Remove stale-while-revalidate from net

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 899 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.
 //
-// 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
-//
-ValidationType HttpResponseHeaders::RequiresValidation(
-    const Time& request_time,
-    const Time& response_time,
-    const Time& current_time) const {
+bool HttpResponseHeaders::RequiresValidation(const Time& request_time,
+                                             const Time& response_time,
+                                             const Time& current_time) const {
   FreshnessLifetimes lifetimes = GetFreshnessLifetimes(response_time);
-  if (lifetimes.freshness.is_zero() && lifetimes.staleness.is_zero())
-    return VALIDATION_SYNCHRONOUS;
+  if (lifetimes.freshness.is_zero())
+    return true;
 
   TimeDelta age = GetCurrentAge(request_time, response_time, current_time);
 
   if (lifetimes.freshness > age)
-    return VALIDATION_NONE;
+    return false;
 
-  if (lifetimes.freshness + lifetimes.staleness > age)
-    return VALIDATION_ASYNCHRONOUS;
-
-  return VALIDATION_SYNCHRONOUS;
+  return true;

[mmenke, 2017/03/23 21:39:35]

optional:  Maybe just replace these last 4 lines with:

return lifetime <= GetCurrentAge(request_time, response_time, current_time);

[scottmg, 2017/03/24 22:46:00]

Done. (I was a bit nervous about messing up on a bool, so I was trying to be a
bit conservative.)

 }
 
 // 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
 //
-// If the stale-while-revalidate directive is present, then it is used to set
-// the |staleness| time, unless it overridden by another directive.
-//
 HttpResponseHeaders::FreshnessLifetimes
 HttpResponseHeaders::GetFreshnessLifetimes(const Time& response_time) const {
   FreshnessLifetimes lifetimes;
   // 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") ||
       // Vary: * is never usable: see RFC 2616 section 13.6.
       HasHeaderValue("vary", "*")) {
     return lifetimes;
   }
 
-  // Cache-Control directive must_revalidate overrides stale-while-revalidate.
   bool must_revalidate = HasHeaderValue("cache-control", "must-revalidate");

[mmenke, 2017/03/23 21:39:35]

Can get rid of the must_revalidate local, and inline the HasHeaderValue call
below.

[scottmg, 2017/03/24 22:46:00]

Done.

 
-  if (must_revalidate || !GetStaleWhileRevalidateValue(&lifetimes.staleness)) {
-    DCHECK_EQ(TimeDelta(), lifetimes.staleness);
-  }
-
   // NOTE: "Cache-Control: max-age" overrides Expires, so we only check the
   // Expires header after checking for max-age in GetFreshnessLifetimes.  This
   // is important since "Expires: <date in the past>" means not fresh, but
   // it should not trump a max-age value.
   if (GetMaxAgeValue(&lifetimes.freshness))
     return lifetimes;
 
   // 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;
@@ skipping 46 matching lines @@
         lifetimes.freshness = (date_value - last_modified_value) / 10;
         return lifetimes;
       }
     }
   }
 
   // These responses are implicitly fresh (unless otherwise overruled):
   if (response_code_ == 300 || response_code_ == 301 || response_code_ == 308 ||
       response_code_ == 410) {
     lifetimes.freshness = TimeDelta::Max();
-    lifetimes.staleness = TimeDelta();  // It should never be stale.
     return lifetimes;
   }
 
   // Our heuristic freshness estimate for this resource is 0 seconds, in
-  // accordance with common browser behaviour. However, stale-while-revalidate
-  // may still apply.
+  // accordance with common browser behaviour.
   DCHECK_EQ(TimeDelta(), lifetimes.freshness);
   return lifetimes;
 }
 
 // From RFC 7234 section 4.2.3:
 //
 // The following data is used for the age calculation:
 //
 //    age_value
 //
@@ skipping 90 matching lines @@
 }
 
 bool HttpResponseHeaders::GetLastModifiedValue(Time* result) const {
   return GetTimeValuedHeader("Last-Modified", result);
 }
 
 bool HttpResponseHeaders::GetExpiresValue(Time* result) const {
   return GetTimeValuedHeader("Expires", result);
 }
 
-bool HttpResponseHeaders::GetStaleWhileRevalidateValue(
-    TimeDelta* result) const {
-  return GetCacheControlDirective("stale-while-revalidate", result);
-}
-
 bool HttpResponseHeaders::GetTimeValuedHeader(const std::string& name,
                                               Time* result) const {
   std::string value;
   if (!EnumerateHeader(nullptr, name, &value))
     return false;
 
   // When parsing HTTP dates it's beneficial to default to GMT because:
   // 1. RFC2616 3.3.1 says times should always be specified in GMT
   // 2. Only counter-example incorrectly appended "UTC" (crbug.com/153759)
   // 3. When adjusting cookie expiration times for clock skew
@@ skipping 160 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