Implement chrome.experimental.downloads.onChanged

chrome/browser/download/download_extension_api.cc

Index: chrome/browser/download/download_extension_api.cc
diff --git a/chrome/browser/download/download_extension_api.cc b/chrome/browser/download/download_extension_api.cc
index cee9a906e683bdd2d2ea93b551bb565b29e7ab4b..35784d1c0f44d31e156e843e68614a236d6aca5b 100644
--- a/chrome/browser/download/download_extension_api.cc
+++ b/chrome/browser/download/download_extension_api.cc
@@ -864,7 +864,9 @@ void DownloadsGetFileIconFunction::OnIconURLExtracted(const std::string& url) {
 
 ExtensionDownloadsEventRouter::ExtensionDownloadsEventRouter(Profile* profile)
   : profile_(profile),
-    manager_(NULL) {
+    manager_(NULL),
+    delete_item_jsons_(&item_jsons_),
+    delete_on_changed_stats_(&on_changed_stats_) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   DCHECK(profile_);
   // Register a callback with the DownloadService for this profile to be called
@@ -880,57 +882,116 @@ ExtensionDownloadsEventRouter::ExtensionDownloadsEventRouter(Profile* profile)
 void ExtensionDownloadsEventRouter::Init(DownloadManager* manager) {
   DCHECK(manager_ == NULL);
   manager_ = manager;
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   manager_->AddObserver(this);
 }
 
 ExtensionDownloadsEventRouter::~ExtensionDownloadsEventRouter() {
   if (manager_ != NULL)
     manager_->RemoveObserver(this);
+  for (ItemMap::const_iterator iter = downloads_.begin();
+       iter != downloads_.end(); ++iter) {
+    if (iter->second != NULL)
+      iter->second->RemoveObserver(this);
+  }
+}
+
+ExtensionDownloadsEventRouter::OnChangedStat::OnChangedStat()
+  : fires(0),
+    total(0) {
+}
+
+ExtensionDownloadsEventRouter::OnChangedStat::~OnChangedStat() {
+  if (total > 0)
+    UMA_HISTOGRAM_PERCENTAGE("Download.OnChanged", (fires * 100 / total));
+}
+
+void ExtensionDownloadsEventRouter::OnDownloadUpdated(DownloadItem* item) {
+  int download_id = item->GetId();
+  if (item->GetState() == DownloadItem::REMOVING) {

[Randy Smith (Not in Mondays), 2012/02/02 18:10:07]

The code would be enhanced by a few comments indicating what each block of code
did.  If someone doesn't know the Observer interface fairly well, they might be
a bit lost.  

[benjhayden, 2012/02/02 20:40:38]

Done.

+    downloads_.erase(download_id);
+    item->RemoveObserver(this);
+    DispatchEvent(extension_event_names::kOnDownloadErased,
+                  base::Value::CreateIntegerValue(download_id));
+    delete item_jsons_[download_id];
+    item_jsons_.erase(download_id);
+    delete on_changed_stats_[download_id];
+    on_changed_stats_.erase(download_id);
+    return;
+  }
+
+  base::DictionaryValue* old_json = item_jsons_[download_id];
+  scoped_ptr<base::DictionaryValue> new_json(DownloadItemToJSON(item));
+  scoped_ptr<base::DictionaryValue> delta(new base::DictionaryValue());
+  delta->SetInteger(kIdKey, download_id);
+  bool changed = false;
+
+  for (base::DictionaryValue::Iterator iter(*new_json.get());
+       iter.HasNext(); iter.Advance()) {
+    if (iter.key() != kBytesReceivedKey) {

[Randy Smith (Not in Mondays), 2012/02/02 18:10:07]

My inclination would be to have changes in BytesReceived show up in the delta
but simple not result in an event dispatch.  Can you give me a sense as to why
you prefer it not to show up (if you do)?

[benjhayden, 2012/02/02 20:40:38]

API purity.
If I write an onChanged listener without reading the docs carefully, and I
notice the bytesReceived field there, then I might think that onChanged is a
good way to listen for bytesReceived events, and wonder why I don't receive them
very often, and I'd probably file a bug. If the only way to find bytesReceived
changes is the correct way (polling search()), then I'll definitely do it the
correct way.

+      base::Value* old_value = NULL;
+      if (!old_json->HasKey(iter.key()) ||
+          (old_json->Get(iter.key(), &old_value) &&
+           !iter.value().Equals(old_value))) {

[Randy Smith (Not in Mondays), 2012/02/02 18:10:07]

This looks like it'll leave out cases in which we've dropped keys in the
old->new transition.  We probably don't have any such cases now, but it's an
interface assumption that might get broken silently in the future; we should
either comment it or handle the case.

