net/dns/host_resolver_impl.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "net/dns/host_resolver_impl.h"
   6
   7 #if defined(OS_WIN)
   8 #include <Winsock2.h>
   9 #elif defined(OS_POSIX)
  10 #include <netdb.h>
  11 #endif
  12
  13 #include <cmath>
  14 #include <utility>
  15 #include <vector>
  16
  17 #include "base/basictypes.h"
  18 #include "base/bind.h"
  19 #include "base/bind_helpers.h"
  20 #include "base/callback.h"
  21 #include "base/compiler_specific.h"
  22 #include "base/debug/debugger.h"
  23 #include "base/debug/stack_trace.h"
  24 #include "base/message_loop/message_loop_proxy.h"
  25 #include "base/metrics/field_trial.h"
  26 #include "base/metrics/histogram.h"
  27 #include "base/profiler/scoped_tracker.h"
  28 #include "base/stl_util.h"
  29 #include "base/strings/string_util.h"
  30 #include "base/strings/utf_string_conversions.h"
  31 #include "base/threading/worker_pool.h"
  32 #include "base/time/time.h"
  33 #include "base/values.h"
  34 #include "net/base/address_family.h"
  35 #include "net/base/address_list.h"
  36 #include "net/base/dns_reloader.h"
  37 #include "net/base/dns_util.h"
  38 #include "net/base/host_port_pair.h"
  39 #include "net/base/ip_endpoint.h"
  40 #include "net/base/net_errors.h"
  41 #include "net/base/net_util.h"
  42 #include "net/dns/address_sorter.h"
  43 #include "net/dns/dns_client.h"
  44 #include "net/dns/dns_config_service.h"
  45 #include "net/dns/dns_protocol.h"
  46 #include "net/dns/dns_response.h"
  47 #include "net/dns/dns_transaction.h"
  48 #include "net/dns/host_resolver_proc.h"
  49 #include "net/log/net_log.h"
  50 #include "net/socket/client_socket_factory.h"
  51 #include "net/udp/datagram_client_socket.h"
  52 #include "url/url_canon_ip.h"
  53
  54 #if defined(OS_WIN)
  55 #include "net/base/winsock_init.h"
  56 #endif
  57
  58 namespace net {
  59
  60 namespace {
  61
  62 // Limit the size of hostnames that will be resolved to combat issues in
  63 // some platform's resolvers.
  64 const size_t kMaxHostLength = 4096;
  65
  66 // Default TTL for successful resolutions with ProcTask.
  67 const unsigned kCacheEntryTTLSeconds = 60;
  68
  69 // Default TTL for unsuccessful resolutions with ProcTask.
  70 const unsigned kNegativeCacheEntryTTLSeconds = 0;
  71
  72 // Minimum TTL for successful resolutions with DnsTask.
  73 const unsigned kMinimumTTLSeconds = kCacheEntryTTLSeconds;
  74
  75 const char kLocalhost[] = "localhost.";
  76
  77 // We use a separate histogram name for each platform to facilitate the
  78 // display of error codes by their symbolic name (since each platform has
  79 // different mappings).
  80 const char kOSErrorsForGetAddrinfoHistogramName[] =
  81 #if defined(OS_WIN)
  82     "Net.OSErrorsForGetAddrinfo_Win";
  83 #elif defined(OS_MACOSX)
  84     "Net.OSErrorsForGetAddrinfo_Mac";
  85 #elif defined(OS_LINUX)
  86     "Net.OSErrorsForGetAddrinfo_Linux";
  87 #else
  88     "Net.OSErrorsForGetAddrinfo";
  89 #endif
  90
  91 // Gets a list of the likely error codes that getaddrinfo() can return
  92 // (non-exhaustive). These are the error codes that we will track via
  93 // a histogram.
  94 std::vector<int> GetAllGetAddrinfoOSErrors() {
  95   int os_errors[] = {
  96 #if defined(OS_POSIX)
  97 #if !defined(OS_FREEBSD)
  98 #if !defined(OS_ANDROID)
  99     // EAI_ADDRFAMILY has been declared obsolete in Android's and
 100     // FreeBSD's netdb.h.
 101     EAI_ADDRFAMILY,
 102 #endif
 103     // EAI_NODATA has been declared obsolete in FreeBSD's netdb.h.
 104     EAI_NODATA,
 105 #endif
 106     EAI_AGAIN,
 107     EAI_BADFLAGS,
 108     EAI_FAIL,
 109     EAI_FAMILY,
 110     EAI_MEMORY,
 111     EAI_NONAME,
 112     EAI_SERVICE,
 113     EAI_SOCKTYPE,
 114     EAI_SYSTEM,
 115 #elif defined(OS_WIN)
 116     // See: http://msdn.microsoft.com/en-us/library/ms738520(VS.85).aspx
 117     WSA_NOT_ENOUGH_MEMORY,
 118     WSAEAFNOSUPPORT,
 119     WSAEINVAL,
 120     WSAESOCKTNOSUPPORT,
 121     WSAHOST_NOT_FOUND,
 122     WSANO_DATA,
 123     WSANO_RECOVERY,
 124     WSANOTINITIALISED,
 125     WSATRY_AGAIN,
 126     WSATYPE_NOT_FOUND,
 127     // The following are not in doc, but might be to appearing in results :-(.
 128     WSA_INVALID_HANDLE,
 129 #endif
 130   };
 131
 132   // Ensure all errors are positive, as histogram only tracks positive values.
 133   for (size_t i = 0; i < arraysize(os_errors); ++i) {
 134     os_errors[i] = std::abs(os_errors[i]);
 135   }
 136
 137   return base::CustomHistogram::ArrayToCustomRanges(os_errors,
 138                                                     arraysize(os_errors));
 139 }
 140
 141 enum DnsResolveStatus {
 142   RESOLVE_STATUS_DNS_SUCCESS = 0,
 143   RESOLVE_STATUS_PROC_SUCCESS,
 144   RESOLVE_STATUS_FAIL,
 145   RESOLVE_STATUS_SUSPECT_NETBIOS,
 146   RESOLVE_STATUS_MAX
 147 };
 148
 149 // ICANN uses this localhost address to indicate a name collision.
 150 //
 151 // The policy in Chromium is to fail host resolving if it resolves to
 152 // this special address.
 153 //
 154 // Not however that IP literals are exempt from this policy, so it is still
 155 // possible to navigate to http://127.0.53.53/ directly.
 156 //
 157 // For more details: https://www.icann.org/news/announcement-2-2014-08-01-en
 158 const unsigned char kIcanNameCollisionIp[] = {127, 0, 53, 53};
 159
 160 void UmaAsyncDnsResolveStatus(DnsResolveStatus result) {
 161   UMA_HISTOGRAM_ENUMERATION("AsyncDNS.ResolveStatus",
 162                             result,
 163                             RESOLVE_STATUS_MAX);
 164 }
 165
 166 bool ResemblesNetBIOSName(const std::string& hostname) {
 167   return (hostname.size() < 16) && (hostname.find('.') == std::string::npos);
 168 }
 169
 170 // True if |hostname| ends with either ".local" or ".local.".
 171 bool ResemblesMulticastDNSName(const std::string& hostname) {
 172   DCHECK(!hostname.empty());
 173   const char kSuffix[] = ".local.";
 174   const size_t kSuffixLen = sizeof(kSuffix) - 1;
 175   const size_t kSuffixLenTrimmed = kSuffixLen - 1;
 176   if (hostname[hostname.size() - 1] == '.') {
 177     return hostname.size() > kSuffixLen &&
 178         !hostname.compare(hostname.size() - kSuffixLen, kSuffixLen, kSuffix);
 179   }
 180   return hostname.size() > kSuffixLenTrimmed &&
 181       !hostname.compare(hostname.size() - kSuffixLenTrimmed, kSuffixLenTrimmed,
 182                         kSuffix, kSuffixLenTrimmed);
 183 }
 184
 185 // Attempts to connect a UDP socket to |dest|:53.
 186 bool IsGloballyReachable(const IPAddressNumber& dest,
 187                          const BoundNetLog& net_log) {
 188   // TODO(eroman): Remove ScopedTracker below once crbug.com/455942 is fixed.
 189   tracked_objects::ScopedTracker tracking_profile_1(
 190       FROM_HERE_WITH_EXPLICIT_FUNCTION("455942 IsGloballyReachable"));
 191
 192   scoped_ptr<DatagramClientSocket> socket(
 193       ClientSocketFactory::GetDefaultFactory()->CreateDatagramClientSocket(
 194           DatagramSocket::DEFAULT_BIND,
 195           RandIntCallback(),
 196           net_log.net_log(),
 197           net_log.source()));
 198   int rv = socket->Connect(IPEndPoint(dest, 53));
 199   if (rv != OK)
 200     return false;
 201   IPEndPoint endpoint;
 202   rv = socket->GetLocalAddress(&endpoint);
 203   if (rv != OK)
 204     return false;
 205   DCHECK_EQ(ADDRESS_FAMILY_IPV6, endpoint.GetFamily());
 206   const IPAddressNumber& address = endpoint.address();
 207   bool is_link_local = (address[0] == 0xFE) && ((address[1] & 0xC0) == 0x80);
 208   if (is_link_local)
 209     return false;
 210   const uint8 kTeredoPrefix[] = { 0x20, 0x01, 0, 0 };
 211   bool is_teredo = std::equal(kTeredoPrefix,
 212                               kTeredoPrefix + arraysize(kTeredoPrefix),
 213                               address.begin());
 214   if (is_teredo)
 215     return false;
 216   return true;
 217 }
 218
 219 // Provide a common macro to simplify code and readability. We must use a
 220 // macro as the underlying HISTOGRAM macro creates static variables.
 221 #define DNS_HISTOGRAM(name, time) UMA_HISTOGRAM_CUSTOM_TIMES(name, time, \
 222     base::TimeDelta::FromMilliseconds(1), base::TimeDelta::FromHours(1), 100)
 223
 224 // A macro to simplify code and readability.
 225 #define DNS_HISTOGRAM_BY_PRIORITY(basename, priority, time) \
 226   do { \
 227     switch (priority) { \
 228       case HIGHEST: DNS_HISTOGRAM(basename "_HIGHEST", time); break; \
 229       case MEDIUM: DNS_HISTOGRAM(basename "_MEDIUM", time); break; \
 230       case LOW: DNS_HISTOGRAM(basename "_LOW", time); break; \
 231       case LOWEST: DNS_HISTOGRAM(basename "_LOWEST", time); break; \
 232       case IDLE: DNS_HISTOGRAM(basename "_IDLE", time); break; \
 233       default: NOTREACHED(); break; \
 234     } \
 235     DNS_HISTOGRAM(basename, time); \
 236   } while (0)
 237
 238 // Record time from Request creation until a valid DNS response.
 239 void RecordTotalTime(bool had_dns_config,
 240                      bool speculative,
 241                      base::TimeDelta duration) {
 242   if (had_dns_config) {
 243     if (speculative) {
 244       DNS_HISTOGRAM("AsyncDNS.TotalTime_speculative", duration);
 245     } else {
 246       DNS_HISTOGRAM("AsyncDNS.TotalTime", duration);
 247     }
 248   } else {
 249     if (speculative) {
 250       DNS_HISTOGRAM("DNS.TotalTime_speculative", duration);
 251     } else {
 252       DNS_HISTOGRAM("DNS.TotalTime", duration);
 253     }
 254   }
 255 }
 256
 257 void RecordTTL(base::TimeDelta ttl) {
 258   UMA_HISTOGRAM_CUSTOM_TIMES("AsyncDNS.TTL", ttl,
 259                              base::TimeDelta::FromSeconds(1),
 260                              base::TimeDelta::FromDays(1), 100);
 261 }
 262
 263 bool ConfigureAsyncDnsNoFallbackFieldTrial() {
 264   const bool kDefault = false;
 265
 266   // Configure the AsyncDns field trial as follows:
 267   // groups AsyncDnsNoFallbackA and AsyncDnsNoFallbackB: return true,
 268   // groups AsyncDnsA and AsyncDnsB: return false,
 269   // groups SystemDnsA and SystemDnsB: return false,
 270   // otherwise (trial absent): return default.
 271   std::string group_name = base::FieldTrialList::FindFullName("AsyncDns");
 272   if (!group_name.empty())
 273     return StartsWithASCII(group_name, "AsyncDnsNoFallback", false);
 274   return kDefault;
 275 }
 276
 277 //-----------------------------------------------------------------------------
 278
 279 AddressList EnsurePortOnAddressList(const AddressList& list, uint16 port) {
 280   if (list.empty() || list.front().port() == port)
 281     return list;
 282   return AddressList::CopyWithPort(list, port);
 283 }
 284
 285 // Returns true if |addresses| contains only IPv4 loopback addresses.
