Sdch view for net-internals

net/base/sdch_manager.cc

 // Copyright (c) 2012 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/base/sdch_manager.h"
 
 #include "base/base64.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
+#include "base/values.h"
 #include "crypto/sha2.h"
 #include "net/base/registry_controlled_domains/registry_controlled_domain.h"
 #include "net/url_request/url_request_http_job.h"
 
 namespace net {
 
 //------------------------------------------------------------------------------
 // static
 
 // Adjust SDCH limits downwards for mobile.
 #if defined(OS_ANDROID) || defined(OS_IOS)
 // static
 const size_t SdchManager::kMaxDictionaryCount = 1;
 const size_t SdchManager::kMaxDictionarySize = 150 * 1000;
 #else
 // static
 const size_t SdchManager::kMaxDictionaryCount = 20;
 const size_t SdchManager::kMaxDictionarySize = 1000 * 1000;
 #endif
 
 // static
 bool SdchManager::g_sdch_enabled_ = true;
 
 // static
 bool SdchManager::g_secure_scheme_supported_ = false;
 
 //------------------------------------------------------------------------------
+
+SdchManager::AddResult::AddResult() : added(false), problem(PROBLEM_CODE_OK) {
+}
+
 SdchManager::Dictionary::Dictionary(const std::string& dictionary_text,
                                     size_t offset,
                                     const std::string& client_hash,
                                     const GURL& gurl,
                                     const std::string& domain,
                                     const std::string& path,
                                     const base::Time& expiration,
                                     const std::set<int>& ports)
     : text_(dictionary_text, offset),
       client_hash_(client_hash),
       url_(gurl),
       domain_(domain),
       path_(path),
       expiration_(expiration),
       ports_(ports) {
 }
 
 SdchManager::Dictionary::~Dictionary() {
 }
 
-bool SdchManager::Dictionary::CanAdvertise(const GURL& target_url) {
+bool SdchManager::Dictionary::CanAdvertise(const GURL& target_url) const {
   /* The specific rules of when a dictionary should be advertised in an
      Avail-Dictionary header are modeled after the rules for cookie scoping. The
      terms "domain-match" and "pathmatch" are defined in RFC 2965 [6]. A
      dictionary may be advertised in the Avail-Dictionaries header exactly when
      all of the following are true:
       1. The server's effective host name domain-matches the Domain attribute of
          the dictionary.
       2. If the dictionary has a Port attribute, the request port is one of the
          ports listed in the Port attribute.
       3. The request URI path-matches the path header of the dictionary.
@@ skipping 10 matching lines @@
     return false;
   if (!SdchManager::secure_scheme_supported() && target_url.SchemeIsSecure())
     return false;
   if (target_url.SchemeIsSecure() != url_.SchemeIsSecure())
     return false;
   if (base::Time::Now() > expiration_)
     return false;
   return true;
 }
 
+base::DictionaryValue* SdchManager::Dictionary::DictionaryInfoToValue() const {
+  base::DictionaryValue* value = new base::DictionaryValue();
+  value->SetString("url", url_.spec());
+  value->SetString("client_hash", client_hash_);
+  value->SetString("domain", domain_);
+  value->SetString("path", path_);
+  value->SetString("expiration",
+                   base::Int64ToString(expiration_.ToInternalValue()));
+  base::ListValue* port_list = new base::ListValue();
+  for (std::set<int>::const_iterator it = ports_.begin(); it != ports_.end();
+       ++it) {
+    port_list->AppendInteger(*it);
+  }
+  value->Set("ports", port_list);
+  return value;
+}
+
 //------------------------------------------------------------------------------
 // Security functions restricting loads and use of dictionaries.
 
 // static
-bool SdchManager::Dictionary::CanSet(const std::string& domain,
-                                     const std::string& path,
-                                     const std::set<int>& ports,
-                                     const GURL& dictionary_url) {
+SdchManager::ProblemCodes SdchManager::Dictionary::CanSet(
+    const std::string& domain,
+    const std::string& path,
+    const std::set<int>& ports,
+    const GURL& dictionary_url) {
   /*
   A dictionary is invalid and must not be stored if any of the following are
   true:
     1. The dictionary has no Domain attribute.
     2. The effective host name that derives from the referer URL host name does
       not domain-match the Domain attribute.
     3. The Domain attribute is a top level domain.
     4. The referer URL host is a host domain name (not IP address) and has the
       form HD, where D is the value of the Domain attribute, and H is a string
       that contains one or more dots.
     5. If the dictionary has a Port attribute and the referer URL's port was not
       in the list.
   */
 
   // TODO(jar): Redirects in dictionary fetches might plausibly be problematic,
   // and hence the conservative approach is to not allow any redirects (if there
   // were any... then don't allow the dictionary to be set).
 
