Implementing recent pages snapshot capture.

chrome/browser/android/offline_pages/recent_tab_helper.cc

 // Copyright (c) 2016 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.
 
 #include "chrome/browser/android/offline_pages/recent_tab_helper.h"
 
+#include <queue>
+#include <vector>
+
+#include "base/bind.h"
+#include "base/location.h"
+#include "base/logging.h"
+#include "base/macros.h"
+#include "base/thread_task_runner_handle.h"
+#include "base/time/time.h"
+#include "chrome/browser/android/offline_pages/offline_page_mhtml_archiver.h"
+#include "chrome/browser/android/offline_pages/offline_page_model_factory.h"
+#include "components/offline_pages/offline_page_item.h"
+#include "components/offline_pages/offline_page_model.h"
+#include "content/public/browser/browser_context.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/navigation_entry.h"
+#include "content/public/browser/navigation_handle.h"
+
 DEFINE_WEB_CONTENTS_USER_DATA_KEY(offline_pages::RecentTabHelper);
 
+namespace {
+const char* kClientNamespace = "last_n";
+
+// Max number of pages to keep. The oldest pages that are over this count are
+// deleted before the next one is saved.
+const size_t kMaxPagesToKeep = 50;
+
+// Predicate for priority_queue used to compute the oldest pages.
+struct ComparePagesForPurge {
+  bool operator()(const offline_pages::OfflinePageItem* left,
+                 const offline_pages::OfflinePageItem* right) const {
+    return left->creation_time > right->creation_time;
+  }
+};
+
+}  // namespace
+
 namespace offline_pages {
 
 RecentTabHelper::RecentTabHelper(content::WebContents* web_contents)
-    : content::WebContentsObserver(web_contents) {
+    : content::WebContentsObserver(web_contents),
+      page_model_(nullptr),
+      weak_ptr_factory_(this) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  snapshot_controller_.reset(new SnapshotController(
+      base::ThreadTaskRunnerHandle::Get(), this));
+  page_model_ = OfflinePageModelFactory::GetForBrowserContext(
+      web_contents->GetBrowserContext());
+
+  // TODO(dimich): When we have BackgroundOffliner, avoid capturing prerenderer
+  // WebContents with its origin as well.
+  never_do_snapshots_ = web_contents->GetBrowserContext()->IsOffTheRecord();
 }
 