 286 bool IsAllIPv4Loopback(const AddressList& addresses) {
 287   for (unsigned i = 0; i < addresses.size(); ++i) {
 288     const IPAddressNumber& address = addresses[i].address();
 289     switch (addresses[i].GetFamily()) {
 290       case ADDRESS_FAMILY_IPV4:
 291         if (address[0] != 127)
 292           return false;
 293         break;
 294       case ADDRESS_FAMILY_IPV6:
 295         return false;
 296       default:
 297         NOTREACHED();
 298         return false;
 299     }
 300   }
 301   return true;
 302 }
 303
 304 // Creates NetLog parameters when the resolve failed.
 305 base::Value* NetLogProcTaskFailedCallback(
 306     uint32 attempt_number,
 307     int net_error,
 308     int os_error,
 309     NetLogCaptureMode /* capture_mode */) {
 310   base::DictionaryValue* dict = new base::DictionaryValue();
 311   if (attempt_number)
 312     dict->SetInteger("attempt_number", attempt_number);
 313
 314   dict->SetInteger("net_error", net_error);
 315
 316   if (os_error) {
 317     dict->SetInteger("os_error", os_error);
 318 #if defined(OS_POSIX)
 319     dict->SetString("os_error_string", gai_strerror(os_error));
 320 #elif defined(OS_WIN)
 321     // Map the error code to a human-readable string.
 322     LPWSTR error_string = NULL;
 323     FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
 324                   0,  // Use the internal message table.
 325                   os_error,
 326                   0,  // Use default language.
 327                   (LPWSTR)&error_string,
 328                   0,  // Buffer size.
 329                   0);  // Arguments (unused).
 330     dict->SetString("os_error_string", base::WideToUTF8(error_string));
 331     LocalFree(error_string);
 332 #endif
 333   }
 334
 335   return dict;
 336 }
 337
 338 // Creates NetLog parameters when the DnsTask failed.
 339 base::Value* NetLogDnsTaskFailedCallback(int net_error,
 340                                          int dns_error,
 341                                          NetLogCaptureMode /* capture_mode */) {
 342   base::DictionaryValue* dict = new base::DictionaryValue();
 343   dict->SetInteger("net_error", net_error);
 344   if (dns_error)
 345     dict->SetInteger("dns_error", dns_error);
 346   return dict;
 347 };
 348
 349 // Creates NetLog parameters containing the information in a RequestInfo object,
 350 // along with the associated NetLog::Source.
 351 base::Value* NetLogRequestInfoCallback(const HostResolver::RequestInfo* info,
 352                                        NetLogCaptureMode /* capture_mode */) {
 353   base::DictionaryValue* dict = new base::DictionaryValue();
 354
 355   dict->SetString("host", info->host_port_pair().ToString());
 356   dict->SetInteger("address_family",
 357                    static_cast<int>(info->address_family()));
 358   dict->SetBoolean("allow_cached_response", info->allow_cached_response());
 359   dict->SetBoolean("is_speculative", info->is_speculative());
 360   return dict;
 361 }
 362
 363 // Creates NetLog parameters for the creation of a HostResolverImpl::Job.
 364 base::Value* NetLogJobCreationCallback(const NetLog::Source& source,
 365                                        const std::string* host,
 366                                        NetLogCaptureMode /* capture_mode */) {
 367   base::DictionaryValue* dict = new base::DictionaryValue();
 368   source.AddToEventParameters(dict);
 369   dict->SetString("host", *host);
 370   return dict;
 371 }
 372
 373 // Creates NetLog parameters for HOST_RESOLVER_IMPL_JOB_ATTACH/DETACH events.
 374 base::Value* NetLogJobAttachCallback(const NetLog::Source& source,
 375                                      RequestPriority priority,
 376                                      NetLogCaptureMode /* capture_mode */) {
 377   base::DictionaryValue* dict = new base::DictionaryValue();
 378   source.AddToEventParameters(dict);
 379   dict->SetString("priority", RequestPriorityToString(priority));
 380   return dict;
 381 }
 382
 383 // Creates NetLog parameters for the DNS_CONFIG_CHANGED event.
 384 base::Value* NetLogDnsConfigCallback(const DnsConfig* config,
 385                                      NetLogCaptureMode /* capture_mode */) {
 386   return config->ToValue();
 387 }
 388
 389 // The logging routines are defined here because some requests are resolved
 390 // without a Request object.
 391
 392 // Logs when a request has just been started.
 393 void LogStartRequest(const BoundNetLog& source_net_log,
 394                      const HostResolver::RequestInfo& info) {
 395   source_net_log.BeginEvent(
 396       NetLog::TYPE_HOST_RESOLVER_IMPL_REQUEST,
 397       base::Bind(&NetLogRequestInfoCallback, &info));
 398 }
 399
 400 // Logs when a request has just completed (before its callback is run).
 401 void LogFinishRequest(const BoundNetLog& source_net_log,
 402                       const HostResolver::RequestInfo& info,
 403                       int net_error) {
 404   source_net_log.EndEventWithNetErrorCode(
 405       NetLog::TYPE_HOST_RESOLVER_IMPL_REQUEST, net_error);
 406 }
 407
 408 // Logs when a request has been cancelled.
 409 void LogCancelRequest(const BoundNetLog& source_net_log,
 410                       const HostResolverImpl::RequestInfo& info) {
 411   source_net_log.AddEvent(NetLog::TYPE_CANCELLED);
 412   source_net_log.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_REQUEST);
 413 }
 414
 415 //-----------------------------------------------------------------------------
 416
 417 // Keeps track of the highest priority.
 418 class PriorityTracker {
 419  public:
 420   explicit PriorityTracker(RequestPriority initial_priority)
 421       : highest_priority_(initial_priority), total_count_(0) {
 422     memset(counts_, 0, sizeof(counts_));
 423   }
 424
 425   RequestPriority highest_priority() const {
 426     return highest_priority_;
 427   }
 428
 429   size_t total_count() const {
 430     return total_count_;
 431   }
 432
 433   void Add(RequestPriority req_priority) {
 434     ++total_count_;
 435     ++counts_[req_priority];
 436     if (highest_priority_ < req_priority)
 437       highest_priority_ = req_priority;
 438   }
 439
 440   void Remove(RequestPriority req_priority) {
 441     DCHECK_GT(total_count_, 0u);
 442     DCHECK_GT(counts_[req_priority], 0u);
 443     --total_count_;
 444     --counts_[req_priority];
 445     size_t i;
 446     for (i = highest_priority_; i > MINIMUM_PRIORITY && !counts_[i]; --i);
 447     highest_priority_ = static_cast<RequestPriority>(i);
 448
 449     // In absence of requests, default to MINIMUM_PRIORITY.
 450     if (total_count_ == 0)
 451       DCHECK_EQ(MINIMUM_PRIORITY, highest_priority_);
 452   }
 453
 454  private:
 455   RequestPriority highest_priority_;
 456   size_t total_count_;
 457   size_t counts_[NUM_PRIORITIES];
 458 };
 459
 460 }  // namespace
 461
 462 //-----------------------------------------------------------------------------
 463
 464 const unsigned HostResolverImpl::kMaximumDnsFailures = 16;
 465
 466 // Holds the data for a request that could not be completed synchronously.
 467 // It is owned by a Job. Canceled Requests are only marked as canceled rather
 468 // than removed from the Job's |requests_| list.
 469 class HostResolverImpl::Request {
 470  public:
 471   Request(const BoundNetLog& source_net_log,
 472           const RequestInfo& info,
 473           RequestPriority priority,
 474           const CompletionCallback& callback,
 475           AddressList* addresses)
 476       : source_net_log_(source_net_log),
 477         info_(info),
 478         priority_(priority),
 479         job_(NULL),
 480         callback_(callback),
 481         addresses_(addresses),
 482         request_time_(base::TimeTicks::Now()) {}
 483
 484   // Mark the request as canceled.
 485   void MarkAsCanceled() {
 486     job_ = NULL;
 487     addresses_ = NULL;
 488     callback_.Reset();
 489   }
 490
 491   bool was_canceled() const {
 492     return callback_.is_null();
 493   }
 494
 495   void set_job(Job* job) {
 496     DCHECK(job);
 497     // Identify which job the request is waiting on.
 498     job_ = job;
 499   }
 500
 501   // Prepare final AddressList and call completion callback.
 502   void OnComplete(int error, const AddressList& addr_list) {
 503     DCHECK(!was_canceled());
 504     if (error == OK)
 505       *addresses_ = EnsurePortOnAddressList(addr_list, info_.port());
 506     CompletionCallback callback = callback_;
 507     MarkAsCanceled();
 508     callback.Run(error);
 509   }
 510
 511   Job* job() const {
 512     return job_;
 513   }
 514
 515   // NetLog for the source, passed in HostResolver::Resolve.
 516   const BoundNetLog& source_net_log() {
 517     return source_net_log_;
 518   }
 519
 520   const RequestInfo& info() const {
 521     return info_;
 522   }
 523
 524   RequestPriority priority() const { return priority_; }
 525
 526   base::TimeTicks request_time() const { return request_time_; }
 527
 528  private:
 529   const BoundNetLog source_net_log_;
 530
 531   // The request info that started the request.
 532   const RequestInfo info_;
 533
 534   // TODO(akalin): Support reprioritization.
 535   const RequestPriority priority_;
 536
 537   // The resolve job that this request is dependent on.
 538   Job* job_;
 539
 540   // The user's callback to invoke when the request completes.
 541   CompletionCallback callback_;
 542
 543   // The address list to save result into.
 544   AddressList* addresses_;
 545
 546   const base::TimeTicks request_time_;
 547
 548   DISALLOW_COPY_AND_ASSIGN(Request);
 549 };
 550
 551 //------------------------------------------------------------------------------
 552
 553 // Calls HostResolverProc on the WorkerPool. Performs retries if necessary.
 554 //
 555 // Whenever we try to resolve the host, we post a delayed task to check if host
 556 // resolution (OnLookupComplete) is completed or not. If the original attempt
 557 // hasn't completed, then we start another attempt for host resolution. We take
 558 // the results from the first attempt that finishes and ignore the results from
 559 // all other attempts.
 560 //
 561 // TODO(szym): Move to separate source file for testing and mocking.
 562 //
 563 class HostResolverImpl::ProcTask
 564     : public base::RefCountedThreadSafe<HostResolverImpl::ProcTask> {
 565  public:
 566   typedef base::Callback<void(int net_error,
 567                               const AddressList& addr_list)> Callback;
 568
 569   ProcTask(const Key& key,
 570            const ProcTaskParams& params,
 571            const Callback& callback,
 572            const BoundNetLog& job_net_log)
 573       : key_(key),
 574         params_(params),
 575         callback_(callback),
 576         origin_loop_(base::MessageLoopProxy::current()),
 577         attempt_number_(0),
 578         completed_attempt_number_(0),
 579         completed_attempt_error_(ERR_UNEXPECTED),
 580         had_non_speculative_request_(false),
 581         net_log_(job_net_log) {
 582     if (!params_.resolver_proc.get())
 583       params_.resolver_proc = HostResolverProc::GetDefault();
 584     // If default is unset, use the system proc.
 585     if (!params_.resolver_proc.get())
 586       params_.resolver_proc = new SystemHostResolverProc();
 587   }
 588
 589   void Start() {
 590     DCHECK(origin_loop_->BelongsToCurrentThread());
 591     net_log_.BeginEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_PROC_TASK);
 592     StartLookupAttempt();
 593   }
 594
 595   // Cancels this ProcTask. It will be orphaned. Any outstanding resolve
 596   // attempts running on worker threads will continue running. Only once all the
 597   // attempts complete will the final reference to this ProcTask be released.
 598   void Cancel() {
 599     DCHECK(origin_loop_->BelongsToCurrentThread());
 600
 601     if (was_canceled() || was_completed())
 602       return;
 603
 604     callback_.Reset();
 605     net_log_.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_PROC_TASK);
 606   }
 607
 608   void set_had_non_speculative_request() {
 609     DCHECK(origin_loop_->BelongsToCurrentThread());
 610     had_non_speculative_request_ = true;
 611   }
 612
 613   bool was_canceled() const {
 614     DCHECK(origin_loop_->BelongsToCurrentThread());
 615     return callback_.is_null();
 616   }
 617
 618   bool was_completed() const {
 619     DCHECK(origin_loop_->BelongsToCurrentThread());
 620     return completed_attempt_number_ > 0;
 621   }
 622
 623  private:
 624   friend class base::RefCountedThreadSafe<ProcTask>;
 625   ~ProcTask() {}
 626
 627   void StartLookupAttempt() {
 628     DCHECK(origin_loop_->BelongsToCurrentThread());
 629     base::TimeTicks start_time = base::TimeTicks::Now();
 630     ++attempt_number_;
 631     // Dispatch the lookup attempt to a worker thread.
