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..3eaad3e1082838840d970a68ca7cfa90337d6210 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"
@@ -81,7 +82,9 @@ 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_(HostResolver::CreateDefaultResolver(net_log)),
+      quick_check_delay_(base::TimeDelta::FromMilliseconds(1000)) {
 }
 
 ProxyScriptDecider::~ProxyScriptDecider() {
@@ -110,7 +113,7 @@ int ProxyScriptDecider::Start(
   pac_sources_ = BuildPacSourcesFallbackList(config);
   DCHECK(!pac_sources_.empty());
 
-  next_state_ = STATE_WAIT;
+  next_state_ = STATE_QUICK_CHECK;
 
   int rv = DoLoop(OK);
   if (rv == ERR_IO_PENDING)
@@ -165,6 +168,9 @@ int ProxyScriptDecider::DoLoop(int result) {
     State state = next_state_;
     next_state_ = STATE_NONE;
     switch (state) {
+      case STATE_QUICK_CHECK:
+        rv = DoQuickCheck();
+        break;
       case STATE_WAIT:
         DCHECK_EQ(OK, rv);
         rv = DoWait();
@@ -186,6 +192,8 @@ int ProxyScriptDecider::DoLoop(int result) {
       case STATE_VERIFY_PAC_SCRIPT_COMPLETE:
         rv = DoVerifyPacScriptComplete(rv);
         break;
+      case STATE_FAILED:
+        break;
       default:
         NOTREACHED() << "bad state";
         rv = ERR_UNEXPECTED;
@@ -201,6 +209,54 @@ void ProxyScriptDecider::DoCallback(int result) {
   callback_.Run(result);
 }
 
+int ProxyScriptDecider::DoQuickCheck() {
+
+  HostResolver::RequestInfo reqinfo(HostPortPair("wpad", 80));
+
+  quick_check_started_ = base::Time::Now();
+  int rv = host_resolver_->Resolve(reqinfo, HIGHEST,  // we block startup...
+                                   &wpad_addrs_,
+                                   base::Bind(
+                                      &ProxyScriptDecider::OnQuickCheckComplete,
+                                      base::Unretained(this)),
+                                   &wpad_req_,
+                                   net_log_);
+
+  if (rv == OK) {
+    // already in cache or something and valid, we're golden
+    next_state_ = STATE_WAIT;
+    return OK;
+  } else if (rv != ERR_IO_PENDING) {
+    // already in cache and invalid, bail now

[szym, 2013/08/21 19:11:21]

We don't actually cache negative results in HostResolverImpl. A synchronous
failure can only happen due to incorrect request (not a well-formed domain name
or IP address) or HostResolverImpl's internal request queue overflowing. So, I'd
probably CHECK here.

+    next_state_ = STATE_FAILED;
+    return rv;
+  }
+
+  quick_check_timer_.Start(FROM_HERE, quick_check_delay_, this,
+                           &ProxyScriptDecider::OnQuickCheckTimerFired);
+
+  next_state_ = STATE_QUICK_CHECK;
+  return ERR_IO_PENDING;
+}
+
+void ProxyScriptDecider::OnQuickCheckTimerFired() {
+  host_resolver_->CancelRequest(wpad_req_);
+  next_state_ = STATE_FAILED;

[szym, 2013/08/21 19:11:21]

You'll probably want to UMA this as well. Putting it in the same histogram would
work. This way you'd be able to completely replace OnQuickCheckTimerFired with
OnQuickCheckComplete(ERR_NAME_NOT_RESOLVED).

+  OnIOCompletion(ERR_NAME_NOT_RESOLVED);
+}
+
+void ProxyScriptDecider::OnQuickCheckComplete(int result) {
+  base::Time quick_check_ended = base::Time::Now();
+  base::TimeDelta delta = quick_check_ended - quick_check_started_;
+  UMA_HISTOGRAM_TIMES("Net.WpadQuickCheck", delta);
+  quick_check_timer_.Stop();
+  if (result == OK)
+    next_state_ = STATE_WAIT;
+  else
+    next_state_ = STATE_FAILED;
+  OnIOCompletion(result);
+}
+
 int ProxyScriptDecider::DoWait() {
   next_state_ = STATE_WAIT_COMPLETE;