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_ 100
