net/base/sdch_dictionary_fetcher.h

   1 // Copyright 2014 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 NET_BASE_SDCH_DICTIONARY_FETCHER_H_
  10 #define NET_BASE_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
  24 class URLFetcher;
  25 class URLRequestContextGetter;
  26
  27 class NET_EXPORT SdchDictionaryFetcher
  28     : public URLFetcherDelegate,
  29       public SdchFetcher,
  30       public base::NonThreadSafe {
  31  public:
  32   // Consumer must guarantee that the SdchManager pointer outlives
  33   // this object.  The current implementation guarantees this by
  34   // the SdchManager owning this object.
  35   SdchDictionaryFetcher(SdchManager* manager,
  36                         URLRequestContextGetter* context);
  37   virtual ~SdchDictionaryFetcher();
  38
  39   // Implementation of SdchFetcher class.
  40   virtual void Schedule(const GURL& dictionary_url) OVERRIDE;
  41   virtual void Cancel() OVERRIDE;
  42
  43  private:
  44   // Delay in ms between Schedule and actual download.
  45   // This leaves the URL in a queue, which is de-duped, so that there is less
  46   // chance we'll try to load the same URL multiple times when a pile of
  47   // page subresources (or tabs opened in parallel) all suggest the dictionary.
  48   static const int kMsDelayFromRequestTillDownload = 100;
  49
  50   // Ensure the download after the above delay.
  51   void ScheduleDelayedRun();
  52
  53   // Make sure we're processing (or waiting for) the the arrival of the next URL
  54   // in the  |fetch_queue_|.
  55   void StartFetching();
  56
  57   // Implementation of URLFetcherDelegate. Called after transmission
  58   // completes (either successfully or with failure).
  59   virtual void OnURLFetchComplete(const URLFetcher* source) OVERRIDE;
  60
  61   SdchManager* const manager_;
  62
  63   // A queue of URLs that are being used to download dictionaries.
  64   std::queue<GURL> fetch_queue_;
  65   // The currently outstanding URL fetch of a dicitonary.
  66   // If this is null, then there is no outstanding request.
  67   scoped_ptr<URLFetcher> current_fetch_;
  68
  69   // Always spread out the dictionary fetches, so that they don't steal
  70   // bandwidth from the actual page load.  Create delayed tasks to spread out
  71   // the download.
  72   base::WeakPtrFactory<SdchDictionaryFetcher> weak_factory_;
  73   bool task_is_pending_;
  74
  75   // Althought the SDCH spec does not preclude a server from using a single URL
  76   // to load several distinct dictionaries (by telling a client to load a
  77   // dictionary from an URL several times), current implementations seem to have
  78   // that 1-1 relationship (i.e., each URL points at a single dictionary, and
  79   // the dictionary content does not change over time, and hence is not worth
  80   // trying to load more than once).  In addition, some dictionaries prove
  81   // unloadable only after downloading them (because they are too large?  ...or
  82   // malformed?). As a protective element, Chromium will *only* load a
  83   // dictionary at most once from a given URL (so that it doesn't waste
  84   // bandwidth trying repeatedly).
  85   // The following set lists all the dictionary URLs that we've tried to load,
  86   // so that we won't try to load from an URL more than once.
  87   // TODO(jar): Try to augment the SDCH proposal to include this restiction.
  88   std::set<GURL> attempted_load_;
  89
  90   // Store the system_url_request_context_getter to use it when we start
  91   // fetching.
  92   scoped_refptr<URLRequestContextGetter> context_;
  93
  94   DISALLOW_COPY_AND_ASSIGN(SdchDictionaryFetcher);
  95 };
  96
  97 }  // namespace net
  98
  99 #endif  // NET_BASE_SDCH_DICTIONARY_FETCHER_H_