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..0d44cc9a0335806d35d24a700ca4f249cf08df27 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 {
 
@@ -45,7 +47,10 @@ bool LooksLikePacScript(const base::string16& script) {
 //
 // For more details, also check out this comment:
 // http://code.google.com/p/chromium/issues/detail?id=18575#c20
-static const char kWpadUrl[] = "http://wpad/wpad.dat";
+namespace {
+const char kWpadUrl[] = "http://wpad/wpad.dat";
+const int kQuickCheckDelayMs = 1000;
+};
 
 base::Value* ProxyScriptDecider::PacSource::NetLogCallback(
     const GURL* effective_pac_url,
@@ -82,6 +87,12 @@ ProxyScriptDecider::ProxyScriptDecider(
       net_log_(BoundNetLog::Make(
           net_log, NetLog::SOURCE_PROXY_SCRIPT_DECIDER)),
       fetch_pac_bytes_(false) {
+  if (proxy_script_fetcher &&
+      proxy_script_fetcher->GetRequestContext() &&
+      proxy_script_fetcher->GetRequestContext()->host_resolver()) {
+      host_resolver_.reset(new SingleRequestHostResolver(
+          proxy_script_fetcher->GetRequestContext()->host_resolver()));
+  }
 }
 
 ProxyScriptDecider::~ProxyScriptDecider() {
@@ -172,6 +183,13 @@ 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();
@@ -221,10 +239,60 @@ 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;
 }
 
+int ProxyScriptDecider::DoQuickCheck() {
+  if (host_resolver_.get() == NULL) {
+    // If we have no resolver, skip QuickCheck altogether.
+    next_state_ = GetStartState();
+    return OK;
+  }
+
+  quick_check_start_time_ = base::Time::Now();
+  HostResolver::RequestInfo reqinfo(HostPortPair("wpad", 80));
+  CompletionCallback callback = base::Bind(
+      &ProxyScriptDecider::OnIOCompletion,
+      base::Unretained(this));
+
+  HostResolverFlags flags = reqinfo.host_resolver_flags();
+  flags |= HOST_RESOLVER_SYSTEM_ONLY;
+  reqinfo.set_host_resolver_flags(flags);

[szym, 2013/09/16 22:15:54]

This is unnecessary. The default flags are 0.

reqinfo.set_host_resolver_flags(HOST_RESOLVER_SYSTEM_ONLY);

..and do it right after reqinfo is constructed in line 254.

[Elly Fong-Jones, 2013/09/17 19:20:23]

Done.

+
+  // We use HIGHEST here because proxy decision blocks doing any other requests.
+  int rv = host_resolver_->Resolve(reqinfo, HIGHEST, &wpad_addresses_,
+                                   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.
+  DCHECK(rv == OK || rv == ERR_IO_PENDING);
+
+  if (rv == OK) {
+    next_state_ = GetStartState();
+  } else {
+    quick_check_timer_.Start(FROM_HERE,
+                             base::TimeDelta::FromMilliseconds(
+                                kQuickCheckDelayMs),
+                             base::Bind(callback, ERR_NAME_NOT_RESOLVED));
+    next_state_ = STATE_QUICK_CHECK_COMPLETE;
+  }
+  return rv;
+}
+
+int ProxyScriptDecider::DoQuickCheckComplete(int result) {
+  base::TimeDelta delta = base::Time::Now() - quick_check_start_time_;
+  if (result == OK)
+    UMA_HISTOGRAM_TIMES("Net.WpadQuickCheckSuccess", delta);
+  else
+    UMA_HISTOGRAM_TIMES("Net.WpadQuickCheckFailure", delta);
+  host_resolver_->Cancel();
+  quick_check_timer_.Stop();
+  if (result == OK)
+    next_state_ = GetStartState();
+  return result;
+}
+
 int ProxyScriptDecider::DoFetchPacScript() {
   DCHECK(fetch_pac_bytes_);