net/dns/dns_transaction.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/dns_transaction.h"
   6
   7 #include <deque>
   8 #include <string>
   9 #include <vector>
  10
  11 #include "base/big_endian.h"
  12 #include "base/bind.h"
  13 #include "base/memory/ref_counted.h"
  14 #include "base/memory/scoped_ptr.h"
  15 #include "base/memory/scoped_vector.h"
  16 #include "base/memory/weak_ptr.h"
  17 #include "base/message_loop/message_loop.h"
  18 #include "base/metrics/histogram.h"
  19 #include "base/rand_util.h"
  20 #include "base/stl_util.h"
  21 #include "base/strings/string_piece.h"
  22 #include "base/threading/non_thread_safe.h"
  23 #include "base/timer/timer.h"
  24 #include "base/values.h"
  25 #include "net/base/completion_callback.h"
  26 #include "net/base/dns_util.h"
  27 #include "net/base/io_buffer.h"
  28 #include "net/base/ip_endpoint.h"
  29 #include "net/base/net_errors.h"
  30 #include "net/base/net_log.h"
  31 #include "net/dns/dns_protocol.h"
  32 #include "net/dns/dns_query.h"
  33 #include "net/dns/dns_response.h"
  34 #include "net/dns/dns_session.h"
  35 #include "net/socket/stream_socket.h"
  36 #include "net/udp/datagram_client_socket.h"
  37
  38 namespace net {
  39
  40 namespace {
  41
  42 // Provide a common macro to simplify code and readability. We must use a
  43 // macro as the underlying HISTOGRAM macro creates static variables.
  44 #define DNS_HISTOGRAM(name, time) UMA_HISTOGRAM_CUSTOM_TIMES(name, time, \
  45     base::TimeDelta::FromMilliseconds(1), base::TimeDelta::FromHours(1), 100)
  46
  47 // Count labels in the fully-qualified name in DNS format.
  48 int CountLabels(const std::string& name) {
  49   size_t count = 0;
  50   for (size_t i = 0; i < name.size() && name[i]; i += name[i] + 1)
  51     ++count;
  52   return count;
  53 }
  54
  55 bool IsIPLiteral(const std::string& hostname) {
  56   IPAddressNumber ip;
  57   return ParseIPLiteralToNumber(hostname, &ip);
  58 }
  59
  60 base::Value* NetLogStartCallback(const std::string* hostname,
  61                            uint16 qtype,
  62                            NetLog::LogLevel /* log_level */) {
  63   base::DictionaryValue* dict = new base::DictionaryValue();
  64   dict->SetString("hostname", *hostname);
  65   dict->SetInteger("query_type", qtype);
  66   return dict;
  67 };
  68
  69 // ----------------------------------------------------------------------------
  70
  71 // A single asynchronous DNS exchange, which consists of sending out a
  72 // DNS query, waiting for a response, and returning the response that it
  73 // matches. Logging is done in the socket and in the outer DnsTransaction.
  74 class DnsAttempt {
  75  public:
  76   explicit DnsAttempt(unsigned server_index)
  77       : result_(ERR_FAILED), server_index_(server_index) {}
  78
  79   virtual ~DnsAttempt() {}
  80   // Starts the attempt. Returns ERR_IO_PENDING if cannot complete synchronously
  81   // and calls |callback| upon completion.
  82   virtual int Start(const CompletionCallback& callback) = 0;
  83
  84   // Returns the query of this attempt.
  85   virtual const DnsQuery* GetQuery() const = 0;
  86
  87   // Returns the response or NULL if has not received a matching response from
  88   // the server.
  89   virtual const DnsResponse* GetResponse() const = 0;
  90
  91   // Returns the net log bound to the source of the socket.
  92   virtual const BoundNetLog& GetSocketNetLog() const = 0;
  93
  94   // Returns the index of the destination server within DnsConfig::nameservers.
  95   unsigned server_index() const { return server_index_; }
  96
  97   // Returns a Value representing the received response, along with a reference
  98   // to the NetLog source source of the UDP socket used.  The request must have
  99   // completed before this is called.
 100   base::Value* NetLogResponseCallback(NetLog::LogLevel log_level) const {
 101     DCHECK(GetResponse()->IsValid());
 102
 103     base::DictionaryValue* dict = new base::DictionaryValue();
 104     dict->SetInteger("rcode", GetResponse()->rcode());
 105     dict->SetInteger("answer_count", GetResponse()->answer_count());
 106     GetSocketNetLog().source().AddToEventParameters(dict);
 107     return dict;
 108   }
 109
 110   void set_result(int result) {
 111     result_ = result;
 112   }
 113
 114   // True if current attempt is pending (waiting for server response).
 115   bool is_pending() const {
 116     return result_ == ERR_IO_PENDING;
 117   }
 118
 119   // True if attempt is completed (received server response).
 120   bool is_completed() const {
 121     return (result_ == OK) || (result_ == ERR_NAME_NOT_RESOLVED) ||
 122         (result_ == ERR_DNS_SERVER_REQUIRES_TCP);
 123   }
 124
 125  private:
 126   // Result of last operation.
