Introduce DownloadJob for DownloadItem refactoring.

content/browser/download/download_job.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_JOB_H_
+#define CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_JOB_H_
+
+#include "base/macros.h"
+#include "base/time/time.h"
+#include "content/common/content_export.h"
+#include "content/public/browser/download_danger_type.h"
+#include "content/public/browser/download_interrupt_reasons.h"
+
+namespace content {
+class WebContents;
+
+// Unknown download progress.
+extern const int kDownloadProgressUnknown;
+
+// Unknown download speed.
+extern const int kDownloadSpeedUnknown;
+
+// 1. DownloadJob contains internal download logic. Subclasses should implement
+// their own state machine.
+// 2. The DownloadJob::Manager(e.g DownloadItemImpl) may provide content public
+// api to the embedder backed by different implementation of DownloadJob
+// internally.
+// 3. The DownloadJob::Manager may maintain multiple DownloadJobs.
+class CONTENT_EXPORT DownloadJob {
+ public:
+  // Types of download jobs.
+  enum Type {
+    FILE = 0,   // Normal download.
+    SAVE_PAGE,  // Save page download.
+  };
+
+  // The owner of DownloadJob(e.g DownloadItemImpl or parallel download job)
+  // should implement this to be informed with important changes from
+  // DownloadJob and modify its states accordingly.
+  class CONTENT_EXPORT Manager {
+   public:
+    // Called when |download_job| starts, and pass the ResponseInfo to the
+    // manager.
+    // TODO(xingliu): Pass ResponseInfo to the manager.
+    virtual void StartSaving(DownloadJob* download_job) = 0;

[qinmin, 2017/01/23 21:46:35]

Shouldn't the manager just call download_job_->StartSaving()? what is the
purpose for the passed in param?

same below

[xingliu, 2017/01/23 22:59:09]

These are the callbacks to DownloadItemImpl which implements
DownloadJob::Manager, as something happens in DownloadJob, like the http
response is processed, it notifies DownloadItemImpl.

In my understanding, DownloadItemImpl eventually only know external state:
DownloadState, and meta data. Internal states should be in DownloadJobs.

[qinmin, 2017/01/23 23:03:15]

Then shouldn't the function name be OnSavingStarted or StartedSaving? 

[xingliu, 2017/01/23 23:26:08]

Done, changed to OnSavingStarted aligned with other functions here.

+
+    // Called when |download_job| is interrupted.
+    virtual void OnDownloadInterrupted(DownloadJob* download_job,
+                                       DownloadInterruptReason reason) = 0;
+
+    // Called when |download_job| is completed and inform the manager.
+    virtual void OnDownloadComplete(DownloadJob* download_job) = 0;
+
+    // Sets the download danger type.
+    virtual void SetDangerType(DownloadDangerType danger_type) = 0;
+  };
+
+  DownloadJob();
+  virtual ~DownloadJob();
+
+  DownloadJob::Manager* manager() { return manager_; }
+
+  Type type() const { return type_; }
+
+  // Called when DownloadJob is attached to DownloadJob::Manager.
+  virtual void OnAttached(DownloadJob::Manager* manager);
+
+  // Called before DownloadJob is detached from its manager.
+  virtual void OnBeforeDetach();
+
+  // Download operations.
+  virtual void Cancel(bool user_cancel) = 0;
+  virtual void Pause() = 0;
+  virtual void Resume() = 0;
+
+  // Return if the download file can be opened.
+  // See |DownloadItem:: CanOpenDownload|.
+  virtual bool CanOpen() const = 0;
+
+  // Return if the download job can be resumed.
+  virtual bool CanResume() const = 0;
+
+  // See |DownloadItem::CanShowInFolder|.
+  virtual bool CanShowInFolder() const = 0;
+
+  // Return if the download job is actively downloading.
+  virtual bool IsActive() const = 0;
+
+  // Return if the download job is paused.
+  virtual bool IsPause() const = 0;
+
+  // Return a number between 0 and 100 to represent the percentage progress of
+  // the download. Return |kDownloadProgressUnknown| if the progress is
+  // indeterminate.
+  virtual int PercentComplete() const = 0;
+
+  // Return the estimated current download speed in bytes per second.
+  // Or return kDownloadSpeedUnknown if the download speed is not measurable.
+  virtual int64_t CurrentSpeed() const = 0;
+
+  // Set the estimated remaining time of the download to |remaining| and return
+  // true if time remaining is available, otherwise return false.
+  virtual bool TimeRemaining(base::TimeDelta* remaining) const = 0;
+
+  // Return the WebContents associated with the download. Usually used to
+  // associate a browser window for any UI that needs to be displayed to the
+  // user.
+  // Or return nullptr if the download is not associated with an active
+  // WebContents.
+  virtual WebContents* GetWebContents() const = 0;
+
+  // Print the debug string including internal states of the download job.
+  virtual std::string DebugString(bool verbose) const = 0;
+
+ protected:
+  // Mark the download as being in-progress.
+  // TODO(xingliu): Pass ResponseInfo to the manager here.
+  void StartedSavingResponse();
+
+  // Mark the download as interrupted.
+  void Interrupt(DownloadInterruptReason reason);
+
+  // Mark the download job as completed.
+  void Complete();
+
+  // Owner of this DownloadJob, Only valid between OnAttached() and
+  // OnBeforeDetach(), inclusive. Otherwise set to nullptr.
+  DownloadJob::Manager* manager_;
+
+  // The type of the download.
+  DownloadJob::Type type_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(DownloadJob);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_JOB_H_