Glue parallel download job and download file together.

content/browser/download/download_worker.h

 // Copyright 2017 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 CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_WORKER_H_
 #define CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_WORKER_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "content/browser/byte_stream.h"
 #include "content/browser/download/download_request_handle.h"
 #include "content/browser/download/url_downloader.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/download_url_parameters.h"
 
 namespace content {
 
 // Helper class used to send subsequent range requests to fetch slices of the
 // file after handling response of the original non-range request.
 // TODO(xingliu): we should consider to reuse this class for single connection
 // download.
 class DownloadWorker : public UrlDownloader::Delegate {
  public:
-  DownloadWorker();
+  class Delegate {
+   public:
+    // Called when the the byte stream is established after server response is
+    // handled. The stream contains data starts from |offset| of the
+    // destination file.
+    virtual void OnByteStreamReady(
+        DownloadWorker* worker,
+        std::unique_ptr<ByteStreamReader> stream_reader) = 0;
+  };
+
+  DownloadWorker(DownloadWorker::Delegate* delegate,
+                 int64_t offset,
+                 int64_t length);
   virtual ~DownloadWorker();
 
+  int64_t offset() const { return offset_; }
+  int64_t length() const { return length_; }
+
   // Send network request to ask for a download.
   void SendRequest(std::unique_ptr<DownloadUrlParameters> params);
 
   // Download operations.
   void Pause();
   void Resume();
   void Cancel();
 
  private:
   // UrlDownloader::Delegate implementation.
   void OnUrlDownloaderStarted(
       std::unique_ptr<DownloadCreateInfo> create_info,
       std::unique_ptr<ByteStreamReader> stream_reader,
       const DownloadUrlParameters::OnStartedCallback& callback) override;
   void OnUrlDownloaderStopped(UrlDownloader* downloader) override;
 
   void AddUrlDownloader(
       std::unique_ptr<UrlDownloader, BrowserThread::DeleteOnIOThread>
           downloader);
 
+  DownloadWorker::Delegate* delegate_;
+
+  // The starting position of the content for this worker to download.
+  int64_t offset_;
+
+  // The length of the request. May be 0 to fetch to the end of the file.
+  int64_t length_;
+
   // Used to control the network request. Live on UI thread.
   std::unique_ptr<DownloadRequestHandleInterface> request_handle_;
 
   // Used to handle the url request. Live and die on IO thread.
   std::unique_ptr<UrlDownloader, BrowserThread::DeleteOnIOThread>
       url_downloader_;
 
   base::WeakPtrFactory<DownloadWorker> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadWorker);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_WORKER_H_