Fast-fail WPAD detection.

net/proxy/proxy_script_decider.cc

Index: net/proxy/proxy_script_decider.cc
diff --git a/net/proxy/proxy_script_decider.cc b/net/proxy/proxy_script_decider.cc
index 38bf751cd4da3e3c89ccdacbe079854911e1c058..3af695a7369479e80f0801ea6b7f6cf550f0bb5d 100644
--- a/net/proxy/proxy_script_decider.cc
+++ b/net/proxy/proxy_script_decider.cc
@@ -9,6 +9,7 @@
 #include "base/compiler_specific.h"
 #include "base/format_macros.h"
 #include "base/logging.h"
+#include "base/metrics/histogram.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/values.h"
@@ -16,6 +17,7 @@
 #include "net/proxy/dhcp_proxy_script_fetcher.h"
 #include "net/proxy/dhcp_proxy_script_fetcher_factory.h"
 #include "net/proxy/proxy_script_fetcher.h"
+#include "net/url_request/url_request_context.h"
 
 namespace net {
 
@@ -47,6 +49,8 @@ bool LooksLikePacScript(const base::string16& script) {
 // http://code.google.com/p/chromium/issues/detail?id=18575#c20
 static const char kWpadUrl[] = "http://wpad/wpad.dat";
 
+static const int kQuickCheckDelayMs = 1000;
+
 base::Value* ProxyScriptDecider::PacSource::NetLogCallback(
     const GURL* effective_pac_url,
     NetLog::LogLevel /* log_level */) const {
@@ -81,7 +85,9 @@ ProxyScriptDecider::ProxyScriptDecider(
       next_state_(STATE_NONE),
       net_log_(BoundNetLog::Make(
           net_log, NetLog::SOURCE_PROXY_SCRIPT_DECIDER)),
-      fetch_pac_bytes_(false) {
+      fetch_pac_bytes_(false),
+      host_resolver_(
+          proxy_script_fetcher->GetRequestContext()->host_resolver()) {
 }
 
 ProxyScriptDecider::~ProxyScriptDecider() {
@@ -172,6 +178,13 @@ int ProxyScriptDecider::DoLoop(int result) {
       case STATE_WAIT_COMPLETE:
         rv = DoWaitComplete(rv);
         break;
+      case STATE_QUICK_CHECK:
+        DCHECK_EQ(OK, rv);
+        rv = DoQuickCheck();
+        break;
+      case STATE_QUICK_CHECK_COMPLETE:
+        rv = DoQuickCheckComplete(rv);
+        break;
       case STATE_FETCH_PAC_SCRIPT:
         DCHECK_EQ(OK, rv);
         rv = DoFetchPacScript();
@@ -201,6 +214,45 @@ void ProxyScriptDecider::DoCallback(int result) {
   callback_.Run(result);
 }
 
+int ProxyScriptDecider::DoQuickCheck() {

[szym, 2013/08/23 20:45:57]

nit: Move both after DoWait() (to match my nit regarding the header)

[Elly Fong-Jones, 2013/08/26 15:17:29]

Done.

+  quick_check_started_ = base::Time::Now();
+  HostResolver::RequestInfo reqinfo(HostPortPair("wpad", 80));
+  CompletionCallback callback = base::Bind(
+      &ProxyScriptDecider::OnIOCompletion,
+      base::Unretained(this));
+
+  int rv = host_resolver_.Resolve(reqinfo, HIGHEST,  // we block startup...

[szym, 2013/08/23 20:45:57]

nit: suggest putting this comment above this line.

Also per code style: "Use full sentences."

[Elly Fong-Jones, 2013/08/26 15:17:29]

Done.

+                                  &wpad_addrs_, callback, net_log_);
+
+  // we can't get an error response - the name is known to be valid, and we
+  // don't cache negative dns responses.
+  CHECK(rv == OK || rv == ERR_IO_PENDING);
+
+  if (rv == OK) {
+    // already in cache or something and valid, we're golden
+    next_state_ = STATE_FETCH_PAC_SCRIPT;

[szym, 2013/08/23 20:45:57]

Perhaps this should be GetStartState()...
... but something tells me that you should after QUICK_CHECK we should always go
to FETCH_PAC_SCRIPT, and after WAIT we should go to either QUICK_CHECK or
VERIFY_PAC_SCRIPT, which means you need to update the other transitions in lines
252 and 276.

Frankly, I'm not quite sure if WAIT should be preceding VERIFY_PAC. I'll need to
read Eric's old comments.

+    return OK;
+  }
+
+  quick_check_timer_.Start(FROM_HERE,
+                           base::TimeDelta::FromMilliseconds(
+                              kQuickCheckDelayMs),
+                           base::Bind(callback, ERR_NAME_NOT_RESOLVED));
+
+  next_state_ = STATE_QUICK_CHECK_COMPLETE;
+  return ERR_IO_PENDING;
+}
+
+int ProxyScriptDecider::DoQuickCheckComplete(int result) {
+  base::TimeDelta delta = base::Time::Now()
+                        - quick_check_started_;
+  UMA_HISTOGRAM_TIMES("Net.WpadQuickCheck", delta);
+  host_resolver_.Cancel();
+  quick_check_timer_.Stop();
+  next_state_ = result == OK ? GetStartState() : STATE_NONE;
+  return result;
+}
+
 int ProxyScriptDecider::DoWait() {
   next_state_ = STATE_WAIT_COMPLETE;
 
@@ -221,7 +273,7 @@ int ProxyScriptDecider::DoWaitComplete(int result) {
     net_log_.EndEventWithNetErrorCode(NetLog::TYPE_PROXY_SCRIPT_DECIDER_WAIT,
                                       result);
   }
-  next_state_ = GetStartState();
+  next_state_ = STATE_QUICK_CHECK;
   return OK;
 }
 
@@ -399,6 +451,8 @@ void ProxyScriptDecider::Cancel() {
     case STATE_FETCH_PAC_SCRIPT_COMPLETE:
       proxy_script_fetcher_->Cancel();
       break;
+    case STATE_FAILED:
+      break;
     default:
       NOTREACHED();
       break;