Implementing URL prefix match for history thumbnail cache.

chrome/browser/history/top_sites_cache.h

 // Copyright (c) 2012 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 CHROME_BROWSER_HISTORY_TOP_SITES_CACHE_H_
 #define CHROME_BROWSER_HISTORY_TOP_SITES_CACHE_H_
 
 #include <map>
 #include <utility>
 
 #include "base/memory/ref_counted.h"
 #include "chrome/browser/history/history_types.h"
+#include "chrome/browser/history/url_utils.h"
 
 namespace history {
 
+// TopSiteCache caches thumbnails for visited pages. Retrieving thumbnails from
+// a given input URL is a two-stage process:
+//
+//   input URL --(map 1)--> canonical URL --(map 2)--> image.
+//
+// (map 1) searches input URL in |canonical_urls_|. canonical URL is
+// assigned to the resulting value if found; else input URL.
+//
+// (map 2) simply looks up canonical URL in |images_|.
+//
+// TopSiteCache also provides GetCanonicalURLsIteratorForPrefix(), which is an
+// alternative implementation of (map 1) that does the following:
+// - if canonical URL is a key in |canonical_urls_|, return the value.
+// - else if canonical URL is a "URL prefix" (see comment in url_utils.h) of
+//   some key in |canonical_urls_|, return the value corresponding to the key.
+// - else return input URL.
+
 // TopSitesCache caches the top sites and thumbnails for TopSites.
 class TopSitesCache {
  public:
   TopSitesCache();
   ~TopSitesCache();
 
   // The top sites.
   void SetTopSites(const MostVisitedURLList& top_sites);
   const MostVisitedURLList& top_sites() const { return top_sites_; }
 
@@ skipping 11 matching lines @@
   bool GetPageThumbnail(const GURL& url,
                         scoped_refptr<base::RefCountedMemory>* bytes);
 
   // Fetches the thumbnail score for the specified url. Returns true if
   // there is a thumbnail score for the specified url.
   bool GetPageThumbnailScore(const GURL& url, ThumbnailScore* score);
 
   // Returns the canonical URL for |url|.
   const GURL& GetCanonicalURL(const GURL& url);
 
+  // Returns the canonical URL for |url_prefix| that matches by prefix.
+  // Multiple matches exst, returns the canonical URL for the first
+  // matching entry under lexicographical order.
+  const GURL& GetCanonicalURLForPrefix(const GURL& url_prefix);
+
   // Returns true if |url| is known.
   bool IsKnownURL(const GURL& url);
 
   // Returns the index into |top_sites_| for |url|.
   size_t GetURLIndex(const GURL& url);
 
  private:
   // The entries in CanonicalURLs, see CanonicalURLs for details. The second
   // argument gives the index of the URL into MostVisitedURLs redirects.
   typedef std::pair<MostVisitedURL*, size_t> CanonicalURLEntry;
 
-  // Comparator used for CanonicalURLs.
+  // Comparator used for CanonicalURLs. Its main purpose

[huangs, 2013/09/12 23:45:33]

Oops, typo here. Will fix.

   class CanonicalURLComparator {
    public:
     bool operator()(const CanonicalURLEntry& e1,
                     const CanonicalURLEntry& e2) const {
-      return e1.first->redirects[e1.second] < e2.first->redirects[e2.second];
+      return CanonicalURLStringCompare(e1.first->redirects[e1.second].spec(),
+                                       e2.first->redirects[e2.second].spec());
     }
   };
 
   // This is used to map from redirect url to the MostVisitedURL the redirect is
   // from. Ideally this would be map<GURL, size_t> (second param indexing into
   // top_sites_), but this results in duplicating all redirect urls. As some
   // sites have a lot of redirects, we instead use the MostVisitedURL* and the
   // index of the redirect as the key, and the index into top_sites_ as the
   // value. This way we aren't duplicating GURLs. CanonicalURLComparator
   // enforces the ordering as if we were using GURLs.
   typedef std::map<CanonicalURLEntry, size_t,
                    CanonicalURLComparator> CanonicalURLs;
 
   // Generates the set of canonical urls from |top_sites_|.
   void GenerateCanonicalURLs();
 
   // Stores a set of redirects. This is used by GenerateCanonicalURLs.
   void StoreRedirectChain(const RedirectList& redirects, size_t destination);
 
-  // Returns the iterator into canconical_urls_ for the specified url.
+  // Returns the iterator into |canonical_urls_| for the |url|.
   CanonicalURLs::iterator GetCanonicalURLsIterator(const GURL& url);
 
+  // Returns the first iterator into |canonical_urls_| for which |prefix_url|
+  // is a URL prefix. Returns |canonical_urls_.end()| if no match is found.
+  CanonicalURLs::iterator GetCanonicalURLsIteratorForPrefix(
+      const GURL& prefix_url);
+
   // The top sites.
   MostVisitedURLList top_sites_;
 
   // The images. These map from canonical url to image.
   URLToImagesMap images_;
 
   // Generated from the redirects to and from the most visited pages. See
   // description above typedef for details.
   CanonicalURLs canonical_urls_;
 
   DISALLOW_COPY_AND_ASSIGN(TopSitesCache);
 };
 
 }  // namespace history
 
 #endif  // CHROME_BROWSER_HISTORY_TOP_SITES_CACHE_H_