RFC: use some in-memory state in SimpleCache to quickly cache-miss some CantConditionalize cases

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 518944650747e6a3dc7f39c58b4b4d7cb1610758..a99e4c8e3c8c15e06274030e9c4e461be9182ebe 100644
--- a/net/http/http_cache_transaction.cc
+++ b/net/http/http_cache_transaction.cc
@@ -2337,40 +2337,57 @@ bool HttpCache::Transaction::RequiresValidation() {
   return validation_required_by_headers;
 }
 
-bool HttpCache::Transaction::ConditionalizeRequest() {
+bool HttpCache::Transaction::ResponseConditionalizable(
+    std::string* etag_value,
+    std::string* last_modified_value) {
   DCHECK(response_.headers.get());
 
-  if (request_->method == "PUT" || request_->method == "DELETE")
-    return false;
-
   // This only makes sense for cached 200 or 206 responses.
   if (response_.headers->response_code() != 200 &&
       response_.headers->response_code() != 206) {
     return false;
   }
 
-  if (fail_conditionalization_for_test_)
-    return false;
-
+  // ### this looks scary.
   DCHECK(response_.headers->response_code() != 206 ||
          response_.headers->HasStrongValidators());
 
   // Just use the first available ETag and/or Last-Modified header value.
   // TODO(darin): Or should we use the last?
 
-  std::string etag_value;
   if (response_.headers->GetHttpVersion() >= HttpVersion(1, 1))
-    response_.headers->EnumerateHeader(NULL, "etag", &etag_value);
+    response_.headers->EnumerateHeader(NULL, "etag", etag_value);
 
-  std::string last_modified_value;
-  if (!vary_mismatch_) {
-    response_.headers->EnumerateHeader(NULL, "last-modified",
-                                       &last_modified_value);
-  }
+  response_.headers->EnumerateHeader(NULL, "last-modified",
+                                     last_modified_value);
+
+  if (etag_value->empty() && last_modified_value->empty())
+    return false;
+
+  return true;
+}
+
+bool HttpCache::Transaction::ConditionalizeRequest() {
+  DCHECK(response_.headers.get());
 
-  if (etag_value.empty() && last_modified_value.empty())
+  if (request_->method == "PUT" || request_->method == "DELETE")
+    return false;
+
+  if (fail_conditionalization_for_test_)
+    return false;
+
+  std::string etag_value;
+  std::string last_modified_value;
+  if (!ResponseConditionalizable(&etag_value, &last_modified_value))
     return false;
 
+  if (vary_mismatch_) {
+    // Can't rely on last-modified if vary is different.
+    last_modified_value.clear();
+    if (etag_value.empty())
+      return false;
+  }
+
   if (!partial_) {
     // Need to customize the request, so this forces us to allocate :(
     custom_request_.reset(new HttpRequestInfo(*request_));
@@ -2410,6 +2427,23 @@ bool HttpCache::Transaction::ConditionalizeRequest() {
   return true;
 }
 
+bool HttpCache::Transaction::CanRejectBasedOnMemoryEntryData(
+    uint8_t in_memory_info) {
+  // We can tell that some entries in cache may be unusable under present
+  // circumstances if:
+  // 1) We aren't using everything because of LOAD_SKIP_CACHE_VALIDATION.
+  // 2) We aren't holding on to results of an unused prefetch.
+  // 3) The entry has zero freshness (so it's known to be expired!)
+  // 4) We know the entry can't be revalidated
+  //    (we may be able to match more things here).
+  if (effective_load_flags_ & LOAD_SKIP_CACHE_VALIDATION)
+    return false;
+
+  return (in_memory_info & HttpCache::OBH_ZERO_LIFETIME) &&
+         (in_memory_info & HttpCache::OBH_RESPONSE_CANT_CONDITIONALIZE) &&
+         !(in_memory_info & OBH_UNUSED_SINCE_PREFETCH);
+}
+
 // We just received some headers from the server. We may have asked for a range,
 // in which case partial_ has an object. This could be the first network request
 // we make to fulfill the original request, or we may be already reading (from
@@ -2631,6 +2665,18 @@ int HttpCache::Transaction::WriteResponseInfoToEntry(bool truncated) {
   data->Done();
 
   io_buf_len_ = data->pickle()->size();
+
+  uint8_t hints = 0;
+  // ### recomputing this too much?
+  if (response_.headers->GetFreshnessLifetimes(response_.response_time)
+          .freshness.is_zero())
+    hints |= HttpCache::OBH_ZERO_LIFETIME;
+  std::string etag_ignored, last_modified_ignored;
+  if (!ResponseConditionalizable(&etag_ignored, &last_modified_ignored))
+    hints |= HttpCache::OBH_RESPONSE_CANT_CONDITIONALIZE;
+  if (response_.unused_since_prefetch)
+    hints |= HttpCache::OBH_UNUSED_SINCE_PREFETCH;
+  cache_->GetCurrentBackend()->SetMemoryEntryData(cache_key_, hints);
   return entry_->disk_entry->WriteData(kResponseInfoIndex, 0, data.get(),
                                        io_buf_len_, io_callback_, true);
 }