Added member data to classes to support download resumption.

content/browser/download/download_item.h

Index: content/browser/download/download_item.h
diff --git a/content/browser/download/download_item.h b/content/browser/download/download_item.h
index 7a19ea014107f293a632e8e043d9a96cf8097beb..9eceba1de61d5a8378253e2712b91e99bbc1d833 100644
--- a/content/browser/download/download_item.h
+++ b/content/browser/download/download_item.h
@@ -157,8 +157,11 @@ class CONTENT_EXPORT DownloadItem {
   // Called when the user has validated the download of a dangerous file.
   void DangerousDownloadValidated();
 
-  // Received a new chunk of data
-  void Update(int64 bytes_so_far);
+  // Received a new chunk of data.
+  // |bytes_so_far| is the number of bytes received so far.
+  // |partial_hash| is the hash up to this point.  It will be an empty string
+  // if we are not calculating hashes.
+  void Update(int64 bytes_so_far, const std::string& partial_hash);

[Randy Smith (Not in Mondays), 2011/10/31 18:46:43]

Currently, Update is just used to send across size data for display purposes
based on a timer on the file thread--it isn't synchronous with OnReadCompleted
or anything.  |hash| isn't for display, so I don't think it makes sense to
include it in the update--it'll come across in OnAllDataSaved or Interrupted.

[ahendrickson, 2011/11/13 21:15:20]

No, Update also sets received_bytes_, which is passed along to the persistent
store.  I want the hash to end up there as well.

Specifically, I want the hash to be periodically updated in the persistent
store, so we can use it when we resume a download after a crash (where we won't
necessarily record a download interruption).

Does that seem reasonable to you?

[Randy Smith (Not in Mondays), 2011/11/15 18:35:25]

Hmmm.  I understand it, but I don't like it; I want to get the hash less
interwoven with the core downloads system, not more.  Let me pull back a bit and
summarize the requirements, then see if I can come up with a different way to
satisfy them.

As I understand what you're saying, you want the hash stored in the persistent
store on a regular basis, and you want that hash associated with a specific
number of bytes received, so that when you resume downloads you can resume hash
computation from a known position and known partial hash.  That strikes me as a
reasonable requirement.  That requirement means that whenever we update
bytes_received in the persistent store, we also need to update the hash value,
atomically with bytes received.  I'm also good with that.

However, I think the regular, periodic update of the hash is so that we can
resume downloads after a crash.  For either shutdown or error cases we'll flush
the information out to the database when we Cancel/Interrupt.  So it seems like
the need for this extra argument is purely for supporting the resumption after
crash case.  I don't feel like supporting that case is very high priority; at
least, I hope we don't crash that often :-}.  

Having said that, we do need to make sure that we we update the hash and
bytes_so_far atomically.  And *avoiding* updating the bytes-so-far if we don't
have the hash is probably a larger hassle than doing what you've got above.  So
yeah, I'm ok with this.  But if it turns into a large hassle I'd probably go the
other way--simplicity :uber alles is going to be my motto here.

 
   // Cancel the download operation. We need to distinguish between cancels at
   // exit (DownloadManager destructor) from user interface initiated cancels
@@ -180,15 +183,18 @@ class CONTENT_EXPORT DownloadItem {
   void CompleteDelayedDownload();
 
   // Called when all data has been saved. Only has display effects.
-  void OnAllDataSaved(int64 size);
+  void OnAllDataSaved(int64 size, const std::string final_hash);
 
   // Called when the downloaded file is removed.
   void OnDownloadedFileRemoved();
 
   // Download operation had an error.
   // |size| is the amount of data received at interruption.
+  // |partial_hash| is the current hash value at interruption.
   // |reason| is the download interrupt reason code that the operation received.
-  void Interrupted(int64 size, InterruptReason reason);
+  void Interrupted(int64 size,
+                   const std::string partial_hash,
+                   InterruptReason reason);
 
   // Deletes the file from disk and removes the download from the views and
   // history.  |user| should be true if this is the result of the user clicking
@@ -277,6 +283,7 @@ class CONTENT_EXPORT DownloadItem {
     total_bytes_ = total_bytes;
   }
   int64 received_bytes() const { return received_bytes_; }
+  const std::string& partial_hash() const { return partial_hash_; }
   int32 id() const { return download_id_; }
   DownloadId global_id() const;
   base::Time start_time() const { return start_time_; }
@@ -306,6 +313,13 @@ class CONTENT_EXPORT DownloadItem {
   void set_opened(bool opened) { opened_ = opened; }
   bool opened() const { return opened_; }
 
+  const std::string& last_modified_time() const { return last_modified_time_; }
+  void set_last_modified_time(const std::string& time) {
+    last_modified_time_ = time;
+  }
+  const std::string& etag() const { return etag_; }
+  void set_etag(const std::string& tag) { etag_ = tag; }
+
   InterruptReason last_reason() const { return last_reason_; }
 
   DownloadPersistentStoreInfo GetPersistentStoreInfo() const;
@@ -351,6 +365,9 @@ class CONTENT_EXPORT DownloadItem {
   // Internal helper for maintaining consistent received and total sizes.
   void UpdateSize(int64 size);
 
+  // Internal helper for keeping track of the hash as we receive data.
+  void UpdateHash(const std::string& partial_hash);
+
   // Called when the entire download operation (including renaming etc)
   // is completed.
   void Completed();
@@ -414,40 +431,49 @@ class CONTENT_EXPORT DownloadItem {
   // It's used to construct a suggested filename.
   std::string referrer_charset_;
 
-  // Total bytes expected
+  // Total bytes expected.
   int64 total_bytes_;
 
-  // Current received bytes
+  // Current received bytes.
   int64 received_bytes_;
 
+  // Current hash value.
+  std::string partial_hash_;
+
+  // Server's time stamp for the file.
+  std::string last_modified_time_;
+
+  // Server's ETAG for the file.
+  std::string etag_;
+
   // Last reason.
   InterruptReason last_reason_;
 
-  // Start time for calculating remaining time
+  // Start time for calculating remaining time.
   base::TimeTicks start_tick_;
 
-  // The current state of this download
+  // The current state of this download.
   DownloadState state_;
 
-  // The views of this item in the download shelf and download tab
+  // The views of this item in the download shelf and download tab.
   ObserverList<Observer> observers_;
 
-  // Time the download was started
+  // Time the download was started.
   base::Time start_time_;
 
-  // Time the download completed
+  // Time the download completed.
   base::Time end_time_;
 
-  // Our persistent store handle
+  // Our persistent store handle.
   int64 db_handle_;
 
-  // Timer for regularly updating our observers
+  // Timer for regularly updating our observers.
   base::RepeatingTimer<DownloadItem> update_timer_;
 
-  // Our owning object
+  // Our owning object.
   DownloadManager* download_manager_;
 
-  // In progress downloads may be paused by the user, we note it here
+  // In progress downloads may be paused by the user, we note it here.
   bool is_paused_;
 
   // A flag for indicating if the download should be opened at completion.