[benjhayden, 2012/02/02 20:40:38]

Good catch!

+        delta->Set(iter.key() + ".new", iter.value().DeepCopy());
+        if (old_value)
+          delta->Set(iter.key() + ".old", old_value->DeepCopy());
+        changed = true;
+      }
+    }
+  }
+
+  ++(on_changed_stats_[download_id]->total);
+  if (changed) {
+    DispatchEvent(extension_event_names::kOnDownloadChanged, delta.release());
+    ++(on_changed_stats_[download_id]->fires);
+  }
+  item_jsons_[download_id]->Swap(new_json.get());
+}
+
+void ExtensionDownloadsEventRouter::OnDownloadOpened(DownloadItem* item) {
 }
 
 void ExtensionDownloadsEventRouter::ModelChanged() {

[Randy Smith (Not in Mondays), 2012/02/02 18:10:07]

Again, I think just one or two comments would help this routine to call out the
set creation, then finding the set difference in order to dispach the events.  

[benjhayden, 2012/02/02 20:40:38]

Done.

+  typedef std::set<int> DownloadIdSet;
+
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   if (manager_ == NULL)
     return;
   DownloadManager::DownloadVector current_vec;
   manager_->SearchDownloads(string16(), &current_vec);
-  DownloadIdSet current_set;
+  DownloadIdSet current_set, prev_set;
+  for (ItemMap::const_iterator iter = downloads_.begin();
+       iter != downloads_.end(); ++iter) {
+    prev_set.insert(iter->first);
+  }
   ItemMap current_map;
   for (DownloadManager::DownloadVector::const_iterator iter =
        current_vec.begin();
        iter != current_vec.end(); ++iter) {
     DownloadItem* item = *iter;
     int item_id = item->GetId();
-    // TODO(benjhayden): Remove the following line when every item's id >= 0,
-    // which will allow firing onErased events for items from the history.
-    if (item_id < 0) continue;
+    CHECK(item_id >= 0);
     DCHECK(current_map.find(item_id) == current_map.end());
     current_set.insert(item_id);
     current_map[item_id] = item;
   }
-  DownloadIdSet new_set;  // current_set - downloads_;
-  DownloadIdSet erased_set;  // downloads_ - current_set;
-  std::insert_iterator<DownloadIdSet> new_insertor(new_set, new_set.begin());
-  std::insert_iterator<DownloadIdSet> erased_insertor(
-      erased_set, erased_set.begin());
+  DownloadIdSet new_set;  // current_set - prev_set;
   std::set_difference(current_set.begin(), current_set.end(),
-                      downloads_.begin(), downloads_.end(),
-                      new_insertor);
-  std::set_difference(downloads_.begin(), downloads_.end(),
-                      current_set.begin(), current_set.end(),
-                      erased_insertor);
+                      prev_set.begin(), prev_set.end(),
+                      std::insert_iterator<DownloadIdSet>(
+                        new_set, new_set.begin()));
   for (DownloadIdSet::const_iterator iter = new_set.begin();
        iter != new_set.end(); ++iter) {
     scoped_ptr<base::DictionaryValue> item(
         DownloadItemToJSON(current_map[*iter]));
-    DispatchEvent(extension_event_names::kOnDownloadCreated, item.release());
-  }
-  for (DownloadIdSet::const_iterator iter = erased_set.begin();
-       iter != erased_set.end(); ++iter) {
-    DispatchEvent(extension_event_names::kOnDownloadErased,
-                  base::Value::CreateIntegerValue(*iter));
+    DispatchEvent(extension_event_names::kOnDownloadCreated, item->DeepCopy());

[Randy Smith (Not in Mondays), 2012/02/02 18:10:07]

I think it's worthwhile having a comment in this routine somewhere (at end?)
indicating why there's not a parallel Download destroyed event dispatch.  (I
actually mentioned this parenthetically when I suggested the code change.)

[benjhayden, 2012/02/02 20:40:38]

Done.

+    DCHECK(item_jsons_.find(*iter) == item_jsons_.end());
+    on_changed_stats_[*iter] = new OnChangedStat();
+    current_map[*iter]->AddObserver(this);
+    item_jsons_[*iter] = item.release();
   }
-  downloads_.swap(current_set);
+  downloads_.swap(current_map);
 }
 
 void ExtensionDownloadsEventRouter::ManagerGoingDown() {