-  if (domain.empty()) {
-    SdchErrorRecovery(DICTIONARY_MISSING_DOMAIN_SPECIFIER);
-    return false;  // Domain is required.
-  }
+  if (domain.empty())
+    return DICTIONARY_MISSING_DOMAIN_SPECIFIER;  // Domain is required.
+
   if (registry_controlled_domains::GetDomainAndRegistry(
-        domain,
-        registry_controlled_domains::INCLUDE_PRIVATE_REGISTRIES).empty()) {
-    SdchErrorRecovery(DICTIONARY_SPECIFIES_TOP_LEVEL_DOMAIN);
-    return false;  // domain was a TLD.
-  }
-  if (!Dictionary::DomainMatch(dictionary_url, domain)) {
-    SdchErrorRecovery(DICTIONARY_DOMAIN_NOT_MATCHING_SOURCE_URL);
-    return false;
-  }
+          domain, registry_controlled_domains::INCLUDE_PRIVATE_REGISTRIES)
+          .empty())
+    return DICTIONARY_SPECIFIES_TOP_LEVEL_DOMAIN;  // domain was a TLD.
+
+  if (!Dictionary::DomainMatch(dictionary_url, domain))
+    return DICTIONARY_DOMAIN_NOT_MATCHING_SOURCE_URL;
 
   std::string referrer_url_host = dictionary_url.host();
   size_t postfix_domain_index = referrer_url_host.rfind(domain);
   // See if it is indeed a postfix, or just an internal string.
   if (referrer_url_host.size() == postfix_domain_index + domain.size()) {
     // It is a postfix... so check to see if there's a dot in the prefix.
     size_t end_of_host_index = referrer_url_host.find_first_of('.');
-    if (referrer_url_host.npos != end_of_host_index  &&
-        end_of_host_index < postfix_domain_index) {
-      SdchErrorRecovery(DICTIONARY_REFERER_URL_HAS_DOT_IN_PREFIX);
-      return false;
-    }
+    if (referrer_url_host.npos != end_of_host_index &&
+        end_of_host_index < postfix_domain_index)
+      return DICTIONARY_REFERER_URL_HAS_DOT_IN_PREFIX;
   }
 
-  if (!ports.empty()
-      && 0 == ports.count(dictionary_url.EffectiveIntPort())) {
-    SdchErrorRecovery(DICTIONARY_PORT_NOT_MATCHING_SOURCE_URL);
-    return false;
-  }
-  return true;
+  if (!ports.empty() && 0 == ports.count(dictionary_url.EffectiveIntPort()))
+    return DICTIONARY_PORT_NOT_MATCHING_SOURCE_URL;
+
+  return PROBLEM_CODE_OK;
 }
 
-// static
-bool SdchManager::Dictionary::CanUse(const GURL& referring_url) {
+SdchManager::ProblemCodes SdchManager::Dictionary::CanUse(
+    const GURL& referring_url) const {
   /*
     1. The request URL's host name domain-matches the Domain attribute of the
       dictionary.
     2. If the dictionary has a Port attribute, the request port is one of the
       ports listed in the Port attribute.
     3. The request URL path-matches the path attribute of the dictionary.
     4. The request is not an HTTPS request.
     We can override (ignore) item (4) only when we have explicitly enabled
     HTTPS support AND the dictionary acquisition scheme matches the target
      url scheme.
   */
-  if (!DomainMatch(referring_url, domain_)) {
-    SdchErrorRecovery(DICTIONARY_FOUND_HAS_WRONG_DOMAIN);
-    return false;
-  }
-  if (!ports_.empty()
-      && 0 == ports_.count(referring_url.EffectiveIntPort())) {
-    SdchErrorRecovery(DICTIONARY_FOUND_HAS_WRONG_PORT_LIST);
-    return false;
-  }
-  if (path_.size() && !PathMatch(referring_url.path(), path_)) {
-    SdchErrorRecovery(DICTIONARY_FOUND_HAS_WRONG_PATH);
-    return false;
-  }
-  if (!SdchManager::secure_scheme_supported() &&
-      referring_url.SchemeIsSecure()) {
-    SdchErrorRecovery(DICTIONARY_FOUND_HAS_WRONG_SCHEME);
-    return false;
-  }
-  if (referring_url.SchemeIsSecure() != url_.SchemeIsSecure()) {
-    SdchErrorRecovery(DICTIONARY_FOUND_HAS_WRONG_SCHEME);
-    return false;
-  }
+  if (!DomainMatch(referring_url, domain_))
+    return DICTIONARY_FOUND_HAS_WRONG_DOMAIN;
+
+  if (!ports_.empty() && 0 == ports_.count(referring_url.EffectiveIntPort()))
+    return DICTIONARY_FOUND_HAS_WRONG_PORT_LIST;
+
+  if (path_.size() && !PathMatch(referring_url.path(), path_))
+    return DICTIONARY_FOUND_HAS_WRONG_PATH;
+
+  if (!SdchManager::secure_scheme_supported() && referring_url.SchemeIsSecure())
+    return DICTIONARY_FOUND_HAS_WRONG_SCHEME;
+
+  if (referring_url.SchemeIsSecure() != url_.SchemeIsSecure())
+    return DICTIONARY_FOUND_HAS_WRONG_SCHEME;
 
