stale-while-revalidate experimental implementation.

net/http/http_response_headers.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.
 
 // The rules for header parsing were borrowed from Firefox:
 // http://lxr.mozilla.org/seamonkey/source/netwerk/protocol/http/src/nsHttpResponseHead.cpp
 // The rules for parsing content-types were also borrowed from Firefox:
 // http://lxr.mozilla.org/mozilla/source/netwerk/base/src/nsURLHelper.cpp#834
 
 #include "net/http/http_response_headers.h"
@@ skipping 938 matching lines @@
 
 // From RFC 2616 section 13.2.4:
 //
 // The calculation to determine if a response has expired is quite simple:
 //
 //   response_is_fresh = (freshness_lifetime > current_age)
 //
 // Of course, there are other factors that can force a response to always be
 // validated or re-fetched.
 //
-bool HttpResponseHeaders::RequiresValidation(const Time& request_time,
-                                             const Time& response_time,
-                                             const Time& current_time) const {
-  TimeDelta lifetime =
-      GetFreshnessLifetime(response_time);
-  if (lifetime == TimeDelta())
-    return true;
+// From RFC 5861 section 3, a stale response may be used while revalidation is
+// performed in the background if
+//
+//   freshness_lifetime + stale_while_revalidate > current_age
+//
+HttpResponseHeaders::ValidationType HttpResponseHeaders::RequiresValidation(
+    const Time& request_time,
+    const Time& response_time,
+    const Time& current_time) const {
+  TimeDelta lifetime;
+  if (GetFreshnessLifetime(response_time, &lifetime) == NEVER_FRESH)
+    return VALIDATION_SYNCHRONOUS;
+  TimeDelta age = GetCurrentAge(request_time, response_time, current_time);
 
-  return lifetime <= GetCurrentAge(request_time, response_time, current_time);
+  if (lifetime > age)
+    return VALIDATION_NONE;
+
+  TimeDelta stale_while_revalidate;
+  if (GetStaleWhileRevalidateValue(&stale_while_revalidate) &&
+      lifetime + stale_while_revalidate > age)
+    return VALIDATION_ASYNCHRONOUS;
+
+  return VALIDATION_SYNCHRONOUS;
 }
 
 // From RFC 2616 section 13.2.4:
 //
 // The max-age directive takes priority over Expires, so if max-age is present
 // in a response, the calculation is simply:
 //
 //   freshness_lifetime = max_age_value
 //
 // Otherwise, if Expires is present in the response, the calculation is:
 //
 //   freshness_lifetime = expires_value - date_value
 //
 // Note that neither of these calculations is vulnerable to clock skew, since
 // all of the information comes from the origin server.
 //
 // Also, if the response does have a Last-Modified time, the heuristic
 // expiration value SHOULD be no more than some fraction of the interval since
 // that time. A typical setting of this fraction might be 10%:
 //
 //   freshness_lifetime = (date_value - last_modified_value) * 0.10
 //
-TimeDelta HttpResponseHeaders::GetFreshnessLifetime(
-    const Time& response_time) const {
+HttpResponseHeaders::FreshnessType HttpResponseHeaders::GetFreshnessLifetime(
+    const Time& response_time,
+    TimeDelta* lifetime) const {
   // Check for headers that force a response to never be fresh.  For backwards
   // compat, we treat "Pragma: no-cache" as a synonym for "Cache-Control:
   // no-cache" even though RFC 2616 does not specify it.
   if (HasHeaderValue("cache-control", "no-cache") ||
       HasHeaderValue("cache-control", "no-store") ||
       HasHeaderValue("pragma", "no-cache") ||
       HasHeaderValue("vary", "*"))  // see RFC 2616 section 13.6
-    return TimeDelta();  // not fresh
+    return NEVER_FRESH;

[yhirano, 2014/08/27 09:24:29]

You should clear *lifetime here. Reverting L1007 change after PS8 is enough.

[Adam Rice, 2014/08/28 03:14:35]

Done.

 
   // NOTE: "Cache-Control: max-age" overrides Expires, so we only check the
   // Expires header after checking for max-age in GetFreshnessLifetime.  This
   // is important since "Expires: <date in the past>" means not fresh, but
   // it should not trump a max-age value.
 
-  TimeDelta max_age_value;
-  if (GetMaxAgeValue(&max_age_value))
-    return max_age_value;
+  if (GetMaxAgeValue(lifetime))
+    return MAYBE_FRESH;
 
+  *lifetime = TimeDelta();
   // If there is no Date header, then assume that the server response was
   // generated at the time when we received the response.
   Time date_value;
   if (!GetDateValue(&date_value))
     date_value = response_time;
 
   Time expires_value;
   if (GetExpiresValue(&expires_value)) {
     // The expires value can be a date in the past!
-    if (expires_value > date_value)
-      return expires_value - date_value;
+    if (expires_value > date_value) {
+      *lifetime = expires_value - date_value;
+      return MAYBE_FRESH;
+    }
 
-    return TimeDelta();  // not fresh
+    return NEVER_FRESH;
   }
 
   // From RFC 2616 section 13.4:
   //
   //   A response received with a status code of 200, 203, 206, 300, 301 or 410
   //   MAY be stored by a cache and used in reply to a subsequent request,
   //   subject to the expiration mechanism, unless a cache-control directive
   //   prohibits caching.
   //   ...
   //   A response received with any other status code (e.g. status codes 302
@@ skipping 12 matching lines @@
   //
   // https://datatracker.ietf.org/doc/draft-reschke-http-status-308/ is an
   // experimental RFC that adds 308 permanent redirect as well, for which "any
   // future references ... SHOULD use one of the returned URIs."
   if ((response_code_ == 200 || response_code_ == 203 ||
        response_code_ == 206) &&
       !HasHeaderValue("cache-control", "must-revalidate")) {
     // TODO(darin): Implement a smarter heuristic.
     Time last_modified_value;
     if (GetLastModifiedValue(&last_modified_value)) {
-      // The last-modified value can be a date in the past!
-      if (last_modified_value <= date_value)
-        return (date_value - last_modified_value) / 10;
+      // The last-modified value can be a date in the future!
+      if (last_modified_value <= date_value) {
+        *lifetime = (date_value - last_modified_value) / 10;
+        return MAYBE_FRESH;
+      }
     }
   }
 
   // These responses are implicitly fresh (unless otherwise overruled):
   if (response_code_ == 300 || response_code_ == 301 || response_code_ == 308 ||
       response_code_ == 410) {
-    return TimeDelta::Max();
+    *lifetime = TimeDelta::Max();
+    return MAYBE_FRESH;
   }
 
-  return TimeDelta();  // not fresh
+  return NEVER_FRESH;
 }
 
 // From RFC 2616 section 13.2.3:
 //
 // Summary of age calculation algorithm, when a cache receives a response:
 //
 //   /*
 //    * age_value
 //    *      is the value of Age: header received by the cache with
 //    *              this response.
@@ skipping 319 matching lines @@
   return true;
 }
 
 bool HttpResponseHeaders::IsChunkEncoded() const {
   // Ignore spurious chunked responses from HTTP/1.0 servers and proxies.
   return GetHttpVersion() >= HttpVersion(1, 1) &&
       HasHeaderValue("Transfer-Encoding", "chunked");
 }
 
 }  // namespace net