 127   int result_;
 128
 129   const unsigned server_index_;
 130 };
 131
 132 class DnsUDPAttempt : public DnsAttempt {
 133  public:
 134   DnsUDPAttempt(unsigned server_index,
 135                 scoped_ptr<DnsSession::SocketLease> socket_lease,
 136                 scoped_ptr<DnsQuery> query)
 137       : DnsAttempt(server_index),
 138         next_state_(STATE_NONE),
 139         received_malformed_response_(false),
 140         socket_lease_(socket_lease.Pass()),
 141         query_(query.Pass()) {}
 142
 143   // DnsAttempt:
 144   virtual int Start(const CompletionCallback& callback) OVERRIDE {
 145     DCHECK_EQ(STATE_NONE, next_state_);
 146     callback_ = callback;
 147     start_time_ = base::TimeTicks::Now();
 148     next_state_ = STATE_SEND_QUERY;
 149     return DoLoop(OK);
 150   }
 151
 152   virtual const DnsQuery* GetQuery() const OVERRIDE {
 153     return query_.get();
 154   }
 155
 156   virtual const DnsResponse* GetResponse() const OVERRIDE {
 157     const DnsResponse* resp = response_.get();
 158     return (resp != NULL && resp->IsValid()) ? resp : NULL;
 159   }
 160
 161   virtual const BoundNetLog& GetSocketNetLog() const OVERRIDE {
 162     return socket_lease_->socket()->NetLog();
 163   }
 164
 165  private:
 166   enum State {
 167     STATE_SEND_QUERY,
 168     STATE_SEND_QUERY_COMPLETE,
 169     STATE_READ_RESPONSE,
 170     STATE_READ_RESPONSE_COMPLETE,
 171     STATE_NONE,
 172   };
 173
 174   DatagramClientSocket* socket() {
 175     return socket_lease_->socket();
 176   }
 177
 178   int DoLoop(int result) {
 179     CHECK_NE(STATE_NONE, next_state_);
 180     int rv = result;
 181     do {
 182       State state = next_state_;
 183       next_state_ = STATE_NONE;
 184       switch (state) {
 185         case STATE_SEND_QUERY:
 186           rv = DoSendQuery();
 187           break;
 188         case STATE_SEND_QUERY_COMPLETE:
 189           rv = DoSendQueryComplete(rv);
 190           break;
 191         case STATE_READ_RESPONSE:
 192           rv = DoReadResponse();
 193           break;
 194         case STATE_READ_RESPONSE_COMPLETE:
 195           rv = DoReadResponseComplete(rv);
 196           break;
 197         default:
 198           NOTREACHED();
 199           break;
 200       }
 201     } while (rv != ERR_IO_PENDING && next_state_ != STATE_NONE);
 202
 203     set_result(rv);
 204     // If we received a malformed response, and are now waiting for another one,
 205     // indicate to the transaction that the server might be misbehaving.
 206     if (rv == ERR_IO_PENDING && received_malformed_response_)
 207       return ERR_DNS_MALFORMED_RESPONSE;
 208     if (rv == OK) {
 209       DCHECK_EQ(STATE_NONE, next_state_);
 210       DNS_HISTOGRAM("AsyncDNS.UDPAttemptSuccess",
 211                     base::TimeTicks::Now() - start_time_);
 212     } else if (rv != ERR_IO_PENDING) {
 213       DNS_HISTOGRAM("AsyncDNS.UDPAttemptFail",
 214                     base::TimeTicks::Now() - start_time_);
 215     }
 216     return rv;
 217   }
 218
 219   int DoSendQuery() {
 220     next_state_ = STATE_SEND_QUERY_COMPLETE;
 221     return socket()->Write(query_->io_buffer(),
 222                            query_->io_buffer()->size(),
 223                            base::Bind(&DnsUDPAttempt::OnIOComplete,
 224                                       base::Unretained(this)));
 225   }
 226
 227   int DoSendQueryComplete(int rv) {
 228     DCHECK_NE(ERR_IO_PENDING, rv);
 229     if (rv < 0)
 230       return rv;
 231
 232     // Writing to UDP should not result in a partial datagram.
 233     if (rv != query_->io_buffer()->size())
 234       return ERR_MSG_TOO_BIG;
 235
 236     next_state_ = STATE_READ_RESPONSE;
 237     return OK;
 238   }
 239
 240   int DoReadResponse() {
 241     next_state_ = STATE_READ_RESPONSE_COMPLETE;
 242     response_.reset(new DnsResponse());
 243     return socket()->Read(response_->io_buffer(),
 244                           response_->io_buffer()->size(),
 245                           base::Bind(&DnsUDPAttempt::OnIOComplete,
 246                                      base::Unretained(this)));
 247   }
 248
 249   int DoReadResponseComplete(int rv) {
 250     DCHECK_NE(ERR_IO_PENDING, rv);
 251     if (rv < 0)
 252       return rv;
 253
 254     DCHECK(rv);
 255     if (!response_->InitParse(rv, *query_)) {
 256       // Other implementations simply ignore mismatched responses. Since each
 257       // DnsUDPAttempt binds to a different port, we might find that responses
 258       // to previously timed out queries lead to failures in the future.
