chrome/browser/net/sdch_dictionary_fetcher.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 // Support modularity by calling to load a new SDCH filter dictionary.
   6 // Note that this sort of calling can't be done in the /net directory, as it has
   7 // no concept of the HTTP cache (which is only visible at the browser level).
   8
   9 #ifndef CHROME_BROWSER_NET_SDCH_DICTIONARY_FETCHER_H_
  10 #define CHROME_BROWSER_NET_SDCH_DICTIONARY_FETCHER_H_
  11
  12 #include <queue>
  13 #include <set>
  14 #include <string>
  15
  16 #include "base/memory/scoped_ptr.h"
  17 #include "base/memory/weak_ptr.h"
  18 #include "base/threading/non_thread_safe.h"
  19 #include "net/base/sdch_manager.h"
  20 #include "net/url_request/url_fetcher_delegate.h"
  21
  22 namespace net {
  23 class URLFetcher;
  24 class URLRequestContextGetter;
  25 }  // namespace net
  26
  27 class SdchDictionaryFetcher
  28     : public net::URLFetcherDelegate,
  29       public net::SdchFetcher,
  30       public base::NonThreadSafe {
  31  public:
  32   explicit SdchDictionaryFetcher(net::URLRequestContextGetter* context);
  33   virtual ~SdchDictionaryFetcher();
  34
  35   // Stop fetching dictionaries, and abandon any current URLFetcheer operations
  36   // so that the IO thread can be stopped.
  37   static void Shutdown();
  38
  39   // Implementation of SdchFetcher class.
  40   // This method gets the requested dictionary, and then calls back into the
  41   // SdchManager class with the dictionary's text.
  42   virtual void Schedule(const GURL& dictionary_url) OVERRIDE;
  43
  44  private:
  45   // Delay in ms between Schedule and actual download.
  46   // This leaves the URL in a queue, which is de-duped, so that there is less
  47   // chance we'll try to load the same URL multiple times when a pile of
  48   // page subresources (or tabs opened in parallel) all suggest the dictionary.
  49   static const int kMsDelayFromRequestTillDownload = 100;
  50
  51   // Ensure the download after the above delay.
  52   void ScheduleDelayedRun();
  53
  54   // Make sure we're processing (or waiting for) the the arrival of the next URL
  55   // in the  |fetch_queue_|.
  56   void StartFetching();
  57
  58   // Implementation of net::URLFetcherDelegate. Called after transmission
  59   // completes (either successfully or with failure).
  60   virtual void OnURLFetchComplete(const net::URLFetcher* source) OVERRIDE;
  61
  62   // A queue of URLs that are being used to download dictionaries.
  63   std::queue<GURL> fetch_queue_;
  64   // The currently outstanding URL fetch of a dicitonary.
  65   // If this is null, then there is no outstanding request.
  66   scoped_ptr<net::URLFetcher> current_fetch_;
  67
  68   // Always spread out the dictionary fetches, so that they don't steal
  69   // bandwidth from the actual page load.  Create delayed tasks to spread out
  70   // the download.
  71   base::WeakPtrFactory<SdchDictionaryFetcher> weak_factory_;
  72   bool task_is_pending_;
  73
  74   // Althought the SDCH spec does not preclude a server from using a single URL
  75   // to load several distinct dictionaries (by telling a client to load a
  76   // dictionary from an URL several times), current implementations seem to have
  77   // that 1-1 relationship (i.e., each URL points at a single dictionary, and
  78   // the dictionary content does not change over time, and hence is not worth
  79   // trying to load more than once).  In addition, some dictionaries prove
  80   // unloadable only after downloading them (because they are too large?  ...or
  81   // malformed?). As a protective element, Chromium will *only* load a
  82   // dictionary at most once from a given URL (so that it doesn't waste
  83   // bandwidth trying repeatedly).
  84   // The following set lists all the dictionary URLs that we've tried to load,
  85   // so that we won't try to load from an URL more than once.
  86   // TODO(jar): Try to augment the SDCH proposal to include this restiction.
  87   std::set<GURL> attempted_load_;
  88
  89   // Store the system_url_request_context_getter to use it when we start
  90   // fetching.
  91   scoped_refptr<net::URLRequestContextGetter> context_;
  92
  93   DISALLOW_COPY_AND_ASSIGN(SdchDictionaryFetcher);
  94 };
  95
  96 #endif  // CHROME_BROWSER_NET_SDCH_DICTIONARY_FETCHER_H_