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webrtc / src / / 501c4f37bfee47b26999ee291c5355ad64554df7 / . / p2p / base / pseudo_tcp.cc
blob: 3aaa2ad0651295a954efc8bb8a930dce18b24735 [file] [log] [blame]
/*
* Copyright 2004 The WebRTC Project Authors. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "p2p/base/pseudo_tcp.h"
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <cstdint>
#include <memory>
#include <set>
#include "rtc_base/byte_buffer.h"
#include "rtc_base/byte_order.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"
#include "rtc_base/numerics/safe_minmax.h"
#include "rtc_base/socket.h"
#include "rtc_base/time_utils.h"
// The following logging is for detailed (packet-level) analysis only.
#define _DBG_NONE 0
#define _DBG_NORMAL 1
#define _DBG_VERBOSE 2
#define _DEBUGMSG _DBG_NONE
namespace cricket {
//////////////////////////////////////////////////////////////////////
// Network Constants
//////////////////////////////////////////////////////////////////////
// Standard MTUs
const uint16_t PACKET_MAXIMUMS[] = {
65535, // Theoretical maximum, Hyperchannel
32000, // Nothing
17914, // 16Mb IBM Token Ring
8166, // IEEE 802.4
// 4464, // IEEE 802.5 (4Mb max)
4352, // FDDI
// 2048, // Wideband Network
2002, // IEEE 802.5 (4Mb recommended)
// 1536, // Expermental Ethernet Networks
// 1500, // Ethernet, Point-to-Point (default)
1492, // IEEE 802.3
1006, // SLIP, ARPANET
// 576, // X.25 Networks
// 544, // DEC IP Portal
// 512, // NETBIOS
508, // IEEE 802/Source-Rt Bridge, ARCNET
296, // Point-to-Point (low delay)
// 68, // Official minimum
0, // End of list marker
};
const uint32_t MAX_PACKET = 65535;
// Note: we removed lowest level because packet overhead was larger!
const uint32_t MIN_PACKET = 296;
const uint32_t IP_HEADER_SIZE = 20; // (+ up to 40 bytes of options?)
const uint32_t UDP_HEADER_SIZE = 8;
// TODO(?): Make JINGLE_HEADER_SIZE transparent to this code?
const uint32_t JINGLE_HEADER_SIZE = 64; // when relay framing is in use
// Default size for receive and send buffer.
const uint32_t DEFAULT_RCV_BUF_SIZE = 60 * 1024;
const uint32_t DEFAULT_SND_BUF_SIZE = 90 * 1024;
//////////////////////////////////////////////////////////////////////
// Global Constants and Functions
//////////////////////////////////////////////////////////////////////
//
// 0 1 2 3
// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// 0 | Conversation Number |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// 4 | Sequence Number |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// 8 | Acknowledgment Number |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// | | |U|A|P|R|S|F| |
// 12 | Control | |R|C|S|S|Y|I| Window |
// | | |G|K|H|T|N|N| |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// 16 | Timestamp sending |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// 20 | Timestamp receiving |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// 24 | data |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//
//////////////////////////////////////////////////////////////////////
#define PSEUDO_KEEPALIVE 0
const uint32_t HEADER_SIZE = 24;
const uint32_t PACKET_OVERHEAD =
HEADER_SIZE + UDP_HEADER_SIZE + IP_HEADER_SIZE + JINGLE_HEADER_SIZE;
const uint32_t MIN_RTO =
250; // 250 ms (RFC1122, Sec 4.2.3.1 "fractions of a second")
const uint32_t DEF_RTO = 3000; // 3 seconds (RFC1122, Sec 4.2.3.1)
const uint32_t MAX_RTO = 60000; // 60 seconds
const uint32_t DEF_ACK_DELAY = 100; // 100 milliseconds
const uint8_t FLAG_CTL = 0x02;
const uint8_t FLAG_RST = 0x04;
const uint8_t CTL_CONNECT = 0;
// TCP options.
const uint8_t TCP_OPT_EOL = 0; // End of list.
const uint8_t TCP_OPT_NOOP = 1; // No-op.
const uint8_t TCP_OPT_MSS = 2; // Maximum segment size.
