Implement exponential back-off mechanism and enforce it at the URLRequestHttpJob level.

net/url_request/url_request_http_job.cc

Index: net/url_request/url_request_http_job.cc
===================================================================
--- net/url_request/url_request_http_job.cc	(revision 66188)
+++ net/url_request/url_request_http_job.cc	(working copy)
@@ -29,6 +29,8 @@
 #include "net/http/http_transaction_factory.h"
 #include "net/http/http_util.h"
 #include "net/url_request/https_prober.h"
+#include "net/url_request/request_throttler_header_adapter.h"
+#include "net/url_request/request_throttler_manager.h"
 #include "net/url_request/url_request.h"
 #include "net/url_request/url_request_context.h"
 #include "net/url_request/url_request_error_job.h"
@@ -92,6 +94,8 @@
           this, &URLRequestHttpJob::OnReadCompleted)),
       read_in_progress_(false),
       transaction_(NULL),
+      throttling_entry_(RequestThrottlerManager::GetInstance()->
+          RegisterRequestUrl(request->url())),
       sdch_dictionary_advertised_(false),
       sdch_test_activated_(false),
       sdch_test_control_(false),
@@ -570,6 +574,11 @@
   // also need this info.
   is_cached_content_ = response_info_->was_cached;
 
+  if (!is_cached_content_) {
+    RequestThrottlerHeaderAdapter response_adapter(response_info_->headers);
+    throttling_entry_->UpdateWithResponse(&response_adapter);
+  }
+
   ProcessStrictTransportSecurityHeader();
 
   if (SdchManager::Global() &&
@@ -617,30 +626,37 @@
   // If we already have a transaction, then we should restart the transaction
   // with auth provided by username_ and password_.
 
-  int rv;
+  int return_value;

[willchan no longer on Chromium, 2010/11/24 10:14:50]

rv is sufficiently common in the network stack that unless we wanted to change
the rest of the network stack, it's better to simply be consistent and continue
using rv here to mean return_value.  i understand why you changed it, but it's
inconsistent with network stack code.

[yzshen, 2010/11/24 19:09:30]

Done.

+
   if (transaction_.get()) {
-    rv = transaction_->RestartWithAuth(username_, password_, &start_callback_);
+    return_value = transaction_->RestartWithAuth(username_,
+        password_, &start_callback_);
     username_.clear();
     password_.clear();
   } else {
     DCHECK(request_->context());
     DCHECK(request_->context()->http_transaction_factory());
 
-    rv = request_->context()->http_transaction_factory()->CreateTransaction(
-        &transaction_);
-    if (rv == net::OK) {
-      rv = transaction_->Start(
-          &request_info_, &start_callback_, request_->net_log());
+    return_value = request_->context()->http_transaction_factory()->
+        CreateTransaction(&transaction_);
+    if (return_value == net::OK) {
+      if (!throttling_entry_->IsDuringExponentialBackoff()) {
+        return_value = transaction_->Start(
+            &request_info_, &start_callback_, request_->net_log());
+      } else {
+        // Special error code for the exponential back-off module.
+        return_value = net::ERR_TEMPORARILY_THROTTLED_BY_DDOS;
+      }
     }
   }
 
-  if (rv == net::ERR_IO_PENDING)
+  if (return_value == net::ERR_IO_PENDING)
     return;
 
   // The transaction started synchronously, but we need to notify the
   // URLRequest delegate via the message loop.
   MessageLoop::current()->PostTask(FROM_HERE, NewRunnableMethod(
-      this, &URLRequestHttpJob::OnStartCompleted, rv));
+      this, &URLRequestHttpJob::OnStartCompleted, return_value));
 }
 
 void URLRequestHttpJob::AddExtraHeaders() {