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/stl_util.h"
  28 #include "base/strings/string_util.h"
  29 #include "base/strings/utf_string_conversions.h"
  30 #include "base/threading/worker_pool.h"
  31 #include "base/time/time.h"
  32 #include "base/values.h"
  33 #include "net/base/address_family.h"
  34 #include "net/base/address_list.h"
  35 #include "net/base/dns_reloader.h"
  36 #include "net/base/dns_util.h"
  37 #include "net/base/host_port_pair.h"
  38 #include "net/base/ip_endpoint.h"
  39 #include "net/base/net_errors.h"
  40 #include "net/base/net_util.h"
  41 #include "net/dns/address_sorter.h"
  42 #include "net/dns/dns_client.h"
  43 #include "net/dns/dns_config_service.h"
  44 #include "net/dns/dns_protocol.h"
  45 #include "net/dns/dns_response.h"
  46 #include "net/dns/dns_transaction.h"
  47 #include "net/dns/host_resolver_proc.h"
  48 #include "net/log/net_log.h"
  49 #include "net/socket/client_socket_factory.h"
  50 #include "net/udp/datagram_client_socket.h"
  51 #include "url/url_canon_ip.h"
  52
  53 #if defined(OS_WIN)
  54 #include "net/base/winsock_init.h"
  55 #endif
  56
  57 namespace net {
  58
  59 namespace {
  60
  61 // Limit the size of hostnames that will be resolved to combat issues in
  62 // some platform's resolvers.
  63 const size_t kMaxHostLength = 4096;
  64
  65 // Default TTL for successful resolutions with ProcTask.
  66 const unsigned kCacheEntryTTLSeconds = 60;
  67
  68 // Default TTL for unsuccessful resolutions with ProcTask.
  69 const unsigned kNegativeCacheEntryTTLSeconds = 0;
  70
  71 // Minimum TTL for successful resolutions with DnsTask.
  72 const unsigned kMinimumTTLSeconds = kCacheEntryTTLSeconds;
  73
  74 const char kLocalhost[] = "localhost.";
  75
  76 // We use a separate histogram name for each platform to facilitate the
  77 // display of error codes by their symbolic name (since each platform has
  78 // different mappings).
  79 const char kOSErrorsForGetAddrinfoHistogramName[] =
  80 #if defined(OS_WIN)
  81     "Net.OSErrorsForGetAddrinfo_Win";
  82 #elif defined(OS_MACOSX)
  83     "Net.OSErrorsForGetAddrinfo_Mac";
  84 #elif defined(OS_LINUX)
  85     "Net.OSErrorsForGetAddrinfo_Linux";
  86 #else
  87     "Net.OSErrorsForGetAddrinfo";
  88 #endif
  89
  90 // Gets a list of the likely error codes that getaddrinfo() can return
  91 // (non-exhaustive). These are the error codes that we will track via
  92 // a histogram.
  93 std::vector<int> GetAllGetAddrinfoOSErrors() {
  94   int os_errors[] = {
  95 #if defined(OS_POSIX)
  96 #if !defined(OS_FREEBSD)
  97 #if !defined(OS_ANDROID)
  98     // EAI_ADDRFAMILY has been declared obsolete in Android's and
  99     // FreeBSD's netdb.h.
 100     EAI_ADDRFAMILY,
 101 #endif
 102     // EAI_NODATA has been declared obsolete in FreeBSD's netdb.h.
 103     EAI_NODATA,
 104 #endif
 105     EAI_AGAIN,
 106     EAI_BADFLAGS,
 107     EAI_FAIL,
 108     EAI_FAMILY,
 109     EAI_MEMORY,
 110     EAI_NONAME,
 111     EAI_SERVICE,
 112     EAI_SOCKTYPE,
 113     EAI_SYSTEM,
 114 #elif defined(OS_WIN)
 115     // See: http://msdn.microsoft.com/en-us/library/ms738520(VS.85).aspx
 116     WSA_NOT_ENOUGH_MEMORY,
 117     WSAEAFNOSUPPORT,
 118     WSAEINVAL,
 119     WSAESOCKTNOSUPPORT,
 120     WSAHOST_NOT_FOUND,
 121     WSANO_DATA,
 122     WSANO_RECOVERY,
 123     WSANOTINITIALISED,
 124     WSATRY_AGAIN,
 125     WSATYPE_NOT_FOUND,
 126     // The following are not in doc, but might be to appearing in results :-(.
 127     WSA_INVALID_HANDLE,
 128 #endif
 129   };
 130
 131   // Ensure all errors are positive, as histogram only tracks positive values.
 132   for (size_t i = 0; i < arraysize(os_errors); ++i) {
 133     os_errors[i] = std::abs(os_errors[i]);
 134   }
 135
 136   return base::CustomHistogram::ArrayToCustomRanges(os_errors,
 137                                                     arraysize(os_errors));
 138 }
 139
 140 enum DnsResolveStatus {
 141   RESOLVE_STATUS_DNS_SUCCESS = 0,
 142   RESOLVE_STATUS_PROC_SUCCESS,
 143   RESOLVE_STATUS_FAIL,
 144   RESOLVE_STATUS_SUSPECT_NETBIOS,
 145   RESOLVE_STATUS_MAX
 146 };
 147
 148 // ICANN uses this localhost address to indicate a name collision.
 149 //
 150 // The policy in Chromium is to fail host resolving if it resolves to
 151 // this special address.
 152 //
 153 // Not however that IP literals are exempt from this policy, so it is still
 154 // possible to navigate to http://127.0.53.53/ directly.
 155 //
 156 // For more details: https://www.icann.org/news/announcement-2-2014-08-01-en
 157 const unsigned char kIcanNameCollisionIp[] = {127, 0, 53, 53};
 158
 159 void UmaAsyncDnsResolveStatus(DnsResolveStatus result) {
 160   UMA_HISTOGRAM_ENUMERATION("AsyncDNS.ResolveStatus",
 161                             result,
 162                             RESOLVE_STATUS_MAX);
 163 }
 164
 165 bool ResemblesNetBIOSName(const std::string& hostname) {
 166   return (hostname.size() < 16) && (hostname.find('.') == std::string::npos);
 167 }
 168
 169 // True if |hostname| ends with either ".local" or ".local.".
 170 bool ResemblesMulticastDNSName(const std::string& hostname) {
 171   DCHECK(!hostname.empty());
 172   const char kSuffix[] = ".local.";
 173   const size_t kSuffixLen = sizeof(kSuffix) - 1;
 174   const size_t kSuffixLenTrimmed = kSuffixLen - 1;
 175   if (hostname[hostname.size() - 1] == '.') {
 176     return hostname.size() > kSuffixLen &&
 177         !hostname.compare(hostname.size() - kSuffixLen, kSuffixLen, kSuffix);
 178   }
 179   return hostname.size() > kSuffixLenTrimmed &&
 180       !hostname.compare(hostname.size() - kSuffixLenTrimmed, kSuffixLenTrimmed,
 181                         kSuffix, kSuffixLenTrimmed);
 182 }
 183
 184 // Attempts to connect a UDP socket to |dest|:53.
 185 bool IsGloballyReachable(const IPAddressNumber& dest,
 186                          const BoundNetLog& net_log) {
 187   scoped_ptr<DatagramClientSocket> socket(
 188       ClientSocketFactory::GetDefaultFactory()->CreateDatagramClientSocket(
 189           DatagramSocket::DEFAULT_BIND,
 190           RandIntCallback(),
 191           net_log.net_log(),
 192           net_log.source()));
 193   int rv = socket->Connect(IPEndPoint(dest, 53));
 194   if (rv != OK)
 195     return false;
 196   IPEndPoint endpoint;
 197   rv = socket->GetLocalAddress(&endpoint);
 198   if (rv != OK)
 199     return false;
 200   DCHECK_EQ(ADDRESS_FAMILY_IPV6, endpoint.GetFamily());
 201   const IPAddressNumber& address = endpoint.address();
 202   bool is_link_local = (address[0] == 0xFE) && ((address[1] & 0xC0) == 0x80);
 203   if (is_link_local)
 204     return false;
 205   const uint8 kTeredoPrefix[] = { 0x20, 0x01, 0, 0 };
 206   bool is_teredo = std::equal(kTeredoPrefix,
 207                               kTeredoPrefix + arraysize(kTeredoPrefix),
 208                               address.begin());
 209   if (is_teredo)
 210     return false;
 211   return true;
 212 }
 213
 214 // Provide a common macro to simplify code and readability. We must use a
 215 // macro as the underlying HISTOGRAM macro creates static variables.
 216 #define DNS_HISTOGRAM(name, time) UMA_HISTOGRAM_CUSTOM_TIMES(name, time, \
 217     base::TimeDelta::FromMilliseconds(1), base::TimeDelta::FromHours(1), 100)
 218
 219 // A macro to simplify code and readability.
 220 #define DNS_HISTOGRAM_BY_PRIORITY(basename, priority, time) \
 221   do { \
 222     switch (priority) { \
 223       case HIGHEST: DNS_HISTOGRAM(basename "_HIGHEST", time); break; \
 224       case MEDIUM: DNS_HISTOGRAM(basename "_MEDIUM", time); break; \
 225       case LOW: DNS_HISTOGRAM(basename "_LOW", time); break; \
 226       case LOWEST: DNS_HISTOGRAM(basename "_LOWEST", time); break; \
 227       case IDLE: DNS_HISTOGRAM(basename "_IDLE", time); break; \
 228       default: NOTREACHED(); break; \
 229     } \
 230     DNS_HISTOGRAM(basename, time); \
 231   } while (0)
 232
 233 // Record time from Request creation until a valid DNS response.
 234 void RecordTotalTime(bool had_dns_config,
 235                      bool speculative,
 236                      base::TimeDelta duration) {
 237   if (had_dns_config) {
 238     if (speculative) {
 239       DNS_HISTOGRAM("AsyncDNS.TotalTime_speculative", duration);
 240     } else {
 241       DNS_HISTOGRAM("AsyncDNS.TotalTime", duration);
 242     }
 243   } else {
 244     if (speculative) {
 245       DNS_HISTOGRAM("DNS.TotalTime_speculative", duration);
 246     } else {
 247       DNS_HISTOGRAM("DNS.TotalTime", duration);
 248     }
 249   }
 250 }
 251
 252 void RecordTTL(base::TimeDelta ttl) {
 253   UMA_HISTOGRAM_CUSTOM_TIMES("AsyncDNS.TTL", ttl,
 254                              base::TimeDelta::FromSeconds(1),
 255                              base::TimeDelta::FromDays(1), 100);
 256 }
 257
 258 bool ConfigureAsyncDnsNoFallbackFieldTrial() {
 259   const bool kDefault = false;
 260
 261   // Configure the AsyncDns field trial as follows:
 262   // groups AsyncDnsNoFallbackA and AsyncDnsNoFallbackB: return true,
 263   // groups AsyncDnsA and AsyncDnsB: return false,
 264   // groups SystemDnsA and SystemDnsB: return false,
 265   // otherwise (trial absent): return default.
 266   std::string group_name = base::FieldTrialList::FindFullName("AsyncDns");
 267   if (!group_name.empty())
 268     return StartsWithASCII(group_name, "AsyncDnsNoFallback", false);
 269   return kDefault;
 270 }
 271
 272 //-----------------------------------------------------------------------------
 273
 274 AddressList EnsurePortOnAddressList(const AddressList& list, uint16 port) {
 275   if (list.empty() || list.front().port() == port)
 276     return list;
 277   return AddressList::CopyWithPort(list, port);
 278 }
 279
 280 // Returns true if |addresses| contains only IPv4 loopback addresses.
 281 bool IsAllIPv4Loopback(const AddressList& addresses) {
 282   for (unsigned i = 0; i < addresses.size(); ++i) {
 283     const IPAddressNumber& address = addresses[i].address();
 284     switch (addresses[i].GetFamily()) {
 285       case ADDRESS_FAMILY_IPV4:
 286         if (address[0] != 127)
 287           return false;
 288         break;
 289       case ADDRESS_FAMILY_IPV6:
 290         return false;
 291       default:
 292         NOTREACHED();
 293         return false;
 294     }
 295   }
 296   return true;
 297 }
 298
 299 // Creates NetLog parameters when the resolve failed.