const uint8_t TCP_OPT_WND_SCALE = 3; // Window scale factor.
const long DEFAULT_TIMEOUT =
4000; // If there are no pending clocks, wake up every 4 seconds
const long CLOSED_TIMEOUT =
60 * 1000; // If the connection is closed, once per minute
#if PSEUDO_KEEPALIVE
// !?! Rethink these times
const uint32_t IDLE_PING =
20 *
1000; // 20 seconds (note: WinXP SP2 firewall udp timeout is 90 seconds)
const uint32_t IDLE_TIMEOUT = 90 * 1000; // 90 seconds;
#endif // PSEUDO_KEEPALIVE
//////////////////////////////////////////////////////////////////////
// Helper Functions
//////////////////////////////////////////////////////////////////////
inline void long_to_bytes(uint32_t val, void* buf) {
*static_cast<uint32_t*>(buf) = rtc::HostToNetwork32(val);
}
inline void short_to_bytes(uint16_t val, void* buf) {
*static_cast<uint16_t*>(buf) = rtc::HostToNetwork16(val);
}
inline uint32_t bytes_to_long(const void* buf) {
return rtc::NetworkToHost32(*static_cast<const uint32_t*>(buf));
}
inline uint16_t bytes_to_short(const void* buf) {
return rtc::NetworkToHost16(*static_cast<const uint16_t*>(buf));
}
//////////////////////////////////////////////////////////////////////
// Debugging Statistics
//////////////////////////////////////////////////////////////////////
#if 0 // Not used yet
enum Stat {
S_SENT_PACKET, // All packet sends
S_RESENT_PACKET, // All packet sends that are retransmits
S_RECV_PACKET, // All packet receives
S_RECV_NEW, // All packet receives that are too new
S_RECV_OLD, // All packet receives that are too old
S_NUM_STATS
};
const char* const STAT_NAMES[S_NUM_STATS] = {
"snt",
"snt-r",
"rcv"
"rcv-n",
"rcv-o"
};
int g_stats[S_NUM_STATS];
inline void Incr(Stat s) { ++g_stats[s]; }
void ReportStats() {
char buffer[256];
size_t len = 0;
for (int i = 0; i < S_NUM_STATS; ++i) {
len += snprintf(buffer, arraysize(buffer), "%s%s:%d",
(i == 0) ? "" : ",", STAT_NAMES[i], g_stats[i]);
g_stats[i] = 0;
}
RTC_LOG(LS_INFO) << "Stats[" << buffer << "]";
}
#endif
//////////////////////////////////////////////////////////////////////
// PseudoTcp
//////////////////////////////////////////////////////////////////////
uint32_t PseudoTcp::Now() {
#if 0 // Use this to synchronize timers with logging timestamps (easier debug)
return static_cast<uint32_t>(rtc::TimeSince(StartTime()));
#else
return rtc::Time32();
#endif
}
PseudoTcp::PseudoTcp(IPseudoTcpNotify* notify, uint32_t conv)
: m_notify(notify),
m_shutdown(SD_NONE),
m_error(0),
m_rbuf_len(DEFAULT_RCV_BUF_SIZE),
m_rbuf(m_rbuf_len),
m_sbuf_len(DEFAULT_SND_BUF_SIZE),
m_sbuf(m_sbuf_len) {
// Sanity check on buffer sizes (needed for OnTcpWriteable notification logic)
RTC_DCHECK(m_rbuf_len + MIN_PACKET < m_sbuf_len);
uint32_t now = Now();
m_state = TCP_LISTEN;
m_conv = conv;
m_rcv_wnd = m_rbuf_len;
m_rwnd_scale = m_swnd_scale = 0;
m_snd_nxt = 0;
m_snd_wnd = 1;
m_snd_una = m_rcv_nxt = 0;
