,
  36     KEY_IDS_VECTOR_TYPE
  37   };
  38
  39   CdmPromise();
  40   virtual ~CdmPromise();
  41
  42   // Used to indicate that the operation failed. |exception_code| must be
  43   // specified. |system_code| is a Key System-specific value for the error
  44   // that occurred, or 0 if there is no associated status code or such status
  45   // codes are not supported by the Key System. |error_message| is optional.
  46   virtual void reject(MediaKeys::Exception exception_code,
  47                       uint32 system_code,
  48                       const std::string& error_message) = 0;
  49
  50   // Used to determine the template type of CdmPromiseTemplate<T> so that
  51   // saved CdmPromise objects can be cast to the correct templated version.
  52   virtual ResolveParameterType GetResolveParameterType() const = 0;
  53
  54  private:
  55   DISALLOW_COPY_AND_ASSIGN(CdmPromise);
  56 };
  57
  58 // For some reason the Windows compiler is not happy with the implementation
  59 // of CdmPromiseTemplate being in the .cc file, so moving it here.
  60 template <typename... T>
  61 struct CdmPromiseTraits {};
  62
  63 template <>
  64 struct CdmPromiseTraits<> {
  65   static const CdmPromise::ResolveParameterType kType = CdmPromise::VOID_TYPE;
  66 };
  67
  68 template <>
  69 struct CdmPromiseTraits<std::string> {
  70   static const CdmPromise::ResolveParameterType kType = CdmPromise::STRING_TYPE;
  71 };
  72
  73 // This class adds the resolve(T) method. This class is still an interface, and
  74 // is used as the type of promise that gets passed around.
  75 template <typename... T>
  76 class MEDIA_EXPORT CdmPromiseTemplate : public CdmPromise {
  77  public:
  78   CdmPromiseTemplate() : is_settled_(false) {}
  79
  80   virtual ~CdmPromiseTemplate() { DCHECK(is_settled_); }
  81
  82   virtual void resolve(const T&... result) = 0;
  83
  84   // CdmPromise implementation.
  85   virtual void reject(MediaKeys::Exception exception_code,
  86                       uint32 system_code,
  87                       const std::string& error_message) = 0;
  88
  89   ResolveParameterType GetResolveParameterType() const override {
  90     return CdmPromiseTraits<T...>::kType;
  91   }
  92
  93  protected:
  94   // All implementations must call this method in resolve() and reject() methods
  95   // to indicate that the promise has been settled.
  96   void MarkPromiseSettled() {
  97     // Promise can only be settled once.
  98     DCHECK(!is_settled_);
  99     is_settled_ = true;
 100   }
 101
 102  private:
 103   // Keep track of whether the promise has been resolved or rejected yet.
 104   bool is_settled_;
 105
 106   DISALLOW_COPY_AND_ASSIGN(CdmPromiseTemplate);
 107 };
 108
 109 }  // namespace media
 110
 111 #endif  // MEDIA_BASE_CDM_PROMISE_H_