content/browser/renderer_host/p2p/socket_host_tcp.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 "content/browser/renderer_host/p2p/socket_host_tcp.h"
   6
   7 #include "base/sys_byteorder.h"
   8 #include "content/common/p2p_messages.h"
   9 #include "ipc/ipc_sender.h"
  10 #include "jingle/glue/fake_ssl_client_socket.h"
  11 #include "jingle/glue/proxy_resolving_client_socket.h"
  12 #include "net/base/io_buffer.h"
  13 #include "net/base/net_errors.h"
  14 #include "net/base/net_util.h"
  15 #include "net/socket/client_socket_factory.h"
  16 #include "net/socket/client_socket_handle.h"
  17 #include "net/socket/ssl_client_socket.h"
  18 #include "net/socket/tcp_client_socket.h"
  19 #include "net/url_request/url_request_context.h"
  20 #include "net/url_request/url_request_context_getter.h"
  21 #include "third_party/webrtc/base/asyncpacketsocket.h"
  22
  23 namespace {
  24
  25 typedef uint16 PacketLength;
  26 const int kPacketHeaderSize = sizeof(PacketLength);
  27 const int kReadBufferSize = 4096;
  28 const int kPacketLengthOffset = 2;
  29 const int kTurnChannelDataHeaderSize = 4;
  30 const int kRecvSocketBufferSize = 128 * 1024;
  31 const int kSendSocketBufferSize = 128 * 1024;
  32
  33 bool IsTlsClientSocket(content::P2PSocketType type) {
  34   return (type == content::P2P_SOCKET_STUN_TLS_CLIENT ||
  35           type == content::P2P_SOCKET_TLS_CLIENT);
  36 }
  37
  38 bool IsPseudoTlsClientSocket(content::P2PSocketType type) {
  39   return (type == content::P2P_SOCKET_SSLTCP_CLIENT ||
  40           type == content::P2P_SOCKET_STUN_SSLTCP_CLIENT);
  41 }
  42
  43 }  // namespace
  44
  45 namespace content {
  46
  47 P2PSocketHostTcpBase::P2PSocketHostTcpBase(
  48     IPC::Sender* message_sender,
  49     int socket_id,
  50     P2PSocketType type,
  51     net::URLRequestContextGetter* url_context)
  52     : P2PSocketHost(message_sender, socket_id),
  53       write_pending_(false),
  54       connected_(false),
  55       type_(type),
  56       url_context_(url_context) {
  57 }
  58
  59 P2PSocketHostTcpBase::~P2PSocketHostTcpBase() {
  60   if (state_ == STATE_OPEN) {
  61     DCHECK(socket_.get());
  62     socket_.reset();
  63   }
  64 }
  65
  66 bool P2PSocketHostTcpBase::InitAccepted(const net::IPEndPoint& remote_address,
  67                                         net::StreamSocket* socket) {
  68   DCHECK(socket);
  69   DCHECK_EQ(state_, STATE_UNINITIALIZED);
  70
  71   remote_address_.ip_address = remote_address;
  72   // TODO(ronghuawu): Add FakeSSLServerSocket.
  73   socket_.reset(socket);
  74   state_ = STATE_OPEN;
  75   DoRead();
  76   return state_ != STATE_ERROR;
  77 }
  78
  79 bool P2PSocketHostTcpBase::Init(const net::IPEndPoint& local_address,
  80                                 const P2PHostAndIPEndPoint& remote_address) {
  81   DCHECK_EQ(state_, STATE_UNINITIALIZED);
  82
  83   remote_address_ = remote_address;
  84   state_ = STATE_CONNECTING;
  85
  86   net::HostPortPair dest_host_port_pair;
  87   // If there is no resolved address, let's try with domain name, assuming
  88   // socket layer will do the DNS resolve.
  89   if (remote_address.ip_address.address().empty()) {
  90     DCHECK(!remote_address.hostname.empty());
  91     dest_host_port_pair = net::HostPortPair::FromString(
  92         remote_address.hostname);
  93   } else {
  94     dest_host_port_pair = net::HostPortPair::FromIPEndPoint(
  95         remote_address.ip_address);
  96   }
  97
  98   // TODO(mallinath) - We are ignoring local_address altogether. We should
  99   // find a way to inject this into ProxyResolvingClientSocket. This could be
 100   // a problem on multi-homed host.
