stale-while-revalidate experimental implementation.

net/http/http_cache_transaction.cc

Index: net/http/http_cache_transaction.cc
diff --git a/net/http/http_cache_transaction.cc b/net/http/http_cache_transaction.cc
index b06e8f3a272b4df533756a423f5a5fc0b321b532..5e901316f486f39bfa2fed42db3ccf33ae5192c6 100644
--- a/net/http/http_cache_transaction.cc
+++ b/net/http/http_cache_transaction.cc
@@ -17,6 +17,7 @@
 #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"
@@ -26,6 +27,7 @@
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.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"
@@ -238,6 +240,18 @@ void RecordNoStoreHeaderHistogram(int load_flags,
   }
 }
 
+base::Value* NetLogAsyncRevalidationInfoCallback(
+    const net::NetLog::Source& source,
+    const net::HttpRequestInfo* request,
+    net::NetLog::LogLevel log_level) {
+  base::DictionaryValue* dict = new base::DictionaryValue();
+  source.AddToEventParameters(dict);
+
+  dict->SetString("url", request->url.possibly_invalid_spec());
+  dict->SetString("method", request->method);
+  return dict;
+}
+
 enum ExternallyConditionalizedType {
   EXTERNALLY_CONDITIONALIZED_CACHE_REQUIRES_VALIDATION,
   EXTERNALLY_CONDITIONALIZED_CACHE_USABLE,
@@ -2110,7 +2124,16 @@ int HttpCache::Transaction::BeginCacheRead() {
 int HttpCache::Transaction::BeginCacheValidation() {
   DCHECK(mode_ == READ_WRITE);
 
-  bool skip_validation = !RequiresValidation();
+  ValidationType required_validation = RequiresValidation();
+
+  bool skip_validation = (required_validation == VALIDATION_NONE);
+
+  if (required_validation == VALIDATION_ASYNCHRONOUS &&
+      !(request_->method == "GET" && (truncated_ || partial_)) && cache_ &&
+      cache_->use_stale_while_revalidate()) {
+    TriggerAsyncValidation();
+    skip_validation = true;
+  }
 
   if (request_->method == "HEAD" &&
       (truncated_ || response_.headers->response_code() == 206)) {
@@ -2140,6 +2163,7 @@ int HttpCache::Transaction::BeginCacheValidation() {
   }
 
   if (skip_validation) {
+    // TODO(ricea): Is this pattern okay for asynchronous revalidations?
     UpdateTransactionPattern(PATTERN_ENTRY_USED);
     RecordOfflineStatus(effective_load_flags_, OFFLINE_STATUS_FRESH_CACHE);
     return SetupEntryForRead();
@@ -2295,37 +2319,42 @@ int HttpCache::Transaction::RestartNetworkRequestWithAuth(
   return rv;
 }
 
-bool HttpCache::Transaction::RequiresValidation() {
+ValidationType HttpCache::Transaction::RequiresValidation() {
   // TODO(darin): need to do more work here:
   //  - make sure we have a matching request method
   //  - watch out for cached responses that depend on authentication
 
   // In playback mode, nothing requires validation.
   if (cache_->mode() == net::HttpCache::PLAYBACK)
-    return false;
+    return VALIDATION_NONE;
 
   if (response_.vary_data.is_valid() &&
       !response_.vary_data.MatchesRequest(*request_,
                                           *response_.headers.get())) {
     vary_mismatch_ = true;
-    return true;
+    return VALIDATION_SYNCHRONOUS;
   }
 
   if (effective_load_flags_ & LOAD_PREFERRING_CACHE)
-    return false;
+    return VALIDATION_NONE;
 
-  if (effective_load_flags_ & LOAD_VALIDATE_CACHE)
-    return true;
+  if (effective_load_flags_ & (LOAD_VALIDATE_CACHE | LOAD_ASYNC_REVALIDATION))
+    return VALIDATION_SYNCHRONOUS;
 
   if (request_->method == "PUT" || request_->method == "DELETE")
-    return true;
+    return VALIDATION_SYNCHRONOUS;
 
-  if (response_.headers->RequiresValidation(
-          response_.request_time, response_.response_time, Time::Now())) {
-    return true;
+  ValidationType validation_required_by_headers =
+      response_.headers->RequiresValidation(
+          response_.request_time, response_.response_time, Time::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 false;
+  return validation_required_by_headers;
 }
 
 bool HttpCache::Transaction::ConditionalizeRequest() {
@@ -2374,12 +2403,9 @@ bool HttpCache::Transaction::ConditionalizeRequest() {
   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.
-    TimeDelta stale_while_revalidate;
-    if (response_.headers->GetStaleWhileRevalidateValue(
-            &stale_while_revalidate) &&
-        stale_while_revalidate > TimeDelta()) {
-      TimeDelta max_age =
-          response_.headers->GetFreshnessLifetime(response_.response_time);
+    HttpResponseHeaders::FreshnessLifetimes lifetime =
+        response_.headers->GetFreshnessLifetimes(response_.response_time);
+    if (lifetime.stale > TimeDelta()) {
       TimeDelta current_age = response_.headers->GetCurrentAge(
           response_.request_time, response_.response_time, Time::Now());
 
@@ -2387,8 +2413,8 @@ bool HttpCache::Transaction::ConditionalizeRequest() {
           kFreshnessHeader,
           base::StringPrintf("max-age=%" PRId64
                              ",stale-while-revalidate=%" PRId64 ",age=%" PRId64,
-                             max_age.InSeconds(),
-                             stale_while_revalidate.InSeconds(),
+                             lifetime.fresh.InSeconds(),
+                             lifetime.stale.InSeconds(),
                              current_age.InSeconds()));
     }
   }
@@ -2557,6 +2583,25 @@ void HttpCache::Transaction::FixHeadersForHead() {
   }
 }
 
+void HttpCache::Transaction::TriggerAsyncValidation() {
+  DCHECK(!request_->upload_data_stream);
+  BoundNetLog async_revalidation_net_log(
+      BoundNetLog::Make(net_log_.net_log(), NetLog::SOURCE_ASYNC_REVALIDATION));
+  net_log_.AddEvent(
+      NetLog::TYPE_HTTP_CACHE_VALIDATE_RESOURCE_ASYNC,
+      async_revalidation_net_log.source().ToEventParametersCallback());
+  async_revalidation_net_log.BeginEvent(
+      NetLog::TYPE_ASYNC_REVALIDATION,
+      base::Bind(
+          &NetLogAsyncRevalidationInfoCallback, net_log_.source(), request_));
+  base::MessageLoop::current()->PostTask(
+      FROM_HERE,
+      base::Bind(&HttpCache::PerformAsyncValidation,
+                 cache_,  // cache_ is a weak pointer.
+                 *request_,
+                 async_revalidation_net_log));
+}
+
 void HttpCache::Transaction::FailRangeRequest() {
   response_ = *new_response_;
   partial_->FixResponseHeaders(response_.headers.get(), false);