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 286a526a3edb2fa39e7101e10429cf3c15b7920a..503587cb566131a5f6f3e73c48b1274c26e000d7 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"
@@ -51,6 +53,13 @@ using base::TimeTicks;
 
 namespace {
 
+typedef net::HttpResponseHeaders::ValidationType ValidationType;
+const ValidationType VALIDATION_NONE = ValidationType::VALIDATION_NONE;

[rvargas (doing something else), 2014/08/29 23:36:07]

I think we should just live with HttpResponseHeaders::VALIDATION_NONE instead.
If that is too ugly, move the enum out of the class.

[Adam Rice, 2014/09/01 14:43:00]

Done.

+const ValidationType VALIDATION_SYNCHRONOUS =
+    ValidationType::VALIDATION_SYNCHRONOUS;
+const ValidationType VALIDATION_ASYNCHRONOUS =
+    ValidationType::VALIDATION_ASYNCHRONOUS;
+
 // TODO(ricea): Move this to HttpResponseHeaders once it is standardised.
 static const char kFreshnessHeader[] = "Resource-Freshness";
 
@@ -238,6 +247,18 @@ 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;
+}
+
 }  // namespace
 
 namespace net {
@@ -412,6 +433,11 @@ const BoundNetLog& HttpCache::Transaction::net_log() const {
   return net_log_;
 }
 
+void HttpCache::Transaction::ValidateInternalCache() {
+  DCHECK(!request_);  // Start() should not have been called.
+  effective_load_flags_ |= LOAD_VALIDATE_CACHE;
+}
+
 int HttpCache::Transaction::Start(const HttpRequestInfo* request,
                                   const CompletionCallback& callback,
                                   const BoundNetLog& net_log) {
@@ -1938,7 +1964,9 @@ void HttpCache::Transaction::SetRequest(const BoundNetLog& net_log,
                                         const HttpRequestInfo* request) {
   net_log_ = net_log;
   request_ = request;
-  effective_load_flags_ = request_->load_flags;
+  // effective_load_flags_ may already have had LOAD_VALIDATE_CACHE set by the
+  // ValidateInternalCache() method.
+  effective_load_flags_ |= request_->load_flags;
 
   switch (cache_->mode()) {
     case NORMAL:
@@ -2093,7 +2121,15 @@ int HttpCache::Transaction::BeginCacheRead() {
 int HttpCache::Transaction::BeginCacheValidation() {
   DCHECK(mode_ == READ_WRITE);
 
-  bool skip_validation = !RequiresValidation();
+  ValidationType required_validation = RequiredValidationType();
+
+  bool skip_validation = required_validation == VALIDATION_NONE;
+
+  if (required_validation == VALIDATION_ASYNCHRONOUS && cache_ &&
+      cache_->use_stale_while_revalidate()) {
+    TriggerAsyncValidation();
+    skip_validation = true;
+  }
 
   if (request_->method == "HEAD" &&
       (truncated_ || response_.headers->response_code() == 206)) {
@@ -2123,6 +2159,7 @@ 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();
@@ -2262,37 +2299,47 @@ int HttpCache::Transaction::RestartNetworkRequestWithAuth(
   return rv;
 }
 
-bool HttpCache::Transaction::RequiresValidation() {
+ValidationType HttpCache::Transaction::RequiredValidationType() {
   // 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;
+    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(

[rvargas (doing something else), 2014/08/29 23:36:06]

If you keep the name for ResponseHeaders::RequiresValidation (which is fine),
you should also keep the name for Transaction::RequiresValidation (conceptually
they do the same thing)

[Adam Rice, 2014/09/01 14:43:00]

Done.

+          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;
+
+    // Asynchronous revalidation of GETs can only be used for completely cached
+    // resources.
+    if (request_->method == "GET" && (truncated_ || partial_))

[rvargas (doing something else), 2014/08/29 23:36:06]

This part belong on the caller side.

[Adam Rice, 2014/09/01 14:43:00]

Done.

+      return VALIDATION_SYNCHRONOUS;
   }
 
-  return false;
+  return validation_required_by_headers;
 }
 
 bool HttpCache::Transaction::ConditionalizeRequest() {
@@ -2341,11 +2388,13 @@ bool HttpCache::Transaction::ConditionalizeRequest() {
     // 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;
+    TimeDelta max_age;
     if (response_.headers->GetStaleWhileRevalidateValue(
             &stale_while_revalidate) &&
+        response_.headers->GetFreshnessLifetime(response_.response_time,

[rvargas (doing something else), 2014/08/29 23:36:07]

This pattern reads very weird: returning a value that looks time related and the
actual time through an out argument, especially considering the name of the
method.

[Adam Rice, 2014/09/01 14:43:00]

I have attempted to improve it. PTAL.

+                                                &max_age) !=
+            HttpResponseHeaders::NEVER_FRESH &&
         stale_while_revalidate > TimeDelta()) {
-      TimeDelta max_age =
-          response_.headers->GetFreshnessLifetime(response_.response_time);
       TimeDelta current_age = response_.headers->GetCurrentAge(
           response_.request_time, response_.response_time, Time::Now());
 
@@ -2523,6 +2572,25 @@ 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_,

[rvargas (doing something else), 2014/08/29 23:36:06]

Is the intention here to use a weak pointer? (I bet it is).

[Adam Rice, 2014/09/01 14:43:00]

Yes. I have added a comment.

+                 *request_,
+                 async_revalidation_net_log));
+}
+
 void HttpCache::Transaction::FailRangeRequest() {
   response_ = *new_response_;
   partial_->FixResponseHeaders(response_.headers.get(), false);