 632     if (!base::WorkerPool::PostTask(
 633             FROM_HERE,
 634             base::Bind(&ProcTask::DoLookup, this, start_time, attempt_number_),
 635             true)) {
 636       NOTREACHED();
 637
 638       // Since we could be running within Resolve() right now, we can't just
 639       // call OnLookupComplete().  Instead we must wait until Resolve() has
 640       // returned (IO_PENDING).
 641       origin_loop_->PostTask(
 642           FROM_HERE,
 643           base::Bind(&ProcTask::OnLookupComplete, this, AddressList(),
 644                      start_time, attempt_number_, ERR_UNEXPECTED, 0));
 645       return;
 646     }
 647
 648     net_log_.AddEvent(
 649         NetLog::TYPE_HOST_RESOLVER_IMPL_ATTEMPT_STARTED,
 650         NetLog::IntegerCallback("attempt_number", attempt_number_));
 651
 652     // If we don't get the results within a given time, RetryIfNotComplete
 653     // will start a new attempt on a different worker thread if none of our
 654     // outstanding attempts have completed yet.
 655     if (attempt_number_ <= params_.max_retry_attempts) {
 656       origin_loop_->PostDelayedTask(
 657           FROM_HERE,
 658           base::Bind(&ProcTask::RetryIfNotComplete, this),
 659           params_.unresponsive_delay);
 660     }
 661   }
 662
 663   // WARNING: This code runs inside a worker pool. The shutdown code cannot
 664   // wait for it to finish, so we must be very careful here about using other
 665   // objects (like MessageLoops, Singletons, etc). During shutdown these objects
 666   // may no longer exist. Multiple DoLookups() could be running in parallel, so
 667   // any state inside of |this| must not mutate .
 668   void DoLookup(const base::TimeTicks& start_time,
 669                 const uint32 attempt_number) {
 670     AddressList results;
 671     int os_error = 0;
 672     // Running on the worker thread
 673     int error = params_.resolver_proc->Resolve(key_.hostname,
 674                                                key_.address_family,
 675                                                key_.host_resolver_flags,
 676                                                &results,
 677                                                &os_error);
 678
 679     // Fail the resolution if the result contains 127.0.53.53. See the comment
 680     // block of kIcanNameCollisionIp for details on why.
 681     for (const auto& it : results) {
 682       const IPAddressNumber& cur = it.address();
 683       if (cur.size() == arraysize(kIcanNameCollisionIp) &&
 684           0 == memcmp(&cur.front(), kIcanNameCollisionIp, cur.size())) {
 685         error = ERR_ICANN_NAME_COLLISION;
 686         break;
 687       }
 688     }
 689
 690     origin_loop_->PostTask(
 691         FROM_HERE,
 692         base::Bind(&ProcTask::OnLookupComplete, this, results, start_time,
 693                    attempt_number, error, os_error));
 694   }
 695
 696   // Makes next attempt if DoLookup() has not finished (runs on origin thread).
 697   void RetryIfNotComplete() {
 698     DCHECK(origin_loop_->BelongsToCurrentThread());
 699
 700     if (was_completed() || was_canceled())
 701       return;
 702
 703     params_.unresponsive_delay *= params_.retry_factor;
 704     StartLookupAttempt();
 705   }
 706
 707   // Callback for when DoLookup() completes (runs on origin thread).
 708   void OnLookupComplete(const AddressList& results,
 709                         const base::TimeTicks& start_time,
 710                         const uint32 attempt_number,
 711                         int error,
 712                         const int os_error) {
 713     DCHECK(origin_loop_->BelongsToCurrentThread());
 714     // If results are empty, we should return an error.
 715     bool empty_list_on_ok = (error == OK && results.empty());
 716     UMA_HISTOGRAM_BOOLEAN("DNS.EmptyAddressListAndNoError", empty_list_on_ok);
 717     if (empty_list_on_ok)
 718       error = ERR_NAME_NOT_RESOLVED;
 719
 720     bool was_retry_attempt = attempt_number > 1;
 721
 722     // Ideally the following code would be part of host_resolver_proc.cc,
 723     // however it isn't safe to call NetworkChangeNotifier from worker threads.
 724     // So we do it here on the IO thread instead.
 725     if (error != OK && NetworkChangeNotifier::IsOffline())
 726       error = ERR_INTERNET_DISCONNECTED;
 727
 728     // If this is the first attempt that is finishing later, then record data
 729     // for the first attempt. Won't contaminate with retry attempt's data.
 730     if (!was_retry_attempt)
 731       RecordPerformanceHistograms(start_time, error, os_error);
 732
 733     RecordAttemptHistograms(start_time, attempt_number, error, os_error);
 734
 735     if (was_canceled())
 736       return;
 737
 738     NetLog::ParametersCallback net_log_callback;
 739     if (error != OK) {
 740       net_log_callback = base::Bind(&NetLogProcTaskFailedCallback,
 741                                     attempt_number,
 742                                     error,
 743                                     os_error);
 744     } else {
 745       net_log_callback = NetLog::IntegerCallback("attempt_number",
 746                                                  attempt_number);
 747     }
 748     net_log_.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_ATTEMPT_FINISHED,
 749                       net_log_callback);
 750
 751     if (was_completed())
 752       return;
 753
 754     // Copy the results from the first worker thread that resolves the host.
 755     results_ = results;
 756     completed_attempt_number_ = attempt_number;
 757     completed_attempt_error_ = error;
 758
 759     if (was_retry_attempt) {
 760       // If retry attempt finishes before 1st attempt, then get stats on how
 761       // much time is saved by having spawned an extra attempt.
 762       retry_attempt_finished_time_ = base::TimeTicks::Now();
 763     }
 764
 765     if (error != OK) {
 766       net_log_callback = base::Bind(&NetLogProcTaskFailedCallback,
 767                                     0, error, os_error);
 768     } else {
 769       net_log_callback = results_.CreateNetLogCallback();
 770     }
 771     net_log_.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_PROC_TASK,
 772                       net_log_callback);
 773
 774     callback_.Run(error, results_);
 775   }
 776
 777   void RecordPerformanceHistograms(const base::TimeTicks& start_time,
 778                                    const int error,
 779                                    const int os_error) const {
 780     DCHECK(origin_loop_->BelongsToCurrentThread());
 781     enum Category {  // Used in UMA_HISTOGRAM_ENUMERATION.
 782       RESOLVE_SUCCESS,
 783       RESOLVE_FAIL,
 784       RESOLVE_SPECULATIVE_SUCCESS,
 785       RESOLVE_SPECULATIVE_FAIL,
 786       RESOLVE_MAX,  // Bounding value.
 787     };
 788     int category = RESOLVE_MAX;  // Illegal value for later DCHECK only.
 789
 790     base::TimeDelta duration = base::TimeTicks::Now() - start_time;
 791     if (error == OK) {
 792       if (had_non_speculative_request_) {
 793         category = RESOLVE_SUCCESS;
 794         DNS_HISTOGRAM("DNS.ResolveSuccess", duration);
 795       } else {
 796         category = RESOLVE_SPECULATIVE_SUCCESS;
 797         DNS_HISTOGRAM("DNS.ResolveSpeculativeSuccess", duration);
 798       }
 799
 800       // Log DNS lookups based on |address_family|. This will help us determine
 801       // if IPv4 or IPv4/6 lookups are faster or slower.
 802       switch(key_.address_family) {
 803         case ADDRESS_FAMILY_IPV4:
 804           DNS_HISTOGRAM("DNS.ResolveSuccess_FAMILY_IPV4", duration);
 805           break;
 806         case ADDRESS_FAMILY_IPV6:
 807           DNS_HISTOGRAM("DNS.ResolveSuccess_FAMILY_IPV6", duration);
 808           break;
 809         case ADDRESS_FAMILY_UNSPECIFIED:
 810           DNS_HISTOGRAM("DNS.ResolveSuccess_FAMILY_UNSPEC", duration);
 811           break;
 812       }
 813     } else {
 814       if (had_non_speculative_request_) {
 815         category = RESOLVE_FAIL;
 816         DNS_HISTOGRAM("DNS.ResolveFail", duration);
 817       } else {
 818         category = RESOLVE_SPECULATIVE_FAIL;
 819         DNS_HISTOGRAM("DNS.ResolveSpeculativeFail", duration);
 820       }
 821       // Log DNS lookups based on |address_family|. This will help us determine
 822       // if IPv4 or IPv4/6 lookups are faster or slower.
 823       switch(key_.address_family) {
 824         case ADDRESS_FAMILY_IPV4:
 825           DNS_HISTOGRAM("DNS.ResolveFail_FAMILY_IPV4", duration);
 826           break;
 827         case ADDRESS_FAMILY_IPV6:
 828           DNS_HISTOGRAM("DNS.ResolveFail_FAMILY_IPV6", duration);
 829           break;
 830         case ADDRESS_FAMILY_UNSPECIFIED:
 831           DNS_HISTOGRAM("DNS.ResolveFail_FAMILY_UNSPEC", duration);
 832           break;
 833       }
 834       UMA_HISTOGRAM_CUSTOM_ENUMERATION(kOSErrorsForGetAddrinfoHistogramName,
 835                                        std::abs(os_error),
 836                                        GetAllGetAddrinfoOSErrors());
 837     }
 838     DCHECK_LT(category, static_cast<int>(RESOLVE_MAX));  // Be sure it was set.
 839
 840     UMA_HISTOGRAM_ENUMERATION("DNS.ResolveCategory", category, RESOLVE_MAX);
 841   }
 842
 843   void RecordAttemptHistograms(const base::TimeTicks& start_time,
 844                                const uint32 attempt_number,
 845                                const int error,
 846                                const int os_error) const {
 847     DCHECK(origin_loop_->BelongsToCurrentThread());
 848     bool first_attempt_to_complete =
 849         completed_attempt_number_ == attempt_number;
 850     bool is_first_attempt = (attempt_number == 1);
 851
 852     if (first_attempt_to_complete) {
 853       // If this was first attempt to complete, then record the resolution
 854       // status of the attempt.
 855       if (completed_attempt_error_ == OK) {
 856         UMA_HISTOGRAM_ENUMERATION(
 857             "DNS.AttemptFirstSuccess", attempt_number, 100);
 858       } else {
 859         UMA_HISTOGRAM_ENUMERATION(
 860             "DNS.AttemptFirstFailure", attempt_number, 100);
 861       }
 862     }
 863
 864     if (error == OK)
 865       UMA_HISTOGRAM_ENUMERATION("DNS.AttemptSuccess", attempt_number, 100);
 866     else
 867       UMA_HISTOGRAM_ENUMERATION("DNS.AttemptFailure", attempt_number, 100);
 868
 869     // If first attempt didn't finish before retry attempt, then calculate stats
 870     // on how much time is saved by having spawned an extra attempt.
 871     if (!first_attempt_to_complete && is_first_attempt && !was_canceled()) {
 872       DNS_HISTOGRAM("DNS.AttemptTimeSavedByRetry",
 873                     base::TimeTicks::Now() - retry_attempt_finished_time_);
 874     }
 875
 876     if (was_canceled() || !first_attempt_to_complete) {
 877       // Count those attempts which completed after the job was already canceled
 878       // OR after the job was already completed by an earlier attempt (so in
 879       // effect).
 880       UMA_HISTOGRAM_ENUMERATION("DNS.AttemptDiscarded", attempt_number, 100);
 881
 882       // Record if job is canceled.
 883       if (was_canceled())
 884         UMA_HISTOGRAM_ENUMERATION("DNS.AttemptCancelled", attempt_number, 100);
 885     }
 886
 887     base::TimeDelta duration = base::TimeTicks::Now() - start_time;
 888     if (error == OK)
 889       DNS_HISTOGRAM("DNS.AttemptSuccessDuration", duration);
 890     else
 891       DNS_HISTOGRAM("DNS.AttemptFailDuration", duration);
 892   }
 893
 894   // Set on the origin thread, read on the worker thread.
 895   Key key_;
 896
 897   // Holds an owning reference to the HostResolverProc that we are going to use.
 898   // This may not be the current resolver procedure by the time we call
 899   // ResolveAddrInfo, but that's OK... we'll use it anyways, and the owning
 900   // reference ensures that it remains valid until we are done.
 901   ProcTaskParams params_;
 902
 903   // The listener to the results of this ProcTask.