   // TODO(jar): Remove overly restrictive failsafe test (added per security
   // review) when we have a need to be more general.
-  if (!referring_url.SchemeIsHTTPOrHTTPS()) {
-    SdchErrorRecovery(ATTEMPT_TO_DECODE_NON_HTTP_DATA);
-    return false;
-  }
+  if (!referring_url.SchemeIsHTTPOrHTTPS())
+    return ATTEMPT_TO_DECODE_NON_HTTP_DATA;
 
-  return true;
+  return PROBLEM_CODE_OK;
 }
 
+// static
 bool SdchManager::Dictionary::PathMatch(const std::string& path,
                                         const std::string& restriction) {
   /*  Must be either:
   1. P2 is equal to P1
   2. P2 is a prefix of P1 and either the final character in P2 is "/" or the
       character following P2 in P1 is "/".
       */
   if (path == restriction)
     return true;
   size_t prefix_length = restriction.size();
@@ skipping 100 matching lines @@
 
 int SdchManager::BlacklistDomainExponential(const std::string& domain) {
   if (exponential_blacklist_count_.end() ==
       exponential_blacklist_count_.find(domain))
     return 0;
   return exponential_blacklist_count_[StringToLowerASCII(domain)];
 }
 
 bool SdchManager::IsInSupportedDomain(const GURL& url) {
   DCHECK(CalledOnValidThread());
+  if (!IsSdchEnabledForUrl(url))

[baranovich, 2014/08/02 21:17:24]

I've split this method into two for 2 reasons:
1) to distinguish between disabled SDCH and blacklisted domain.
2) do not call SdchErrorRecovery via IsInSupportedDomain from AddSdchDictionary
and GetVcdiffDictionary. It is done from the outside now.

+    return false;
+
+  if (IsInBlacklistedDomain(url)) {
+    SdchErrorRecovery(DOMAIN_BLACKLIST_INCLUDES_TARGET);
+    return false;
+  }
+  return true;
+}
+
+// static
+bool SdchManager::IsSdchEnabledForUrl(const GURL& url) {
   if (!g_sdch_enabled_ )
     return false;
 
   if (!secure_scheme_supported() && url.SchemeIsSecure())
     return false;
 
+  return true;
+}
+
+bool SdchManager::IsInBlacklistedDomain(const GURL& url) {
   if (blacklisted_domains_.empty())
-    return true;
+    return false;
 
   std::string domain(StringToLowerASCII(url.host()));
   DomainCounter::iterator it = blacklisted_domains_.find(domain);
   if (blacklisted_domains_.end() == it)
-    return true;
+    return false;
 
   int count = it->second - 1;
   if (count > 0)
     blacklisted_domains_[domain] = count;
   else
     blacklisted_domains_.erase(domain);
-  SdchErrorRecovery(DOMAIN_BLACKLIST_INCLUDES_TARGET);
-  return false;
+
+  return true;
 }
 
-void SdchManager::FetchDictionary(const GURL& request_url,
-                                  const GURL& dictionary_url) {
+SdchManager::ProblemCodes SdchManager::FetchDictionary(
+    const GURL& request_url,
+    const GURL& dictionary_url) {
   DCHECK(CalledOnValidThread());
-  if (CanFetchDictionary(request_url, dictionary_url) && fetcher_.get())
+  ProblemCodes rv = CanFetchDictionary(request_url, dictionary_url);
+  if (rv != PROBLEM_CODE_OK)
+    return rv;
+
+  if (fetcher_.get())
     fetcher_->Schedule(dictionary_url);
+
+  return PROBLEM_CODE_OK;
 }
 