 259       // Our solution is to make another attempt, in case the query truly
 260       // failed, but keep this attempt alive, in case it was a false alarm.
 261       received_malformed_response_ = true;
 262       next_state_ = STATE_READ_RESPONSE;
 263       return OK;
 264     }
 265     if (response_->flags() & dns_protocol::kFlagTC)
 266       return ERR_DNS_SERVER_REQUIRES_TCP;
 267     // TODO(szym): Extract TTL for NXDOMAIN results. http://crbug.com/115051
 268     if (response_->rcode() == dns_protocol::kRcodeNXDOMAIN)
 269       return ERR_NAME_NOT_RESOLVED;
 270     if (response_->rcode() != dns_protocol::kRcodeNOERROR)
 271       return ERR_DNS_SERVER_FAILED;
 272
 273     return OK;
 274   }
 275
 276   void OnIOComplete(int rv) {
 277     rv = DoLoop(rv);
 278     if (rv != ERR_IO_PENDING)
 279       callback_.Run(rv);
 280   }
 281
 282   State next_state_;
 283   bool received_malformed_response_;
 284   base::TimeTicks start_time_;
 285
 286   scoped_ptr<DnsSession::SocketLease> socket_lease_;
 287   scoped_ptr<DnsQuery> query_;
 288
 289   scoped_ptr<DnsResponse> response_;
 290
 291   CompletionCallback callback_;
 292
 293   DISALLOW_COPY_AND_ASSIGN(DnsUDPAttempt);
 294 };
 295
 296 class DnsTCPAttempt : public DnsAttempt {
 297  public:
 298   DnsTCPAttempt(unsigned server_index,
 299                 scoped_ptr<StreamSocket> socket,
 300                 scoped_ptr<DnsQuery> query)
 301       : DnsAttempt(server_index),
 302         next_state_(STATE_NONE),
 303         socket_(socket.Pass()),
 304         query_(query.Pass()),
 305         length_buffer_(new IOBufferWithSize(sizeof(uint16))),
 306         response_length_(0) {}
 307
 308   // DnsAttempt:
 309   virtual int Start(const CompletionCallback& callback) OVERRIDE {
 310     DCHECK_EQ(STATE_NONE, next_state_);
 311     callback_ = callback;
 312     start_time_ = base::TimeTicks::Now();
 313     next_state_ = STATE_CONNECT_COMPLETE;
 314     int rv = socket_->Connect(base::Bind(&DnsTCPAttempt::OnIOComplete,
 315                                          base::Unretained(this)));
 316     if (rv == ERR_IO_PENDING) {
 317       set_result(rv);
 318       return rv;
 319     }
 320     return DoLoop(rv);
 321   }
 322
 323   virtual const DnsQuery* GetQuery() const OVERRIDE {
 324     return query_.get();
 325   }
 326
 327   virtual const DnsResponse* GetResponse() const OVERRIDE {
 328     const DnsResponse* resp = response_.get();
 329     return (resp != NULL && resp->IsValid()) ? resp : NULL;
 330   }
 331
 332   virtual const BoundNetLog& GetSocketNetLog() const OVERRIDE {
 333     return socket_->NetLog();
 334   }
 335
 336  private:
 337   enum State {
 338     STATE_CONNECT_COMPLETE,
 339     STATE_SEND_LENGTH,
 340     STATE_SEND_QUERY,
 341     STATE_READ_LENGTH,
 342     STATE_READ_LENGTH_COMPLETE,
 343     STATE_READ_RESPONSE,
 344     STATE_READ_RESPONSE_COMPLETE,
 345     STATE_NONE,
 346   };
 347
 348   int DoLoop(int result) {
 349     CHECK_NE(STATE_NONE, next_state_);
 350     int rv = result;
 351     do {
 352       State state = next_state_;
 353       next_state_ = STATE_NONE;
 354       switch (state) {
 355         case STATE_CONNECT_COMPLETE:
 356           rv = DoConnectComplete(rv);
 357           break;
 358         case STATE_SEND_LENGTH:
 359           rv = DoSendLength(rv);
 360           break;
 361         case STATE_SEND_QUERY:
 362           rv = DoSendQuery(rv);
 363           break;
 364         case STATE_READ_LENGTH:
 365           rv = DoReadLength(rv);
 366           break;
 367         case STATE_READ_LENGTH_COMPLETE:
 368           rv = DoReadLengthComplete(rv);
 369           break;
 370         case STATE_READ_RESPONSE:
 371           rv = DoReadResponse(rv);
 372           break;
 373         case STATE_READ_RESPONSE_COMPLETE:
 374           rv = DoReadResponseComplete(rv);
 375           break;
 376         default:
 377           NOTREACHED();
 378           break;
 379       }
 380     } while (rv != ERR_IO_PENDING && next_state_ != STATE_NONE);
