Prevent SDCH from re-trying to download a dicitionary

Some dicitoaries provided by an SDCH server may be larger than
allowed by Chromium (which holds the dictionary memory-resident).
This CL prevents Chromium from endlessly re-trying such dicitonary loads, 

BUG=7722

r=huanr
Review URL: http://codereview.chromium.org/119198

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@17699 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 23 insertions, 0 deletions

diff --git a/chrome/browser/net/sdch_dictionary_fetcher.cc b/chrome/browser/net/sdch_dictionary_fetcher.cc
index b063748..08ed763 100644
--- a/chrome/browser/net/sdch_dictionary_fetcher.cc
+++ b/chrome/browser/net/sdch_dictionary_fetcher.cc
@@ -16,6 +16,12 @@ void SdchDictionaryFetcher::Schedule(const GURL& dictionary_url) {
         SdchManager::DICTIONARY_ALREADY_SCHEDULED_TO_DOWNLOAD);
     return;
   }
+  if (attempted_load_.find(dictionary_url) != attempted_load_.end()) {
+    SdchManager::SdchErrorRecovery(
+        SdchManager::DICTIONARY_ALREADY_TRIED_TO_DOWNLOAD);
+    return;
+  }
+  attempted_load_.insert(dictionary_url);
   fetch_queue_.push(dictionary_url);
   ScheduleDelayedRun();
 }
diff --git a/chrome/browser/net/sdch_dictionary_fetcher.h b/chrome/browser/net/sdch_dictionary_fetcher.h
index e9e092c..12c022a 100644
--- a/chrome/browser/net/sdch_dictionary_fetcher.h
+++ b/chrome/browser/net/sdch_dictionary_fetcher.h
@@ -10,6 +10,7 @@
 #define CHROME_BROWSER_NET_SDCH_DICTIONARY_FETCHER_H_
 
 #include <queue>
+#include <set>
 #include <string>
 
 #include "base/compiler_specific.h"
@@ -70,6 +71,22 @@ class SdchDictionaryFetcher : public URLFetcher::Delegate,
   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);
 };