-bool SdchManager::CanFetchDictionary(const GURL& referring_url,
-                                     const GURL& dictionary_url) const {
+SdchManager::ProblemCodes SdchManager::CanFetchDictionary(
+    const GURL& referring_url,
+    const GURL& dictionary_url) const {
   DCHECK(CalledOnValidThread());
   /* The user agent may retrieve a dictionary from the dictionary URL if all of
      the following are true:
        1 The dictionary URL host name matches the referrer URL host name and
            scheme.
        2 The dictionary URL host name domain matches the parent domain of the
            referrer URL host name
        3 The parent domain of the referrer URL host name is not a top level
            domain
        4 The dictionary URL is not an HTTPS URL.
    */
   // Item (1) above implies item (2).  Spec should be updated.
   // I take "host name match" to be "is identical to"
   if (referring_url.host() != dictionary_url.host() ||
-      referring_url.scheme() != dictionary_url.scheme()) {
-    SdchErrorRecovery(DICTIONARY_LOAD_ATTEMPT_FROM_DIFFERENT_HOST);
-    return false;
-  }
-  if (!secure_scheme_supported() && referring_url.SchemeIsSecure()) {
-    SdchErrorRecovery(DICTIONARY_SELECTED_FOR_SSL);
-    return false;
-  }
+      referring_url.scheme() != dictionary_url.scheme())
+    return DICTIONARY_LOAD_ATTEMPT_FROM_DIFFERENT_HOST;
+
+  if (!secure_scheme_supported() && referring_url.SchemeIsSecure())
+    return DICTIONARY_SELECTED_FOR_SSL;
 
   // TODO(jar): Remove this failsafe conservative hack which is more restrictive
   // than current SDCH spec when needed, and justified by security audit.
-  if (!referring_url.SchemeIsHTTPOrHTTPS()) {
-    SdchErrorRecovery(DICTIONARY_SELECTED_FROM_NON_HTTP);
-    return false;
-  }
+  if (!referring_url.SchemeIsHTTPOrHTTPS())
+    return DICTIONARY_SELECTED_FROM_NON_HTTP;
 
-  return true;
+  return PROBLEM_CODE_OK;
 }
 
-bool SdchManager::AddSdchDictionary(const std::string& dictionary_text,
+SdchManager::AddResult SdchManager::AddSdchDictionary(
+    const std::string& dictionary_text,
     const GURL& dictionary_url) {
   DCHECK(CalledOnValidThread());
   std::string client_hash;
   std::string server_hash;
   GenerateHash(dictionary_text, &client_hash, &server_hash);
+  AddResult rv;
   if (dictionaries_.find(server_hash) != dictionaries_.end()) {
-    SdchErrorRecovery(DICTIONARY_ALREADY_LOADED);
-    return false;  // Already loaded.
+    rv.problem = DICTIONARY_ALREADY_LOADED;  // Already loaded.
+    return rv;
   }
 
   std::string domain, path;
   std::set<int> ports;
   base::Time expiration(base::Time::Now() + base::TimeDelta::FromDays(30));
 
   if (dictionary_text.empty()) {
-    SdchErrorRecovery(DICTIONARY_HAS_NO_TEXT);
-    return false;  // Missing header.
+    rv.problem = DICTIONARY_HAS_NO_TEXT;  // Empty response.
+    return rv;
   }
 
   size_t header_end = dictionary_text.find("\n\n");
   if (std::string::npos == header_end) {
-    SdchErrorRecovery(DICTIONARY_HAS_NO_HEADER);
-    return false;  // Missing header.
+    rv.problem = DICTIONARY_HAS_NO_HEADER;  // Missing header.
+    return rv;
   }
+
   size_t line_start = 0;  // Start of line being parsed.
   while (1) {
     size_t line_end = dictionary_text.find('\n', line_start);
     DCHECK(std::string::npos != line_end);
     DCHECK_LE(line_end, header_end);
 
     size_t colon_index = dictionary_text.find(':', line_start);
     if (std::string::npos == colon_index) {
-      SdchErrorRecovery(DICTIONARY_HEADER_LINE_MISSING_COLON);
-      return false;  // Illegal line missing a colon.
+      // Illegal line missing a colon.
+      rv.problem = DICTIONARY_HEADER_LINE_MISSING_COLON;
+      return rv;
     }
 