 300 base::Value* NetLogProcTaskFailedCallback(uint32 attempt_number,
 301                                           int net_error,
 302                                           int os_error,
 303                                           NetLog::LogLevel /* log_level */) {
 304   base::DictionaryValue* dict = new base::DictionaryValue();
 305   if (attempt_number)
 306     dict->SetInteger("attempt_number", attempt_number);
 307
 308   dict->SetInteger("net_error", net_error);
 309
 310   if (os_error) {
 311     dict->SetInteger("os_error", os_error);
 312 #if defined(OS_POSIX)
 313     dict->SetString("os_error_string", gai_strerror(os_error));
 314 #elif defined(OS_WIN)
 315     // Map the error code to a human-readable string.
 316     LPWSTR error_string = NULL;
 317     FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
 318                   0,  // Use the internal message table.
 319                   os_error,
 320                   0,  // Use default language.
 321                   (LPWSTR)&error_string,
 322                   0,  // Buffer size.
 323                   0);  // Arguments (unused).
 324     dict->SetString("os_error_string", base::WideToUTF8(error_string));
 325     LocalFree(error_string);
 326 #endif
 327   }
 328
 329   return dict;
 330 }
 331
 332 // Creates NetLog parameters when the DnsTask failed.
 333 base::Value* NetLogDnsTaskFailedCallback(int net_error,
 334                                          int dns_error,
 335                                          NetLog::LogLevel /* log_level */) {
 336   base::DictionaryValue* dict = new base::DictionaryValue();
 337   dict->SetInteger("net_error", net_error);
 338   if (dns_error)
 339     dict->SetInteger("dns_error", dns_error);
 340   return dict;
 341 };
 342
 343 // Creates NetLog parameters containing the information in a RequestInfo object,
 344 // along with the associated NetLog::Source.
 345 base::Value* NetLogRequestInfoCallback(const HostResolver::RequestInfo* info,
 346                                        NetLog::LogLevel /* log_level */) {
 347   base::DictionaryValue* dict = new base::DictionaryValue();
 348
 349   dict->SetString("host", info->host_port_pair().ToString());
 350   dict->SetInteger("address_family",
 351                    static_cast<int>(info->address_family()));
 352   dict->SetBoolean("allow_cached_response", info->allow_cached_response());
 353   dict->SetBoolean("is_speculative", info->is_speculative());
 354   return dict;
 355 }
 356
 357 // Creates NetLog parameters for the creation of a HostResolverImpl::Job.
 358 base::Value* NetLogJobCreationCallback(const NetLog::Source& source,
 359                                        const std::string* host,
 360                                        NetLog::LogLevel /* log_level */) {
 361   base::DictionaryValue* dict = new base::DictionaryValue();
 362   source.AddToEventParameters(dict);
 363   dict->SetString("host", *host);
 364   return dict;
 365 }
 366
 367 // Creates NetLog parameters for HOST_RESOLVER_IMPL_JOB_ATTACH/DETACH events.
 368 base::Value* NetLogJobAttachCallback(const NetLog::Source& source,
 369                                      RequestPriority priority,
 370                                      NetLog::LogLevel /* log_level */) {
 371   base::DictionaryValue* dict = new base::DictionaryValue();
 372   source.AddToEventParameters(dict);
 373   dict->SetString("priority", RequestPriorityToString(priority));
 374   return dict;
 375 }
 376
 377 // Creates NetLog parameters for the DNS_CONFIG_CHANGED event.
 378 base::Value* NetLogDnsConfigCallback(const DnsConfig* config,
 379                                      NetLog::LogLevel /* log_level */) {
 380   return config->ToValue();
 381 }
 382
 383 // The logging routines are defined here because some requests are resolved
 384 // without a Request object.
 385
 386 // Logs when a request has just been started.
 387 void LogStartRequest(const BoundNetLog& source_net_log,
 388                      const HostResolver::RequestInfo& info) {
 389   source_net_log.BeginEvent(
 390       NetLog::TYPE_HOST_RESOLVER_IMPL_REQUEST,
 391       base::Bind(&NetLogRequestInfoCallback, &info));
 392 }
 393
 394 // Logs when a request has just completed (before its callback is run).
 395 void LogFinishRequest(const BoundNetLog& source_net_log,
 396                       const HostResolver::RequestInfo& info,
 397                       int net_error) {
 398   source_net_log.EndEventWithNetErrorCode(
 399       NetLog::TYPE_HOST_RESOLVER_IMPL_REQUEST, net_error);
 400 }
 401
 402 // Logs when a request has been cancelled.
 403 void LogCancelRequest(const BoundNetLog& source_net_log,
 404                       const HostResolverImpl::RequestInfo& info) {
 405   source_net_log.AddEvent(NetLog::TYPE_CANCELLED);
 406   source_net_log.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_REQUEST);
 407 }
 408
 409 //-----------------------------------------------------------------------------
 410
 411 // Keeps track of the highest priority.
 412 class PriorityTracker {
 413  public:
 414   explicit PriorityTracker(RequestPriority initial_priority)
 415       : highest_priority_(initial_priority), total_count_(0) {
 416     memset(counts_, 0, sizeof(counts_));
 417   }
 418
 419   RequestPriority highest_priority() const {
 420     return highest_priority_;
 421   }
 422
 423   size_t total_count() const {
 424     return total_count_;
 425   }
 426
 427   void Add(RequestPriority req_priority) {
 428     ++total_count_;
 429     ++counts_[req_priority];
 430     if (highest_priority_ < req_priority)
 431       highest_priority_ = req_priority;
 432   }
 433
 434   void Remove(RequestPriority req_priority) {
 435     DCHECK_GT(total_count_, 0u);
 436     DCHECK_GT(counts_[req_priority], 0u);
 437     --total_count_;
 438     --counts_[req_priority];
 439     size_t i;
 440     for (i = highest_priority_; i > MINIMUM_PRIORITY && !counts_[i]; --i);
 441     highest_priority_ = static_cast<RequestPriority>(i);
 442
 443     // In absence of requests, default to MINIMUM_PRIORITY.
 444     if (total_count_ == 0)
 445       DCHECK_EQ(MINIMUM_PRIORITY, highest_priority_);
 446   }
 447
 448  private:
 449   RequestPriority highest_priority_;
 450   size_t total_count_;
 451   size_t counts_[NUM_PRIORITIES];
 452 };
 453
 454 }  // namespace
 455
 456 //-----------------------------------------------------------------------------
 457
 458 const unsigned HostResolverImpl::kMaximumDnsFailures = 16;
 459
 460 // Holds the data for a request that could not be completed synchronously.
 461 // It is owned by a Job. Canceled Requests are only marked as canceled rather
 462 // than removed from the Job's |requests_| list.
 463 class HostResolverImpl::Request {
 464  public:
 465   Request(const BoundNetLog& source_net_log,
 466           const RequestInfo& info,
 467           RequestPriority priority,
 468           const CompletionCallback& callback,
 469           AddressList* addresses)
 470       : source_net_log_(source_net_log),
 471         info_(info),
 472         priority_(priority),
 473         job_(NULL),
 474         callback_(callback),
 475         addresses_(addresses),
 476         request_time_(base::TimeTicks::Now()) {}
 477
 478   // Mark the request as canceled.
 479   void MarkAsCanceled() {
 480     job_ = NULL;
 481     addresses_ = NULL;
 482     callback_.Reset();
 483   }
 484
 485   bool was_canceled() const {
 486     return callback_.is_null();
 487   }
 488
 489   void set_job(Job* job) {
 490     DCHECK(job);
 491     // Identify which job the request is waiting on.
 492     job_ = job;
 493   }
 494
 495   // Prepare final AddressList and call completion callback.
 496   void OnComplete(int error, const AddressList& addr_list) {
 497     DCHECK(!was_canceled());
 498     if (error == OK)
 499       *addresses_ = EnsurePortOnAddressList(addr_list, info_.port());
 500     CompletionCallback callback = callback_;
 501     MarkAsCanceled();
 502     callback.Run(error);
 503   }
 504
 505   Job* job() const {
 506     return job_;
 507   }
 508
 509   // NetLog for the source, passed in HostResolver::Resolve.
 510   const BoundNetLog& source_net_log() {
 511     return source_net_log_;
 512   }
 513
 514   const RequestInfo& info() const {
 515     return info_;
 516   }
 517
 518   RequestPriority priority() const { return priority_; }
 519
 520   base::TimeTicks request_time() const { return request_time_; }
 521
 522  private:
 523   const BoundNetLog source_net_log_;
 524
 525   // The request info that started the request.
 526   const RequestInfo info_;
 527
 528   // TODO(akalin): Support reprioritization.
 529   const RequestPriority priority_;
 530
 531   // The resolve job that this request is dependent on.
 532   Job* job_;
 533
 534   // The user's callback to invoke when the request completes.
 535   CompletionCallback callback_;
 536
 537   // The address list to save result into.
 538   AddressList* addresses_;
 539
 540   const base::TimeTicks request_time_;
 541
 542   DISALLOW_COPY_AND_ASSIGN(Request);
 543 };
 544
 545 //------------------------------------------------------------------------------
 546
 547 // Calls HostResolverProc on the WorkerPool. Performs retries if necessary.
 548 //
 549 // Whenever we try to resolve the host, we post a delayed task to check if host
 550 // resolution (OnLookupComplete) is completed or not. If the original attempt
 551 // hasn't completed, then we start another attempt for host resolution. We take
 552 // the results from the first attempt that finishes and ignore the results from
 553 // all other attempts.
 554 //
 555 // TODO(szym): Move to separate source file for testing and mocking.
 556 //
 557 class HostResolverImpl::ProcTask
 558     : public base::RefCountedThreadSafe<HostResolverImpl::ProcTask> {
 559  public:
 560   typedef base::Callback<void(int net_error,
 561                               const AddressList& addr_list)> Callback;
 562
 563   ProcTask(const Key& key,
 564            const ProcTaskParams& params,
 565            const Callback& callback,
 566            const BoundNetLog& job_net_log)
 567       : key_(key),
 568         params_(params),
 569         callback_(callback),
 570         origin_loop_(base::MessageLoopProxy::current()),
 571         attempt_number_(0),
 572         completed_attempt_number_(0),
 573         completed_attempt_error_(ERR_UNEXPECTED),
 574         had_non_speculative_request_(false),
 575         net_log_(job_net_log) {
 576     if (!params_.resolver_proc.get())
 577       params_.resolver_proc = HostResolverProc::GetDefault();
 578     // If default is unset, use the system proc.
 579     if (!params_.resolver_proc.get())
 580       params_.resolver_proc = new SystemHostResolverProc();
 581   }
 582
 583   void Start() {
 584     DCHECK(origin_loop_->BelongsToCurrentThread());
 585     net_log_.BeginEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_PROC_TASK);
 586     StartLookupAttempt();
 587   }
 588
 589   // Cancels this ProcTask. It will be orphaned. Any outstanding resolve
 590   // attempts running on worker threads will continue running. Only once all the
 591   // attempts complete will the final reference to this ProcTask be released.
 592   void Cancel() {
 593     DCHECK(origin_loop_->BelongsToCurrentThread());
 594
 595     if (was_canceled() || was_completed())
 596       return;
 597
 598     callback_.Reset();
 599     net_log_.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_PROC_TASK);
 600   }
 601
 602   void set_had_non_speculative_request() {
 603     DCHECK(origin_loop_->BelongsToCurrentThread());
 604     had_non_speculative_request_ = true;
 605   }
 606
 607   bool was_canceled() const {
 608     DCHECK(origin_loop_->BelongsToCurrentThread());
 609     return callback_.is_null();
 610   }
 611
 612   bool was_completed() const {
 613     DCHECK(origin_loop_->BelongsToCurrentThread());
 614     return completed_attempt_number_ > 0;
 615   }
 616
 617  private:
 618   friend class base::RefCountedThreadSafe<ProcTask>;
 619   ~ProcTask() {}
 620
 621   void StartLookupAttempt() {
 622     DCHECK(origin_loop_->BelongsToCurrentThread());
 623     base::TimeTicks start_time = base::TimeTicks::Now();
 624     ++attempt_number_;
 625     // Dispatch the lookup attempt to a worker thread.
 626     if (!base::WorkerPool::PostTask(
 627             FROM_HERE,
 628             base::Bind(&ProcTask::DoLookup, this, start_time, attempt_number_),
 629             true)) {
 630       NOTREACHED();
 631
 632       // Since we could be running within Resolve() right now, we can't just
 633       // call OnLookupComplete().  Instead we must wait until Resolve() has
 634       // returned (IO_PENDING).
