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// Copyright (c) 2011 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.
// Support modularity by calling to load a new SDCH filter dictionary.
// Note that this sort of calling can't be done in the /net directory, as it has
// no concept of the HTTP cache (which is only visible at the browser level).
#ifndef CHROME_BROWSER_NET_SDCH_DICTIONARY_FETCHER_H_
#define CHROME_BROWSER_NET_SDCH_DICTIONARY_FETCHER_H_
#pragma once
#include <queue>
#include <set>
#include <string>
#include "base/memory/scoped_ptr.h"
#include "base/task.h"
#include "content/public/common/url_fetcher_delegate.h"
#include "net/base/sdch_manager.h"
class SdchDictionaryFetcher : public content::URLFetcherDelegate,
public net::SdchFetcher {
public:
SdchDictionaryFetcher();
virtual ~SdchDictionaryFetcher();
// Stop fetching dictionaries, and abandon any current URLFetcheer operations
// so that the IO thread can be stopped.
static void Shutdown();
// Implementation of SdchFetcher class.
// This method gets the requested dictionary, and then calls back into the
// SdchManager class with the dictionary's text.
virtual void Schedule(const GURL& dictionary_url);
private:
// Delay in ms between Schedule and actual download.
// This leaves the URL in a queue, which is de-duped, so that there is less
// chance we'll try to load the same URL multiple times when a pile of
// page subresources (or tabs opened in parallel) all suggest the dictionary.
static const int kMsDelayFromRequestTillDownload = 100;
// Ensure the download after the above delay.
void ScheduleDelayedRun();
// Make sure we're processing (or waiting for) the the arrival of the next URL
// in the |fetch_queue_|.
void StartFetching();
// Implementation of content::URLFetcherDelegate. Called after transmission
// completes (either successfully or with failure).
virtual void OnURLFetchComplete(const content::URLFetcher* source) OVERRIDE;
// A queue of URLs that are being used to download dictionaries.
std::queue<GURL> fetch_queue_;
// The currently outstanding URL fetch of a dicitonary.
// If this is null, then there is no outstanding request.
scoped_ptr<content::URLFetcher> current_fetch_;
// Always spread out the dictionary fetches, so that they don't steal
// bandwidth from the actual page load. Create delayed tasks to spread out
// the download.
ScopedRunnableMethodFactory<SdchDictionaryFetcher> method_factory_;
bool task_is_pending_;
// Althought the SDCH spec does not preclude a server from using a single URL
// to load several distinct dictionaries (by telling a client to load a
// dictionary from an URL several times), current implementations seem to have
// that 1-1 relationship (i.e., each URL points at a single dictionary, and
// the dictionary content does not change over time, and hence is not worth
// trying to load more than once). In addition, some dictionaries prove
// unloadable only after downloading them (because they are too large? ...or
// malformed?). As a protective element, Chromium will *only* load a
// dictionary at most once from a given URL (so that it doesn't waste
// bandwidth trying repeatedly).
// The following set lists all the dictionary URLs that we've tried to load,
// so that we won't try to load from an URL more than once.
// TODO(jar): Try to augment the SDCH proposal to include this restiction.
std::set<GURL> attempted_load_;
DISALLOW_COPY_AND_ASSIGN(SdchDictionaryFetcher);
};
#endif // CHROME_BROWSER_NET_SDCH_DICTIONARY_FETCHER_H_
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