 101
 102   // The default SSLConfig is good enough for us for now.
 103   const net::SSLConfig ssl_config;
 104   socket_.reset(new jingle_glue::ProxyResolvingClientSocket(
 105                     NULL,     // Default socket pool provided by the net::Proxy.
 106                     url_context_,
 107                     ssl_config,
 108                     dest_host_port_pair));
 109
 110   int status = socket_->Connect(
 111       base::Bind(&P2PSocketHostTcpBase::OnConnected,
 112                  base::Unretained(this)));
 113   if (status != net::ERR_IO_PENDING) {
 114     // We defer execution of ProcessConnectDone instead of calling it
 115     // directly here as the caller may not expect an error/close to
 116     // happen here.  This is okay, as from the caller's point of view,
 117     // the connect always happens asynchronously.
 118     base::MessageLoop* message_loop = base::MessageLoop::current();
 119     CHECK(message_loop);
 120     message_loop->PostTask(
 121         FROM_HERE,
 122         base::Bind(&P2PSocketHostTcpBase::OnConnected,
 123                    base::Unretained(this), status));
 124   }
 125
 126   return state_ != STATE_ERROR;
 127 }
 128
 129 void P2PSocketHostTcpBase::OnError() {
 130   socket_.reset();
 131
 132   if (state_ == STATE_UNINITIALIZED || state_ == STATE_CONNECTING ||
 133       state_ == STATE_TLS_CONNECTING || state_ == STATE_OPEN) {
 134     message_sender_->Send(new P2PMsg_OnError(id_));
 135   }
 136
 137   state_ = STATE_ERROR;
 138 }
 139
 140 void P2PSocketHostTcpBase::OnConnected(int result) {
 141   DCHECK_EQ(state_, STATE_CONNECTING);
 142   DCHECK_NE(result, net::ERR_IO_PENDING);
 143
 144   if (result != net::OK) {
 145     OnError();
 146     return;
 147   }
 148
 149   if (IsTlsClientSocket(type_)) {
 150     state_ = STATE_TLS_CONNECTING;
 151     StartTls();
 152   } else if (IsPseudoTlsClientSocket(type_)) {
 153     scoped_ptr<net::StreamSocket> transport_socket = socket_.Pass();
 154     socket_.reset(
 155         new jingle_glue::FakeSSLClientSocket(transport_socket.Pass()));
 156     state_ = STATE_TLS_CONNECTING;
 157     int status = socket_->Connect(
 158         base::Bind(&P2PSocketHostTcpBase::ProcessTlsSslConnectDone,
 159                    base::Unretained(this)));
 160     if (status != net::ERR_IO_PENDING) {
 161       ProcessTlsSslConnectDone(status);
 162     }
 163   } else {
 164     // If we are not doing TLS, we are ready to send data now.
 165     // In case of TLS, SignalConnect will be sent only after TLS handshake is
 166     // successfull. So no buffering will be done at socket handlers if any
 167     // packets sent before that by the application.
 168     OnOpen();
 169   }
 170 }
 171
 172 void P2PSocketHostTcpBase::StartTls() {
 173   DCHECK_EQ(state_, STATE_TLS_CONNECTING);
 174   DCHECK(socket_.get());
 175
 176   scoped_ptr<net::ClientSocketHandle> socket_handle(
 177       new net::ClientSocketHandle());
 178   socket_handle->SetSocket(socket_.Pass());
 179
 180   net::SSLClientSocketContext context;
 181   context.cert_verifier = url_context_->GetURLRequestContext()->cert_verifier();
 182   context.transport_security_state =
 183       url_context_->GetURLRequestContext()->transport_security_state();
 184   DCHECK(context.transport_security_state);
 185
 186   // Default ssl config.
 187   const net::SSLConfig ssl_config;
 188   net::HostPortPair dest_host_port_pair;
 189
 190   // Calling net::HostPortPair::FromIPEndPoint will crash if the IP address is
 191   // empty.