 381
 382     set_result(rv);
 383     if (rv == OK) {
 384       DCHECK_EQ(STATE_NONE, next_state_);
 385       DNS_HISTOGRAM("AsyncDNS.TCPAttemptSuccess",
 386                     base::TimeTicks::Now() - start_time_);
 387     } else if (rv != ERR_IO_PENDING) {
 388       DNS_HISTOGRAM("AsyncDNS.TCPAttemptFail",
 389                     base::TimeTicks::Now() - start_time_);
 390     }
 391     return rv;
 392   }
 393
 394   int DoConnectComplete(int rv) {
 395     DCHECK_NE(ERR_IO_PENDING, rv);
 396     if (rv < 0)
 397       return rv;
 398
 399     base::WriteBigEndian<uint16>(length_buffer_->data(),
 400                                  query_->io_buffer()->size());
 401     buffer_ =
 402         new DrainableIOBuffer(length_buffer_.get(), length_buffer_->size());
 403     next_state_ = STATE_SEND_LENGTH;
 404     return OK;
 405   }
 406
 407   int DoSendLength(int rv) {
 408     DCHECK_NE(ERR_IO_PENDING, rv);
 409     if (rv < 0)
 410       return rv;
 411
 412     buffer_->DidConsume(rv);
 413     if (buffer_->BytesRemaining() > 0) {
 414       next_state_ = STATE_SEND_LENGTH;
 415       return socket_->Write(
 416           buffer_.get(),
 417           buffer_->BytesRemaining(),
 418           base::Bind(&DnsTCPAttempt::OnIOComplete, base::Unretained(this)));
 419     }
 420     buffer_ = new DrainableIOBuffer(query_->io_buffer(),
 421                                     query_->io_buffer()->size());
 422     next_state_ = STATE_SEND_QUERY;
 423     return OK;
 424   }
 425
 426   int DoSendQuery(int rv) {
 427     DCHECK_NE(ERR_IO_PENDING, rv);
 428     if (rv < 0)
 429       return rv;
 430
 431     buffer_->DidConsume(rv);
 432     if (buffer_->BytesRemaining() > 0) {
 433       next_state_ = STATE_SEND_QUERY;
 434       return socket_->Write(
 435           buffer_.get(),
 436           buffer_->BytesRemaining(),
 437           base::Bind(&DnsTCPAttempt::OnIOComplete, base::Unretained(this)));
 438     }
 439     buffer_ =
 440         new DrainableIOBuffer(length_buffer_.get(), length_buffer_->size());
 441     next_state_ = STATE_READ_LENGTH;
 442     return OK;
 443   }
 444
 445   int DoReadLength(int rv) {
 446     DCHECK_EQ(OK, rv);
 447
 448     next_state_ = STATE_READ_LENGTH_COMPLETE;
 449     return ReadIntoBuffer();
 450   }
 451
 452   int DoReadLengthComplete(int rv) {
 453     DCHECK_NE(ERR_IO_PENDING, rv);
 454     if (rv < 0)
 455       return rv;
 456     if (rv == 0)
 457       return ERR_CONNECTION_CLOSED;
 458
 459     buffer_->DidConsume(rv);
 460     if (buffer_->BytesRemaining() > 0) {
 461       next_state_ = STATE_READ_LENGTH;
 462       return OK;
 463     }
 464
 465     base::ReadBigEndian<uint16>(length_buffer_->data(), &response_length_);
 466     // Check if advertised response is too short. (Optimization only.)
 467     if (response_length_ < query_->io_buffer()->size())
 468       return ERR_DNS_MALFORMED_RESPONSE;
 469     // Allocate more space so that DnsResponse::InitParse sanity check passes.
 470     response_.reset(new DnsResponse(response_length_ + 1));
 471     buffer_ = new DrainableIOBuffer(response_->io_buffer(), response_length_);
 472     next_state_ = STATE_READ_RESPONSE;
 473     return OK;
 474   }
 475
 476   int DoReadResponse(int rv) {
 477     DCHECK_EQ(OK, rv);
 478
 479     next_state_ = STATE_READ_RESPONSE_COMPLETE;
 480     return ReadIntoBuffer();
 481   }
 482
 483   int DoReadResponseComplete(int rv) {
 484     DCHECK_NE(ERR_IO_PENDING, rv);
 485     if (rv < 0)
 486       return rv;
 487     if (rv == 0)
 488       return ERR_CONNECTION_CLOSED;
 489
 490     buffer_->DidConsume(rv);
 491     if (buffer_->BytesRemaining() > 0) {
 492       next_state_ = STATE_READ_RESPONSE;
 493       return OK;
 494     }
 495
 496     if (!response_->InitParse(buffer_->BytesConsumed(), *query_))
 497       return ERR_DNS_MALFORMED_RESPONSE;
 498     if (response_->flags() & dns_protocol::kFlagTC)
 499       return ERR_UNEXPECTED;
 500     // TODO(szym): Frankly, none of these are expected.
