Let prefetched resources skip cache revalidation once for a short duration.

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>
 #endif
 
 #include <algorithm>
 #include <string>
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/format_macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/sparse_histogram.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/rand_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_piece.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
+#include "base/time/clock.h"
 #include "base/time/time.h"
 #include "base/values.h"
 #include "net/base/completion_callback.h"
 #include "net/base/io_buffer.h"
 #include "net/base/load_flags.h"
 #include "net/base/load_timing_info.h"
 #include "net/base/net_errors.h"
 #include "net/base/net_log.h"
 #include "net/base/upload_data_stream.h"
 #include "net/cert/cert_status_flags.h"
@@ skipping 1487 matching lines @@
 // We received 304 or 206 and we want to update the cached response headers.
 int HttpCache::Transaction::DoUpdateCachedResponse() {
   next_state_ = STATE_UPDATE_CACHED_RESPONSE_COMPLETE;
   int rv = OK;
   // Update cached response based on headers in new_response.
   // TODO(wtc): should we update cached certificate (response_.ssl_info), too?
   response_.headers->Update(*new_response_->headers.get());
   response_.response_time = new_response_->response_time;
   response_.request_time = new_response_->request_time;
   response_.network_accessed = new_response_->network_accessed;
+  response_.unused_since_prefetch = new_response_->unused_since_prefetch;
 
   if (response_.headers->HasHeaderValue("cache-control", "no-store")) {
     if (!entry_->doomed) {
       int ret = cache_->DoomEntry(cache_key_, NULL);
       DCHECK_EQ(OK, ret);
     }
   } else {
     // If we are already reading, we already updated the headers for this
     // request; doing it again will change Content-Length.
     if (!reading_) {
@@ skipping 13 matching lines @@
     //
     // By closing the cached entry now, we make sure that the 304 rather than
     // the cached 200 response, is what will be returned to the user.
     DoneWritingToEntry(true);
   } else if (entry_ && !handling_206_) {
     DCHECK_EQ(READ_WRITE, mode_);
     if (!partial_.get() || partial_->IsLastRange()) {
       cache_->ConvertWriterToReader(entry_);
       mode_ = READ;
     }
-    // We no longer need the network transaction, so destroy it.
-    final_upload_progress_ = network_trans_->GetUploadProgress();
-    ResetNetworkTransaction();
+
+    if (network_trans_) {
+      // We no longer need the network transaction, so destroy it.
+      final_upload_progress_ = network_trans_->GetUploadProgress();
+      ResetNetworkTransaction();
+    }
   } else if (entry_ && handling_206_ && truncated_ &&
              partial_->initial_validation()) {
     // We just finished the validation of a truncated entry, and the server
     // is willing to resume the operation. Now we go back and start serving
     // the first part to the user.
     ResetNetworkTransaction();
     new_response_ = NULL;
     next_state_ = STATE_START_PARTIAL_CACHE_VALIDATION;
     partial_->SetRangeToStartDownload();
     return OK;
@@ skipping 582 matching lines @@
     // 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) {
     // TODO(ricea): Is this pattern okay for asynchronous revalidations?
     UpdateTransactionPattern(PATTERN_ENTRY_USED);
     RecordOfflineStatus(effective_load_flags_, OFFLINE_STATUS_FRESH_CACHE);
+
+    if (response_.unused_since_prefetch ||
+        (!response_.unused_since_prefetch &&
+         request_->load_flags & LOAD_PREFETCH)) {
+      // Either this is the first use of an entry since it was prefetched or
+      // this is a prefetch. Flip the bit on response.unused_since_prefetch and
+      // write it back to the cache before reading.
+      response_.unused_since_prefetch = !response_.unused_since_prefetch;

[rvargas (doing something else), 2014/12/12 02:20:49]

READ and UPDATE requests don't go through this code so this should not be done
here. The decision has to be made from DoCacheReadResponseComplete.

[jkarlin, 2014/12/15 17:19:25]

Done.

+      target_state_ = STATE_UPDATE_CACHED_RESPONSE_COMPLETE;

[rvargas (doing something else), 2014/12/12 02:20:49]

Joining back in DoUpdateCachedResponseComplete looks weird as that state
implicitly assumes that we are handling 304 or 206 from the server... (and
jumping to FooComplete from anywhere else but Foo is unexpected)

[jkarlin, 2014/12/15 17:19:25]

Done.

+      next_state_ = STATE_CACHE_WRITE_RESPONSE;
+      return OK;
+    }
+
     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.  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;
@@ skipping 152 matching lines @@
   if (response_.vary_data.is_valid() &&
       !response_.vary_data.MatchesRequest(*request_,
                                           *response_.headers.get())) {
     vary_mismatch_ = true;
     return VALIDATION_SYNCHRONOUS;
   }
 
   if (effective_load_flags_ & LOAD_PREFERRING_CACHE)
     return VALIDATION_NONE;
 
+  if (response_.unused_since_prefetch &&
+      response_.headers->GetCurrentAge(
+          response_.request_time, response_.response_time,
+          cache_->clock_->Now()) < TimeDelta::FromMinutes(kPrefetchReuseMins)) {
+    // The first use of a resource after prefetch within a short window skips
+    // validation.
+    return VALIDATION_NONE;
+  }
+
   if (effective_load_flags_ & (LOAD_VALIDATE_CACHE | LOAD_ASYNC_REVALIDATION))
     return VALIDATION_SYNCHRONOUS;
 
   if (request_->method == "PUT" || request_->method == "DELETE")
     return VALIDATION_SYNCHRONOUS;
 
   ValidationType validation_required_by_headers =
-      response_.headers->RequiresValidation(
-          response_.request_time, response_.response_time, Time::Now());
+      response_.headers->RequiresValidation(response_.request_time,
+                                            response_.response_time,
+                                            cache_->clock_->Now());
 
   if (validation_required_by_headers == VALIDATION_ASYNCHRONOUS) {
     // Asynchronous revalidation is only supported for GET and HEAD methods.
     if (request_->method != "GET" && request_->method != "HEAD")
       return VALIDATION_SYNCHRONOUS;
   }
 
   return validation_required_by_headers;
 }
 
@@ skipping 40 matching lines @@
   bool use_if_range = partial_.get() && !partial_->IsCurrentRangeCached() &&
                       !invalid_range_;
 
   if (!use_if_range) {
     // stale-while-revalidate is not useful when we only have a partial response
     // cached, so don't set the header in that case.
     HttpResponseHeaders::FreshnessLifetimes lifetimes =
         response_.headers->GetFreshnessLifetimes(response_.response_time);
     if (lifetimes.staleness > TimeDelta()) {
       TimeDelta current_age = response_.headers->GetCurrentAge(
-          response_.request_time, response_.response_time, Time::Now());
+          response_.request_time, response_.response_time,
+          cache_->clock_->Now());
 
       custom_request_->extra_headers.SetHeader(
           kFreshnessHeader,
           base::StringPrintf("max-age=%" PRId64
                              ",stale-while-revalidate=%" PRId64 ",age=%" PRId64,
                              lifetimes.freshness.InSeconds(),
                              lifetimes.staleness.InSeconds(),
                              current_age.InSeconds()));
     }
   }
@@ skipping 525 matching lines @@
 
 void HttpCache::Transaction::OnIOComplete(int result) {
   // TODO(vadimt): Remove ScopedTracker below once crbug.com/422516 is fixed.
   tracked_objects::ScopedTracker tracking_profile(
       FROM_HERE_WITH_EXPLICIT_FUNCTION("422516 Transaction::OnIOComplete"));
 
   DoLoop(result);
 }
 
 }  // namespace net