Fast-fail WPAD detection.

net/proxy/proxy_script_decider.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/proxy/proxy_script_decider.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #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"
 #include "net/base/net_errors.h"
 #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 {
 
 namespace {
 
 bool LooksLikePacScript(const base::string16& script) {
   // Note: this is only an approximation! It may not always work correctly,
   // however it is very likely that legitimate scripts have this exact string,
   // since they must minimally define a function of this name. Conversely, a
   // file not containing the string is not likely to be a PAC script.
   //
   // An exact test would have to load the script in a javascript evaluator.
   return script.find(ASCIIToUTF16("FindProxyForURL")) != base::string16::npos;
 }
 
 }
 
 // This is the hard-coded location used by the DNS portion of web proxy
 // auto-discovery.
 //
 // Note that we not use DNS devolution to find the WPAD host, since that could
 // be dangerous should our top level domain registry  become out of date.
 //
 // Instead we directly resolve "wpad", and let the operating system apply the
 // DNS suffix search paths. This is the same approach taken by Firefox, and
 // compatibility hasn't been an issue.
 //
 // 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,
     NetLog::LogLevel /* log_level */) const {
   base::DictionaryValue* dict = new base::DictionaryValue();
   std::string source;
   switch (type) {
     case PacSource::WPAD_DHCP:
       source = "WPAD DHCP";
       break;
@@ skipping 16 matching lines @@
     NetLog* net_log)
     : resolver_(NULL),
       proxy_script_fetcher_(proxy_script_fetcher),
       dhcp_proxy_script_fetcher_(dhcp_proxy_script_fetcher),
       current_pac_source_index_(0u),
       pac_mandatory_(false),
       next_state_(STATE_NONE),
       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() {
   if (next_state_ != STATE_NONE)
     Cancel();
 }
 
 int ProxyScriptDecider::Start(
     const ProxyConfig& config, const base::TimeDelta wait_delay,
     bool fetch_pac_bytes, const CompletionCallback& callback) {
@@ skipping 70 matching lines @@
     State state = next_state_;
     next_state_ = STATE_NONE;
     switch (state) {
       case STATE_WAIT:
         DCHECK_EQ(OK, rv);
         rv = DoWait();
         break;
       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();
         break;
       case STATE_FETCH_PAC_SCRIPT_COMPLETE:
         rv = DoFetchPacScriptComplete(rv);
         break;
       case STATE_VERIFY_PAC_SCRIPT:
         DCHECK_EQ(OK, rv);
         rv = DoVerifyPacScript();
@@ skipping 29 matching lines @@
   net_log_.BeginEvent(NetLog::TYPE_PROXY_SCRIPT_DECIDER_WAIT);
   return ERR_IO_PENDING;
 }
 
 int ProxyScriptDecider::DoWaitComplete(int result) {
   DCHECK_EQ(OK, result);
   if (wait_delay_.ToInternalValue() != 0) {
     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_);
 
   next_state_ = STATE_FETCH_PAC_SCRIPT_COMPLETE;
 
   const PacSource& pac_source = current_pac_source();
 
   GURL effective_pac_url;
   DetermineURL(pac_source, &effective_pac_url);
 
@@ skipping 167 matching lines @@
   }
 
   // This is safe to call in any state.
   if (dhcp_proxy_script_fetcher_)
     dhcp_proxy_script_fetcher_->Cancel();
 
   DidComplete();
 }
 
 }  // namespace net