 501     if (response_->rcode() == dns_protocol::kRcodeNXDOMAIN)
 502       return ERR_NAME_NOT_RESOLVED;
 503     if (response_->rcode() != dns_protocol::kRcodeNOERROR)
 504       return ERR_DNS_SERVER_FAILED;
 505
 506     return OK;
 507   }
 508
 509   void OnIOComplete(int rv) {
 510     rv = DoLoop(rv);
 511     if (rv != ERR_IO_PENDING)
 512       callback_.Run(rv);
 513   }
 514
 515   int ReadIntoBuffer() {
 516     return socket_->Read(
 517         buffer_.get(),
 518         buffer_->BytesRemaining(),
 519         base::Bind(&DnsTCPAttempt::OnIOComplete, base::Unretained(this)));
 520   }
 521
 522   State next_state_;
 523   base::TimeTicks start_time_;
 524
 525   scoped_ptr<StreamSocket> socket_;
 526   scoped_ptr<DnsQuery> query_;
 527   scoped_refptr<IOBufferWithSize> length_buffer_;
 528   scoped_refptr<DrainableIOBuffer> buffer_;
 529
 530   uint16 response_length_;
 531   scoped_ptr<DnsResponse> response_;
 532
 533   CompletionCallback callback_;
 534
 535   DISALLOW_COPY_AND_ASSIGN(DnsTCPAttempt);
 536 };
 537
 538 // ----------------------------------------------------------------------------
 539
 540 // Implements DnsTransaction. Configuration is supplied by DnsSession.
 541 // The suffix list is built according to the DnsConfig from the session.
 542 // The timeout for each DnsUDPAttempt is given by DnsSession::NextTimeout.
 543 // The first server to attempt on each query is given by
 544 // DnsSession::NextFirstServerIndex, and the order is round-robin afterwards.
 545 // Each server is attempted DnsConfig::attempts times.
 546 class DnsTransactionImpl : public DnsTransaction,
 547                            public base::NonThreadSafe,
 548                            public base::SupportsWeakPtr<DnsTransactionImpl> {
 549  public:
 550   DnsTransactionImpl(DnsSession* session,
 551                      const std::string& hostname,
 552                      uint16 qtype,
 553                      const DnsTransactionFactory::CallbackType& callback,
 554                      const BoundNetLog& net_log)
 555     : session_(session),
 556       hostname_(hostname),
 557       qtype_(qtype),
 558       callback_(callback),
 559       net_log_(net_log),
 560       qnames_initial_size_(0),
 561       attempts_count_(0),
 562       had_tcp_attempt_(false),
 563       first_server_index_(0) {
 564     DCHECK(session_.get());
 565     DCHECK(!hostname_.empty());
 566     DCHECK(!callback_.is_null());
 567     DCHECK(!IsIPLiteral(hostname_));
 568   }
 569
 570   virtual ~DnsTransactionImpl() {
 571     if (!callback_.is_null()) {
 572       net_log_.EndEventWithNetErrorCode(NetLog::TYPE_DNS_TRANSACTION,
 573                                         ERR_ABORTED);
 574     }  // otherwise logged in DoCallback or Start
 575   }
 576
 577   virtual const std::string& GetHostname() const OVERRIDE {
 578     DCHECK(CalledOnValidThread());
 579     return hostname_;
 580   }
 581
 582   virtual uint16 GetType() const OVERRIDE {
 583     DCHECK(CalledOnValidThread());
 584     return qtype_;
 585   }
 586
 587   virtual void Start() OVERRIDE {
 588     DCHECK(!callback_.is_null());
 589     DCHECK(attempts_.empty());
 590     net_log_.BeginEvent(NetLog::TYPE_DNS_TRANSACTION,
 591                         base::Bind(&NetLogStartCallback, &hostname_, qtype_));
 592     AttemptResult result(PrepareSearch(), NULL);
 593     if (result.rv == OK) {
 594       qnames_initial_size_ = qnames_.size();
 595       if (qtype_ == dns_protocol::kTypeA)
 596         UMA_HISTOGRAM_COUNTS("AsyncDNS.SuffixSearchStart", qnames_.size());
 597       result = ProcessAttemptResult(StartQuery());
 598     }
 599
 600     // Must always return result asynchronously, to avoid reentrancy.
 601     if (result.rv != ERR_IO_PENDING) {
 602       base::MessageLoop::current()->PostTask(
 603           FROM_HERE,
 604           base::Bind(&DnsTransactionImpl::DoCallback, AsWeakPtr(), result));
 605     }
 606   }
 607
 608  private:
 609   // Wrapper for the result of a DnsUDPAttempt.
 610   struct AttemptResult {
 611     AttemptResult(int rv, const DnsAttempt* attempt)
 612         : rv(rv), attempt(attempt) {}
 613
 614     int rv;
 615     const DnsAttempt* attempt;
 616   };
 617
 618   // Prepares |qnames_| according to the DnsConfig.
 619   int PrepareSearch() {
 620     const DnsConfig& config = session_->config();
 621
 622     std::string labeled_hostname;
 623     if (!DNSDomainFromDot(hostname_, &labeled_hostname))
 624       return ERR_INVALID_ARGUMENT;
 625
 626     if (hostname_[hostname_.size() - 1] == '.') {
 627       // It's a fully-qualified name, no suffix search.