m_bReadEnable = true;
m_bWriteEnable = false;
m_t_ack = 0;
m_msslevel = 0;
m_largest = 0;
RTC_DCHECK(MIN_PACKET > PACKET_OVERHEAD);
m_mss = MIN_PACKET - PACKET_OVERHEAD;
m_mtu_advise = MAX_PACKET;
m_rto_base = 0;
m_cwnd = 2 * m_mss;
m_ssthresh = m_rbuf_len;
m_lastrecv = m_lastsend = m_lasttraffic = now;
m_bOutgoing = false;
m_dup_acks = 0;
m_recover = 0;
m_ts_recent = m_ts_lastack = 0;
m_rx_rto = DEF_RTO;
m_rx_srtt = m_rx_rttvar = 0;
m_use_nagling = true;
m_ack_delay = DEF_ACK_DELAY;
m_support_wnd_scale = true;
}
PseudoTcp::~PseudoTcp() {}
int PseudoTcp::Connect() {
if (m_state != TCP_LISTEN) {
m_error = EINVAL;
return -1;
}
m_state = TCP_SYN_SENT;
RTC_LOG(LS_INFO) << "State: TCP_SYN_SENT";
queueConnectMessage();
attemptSend();
return 0;
}
void PseudoTcp::NotifyMTU(uint16_t mtu) {
m_mtu_advise = mtu;
if (m_state == TCP_ESTABLISHED) {
adjustMTU();
}
}
void PseudoTcp::NotifyClock(uint32_t now) {
if (m_state == TCP_CLOSED)
return;
// Check if it's time to retransmit a segment
if (m_rto_base && (rtc::TimeDiff32(m_rto_base + m_rx_rto, now) <= 0)) {
if (m_slist.empty()) {
RTC_DCHECK_NOTREACHED();
} else {
// Note: (m_slist.front().xmit == 0)) {
// retransmit segments
#if _DEBUGMSG >= _DBG_NORMAL
RTC_LOG(LS_INFO) << "timeout retransmit (rto: " << m_rx_rto
<< ") (rto_base: " << m_rto_base << ") (now: " << now
<< ") (dup_acks: " << static_cast<unsigned>(m_dup_acks)
<< ")";
#endif // _DEBUGMSG
if (!transmit(m_slist.begin(), now)) {
closedown(ECONNABORTED);
return;
}
uint32_t nInFlight = m_snd_nxt - m_snd_una;
m_ssthresh = std::max(nInFlight / 2, 2 * m_mss);
// RTC_LOG(LS_INFO) << "m_ssthresh: " << m_ssthresh << " nInFlight: " <<
// nInFlight << " m_mss: " << m_mss;
m_cwnd = m_mss;
// Back off retransmit timer. Note: the limit is lower when connecting.
uint32_t rto_limit = (m_state < TCP_ESTABLISHED) ? DEF_RTO : MAX_RTO;
m_rx_rto = std::min(rto_limit, m_rx_rto * 2);
m_rto_base = now;
}
}
// Check if it's time to probe closed windows
if ((m_snd_wnd == 0) && (rtc::TimeDiff32(m_lastsend + m_rx_rto, now) <= 0)) {
if (rtc::TimeDiff32(now, m_lastrecv) >= 15000) {
closedown(ECONNABORTED);
return;
}
// probe the window
packet(m_snd_nxt - 1, 0, 0, 0);
m_lastsend = now;
// back off retransmit timer
m_rx_rto = std::min(MAX_RTO, m_rx_rto * 2);
}
// Check if it's time to send delayed acks
if (m_t_ack && (rtc::TimeDiff32(m_t_ack + m_ack_delay, now) <= 0)) {
packet(m_snd_nxt, 0, 0, 0);
}
#if PSEUDO_KEEPALIVE
// Check for idle timeout
if ((m_state == TCP_ESTABLISHED) &&
(TimeDiff32(m_lastrecv + IDLE_TIMEOUT, now) <= 0)) {
closedown(ECONNABORTED);
return;
}
// Check for ping timeout (to keep udp mapping open)
if ((m_state == TCP_ESTABLISHED) &&
(TimeDiff32(m_lasttraffic + (m_bOutgoing ? IDLE_PING * 3 / 2 : IDLE_PING),
now) <= 0)) {
packet(m_snd_nxt, 0, 0, 0);
}
#endif // PSEUDO_KEEPALIVE
}
bool PseudoTcp::NotifyPacket(const char* buffer, size_t len) {
