Pin dictionaries from being deleted while request is outstanding.

net/filter/sdch_filter.cc

 // 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.
 
 #include "net/filter/sdch_filter.h"
 
 #include <ctype.h>
 #include <limits.h>
 
 #include <algorithm>
@@ skipping 226 matching lines @@
         // is compressed data etc.  For now, we do nothing, which gets us into
         // the meta-refresh result.
         // TODO(jar): Improve robustness by sniffing for valid text that we can
         // actual use re: decoding_status_ = PASS_THROUGH;
         cause = RESPONSE_TENTATIVE_SDCH;
       } else if (dictionary_hash_is_plausible_) {
         // We need a meta-refresh since we don't have the dictionary.
         // The common cause is a restart of the browser, where we try to render
         // cached content that was saved when we had a dictionary.
         cause = RESPONSE_NO_DICTIONARY;
-      } else if (filter_context_.SdchResponseExpected()) {
+      } else if (filter_context_.SdchDictionariesAdvertised()) {
         // This is a very corrupt SDCH request response.  We can't decode it.
         // We'll use a meta-refresh, and get content without asking for SDCH.
         // This will also progressively disable SDCH for this domain.
         cause = RESPONSE_CORRUPT_SDCH;
       } else {
         // One of the first 9 bytes precluded consideration as a hash.
         // This can't be an SDCH payload, even though the server said it was.
         // This is a major error, as the server or proxy tagged this SDCH even
         // though it is not!
         // Meta-refresh won't help, as we didn't advertise an SDCH dictionary!!
@@ skipping 126 matching lines @@
   }
   dictionary_hash_.append(next_stream_data_, bytes_needed);
   DCHECK(kServerIdLength == dictionary_hash_.size());
   stream_data_len_ -= bytes_needed;
   DCHECK_LE(0, stream_data_len_);
   if (stream_data_len_ > 0)
     next_stream_data_ += bytes_needed;
   else
     next_stream_data_ = NULL;
 
-  DCHECK(!dictionary_.get());
+  DCHECK(!dictionary_);
   dictionary_hash_is_plausible_ = true;  // Assume plausible, but check.
 
   if ('\0' == dictionary_hash_[kServerIdLength - 1]) {
-    SdchManager* manager(url_request_context_->sdch_manager());
-    manager->GetVcdiffDictionary(
-        std::string(dictionary_hash_, 0, kServerIdLength - 1),
-        url_, &dictionary_);
+    std::string server_hash(dictionary_hash_, 0, kServerIdLength - 1);
+    SdchManager::DictionarySet* handle =
+        filter_context_.SdchDictionariesAdvertised();
+    if (handle)
+      dictionary_ = handle->Dictionary(server_hash);
+    if (!dictionary_) {
+      // This is a hack.  Naively, the dictionaries available for
+      // decoding should be only the ones advertised.  However, there are
+      // cases, specifically resources encoded with old dictionaries living
+      // in the cache, that mean the full set of dictionaries should be made
+      // available for decoding.  It's not known how often this happens;
+      // if it happens rarely enough, this code can be removed.
+      //
+      // TODO(rdsmith): Long-term, a better solution is necessary, since
+      // an entry in the cache being encoded with the dictionary doesn't
+      // guarantee that the dictionary is present.  That solution probably
+      // involves storing unencoded resources in the cache, but might
+      // involve evicting encoded resources on dictionary removal.

[Ryan Sleevi, 2014/11/14 03:21:25]

Whenever someone adds a TODO like this, I like to ask - can you file a crbug for
this to explain more of the motivations?

[Randy Smith (Not in Mondays), 2014/11/17 17:04:22]

I've added a pointer to the relevant bug in the TODO, but I'm not sure how much
more background is there (the bug consists of a pointer to a net-dev discussion,
and a follow-on note from me about the evicting encoded resources suggestion
that Matt made in recent email tome).  Let me know if you want more.

+      unexpected_dictionary_handle_ =
+          url_request_context_->sdch_manager()->GetDictionarySetByHash(
+              url_, server_hash);
+      if (unexpected_dictionary_handle_.get()) {
+        dictionary_ = unexpected_dictionary_handle_->Dictionary(server_hash);
+        SdchManager::SdchErrorRecovery(
+            filter_context_.IsCachedContent() ?
+            SdchManager::UNADVERTISED_SDCH_DICTIONARY_USED_CACHED :
+            SdchManager::UNADVERTISED_SDCH_DICTIONARY_USED);
+      }
+    }
   } else {
     dictionary_hash_is_plausible_ = false;
   }
 
-  if (!dictionary_.get()) {
+  if (!dictionary_) {
     DCHECK(dictionary_hash_.size() == kServerIdLength);
     // Since dictionary was not found, check to see if hash was even plausible.
     for (size_t i = 0; i < kServerIdLength - 1; ++i) {
       char base64_char = dictionary_hash_[i];
       if (!isalnum(base64_char) && '-' != base64_char && '_' != base64_char) {
         dictionary_hash_is_plausible_ = false;
         break;
       }
     }
     if (dictionary_hash_is_plausible_)
@@ skipping 23 matching lines @@
   dest_buffer_excess_index_ += amount;
   if (dest_buffer_excess_.size() <= dest_buffer_excess_index_) {
     DCHECK(dest_buffer_excess_.size() == dest_buffer_excess_index_);
     dest_buffer_excess_.clear();
     dest_buffer_excess_index_ = 0;
   }
   return amount;
 }
 
 }  // namespace net