     if (colon_index > line_end)
       break;
 
     size_t value_start = dictionary_text.find_first_not_of(" \t",
                                                            colon_index + 1);
     if (std::string::npos != value_start) {
       if (value_start >= line_end)
         break;
       std::string name(dictionary_text, line_start, colon_index - line_start);
       std::string value(dictionary_text, value_start, line_end - value_start);
       name = StringToLowerASCII(name);
       if (name == "domain") {
         domain = value;
       } else if (name == "path") {
         path = value;
       } else if (name == "format-version") {
-        if (value != "1.0")
-          return false;
+        if (value != "1.0") {
+          // TODO(baranovich): add problem code to track unsupported versions?
+          return rv;
+        }
       } else if (name == "max-age") {
         int64 seconds;
         base::StringToInt64(value, &seconds);
         expiration = base::Time::Now() + base::TimeDelta::FromSeconds(seconds);
       } else if (name == "port") {
         int port;
         base::StringToInt(value, &port);
         if (port >= 0)
           ports.insert(port);
       }
     }
 
     if (line_end >= header_end)
       break;
     line_start = line_end + 1;
   }
 
-  if (!IsInSupportedDomain(dictionary_url))
-    return false;
+  if (!IsSdchEnabledForUrl(dictionary_url))
+    return rv;
 
-  if (!Dictionary::CanSet(domain, path, ports, dictionary_url))
-    return false;
+  if (IsInBlacklistedDomain(dictionary_url)) {
+    rv.problem = DOMAIN_BLACKLIST_INCLUDES_TARGET;
+    return rv;
+  }
+
+  ProblemCodes err = Dictionary::CanSet(domain, path, ports, dictionary_url);
+  if (err != PROBLEM_CODE_OK) {
+    rv.problem = err;
+    return rv;
+  }
 
   // TODO(jar): Remove these hacks to preclude a DOS attack involving piles of
   // useless dictionaries.  We should probably have a cache eviction plan,
   // instead of just blocking additions.  For now, with the spec in flux, it
   // is probably not worth doing eviction handling.
   if (kMaxDictionarySize < dictionary_text.size()) {
-    SdchErrorRecovery(DICTIONARY_IS_TOO_LARGE);
-    return false;
+    rv.problem = DICTIONARY_IS_TOO_LARGE;
+    return rv;
   }
   if (kMaxDictionaryCount <= dictionaries_.size()) {
-    SdchErrorRecovery(DICTIONARY_COUNT_EXCEEDED);
-    return false;
+    rv.problem = DICTIONARY_COUNT_EXCEEDED;
+    return rv;
   }
 
   UMA_HISTOGRAM_COUNTS("Sdch3.Dictionary size loaded", dictionary_text.size());
   DVLOG(1) << "Loaded dictionary with client hash " << client_hash
            << " and server hash " << server_hash;
   Dictionary* dictionary =
       new Dictionary(dictionary_text, header_end + 2, client_hash,
                      dictionary_url, domain, path, expiration, ports);
   dictionaries_[server_hash] = dictionary;
-  return true;
+
+  rv.added = true;
+  return rv;
 }
 
-void SdchManager::GetVcdiffDictionary(
+SdchManager::ProblemCodes SdchManager::GetVcdiffDictionary(
     const std::string& server_hash,
     const GURL& referring_url,
     scoped_refptr<Dictionary>* dictionary) {
   DCHECK(CalledOnValidThread());
   *dictionary = NULL;
   DictionaryMap::iterator it = dictionaries_.find(server_hash);
-  if (it == dictionaries_.end()) {
-    return;
-  }
+  if (it == dictionaries_.end())
+    return PROBLEM_CODE_OK;  // not a problem. Just no dictionary.
+
   scoped_refptr<Dictionary> matching_dictionary = it->second;
-  if (!IsInSupportedDomain(referring_url))
-    return;
-  if (!matching_dictionary->CanUse(referring_url))
-    return;
-  *dictionary = matching_dictionary;
+  if (!IsSdchEnabledForUrl(referring_url))
+    return PROBLEM_CODE_OK;  // not a problem. SDCH is disabled.
+
+  if (IsInBlacklistedDomain(referring_url))
+    return DOMAIN_BLACKLIST_INCLUDES_TARGET;
+
+  ProblemCodes rv = matching_dictionary->CanUse(referring_url);
+  if (rv == PROBLEM_CODE_OK)
+    *dictionary = matching_dictionary;
+  return rv;
 }
 