if (len > MAX_PACKET) {
RTC_LOG_F(LS_WARNING) << "packet too large";
return false;
}
return parse(reinterpret_cast<const uint8_t*>(buffer), uint32_t(len));
}
bool PseudoTcp::GetNextClock(uint32_t now, long& timeout) {
return clock_check(now, timeout);
}
void PseudoTcp::GetOption(Option opt, int* value) {
if (opt == OPT_NODELAY) {
*value = m_use_nagling ? 0 : 1;
} else if (opt == OPT_ACKDELAY) {
*value = m_ack_delay;
} else if (opt == OPT_SNDBUF) {
*value = m_sbuf_len;
} else if (opt == OPT_RCVBUF) {
*value = m_rbuf_len;
} else {
RTC_DCHECK_NOTREACHED();
}
}
void PseudoTcp::SetOption(Option opt, int value) {
if (opt == OPT_NODELAY) {
m_use_nagling = value == 0;
} else if (opt == OPT_ACKDELAY) {
m_ack_delay = value;
} else if (opt == OPT_SNDBUF) {
RTC_DCHECK(m_state == TCP_LISTEN);
resizeSendBuffer(value);
} else if (opt == OPT_RCVBUF) {
RTC_DCHECK(m_state == TCP_LISTEN);
resizeReceiveBuffer(value);
} else {
RTC_DCHECK_NOTREACHED();
}
}
uint32_t PseudoTcp::GetCongestionWindow() const {
return m_cwnd;
}
uint32_t PseudoTcp::GetBytesInFlight() const {
return m_snd_nxt - m_snd_una;
}
uint32_t PseudoTcp::GetBytesBufferedNotSent() const {
return static_cast<uint32_t>(m_snd_una + m_sbuf.GetBuffered() - m_snd_nxt);
}
uint32_t PseudoTcp::GetRoundTripTimeEstimateMs() const {
return m_rx_srtt;
}
//
// IPStream Implementation
//
int PseudoTcp::Recv(char* buffer, size_t len) {
if (m_state != TCP_ESTABLISHED) {
m_error = ENOTCONN;
return SOCKET_ERROR;
}
size_t read = 0;
if (!m_rbuf.Read(buffer, len, &read)) {
m_bReadEnable = true;
m_error = EWOULDBLOCK;
return SOCKET_ERROR;
}
size_t available_space = 0;
m_rbuf.GetWriteRemaining(&available_space);
if (uint32_t(available_space) - m_rcv_wnd >=
std::min<uint32_t>(m_rbuf_len / 2, m_mss)) {
// TODO(jbeda): !?! Not sure about this was closed business
bool bWasClosed = (m_rcv_wnd == 0);
m_rcv_wnd = static_cast<uint32_t>(available_space);
if (bWasClosed) {
attemptSend(sfImmediateAck);
}
}
return static_cast<int>(read);
}
int PseudoTcp::Send(const char* buffer, size_t len) {
if (m_state != TCP_ESTABLISHED) {
m_error = ENOTCONN;
return SOCKET_ERROR;
}
size_t available_space = 0;
m_sbuf.GetWriteRemaining(&available_space);
if (!available_space) {
m_bWriteEnable = true;
m_error = EWOULDBLOCK;
return SOCKET_ERROR;
}
int written = queue(buffer, uint32_t(len), false);
attemptSend();
return written;
}
void PseudoTcp::Close(bool force) {
RTC_LOG_F(LS_VERBOSE) << "(" << (force ? "true" : "false") << ")";
m_shutdown = force ? SD_FORCEFUL : SD_GRACEFUL;
}
int PseudoTcp::GetError() {
return m_error;
}
//
// Internal Implementation
//
uint32_t PseudoTcp::queue(const char* data, uint32_t len, bool bCtrl) {
size_t available_space = 0;
m_sbuf.GetWriteRemaining(&available_space);
if (len > static_cast<uint32_t>(available_space)) {
RTC_DCHECK(!bCtrl);
len = static_cast<uint32_t>(available_space);
}