 635       origin_loop_->PostTask(
 636           FROM_HERE,
 637           base::Bind(&ProcTask::OnLookupComplete, this, AddressList(),
 638                      start_time, attempt_number_, ERR_UNEXPECTED, 0));
 639       return;
 640     }
 641
 642     net_log_.AddEvent(
 643         NetLog::TYPE_HOST_RESOLVER_IMPL_ATTEMPT_STARTED,
 644         NetLog::IntegerCallback("attempt_number", attempt_number_));
 645
 646     // If we don't get the results within a given time, RetryIfNotComplete
 647     // will start a new attempt on a different worker thread if none of our
 648     // outstanding attempts have completed yet.
 649     if (attempt_number_ <= params_.max_retry_attempts) {
 650       origin_loop_->PostDelayedTask(
 651           FROM_HERE,
 652           base::Bind(&ProcTask::RetryIfNotComplete, this),
 653           params_.unresponsive_delay);
 654     }
 655   }
 656
 657   // WARNING: This code runs inside a worker pool. The shutdown code cannot
 658   // wait for it to finish, so we must be very careful here about using other
 659   // objects (like MessageLoops, Singletons, etc). During shutdown these objects
 660   // may no longer exist. Multiple DoLookups() could be running in parallel, so
 661   // any state inside of |this| must not mutate .
 662   void DoLookup(const base::TimeTicks& start_time,
 663                 const uint32 attempt_number) {
 664     AddressList results;
 665     int os_error = 0;
 666     // Running on the worker thread
 667     int error = params_.resolver_proc->Resolve(key_.hostname,
 668                                                key_.address_family,
 669                                                key_.host_resolver_flags,
 670                                                &results,
 671                                                &os_error);
 672
 673     // Fail the resolution if the result contains 127.0.53.53. See the comment
 674     // block of kIcanNameCollisionIp for details on why.
 675     for (const auto& it : results) {
 676       const IPAddressNumber& cur = it.address();
 677       if (cur.size() == arraysize(kIcanNameCollisionIp) &&
 678           0 == memcmp(&cur.front(), kIcanNameCollisionIp, cur.size())) {
 679         error = ERR_ICANN_NAME_COLLISION;
 680         break;
 681       }
 682     }
 683
 684     origin_loop_->PostTask(
 685         FROM_HERE,
 686         base::Bind(&ProcTask::OnLookupComplete, this, results, start_time,
 687                    attempt_number, error, os_error));
 688   }
 689
 690   // Makes next attempt if DoLookup() has not finished (runs on origin thread).
 691   void RetryIfNotComplete() {
 692     DCHECK(origin_loop_->BelongsToCurrentThread());
 693
 694     if (was_completed() || was_canceled())
 695       return;
 696
 697     params_.unresponsive_delay *= params_.retry_factor;
 698     StartLookupAttempt();
 699   }
 700
 701   // Callback for when DoLookup() completes (runs on origin thread).
 702   void OnLookupComplete(const AddressList& results,
 703                         const base::TimeTicks& start_time,
 704                         const uint32 attempt_number,
 705                         int error,
 706                         const int os_error) {
 707     DCHECK(origin_loop_->BelongsToCurrentThread());
 708     // If results are empty, we should return an error.
 709     bool empty_list_on_ok = (error == OK && results.empty());
 710     UMA_HISTOGRAM_BOOLEAN("DNS.EmptyAddressListAndNoError", empty_list_on_ok);
 711     if (empty_list_on_ok)
 712       error = ERR_NAME_NOT_RESOLVED;
 713
 714     bool was_retry_attempt = attempt_number > 1;
 715
 716     // Ideally the following code would be part of host_resolver_proc.cc,
 717     // however it isn't safe to call NetworkChangeNotifier from worker threads.
 718     // So we do it here on the IO thread instead.
 719     if (error != OK && NetworkChangeNotifier::IsOffline())
 720       error = ERR_INTERNET_DISCONNECTED;
 721
 722     // If this is the first attempt that is finishing later, then record data
 723     // for the first attempt. Won't contaminate with retry attempt's data.
 724     if (!was_retry_attempt)
 725       RecordPerformanceHistograms(start_time, error, os_error);
 726
 727     RecordAttemptHistograms(start_time, attempt_number, error, os_error);
 728
 729     if (was_canceled())
 730       return;
 731
 732     NetLog::ParametersCallback net_log_callback;
 733     if (error != OK) {
 734       net_log_callback = base::Bind(&NetLogProcTaskFailedCallback,
 735                                     attempt_number,
 736                                     error,
 737                                     os_error);
 738     } else {
 739       net_log_callback = NetLog::IntegerCallback("attempt_number",
 740                                                  attempt_number);
 741     }
 742     net_log_.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_ATTEMPT_FINISHED,
 743                       net_log_callback);
 744
 745     if (was_completed())
 746       return;
 747
 748     // Copy the results from the first worker thread that resolves the host.
 749     results_ = results;
 750     completed_attempt_number_ = attempt_number;
 751     completed_attempt_error_ = error;
 752
 753     if (was_retry_attempt) {
 754       // If retry attempt finishes before 1st attempt, then get stats on how
 755       // much time is saved by having spawned an extra attempt.
 756       retry_attempt_finished_time_ = base::TimeTicks::Now();
 757     }
 758
 759     if (error != OK) {
 760       net_log_callback = base::Bind(&NetLogProcTaskFailedCallback,
 761                                     0, error, os_error);
 762     } else {
 763       net_log_callback = results_.CreateNetLogCallback();
 764     }
 765     net_log_.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_PROC_TASK,
 766                       net_log_callback);
 767
 768     callback_.Run(error, results_);
 769   }
 770
 771   void RecordPerformanceHistograms(const base::TimeTicks& start_time,
 772                                    const int error,
 773                                    const int os_error) const {
 774     DCHECK(origin_loop_->BelongsToCurrentThread());
 775     enum Category {  // Used in UMA_HISTOGRAM_ENUMERATION.
 776       RESOLVE_SUCCESS,
 777       RESOLVE_FAIL,
 778       RESOLVE_SPECULATIVE_SUCCESS,
 779       RESOLVE_SPECULATIVE_FAIL,
 780       RESOLVE_MAX,  // Bounding value.
 781     };
 782     int category = RESOLVE_MAX;  // Illegal value for later DCHECK only.
 783
 784     base::TimeDelta duration = base::TimeTicks::Now() - start_time;
 785     if (error == OK) {
 786       if (had_non_speculative_request_) {
 787         category = RESOLVE_SUCCESS;
 788         DNS_HISTOGRAM("DNS.ResolveSuccess", duration);
 789       } else {
 790         category = RESOLVE_SPECULATIVE_SUCCESS;
 791         DNS_HISTOGRAM("DNS.ResolveSpeculativeSuccess", duration);
 792       }
 793
 794       // Log DNS lookups based on |address_family|. This will help us determine
 795       // if IPv4 or IPv4/6 lookups are faster or slower.
 796       switch(key_.address_family) {
 797         case ADDRESS_FAMILY_IPV4:
 798           DNS_HISTOGRAM("DNS.ResolveSuccess_FAMILY_IPV4", duration);
 799           break;
 800         case ADDRESS_FAMILY_IPV6:
 801           DNS_HISTOGRAM("DNS.ResolveSuccess_FAMILY_IPV6", duration);
 802           break;
 803         case ADDRESS_FAMILY_UNSPECIFIED:
 804           DNS_HISTOGRAM("DNS.ResolveSuccess_FAMILY_UNSPEC", duration);
 805           break;
 806       }
 807     } else {
 808       if (had_non_speculative_request_) {
 809         category = RESOLVE_FAIL;
 810         DNS_HISTOGRAM("DNS.ResolveFail", duration);
 811       } else {
 812         category = RESOLVE_SPECULATIVE_FAIL;
 813         DNS_HISTOGRAM("DNS.ResolveSpeculativeFail", duration);
 814       }
 815       // Log DNS lookups based on |address_family|. This will help us determine
 816       // if IPv4 or IPv4/6 lookups are faster or slower.
 817       switch(key_.address_family) {
 818         case ADDRESS_FAMILY_IPV4:
 819           DNS_HISTOGRAM("DNS.ResolveFail_FAMILY_IPV4", duration);
 820           break;
 821         case ADDRESS_FAMILY_IPV6:
 822           DNS_HISTOGRAM("DNS.ResolveFail_FAMILY_IPV6", duration);
 823           break;
 824         case ADDRESS_FAMILY_UNSPECIFIED:
 825           DNS_HISTOGRAM("DNS.ResolveFail_FAMILY_UNSPEC", duration);
 826           break;
 827       }
 828       UMA_HISTOGRAM_CUSTOM_ENUMERATION(kOSErrorsForGetAddrinfoHistogramName,
 829                                        std::abs(os_error),
 830                                        GetAllGetAddrinfoOSErrors());
 831     }
 832     DCHECK_LT(category, static_cast<int>(RESOLVE_MAX));  // Be sure it was set.
 833
 834     UMA_HISTOGRAM_ENUMERATION("DNS.ResolveCategory", category, RESOLVE_MAX);
 835   }
 836
 837   void RecordAttemptHistograms(const base::TimeTicks& start_time,
 838                                const uint32 attempt_number,
 839                                const int error,
 840                                const int os_error) const {
 841     DCHECK(origin_loop_->BelongsToCurrentThread());
 842     bool first_attempt_to_complete =
 843         completed_attempt_number_ == attempt_number;
 844     bool is_first_attempt = (attempt_number == 1);
 845
 846     if (first_attempt_to_complete) {
 847       // If this was first attempt to complete, then record the resolution
 848       // status of the attempt.
 849       if (completed_attempt_error_ == OK) {
 850         UMA_HISTOGRAM_ENUMERATION(
 851             "DNS.AttemptFirstSuccess", attempt_number, 100);
 852       } else {
 853         UMA_HISTOGRAM_ENUMERATION(
 854             "DNS.AttemptFirstFailure", attempt_number, 100);
 855       }
 856     }
 857
 858     if (error == OK)
 859       UMA_HISTOGRAM_ENUMERATION("DNS.AttemptSuccess", attempt_number, 100);
 860     else
 861       UMA_HISTOGRAM_ENUMERATION("DNS.AttemptFailure", attempt_number, 100);
 862
 863     // If first attempt didn't finish before retry attempt, then calculate stats
 864     // on how much time is saved by having spawned an extra attempt.
 865     if (!first_attempt_to_complete && is_first_attempt && !was_canceled()) {
 866       DNS_HISTOGRAM("DNS.AttemptTimeSavedByRetry",
 867                     base::TimeTicks::Now() - retry_attempt_finished_time_);
 868     }
 869
 870     if (was_canceled() || !first_attempt_to_complete) {
 871       // Count those attempts which completed after the job was already canceled
 872       // OR after the job was already completed by an earlier attempt (so in
 873       // effect).
 874       UMA_HISTOGRAM_ENUMERATION("DNS.AttemptDiscarded", attempt_number, 100);
 875
 876       // Record if job is canceled.
 877       if (was_canceled())
 878         UMA_HISTOGRAM_ENUMERATION("DNS.AttemptCancelled", attempt_number, 100);
 879     }
 880
 881     base::TimeDelta duration = base::TimeTicks::Now() - start_time;
 882     if (error == OK)
 883       DNS_HISTOGRAM("DNS.AttemptSuccessDuration", duration);
 884     else
 885       DNS_HISTOGRAM("DNS.AttemptFailDuration", duration);
 886   }
 887
 888   // Set on the origin thread, read on the worker thread.
 889   Key key_;
 890
 891   // Holds an owning reference to the HostResolverProc that we are going to use.
 892   // This may not be the current resolver procedure by the time we call
 893   // ResolveAddrInfo, but that's OK... we'll use it anyways, and the owning
 894   // reference ensures that it remains valid until we are done.
 895   ProcTaskParams params_;
 896
 897   // The listener to the results of this ProcTask.
 898   Callback callback_;
 899
 900   // Used to post ourselves onto the origin thread.
 901   scoped_refptr<base::MessageLoopProxy> origin_loop_;
 902
 903   // Keeps track of the number of attempts we have made so far to resolve the
 904   // host. Whenever we start an attempt to resolve the host, we increase this
 905   // number.
 906   uint32 attempt_number_;
 907
 908   // The index of the attempt which finished first (or 0 if the job is still in
 909   // progress).
