[Blob] BlobReader class & tests, and removal of all redundant reading.

storage/browser/blob/blob_data_handle.h

 // Copyright (c) 2013 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 STORAGE_BROWSER_BLOB_BLOB_DATA_HANDLE_H_
 #define STORAGE_BROWSER_BLOB_BLOB_DATA_HANDLE_H_
 
 #include <string>
 
 #include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/supports_user_data.h"
 #include "storage/browser/storage_browser_export.h"
 
 namespace base {
 class SequencedTaskRunner;
+class SingleThreadTaskRunner;
 }
 
 namespace storage {
 
 class BlobDataSnapshot;
+class BlobReader;
 class BlobStorageContext;
+class FileSystemContext;
 
 // BlobDataHandle ensures that the underlying blob (keyed by the uuid) remains
 // in the BlobStorageContext's collection while this object is alive. Anything
 // that needs to keep a blob alive needs to store this handle.
 // When the blob data itself is needed, clients must call the CreateSnapshot()
 // method on the IO thread to create a snapshot of the blob data.  This snapshot
 // is not intended to be persisted, and serves to ensure that the backing
 // resources remain around for the duration of reading the blob.  This snapshot
 // can be read on any thread, but it must be destructed on the IO thread.
 // This object has delete semantics and may be deleted on any thread.
 class STORAGE_EXPORT BlobDataHandle
     : public base::SupportsUserData::Data {
  public:
   BlobDataHandle(const BlobDataHandle& other);  // May be copied on any thread.
   ~BlobDataHandle() override;                   // May be deleted on any thread.
 
-  // A BlobDataSnapshot is used to read the data from the blob.  This object is
+  // A BlobReader is used to read the data from the blob.  This object is
   // intended to be transient and should not be stored for any extended period
   // of time.
+  scoped_ptr<BlobReader> CreateReader(
+      FileSystemContext* file_system_context,
+      base::SingleThreadTaskRunner* file_task_runner) const;

[michaeln, 2015/09/17 00:45:37]

Does this really need to be a SingleThreadTaskRunner or would a
SequencedTaskRunner be sufficient?

[dmurph, 2015/09/19 00:33:43]

Sure.

+
+  // May be accessed on any thread.
+  const std::string& uuid() const;
+  // May be accessed on any thread.
+  const std::string& content_type() const;
+  // May be accessed on any thread.
+  const std::string& content_disposition() const;
+
   // This call and the destruction of the returned snapshot must be called
   // on the IO thread.
+  // TODO(dmurph): Make this protected, where only the BlobReader can call it.
   scoped_ptr<BlobDataSnapshot> CreateSnapshot() const;
 
-  const std::string& uuid() const;  // May be accessed on any thread.
-
  private:
   // Internal class whose destructor is guarenteed to be called on the IO
   // thread.
   class BlobDataHandleShared
       : public base::RefCountedThreadSafe<BlobDataHandleShared> {
    public:
     BlobDataHandleShared(const std::string& uuid,
-                         BlobStorageContext* context,
-                         base::SequencedTaskRunner* task_runner);
+                         const std::string& content_type,
+                         const std::string& content_disposition,
+                         BlobStorageContext* context);
 
     scoped_ptr<BlobDataSnapshot> CreateSnapshot() const;
-    const std::string& uuid() const;
 
    private:
     friend class base::DeleteHelper<BlobDataHandleShared>;
     friend class base::RefCountedThreadSafe<BlobDataHandleShared>;
     friend class BlobDataHandle;
 
     virtual ~BlobDataHandleShared();
 
     const std::string uuid_;
+    const std::string content_type_;
+    const std::string content_disposition_;
     base::WeakPtr<BlobStorageContext> context_;
 
     DISALLOW_COPY_AND_ASSIGN(BlobDataHandleShared);
   };
 
   friend class BlobStorageContext;
   BlobDataHandle(const std::string& uuid,
+                 const std::string& content_type,
+                 const std::string& content_disposition,
                  BlobStorageContext* context,
                  base::SequencedTaskRunner* task_runner);
 
   scoped_refptr<base::SequencedTaskRunner> io_task_runner_;
   scoped_refptr<BlobDataHandleShared> shared_;
 };
 
 }  // namespace storage
 
 #endif  // STORAGE_BROWSER_BLOB_BLOB_DATA_HANDLE_H_