 904   Callback callback_;
 905
 906   // Used to post ourselves onto the origin thread.
 907   scoped_refptr<base::MessageLoopProxy> origin_loop_;
 908
 909   // Keeps track of the number of attempts we have made so far to resolve the
 910   // host. Whenever we start an attempt to resolve the host, we increase this
 911   // number.
 912   uint32 attempt_number_;
 913
 914   // The index of the attempt which finished first (or 0 if the job is still in
 915   // progress).
 916   uint32 completed_attempt_number_;
 917
 918   // The result (a net error code) from the first attempt to complete.
 919   int completed_attempt_error_;
 920
 921   // The time when retry attempt was finished.
 922   base::TimeTicks retry_attempt_finished_time_;
 923
 924   // True if a non-speculative request was ever attached to this job
 925   // (regardless of whether or not it was later canceled.
 926   // This boolean is used for histogramming the duration of jobs used to
 927   // service non-speculative requests.
 928   bool had_non_speculative_request_;
 929
 930   AddressList results_;
 931
 932   BoundNetLog net_log_;
 933
 934   DISALLOW_COPY_AND_ASSIGN(ProcTask);
 935 };
 936
 937 //-----------------------------------------------------------------------------
 938
 939 // Wraps a call to HaveOnlyLoopbackAddresses to be executed on the WorkerPool as
 940 // it takes 40-100ms and should not block initialization.
 941 class HostResolverImpl::LoopbackProbeJob {
 942  public:
 943   explicit LoopbackProbeJob(const base::WeakPtr<HostResolverImpl>& resolver)
 944       : resolver_(resolver),
 945         result_(false) {
 946     DCHECK(resolver.get());
 947     const bool kIsSlow = true;
 948     base::WorkerPool::PostTaskAndReply(
 949         FROM_HERE,
 950         base::Bind(&LoopbackProbeJob::DoProbe, base::Unretained(this)),
 951         base::Bind(&LoopbackProbeJob::OnProbeComplete, base::Owned(this)),
 952         kIsSlow);
 953   }
 954
 955   virtual ~LoopbackProbeJob() {}
 956
 957  private:
 958   // Runs on worker thread.
 959   void DoProbe() {
 960     result_ = HaveOnlyLoopbackAddresses();
 961   }
 962
 963   void OnProbeComplete() {
 964     if (!resolver_.get())
 965       return;
 966     resolver_->SetHaveOnlyLoopbackAddresses(result_);
 967   }
 968
 969   // Used/set only on origin thread.
 970   base::WeakPtr<HostResolverImpl> resolver_;
 971
 972   bool result_;
 973
 974   DISALLOW_COPY_AND_ASSIGN(LoopbackProbeJob);
 975 };
 976
 977 //-----------------------------------------------------------------------------
 978
 979 // Resolves the hostname using DnsTransaction.
 980 // TODO(szym): This could be moved to separate source file as well.
 981 class HostResolverImpl::DnsTask : public base::SupportsWeakPtr<DnsTask> {
 982  public:
 983   class Delegate {
 984    public:
 985     virtual void OnDnsTaskComplete(base::TimeTicks start_time,
 986                                    int net_error,
 987                                    const AddressList& addr_list,
 988                                    base::TimeDelta ttl) = 0;
 989
 990     // Called when the first of two jobs succeeds.  If the first completed
 991     // transaction fails, this is not called.  Also not called when the DnsTask
 992     // only needs to run one transaction.
 993     virtual void OnFirstDnsTransactionComplete() = 0;
 994
 995    protected:
 996     Delegate() {}
 997     virtual ~Delegate() {}
 998   };
 999
1000   DnsTask(DnsClient* client,
1001           const Key& key,
1002           Delegate* delegate,
1003           const BoundNetLog& job_net_log)
1004       : client_(client),
1005         key_(key),
1006         delegate_(delegate),
1007         net_log_(job_net_log),
1008         num_completed_transactions_(0),
1009         task_start_time_(base::TimeTicks::Now()) {
1010     DCHECK(client);
1011     DCHECK(delegate_);
1012   }
1013
1014   bool needs_two_transactions() const {
1015     return key_.address_family == ADDRESS_FAMILY_UNSPECIFIED;
1016   }
1017
1018   bool needs_another_transaction() const {
1019     return needs_two_transactions() && !transaction_aaaa_;
1020   }
1021
1022   void StartFirstTransaction() {
1023     DCHECK_EQ(0u, num_completed_transactions_);
1024     net_log_.BeginEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_DNS_TASK);
1025     if (key_.address_family == ADDRESS_FAMILY_IPV6) {
1026       StartAAAA();
1027     } else {
1028       StartA();
1029     }
1030   }
1031
1032   void StartSecondTransaction() {
1033     DCHECK(needs_two_transactions());
1034     StartAAAA();
1035   }
1036
1037  private:
1038   void StartA() {
1039     DCHECK(!transaction_a_);
1040     DCHECK_NE(ADDRESS_FAMILY_IPV6, key_.address_family);
1041     transaction_a_ = CreateTransaction(ADDRESS_FAMILY_IPV4);
1042     transaction_a_->Start();
1043   }
1044
1045   void StartAAAA() {
1046     DCHECK(!transaction_aaaa_);
1047     DCHECK_NE(ADDRESS_FAMILY_IPV4, key_.address_family);
1048     transaction_aaaa_ = CreateTransaction(ADDRESS_FAMILY_IPV6);
1049     transaction_aaaa_->Start();
1050   }
1051
1052   scoped_ptr<DnsTransaction> CreateTransaction(AddressFamily family) {
1053     DCHECK_NE(ADDRESS_FAMILY_UNSPECIFIED, family);
1054     return client_->GetTransactionFactory()->CreateTransaction(
1055         key_.hostname,
1056         family == ADDRESS_FAMILY_IPV6 ? dns_protocol::kTypeAAAA :
1057                                         dns_protocol::kTypeA,
1058         base::Bind(&DnsTask::OnTransactionComplete, base::Unretained(this),
1059                    base::TimeTicks::Now()),
1060         net_log_);
1061   }
1062
1063   void OnTransactionComplete(const base::TimeTicks& start_time,
1064                              DnsTransaction* transaction,
1065                              int net_error,
1066                              const DnsResponse* response) {
1067     DCHECK(transaction);
1068     base::TimeDelta duration = base::TimeTicks::Now() - start_time;
1069     if (net_error != OK) {
1070       DNS_HISTOGRAM("AsyncDNS.TransactionFailure", duration);
1071       OnFailure(net_error, DnsResponse::DNS_PARSE_OK);
1072       return;
1073     }
1074
1075     DNS_HISTOGRAM("AsyncDNS.TransactionSuccess", duration);
1076     switch (transaction->GetType()) {
1077       case dns_protocol::kTypeA:
1078         DNS_HISTOGRAM("AsyncDNS.TransactionSuccess_A", duration);
1079         break;
1080       case dns_protocol::kTypeAAAA:
1081         DNS_HISTOGRAM("AsyncDNS.TransactionSuccess_AAAA", duration);
1082         break;
1083     }
1084
1085     AddressList addr_list;
1086     base::TimeDelta ttl;
1087     DnsResponse::Result result = response->ParseToAddressList(&addr_list, &ttl);
1088     UMA_HISTOGRAM_ENUMERATION("AsyncDNS.ParseToAddressList",
1089                               result,
1090                               DnsResponse::DNS_PARSE_RESULT_MAX);
1091     if (result != DnsResponse::DNS_PARSE_OK) {
1092       // Fail even if the other query succeeds.
1093       OnFailure(ERR_DNS_MALFORMED_RESPONSE, result);
1094       return;
1095     }
1096
1097     ++num_completed_transactions_;
1098     if (num_completed_transactions_ == 1) {
1099       ttl_ = ttl;
1100     } else {
1101       ttl_ = std::min(ttl_, ttl);
1102     }
1103
1104     if (transaction->GetType() == dns_protocol::kTypeA) {
1105       DCHECK_EQ(transaction_a_.get(), transaction);
1106       // Place IPv4 addresses after IPv6.
1107       addr_list_.insert(addr_list_.end(), addr_list.begin(), addr_list.end());
1108     } else {
1109       DCHECK_EQ(transaction_aaaa_.get(), transaction);
1110       // Place IPv6 addresses before IPv4.
1111       addr_list_.insert(addr_list_.begin(), addr_list.begin(), addr_list.end());
1112     }
1113
1114     if (needs_two_transactions() && num_completed_transactions_ == 1) {
1115       // No need to repeat the suffix search.
1116       key_.hostname = transaction->GetHostname();
1117       delegate_->OnFirstDnsTransactionComplete();
1118       return;
1119     }
1120
1121     if (addr_list_.empty()) {
1122       // TODO(szym): Don't fallback to ProcTask in this case.
1123       OnFailure(ERR_NAME_NOT_RESOLVED, DnsResponse::DNS_PARSE_OK);
1124       return;
1125     }
1126
1127     // If there are multiple addresses, and at least one is IPv6, need to sort
1128     // them.  Note that IPv6 addresses are always put before IPv4 ones, so it's
1129     // sufficient to just check the family of the first address.
1130     if (addr_list_.size() > 1 &&
1131         addr_list_[0].GetFamily() == ADDRESS_FAMILY_IPV6) {
1132       // Sort addresses if needed.  Sort could complete synchronously.
1133       client_->GetAddressSorter()->Sort(
1134           addr_list_,
1135           base::Bind(&DnsTask::OnSortComplete,
1136                      AsWeakPtr(),
1137                      base::TimeTicks::Now()));
1138     } else {
1139       OnSuccess(addr_list_);
1140     }
1141   }
1142
1143   void OnSortComplete(base::TimeTicks start_time,
1144                       bool success,
1145                       const AddressList& addr_list) {
1146     if (!success) {
1147       DNS_HISTOGRAM("AsyncDNS.SortFailure",
1148                     base::TimeTicks::Now() - start_time);
1149       OnFailure(ERR_DNS_SORT_ERROR, DnsResponse::DNS_PARSE_OK);
1150       return;
1151     }
1152
1153     DNS_HISTOGRAM("AsyncDNS.SortSuccess",
1154                   base::TimeTicks::Now() - start_time);
1155
1156     // AddressSorter prunes unusable destinations.
1157     if (addr_list.empty()) {
1158       LOG(WARNING) << "Address list empty after RFC3484 sort";
1159       OnFailure(ERR_NAME_NOT_RESOLVED, DnsResponse::DNS_PARSE_OK);
1160       return;
1161     }
1162
1163     OnSuccess(addr_list);
1164   }
1165
1166   void OnFailure(int net_error, DnsResponse::Result result) {
1167     DCHECK_NE(OK, net_error);
1168     net_log_.EndEvent(
1169         NetLog::TYPE_HOST_RESOLVER_IMPL_DNS_TASK,
1170         base::Bind(&NetLogDnsTaskFailedCallback, net_error, result));
1171     delegate_->OnDnsTaskComplete(task_start_time_, net_error, AddressList(),
1172                                  base::TimeDelta());
1173   }
1174
1175   void OnSuccess(const AddressList& addr_list) {
1176     net_log_.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_DNS_TASK,
1177                       addr_list.CreateNetLogCallback());
1178     delegate_->OnDnsTaskComplete(task_start_time_, OK, addr_list, ttl_);
1179   }
1180
1181   DnsClient* client_;
1182   Key key_;
1183
1184   // The listener to the results of this DnsTask.
1185   Delegate* delegate_;
1186   const BoundNetLog net_log_;
1187
1188   scoped_ptr<DnsTransaction> transaction_a_;
1189   scoped_ptr<DnsTransaction> transaction_aaaa_;
1190
1191   unsigned num_completed_transactions_;
1192
1193   // These are updated as each transaction completes.
1194   base::TimeDelta ttl_;
1195   // IPv6 addresses must appear first in the list.
1196   AddressList addr_list_;
1197
1198   base::TimeTicks task_start_time_;
1199
1200   DISALLOW_COPY_AND_ASSIGN(DnsTask);
1201 };
1202
1203 //-----------------------------------------------------------------------------
1204
1205 // Aggregates all Requests for the same Key. Dispatched via PriorityDispatch.
1206 class HostResolverImpl::Job : public PrioritizedDispatcher::Job,
1207                               public HostResolverImpl::DnsTask::Delegate {
1208  public:
1209   // Creates new job for |key| where |request_net_log| is bound to the
1210   // request that spawned it.
