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_
 #pragma once
 
 #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
+  //    error code while finishing request.

[wtc, 2012/07/13 22:55:14]

Remove "This code will be used as error code while finishing request."
because it seems to be stating the obvious.

[wtc, 2012/07/14 00:08:55]

Thank you for the clarification.  I didn't realize that by
"request" you're referring to the URLRequestSimpleJob rather
than the GetData call.  I suggest rewriting this sentence as
follows:

  This code will be used as the error code in the
  URLRequestStatus for the request.

or

  This code will be used as the error code in the
  URLRequestStatus when the URLRequest is finished.

Note: you tend to omit unimportant words such as "a", "the",
"this" in your comments.  Sometimes this makes the comments
a little hard to read.  However, in this case I misinterpreted
"request" as "call" or "operation".

+  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_