Offload disk accesses to WorkerPool in ExtensionProtocolHandler

net/url_request/url_request_simple_job.h

 // Copyright (c) 2011 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 NET_URL_REQUEST_URL_REQUEST_SIMPLE_JOB_H_
 #define NET_URL_REQUEST_URL_REQUEST_SIMPLE_JOB_H_
 
 #include <string>
 
 #include "base/memory/weak_ptr.h"
+#include "net/base/completion_callback.h"
 #include "net/base/net_export.h"
 #include "net/url_request/url_request_job.h"
 
 namespace net {
 
 class URLRequest;
 
 class NET_EXPORT URLRequestSimpleJob : public URLRequestJob {
  public:
   explicit URLRequestSimpleJob(URLRequest* request);
 
   virtual void Start() OVERRIDE;
   virtual bool ReadRawData(IOBuffer* buf,
                            int buf_size,
                            int *bytes_read) OVERRIDE;
   virtual bool GetMimeType(std::string* mime_type) const OVERRIDE;
   virtual bool GetCharset(std::string* charset) OVERRIDE;
 
  protected:
   virtual ~URLRequestSimpleJob();
 
-  // subclasses must override the way response data is determined.
-  virtual bool GetData(std::string* mime_type,
-                       std::string* charset,
-                       std::string* data) const = 0;
+  // Subclasses must override the way response data is determined.
+  // The return value should be:
+  //  - OK if data is obtained;
+  //  - ERR_IO_PENDING if async processing is needed to finish obtaining data.
+  //    This is the only case when |callback| should be called after
+  //    completion of the operation. In other situations |callback| should
+  //    never be called;
+  //  - any other ERR_* code to indicate an error. This code will be used
+  //    as the error code in the URLRequestStatus when the URLRequest
+  //    is finished.
+  virtual int GetData(std::string* mime_type,
+                      std::string* charset,
+                      std::string* data,
+                      const CompletionCallback& callback) const = 0;
 
  protected:
   void StartAsync();
 
  private:
+  void OnGetDataCompleted(int result);
+
   std::string mime_type_;
   std::string charset_;
   std::string data_;
   int data_offset_;
   base::WeakPtrFactory<URLRequestSimpleJob> weak_factory_;
 };
 
 }  // namespace net
 
 #endif  // NET_URL_REQUEST_URL_REQUEST_SIMPLE_JOB_H_