1211   Job(const base::WeakPtr<HostResolverImpl>& resolver,
1212       const Key& key,
1213       RequestPriority priority,
1214       const BoundNetLog& source_net_log)
1215       : resolver_(resolver),
1216         key_(key),
1217         priority_tracker_(priority),
1218         had_non_speculative_request_(false),
1219         had_dns_config_(false),
1220         num_occupied_job_slots_(0),
1221         dns_task_error_(OK),
1222         creation_time_(base::TimeTicks::Now()),
1223         priority_change_time_(creation_time_),
1224         net_log_(BoundNetLog::Make(source_net_log.net_log(),
1225                                    NetLog::SOURCE_HOST_RESOLVER_IMPL_JOB)) {
1226     source_net_log.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_CREATE_JOB);
1227
1228     net_log_.BeginEvent(
1229         NetLog::TYPE_HOST_RESOLVER_IMPL_JOB,
1230         base::Bind(&NetLogJobCreationCallback,
1231                    source_net_log.source(),
1232                    &key_.hostname));
1233   }
1234
1235   ~Job() override {
1236     if (is_running()) {
1237       // |resolver_| was destroyed with this Job still in flight.
1238       // Clean-up, record in the log, but don't run any callbacks.
1239       if (is_proc_running()) {
1240         proc_task_->Cancel();
1241         proc_task_ = NULL;
1242       }
1243       // Clean up now for nice NetLog.
1244       KillDnsTask();
1245       net_log_.EndEventWithNetErrorCode(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB,
1246                                         ERR_ABORTED);
1247     } else if (is_queued()) {
1248       // |resolver_| was destroyed without running this Job.
1249       // TODO(szym): is there any benefit in having this distinction?
1250       net_log_.AddEvent(NetLog::TYPE_CANCELLED);
1251       net_log_.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB);
1252     }
1253     // else CompleteRequests logged EndEvent.
1254
1255     // Log any remaining Requests as cancelled.
1256     for (RequestsList::const_iterator it = requests_.begin();
1257          it != requests_.end(); ++it) {
1258       Request* req = *it;
1259       if (req->was_canceled())
1260         continue;
1261       DCHECK_EQ(this, req->job());
1262       LogCancelRequest(req->source_net_log(), req->info());
1263     }
1264   }
1265
1266   // Add this job to the dispatcher.  If "at_head" is true, adds at the front
1267   // of the queue.
1268   void Schedule(bool at_head) {
1269     DCHECK(!is_queued());
1270     PrioritizedDispatcher::Handle handle;
1271     if (!at_head) {
1272       handle = resolver_->dispatcher_->Add(this, priority());
1273     } else {
1274       handle = resolver_->dispatcher_->AddAtHead(this, priority());
1275     }
1276     // The dispatcher could have started |this| in the above call to Add, which
1277     // could have called Schedule again. In that case |handle| will be null,
1278     // but |handle_| may have been set by the other nested call to Schedule.
1279     if (!handle.is_null()) {
1280       DCHECK(handle_.is_null());
1281       handle_ = handle;
1282     }
1283   }
1284
1285   void AddRequest(scoped_ptr<Request> req) {
1286     // .localhost queries are redirected to "localhost." to make sure
1287     // that they are never sent out on the network, per RFC 6761.
1288     if (IsLocalhostTLD(req->info().hostname())) {
1289       DCHECK_EQ(key_.hostname, kLocalhost);
1290     } else {
1291       DCHECK_EQ(key_.hostname, req->info().hostname());
1292     }
1293
1294     req->set_job(this);
1295     priority_tracker_.Add(req->priority());
1296
1297     req->source_net_log().AddEvent(
1298         NetLog::TYPE_HOST_RESOLVER_IMPL_JOB_ATTACH,
1299         net_log_.source().ToEventParametersCallback());
1300
1301     net_log_.AddEvent(
1302         NetLog::TYPE_HOST_RESOLVER_IMPL_JOB_REQUEST_ATTACH,
1303         base::Bind(&NetLogJobAttachCallback,
1304                    req->source_net_log().source(),
1305                    priority()));
1306
1307     // TODO(szym): Check if this is still needed.
1308     if (!req->info().is_speculative()) {
1309       had_non_speculative_request_ = true;
1310       if (proc_task_.get())
1311         proc_task_->set_had_non_speculative_request();
1312     }
1313
1314     requests_.push_back(req.release());
1315
1316     UpdatePriority();
1317   }
1318
1319   // Marks |req| as cancelled. If it was the last active Request, also finishes
1320   // this Job, marking it as cancelled, and deletes it.
1321   void CancelRequest(Request* req) {
1322     DCHECK_EQ(key_.hostname, req->info().hostname());
1323     DCHECK(!req->was_canceled());
1324
1325     // Don't remove it from |requests_| just mark it canceled.
1326     req->MarkAsCanceled();
1327     LogCancelRequest(req->source_net_log(), req->info());
1328
1329     priority_tracker_.Remove(req->priority());
1330     net_log_.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB_REQUEST_DETACH,
1331                       base::Bind(&NetLogJobAttachCallback,
1332                                  req->source_net_log().source(),
1333                                  priority()));
1334
1335     if (num_active_requests() > 0) {
1336       UpdatePriority();
1337     } else {
1338       // If we were called from a Request's callback within CompleteRequests,
1339       // that Request could not have been cancelled, so num_active_requests()
1340       // could not be 0. Therefore, we are not in CompleteRequests().
1341       CompleteRequestsWithError(OK /* cancelled */);
1342     }
1343   }
1344
1345   // Called from AbortAllInProgressJobs. Completes all requests and destroys
1346   // the job. This currently assumes the abort is due to a network change.
1347   void Abort() {
1348     DCHECK(is_running());
1349     CompleteRequestsWithError(ERR_NETWORK_CHANGED);
1350   }
1351
1352   // If DnsTask present, abort it and fall back to ProcTask.
1353   void AbortDnsTask() {
1354     if (dns_task_) {
1355       KillDnsTask();
1356       dns_task_error_ = OK;
1357       StartProcTask();
1358     }
1359   }
1360
1361   // Called by HostResolverImpl when this job is evicted due to queue overflow.
1362   // Completes all requests and destroys the job.
1363   void OnEvicted() {
1364     DCHECK(!is_running());
1365     DCHECK(is_queued());
1366     handle_.Reset();
1367
1368     net_log_.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB_EVICTED);
1369
1370     // This signals to CompleteRequests that this job never ran.
1371     CompleteRequestsWithError(ERR_HOST_RESOLVER_QUEUE_TOO_LARGE);
1372   }
1373
1374   // Attempts to serve the job from HOSTS. Returns true if succeeded and
1375   // this Job was destroyed.
1376   bool ServeFromHosts() {
1377     DCHECK_GT(num_active_requests(), 0u);
1378     AddressList addr_list;
1379     if (resolver_->ServeFromHosts(key(),
1380                                   requests_.front()->info(),
1381                                   &addr_list)) {
1382       // This will destroy the Job.
1383       CompleteRequests(
1384           HostCache::Entry(OK, MakeAddressListForRequest(addr_list)),
1385           base::TimeDelta());
1386       return true;
1387     }
1388     return false;
1389   }
1390
1391   const Key key() const {
1392     return key_;
1393   }
1394
1395   bool is_queued() const {
1396     return !handle_.is_null();
1397   }
1398
1399   bool is_running() const {
1400     return is_dns_running() || is_proc_running();
1401   }
1402
1403  private:
1404   void KillDnsTask() {
1405     if (dns_task_) {
1406       ReduceToOneJobSlot();
1407       dns_task_.reset();
1408     }
1409   }
1410
1411   // Reduce the number of job slots occupied and queued in the dispatcher
1412   // to one. If the second Job slot is queued in the dispatcher, cancels the
1413   // queued job. Otherwise, the second Job has been started by the
1414   // PrioritizedDispatcher, so signals it is complete.
1415   void ReduceToOneJobSlot() {
1416     DCHECK_GE(num_occupied_job_slots_, 1u);
1417     if (is_queued()) {
1418       resolver_->dispatcher_->Cancel(handle_);
1419       handle_.Reset();
1420     } else if (num_occupied_job_slots_ > 1) {
1421       resolver_->dispatcher_->OnJobFinished();
1422       --num_occupied_job_slots_;
1423     }
1424     DCHECK_EQ(1u, num_occupied_job_slots_);
1425   }
1426
1427   void UpdatePriority() {
1428     if (is_queued()) {
1429       if (priority() != static_cast<RequestPriority>(handle_.priority()))
1430         priority_change_time_ = base::TimeTicks::Now();
1431       handle_ = resolver_->dispatcher_->ChangePriority(handle_, priority());
1432     }
1433   }
1434
1435   AddressList MakeAddressListForRequest(const AddressList& list) const {
1436     if (requests_.empty())
1437       return list;
1438     return AddressList::CopyWithPort(list, requests_.front()->info().port());
1439   }
1440
1441   // PriorityDispatch::Job:
1442   void Start() override {
1443     DCHECK_LE(num_occupied_job_slots_, 1u);
1444
1445     handle_.Reset();
1446     ++num_occupied_job_slots_;
1447
1448     if (num_occupied_job_slots_ == 2) {
1449       StartSecondDnsTransaction();
1450       return;
1451     }
1452
1453     DCHECK(!is_running());
1454
1455     net_log_.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB_STARTED);
1456
1457     had_dns_config_ = resolver_->HaveDnsConfig();
1458
1459     base::TimeTicks now = base::TimeTicks::Now();
1460     base::TimeDelta queue_time = now - creation_time_;
1461     base::TimeDelta queue_time_after_change = now - priority_change_time_;
1462
1463     if (had_dns_config_) {
1464       DNS_HISTOGRAM_BY_PRIORITY("AsyncDNS.JobQueueTime", priority(),
1465                                 queue_time);
1466       DNS_HISTOGRAM_BY_PRIORITY("AsyncDNS.JobQueueTimeAfterChange", priority(),
1467                                 queue_time_after_change);
1468     } else {
1469       DNS_HISTOGRAM_BY_PRIORITY("DNS.JobQueueTime", priority(), queue_time);
1470       DNS_HISTOGRAM_BY_PRIORITY("DNS.JobQueueTimeAfterChange", priority(),
1471                                 queue_time_after_change);
1472     }
1473
1474     bool system_only =
1475         (key_.host_resolver_flags & HOST_RESOLVER_SYSTEM_ONLY) != 0;
1476
1477     // Caution: Job::Start must not complete synchronously.
1478     if (!system_only && had_dns_config_ &&
1479         !ResemblesMulticastDNSName(key_.hostname)) {
1480       StartDnsTask();
1481     } else {
1482       StartProcTask();
1483     }
1484   }
1485
1486   // TODO(szym): Since DnsTransaction does not consume threads, we can increase
1487   // the limits on |dispatcher_|. But in order to keep the number of WorkerPool
1488   // threads low, we will need to use an "inner" PrioritizedDispatcher with
1489   // tighter limits.
1490   void StartProcTask() {
1491     DCHECK(!is_dns_running());
1492     proc_task_ = new ProcTask(
1493         key_,
1494         resolver_->proc_params_,
1495         base::Bind(&Job::OnProcTaskComplete, base::Unretained(this),
1496                    base::TimeTicks::Now()),
1497         net_log_);
1498
1499     if (had_non_speculative_request_)
1500       proc_task_->set_had_non_speculative_request();
1501     // Start() could be called from within Resolve(), hence it must NOT directly
1502     // call OnProcTaskComplete, for example, on synchronous failure.
1503     proc_task_->Start();
1504   }
1505
1506   // Called by ProcTask when it completes.
1507   void OnProcTaskComplete(base::TimeTicks start_time,
1508                           int net_error,
1509                           const AddressList& addr_list) {
1510     DCHECK(is_proc_running());
1511
1512     if (!resolver_->resolved_known_ipv6_hostname_ &&
1513         net_error == OK &&
1514         key_.address_family == ADDRESS_FAMILY_UNSPECIFIED) {
1515       if (key_.hostname == "www.google.com") {
1516         resolver_->resolved_known_ipv6_hostname_ = true;
1517         bool got_ipv6_address = false;
1518         for (size_t i = 0; i < addr_list.size(); ++i) {
1519           if (addr_list[i].GetFamily() == ADDRESS_FAMILY_IPV6) {
1520             got_ipv6_address = true;
1521             break;
1522           }
1523         }
1524         UMA_HISTOGRAM_BOOLEAN("Net.UnspecResolvedIPv6", got_ipv6_address);
1525       }
1526     }
1527
1528     if (dns_task_error_ != OK) {
1529       base::TimeDelta duration = base::TimeTicks::Now() - start_time;
1530       if (net_error == OK) {
1531         DNS_HISTOGRAM("AsyncDNS.FallbackSuccess", duration);
1532         if ((dns_task_error_ == ERR_NAME_NOT_RESOLVED) &&
1533             ResemblesNetBIOSName(key_.hostname)) {
1534           UmaAsyncDnsResolveStatus(RESOLVE_STATUS_SUSPECT_NETBIOS);
1535         } else {
1536           UmaAsyncDnsResolveStatus(RESOLVE_STATUS_PROC_SUCCESS);
1537         }
1538         UMA_HISTOGRAM_CUSTOM_ENUMERATION("AsyncDNS.ResolveError",
1539                                          std::abs(dns_task_error_),
1540                                          GetAllErrorCodesForUma());
1541         resolver_->OnDnsTaskResolve(dns_task_error_);
1542       } else {
1543         DNS_HISTOGRAM("AsyncDNS.FallbackFail", duration);
1544         UmaAsyncDnsResolveStatus(RESOLVE_STATUS_FAIL);
1545       }
1546     }
1547
1548     base::TimeDelta ttl =
1549         base::TimeDelta::FromSeconds(kNegativeCacheEntryTTLSeconds);
1550     if (net_error == OK)
1551       ttl = base::TimeDelta::FromSeconds(kCacheEntryTTLSeconds);
1552
1553     // Don't store the |ttl| in cache since it's not obtained from the server.