 910   uint32 completed_attempt_number_;
 911
 912   // The result (a net error code) from the first attempt to complete.
 913   int completed_attempt_error_;
 914
 915   // The time when retry attempt was finished.
 916   base::TimeTicks retry_attempt_finished_time_;
 917
 918   // True if a non-speculative request was ever attached to this job
 919   // (regardless of whether or not it was later canceled.
 920   // This boolean is used for histogramming the duration of jobs used to
 921   // service non-speculative requests.
 922   bool had_non_speculative_request_;
 923
 924   AddressList results_;
 925
 926   BoundNetLog net_log_;
 927
 928   DISALLOW_COPY_AND_ASSIGN(ProcTask);
 929 };
 930
 931 //-----------------------------------------------------------------------------
 932
 933 // Wraps a call to HaveOnlyLoopbackAddresses to be executed on the WorkerPool as
 934 // it takes 40-100ms and should not block initialization.
 935 class HostResolverImpl::LoopbackProbeJob {
 936  public:
 937   explicit LoopbackProbeJob(const base::WeakPtr<HostResolverImpl>& resolver)
 938       : resolver_(resolver),
 939         result_(false) {
 940     DCHECK(resolver.get());
 941     const bool kIsSlow = true;
 942     base::WorkerPool::PostTaskAndReply(
 943         FROM_HERE,
 944         base::Bind(&LoopbackProbeJob::DoProbe, base::Unretained(this)),
 945         base::Bind(&LoopbackProbeJob::OnProbeComplete, base::Owned(this)),
 946         kIsSlow);
 947   }
 948
 949   virtual ~LoopbackProbeJob() {}
 950
 951  private:
 952   // Runs on worker thread.
 953   void DoProbe() {
 954     result_ = HaveOnlyLoopbackAddresses();
 955   }
 956
 957   void OnProbeComplete() {
 958     if (!resolver_.get())
 959       return;
 960     resolver_->SetHaveOnlyLoopbackAddresses(result_);
 961   }
 962
 963   // Used/set only on origin thread.
 964   base::WeakPtr<HostResolverImpl> resolver_;
 965
 966   bool result_;
 967
 968   DISALLOW_COPY_AND_ASSIGN(LoopbackProbeJob);
 969 };
 970
 971 //-----------------------------------------------------------------------------
 972
 973 // Resolves the hostname using DnsTransaction.
 974 // TODO(szym): This could be moved to separate source file as well.
 975 class HostResolverImpl::DnsTask : public base::SupportsWeakPtr<DnsTask> {
 976  public:
 977   class Delegate {
 978    public:
 979     virtual void OnDnsTaskComplete(base::TimeTicks start_time,
 980                                    int net_error,
 981                                    const AddressList& addr_list,
 982                                    base::TimeDelta ttl) = 0;
 983
 984     // Called when the first of two jobs succeeds.  If the first completed
 985     // transaction fails, this is not called.  Also not called when the DnsTask
 986     // only needs to run one transaction.
 987     virtual void OnFirstDnsTransactionComplete() = 0;
 988
 989    protected:
 990     Delegate() {}
 991     virtual ~Delegate() {}
 992   };
 993
 994   DnsTask(DnsClient* client,
 995           const Key& key,
 996           Delegate* delegate,
 997           const BoundNetLog& job_net_log)
 998       : client_(client),
 999         key_(key),
1000         delegate_(delegate),
1001         net_log_(job_net_log),
1002         num_completed_transactions_(0),
1003         task_start_time_(base::TimeTicks::Now()) {
1004     DCHECK(client);
1005     DCHECK(delegate_);
1006   }
1007
1008   bool needs_two_transactions() const {
1009     return key_.address_family == ADDRESS_FAMILY_UNSPECIFIED;
1010   }
1011
1012   bool needs_another_transaction() const {
1013     return needs_two_transactions() && !transaction_aaaa_;
1014   }
1015
1016   void StartFirstTransaction() {
1017     DCHECK_EQ(0u, num_completed_transactions_);
1018     net_log_.BeginEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_DNS_TASK);
1019     if (key_.address_family == ADDRESS_FAMILY_IPV6) {
1020       StartAAAA();
1021     } else {
1022       StartA();
1023     }
1024   }
1025
1026   void StartSecondTransaction() {
1027     DCHECK(needs_two_transactions());
1028     StartAAAA();
1029   }
1030
1031  private:
1032   void StartA() {
1033     DCHECK(!transaction_a_);
1034     DCHECK_NE(ADDRESS_FAMILY_IPV6, key_.address_family);
1035     transaction_a_ = CreateTransaction(ADDRESS_FAMILY_IPV4);
1036     transaction_a_->Start();
1037   }
1038
1039   void StartAAAA() {
1040     DCHECK(!transaction_aaaa_);
1041     DCHECK_NE(ADDRESS_FAMILY_IPV4, key_.address_family);
1042     transaction_aaaa_ = CreateTransaction(ADDRESS_FAMILY_IPV6);
1043     transaction_aaaa_->Start();
1044   }
1045
1046   scoped_ptr<DnsTransaction> CreateTransaction(AddressFamily family) {
1047     DCHECK_NE(ADDRESS_FAMILY_UNSPECIFIED, family);
1048     return client_->GetTransactionFactory()->CreateTransaction(
1049         key_.hostname,
1050         family == ADDRESS_FAMILY_IPV6 ? dns_protocol::kTypeAAAA :
1051                                         dns_protocol::kTypeA,
1052         base::Bind(&DnsTask::OnTransactionComplete, base::Unretained(this),
1053                    base::TimeTicks::Now()),
1054         net_log_);
1055   }
1056
1057   void OnTransactionComplete(const base::TimeTicks& start_time,
1058                              DnsTransaction* transaction,
1059                              int net_error,
1060                              const DnsResponse* response) {
1061     DCHECK(transaction);
1062     base::TimeDelta duration = base::TimeTicks::Now() - start_time;
1063     if (net_error != OK) {
1064       DNS_HISTOGRAM("AsyncDNS.TransactionFailure", duration);
1065       OnFailure(net_error, DnsResponse::DNS_PARSE_OK);
1066       return;
1067     }
1068
1069     DNS_HISTOGRAM("AsyncDNS.TransactionSuccess", duration);
1070     switch (transaction->GetType()) {
1071       case dns_protocol::kTypeA:
1072         DNS_HISTOGRAM("AsyncDNS.TransactionSuccess_A", duration);
1073         break;
1074       case dns_protocol::kTypeAAAA:
1075         DNS_HISTOGRAM("AsyncDNS.TransactionSuccess_AAAA", duration);
1076         break;
1077     }
1078
1079     AddressList addr_list;
1080     base::TimeDelta ttl;
1081     DnsResponse::Result result = response->ParseToAddressList(&addr_list, &ttl);
1082     UMA_HISTOGRAM_ENUMERATION("AsyncDNS.ParseToAddressList",
1083                               result,
1084                               DnsResponse::DNS_PARSE_RESULT_MAX);
1085     if (result != DnsResponse::DNS_PARSE_OK) {
1086       // Fail even if the other query succeeds.
1087       OnFailure(ERR_DNS_MALFORMED_RESPONSE, result);
1088       return;
1089     }
1090
1091     ++num_completed_transactions_;
1092     if (num_completed_transactions_ == 1) {
1093       ttl_ = ttl;
1094     } else {
1095       ttl_ = std::min(ttl_, ttl);
1096     }
1097
1098     if (transaction->GetType() == dns_protocol::kTypeA) {
1099       DCHECK_EQ(transaction_a_.get(), transaction);
1100       // Place IPv4 addresses after IPv6.
1101       addr_list_.insert(addr_list_.end(), addr_list.begin(), addr_list.end());
1102     } else {
1103       DCHECK_EQ(transaction_aaaa_.get(), transaction);
1104       // Place IPv6 addresses before IPv4.
1105       addr_list_.insert(addr_list_.begin(), addr_list.begin(), addr_list.end());
1106     }
1107
1108     if (needs_two_transactions() && num_completed_transactions_ == 1) {
1109       // No need to repeat the suffix search.
1110       key_.hostname = transaction->GetHostname();
1111       delegate_->OnFirstDnsTransactionComplete();
1112       return;
1113     }
1114
1115     if (addr_list_.empty()) {
1116       // TODO(szym): Don't fallback to ProcTask in this case.
1117       OnFailure(ERR_NAME_NOT_RESOLVED, DnsResponse::DNS_PARSE_OK);
1118       return;
1119     }
1120
1121     // If there are multiple addresses, and at least one is IPv6, need to sort
1122     // them.  Note that IPv6 addresses are always put before IPv4 ones, so it's
1123     // sufficient to just check the family of the first address.
1124     if (addr_list_.size() > 1 &&
1125         addr_list_[0].GetFamily() == ADDRESS_FAMILY_IPV6) {
1126       // Sort addresses if needed.  Sort could complete synchronously.
1127       client_->GetAddressSorter()->Sort(
1128           addr_list_,
1129           base::Bind(&DnsTask::OnSortComplete,
1130                      AsWeakPtr(),
1131                      base::TimeTicks::Now()));
1132     } else {
1133       OnSuccess(addr_list_);
1134     }
1135   }
1136
1137   void OnSortComplete(base::TimeTicks start_time,
1138                       bool success,
1139                       const AddressList& addr_list) {
1140     if (!success) {
1141       DNS_HISTOGRAM("AsyncDNS.SortFailure",
1142                     base::TimeTicks::Now() - start_time);
1143       OnFailure(ERR_DNS_SORT_ERROR, DnsResponse::DNS_PARSE_OK);
1144       return;
1145     }
1146
1147     DNS_HISTOGRAM("AsyncDNS.SortSuccess",
1148                   base::TimeTicks::Now() - start_time);
1149
1150     // AddressSorter prunes unusable destinations.
1151     if (addr_list.empty()) {
1152       LOG(WARNING) << "Address list empty after RFC3484 sort";
1153       OnFailure(ERR_NAME_NOT_RESOLVED, DnsResponse::DNS_PARSE_OK);
1154       return;
1155     }
1156
1157     OnSuccess(addr_list);
1158   }
1159
1160   void OnFailure(int net_error, DnsResponse::Result result) {
1161     DCHECK_NE(OK, net_error);
1162     net_log_.EndEvent(
1163         NetLog::TYPE_HOST_RESOLVER_IMPL_DNS_TASK,
1164         base::Bind(&NetLogDnsTaskFailedCallback, net_error, result));
1165     delegate_->OnDnsTaskComplete(task_start_time_, net_error, AddressList(),
1166                                  base::TimeDelta());
1167   }
1168
1169   void OnSuccess(const AddressList& addr_list) {
1170     net_log_.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_DNS_TASK,
1171                       addr_list.CreateNetLogCallback());
1172     delegate_->OnDnsTaskComplete(task_start_time_, OK, addr_list, ttl_);
1173   }
1174
1175   DnsClient* client_;
1176   Key key_;
1177
1178   // The listener to the results of this DnsTask.
1179   Delegate* delegate_;
1180   const BoundNetLog net_log_;
1181
1182   scoped_ptr<DnsTransaction> transaction_a_;
1183   scoped_ptr<DnsTransaction> transaction_aaaa_;
1184
1185   unsigned num_completed_transactions_;
1186
1187   // These are updated as each transaction completes.
1188   base::TimeDelta ttl_;
1189   // IPv6 addresses must appear first in the list.
1190   AddressList addr_list_;
1191
1192   base::TimeTicks task_start_time_;
1193
1194   DISALLOW_COPY_AND_ASSIGN(DnsTask);
1195 };
1196
1197 //-----------------------------------------------------------------------------
1198
1199 // Aggregates all Requests for the same Key. Dispatched via PriorityDispatch.
1200 class HostResolverImpl::Job : public PrioritizedDispatcher::Job,
1201                               public HostResolverImpl::DnsTask::Delegate {
1202  public:
1203   // Creates new job for |key| where |request_net_log| is bound to the
1204   // request that spawned it.