 192   if (!remote_address_.ip_address.address().empty()) {
 193       net::HostPortPair::FromIPEndPoint(remote_address_.ip_address);
 194   } else {
 195     dest_host_port_pair.set_port(remote_address_.ip_address.port());
 196   }
 197   if (!remote_address_.hostname.empty())
 198     dest_host_port_pair.set_host(remote_address_.hostname);
 199
 200   net::ClientSocketFactory* socket_factory =
 201       net::ClientSocketFactory::GetDefaultFactory();
 202   DCHECK(socket_factory);
 203
 204   socket_ = socket_factory->CreateSSLClientSocket(
 205       socket_handle.Pass(), dest_host_port_pair, ssl_config, context);
 206   int status = socket_->Connect(
 207       base::Bind(&P2PSocketHostTcpBase::ProcessTlsSslConnectDone,
 208                  base::Unretained(this)));
 209   if (status != net::ERR_IO_PENDING) {
 210     ProcessTlsSslConnectDone(status);
 211   }
 212 }
 213
 214 void P2PSocketHostTcpBase::ProcessTlsSslConnectDone(int status) {
 215   DCHECK_NE(status, net::ERR_IO_PENDING);
 216   DCHECK_EQ(state_, STATE_TLS_CONNECTING);
 217   if (status != net::OK) {
 218     OnError();
 219     return;
 220   }
 221   OnOpen();
 222 }
 223
 224 void P2PSocketHostTcpBase::OnOpen() {
 225   state_ = STATE_OPEN;
 226   // Setting socket send and receive buffer size.
 227   if (net::OK != socket_->SetReceiveBufferSize(kRecvSocketBufferSize)) {
 228     LOG(WARNING) << "Failed to set socket receive buffer size to "
 229                  << kRecvSocketBufferSize;
 230   }
 231
 232   if (net::OK != socket_->SetSendBufferSize(kSendSocketBufferSize)) {
 233     LOG(WARNING) << "Failed to set socket send buffer size to "
 234                  << kSendSocketBufferSize;
 235   }
 236
 237   DoSendSocketCreateMsg();
 238   DoRead();
 239 }
 240
 241 void P2PSocketHostTcpBase::DoSendSocketCreateMsg() {
 242   DCHECK(socket_.get());
 243
 244   net::IPEndPoint local_address;
 245   int result = socket_->GetLocalAddress(&local_address);
 246   if (result < 0) {
 247     LOG(ERROR) << "P2PSocketHostTcpBase::OnConnected: unable to get local"
 248                << " address: " << result;
 249     OnError();
 250     return;
 251   }
 252
 253   VLOG(1) << "Local address: " << local_address.ToString();
 254
 255   net::IPEndPoint remote_address;
 256   result = socket_->GetPeerAddress(&remote_address);
 257   if (result < 0) {
 258     LOG(ERROR) << "P2PSocketHostTcpBase::OnConnected: unable to get peer"
 259                << " address: " << result;
 260     OnError();
 261     return;
 262   }
 263   VLOG(1) << "Remote address: " << remote_address.ToString();
 264   if (remote_address_.ip_address.address().empty()) {
 265     // Save |remote_address| if address is empty.
 266     remote_address_.ip_address = remote_address;
 267   }
 268
 269   // If we are not doing TLS, we are ready to send data now.
 270   // In case of TLS SignalConnect will be sent only after TLS handshake is
 271   // successfull. So no buffering will be done at socket handlers if any
 272   // packets sent before that by the application.
 273   message_sender_->Send(new P2PMsg_OnSocketCreated(
 274       id_, local_address, remote_address));
 275 }
 276
 277 void P2PSocketHostTcpBase::DoRead() {
 278   int result;
 279   do {
 280     if (!read_buffer_.get()) {
 281       read_buffer_ = new net::GrowableIOBuffer();
 282       read_buffer_->SetCapacity(kReadBufferSize);
 283     } else if (read_buffer_->RemainingCapacity() < kReadBufferSize) {
 284       // Make sure that we always have at least kReadBufferSize of
 285       // remaining capacity in the read buffer. Normally all packets
 286       // are smaller than kReadBufferSize, so this is not really
 287       // required.