1554     CompleteRequests(
1555         HostCache::Entry(net_error, MakeAddressListForRequest(addr_list)),
1556         ttl);
1557   }
1558
1559   void StartDnsTask() {
1560     DCHECK(resolver_->HaveDnsConfig());
1561     dns_task_.reset(new DnsTask(resolver_->dns_client_.get(), key_, this,
1562                                 net_log_));
1563
1564     dns_task_->StartFirstTransaction();
1565     // Schedule a second transaction, if needed.
1566     if (dns_task_->needs_two_transactions())
1567       Schedule(true);
1568   }
1569
1570   void StartSecondDnsTransaction() {
1571     DCHECK(dns_task_->needs_two_transactions());
1572     dns_task_->StartSecondTransaction();
1573   }
1574
1575   // Called if DnsTask fails. It is posted from StartDnsTask, so Job may be
1576   // deleted before this callback. In this case dns_task is deleted as well,
1577   // so we use it as indicator whether Job is still valid.
1578   void OnDnsTaskFailure(const base::WeakPtr<DnsTask>& dns_task,
1579                         base::TimeDelta duration,
1580                         int net_error) {
1581     DNS_HISTOGRAM("AsyncDNS.ResolveFail", duration);
1582
1583     if (dns_task == NULL)
1584       return;
1585
1586     dns_task_error_ = net_error;
1587
1588     // TODO(szym): Run ServeFromHosts now if nsswitch.conf says so.
1589     // http://crbug.com/117655
1590
1591     // TODO(szym): Some net errors indicate lack of connectivity. Starting
1592     // ProcTask in that case is a waste of time.
1593     if (resolver_->fallback_to_proctask_) {
1594       KillDnsTask();
1595       StartProcTask();
1596     } else {
1597       UmaAsyncDnsResolveStatus(RESOLVE_STATUS_FAIL);
1598       CompleteRequestsWithError(net_error);
1599     }
1600   }
1601
1602
1603   // HostResolverImpl::DnsTask::Delegate implementation:
1604
1605   void OnDnsTaskComplete(base::TimeTicks start_time,
1606                          int net_error,
1607                          const AddressList& addr_list,
1608                          base::TimeDelta ttl) override {
1609     DCHECK(is_dns_running());
1610
1611     base::TimeDelta duration = base::TimeTicks::Now() - start_time;
1612     if (net_error != OK) {
1613       OnDnsTaskFailure(dns_task_->AsWeakPtr(), duration, net_error);
1614       return;
1615     }
1616     DNS_HISTOGRAM("AsyncDNS.ResolveSuccess", duration);
1617     // Log DNS lookups based on |address_family|.
1618     switch(key_.address_family) {
1619       case ADDRESS_FAMILY_IPV4:
1620         DNS_HISTOGRAM("AsyncDNS.ResolveSuccess_FAMILY_IPV4", duration);
1621         break;
1622       case ADDRESS_FAMILY_IPV6:
1623         DNS_HISTOGRAM("AsyncDNS.ResolveSuccess_FAMILY_IPV6", duration);
1624         break;
1625       case ADDRESS_FAMILY_UNSPECIFIED:
1626         DNS_HISTOGRAM("AsyncDNS.ResolveSuccess_FAMILY_UNSPEC", duration);
1627         break;
1628     }
1629
1630     UmaAsyncDnsResolveStatus(RESOLVE_STATUS_DNS_SUCCESS);
1631     RecordTTL(ttl);
1632
1633     resolver_->OnDnsTaskResolve(OK);
1634
1635     base::TimeDelta bounded_ttl =
1636         std::max(ttl, base::TimeDelta::FromSeconds(kMinimumTTLSeconds));
1637
1638     CompleteRequests(
1639         HostCache::Entry(net_error, MakeAddressListForRequest(addr_list), ttl),
1640         bounded_ttl);
1641   }
1642
1643   void OnFirstDnsTransactionComplete() override {
1644     DCHECK(dns_task_->needs_two_transactions());
1645     DCHECK_EQ(dns_task_->needs_another_transaction(), is_queued());
1646     // No longer need to occupy two dispatcher slots.
1647     ReduceToOneJobSlot();
1648
1649     // We already have a job slot at the dispatcher, so if the second
1650     // transaction hasn't started, reuse it now instead of waiting in the queue
1651     // for the second slot.
1652     if (dns_task_->needs_another_transaction())
1653       dns_task_->StartSecondTransaction();
1654   }
1655
1656   // Performs Job's last rites. Completes all Requests. Deletes this.
1657   void CompleteRequests(const HostCache::Entry& entry,
1658                         base::TimeDelta ttl) {
1659     CHECK(resolver_.get());
1660
1661     // This job must be removed from resolver's |jobs_| now to make room for a
1662     // new job with the same key in case one of the OnComplete callbacks decides
1663     // to spawn one. Consequently, the job deletes itself when CompleteRequests
1664     // is done.
1665     scoped_ptr<Job> self_deleter(this);
1666
1667     resolver_->RemoveJob(this);
1668
1669     if (is_running()) {
1670       if (is_proc_running()) {
1671         DCHECK(!is_queued());
1672         proc_task_->Cancel();
1673         proc_task_ = NULL;
1674       }
1675       KillDnsTask();
1676
1677       // Signal dispatcher that a slot has opened.
1678       resolver_->dispatcher_->OnJobFinished();
1679     } else if (is_queued()) {
1680       resolver_->dispatcher_->Cancel(handle_);
1681       handle_.Reset();
1682     }
1683
1684     if (num_active_requests() == 0) {
1685       net_log_.AddEvent(NetLog::TYPE_CANCELLED);
1686       net_log_.EndEventWithNetErrorCode(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB,
1687                                         OK);
1688       return;
1689     }
1690
1691     net_log_.EndEventWithNetErrorCode(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB,
1692                                       entry.error);
1693
1694     DCHECK(!requests_.empty());
1695
1696     if (entry.error == OK) {
1697       // Record this histogram here, when we know the system has a valid DNS
1698       // configuration.
1699       UMA_HISTOGRAM_BOOLEAN("AsyncDNS.HaveDnsConfig",
1700                             resolver_->received_dns_config_);
1701     }
1702
1703     bool did_complete = (entry.error != ERR_NETWORK_CHANGED) &&
1704                         (entry.error != ERR_HOST_RESOLVER_QUEUE_TOO_LARGE);
1705     if (did_complete)
1706       resolver_->CacheResult(key_, entry, ttl);
1707
1708     // Complete all of the requests that were attached to the job.
1709     for (RequestsList::const_iterator it = requests_.begin();
1710          it != requests_.end(); ++it) {
1711       Request* req = *it;
1712
1713       if (req->was_canceled())
1714         continue;
1715
1716       DCHECK_EQ(this, req->job());
1717       // Update the net log and notify registered observers.
1718       LogFinishRequest(req->source_net_log(), req->info(), entry.error);
1719       if (did_complete) {
1720         // Record effective total time from creation to completion.
1721         RecordTotalTime(had_dns_config_, req->info().is_speculative(),
1722                         base::TimeTicks::Now() - req->request_time());
1723       }
1724       req->OnComplete(entry.error, entry.addrlist);
1725
1726       // Check if the resolver was destroyed as a result of running the
1727       // callback. If it was, we could continue, but we choose to bail.
1728       if (!resolver_.get())
1729         return;
1730     }
1731   }
1732
1733   // Convenience wrapper for CompleteRequests in case of failure.
1734   void CompleteRequestsWithError(int net_error) {
1735     CompleteRequests(HostCache::Entry(net_error, AddressList()),
1736                      base::TimeDelta());
1737   }
1738
1739   RequestPriority priority() const {
1740     return priority_tracker_.highest_priority();
1741   }
1742
1743   // Number of non-canceled requests in |requests_|.
1744   size_t num_active_requests() const {
1745     return priority_tracker_.total_count();
1746   }
1747
1748   bool is_dns_running() const {
1749     return dns_task_.get() != NULL;
1750   }
1751
1752   bool is_proc_running() const {
1753     return proc_task_.get() != NULL;
1754   }
1755
1756   base::WeakPtr<HostResolverImpl> resolver_;
1757
1758   Key key_;
1759
1760   // Tracks the highest priority across |requests_|.
1761   PriorityTracker priority_tracker_;
1762
1763   bool had_non_speculative_request_;
1764
1765   // Distinguishes measurements taken while DnsClient was fully configured.
1766   bool had_dns_config_;
1767
1768   // Number of slots occupied by this Job in resolver's PrioritizedDispatcher.
1769   unsigned num_occupied_job_slots_;
1770
1771   // Result of DnsTask.
1772   int dns_task_error_;
1773
1774   const base::TimeTicks creation_time_;
1775   base::TimeTicks priority_change_time_;
1776
1777   BoundNetLog net_log_;
1778
1779   // Resolves the host using a HostResolverProc.
1780   scoped_refptr<ProcTask> proc_task_;
1781
1782   // Resolves the host using a DnsTransaction.
1783   scoped_ptr<DnsTask> dns_task_;
1784
1785   // All Requests waiting for the result of this Job. Some can be canceled.
1786   RequestsList requests_;
1787
1788   // A handle used in |HostResolverImpl::dispatcher_|.
1789   PrioritizedDispatcher::Handle handle_;
1790 };
1791
1792 //-----------------------------------------------------------------------------
1793
1794 HostResolverImpl::ProcTaskParams::ProcTaskParams(
1795     HostResolverProc* resolver_proc,
1796     size_t max_retry_attempts)
1797     : resolver_proc(resolver_proc),
1798       max_retry_attempts(max_retry_attempts),
1799       unresponsive_delay(base::TimeDelta::FromMilliseconds(6000)),
1800       retry_factor(2) {
1801   // Maximum of 4 retry attempts for host resolution.
1802   static const size_t kDefaultMaxRetryAttempts = 4u;
1803   if (max_retry_attempts == HostResolver::kDefaultRetryAttempts)
1804     max_retry_attempts = kDefaultMaxRetryAttempts;
1805 }
1806
1807 HostResolverImpl::ProcTaskParams::~ProcTaskParams() {}
1808
1809 HostResolverImpl::HostResolverImpl(const Options& options, NetLog* net_log)
1810     : max_queued_jobs_(0),
1811       proc_params_(NULL, options.max_retry_attempts),
1812       net_log_(net_log),
1813       default_address_family_(ADDRESS_FAMILY_UNSPECIFIED),
1814       received_dns_config_(false),
1815       num_dns_failures_(0),
1816       probe_ipv6_support_(true),
1817       use_local_ipv6_(false),
1818       resolved_known_ipv6_hostname_(false),
1819       additional_resolver_flags_(0),
1820       fallback_to_proctask_(true),
1821       weak_ptr_factory_(this),
1822       probe_weak_ptr_factory_(this) {
1823   if (options.enable_caching)
1824     cache_ = HostCache::CreateDefaultCache();
1825
1826   PrioritizedDispatcher::Limits job_limits = options.GetDispatcherLimits();
1827   dispatcher_.reset(new PrioritizedDispatcher(job_limits));
1828   max_queued_jobs_ = job_limits.total_jobs * 100u;
1829
1830   DCHECK_GE(dispatcher_->num_priorities(), static_cast<size_t>(NUM_PRIORITIES));
1831
1832 #if defined(OS_WIN)
1833   EnsureWinsockInit();
1834 #endif
1835 #if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_ANDROID)
1836   new LoopbackProbeJob(weak_ptr_factory_.GetWeakPtr());
1837 #endif
1838   NetworkChangeNotifier::AddIPAddressObserver(this);
1839   NetworkChangeNotifier::AddDNSObserver(this);
1840 #if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD) && \
1841     !defined(OS_ANDROID)
1842   EnsureDnsReloaderInit();
1843 #endif
1844
1845   {
1846     DnsConfig dns_config;
1847     NetworkChangeNotifier::GetDnsConfig(&dns_config);
1848     received_dns_config_ = dns_config.IsValid();
1849     // Conservatively assume local IPv6 is needed when DnsConfig is not valid.