1205   Job(const base::WeakPtr<HostResolverImpl>& resolver,
1206       const Key& key,
1207       RequestPriority priority,
1208       const BoundNetLog& source_net_log)
1209       : resolver_(resolver),
1210         key_(key),
1211         priority_tracker_(priority),
1212         had_non_speculative_request_(false),
1213         had_dns_config_(false),
1214         num_occupied_job_slots_(0),
1215         dns_task_error_(OK),
1216         creation_time_(base::TimeTicks::Now()),
1217         priority_change_time_(creation_time_),
1218         net_log_(BoundNetLog::Make(source_net_log.net_log(),
1219                                    NetLog::SOURCE_HOST_RESOLVER_IMPL_JOB)) {
1220     source_net_log.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_CREATE_JOB);
1221
1222     net_log_.BeginEvent(
1223         NetLog::TYPE_HOST_RESOLVER_IMPL_JOB,
1224         base::Bind(&NetLogJobCreationCallback,
1225                    source_net_log.source(),
1226                    &key_.hostname));
1227   }
1228
1229   ~Job() override {
1230     if (is_running()) {
1231       // |resolver_| was destroyed with this Job still in flight.
1232       // Clean-up, record in the log, but don't run any callbacks.
1233       if (is_proc_running()) {
1234         proc_task_->Cancel();
1235         proc_task_ = NULL;
1236       }
1237       // Clean up now for nice NetLog.
1238       KillDnsTask();
1239       net_log_.EndEventWithNetErrorCode(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB,
1240                                         ERR_ABORTED);
1241     } else if (is_queued()) {
1242       // |resolver_| was destroyed without running this Job.
1243       // TODO(szym): is there any benefit in having this distinction?
1244       net_log_.AddEvent(NetLog::TYPE_CANCELLED);
1245       net_log_.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB);
1246     }
1247     // else CompleteRequests logged EndEvent.
1248
1249     // Log any remaining Requests as cancelled.
1250     for (RequestsList::const_iterator it = requests_.begin();
1251          it != requests_.end(); ++it) {
1252       Request* req = *it;
1253       if (req->was_canceled())
1254         continue;
1255       DCHECK_EQ(this, req->job());
1256       LogCancelRequest(req->source_net_log(), req->info());
1257     }
1258   }
1259
1260   // Add this job to the dispatcher.  If "at_head" is true, adds at the front
1261   // of the queue.
1262   void Schedule(bool at_head) {
1263     DCHECK(!is_queued());
1264     PrioritizedDispatcher::Handle handle;
1265     if (!at_head) {
1266       handle = resolver_->dispatcher_->Add(this, priority());
1267     } else {
1268       handle = resolver_->dispatcher_->AddAtHead(this, priority());
1269     }
1270     // The dispatcher could have started |this| in the above call to Add, which
1271     // could have called Schedule again. In that case |handle| will be null,
1272     // but |handle_| may have been set by the other nested call to Schedule.
1273     if (!handle.is_null()) {
1274       DCHECK(handle_.is_null());
1275       handle_ = handle;
1276     }
1277   }
1278
1279   void AddRequest(scoped_ptr<Request> req) {
1280     // .localhost queries are redirected to "localhost." to make sure
1281     // that they are never sent out on the network, per RFC 6761.
1282     if (IsLocalhostTLD(req->info().hostname())) {
1283       DCHECK_EQ(key_.hostname, kLocalhost);
1284     } else {
1285       DCHECK_EQ(key_.hostname, req->info().hostname());
1286     }
1287
1288     req->set_job(this);
1289     priority_tracker_.Add(req->priority());
1290
1291     req->source_net_log().AddEvent(
1292         NetLog::TYPE_HOST_RESOLVER_IMPL_JOB_ATTACH,
1293         net_log_.source().ToEventParametersCallback());
1294
1295     net_log_.AddEvent(
1296         NetLog::TYPE_HOST_RESOLVER_IMPL_JOB_REQUEST_ATTACH,
1297         base::Bind(&NetLogJobAttachCallback,
1298                    req->source_net_log().source(),
1299                    priority()));
1300
1301     // TODO(szym): Check if this is still needed.
1302     if (!req->info().is_speculative()) {
1303       had_non_speculative_request_ = true;
1304       if (proc_task_.get())
1305         proc_task_->set_had_non_speculative_request();
1306     }
1307
1308     requests_.push_back(req.release());
1309
1310     UpdatePriority();
1311   }
1312
1313   // Marks |req| as cancelled. If it was the last active Request, also finishes
1314   // this Job, marking it as cancelled, and deletes it.
1315   void CancelRequest(Request* req) {
1316     DCHECK_EQ(key_.hostname, req->info().hostname());
1317     DCHECK(!req->was_canceled());
1318
1319     // Don't remove it from |requests_| just mark it canceled.
1320     req->MarkAsCanceled();
1321     LogCancelRequest(req->source_net_log(), req->info());
1322
1323     priority_tracker_.Remove(req->priority());
1324     net_log_.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB_REQUEST_DETACH,
1325                       base::Bind(&NetLogJobAttachCallback,
1326                                  req->source_net_log().source(),
1327                                  priority()));
1328
1329     if (num_active_requests() > 0) {
1330       UpdatePriority();
1331     } else {
1332       // If we were called from a Request's callback within CompleteRequests,
1333       // that Request could not have been cancelled, so num_active_requests()
1334       // could not be 0. Therefore, we are not in CompleteRequests().
1335       CompleteRequestsWithError(OK /* cancelled */);
1336     }
1337   }
1338
1339   // Called from AbortAllInProgressJobs. Completes all requests and destroys
1340   // the job. This currently assumes the abort is due to a network change.
1341   void Abort() {
1342     DCHECK(is_running());
1343     CompleteRequestsWithError(ERR_NETWORK_CHANGED);
1344   }
1345
1346   // If DnsTask present, abort it and fall back to ProcTask.
1347   void AbortDnsTask() {
1348     if (dns_task_) {
1349       KillDnsTask();
1350       dns_task_error_ = OK;
1351       StartProcTask();
1352     }
1353   }
1354
1355   // Called by HostResolverImpl when this job is evicted due to queue overflow.
1356   // Completes all requests and destroys the job.
1357   void OnEvicted() {
1358     DCHECK(!is_running());
1359     DCHECK(is_queued());
1360     handle_.Reset();
1361
1362     net_log_.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB_EVICTED);
1363
1364     // This signals to CompleteRequests that this job never ran.
1365     CompleteRequestsWithError(ERR_HOST_RESOLVER_QUEUE_TOO_LARGE);
1366   }
1367
1368   // Attempts to serve the job from HOSTS. Returns true if succeeded and
1369   // this Job was destroyed.
1370   bool ServeFromHosts() {
1371     DCHECK_GT(num_active_requests(), 0u);
1372     AddressList addr_list;
1373     if (resolver_->ServeFromHosts(key(),
1374                                   requests_.front()->info(),
1375                                   &addr_list)) {
1376       // This will destroy the Job.
1377       CompleteRequests(
1378           HostCache::Entry(OK, MakeAddressListForRequest(addr_list)),
1379           base::TimeDelta());
1380       return true;
1381     }
1382     return false;
1383   }
1384
1385   const Key key() const {
1386     return key_;
1387   }
1388
1389   bool is_queued() const {
1390     return !handle_.is_null();
1391   }
1392
1393   bool is_running() const {
1394     return is_dns_running() || is_proc_running();
1395   }
1396
1397  private:
1398   void KillDnsTask() {
1399     if (dns_task_) {
1400       ReduceToOneJobSlot();
1401       dns_task_.reset();
1402     }
1403   }
1404
1405   // Reduce the number of job slots occupied and queued in the dispatcher
1406   // to one. If the second Job slot is queued in the dispatcher, cancels the
1407   // queued job. Otherwise, the second Job has been started by the
1408   // PrioritizedDispatcher, so signals it is complete.
1409   void ReduceToOneJobSlot() {
1410     DCHECK_GE(num_occupied_job_slots_, 1u);
1411     if (is_queued()) {
1412       resolver_->dispatcher_->Cancel(handle_);
1413       handle_.Reset();
1414     } else if (num_occupied_job_slots_ > 1) {
1415       resolver_->dispatcher_->OnJobFinished();
1416       --num_occupied_job_slots_;
1417     }
1418     DCHECK_EQ(1u, num_occupied_job_slots_);
1419   }
1420
1421   void UpdatePriority() {
1422     if (is_queued()) {
1423       if (priority() != static_cast<RequestPriority>(handle_.priority()))
1424         priority_change_time_ = base::TimeTicks::Now();
1425       handle_ = resolver_->dispatcher_->ChangePriority(handle_, priority());
1426     }
1427   }
1428
1429   AddressList MakeAddressListForRequest(const AddressList& list) const {
1430     if (requests_.empty())
1431       return list;
1432     return AddressList::CopyWithPort(list, requests_.front()->info().port());
1433   }
1434
1435   // PriorityDispatch::Job:
1436   void Start() override {
1437     DCHECK_LE(num_occupied_job_slots_, 1u);
1438
1439     handle_.Reset();
1440     ++num_occupied_job_slots_;
1441
1442     if (num_occupied_job_slots_ == 2) {
1443       StartSecondDnsTransaction();
1444       return;
1445     }
1446
1447     DCHECK(!is_running());
1448
1449     net_log_.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB_STARTED);
1450
1451     had_dns_config_ = resolver_->HaveDnsConfig();
1452
1453     base::TimeTicks now = base::TimeTicks::Now();
1454     base::TimeDelta queue_time = now - creation_time_;
1455     base::TimeDelta queue_time_after_change = now - priority_change_time_;
1456
1457     if (had_dns_config_) {
1458       DNS_HISTOGRAM_BY_PRIORITY("AsyncDNS.JobQueueTime", priority(),
1459                                 queue_time);
1460       DNS_HISTOGRAM_BY_PRIORITY("AsyncDNS.JobQueueTimeAfterChange", priority(),
1461                                 queue_time_after_change);
1462     } else {
1463       DNS_HISTOGRAM_BY_PRIORITY("DNS.JobQueueTime", priority(), queue_time);
1464       DNS_HISTOGRAM_BY_PRIORITY("DNS.JobQueueTimeAfterChange", priority(),
1465                                 queue_time_after_change);
1466     }
1467
1468     bool system_only =
1469         (key_.host_resolver_flags & HOST_RESOLVER_SYSTEM_ONLY) != 0;
1470
1471     // Caution: Job::Start must not complete synchronously.
1472     if (!system_only && had_dns_config_ &&
1473         !ResemblesMulticastDNSName(key_.hostname)) {
1474       StartDnsTask();
1475     } else {
1476       StartProcTask();
1477     }
1478   }
1479
1480   // TODO(szym): Since DnsTransaction does not consume threads, we can increase
1481   // the limits on |dispatcher_|. But in order to keep the number of WorkerPool
1482   // threads low, we will need to use an "inner" PrioritizedDispatcher with
1483   // tighter limits.
1484   void StartProcTask() {
1485     DCHECK(!is_dns_running());
1486     proc_task_ = new ProcTask(
1487         key_,
1488         resolver_->proc_params_,
1489         base::Bind(&Job::OnProcTaskComplete, base::Unretained(this),
1490                    base::TimeTicks::Now()),
1491         net_log_);
1492
1493     if (had_non_speculative_request_)
1494       proc_task_->set_had_non_speculative_request();
1495     // Start() could be called from within Resolve(), hence it must NOT directly
1496     // call OnProcTaskComplete, for example, on synchronous failure.
1497     proc_task_->Start();
1498   }
1499
1500   // Called by ProcTask when it completes.