 628       qnames_.push_back(labeled_hostname);
 629       return OK;
 630     }
 631
 632     int ndots = CountLabels(labeled_hostname) - 1;
 633
 634     if (ndots > 0 && !config.append_to_multi_label_name) {
 635       qnames_.push_back(labeled_hostname);
 636       return OK;
 637     }
 638
 639     // Set true when |labeled_hostname| is put on the list.
 640     bool had_hostname = false;
 641
 642     if (ndots >= config.ndots) {
 643       qnames_.push_back(labeled_hostname);
 644       had_hostname = true;
 645     }
 646
 647     std::string qname;
 648     for (size_t i = 0; i < config.search.size(); ++i) {
 649       // Ignore invalid (too long) combinations.
 650       if (!DNSDomainFromDot(hostname_ + "." + config.search[i], &qname))
 651         continue;
 652       if (qname.size() == labeled_hostname.size()) {
 653         if (had_hostname)
 654           continue;
 655         had_hostname = true;
 656       }
 657       qnames_.push_back(qname);
 658     }
 659
 660     if (ndots > 0 && !had_hostname)
 661       qnames_.push_back(labeled_hostname);
 662
 663     return qnames_.empty() ? ERR_DNS_SEARCH_EMPTY : OK;
 664   }
 665
 666   void DoCallback(AttemptResult result) {
 667     DCHECK(!callback_.is_null());
 668     DCHECK_NE(ERR_IO_PENDING, result.rv);
 669     const DnsResponse* response = result.attempt ?
 670         result.attempt->GetResponse() : NULL;
 671     CHECK(result.rv != OK || response != NULL);
 672
 673     timer_.Stop();
 674     RecordLostPacketsIfAny();
 675     if (result.rv == OK)
 676       UMA_HISTOGRAM_COUNTS("AsyncDNS.AttemptCountSuccess", attempts_count_);
 677     else
 678       UMA_HISTOGRAM_COUNTS("AsyncDNS.AttemptCountFail", attempts_count_);
 679
 680     if (response && qtype_ == dns_protocol::kTypeA) {
 681       UMA_HISTOGRAM_COUNTS("AsyncDNS.SuffixSearchRemain", qnames_.size());
 682       UMA_HISTOGRAM_COUNTS("AsyncDNS.SuffixSearchDone",
 683                            qnames_initial_size_ - qnames_.size());
 684     }
 685
 686     DnsTransactionFactory::CallbackType callback = callback_;
 687     callback_.Reset();
 688
 689     net_log_.EndEventWithNetErrorCode(NetLog::TYPE_DNS_TRANSACTION, result.rv);
 690     callback.Run(this, result.rv, response);
 691   }
 692
 693   // Makes another attempt at the current name, |qnames_.front()|, using the
 694   // next nameserver.
 695   AttemptResult MakeAttempt() {
 696     unsigned attempt_number = attempts_.size();
 697
 698     uint16 id = session_->NextQueryId();
 699     scoped_ptr<DnsQuery> query;
 700     if (attempts_.empty()) {
 701       query.reset(new DnsQuery(id, qnames_.front(), qtype_));
 702     } else {
 703       query.reset(attempts_[0]->GetQuery()->CloneWithNewId(id));
 704     }
 705
 706     const DnsConfig& config = session_->config();
 707
 708     unsigned server_index =
 709         (first_server_index_ + attempt_number) % config.nameservers.size();
 710     // Skip over known failed servers.
 711     server_index = session_->NextGoodServerIndex(server_index);
 712
 713     scoped_ptr<DnsSession::SocketLease> lease =
 714         session_->AllocateSocket(server_index, net_log_.source());
 715
 716     bool got_socket = !!lease.get();
 717
 718     DnsUDPAttempt* attempt =
 719         new DnsUDPAttempt(server_index, lease.Pass(), query.Pass());
 720
 721     attempts_.push_back(attempt);
 722     ++attempts_count_;
 723
 724     if (!got_socket)
 725       return AttemptResult(ERR_CONNECTION_REFUSED, NULL);
 726
 727     net_log_.AddEvent(
 728         NetLog::TYPE_DNS_TRANSACTION_ATTEMPT,
 729         attempt->GetSocketNetLog().source().ToEventParametersCallback());
 730
 731     int rv = attempt->Start(
 732         base::Bind(&DnsTransactionImpl::OnUdpAttemptComplete,
 733                    base::Unretained(this), attempt_number,
 734                    base::TimeTicks::Now()));
 735     if (rv == ERR_IO_PENDING) {
 736       base::TimeDelta timeout = session_->NextTimeout(server_index,
 737                                                       attempt_number);
 738       timer_.Start(FROM_HERE, timeout, this, &DnsTransactionImpl::OnTimeout);
 739     }
 740     return AttemptResult(rv, attempt);
 741   }
 742
 743   AttemptResult MakeTCPAttempt(const DnsAttempt* previous_attempt) {
 744     DCHECK(previous_attempt);
 745     DCHECK(!had_tcp_attempt_);
 746
 747     unsigned server_index = previous_attempt->server_index();
 748
 749     scoped_ptr<StreamSocket> socket(
 750         session_->CreateTCPSocket(server_index, net_log_.source()));
 751
 752     // TODO(szym): Reuse the same id to help the server?
