[Suggestions] Adding a Thumbnail Manager for the Suggestions Service

chrome/browser/search/suggestions/thumbnail_manager.cc

+// Copyright 2014 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/search/suggestions/thumbnail_manager.h"
+
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/search/suggestions/proto/suggestions.pb.h"
+#include "content/public/browser/browser_thread.h"
+#include "net/base/load_flags.h"
+
+namespace suggestions {
+
+ThumbnailManager::ThumbnailManager(Profile* profile)
+    : url_request_context_(profile->GetRequestContext()) {}
+
+ThumbnailManager::~ThumbnailManager() {}
+
+ThumbnailManager::ThumbnailRequest::ThumbnailRequest() : fetcher(NULL) {}
+
+ThumbnailManager::ThumbnailRequest::ThumbnailRequest(chrome::BitmapFetcher* f)
+    : fetcher(f) {}
+
+ThumbnailManager::ThumbnailRequest::~ThumbnailRequest() {
+  delete fetcher;
+}
+
+void ThumbnailManager::InitializeThumbnailMap(
+    const SuggestionsProfile& suggestions) {
+  thumbnail_map_.clear();
+  for (int i = 0; i < suggestions.suggestions_size(); ++i) {
+    const ChromeSuggestion& suggestion = suggestions.suggestions(i);
+    if (suggestion.has_thumbnail()) {
+      thumbnail_map_[GURL(suggestion.url())] = GURL(suggestion.thumbnail());
+    }
+  }
+}
+
+void ThumbnailManager::GetPageThumbnail(
+    const GURL& url,
+    base::Callback<void(const GURL&, const SkBitmap*)> callback) {
+  DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
+  // If |url| is not found in |thumbnail_map_|, then invoke |callback| with NULL
+  // since there is no associated thumbnail.
+  GURL thumbnail_url;
+  if (!GetThumbnailURL(url, &thumbnail_url)) {
+    callback.Run(url, NULL);
+    return;
+  }
+
+  // Look for a request in progress for |thumbnail_url|.
+  ThumbnailRequestMap::iterator it = pending_requests_.find(thumbnail_url);
+  if (it == pending_requests_.end()) {
+    // |thumbnail_url| is not being fetched, so create a request and initiate
+    // the fetch.
+    ThumbnailRequest request(new chrome::BitmapFetcher(thumbnail_url, this));
+    request.url = url;
+    request.callbacks.push_back(callback);
+    request.fetcher->Start(
+        url_request_context_, std::string(),
+        net::URLRequest::CLEAR_REFERRER_ON_TRANSITION_FROM_SECURE_TO_INSECURE,
+        net::LOAD_NORMAL);
+    pending_requests_[thumbnail_url] = request;

[huangs, 2014/05/24 03:45:40]

Wouldn't |request|'s destructor get called when it goes out of scope, resulting
in use-after-free?  Here's a test program:
********
#include <iostream>
#include <map>

class Test {
 public:
  Test() : x(0) {}
  explicit Test (int x_in) : x(x_in) {}
  ~Test() { std::cerr << "Destroy " << x << std::endl;}
  int x;
};

int main () {
  std::map<int, Test> m;
  Test a(5);
  m[3] = a;
  return 0;
}
********
Output is:
========
Destroy 0      (some temporary while computing |m[3]|?)
Destroy 0      (old value of |m[3]|).
Destroy 5      (new value of |m[3]|).
Destroy 5      (temp variable |a|)
========

Perhaps we can implement our own swap() in ThumbnailRequest()?  So:

(.h file change etc.)

#include <algorithm>
...
ThumbnailManager::ThumbnailRequest::swap(ThumbnailManager::ThumbnailRequest*
other) {
  std::swap(fetcher, other->fetcher);
}
...
pending_requests_[thumbnail_url].swap(&request);

[Mathieu, 2014/05/26 18:55:30]

Good catch, thanks for paying attention. See new patch.

[Jered, 2014/05/27 15:27:00]

:-/ Sorry I missed that. This is a little unfortunate. Anyway probably enough
C++ gymnastics for this CL.

+  } else {
+    // Request in progress. Register as an interested callback.
+    it->second.callbacks.push_back(callback);
+  }
+}
+
+void ThumbnailManager::OnFetchComplete(const GURL thumbnail_url,
+                                       const SkBitmap* bitmap) {
+  DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
+
+  ThumbnailRequestMap::iterator it = pending_requests_.find(thumbnail_url);
+  DCHECK(it != pending_requests_.end());
+
+  ThumbnailRequest* request = &it->second;
+
+  // Here |bitmap| could be NULL or a pointer to a bitmap which is owned by the
+  // BitmapFetcher and which ceases to exist after this function. Pass the
+  // un-owned pointer to the registered callbacks.
+  for (CallbackVector::iterator it = request->callbacks.begin();
+       it != request->callbacks.end(); ++it) {
+    it->Run(request->url, bitmap);
+  }
+  pending_requests_.erase(it);
+}
+
+bool ThumbnailManager::GetThumbnailURL(const GURL& url, GURL* thumbnail_url) {
+  std::map<GURL, GURL>::iterator it = thumbnail_map_.find(url);
+  if (it == thumbnail_map_.end()) return false;  // Not found.
+  *thumbnail_url = it->second;
+  return true;
+}
+
+}  // namespace suggestions