1850     use_local_ipv6_ = !dns_config.IsValid() || dns_config.use_local_ipv6;
1851   }
1852
1853   fallback_to_proctask_ = !ConfigureAsyncDnsNoFallbackFieldTrial();
1854 }
1855
1856 HostResolverImpl::~HostResolverImpl() {
1857   // Prevent the dispatcher from starting new jobs.
1858   dispatcher_->SetLimitsToZero();
1859   // It's now safe for Jobs to call KillDsnTask on destruction, because
1860   // OnJobComplete will not start any new jobs.
1861   STLDeleteValues(&jobs_);
1862
1863   NetworkChangeNotifier::RemoveIPAddressObserver(this);
1864   NetworkChangeNotifier::RemoveDNSObserver(this);
1865 }
1866
1867 void HostResolverImpl::SetMaxQueuedJobs(size_t value) {
1868   DCHECK_EQ(0u, dispatcher_->num_queued_jobs());
1869   DCHECK_GT(value, 0u);
1870   max_queued_jobs_ = value;
1871 }
1872
1873 int HostResolverImpl::Resolve(const RequestInfo& info,
1874                               RequestPriority priority,
1875                               AddressList* addresses,
1876                               const CompletionCallback& callback,
1877                               RequestHandle* out_req,
1878                               const BoundNetLog& source_net_log) {
1879   DCHECK(addresses);
1880   DCHECK(CalledOnValidThread());
1881   DCHECK_EQ(false, callback.is_null());
1882
1883   // Check that the caller supplied a valid hostname to resolve.
1884   std::string labeled_hostname;
1885   if (!DNSDomainFromDot(info.hostname(), &labeled_hostname))
1886     return ERR_NAME_NOT_RESOLVED;
1887
1888   LogStartRequest(source_net_log, info);
1889
1890   IPAddressNumber ip_number;
1891   IPAddressNumber* ip_number_ptr = nullptr;
1892   if (ParseIPLiteralToNumber(info.hostname(), &ip_number))
1893     ip_number_ptr = &ip_number;
1894
1895   // Build a key that identifies the request in the cache and in the
1896   // outstanding jobs map.
1897   Key key = GetEffectiveKeyForRequest(info, ip_number_ptr, source_net_log);
1898
1899   int rv = ResolveHelper(key, info, ip_number_ptr, addresses, source_net_log);
1900   if (rv != ERR_DNS_CACHE_MISS) {
1901     LogFinishRequest(source_net_log, info, rv);
1902     RecordTotalTime(HaveDnsConfig(), info.is_speculative(), base::TimeDelta());
1903     return rv;
1904   }
1905
1906   // Next we need to attach our request to a "job". This job is responsible for
1907   // calling "getaddrinfo(hostname)" on a worker thread.
1908
1909   JobMap::iterator jobit = jobs_.find(key);
1910   Job* job;
1911   if (jobit == jobs_.end()) {
1912     job =
1913         new Job(weak_ptr_factory_.GetWeakPtr(), key, priority, source_net_log);
1914     job->Schedule(false);
1915
1916     // Check for queue overflow.
1917     if (dispatcher_->num_queued_jobs() > max_queued_jobs_) {
1918       Job* evicted = static_cast<Job*>(dispatcher_->EvictOldestLowest());
1919       DCHECK(evicted);
1920       evicted->OnEvicted();  // Deletes |evicted|.
1921       if (evicted == job) {
1922         rv = ERR_HOST_RESOLVER_QUEUE_TOO_LARGE;
1923         LogFinishRequest(source_net_log, info, rv);
1924         return rv;
1925       }
1926     }
1927     jobs_.insert(jobit, std::make_pair(key, job));
1928   } else {
1929     job = jobit->second;
1930   }
1931
1932   // Can't complete synchronously. Create and attach request.
1933   scoped_ptr<Request> req(new Request(
1934       source_net_log, info, priority, callback, addresses));
1935   if (out_req)
1936     *out_req = reinterpret_cast<RequestHandle>(req.get());
1937
1938   job->AddRequest(req.Pass());
1939   // Completion happens during Job::CompleteRequests().
1940   return ERR_IO_PENDING;
1941 }
1942
1943 int HostResolverImpl::ResolveHelper(const Key& key,
1944                                     const RequestInfo& info,
1945                                     const IPAddressNumber* ip_number,
1946                                     AddressList* addresses,
1947                                     const BoundNetLog& source_net_log) {
1948   // The result of |getaddrinfo| for empty hosts is inconsistent across systems.
1949   // On Windows it gives the default interface's address, whereas on Linux it
1950   // gives an error. We will make it fail on all platforms for consistency.
1951   if (info.hostname().empty() || info.hostname().size() > kMaxHostLength)
1952     return ERR_NAME_NOT_RESOLVED;
1953
1954   int net_error = ERR_UNEXPECTED;
1955   if (ResolveAsIP(key, info, ip_number, &net_error, addresses))
1956     return net_error;
1957   if (ServeFromCache(key, info, &net_error, addresses)) {
1958     source_net_log.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_CACHE_HIT);
1959     return net_error;
1960   }
1961   // TODO(szym): Do not do this if nsswitch.conf instructs not to.
1962   // http://crbug.com/117655
1963   if (ServeFromHosts(key, info, addresses)) {
1964     source_net_log.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_HOSTS_HIT);
1965     return OK;
1966   }
1967   return ERR_DNS_CACHE_MISS;
1968 }
1969
1970 int HostResolverImpl::ResolveFromCache(const RequestInfo& info,
1971                                        AddressList* addresses,
1972                                        const BoundNetLog& source_net_log) {
1973   DCHECK(CalledOnValidThread());
1974   DCHECK(addresses);
1975
1976   // Update the net log and notify registered observers.
1977   LogStartRequest(source_net_log, info);
1978
1979   IPAddressNumber ip_number;
1980   IPAddressNumber* ip_number_ptr = nullptr;
1981   if (ParseIPLiteralToNumber(info.hostname(), &ip_number))
1982     ip_number_ptr = &ip_number;
1983
1984   Key key = GetEffectiveKeyForRequest(info, ip_number_ptr, source_net_log);
1985
1986   int rv = ResolveHelper(key, info, ip_number_ptr, addresses, source_net_log);
1987   LogFinishRequest(source_net_log, info, rv);
1988   return rv;
1989 }
1990
1991 void HostResolverImpl::CancelRequest(RequestHandle req_handle) {
1992   DCHECK(CalledOnValidThread());
1993   Request* req = reinterpret_cast<Request*>(req_handle);
1994   DCHECK(req);
1995   Job* job = req->job();
1996   DCHECK(job);
1997   job->CancelRequest(req);
1998 }
1999
2000 void HostResolverImpl::SetDefaultAddressFamily(AddressFamily address_family) {
2001   DCHECK(CalledOnValidThread());
2002   default_address_family_ = address_family;
2003   probe_ipv6_support_ = false;
2004 }
2005
2006 AddressFamily HostResolverImpl::GetDefaultAddressFamily() const {
2007   return default_address_family_;
2008 }
2009
2010 void HostResolverImpl::SetDnsClientEnabled(bool enabled) {
2011   DCHECK(CalledOnValidThread());
2012 #if defined(ENABLE_BUILT_IN_DNS)
2013   if (enabled && !dns_client_) {
2014     SetDnsClient(DnsClient::CreateClient(net_log_));
2015   } else if (!enabled && dns_client_) {
2016     SetDnsClient(scoped_ptr<DnsClient>());
2017   }
2018 #endif
2019 }
2020
2021 HostCache* HostResolverImpl::GetHostCache() {
2022   return cache_.get();
2023 }
2024
2025 base::Value* HostResolverImpl::GetDnsConfigAsValue() const {
2026   // Check if async DNS is disabled.
2027   if (!dns_client_.get())
2028     return NULL;
2029
2030   // Check if async DNS is enabled, but we currently have no configuration
2031   // for it.
2032   const DnsConfig* dns_config = dns_client_->GetConfig();
2033   if (dns_config == NULL)
2034     return new base::DictionaryValue();
2035
2036   return dns_config->ToValue();
2037 }
2038
2039 bool HostResolverImpl::ResolveAsIP(const Key& key,
2040                                    const RequestInfo& info,
2041                                    const IPAddressNumber* ip_number,
2042                                    int* net_error,
2043                                    AddressList* addresses) {
2044   DCHECK(addresses);
2045   DCHECK(net_error);
2046   if (ip_number == nullptr)
2047     return false;
2048
2049   DCHECK_EQ(key.host_resolver_flags &
2050       ~(HOST_RESOLVER_CANONNAME | HOST_RESOLVER_LOOPBACK_ONLY |
2051         HOST_RESOLVER_DEFAULT_FAMILY_SET_DUE_TO_NO_IPV6),
2052             0) << " Unhandled flag";
2053
2054   *net_error = OK;
2055   AddressFamily family = GetAddressFamily(*ip_number);
2056   if (family == ADDRESS_FAMILY_IPV6 &&
2057       !probe_ipv6_support_ &&
2058       default_address_family_ == ADDRESS_FAMILY_IPV4) {
2059     // Don't return IPv6 addresses if default address family is set to IPv4,
2060     // and probes are disabled.
2061     *net_error = ERR_NAME_NOT_RESOLVED;
2062   } else if (key.address_family != ADDRESS_FAMILY_UNSPECIFIED &&
2063              key.address_family != family) {
2064     // Don't return IPv6 addresses for IPv4 queries, and vice versa.
2065     *net_error = ERR_NAME_NOT_RESOLVED;
2066   } else {
2067     *addresses = AddressList::CreateFromIPAddress(*ip_number, info.port());
2068     if (key.host_resolver_flags & HOST_RESOLVER_CANONNAME)
2069       addresses->SetDefaultCanonicalName();
2070   }
2071   return true;
2072 }
2073
2074 bool HostResolverImpl::ServeFromCache(const Key& key,
2075                                       const RequestInfo& info,
2076                                       int* net_error,
2077                                       AddressList* addresses) {
2078   DCHECK(addresses);
2079   DCHECK(net_error);
2080   if (!info.allow_cached_response() || !cache_.get())
2081     return false;
2082
2083   const HostCache::Entry* cache_entry = cache_->Lookup(
2084       key, base::TimeTicks::Now());
2085   if (!cache_entry)
2086     return false;
2087
2088   *net_error = cache_entry->error;
2089   if (*net_error == OK) {
2090     if (cache_entry->has_ttl())
2091       RecordTTL(cache_entry->ttl);
2092     *addresses = EnsurePortOnAddressList(cache_entry->addrlist, info.port());
2093   }
2094   return true;
2095 }
2096
2097 bool HostResolverImpl::ServeFromHosts(const Key& key,
2098                                       const RequestInfo& info,
2099                                       AddressList* addresses) {
2100   DCHECK(addresses);
2101   if (!HaveDnsConfig())
2102     return false;
2103   addresses->clear();
2104
2105   // HOSTS lookups are case-insensitive.
2106   std::string hostname = base::StringToLowerASCII(key.hostname);
2107
2108   const DnsHosts& hosts = dns_client_->GetConfig()->hosts;
2109
2110   // If |address_family| is ADDRESS_FAMILY_UNSPECIFIED other implementations
2111   // (glibc and c-ares) return the first matching line. We have more
2112   // flexibility, but lose implicit ordering.
2113   // We prefer IPv6 because "happy eyeballs" will fall back to IPv4 if
2114   // necessary.
2115   if (key.address_family == ADDRESS_FAMILY_IPV6 ||
2116       key.address_family == ADDRESS_FAMILY_UNSPECIFIED) {
2117     DnsHosts::const_iterator it = hosts.find(
2118         DnsHostsKey(hostname, ADDRESS_FAMILY_IPV6));
2119     if (it != hosts.end())
2120       addresses->push_back(IPEndPoint(it->second, info.port()));
2121   }
2122
2123   if (key.address_family == ADDRESS_FAMILY_IPV4 ||
2124       key.address_family == ADDRESS_FAMILY_UNSPECIFIED) {
2125     DnsHosts::const_iterator it = hosts.find(
2126         DnsHostsKey(hostname, ADDRESS_FAMILY_IPV4));
2127     if (it != hosts.end())
2128       addresses->push_back(IPEndPoint(it->second, info.port()));
2129   }
2130
2131   // If got only loopback addresses and the family was restricted, resolve
2132   // again, without restrictions. See SystemHostResolverCall for rationale.
