Cache failover to LOAD_PREFERRING_CACHE if network response suggests offline.

net/http/http_cache_transaction.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/http/http_cache_transaction.h"
 
 #include "build/build_config.h"
 
 #if defined(OS_POSIX)
 #include <unistd.h>
@@ skipping 35 matching lines @@
 namespace {
 
 // From http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-21#section-6
 //      a "non-error response" is one with a 2xx (Successful) or 3xx
 //      (Redirection) status code.
 bool NonErrorResponse(int status_code) {
   int status_code_range = status_code / 100;
   return status_code_range == 2 || status_code_range == 3;
 }
 
+// Error codes that will be considered indicative of a page being offline/
+// unreachable for LOAD_FROM_CACHE_IF_OFFLINE.
+bool IsOfflineError(int error) {
+  return (error == net::ERR_NAME_NOT_RESOLVED ||
+          error == net::ERR_INTERNET_DISCONNECTED ||
+          error == net::ERR_ADDRESS_UNREACHABLE ||
+          error == net::ERR_CONNECTION_TIMED_OUT);
+}
+
 }  // namespace
 
 namespace net {
 
 struct HeaderNameAndValue {
   const char* name;
   const char* value;
 };
 
 // If the request includes one of these request headers, then avoid caching
@@ skipping 69 matching lines @@
       target_state_(STATE_NONE),
       reading_(false),
       invalid_range_(false),
       truncated_(false),
       is_sparse_(false),
       range_requested_(false),
       handling_206_(false),
       cache_pending_(false),
       done_reading_(false),
       vary_mismatch_(false),
+      couldnt_conditionalize_request_(false),
       io_buf_len_(0),
       read_offset_(0),
       effective_load_flags_(0),
       write_len_(0),
       ALLOW_THIS_IN_INITIALIZER_LIST(weak_factory_(this)),
       ALLOW_THIS_IN_INITIALIZER_LIST(io_callback_(
           base::Bind(&Transaction::OnIOComplete,
                      weak_factory_.GetWeakPtr()))),
       transaction_pattern_(PATTERN_UNDEFINED),
       defer_cache_sensitivity_delay_(false),
@@ skipping 651 matching lines @@
   rv = network_trans_->Start(request_, io_callback_, net_log_);
   return rv;
 }
 
 int HttpCache::Transaction::DoSendRequestComplete(int result) {
   ReportNetworkActionFinish();
 
   if (!cache_)
     return ERR_UNEXPECTED;
 
+  // If requested, and we have a readable cache entry, and we have
+  // an error indicating that we're offline as opposed to in contact
+  // with a bad server, read from cache anyway.
+  if ((effective_load_flags_ & LOAD_FROM_CACHE_IF_OFFLINE) &&
+      IsOfflineError(result) && mode_ == READ_WRITE && entry_ && !partial_) {
+    UpdateTransactionPattern(PATTERN_NOT_COVERED);
+    response_.server_data_unavailable = true;
+    return SetupEntryForRead();
+  }
+
+  // If we tried to conditionalize the request and failed, we know
+  // we won't be reading from the cache after this point.
+  if (couldnt_conditionalize_request_)
+    mode_ = WRITE;
+
   if (result == OK) {
     next_state_ = STATE_SUCCESSFUL_SEND_REQUEST;
     return OK;
   }
 
   // Do not record requests that have network errors or restarts.
   UpdateTransactionPattern(PATTERN_NOT_COVERED);
   if (IsCertificateError(result)) {
     const HttpResponseInfo* response = network_trans_->GetResponseInfo();
     // If we get a certificate error, then there is a certificate in ssl_info,
@@ skipping 933 matching lines @@
   if (partial_.get() && (is_sparse_ || truncated_) &&
       (!partial_->IsCurrentRangeCached() || invalid_range_)) {
     // Force revalidation for sparse or truncated entries. Note that we don't
     // want to ignore the regular validation logic just because a byte range was
     // part of the request.
     skip_validation = false;
   }
 
   if (skip_validation) {
     UpdateTransactionPattern(PATTERN_ENTRY_USED);
-    if (partial_.get()) {
-      if (truncated_ || is_sparse_ || !invalid_range_) {
-        // We are going to return the saved response headers to the caller, so
-        // we may need to adjust them first.
-        next_state_ = STATE_PARTIAL_HEADERS_RECEIVED;
-        return OK;
-      } else {
-        partial_.reset();
-      }
-    }
-    cache_->ConvertWriterToReader(entry_);
-    mode_ = READ;
-
-    if (entry_->disk_entry->GetDataSize(kMetadataIndex))
-      next_state_ = STATE_CACHE_READ_METADATA;
+    return SetupEntryForRead();
   } else {
     // Make the network request conditional, to see if we may reuse our cached
     // response.  If we cannot do so, then we just resort to a normal fetch.
-    // Our mode remains READ_WRITE for a conditional request.  We'll switch to
-    // either READ or WRITE mode once we hear back from the server.
+    // Our mode remains READ_WRITE for a conditional request.  Even if the
+    // conditionalization fails, we don't switch to WRITE mode until we
+    // know we won't be falling back to using the cache entry in the
+    // LOAD_FROM_CACHE_IF_OFFLINE case.
     if (!ConditionalizeRequest()) {
+      couldnt_conditionalize_request_ = true;
       UpdateTransactionPattern(PATTERN_ENTRY_CANT_CONDITIONALIZE);
       if (partial_.get())
         return DoRestartPartialRequest();
 
       DCHECK_NE(206, response_.headers->response_code());
-      mode_ = WRITE;
     }
     next_state_ = STATE_SEND_REQUEST;
   }
   return OK;
 }
 
 int HttpCache::Transaction::BeginPartialCacheValidation() {
   DCHECK(mode_ == READ_WRITE);
 
   if (response_.headers->response_code() != 206 && !partial_.get() &&
@@ skipping 335 matching lines @@
   partial_.reset(NULL);
   entry_ = NULL;
   mode_ = NONE;
 }
 
 void HttpCache::Transaction::FailRangeRequest() {
   response_ = *new_response_;
   partial_->FixResponseHeaders(response_.headers, false);
 }
 
+int HttpCache::Transaction::SetupEntryForRead() {
+  network_trans_.reset();
+  if (partial_.get()) {
+    if (truncated_ || is_sparse_ || !invalid_range_) {
+      // We are going to return the saved response headers to the caller, so
+      // we may need to adjust them first.
+      next_state_ = STATE_PARTIAL_HEADERS_RECEIVED;
+      return OK;
+    } else {
+      partial_.reset();
+    }
+  }
+  cache_->ConvertWriterToReader(entry_);
+  mode_ = READ;
+
+  if (entry_->disk_entry->GetDataSize(kMetadataIndex))
+    next_state_ = STATE_CACHE_READ_METADATA;
+  return OK;
+}
+
+
 int HttpCache::Transaction::ReadFromNetwork(IOBuffer* data, int data_len) {
   read_buf_ = data;
   io_buf_len_ = data_len;
   next_state_ = STATE_NETWORK_READ;
   return DoLoop(OK);
 }
 
 int HttpCache::Transaction::ReadFromEntry(IOBuffer* data, int data_len) {
   read_buf_ = data;
   io_buf_len_ = data_len;
@@ skipping 415 matching lines @@
       entry_path += " -> ";
     entry_path += state_names[*it];
   }
   LOG(WARNING) << "Path state transitions for " << cache_key_
                << ": " << entry_path;
 }
 
 #endif
 
 }  // namespace net