 288       read_buffer_->SetCapacity(read_buffer_->capacity() + kReadBufferSize -
 289                                 read_buffer_->RemainingCapacity());
 290     }
 291     result = socket_->Read(
 292         read_buffer_.get(),
 293         read_buffer_->RemainingCapacity(),
 294         base::Bind(&P2PSocketHostTcp::OnRead, base::Unretained(this)));
 295     DidCompleteRead(result);
 296   } while (result > 0);
 297 }
 298
 299 void P2PSocketHostTcpBase::OnRead(int result) {
 300   DidCompleteRead(result);
 301   if (state_ == STATE_OPEN) {
 302     DoRead();
 303   }
 304 }
 305
 306 void P2PSocketHostTcpBase::OnPacket(const std::vector<char>& data) {
 307   if (!connected_) {
 308     P2PSocketHost::StunMessageType type;
 309     bool stun = GetStunPacketType(&*data.begin(), data.size(), &type);
 310     if (stun && IsRequestOrResponse(type)) {
 311       connected_ = true;
 312     } else if (!stun || type == STUN_DATA_INDICATION) {
 313       LOG(ERROR) << "Received unexpected data packet from "
 314                  << remote_address_.ip_address.ToString()
 315                  << " before STUN binding is finished. "
 316                  << "Terminating connection.";
 317       OnError();
 318       return;
 319     }
 320   }
 321
 322   message_sender_->Send(new P2PMsg_OnDataReceived(
 323       id_, remote_address_.ip_address, data, base::TimeTicks::Now()));
 324
 325   if (dump_incoming_rtp_packet_)
 326     DumpRtpPacket(&data[0], data.size(), true);
 327 }
 328
 329 // Note: dscp is not actually used on TCP sockets as this point,
 330 // but may be honored in the future.
 331 void P2PSocketHostTcpBase::Send(const net::IPEndPoint& to,
 332                                 const std::vector<char>& data,
 333                                 const rtc::PacketOptions& options,
 334                                 uint64 packet_id) {
 335   if (!socket_) {
 336     // The Send message may be sent after the an OnError message was
 337     // sent by hasn't been processed the renderer.
 338     return;
 339   }
 340
 341   if (!(to == remote_address_.ip_address)) {
 342     // Renderer should use this socket only to send data to |remote_address_|.
 343     NOTREACHED();
 344     OnError();
 345     return;
 346   }
 347
 348   if (!connected_) {
 349     P2PSocketHost::StunMessageType type = P2PSocketHost::StunMessageType();
 350     bool stun = GetStunPacketType(&*data.begin(), data.size(), &type);
 351     if (!stun || type == STUN_DATA_INDICATION) {
 352       LOG(ERROR) << "Page tried to send a data packet to " << to.ToString()
 353                  << " before STUN binding is finished.";
 354       OnError();
 355       return;
 356     }
 357   }
 358
 359   DoSend(to, data, options);
 360 }
 361
 362 void P2PSocketHostTcpBase::WriteOrQueue(
 363     scoped_refptr<net::DrainableIOBuffer>& buffer) {
 364   if (write_buffer_.get()) {
 365     write_queue_.push(buffer);
 366     return;
 367   }
 368
 369   write_buffer_ = buffer;
 370   DoWrite();
 371 }
 372
 373 void P2PSocketHostTcpBase::DoWrite() {
 374   while (write_buffer_.get() && state_ == STATE_OPEN && !write_pending_) {
 375     int result = socket_->Write(
 376         write_buffer_.get(),
 377         write_buffer_->BytesRemaining(),
 378         base::Bind(&P2PSocketHostTcp::OnWritten, base::Unretained(this)));
 379     HandleWriteResult(result);
 380   }
 381 }
 382
 383 void P2PSocketHostTcpBase::OnWritten(int result) {
 384   DCHECK(write_pending_);
 385   DCHECK_NE(result, net::ERR_IO_PENDING);
 386
 387   write_pending_ = false;
 388   HandleWriteResult(result);
 389   DoWrite();
 390 }
 391
 392 void P2PSocketHostTcpBase::HandleWriteResult(int result) {
 393   DCHECK(write_buffer_.get());
 394   if (result >= 0) {
 395     write_buffer_->DidConsume(result);
 396     if (write_buffer_->BytesRemaining() == 0) {
 397       message_sender_->Send(new P2PMsg_OnSendComplete(id_));
 398       if (write_queue_.empty()) {
 399         write_buffer_ = NULL;
 400       } else {
 401         write_buffer_ = write_queue_.front();
 402         write_queue_.pop();
 403       }
 404     }
 405   } else if (result == net::ERR_IO_PENDING) {
 406     write_pending_ = true;
 407   } else {
 408     LOG(ERROR) << "Error when sending data in TCP socket: " << result;
 409     OnError();
 410   }
 411 }
 412
 413 P2PSocketHost* P2PSocketHostTcpBase::AcceptIncomingTcpConnection(
 414     const net::IPEndPoint& remote_address, int id) {
 415   NOTREACHED();
 416   OnError();
 417   return NULL;
 418 }
 419
 420 void P2PSocketHostTcpBase::DidCompleteRead(int result) {
 421   DCHECK_EQ(state_, STATE_OPEN);
 422
 423   if (result == net::ERR_IO_PENDING) {
 424     return;
 425   } else if (result < 0) {
 426     LOG(ERROR) << "Error when reading from TCP socket: " << result;
 427     OnError();
 428     return;
 429   }
 430
 431   read_buffer_->set_offset(read_buffer_->offset() + result);
 432   char* head = read_buffer_->StartOfBuffer();  // Purely a convenience.