1501   void OnProcTaskComplete(base::TimeTicks start_time,
1502                           int net_error,
1503                           const AddressList& addr_list) {
1504     DCHECK(is_proc_running());
1505
1506     if (!resolver_->resolved_known_ipv6_hostname_ &&
1507         net_error == OK &&
1508         key_.address_family == ADDRESS_FAMILY_UNSPECIFIED) {
1509       if (key_.hostname == "www.google.com") {
1510         resolver_->resolved_known_ipv6_hostname_ = true;
1511         bool got_ipv6_address = false;
1512         for (size_t i = 0; i < addr_list.size(); ++i) {
1513           if (addr_list[i].GetFamily() == ADDRESS_FAMILY_IPV6) {
1514             got_ipv6_address = true;
1515             break;
1516           }
1517         }
1518         UMA_HISTOGRAM_BOOLEAN("Net.UnspecResolvedIPv6", got_ipv6_address);
1519       }
1520     }
1521
1522     if (dns_task_error_ != OK) {
1523       base::TimeDelta duration = base::TimeTicks::Now() - start_time;
1524       if (net_error == OK) {
1525         DNS_HISTOGRAM("AsyncDNS.FallbackSuccess", duration);
1526         if ((dns_task_error_ == ERR_NAME_NOT_RESOLVED) &&
1527             ResemblesNetBIOSName(key_.hostname)) {
1528           UmaAsyncDnsResolveStatus(RESOLVE_STATUS_SUSPECT_NETBIOS);
1529         } else {
1530           UmaAsyncDnsResolveStatus(RESOLVE_STATUS_PROC_SUCCESS);
1531         }
1532         UMA_HISTOGRAM_CUSTOM_ENUMERATION("AsyncDNS.ResolveError",
1533                                          std::abs(dns_task_error_),
1534                                          GetAllErrorCodesForUma());
1535         resolver_->OnDnsTaskResolve(dns_task_error_);
1536       } else {
1537         DNS_HISTOGRAM("AsyncDNS.FallbackFail", duration);
1538         UmaAsyncDnsResolveStatus(RESOLVE_STATUS_FAIL);
1539       }
1540     }
1541
1542     base::TimeDelta ttl =
1543         base::TimeDelta::FromSeconds(kNegativeCacheEntryTTLSeconds);
1544     if (net_error == OK)
1545       ttl = base::TimeDelta::FromSeconds(kCacheEntryTTLSeconds);
1546
1547     // Don't store the |ttl| in cache since it's not obtained from the server.
1548     CompleteRequests(
1549         HostCache::Entry(net_error, MakeAddressListForRequest(addr_list)),
1550         ttl);
1551   }
1552
1553   void StartDnsTask() {
1554     DCHECK(resolver_->HaveDnsConfig());
1555     dns_task_.reset(new DnsTask(resolver_->dns_client_.get(), key_, this,
1556                                 net_log_));
1557
1558     dns_task_->StartFirstTransaction();
1559     // Schedule a second transaction, if needed.
1560     if (dns_task_->needs_two_transactions())
1561       Schedule(true);
1562   }
1563
1564   void StartSecondDnsTransaction() {
1565     DCHECK(dns_task_->needs_two_transactions());
1566     dns_task_->StartSecondTransaction();
1567   }
1568
1569   // Called if DnsTask fails. It is posted from StartDnsTask, so Job may be
1570   // deleted before this callback. In this case dns_task is deleted as well,
1571   // so we use it as indicator whether Job is still valid.
1572   void OnDnsTaskFailure(const base::WeakPtr<DnsTask>& dns_task,
1573                         base::TimeDelta duration,
1574                         int net_error) {
1575     DNS_HISTOGRAM("AsyncDNS.ResolveFail", duration);
1576
1577     if (dns_task == NULL)
1578       return;
1579
1580     dns_task_error_ = net_error;
1581
1582     // TODO(szym): Run ServeFromHosts now if nsswitch.conf says so.
1583     // http://crbug.com/117655
1584
1585     // TODO(szym): Some net errors indicate lack of connectivity. Starting
1586     // ProcTask in that case is a waste of time.
1587     if (resolver_->fallback_to_proctask_) {
1588       KillDnsTask();
1589       StartProcTask();
1590     } else {
1591       UmaAsyncDnsResolveStatus(RESOLVE_STATUS_FAIL);
1592       CompleteRequestsWithError(net_error);
1593     }
1594   }
1595
1596
1597   // HostResolverImpl::DnsTask::Delegate implementation:
1598
1599   void OnDnsTaskComplete(base::TimeTicks start_time,
1600                          int net_error,
1601                          const AddressList& addr_list,
1602                          base::TimeDelta ttl) override {
1603     DCHECK(is_dns_running());
1604
1605     base::TimeDelta duration = base::TimeTicks::Now() - start_time;
1606     if (net_error != OK) {
1607       OnDnsTaskFailure(dns_task_->AsWeakPtr(), duration, net_error);
1608       return;
1609     }
1610     DNS_HISTOGRAM("AsyncDNS.ResolveSuccess", duration);
1611     // Log DNS lookups based on |address_family|.
1612     switch(key_.address_family) {
1613       case ADDRESS_FAMILY_IPV4:
1614         DNS_HISTOGRAM("AsyncDNS.ResolveSuccess_FAMILY_IPV4", duration);
1615         break;
1616       case ADDRESS_FAMILY_IPV6:
1617         DNS_HISTOGRAM("AsyncDNS.ResolveSuccess_FAMILY_IPV6", duration);
1618         break;
1619       case ADDRESS_FAMILY_UNSPECIFIED:
1620         DNS_HISTOGRAM("AsyncDNS.ResolveSuccess_FAMILY_UNSPEC", duration);
1621         break;
1622     }
1623
1624     UmaAsyncDnsResolveStatus(RESOLVE_STATUS_DNS_SUCCESS);
1625     RecordTTL(ttl);
1626
1627     resolver_->OnDnsTaskResolve(OK);
1628
1629     base::TimeDelta bounded_ttl =
1630         std::max(ttl, base::TimeDelta::FromSeconds(kMinimumTTLSeconds));
1631
1632     CompleteRequests(
1633         HostCache::Entry(net_error, MakeAddressListForRequest(addr_list), ttl),
1634         bounded_ttl);
1635   }
1636
1637   void OnFirstDnsTransactionComplete() override {
1638     DCHECK(dns_task_->needs_two_transactions());
1639     DCHECK_EQ(dns_task_->needs_another_transaction(), is_queued());
1640     // No longer need to occupy two dispatcher slots.
1641     ReduceToOneJobSlot();
1642
1643     // We already have a job slot at the dispatcher, so if the second
1644     // transaction hasn't started, reuse it now instead of waiting in the queue
1645     // for the second slot.
1646     if (dns_task_->needs_another_transaction())
1647       dns_task_->StartSecondTransaction();
1648   }
1649
1650   // Performs Job's last rites. Completes all Requests. Deletes this.
1651   void CompleteRequests(const HostCache::Entry& entry,
1652                         base::TimeDelta ttl) {
1653     CHECK(resolver_.get());
1654
1655     // This job must be removed from resolver's |jobs_| now to make room for a
1656     // new job with the same key in case one of the OnComplete callbacks decides
1657     // to spawn one. Consequently, the job deletes itself when CompleteRequests
1658     // is done.
1659     scoped_ptr<Job> self_deleter(this);
1660
1661     resolver_->RemoveJob(this);
1662
1663     if (is_running()) {
1664       if (is_proc_running()) {
1665         DCHECK(!is_queued());
1666         proc_task_->Cancel();
1667         proc_task_ = NULL;
1668       }
1669       KillDnsTask();
1670
1671       // Signal dispatcher that a slot has opened.
1672       resolver_->dispatcher_->OnJobFinished();
1673     } else if (is_queued()) {
1674       resolver_->dispatcher_->Cancel(handle_);
1675       handle_.Reset();
1676     }
1677
1678     if (num_active_requests() == 0) {
1679       net_log_.AddEvent(NetLog::TYPE_CANCELLED);
1680       net_log_.EndEventWithNetErrorCode(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB,
1681                                         OK);
1682       return;
1683     }
1684
1685     net_log_.EndEventWithNetErrorCode(NetLog::TYPE_HOST_RESOLVER_IMPL_JOB,
1686                                       entry.error);
1687
1688     DCHECK(!requests_.empty());
1689
1690     if (entry.error == OK) {
1691       // Record this histogram here, when we know the system has a valid DNS
1692       // configuration.
1693       UMA_HISTOGRAM_BOOLEAN("AsyncDNS.HaveDnsConfig",
1694                             resolver_->received_dns_config_);
1695     }
1696
1697     bool did_complete = (entry.error != ERR_NETWORK_CHANGED) &&
1698                         (entry.error != ERR_HOST_RESOLVER_QUEUE_TOO_LARGE);
1699     if (did_complete)
1700       resolver_->CacheResult(key_, entry, ttl);
1701
1702     // Complete all of the requests that were attached to the job.
1703     for (RequestsList::const_iterator it = requests_.begin();
1704          it != requests_.end(); ++it) {
1705       Request* req = *it;
1706
1707       if (req->was_canceled())
1708         continue;
1709
1710       DCHECK_EQ(this, req->job());
1711       // Update the net log and notify registered observers.
1712       LogFinishRequest(req->source_net_log(), req->info(), entry.error);
1713       if (did_complete) {
1714         // Record effective total time from creation to completion.
1715         RecordTotalTime(had_dns_config_, req->info().is_speculative(),
1716                         base::TimeTicks::Now() - req->request_time());
1717       }
1718       req->OnComplete(entry.error, entry.addrlist);
1719
1720       // Check if the resolver was destroyed as a result of running the
1721       // callback. If it was, we could continue, but we choose to bail.
1722       if (!resolver_.get())
1723         return;
1724     }
1725   }
1726
1727   // Convenience wrapper for CompleteRequests in case of failure.
1728   void CompleteRequestsWithError(int net_error) {
1729     CompleteRequests(HostCache::Entry(net_error, AddressList()),
1730                      base::TimeDelta());
1731   }
1732
1733   RequestPriority priority() const {
1734     return priority_tracker_.highest_priority();
1735   }
1736
1737   // Number of non-canceled requests in |requests_|.
1738   size_t num_active_requests() const {
1739     return priority_tracker_.total_count();
1740   }
1741
1742   bool is_dns_running() const {
1743     return dns_task_.get() != NULL;
1744   }
1745
1746   bool is_proc_running() const {
1747     return proc_task_.get() != NULL;
1748   }
1749
1750   base::WeakPtr<HostResolverImpl> resolver_;
1751
1752   Key key_;
1753
1754   // Tracks the highest priority across |requests_|.
1755   PriorityTracker priority_tracker_;
1756
1757   bool had_non_speculative_request_;
1758
1759   // Distinguishes measurements taken while DnsClient was fully configured.
1760   bool had_dns_config_;
1761
1762   // Number of slots occupied by this Job in resolver's PrioritizedDispatcher.
1763   unsigned num_occupied_job_slots_;
1764
1765   // Result of DnsTask.
1766   int dns_task_error_;
1767
1768   const base::TimeTicks creation_time_;
1769   base::TimeTicks priority_change_time_;
1770
1771   BoundNetLog net_log_;
1772
1773   // Resolves the host using a HostResolverProc.
1774   scoped_refptr<ProcTask> proc_task_;
1775
1776   // Resolves the host using a DnsTransaction.
1777   scoped_ptr<DnsTask> dns_task_;
1778
1779   // All Requests waiting for the result of this Job. Some can be canceled.
1780   RequestsList requests_;
1781
1782   // A handle used in |HostResolverImpl::dispatcher_|.
1783   PrioritizedDispatcher::Handle handle_;
1784 };
1785
1786 //-----------------------------------------------------------------------------
1787
1788 HostResolverImpl::ProcTaskParams::ProcTaskParams(
1789     HostResolverProc* resolver_proc,
1790     size_t max_retry_attempts)
1791     : resolver_proc(resolver_proc),
1792       max_retry_attempts(max_retry_attempts),
1793       unresponsive_delay(base::TimeDelta::FromMilliseconds(6000)),
1794       retry_factor(2) {
1795   // Maximum of 4 retry attempts for host resolution.
1796   static const size_t kDefaultMaxRetryAttempts = 4u;
1797   if (max_retry_attempts == HostResolver::kDefaultRetryAttempts)
1798     max_retry_attempts = kDefaultMaxRetryAttempts;
1799 }
1800
1801 HostResolverImpl::ProcTaskParams::~ProcTaskParams() {}
1802
1803 HostResolverImpl::HostResolverImpl(const Options& options, NetLog* net_log)
1804     : max_queued_jobs_(0),
1805       proc_params_(NULL, options.max_retry_attempts),
1806       net_log_(net_log),
1807       default_address_family_(ADDRESS_FAMILY_UNSPECIFIED),
1808       received_dns_config_(false),
1809       num_dns_failures_(0),
1810       probe_ipv6_support_(true),
1811       use_local_ipv6_(false),
1812       resolved_known_ipv6_hostname_(false),
1813       additional_resolver_flags_(0),
1814       fallback_to_proctask_(true),
1815       weak_ptr_factory_(this),
1816       probe_weak_ptr_factory_(this) {
1817   if (options.enable_caching)
1818     cache_ = HostCache::CreateDefaultCache();
1819
1820   PrioritizedDispatcher::Limits job_limits = options.GetDispatcherLimits();
1821   dispatcher_.reset(new PrioritizedDispatcher(job_limits));
1822   max_queued_jobs_ = job_limits.total_jobs * 100u;
1823
1824   DCHECK_GE(dispatcher_->num_priorities(), static_cast<size_t>(NUM_PRIORITIES));
1825
1826 #if defined(OS_WIN)
1827   EnsureWinsockInit();
1828 #endif
1829 #if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_ANDROID)
1830   new LoopbackProbeJob(weak_ptr_factory_.GetWeakPtr());
1831 #endif
1832   NetworkChangeNotifier::AddIPAddressObserver(this);
1833   NetworkChangeNotifier::AddDNSObserver(this);
1834 #if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD) && \
1835     !defined(OS_ANDROID)
1836   EnsureDnsReloaderInit();
1837 #endif
1838
1839   {
1840     DnsConfig dns_config;
1841     NetworkChangeNotifier::GetDnsConfig(&dns_config);
1842     received_dns_config_ = dns_config.IsValid();
1843     // Conservatively assume local IPv6 is needed when DnsConfig is not valid.