// We can concatenate data if the last segment is the same type
// (control v. regular data), and has not been transmitted yet
if (!m_slist.empty() && (m_slist.back().bCtrl == bCtrl) &&
(m_slist.back().xmit == 0)) {
m_slist.back().len += len;
} else {
SSegment sseg(static_cast<uint32_t>(m_snd_una + m_sbuf.GetBuffered()), len,
bCtrl);
m_slist.push_back(sseg);
}
size_t written = 0;
m_sbuf.Write(data, len, &written);
return static_cast<uint32_t>(written);
}
IPseudoTcpNotify::WriteResult PseudoTcp::packet(uint32_t seq,
uint8_t flags,
uint32_t offset,
uint32_t len) {
RTC_DCHECK(HEADER_SIZE + len <= MAX_PACKET);
uint32_t now = Now();
std::unique_ptr<uint8_t[]> buffer(new uint8_t[MAX_PACKET]);
long_to_bytes(m_conv, buffer.get());
long_to_bytes(seq, buffer.get() + 4);
long_to_bytes(m_rcv_nxt, buffer.get() + 8);
buffer[12] = 0;
buffer[13] = flags;
short_to_bytes(static_cast<uint16_t>(m_rcv_wnd >> m_rwnd_scale),
buffer.get() + 14);
// Timestamp computations
long_to_bytes(now, buffer.get() + 16);
long_to_bytes(m_ts_recent, buffer.get() + 20);
m_ts_lastack = m_rcv_nxt;
if (len) {
size_t bytes_read = 0;
bool result =
m_sbuf.ReadOffset(buffer.get() + HEADER_SIZE, len, offset, &bytes_read);
RTC_DCHECK(result);
RTC_DCHECK(static_cast<uint32_t>(bytes_read) == len);
}
#if _DEBUGMSG >= _DBG_VERBOSE
RTC_LOG(LS_INFO) << "<-- <CONV=" << m_conv
<< "><FLG=" << static_cast<unsigned>(flags)
<< "><SEQ=" << seq << ":" << seq + len
<< "><ACK=" << m_rcv_nxt << "><WND=" << m_rcv_wnd
<< "><TS=" << (now % 10000)
<< "><TSR=" << (m_ts_recent % 10000) << "><LEN=" << len
<< ">";
#endif // _DEBUGMSG
IPseudoTcpNotify::WriteResult wres = m_notify->TcpWritePacket(
this, reinterpret_cast<char*>(buffer.get()), len + HEADER_SIZE);
// Note: When len is 0, this is an ACK packet. We don't read the return value
// for those, and thus we won't retry. So go ahead and treat the packet as a
// success (basically simulate as if it were dropped), which will prevent our
// timers from being messed up.
if ((wres != IPseudoTcpNotify::WR_SUCCESS) && (0 != len))
return wres;
m_t_ack = 0;
if (len > 0) {
m_lastsend = now;
}
m_lasttraffic = now;
m_bOutgoing = true;
return IPseudoTcpNotify::WR_SUCCESS;
}
bool PseudoTcp::parse(const uint8_t* buffer, uint32_t size) {
if (size < HEADER_SIZE)
return false;
Segment seg;
seg.conv = bytes_to_long(buffer);
seg.seq = bytes_to_long(buffer + 4);
seg.ack = bytes_to_long(buffer + 8);
seg.flags = buffer[13];
seg.wnd = bytes_to_short(buffer + 14);
seg.tsval = bytes_to_long(buffer + 16);
seg.tsecr = bytes_to_long(buffer + 20);
seg.data = reinterpret_cast<const char*>(buffer) + HEADER_SIZE;
seg.len = size - HEADER_SIZE;
#if _DEBUGMSG >= _DBG_VERBOSE
RTC_LOG(LS_INFO) << "--> <CONV=" << seg.conv
<< "><FLG=" << static_cast<unsigned>(seg.flags)
<< "><SEQ=" << seg.seq << ":" << seg.seq + seg.len
<< "><ACK=" << seg.ack << "><WND=" << seg.wnd
<< "><TS=" << (seg.tsval % 10000)