 433   int pos = 0;
 434   while (pos <= read_buffer_->offset() && state_ == STATE_OPEN) {
 435     int consumed = ProcessInput(head + pos, read_buffer_->offset() - pos);
 436     if (!consumed)
 437       break;
 438     pos += consumed;
 439   }
 440   // We've consumed all complete packets from the buffer; now move any remaining
 441   // bytes to the head of the buffer and set offset to reflect this.
 442   if (pos && pos <= read_buffer_->offset()) {
 443     memmove(head, head + pos, read_buffer_->offset() - pos);
 444     read_buffer_->set_offset(read_buffer_->offset() - pos);
 445   }
 446 }
 447
 448 bool P2PSocketHostTcpBase::SetOption(P2PSocketOption option, int value) {
 449   DCHECK_EQ(STATE_OPEN, state_);
 450   switch (option) {
 451     case P2P_SOCKET_OPT_RCVBUF:
 452       return socket_->SetReceiveBufferSize(value) == net::OK;
 453     case P2P_SOCKET_OPT_SNDBUF:
 454       return socket_->SetSendBufferSize(value) == net::OK;
 455     case P2P_SOCKET_OPT_DSCP:
 456       return false;  // For TCP sockets DSCP setting is not available.
 457     default:
 458       NOTREACHED();
 459       return false;
 460   }
 461 }
 462
 463 P2PSocketHostTcp::P2PSocketHostTcp(IPC::Sender* message_sender,
 464                                    int socket_id,
 465                                    P2PSocketType type,
 466                                    net::URLRequestContextGetter* url_context)
 467     : P2PSocketHostTcpBase(message_sender, socket_id, type, url_context) {
 468   DCHECK(type == P2P_SOCKET_TCP_CLIENT ||
 469          type == P2P_SOCKET_SSLTCP_CLIENT ||
 470          type == P2P_SOCKET_TLS_CLIENT);
 471 }
 472
 473 P2PSocketHostTcp::~P2PSocketHostTcp() {
 474 }
 475
 476 int P2PSocketHostTcp::ProcessInput(char* input, int input_len) {
 477   if (input_len < kPacketHeaderSize)
 478     return 0;
 479   int packet_size = base::NetToHost16(*reinterpret_cast<uint16*>(input));
 480   if (input_len < packet_size + kPacketHeaderSize)
 481     return 0;
 482
 483   int consumed = kPacketHeaderSize;
 484   char* cur = input + consumed;
 485   std::vector<char> data(cur, cur + packet_size);
 486   OnPacket(data);
 487   consumed += packet_size;
 488   return consumed;
 489 }
 490
 491 void P2PSocketHostTcp::DoSend(const net::IPEndPoint& to,
 492                               const std::vector<char>& data,
 493                               const rtc::PacketOptions& options) {
 494   int size = kPacketHeaderSize + data.size();
 495   scoped_refptr<net::DrainableIOBuffer> buffer =
 496       new net::DrainableIOBuffer(new net::IOBuffer(size), size);
 497   *reinterpret_cast<uint16*>(buffer->data()) = base::HostToNet16(data.size());
 498   memcpy(buffer->data() + kPacketHeaderSize, &data[0], data.size());
 499
 500   packet_processing_helpers::ApplyPacketOptions(
 501       buffer->data() + kPacketHeaderSize,
 502       buffer->BytesRemaining() - kPacketHeaderSize,
 503       options, 0);
 504
 505   WriteOrQueue(buffer);
 506 }
 507
 508 // P2PSocketHostStunTcp
 509 P2PSocketHostStunTcp::P2PSocketHostStunTcp(
 510     IPC::Sender* message_sender,
 511     int socket_id,
 512     P2PSocketType type,
 513     net::URLRequestContextGetter* url_context)
 514     : P2PSocketHostTcpBase(message_sender, socket_id, type, url_context) {