1844     use_local_ipv6_ = !dns_config.IsValid() || dns_config.use_local_ipv6;
1845   }
1846
1847   fallback_to_proctask_ = !ConfigureAsyncDnsNoFallbackFieldTrial();
1848 }
1849
1850 HostResolverImpl::~HostResolverImpl() {
1851   // Prevent the dispatcher from starting new jobs.
1852   dispatcher_->SetLimitsToZero();
1853   // It's now safe for Jobs to call KillDsnTask on destruction, because
1854   // OnJobComplete will not start any new jobs.
1855   STLDeleteValues(&jobs_);
1856
1857   NetworkChangeNotifier::RemoveIPAddressObserver(this);
1858   NetworkChangeNotifier::RemoveDNSObserver(this);
1859 }
1860
1861 void HostResolverImpl::SetMaxQueuedJobs(size_t value) {
1862   DCHECK_EQ(0u, dispatcher_->num_queued_jobs());
1863   DCHECK_GT(value, 0u);
1864   max_queued_jobs_ = value;
1865 }
1866
1867 int HostResolverImpl::Resolve(const RequestInfo& info,
1868                               RequestPriority priority,
1869                               AddressList* addresses,
1870                               const CompletionCallback& callback,
1871                               RequestHandle* out_req,
1872                               const BoundNetLog& source_net_log) {
1873   DCHECK(addresses);
1874   DCHECK(CalledOnValidThread());
1875   DCHECK_EQ(false, callback.is_null());
1876
1877   // Check that the caller supplied a valid hostname to resolve.
1878   std::string labeled_hostname;
1879   if (!DNSDomainFromDot(info.hostname(), &labeled_hostname))
1880     return ERR_NAME_NOT_RESOLVED;
1881
1882   LogStartRequest(source_net_log, info);
1883
1884   // Build a key that identifies the request in the cache and in the
1885   // outstanding jobs map.
1886   Key key = GetEffectiveKeyForRequest(info, source_net_log);
1887
1888   int rv = ResolveHelper(key, info, addresses, source_net_log);
1889   if (rv != ERR_DNS_CACHE_MISS) {
1890     LogFinishRequest(source_net_log, info, rv);
1891     RecordTotalTime(HaveDnsConfig(), info.is_speculative(), base::TimeDelta());
1892     return rv;
1893   }
1894
1895   // Next we need to attach our request to a "job". This job is responsible for
1896   // calling "getaddrinfo(hostname)" on a worker thread.
1897
1898   JobMap::iterator jobit = jobs_.find(key);
1899   Job* job;
1900   if (jobit == jobs_.end()) {
1901     job =
1902         new Job(weak_ptr_factory_.GetWeakPtr(), key, priority, source_net_log);
1903     job->Schedule(false);
1904
1905     // Check for queue overflow.
1906     if (dispatcher_->num_queued_jobs() > max_queued_jobs_) {
1907       Job* evicted = static_cast<Job*>(dispatcher_->EvictOldestLowest());
1908       DCHECK(evicted);
1909       evicted->OnEvicted();  // Deletes |evicted|.
1910       if (evicted == job) {
1911         rv = ERR_HOST_RESOLVER_QUEUE_TOO_LARGE;
1912         LogFinishRequest(source_net_log, info, rv);
1913         return rv;
1914       }
1915     }
1916     jobs_.insert(jobit, std::make_pair(key, job));
1917   } else {
1918     job = jobit->second;
1919   }
1920
1921   // Can't complete synchronously. Create and attach request.
1922   scoped_ptr<Request> req(new Request(
1923       source_net_log, info, priority, callback, addresses));
1924   if (out_req)
1925     *out_req = reinterpret_cast<RequestHandle>(req.get());
1926
1927   job->AddRequest(req.Pass());
1928   // Completion happens during Job::CompleteRequests().
1929   return ERR_IO_PENDING;
1930 }
1931
1932 int HostResolverImpl::ResolveHelper(const Key& key,
1933                                     const RequestInfo& info,
1934                                     AddressList* addresses,
1935                                     const BoundNetLog& source_net_log) {
1936   // The result of |getaddrinfo| for empty hosts is inconsistent across systems.
1937   // On Windows it gives the default interface's address, whereas on Linux it
1938   // gives an error. We will make it fail on all platforms for consistency.
1939   if (info.hostname().empty() || info.hostname().size() > kMaxHostLength)
1940     return ERR_NAME_NOT_RESOLVED;
1941
1942   int net_error = ERR_UNEXPECTED;
1943   if (ResolveAsIP(key, info, &net_error, addresses))
1944     return net_error;
1945   if (ServeFromCache(key, info, &net_error, addresses)) {
1946     source_net_log.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_CACHE_HIT);
1947     return net_error;
1948   }
1949   // TODO(szym): Do not do this if nsswitch.conf instructs not to.
1950   // http://crbug.com/117655
1951   if (ServeFromHosts(key, info, addresses)) {
1952     source_net_log.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_HOSTS_HIT);
1953     return OK;
1954   }
1955   return ERR_DNS_CACHE_MISS;
1956 }
1957
1958 int HostResolverImpl::ResolveFromCache(const RequestInfo& info,
1959                                        AddressList* addresses,
1960                                        const BoundNetLog& source_net_log) {
1961   DCHECK(CalledOnValidThread());
1962   DCHECK(addresses);
1963
1964   // Update the net log and notify registered observers.
1965   LogStartRequest(source_net_log, info);
1966
1967   Key key = GetEffectiveKeyForRequest(info, source_net_log);
1968
1969   int rv = ResolveHelper(key, info, addresses, source_net_log);
1970   LogFinishRequest(source_net_log, info, rv);
1971   return rv;
1972 }
1973
1974 void HostResolverImpl::CancelRequest(RequestHandle req_handle) {
1975   DCHECK(CalledOnValidThread());
1976   Request* req = reinterpret_cast<Request*>(req_handle);
1977   DCHECK(req);
1978   Job* job = req->job();
1979   DCHECK(job);
1980   job->CancelRequest(req);
1981 }
1982
1983 void HostResolverImpl::SetDefaultAddressFamily(AddressFamily address_family) {
1984   DCHECK(CalledOnValidThread());
1985   default_address_family_ = address_family;
1986   probe_ipv6_support_ = false;
1987 }
1988
1989 AddressFamily HostResolverImpl::GetDefaultAddressFamily() const {
1990   return default_address_family_;
1991 }
1992
1993 void HostResolverImpl::SetDnsClientEnabled(bool enabled) {
1994   DCHECK(CalledOnValidThread());
1995 #if defined(ENABLE_BUILT_IN_DNS)
1996   if (enabled && !dns_client_) {
1997     SetDnsClient(DnsClient::CreateClient(net_log_));
1998   } else if (!enabled && dns_client_) {
1999     SetDnsClient(scoped_ptr<DnsClient>());
2000   }
2001 #endif
2002 }
2003
2004 HostCache* HostResolverImpl::GetHostCache() {
2005   return cache_.get();
2006 }
2007
2008 base::Value* HostResolverImpl::GetDnsConfigAsValue() const {
2009   // Check if async DNS is disabled.
2010   if (!dns_client_.get())
2011     return NULL;
2012
2013   // Check if async DNS is enabled, but we currently have no configuration
2014   // for it.
2015   const DnsConfig* dns_config = dns_client_->GetConfig();
2016   if (dns_config == NULL)
2017     return new base::DictionaryValue();
2018
2019   return dns_config->ToValue();
2020 }
2021
2022 bool HostResolverImpl::ResolveAsIP(const Key& key,
2023                                    const RequestInfo& info,
2024                                    int* net_error,
2025                                    AddressList* addresses) {
2026   DCHECK(addresses);
2027   DCHECK(net_error);
2028   IPAddressNumber ip_number;
2029   if (!ParseIPLiteralToNumber(key.hostname, &ip_number))
2030     return false;
2031
2032   DCHECK_EQ(key.host_resolver_flags &
2033       ~(HOST_RESOLVER_CANONNAME | HOST_RESOLVER_LOOPBACK_ONLY |
2034         HOST_RESOLVER_DEFAULT_FAMILY_SET_DUE_TO_NO_IPV6),
2035             0) << " Unhandled flag";
2036
2037   *net_error = OK;
2038   AddressFamily family = GetAddressFamily(ip_number);
2039   if (family == ADDRESS_FAMILY_IPV6 &&
2040       !probe_ipv6_support_ &&
2041       default_address_family_ == ADDRESS_FAMILY_IPV4) {
2042     // Don't return IPv6 addresses if default address family is set to IPv4,
2043     // and probes are disabled.
2044     *net_error = ERR_NAME_NOT_RESOLVED;
2045   } else if (key.address_family != ADDRESS_FAMILY_UNSPECIFIED &&
2046              key.address_family != family) {
2047     // Don't return IPv6 addresses for IPv4 queries, and vice versa.
2048     *net_error = ERR_NAME_NOT_RESOLVED;
2049   } else {
2050     *addresses = AddressList::CreateFromIPAddress(ip_number, info.port());
2051     if (key.host_resolver_flags & HOST_RESOLVER_CANONNAME)
2052       addresses->SetDefaultCanonicalName();
2053   }
2054   return true;
2055 }
2056
2057 bool HostResolverImpl::ServeFromCache(const Key& key,
2058                                       const RequestInfo& info,
2059                                       int* net_error,
2060                                       AddressList* addresses) {
2061   DCHECK(addresses);
2062   DCHECK(net_error);
2063   if (!info.allow_cached_response() || !cache_.get())
2064     return false;
2065
2066   const HostCache::Entry* cache_entry = cache_->Lookup(
2067       key, base::TimeTicks::Now());
2068   if (!cache_entry)
2069     return false;
2070
2071   *net_error = cache_entry->error;
2072   if (*net_error == OK) {
2073     if (cache_entry->has_ttl())
2074       RecordTTL(cache_entry->ttl);
2075     *addresses = EnsurePortOnAddressList(cache_entry->addrlist, info.port());
2076   }
2077   return true;
2078 }
2079
2080 bool HostResolverImpl::ServeFromHosts(const Key& key,
2081                                       const RequestInfo& info,
2082                                       AddressList* addresses) {
2083   DCHECK(addresses);
2084   if (!HaveDnsConfig())
2085     return false;
2086   addresses->clear();
2087
2088   // HOSTS lookups are case-insensitive.
2089   std::string hostname = base::StringToLowerASCII(key.hostname);
2090
2091   const DnsHosts& hosts = dns_client_->GetConfig()->hosts;
2092
2093   // If |address_family| is ADDRESS_FAMILY_UNSPECIFIED other implementations
2094   // (glibc and c-ares) return the first matching line. We have more
2095   // flexibility, but lose implicit ordering.
2096   // We prefer IPv6 because "happy eyeballs" will fall back to IPv4 if
2097   // necessary.
2098   if (key.address_family == ADDRESS_FAMILY_IPV6 ||
2099       key.address_family == ADDRESS_FAMILY_UNSPECIFIED) {
2100     DnsHosts::const_iterator it = hosts.find(
2101         DnsHostsKey(hostname, ADDRESS_FAMILY_IPV6));
2102     if (it != hosts.end())
2103       addresses->push_back(IPEndPoint(it->second, info.port()));
2104   }
2105
2106   if (key.address_family == ADDRESS_FAMILY_IPV4 ||
2107       key.address_family == ADDRESS_FAMILY_UNSPECIFIED) {
2108     DnsHosts::const_iterator it = hosts.find(
2109         DnsHostsKey(hostname, ADDRESS_FAMILY_IPV4));
2110     if (it != hosts.end())
2111       addresses->push_back(IPEndPoint(it->second, info.port()));
2112   }
2113
2114   // If got only loopback addresses and the family was restricted, resolve
2115   // again, without restrictions. See SystemHostResolverCall for rationale.