 753     uint16 id = session_->NextQueryId();
 754     scoped_ptr<DnsQuery> query(
 755         previous_attempt->GetQuery()->CloneWithNewId(id));
 756
 757     RecordLostPacketsIfAny();
 758     // Cancel all other attempts, no point waiting on them.
 759     attempts_.clear();
 760
 761     unsigned attempt_number = attempts_.size();
 762
 763     DnsTCPAttempt* attempt = new DnsTCPAttempt(server_index, socket.Pass(),
 764                                                query.Pass());
 765
 766     attempts_.push_back(attempt);
 767     ++attempts_count_;
 768     had_tcp_attempt_ = true;
 769
 770     net_log_.AddEvent(
 771         NetLog::TYPE_DNS_TRANSACTION_TCP_ATTEMPT,
 772         attempt->GetSocketNetLog().source().ToEventParametersCallback());
 773
 774     int rv = attempt->Start(base::Bind(&DnsTransactionImpl::OnAttemptComplete,
 775                                        base::Unretained(this),
 776                                        attempt_number));
 777     if (rv == ERR_IO_PENDING) {
 778       // Custom timeout for TCP attempt.
 779       base::TimeDelta timeout = timer_.GetCurrentDelay() * 2;
 780       timer_.Start(FROM_HERE, timeout, this, &DnsTransactionImpl::OnTimeout);
 781     }
 782     return AttemptResult(rv, attempt);
 783   }
 784
 785   // Begins query for the current name. Makes the first attempt.
 786   AttemptResult StartQuery() {
 787     std::string dotted_qname = DNSDomainToString(qnames_.front());
 788     net_log_.BeginEvent(NetLog::TYPE_DNS_TRANSACTION_QUERY,
 789                         NetLog::StringCallback("qname", &dotted_qname));
 790
 791     first_server_index_ = session_->NextFirstServerIndex();
 792     RecordLostPacketsIfAny();
 793     attempts_.clear();
 794     had_tcp_attempt_ = false;
 795     return MakeAttempt();
 796   }
 797
 798   void OnUdpAttemptComplete(unsigned attempt_number,
 799                             base::TimeTicks start,
 800                             int rv) {
 801     DCHECK_LT(attempt_number, attempts_.size());
 802     const DnsAttempt* attempt = attempts_[attempt_number];
 803     if (attempt->GetResponse()) {
 804       session_->RecordRTT(attempt->server_index(),
 805                           base::TimeTicks::Now() - start);
 806     }
 807     OnAttemptComplete(attempt_number, rv);
 808   }
 809
 810   void OnAttemptComplete(unsigned attempt_number, int rv) {
 811     if (callback_.is_null())
 812       return;
 813     DCHECK_LT(attempt_number, attempts_.size());
 814     const DnsAttempt* attempt = attempts_[attempt_number];
 815     AttemptResult result = ProcessAttemptResult(AttemptResult(rv, attempt));
 816     if (result.rv != ERR_IO_PENDING)
 817       DoCallback(result);
 818   }
 819
 820   // Record packet loss for any incomplete attempts.
 821   void RecordLostPacketsIfAny() {
 822     // Loop through attempts until we find first that is completed
 823     size_t first_completed = 0;
 824     for (first_completed = 0; first_completed < attempts_.size();
 825         ++first_completed) {
 826       if (attempts_[first_completed]->is_completed())
 827         break;
 828     }
 829     // If there were no completed attempts, then we must be offline, so don't
 830     // record any attempts as lost packets.
 831     if (first_completed == attempts_.size())
 832       return;
 833
 834     size_t num_servers = session_->config().nameservers.size();
 835     std::vector<int> server_attempts(num_servers);
 836     for (size_t i = 0; i < first_completed; ++i) {
 837       unsigned server_index = attempts_[i]->server_index();
 838       int server_attempt = server_attempts[server_index]++;
 839       // Don't record lost packet unless attempt is in pending state.
 840       if (!attempts_[i]->is_pending())
 841         continue;
 842       session_->RecordLostPacket(server_index, server_attempt);
 843     }
 844   }
 845
 846   void LogResponse(const DnsAttempt* attempt) {
 847     if (attempt && attempt->GetResponse()) {
 848       net_log_.AddEvent(
 849           NetLog::TYPE_DNS_TRANSACTION_RESPONSE,
 850           base::Bind(&DnsAttempt::NetLogResponseCallback,
 851                      base::Unretained(attempt)));
 852     }
 853   }
 854
 855   bool MoreAttemptsAllowed() const {
 856     if (had_tcp_attempt_)
 857       return false;
 858     const DnsConfig& config = session_->config();
 859     return attempts_.size() < config.attempts * config.nameservers.size();
 860   }
 861
 862   // Resolves the result of a DnsAttempt until a terminal result is reached
 863   // or it will complete asynchronously (ERR_IO_PENDING).