<< "><TSR=" << (seg.tsecr % 10000) << "><LEN=" << seg.len
<< ">";
#endif // _DEBUGMSG
return process(seg);
}
bool PseudoTcp::clock_check(uint32_t now, long& nTimeout) {
if (m_shutdown == SD_FORCEFUL)
return false;
if ((m_shutdown == SD_GRACEFUL) &&
((m_state != TCP_ESTABLISHED) ||
((m_sbuf.GetBuffered() == 0) && (m_t_ack == 0)))) {
return false;
}
if (m_state == TCP_CLOSED) {
nTimeout = CLOSED_TIMEOUT;
return true;
}
nTimeout = DEFAULT_TIMEOUT;
if (m_t_ack) {
nTimeout = std::min<int32_t>(nTimeout,
rtc::TimeDiff32(m_t_ack + m_ack_delay, now));
}
if (m_rto_base) {
nTimeout = std::min<int32_t>(nTimeout,
rtc::TimeDiff32(m_rto_base + m_rx_rto, now));
}
if (m_snd_wnd == 0) {
nTimeout = std::min<int32_t>(nTimeout,
rtc::TimeDiff32(m_lastsend + m_rx_rto, now));
}
#if PSEUDO_KEEPALIVE
if (m_state == TCP_ESTABLISHED) {
nTimeout = std::min<int32_t>(
nTimeout,
rtc::TimeDiff32(
m_lasttraffic + (m_bOutgoing ? IDLE_PING * 3 / 2 : IDLE_PING),
now));
}
#endif // PSEUDO_KEEPALIVE
return true;
}
bool PseudoTcp::process(Segment& seg) {
// If this is the wrong conversation, send a reset!?! (with the correct
// conversation?)
if (seg.conv != m_conv) {
// if ((seg.flags & FLAG_RST) == 0) {
// packet(tcb, seg.ack, 0, FLAG_RST, 0, 0);
//}
RTC_LOG_F(LS_ERROR) << "wrong conversation";
return false;
}
uint32_t now = Now();
m_lasttraffic = m_lastrecv = now;
m_bOutgoing = false;
if (m_state == TCP_CLOSED) {
// !?! send reset?
RTC_LOG_F(LS_ERROR) << "closed";
return false;
}
// Check if this is a reset segment
if (seg.flags & FLAG_RST) {
closedown(ECONNRESET);
return false;
}
// Check for control data
bool bConnect = false;
if (seg.flags & FLAG_CTL) {
if (seg.len == 0) {
RTC_LOG_F(LS_ERROR) << "Missing control code";
return false;
} else if (seg.data[0] == CTL_CONNECT) {
bConnect = true;
// TCP options are in the remainder of the payload after CTL_CONNECT.
parseOptions(&seg.data[1], seg.len - 1);
if (m_state == TCP_LISTEN) {
m_state = TCP_SYN_RECEIVED;
RTC_LOG(LS_INFO) << "State: TCP_SYN_RECEIVED";
// m_notify->associate(addr);
queueConnectMessage();
} else if (m_state == TCP_SYN_SENT) {
m_state = TCP_ESTABLISHED;
RTC_LOG(LS_INFO) << "State: TCP_ESTABLISHED";
adjustMTU();
if (m_notify) {
m_notify->OnTcpOpen(this);
}
// notify(evOpen);
}
} else {
RTC_LOG_F(LS_WARNING) << "Unknown control code: " << seg.data[0];
return false;
}
}
// Update timestamp
if ((seg.seq <= m_ts_lastack) && (m_ts_lastack < seg.seq + seg.len)) {
m_ts_recent = seg.tsval;
}
// Check if this is a valuable ack
if ((seg.ack > m_snd_una) && (seg.ack <= m_snd_nxt)) {
// Calculate round-trip time
if (seg.tsecr) {
int32_t rtt = rtc::TimeDiff32(now, seg.tsecr);
if (rtt >= 0) {
if (m_rx_srtt == 0) {
m_rx_srtt = rtt;
m_rx_rttvar = rtt / 2;
} else {
uint32_t unsigned_rtt = static_cast<uint32_t>(rtt);
uint32_t abs_err = unsigned_rtt > m_rx_srtt
? unsigned_rtt - m_rx_srtt