2116   if ((key.host_resolver_flags &
2117           HOST_RESOLVER_DEFAULT_FAMILY_SET_DUE_TO_NO_IPV6) &&
2118       IsAllIPv4Loopback(*addresses)) {
2119     Key new_key(key);
2120     new_key.address_family = ADDRESS_FAMILY_UNSPECIFIED;
2121     new_key.host_resolver_flags &=
2122         ~HOST_RESOLVER_DEFAULT_FAMILY_SET_DUE_TO_NO_IPV6;
2123     return ServeFromHosts(new_key, info, addresses);
2124   }
2125   return !addresses->empty();
2126 }
2127
2128 void HostResolverImpl::CacheResult(const Key& key,
2129                                    const HostCache::Entry& entry,
2130                                    base::TimeDelta ttl) {
2131   if (cache_.get())
2132     cache_->Set(key, entry, base::TimeTicks::Now(), ttl);
2133 }
2134
2135 void HostResolverImpl::RemoveJob(Job* job) {
2136   DCHECK(job);
2137   JobMap::iterator it = jobs_.find(job->key());
2138   if (it != jobs_.end() && it->second == job)
2139     jobs_.erase(it);
2140 }
2141
2142 void HostResolverImpl::SetHaveOnlyLoopbackAddresses(bool result) {
2143   if (result) {
2144     additional_resolver_flags_ |= HOST_RESOLVER_LOOPBACK_ONLY;
2145   } else {
2146     additional_resolver_flags_ &= ~HOST_RESOLVER_LOOPBACK_ONLY;
2147   }
2148 }
2149
2150 HostResolverImpl::Key HostResolverImpl::GetEffectiveKeyForRequest(
2151     const RequestInfo& info, const BoundNetLog& net_log) const {
2152   HostResolverFlags effective_flags =
2153       info.host_resolver_flags() | additional_resolver_flags_;
2154   AddressFamily effective_address_family = info.address_family();
2155
2156   if (info.address_family() == ADDRESS_FAMILY_UNSPECIFIED) {
2157     unsigned char ip_number[4];
2158     url::Component host_comp(0, info.hostname().size());
2159     int num_components;
2160     if (probe_ipv6_support_ && !use_local_ipv6_ &&
2161         // Don't bother IPv6 probing when resolving IPv4 literals.
2162         url::IPv4AddressToNumber(info.hostname().c_str(), host_comp, ip_number,
2163                                  &num_components) != url::CanonHostInfo::IPV4) {
2164       // Google DNS address.
2165       const uint8 kIPv6Address[] =
2166           { 0x20, 0x01, 0x48, 0x60, 0x48, 0x60, 0x00, 0x00,
2167             0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x88, 0x88 };
2168       IPAddressNumber address(kIPv6Address,
2169                               kIPv6Address + arraysize(kIPv6Address));
2170       BoundNetLog probe_net_log = BoundNetLog::Make(
2171           net_log.net_log(), NetLog::SOURCE_IPV6_REACHABILITY_CHECK);
2172       probe_net_log.BeginEvent(NetLog::TYPE_IPV6_REACHABILITY_CHECK,
2173                                net_log.source().ToEventParametersCallback());
2174       bool rv6 = IsGloballyReachable(address, probe_net_log);
2175       probe_net_log.EndEvent(NetLog::TYPE_IPV6_REACHABILITY_CHECK);
2176       if (rv6) {
2177         net_log.AddEvent(NetLog::TYPE_HOST_RESOLVER_IMPL_IPV6_SUPPORTED);
2178       } else {
2179         effective_address_family = ADDRESS_FAMILY_IPV4;
2180         effective_flags |= HOST_RESOLVER_DEFAULT_FAMILY_SET_DUE_TO_NO_IPV6;
2181       }
2182     } else {
2183       effective_address_family = default_address_family_;
2184     }
2185   }
2186
2187   std::string hostname = info.hostname();
2188   // Redirect .localhost queries to "localhost." to make sure that they
2189   // are never sent out on the network, per RFC 6761.
2190   if (IsLocalhostTLD(info.hostname()))
2191     hostname = kLocalhost;
2192
2193   return Key(hostname, effective_address_family, effective_flags);
2194 }
2195
2196 void HostResolverImpl::AbortAllInProgressJobs() {
2197   // In Abort, a Request callback could spawn new Jobs with matching keys, so
2198   // first collect and remove all running jobs from |jobs_|.
2199   ScopedVector<Job> jobs_to_abort;
2200   for (JobMap::iterator it = jobs_.begin(); it != jobs_.end(); ) {
2201     Job* job = it->second;
2202     if (job->is_running()) {
2203       jobs_to_abort.push_back(job);
2204       jobs_.erase(it++);
2205     } else {
2206       DCHECK(job->is_queued());
2207       ++it;
2208     }
2209   }
2210
2211   // Pause the dispatcher so it won't start any new dispatcher jobs while
2212   // aborting the old ones.  This is needed so that it won't start the second
2213   // DnsTransaction for a job in |jobs_to_abort| if the DnsConfig just became
2214   // invalid.
2215   PrioritizedDispatcher::Limits limits = dispatcher_->GetLimits();
2216   dispatcher_->SetLimits(
2217       PrioritizedDispatcher::Limits(limits.reserved_slots.size(), 0));
2218
2219   // Life check to bail once |this| is deleted.
2220   base::WeakPtr<HostResolverImpl> self = weak_ptr_factory_.GetWeakPtr();
2221
2222   // Then Abort them.
2223   for (size_t i = 0; self.get() && i < jobs_to_abort.size(); ++i) {
2224     jobs_to_abort[i]->Abort();
2225     jobs_to_abort[i] = NULL;
2226   }
2227
2228   if (self)
2229     dispatcher_->SetLimits(limits);
2230 }
2231
2232 void HostResolverImpl::AbortDnsTasks() {
2233   // Pause the dispatcher so it won't start any new dispatcher jobs while
2234   // aborting the old ones.  This is needed so that it won't start the second
2235   // DnsTransaction for a job if the DnsConfig just changed.
2236   PrioritizedDispatcher::Limits limits = dispatcher_->GetLimits();
2237   dispatcher_->SetLimits(
2238       PrioritizedDispatcher::Limits(limits.reserved_slots.size(), 0));
2239
2240   for (JobMap::iterator it = jobs_.begin(); it != jobs_.end(); ++it)
2241     it->second->AbortDnsTask();
2242   dispatcher_->SetLimits(limits);
2243 }
2244
2245 void HostResolverImpl::TryServingAllJobsFromHosts() {
2246   if (!HaveDnsConfig())
2247     return;
2248
2249   // TODO(szym): Do not do this if nsswitch.conf instructs not to.
2250   // http://crbug.com/117655
2251
2252   // Life check to bail once |this| is deleted.
2253   base::WeakPtr<HostResolverImpl> self = weak_ptr_factory_.GetWeakPtr();
2254
2255   for (JobMap::iterator it = jobs_.begin(); self.get() && it != jobs_.end();) {
2256     Job* job = it->second;
2257     ++it;
2258     // This could remove |job| from |jobs_|, but iterator will remain valid.
2259     job->ServeFromHosts();
2260   }
2261 }
2262
2263 void HostResolverImpl::OnIPAddressChanged() {
2264   resolved_known_ipv6_hostname_ = false;
2265   // Abandon all ProbeJobs.
2266   probe_weak_ptr_factory_.InvalidateWeakPtrs();
2267   if (cache_.get())
2268     cache_->clear();
2269 #if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_ANDROID)
2270   new LoopbackProbeJob(probe_weak_ptr_factory_.GetWeakPtr());
2271 #endif
2272   AbortAllInProgressJobs();
2273   // |this| may be deleted inside AbortAllInProgressJobs().
2274 }
2275
2276 void HostResolverImpl::OnDNSChanged() {
2277   DnsConfig dns_config;
2278   NetworkChangeNotifier::GetDnsConfig(&dns_config);
2279
2280   if (net_log_) {
2281     net_log_->AddGlobalEntry(
2282         NetLog::TYPE_DNS_CONFIG_CHANGED,
2283         base::Bind(&NetLogDnsConfigCallback, &dns_config));
2284   }
2285
2286   // TODO(szym): Remove once http://crbug.com/137914 is resolved.
2287   received_dns_config_ = dns_config.IsValid();
2288   // Conservatively assume local IPv6 is needed when DnsConfig is not valid.
2289   use_local_ipv6_ = !dns_config.IsValid() || dns_config.use_local_ipv6;
2290
2291   num_dns_failures_ = 0;
2292
2293   // We want a new DnsSession in place, before we Abort running Jobs, so that
2294   // the newly started jobs use the new config.
2295   if (dns_client_.get()) {
2296     dns_client_->SetConfig(dns_config);
2297     if (dns_client_->GetConfig())
2298       UMA_HISTOGRAM_BOOLEAN("AsyncDNS.DnsClientEnabled", true);
2299   }
2300
2301   // If the DNS server has changed, existing cached info could be wrong so we
2302   // have to drop our internal cache :( Note that OS level DNS caches, such
2303   // as NSCD's cache should be dropped automatically by the OS when
2304   // resolv.conf changes so we don't need to do anything to clear that cache.
2305   if (cache_.get())
2306     cache_->clear();
2307
2308   // Life check to bail once |this| is deleted.
2309   base::WeakPtr<HostResolverImpl> self = weak_ptr_factory_.GetWeakPtr();
2310
2311   // Existing jobs will have been sent to the original server so they need to
2312   // be aborted.
2313   AbortAllInProgressJobs();
2314
2315   // |this| may be deleted inside AbortAllInProgressJobs().
2316   if (self.get())
2317     TryServingAllJobsFromHosts();
2318 }
2319
2320 bool HostResolverImpl::HaveDnsConfig() const {
2321   // Use DnsClient only if it's fully configured and there is no override by
2322   // ScopedDefaultHostResolverProc.
2323   // The alternative is to use NetworkChangeNotifier to override DnsConfig,
2324   // but that would introduce construction order requirements for NCN and SDHRP.
2325   return (dns_client_.get() != NULL) && (dns_client_->GetConfig() != NULL) &&
2326          !(proc_params_.resolver_proc.get() == NULL &&
2327            HostResolverProc::GetDefault() != NULL);
2328 }
2329
2330 void HostResolverImpl::OnDnsTaskResolve(int net_error) {
2331   DCHECK(dns_client_);
2332   if (net_error == OK) {
2333     num_dns_failures_ = 0;
2334     return;
2335   }
2336   ++num_dns_failures_;
2337   if (num_dns_failures_ < kMaximumDnsFailures)
2338     return;
2339
2340   // Disable DnsClient until the next DNS change.  Must be done before aborting
2341   // DnsTasks, since doing so may start new jobs.
2342   dns_client_->SetConfig(DnsConfig());
2343
2344   // Switch jobs with active DnsTasks over to using ProcTasks.
2345   AbortDnsTasks();
2346
2347   UMA_HISTOGRAM_BOOLEAN("AsyncDNS.DnsClientEnabled", false);
2348   UMA_HISTOGRAM_CUSTOM_ENUMERATION("AsyncDNS.DnsClientDisabledReason",
2349                                    std::abs(net_error),
2350                                    GetAllErrorCodesForUma());
2351 }
2352
2353 void HostResolverImpl::SetDnsClient(scoped_ptr<DnsClient> dns_client) {
2354   // DnsClient and config must be updated before aborting DnsTasks, since doing
2355   // so may start new jobs.
2356   dns_client_ = dns_client.Pass();
2357   if (dns_client_ && !dns_client_->GetConfig() &&
2358       num_dns_failures_ < kMaximumDnsFailures) {
2359     DnsConfig dns_config;
2360     NetworkChangeNotifier::GetDnsConfig(&dns_config);
2361     dns_client_->SetConfig(dns_config);
2362     num_dns_failures_ = 0;
2363     if (dns_client_->GetConfig())
2364       UMA_HISTOGRAM_BOOLEAN("AsyncDNS.DnsClientEnabled", true);
2365   }
2366
2367   AbortDnsTasks();
2368 }
2369
2370 }  // namespace net