 864   AttemptResult ProcessAttemptResult(AttemptResult result) {
 865     while (result.rv != ERR_IO_PENDING) {
 866       LogResponse(result.attempt);
 867
 868       switch (result.rv) {
 869         case OK:
 870           session_->RecordServerSuccess(result.attempt->server_index());
 871           net_log_.EndEventWithNetErrorCode(NetLog::TYPE_DNS_TRANSACTION_QUERY,
 872                                             result.rv);
 873           DCHECK(result.attempt);
 874           DCHECK(result.attempt->GetResponse());
 875           return result;
 876         case ERR_NAME_NOT_RESOLVED:
 877           session_->RecordServerSuccess(result.attempt->server_index());
 878           net_log_.EndEventWithNetErrorCode(NetLog::TYPE_DNS_TRANSACTION_QUERY,
 879                                             result.rv);
 880           // Try next suffix.
 881           qnames_.pop_front();
 882           if (qnames_.empty()) {
 883             return AttemptResult(ERR_NAME_NOT_RESOLVED, NULL);
 884           } else {
 885             result = StartQuery();
 886           }
 887           break;
 888         case ERR_CONNECTION_REFUSED:
 889         case ERR_DNS_TIMED_OUT:
 890           if (result.attempt)
 891             session_->RecordServerFailure(result.attempt->server_index());
 892           if (MoreAttemptsAllowed()) {
 893             result = MakeAttempt();
 894           } else {
 895             return result;
 896           }
 897           break;
 898         case ERR_DNS_SERVER_REQUIRES_TCP:
 899           result = MakeTCPAttempt(result.attempt);
 900           break;
 901         default:
 902           // Server failure.
 903           DCHECK(result.attempt);
 904           if (result.attempt != attempts_.back()) {
 905             // This attempt already timed out. Ignore it.
 906             session_->RecordServerFailure(result.attempt->server_index());
 907             return AttemptResult(ERR_IO_PENDING, NULL);
 908           }
 909           if (MoreAttemptsAllowed()) {
 910             result = MakeAttempt();
 911           } else if (result.rv == ERR_DNS_MALFORMED_RESPONSE &&
 912                      !had_tcp_attempt_) {
 913             // For UDP only, ignore the response and wait until the last attempt
 914             // times out.
 915             return AttemptResult(ERR_IO_PENDING, NULL);
 916           } else {
 917             return AttemptResult(result.rv, NULL);
 918           }
 919           break;
 920       }
 921     }
 922     return result;
 923   }
 924
 925   void OnTimeout() {
 926     if (callback_.is_null())
 927       return;
 928     DCHECK(!attempts_.empty());
 929     AttemptResult result = ProcessAttemptResult(
 930         AttemptResult(ERR_DNS_TIMED_OUT, attempts_.back()));
 931     if (result.rv != ERR_IO_PENDING)
 932       DoCallback(result);
 933   }
 934
 935   scoped_refptr<DnsSession> session_;
 936   std::string hostname_;
 937   uint16 qtype_;
 938   // Cleared in DoCallback.
 939   DnsTransactionFactory::CallbackType callback_;
 940
 941   BoundNetLog net_log_;
 942
 943   // Search list of fully-qualified DNS names to query next (in DNS format).
 944   std::deque<std::string> qnames_;
 945   size_t qnames_initial_size_;
 946
 947   // List of attempts for the current name.
 948   ScopedVector<DnsAttempt> attempts_;
 949   // Count of attempts, not reset when |attempts_| vector is cleared.
 950   int  attempts_count_;
 951   bool had_tcp_attempt_;
 952
 953   // Index of the first server to try on each search query.
 954   int first_server_index_;
 955
 956   base::OneShotTimer<DnsTransactionImpl> timer_;
 957
 958   DISALLOW_COPY_AND_ASSIGN(DnsTransactionImpl);
 959 };
 960
 961 // ----------------------------------------------------------------------------
 962
 963 // Implementation of DnsTransactionFactory that returns instances of
 964 // DnsTransactionImpl.
 965 class DnsTransactionFactoryImpl : public DnsTransactionFactory {
 966  public:
 967   explicit DnsTransactionFactoryImpl(DnsSession* session) {
 968     session_ = session;
 969   }
 970
 971   virtual scoped_ptr<DnsTransaction> CreateTransaction(
 972       const std::string& hostname,
 973       uint16 qtype,
 974       const CallbackType& callback,
 975       const BoundNetLog& net_log) OVERRIDE {
 976     return scoped_ptr<DnsTransaction>(new DnsTransactionImpl(
 977         session_.get(), hostname, qtype, callback, net_log));
 978   }
 979
 980  private:
 981   scoped_refptr<DnsSession> session_;
 982 };
 983
 984 }  // namespace
 985
 986 // static
 987 scoped_ptr<DnsTransactionFactory> DnsTransactionFactory::CreateFactory(
 988     DnsSession* session) {
 989   return scoped_ptr<DnsTransactionFactory>(
 990       new DnsTransactionFactoryImpl(session));
 991 }
 992
 993 }  // namespace net