2133   if ((key.host_resolver_flags &
2134           HOST_RESOLVER_DEFAULT_FAMILY_SET_DUE_TO_NO_IPV6) &&
2135       IsAllIPv4Loopback(*addresses)) {
2136     Key new_key(key);
2137     new_key.address_family = ADDRESS_FAMILY_UNSPECIFIED;
2138     new_key.host_resolver_flags &=
2139         ~HOST_RESOLVER_DEFAULT_FAMILY_SET_DUE_TO_NO_IPV6;
2140     return ServeFromHosts(new_key, info, addresses);
2141   }
2142   return !addresses->empty();
2143 }
2144
2145 void HostResolverImpl::CacheResult(const Key& key,
2146                                    const HostCache::Entry& entry,
2147                                    base::TimeDelta ttl) {
2148   if (cache_.get())
2149     cache_->Set(key, entry, base::TimeTicks::Now(), ttl);
2150 }
2151
2152 void HostResolverImpl::RemoveJob(Job* job) {
2153   DCHECK(job);
2154   JobMap::iterator it = jobs_.find(job->key());
2155   if (it != jobs_.end() && it->second == job)
2156     jobs_.erase(it);
2157 }
2158
2159 void HostResolverImpl::SetHaveOnlyLoopbackAddresses(bool result) {
2160   if (result) {
2161     additional_resolver_flags_ |= HOST_RESOLVER_LOOPBACK_ONLY;
2162   } else {
2163     additional_resolver_flags_ &= ~HOST_RESOLVER_LOOPBACK_ONLY;
2164   }
2165 }
2166
2167 HostResolverImpl::Key HostResolverImpl::GetEffectiveKeyForRequest(
2168     const RequestInfo& info,
2169     const IPAddressNumber* ip_number,
2170     const BoundNetLog& net_log) const {
2171   HostResolverFlags effective_flags =
2172       info.host_resolver_flags() | additional_resolver_flags_;
2173   AddressFamily effective_address_family = info.address_family();
2174
2175   if (info.address_family() == ADDRESS_FAMILY_UNSPECIFIED) {
2176     if (probe_ipv6_support_ && !use_local_ipv6_ &&
2177         // When resolving IPv4 literals, there's no need to probe for IPv6.
2178         // When resolving IPv6 literals, there's no benefit to artificially
2179         // limiting our resolution based on a probe.  Prior logic ensures
2180         // that this query is UNSPECIFIED (see info.address_family()
2181         // check above) and that |default_address_family_| is UNSPECIFIED
2182         // (|prove_ipv6_support_| is false if |default_address_family_| is
2183         // set) so the code requesting the resolution should be amenable to
2184         // receiving a IPv6 resolution.
2185         ip_number == nullptr) {
2186       // Google DNS address.
2187       const uint8 kIPv6Address[] =
2188           { 0x20, 0x01, 0x48, 0x60, 0x48, 0x60, 0x00, 0x00,
2189             0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x88, 0x88 };
2190       IPAddressNumber address(kIPv6Address,
2191                               kIPv6Address + arraysize(kIPv6Address));
2192       bool rv6 = IsGloballyReachable(address, net_log);
2193       net_log.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_IPV6_REACHABILITY_CHECK,
2194                        NetLog::BoolCallback("ipv6_available", rv6));
2195       if (!rv6) {
2196         effective_address_family = ADDRESS_FAMILY_IPV4;
2197         effective_flags |= HOST_RESOLVER_DEFAULT_FAMILY_SET_DUE_TO_NO_IPV6;
2198       }
2199     } else {
2200       effective_address_family = default_address_family_;
2201     }
2202   }
2203
2204   std::string hostname = info.hostname();
2205   // Redirect .localhost queries to "localhost." to make sure that they
2206   // are never sent out on the network, per RFC 6761.
2207   if (IsLocalhostTLD(info.hostname()))
2208     hostname = kLocalhost;
2209
2210   return Key(hostname, effective_address_family, effective_flags);
2211 }
2212
2213 void HostResolverImpl::AbortAllInProgressJobs() {
2214   // In Abort, a Request callback could spawn new Jobs with matching keys, so
2215   // first collect and remove all running jobs from |jobs_|.
2216   ScopedVector<Job> jobs_to_abort;
2217   for (JobMap::iterator it = jobs_.begin(); it != jobs_.end(); ) {
2218     Job* job = it->second;
2219     if (job->is_running()) {
2220       jobs_to_abort.push_back(job);
2221       jobs_.erase(it++);
2222     } else {
2223       DCHECK(job->is_queued());
2224       ++it;
2225     }
2226   }
2227
2228   // Pause the dispatcher so it won't start any new dispatcher jobs while
2229   // aborting the old ones.  This is needed so that it won't start the second
2230   // DnsTransaction for a job in |jobs_to_abort| if the DnsConfig just became
2231   // invalid.
2232   PrioritizedDispatcher::Limits limits = dispatcher_->GetLimits();
2233   dispatcher_->SetLimits(
2234       PrioritizedDispatcher::Limits(limits.reserved_slots.size(), 0));
2235
2236   // Life check to bail once |this| is deleted.
2237   base::WeakPtr<HostResolverImpl> self = weak_ptr_factory_.GetWeakPtr();
2238
2239   // Then Abort them.
2240   for (size_t i = 0; self.get() && i < jobs_to_abort.size(); ++i) {
2241     jobs_to_abort[i]->Abort();
2242     jobs_to_abort[i] = NULL;
2243   }
2244
2245   if (self)
2246     dispatcher_->SetLimits(limits);
2247 }
2248
2249 void HostResolverImpl::AbortDnsTasks() {
2250   // Pause the dispatcher so it won't start any new dispatcher jobs while
2251   // aborting the old ones.  This is needed so that it won't start the second
2252   // DnsTransaction for a job if the DnsConfig just changed.
2253   PrioritizedDispatcher::Limits limits = dispatcher_->GetLimits();
2254   dispatcher_->SetLimits(
2255       PrioritizedDispatcher::Limits(limits.reserved_slots.size(), 0));
2256
2257   for (JobMap::iterator it = jobs_.begin(); it != jobs_.end(); ++it)
2258     it->second->AbortDnsTask();
2259   dispatcher_->SetLimits(limits);
2260 }
2261
2262 void HostResolverImpl::TryServingAllJobsFromHosts() {
2263   if (!HaveDnsConfig())
2264     return;
2265
2266   // TODO(szym): Do not do this if nsswitch.conf instructs not to.
2267   // http://crbug.com/117655
2268
2269   // Life check to bail once |this| is deleted.
2270   base::WeakPtr<HostResolverImpl> self = weak_ptr_factory_.GetWeakPtr();
2271
2272   for (JobMap::iterator it = jobs_.begin(); self.get() && it != jobs_.end();) {
2273     Job* job = it->second;
2274     ++it;
2275     // This could remove |job| from |jobs_|, but iterator will remain valid.
2276     job->ServeFromHosts();
2277   }
2278 }
2279
2280 void HostResolverImpl::OnIPAddressChanged() {
2281   resolved_known_ipv6_hostname_ = false;
2282   // Abandon all ProbeJobs.
2283   probe_weak_ptr_factory_.InvalidateWeakPtrs();
2284   if (cache_.get())
2285     cache_->clear();
2286 #if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_ANDROID)
2287   new LoopbackProbeJob(probe_weak_ptr_factory_.GetWeakPtr());
2288 #endif
2289   AbortAllInProgressJobs();
2290   // |this| may be deleted inside AbortAllInProgressJobs().
2291 }
2292
2293 void HostResolverImpl::OnInitialDNSConfigRead() {
2294   UpdateDNSConfig(false);
2295 }
2296
2297 void HostResolverImpl::OnDNSChanged() {
2298   UpdateDNSConfig(true);
2299 }
2300
2301 void HostResolverImpl::UpdateDNSConfig(bool config_changed) {
2302   DnsConfig dns_config;
2303   NetworkChangeNotifier::GetDnsConfig(&dns_config);
2304
2305   if (net_log_) {
2306     net_log_->AddGlobalEntry(
2307         NetLog::TYPE_DNS_CONFIG_CHANGED,
2308         base::Bind(&NetLogDnsConfigCallback, &dns_config));
2309   }
2310
2311   // TODO(szym): Remove once http://crbug.com/137914 is resolved.
2312   received_dns_config_ = dns_config.IsValid();
2313   // Conservatively assume local IPv6 is needed when DnsConfig is not valid.
2314   use_local_ipv6_ = !dns_config.IsValid() || dns_config.use_local_ipv6;
2315
2316   num_dns_failures_ = 0;
2317
2318   // We want a new DnsSession in place, before we Abort running Jobs, so that
2319   // the newly started jobs use the new config.
2320   if (dns_client_.get()) {
2321     dns_client_->SetConfig(dns_config);
2322     if (dns_client_->GetConfig()) {
2323       UMA_HISTOGRAM_BOOLEAN("AsyncDNS.DnsClientEnabled", true);
2324       // If we just switched DnsClients, restart jobs using new resolver.
2325       // TODO(pauljensen): Is this necessary?
2326       config_changed = true;
2327     }
2328   }
2329
2330   if (config_changed) {
2331     // If the DNS server has changed, existing cached info could be wrong so we
2332     // have to drop our internal cache :( Note that OS level DNS caches, such
2333     // as NSCD's cache should be dropped automatically by the OS when
2334     // resolv.conf changes so we don't need to do anything to clear that cache.
2335     if (cache_.get())
2336       cache_->clear();
2337
2338     // Life check to bail once |this| is deleted.
2339     base::WeakPtr<HostResolverImpl> self = weak_ptr_factory_.GetWeakPtr();
2340
2341     // Existing jobs will have been sent to the original server so they need to
2342     // be aborted.
2343     AbortAllInProgressJobs();
2344
2345     // |this| may be deleted inside AbortAllInProgressJobs().
2346     if (self.get())
2347       TryServingAllJobsFromHosts();
2348   }
2349 }
2350
2351 bool HostResolverImpl::HaveDnsConfig() const {
2352   // Use DnsClient only if it's fully configured and there is no override by
2353   // ScopedDefaultHostResolverProc.
2354   // The alternative is to use NetworkChangeNotifier to override DnsConfig,
2355   // but that would introduce construction order requirements for NCN and SDHRP.
2356   return (dns_client_.get() != NULL) && (dns_client_->GetConfig() != NULL) &&
2357          !(proc_params_.resolver_proc.get() == NULL &&
2358            HostResolverProc::GetDefault() != NULL);
2359 }
2360
2361 void HostResolverImpl::OnDnsTaskResolve(int net_error) {
2362   DCHECK(dns_client_);
2363   if (net_error == OK) {
2364     num_dns_failures_ = 0;
2365     return;
2366   }
2367   ++num_dns_failures_;
2368   if (num_dns_failures_ < kMaximumDnsFailures)
2369     return;
2370
2371   // Disable DnsClient until the next DNS change.  Must be done before aborting
2372   // DnsTasks, since doing so may start new jobs.
2373   dns_client_->SetConfig(DnsConfig());
2374
2375   // Switch jobs with active DnsTasks over to using ProcTasks.
2376   AbortDnsTasks();
2377
2378   UMA_HISTOGRAM_BOOLEAN("AsyncDNS.DnsClientEnabled", false);
2379   UMA_HISTOGRAM_CUSTOM_ENUMERATION("AsyncDNS.DnsClientDisabledReason",
2380                                    std::abs(net_error),
2381                                    GetAllErrorCodesForUma());
2382 }
2383
2384 void HostResolverImpl::SetDnsClient(scoped_ptr<DnsClient> dns_client) {
2385   // DnsClient and config must be updated before aborting DnsTasks, since doing
2386   // so may start new jobs.
2387   dns_client_ = dns_client.Pass();
2388   if (dns_client_ && !dns_client_->GetConfig() &&
2389       num_dns_failures_ < kMaximumDnsFailures) {
2390     DnsConfig dns_config;
2391     NetworkChangeNotifier::GetDnsConfig(&dns_config);
2392     dns_client_->SetConfig(dns_config);
2393     num_dns_failures_ = 0;
2394     if (dns_client_->GetConfig())
2395       UMA_HISTOGRAM_BOOLEAN("AsyncDNS.DnsClientEnabled", true);
2396   }
2397
2398   AbortDnsTasks();
2399 }
2400
2401 }  // namespace net