Make SDCH dictionaries persistent across browser restart.

net/url_request/sdch_dictionary_fetcher.h

 // Copyright 2014 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.
 
 // TODO(rdsmith): This class needs to delegate URLRequest::Delegate methods
 // to the net/ embedder for correct implementation of authentication.
 // Specifically, this class needs the embedder to provide functionality
 // corresponding to
 // URLRequest::Delegate::{OnAuthRequired,OnCertificateRequested}.
 
@@ skipping 27 matching lines @@
 // attempting to fetch each dictionary once.
 class NET_EXPORT SdchDictionaryFetcher : public URLRequest::Delegate,
                                          public base::NonThreadSafe {
  public:
   typedef base::Callback<void(const std::string& dictionary_text,
                               const GURL& dictionary_url,
                               const BoundNetLog& net_log)>
       OnDictionaryFetchedCallback;
 
   // The consumer must guarantee that |*context| outlives this object.
-  // |callback| will be called on successful dictionary fetch
-  // requested through Schedule().  |callback| will not be called
-  // after object destruction.
-  SdchDictionaryFetcher(URLRequestContext* context,
-                        const OnDictionaryFetchedCallback& callback);
+  SdchDictionaryFetcher(URLRequestContext* context);
   ~SdchDictionaryFetcher() override;
 
-  // Request a new dictionary fetch.
-  void Schedule(const GURL& dictionary_url);
+  // Request a new dictionary fetch.  The callback will be called
+  // only if the dictionary is successfully fetched.
+  void Schedule(const GURL& dictionary_url,
+                const OnDictionaryFetchedCallback& callback);
+
+  // Request a dictionary fetch from cache only.  The callback will be called
+  // only if the dictionary is successfully fetched.
+  void ScheduleReload(const GURL& dictionary_url,
+                      const OnDictionaryFetchedCallback& callback);
 
   // Cancel any in-progress requests.
   void Cancel();
 
   // Implementation of URLRequest::Delegate methods.
   void OnResponseStarted(URLRequest* request) override;
   void OnReadCompleted(URLRequest* request, int bytes_read) override;
 
  private:
   enum State {
     STATE_NONE,
     STATE_SEND_REQUEST,
     STATE_SEND_REQUEST_COMPLETE,
     STATE_READ_BODY,
     STATE_READ_BODY_COMPLETE,
     STATE_REQUEST_COMPLETE,
   };
 
+  struct QueuedInfo {
+    const GURL url;
+    bool download_only_from_cache;
+    OnDictionaryFetchedCallback callback;
+
+    QueuedInfo();
+    QueuedInfo(const GURL& url,
+               bool download_only_from_cache,
+               const OnDictionaryFetchedCallback& callback);
+    QueuedInfo(const QueuedInfo& rhs) = default;

[Bernhard Bauer, 2015/02/06 16:40:27]

Hm... I think technically this defines the constructor inline, which you're not
supposed to do for nontrivial implementations. I think the right thing here
would be to just declare it here, and use default for the definition: 

{
  [...]
  QueuedInfo(const QueuedInfo& rhs);
  [...]
}

QueuedInfo::QueuedInfo(const QueuedInfo& rhs) = default;

Or, you could could only forward-declare the struct here and then define it in
the .cc file, at which point it wouldn't really matter whether the methods are
inlined or not.

[Elly Fong-Jones, 2015/02/06 18:44:09]

Done. We can only have an operator= if the GURL member is not const, so I made
it not const.

[Bernhard Bauer, 2015/02/06 20:12:18]

Makes sense, if we allow assignment.

(What does that mean for the old version? Did we silently ignore assigning the
URL?)

+    QueuedInfo& operator=(const QueuedInfo& rhs) = default;
+
+    ~QueuedInfo();
+  };
+
+  // Schedule implementation.
+  void ScheduleInternal(const GURL& dictionary_url,
+                        bool reload,
+                        const OnDictionaryFetchedCallback& callback);
+
+  // Null out the current request and push the state machine to the
+  // next request, if any.
+  void ResetRequest();
+
   // State machine implementation.
   int DoLoop(int rv);
   int DoSendRequest(int rv);
   int DoSendRequestComplete(int rv);
   int DoReadBody(int rv);
   int DoReadBodyComplete(int rv);
   int DoCompleteRequest(int rv);
 
   State next_state_;
   bool in_loop_;
 
   // A queue of URLs that are being used to download dictionaries.
-  std::queue<GURL> fetch_queue_;
+  // |fetch_queue_[n].second| indicated whether the download should occur
+  // only from cache.
+  std::queue<QueuedInfo> fetch_queue_;
 
-  // The request and buffer used for getting the current dictionary
-  // Both are null when a fetch is not in progress.
+  // The request, buffer, and consumer supplied data used for getting
+  // the current dictionary.  All are null when a fetch is not in progress.
   scoped_ptr<URLRequest> current_request_;
   scoped_refptr<IOBuffer> buffer_;
+  OnDictionaryFetchedCallback current_callback_;
 
   // The currently accumulating dictionary.
   std::string dictionary_;
 
   // 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_;
 
   // Store the URLRequestContext associated with the owning SdchManager for
   // use while fetching.
   URLRequestContext* const context_;
 
-  const OnDictionaryFetchedCallback dictionary_fetched_callback_;
-
   base::WeakPtrFactory<SdchDictionaryFetcher> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SdchDictionaryFetcher);
 };
 
 }  // namespace net
 
 #endif  // NET_URL_REQUEST_SDCH_DICTIONARY_FETCHER_H_