 // TODO(jar): If we have evictions from the dictionaries_, then we need to
 // change this interface to return a list of reference counted Dictionary
 // instances that can be used if/when a server specifies one.
 void SdchManager::GetAvailDictionaryList(const GURL& target_url,
                                          std::string* list) {
   DCHECK(CalledOnValidThread());
   int count = 0;
   for (DictionaryMap::iterator it = dictionaries_.begin();
        it != dictionaries_.end(); ++it) {
-    if (!IsInSupportedDomain(target_url))
+    if (!IsInSupportedDomain(target_url)) {
       continue;
+    }
     if (!it->second->CanAdvertise(target_url))
       continue;
     ++count;
     if (!list->empty())
       list->append(",");
     list->append(it->second->client_hash());
   }
   // Watch to see if we have corrupt or numerous dictionaries.
   if (count > 0)
     UMA_HISTOGRAM_COUNTS("Sdch3.Advertisement_Count", count);
 }
 
 // static
 void SdchManager::GenerateHash(const std::string& dictionary_text,
     std::string* client_hash, std::string* server_hash) {
   char binary_hash[32];
   crypto::SHA256HashString(dictionary_text, binary_hash, sizeof(binary_hash));
 
   std::string first_48_bits(&binary_hash[0], 6);
   std::string second_48_bits(&binary_hash[6], 6);
   UrlSafeBase64Encode(first_48_bits, client_hash);
   UrlSafeBase64Encode(second_48_bits, server_hash);
 
   DCHECK_EQ(server_hash->length(), 8u);
   DCHECK_EQ(client_hash->length(), 8u);
 }
 
+base::Value* SdchManager::SdchInfoToValue() const {
+  base::DictionaryValue* value = new base::DictionaryValue();
+
+  value->SetBoolean("sdch_enabled", sdch_enabled());
+  value->SetBoolean("secure_scheme_support", secure_scheme_supported());
+
+  base::ListValue* entry_list = new base::ListValue();
+  for (DictionaryMap::const_iterator it = dictionaries_.begin();
+       it != dictionaries_.end();
+       ++it) {
+    base::DictionaryValue* entry_dict = it->second->DictionaryInfoToValue();
+    entry_dict->SetString("server_hash", it->first);
+    entry_list->Append(entry_dict);
+  }
+  value->Set("dictionaries", entry_list);
+
+  entry_list = new base::ListValue();
+  for (DomainCounter::const_iterator it = blacklisted_domains_.begin();
+       it != blacklisted_domains_.end();
+       ++it) {
+    base::DictionaryValue* entry_dict = new base::DictionaryValue();
+    entry_dict->SetString("domain", it->first);
+    if (it->second != INT_MAX)
+      entry_dict->SetInteger("tries", it->second);
+    entry_list->Append(entry_dict);
+  }
+  value->Set("blacklisted", entry_list);
+
+  return value;
+}
+
 //------------------------------------------------------------------------------
 // Methods for supporting latency experiments.
 
 bool SdchManager::AllowLatencyExperiment(const GURL& url) const {
   DCHECK(CalledOnValidThread());
   return allow_latency_experiment_.end() !=
       allow_latency_experiment_.find(url.host());
 }
 
 void SdchManager::SetAllowLatencyExperiment(const GURL& url, bool enable) {
   DCHECK(CalledOnValidThread());
   if (enable) {
     allow_latency_experiment_.insert(url.host());
     return;
   }
   ExperimentSet::iterator it = allow_latency_experiment_.find(url.host());
   if (allow_latency_experiment_.end() == it)
     return;  // It was already erased, or never allowed.
+
+  // Do not send error up. It's internal stuff, I guess.
   SdchErrorRecovery(LATENCY_TEST_DISALLOWED);
   allow_latency_experiment_.erase(it);
 }
 
 // static
 void SdchManager::UrlSafeBase64Encode(const std::string& input,
                                       std::string* output) {
   // Since this is only done during a dictionary load, and hashes are only 8
   // characters, we just do the simple fixup, rather than rewriting the encoder.
   base::Base64Encode(input, output);
   for (size_t i = 0; i < output->size(); ++i) {
     switch (output->data()[i]) {
       case '+':
         (*output)[i] = '-';
         continue;
       case '/':
         (*output)[i] = '_';
         continue;
       default:
         continue;
     }
   }
 }
 
 }  // namespace net