 515   DCHECK(type == P2P_SOCKET_STUN_TCP_CLIENT ||
 516          type == P2P_SOCKET_STUN_SSLTCP_CLIENT ||
 517          type == P2P_SOCKET_STUN_TLS_CLIENT);
 518 }
 519
 520 P2PSocketHostStunTcp::~P2PSocketHostStunTcp() {
 521 }
 522
 523 int P2PSocketHostStunTcp::ProcessInput(char* input, int input_len) {
 524   if (input_len < kPacketHeaderSize + kPacketLengthOffset)
 525     return 0;
 526
 527   int pad_bytes;
 528   int packet_size = GetExpectedPacketSize(
 529       input, input_len, &pad_bytes);
 530
 531   if (input_len < packet_size + pad_bytes)
 532     return 0;
 533
 534   // We have a complete packet. Read through it.
 535   int consumed = 0;
 536   char* cur = input;
 537   std::vector<char> data(cur, cur + packet_size);
 538   OnPacket(data);
 539   consumed += packet_size;
 540   consumed += pad_bytes;
 541   return consumed;
 542 }
 543
 544 void P2PSocketHostStunTcp::DoSend(const net::IPEndPoint& to,
 545                                   const std::vector<char>& data,
 546                                   const rtc::PacketOptions& options) {
 547   // Each packet is expected to have header (STUN/TURN ChannelData), where
 548   // header contains message type and and length of message.
 549   if (data.size() < kPacketHeaderSize + kPacketLengthOffset) {
 550     NOTREACHED();
 551     OnError();
 552     return;
 553   }
 554
 555   int pad_bytes;
 556   size_t expected_len = GetExpectedPacketSize(
 557       &data[0], data.size(), &pad_bytes);
 558
 559   // Accepts only complete STUN/TURN packets.
 560   if (data.size() != expected_len) {
 561     NOTREACHED();
 562     OnError();
 563     return;
 564   }
 565
 566   // Add any pad bytes to the total size.
 567   int size = data.size() + pad_bytes;
 568
 569   scoped_refptr<net::DrainableIOBuffer> buffer =
 570       new net::DrainableIOBuffer(new net::IOBuffer(size), size);
 571   memcpy(buffer->data(), &data[0], data.size());
 572
 573   packet_processing_helpers::ApplyPacketOptions(
 574       buffer->data(), data.size(), options, 0);
 575
 576   if (pad_bytes) {
 577     char padding[4] = {0};
 578     DCHECK_LE(pad_bytes, 4);
 579     memcpy(buffer->data() + data.size(), padding, pad_bytes);
 580   }
 581   WriteOrQueue(buffer);
 582
 583   if (dump_outgoing_rtp_packet_)
 584     DumpRtpPacket(buffer->data(), data.size(), false);
 585 }
 586
 587 int P2PSocketHostStunTcp::GetExpectedPacketSize(
 588     const char* data, int len, int* pad_bytes) {
 589   DCHECK_LE(kTurnChannelDataHeaderSize, len);
 590   // Both stun and turn had length at offset 2.
 591   int packet_size = base::NetToHost16(*reinterpret_cast<const uint16*>(
 592       data + kPacketLengthOffset));
 593
 594   // Get packet type (STUN or TURN).
 595   uint16 msg_type = base::NetToHost16(*reinterpret_cast<const uint16*>(data));
 596
 597   *pad_bytes = 0;
 598   // Add heder length to packet length.
 599   if ((msg_type & 0xC000) == 0) {
 600     packet_size += kStunHeaderSize;
 601   } else {
 602     packet_size += kTurnChannelDataHeaderSize;
 603     // Calculate any padding if present.
 604     if (packet_size % 4)
 605       *pad_bytes = 4 - packet_size % 4;
 606   }
 607   return packet_size;
 608 }
 609
 610 }  // namespace content