net: Allow URLFetcher users to inject custom URLFetcherResponseWriter

net/url_request/url_fetcher_response_writer.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 NET_URL_REQUEST_URL_FETCHER_RESPONSE_WRITER_H_
 #define NET_URL_REQUEST_URL_FETCHER_RESPONSE_WRITER_H_
 
 #include "base/basictypes.h"
 #include "base/files/file_path.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "net/base/completion_callback.h"
+#include "net/base/net_export.h"
 
 namespace base {
 class TaskRunner;
 }  // namespace base
 
 namespace net {
 
 class DrainableIOBuffer;
 class FileStream;
 class IOBuffer;
 class URLFetcherFileWriter;
 class URLFetcherStringWriter;
 
 // This class encapsulates all state involved in writing URLFetcher response
 // bytes to the destination.
-class URLFetcherResponseWriter {
+class NET_EXPORT URLFetcherResponseWriter {
  public:
   virtual ~URLFetcherResponseWriter() {}
 
   // Initializes this instance. If ERR_IO_PENDING is returned, |callback| will
   // be run later with the result. Calling this method again after a
   // Initialize() success results in discarding already written data.
   virtual int Initialize(const CompletionCallback& callback) = 0;
 
   // Writes |num_bytes| bytes in |buffer|, and returns the number of bytes
   // written or an error code. If ERR_IO_PENDING is returned, |callback| will be
   // run later with the result.
   virtual int Write(IOBuffer* buffer,
                     int num_bytes,
                     const CompletionCallback& callback) = 0;
 
   // Finishes writing. If ERR_IO_PENDING is returned, |callback| will be run
   // later with the result.
   virtual int Finish(const CompletionCallback& callback) = 0;
 
   // Returns this instance's pointer as URLFetcherStringWriter when possible.
   virtual URLFetcherStringWriter* AsStringWriter();
 
   // Returns this instance's pointer as URLFetcherFileWriter when possible.
   virtual URLFetcherFileWriter* AsFileWriter();
 };
 
 // URLFetcherResponseWriter implementation for std::string.
-class URLFetcherStringWriter : public URLFetcherResponseWriter {
+class NET_EXPORT URLFetcherStringWriter : public URLFetcherResponseWriter {
  public:
   URLFetcherStringWriter();
   virtual ~URLFetcherStringWriter();
 
   const std::string& data() const { return data_; }
 
   // URLFetcherResponseWriter overrides:
   virtual int Initialize(const CompletionCallback& callback) OVERRIDE;
   virtual int Write(IOBuffer* buffer,
                     int num_bytes,
                     const CompletionCallback& callback) OVERRIDE;
   virtual int Finish(const CompletionCallback& callback) OVERRIDE;
   virtual URLFetcherStringWriter* AsStringWriter() OVERRIDE;
 
  private:
   std::string data_;
 
   DISALLOW_COPY_AND_ASSIGN(URLFetcherStringWriter);
 };
 
 // URLFetcherResponseWriter implementation for files.
-class URLFetcherFileWriter : public URLFetcherResponseWriter {
+class NET_EXPORT URLFetcherFileWriter : public URLFetcherResponseWriter {

[wtc, 2013/10/14 19:57:23]

Nit: I understand why we need to export the base class URLFetcherResponseWriter.
Do we also need to export the derived classes URLFetcherStringWriter and
URLFetcherFileWriter?

[hashimoto, 2013/10/15 01:00:35]

By exporting these derived classes, URLFetcher user code can implement custom
URLFetcherResponseWriter easily, without implementing the whole class from
scratch. (e.g. Our Google Drive code will use a flavored URLFetcherFileWriter
with OnURLFetchDownloadData() equivalent functionality.)

  public:
   // |file_path| is used as the destination path. If |file_path| is empty,
   // Initialize() will create a temporary file.
   URLFetcherFileWriter(scoped_refptr<base::TaskRunner> file_task_runner,
                        const base::FilePath& file_path);
   virtual ~URLFetcherFileWriter();
 
   const base::FilePath& file_path() const { return file_path_; }
 
   // URLFetcherResponseWriter overrides:
@@ skipping 41 matching lines @@
   bool owns_file_;
 
   scoped_ptr<FileStream> file_stream_;
 
   DISALLOW_COPY_AND_ASSIGN(URLFetcherFileWriter);
 };
 
 }  // namespace net
 
 #endif  // NET_URL_REQUEST_URL_FETCHER_RESPONSE_WRITER_H_