 RecentTabHelper::~RecentTabHelper() {
 }
 
+void RecentTabHelper::DidFinishNavigation(
+    content::NavigationHandle* navigation_handle) {
+  if (navigation_handle->IsInMainFrame() &&
+      navigation_handle->HasCommitted() &&
+      !navigation_handle->IsErrorPage()) {
+    // New navigation, new snapshot session.
+    snapshot_controller_->Reset();
+    snapshot_url_ = GURL::EmptyGURL();
+  }
+}
+
+void RecentTabHelper::DocumentAvailableInMainFrame() {
+  snapshot_controller_->DocumentAvailableInMainFrame();
+}
+
+void RecentTabHelper::DocumentOnLoadCompletedInMainFrame() {
+  snapshot_controller_->DocumentOnLoadCompletedInMainFrame();
+}
+
+// This starts a sequence of async operations chained through callbacks:
+// - compute the set of old 'last_n' pages that have to be purged
+// - delete the pages found in the previous step
+// - snapshot the current web contents
+// Along the chain, the original URL is passed and compared, to detect
+// possible navigation and cancel snapshot in that case.
+void RecentTabHelper::StartSnapshot() {
+  if (never_do_snapshots_)
+    return;
+
+  GURL url = web_contents()->GetLastCommittedURL();
+  if (!page_model_->CanSavePage(url)) {
+    // TODO(dimich): Add UMA. Bug 608112.
+    return;
+  }
+
+  snapshot_url_ = url;
+
+  // TODO(dimich): Implement automatic cleanup as per design doc, based on
+  // storage limits and page age.
+  // This algorithm (remove pages before making sure the save was successful)
+  // prefers keeping the storage use low and under control by potentially
+  // sacrificing the current snapshot.
+  page_model_->GetOfflineIdsForClientId(
+    client_id(),
+    base::Bind(&RecentTabHelper::ContinueSnapshotWithIdsToPurge,
+               weak_ptr_factory_.GetWeakPtr()));
+}
+
+// Collects following pages from lastN namespace:
+// - the ones with the same online URL
+// - the oldest pages, enough to keep kMaxPagesToKeep limit.
+void RecentTabHelper::ContinueSnapshotWithIdsToPurge(
+    const std::vector<int64_t>& page_ids) {
+
+  std::vector<int64_t> pages_to_purge;
+  // Use priority queue to figure out the set of oldest pages to purge.
+  std::priority_queue<const OfflinePageItem*,
+                      std::vector<const OfflinePageItem*>,
+                      ComparePagesForPurge> pages_queue;
+
+  for (const auto& offline_id : page_ids) {
+    // TODO(dimich): get rid of 'Maybe'. Maybe make it return multiple pages.
+    const OfflinePageItem* page =
+        page_model_->MaybeGetPageByOfflineId(offline_id);
+    // If there is already a snapshot of this page, remove it so we don't
+    // have multiple snapshots of the same page.
+    if (page->url == snapshot_url_) {
+      pages_to_purge.push_back(offline_id);
+    } else {
+      pages_queue.push(page);
+    }
+  }
+
+  // Negative counter means nothing else to purge.
+  int count_to_purge =
+      page_ids.size() - kMaxPagesToKeep - pages_to_purge.size();
+
+  for (int count = 0; count < count_to_purge; ++count) {
+    pages_to_purge.push_back(pages_queue.top()->offline_id);
+    pages_queue.pop();
+  }
+
+  page_model_->DeletePagesByOfflineId(
+      pages_to_purge, base::Bind(&RecentTabHelper::ContinueSnapshotAfterPurge,
+                                 weak_ptr_factory_.GetWeakPtr()));
+}
+
+void RecentTabHelper::ContinueSnapshotAfterPurge(
+    OfflinePageModel::DeletePageResult result) {
+  // NOT_FOUND is because it's what we get when passing empty vector of ids.
+  // TODO(dimich): remove NOT_FOUND when bug 608057 is fixed.
+  if (result != OfflinePageModel::DeletePageResult::SUCCESS &&
+      result != OfflinePageModel::DeletePageResult::NOT_FOUND) {
+    // If previous pages can't be deleted, don't add new ones.
+    ReportSnapshotCompleted();
+    return;
+  }
+
+  if (!IsSamePage()) {
+    ReportSnapshotCompleted();
+    return;
+  }
+
+  // Create either test Archiver or a regular one.
+  std::unique_ptr<OfflinePageArchiver> archiver;
+  if (test_archive_factory_.get()) {
+    archiver = test_archive_factory_->CreateArchiver(web_contents());
+  } else {
+    archiver.reset(new OfflinePageMHTMLArchiver(web_contents()));
+  }
+
+  page_model_->SavePage(
+      snapshot_url_, client_id(), std::move(archiver),
+      base::Bind(&RecentTabHelper::SavePageCallback,
+                 weak_ptr_factory_.GetWeakPtr()));
+}
+
+void RecentTabHelper::SavePageCallback(OfflinePageModel::SavePageResult result,
+                                       int64_t offline_id) {
+  // TODO(dimich): add UMA, including result. Bug 608112.
+  ReportSnapshotCompleted();
+}
+
+void RecentTabHelper::ReportSnapshotCompleted() {
+  snapshot_controller_->PendingSnapshotCompleted();
+}
+
+bool RecentTabHelper::IsSamePage() const {
+  return web_contents() &&
+         (web_contents()->GetLastCommittedURL() == snapshot_url_);
+}
+
+ClientId RecentTabHelper::client_id() const {
+  return ClientId(kClientNamespace, "");
+}
+
+void RecentTabHelper::SetArchiveFactoryForTest(
+    std::unique_ptr<TestArchiveFactory> test_archive_factory) {
+  test_archive_factory_ = std::move(test_archive_factory);
+}
+
+void RecentTabHelper::SetTaskRunnerForTest(
+    const scoped_refptr<base::SingleThreadTaskRunner>& task_runner) {
+  snapshot_controller_.reset(new SnapshotController(task_runner, this));
+}
+
 }  // namespace offline_pages