: m_rx_srtt - unsigned_rtt;
m_rx_rttvar = (3 * m_rx_rttvar + abs_err) / 4;
m_rx_srtt = (7 * m_rx_srtt + rtt) / 8;
}
m_rx_rto = rtc::SafeClamp(m_rx_srtt + rtc::SafeMax(1, 4 * m_rx_rttvar),
MIN_RTO, MAX_RTO);
#if _DEBUGMSG >= _DBG_VERBOSE
RTC_LOG(LS_INFO) << "rtt: " << rtt << " srtt: " << m_rx_srtt
<< " rto: " << m_rx_rto;
#endif // _DEBUGMSG
} else {
RTC_LOG(LS_WARNING) << "rtt < 0";
}
}
m_snd_wnd = static_cast<uint32_t>(seg.wnd) << m_swnd_scale;
uint32_t nAcked = seg.ack - m_snd_una;
m_snd_una = seg.ack;
m_rto_base = (m_snd_una == m_snd_nxt) ? 0 : now;
m_sbuf.ConsumeReadData(nAcked);
for (uint32_t nFree = nAcked; nFree > 0;) {
RTC_DCHECK(!m_slist.empty());
if (nFree < m_slist.front().len) {
m_slist.front().len -= nFree;
nFree = 0;
} else {
if (m_slist.front().len > m_largest) {
m_largest = m_slist.front().len;
}
nFree -= m_slist.front().len;
m_slist.pop_front();
}
}
if (m_dup_acks >= 3) {
if (m_snd_una >= m_recover) { // NewReno
uint32_t nInFlight = m_snd_nxt - m_snd_una;
m_cwnd = std::min(m_ssthresh, nInFlight + m_mss); // (Fast Retransmit)
#if _DEBUGMSG >= _DBG_NORMAL
RTC_LOG(LS_INFO) << "exit recovery";
#endif // _DEBUGMSG
m_dup_acks = 0;
} else {
#if _DEBUGMSG >= _DBG_NORMAL
RTC_LOG(LS_INFO) << "recovery retransmit";
#endif // _DEBUGMSG
if (!transmit(m_slist.begin(), now)) {
closedown(ECONNABORTED);
return false;
}
m_cwnd += m_mss - std::min(nAcked, m_cwnd);
}
} else {
m_dup_acks = 0;
// Slow start, congestion avoidance
if (m_cwnd < m_ssthresh) {
m_cwnd += m_mss;
} else {
m_cwnd += std::max<uint32_t>(1, m_mss * m_mss / m_cwnd);
}
}
} else if (seg.ack == m_snd_una) {
// !?! Note, tcp says don't do this... but otherwise how does a closed
// window become open?
m_snd_wnd = static_cast<uint32_t>(seg.wnd) << m_swnd_scale;
// Check duplicate acks
if (seg.len > 0) {
// it's a dup ack, but with a data payload, so don't modify m_dup_acks
} else if (m_snd_una != m_snd_nxt) {
m_dup_acks += 1;
if (m_dup_acks == 3) { // (Fast Retransmit)
#if _DEBUGMSG >= _DBG_NORMAL
RTC_LOG(LS_INFO) << "enter recovery";
RTC_LOG(LS_INFO) << "recovery retransmit";
#endif // _DEBUGMSG
if (!transmit(m_slist.begin(), now)) {
closedown(ECONNABORTED);
return false;
}
m_recover = m_snd_nxt;
uint32_t nInFlight = m_snd_nxt - m_snd_una;
m_ssthresh = std::max(nInFlight / 2, 2 * m_mss);
// RTC_LOG(LS_INFO) << "m_ssthresh: " << m_ssthresh << " nInFlight: "
// << nInFlight << " m_mss: " << m_mss;
m_cwnd = m_ssthresh + 3 * m_mss;
} else if (m_dup_acks > 3) {
m_cwnd += m_mss;
}
} else {
m_dup_acks = 0;
}
}
// !?! A bit hacky
if ((m_state == TCP_SYN_RECEIVED) && !bConnect) {
m_state = TCP_ESTABLISHED;
RTC_LOG(LS_INFO) << "State: TCP_ESTABLISHED";
adjustMTU();
if (m_notify) {
m_notify->OnTcpOpen(this);
}
// notify(evOpen);
}
// If we make room in the send queue, notify the user
// The goal it to make sure we always have at least enough data to fill the
// window. We'd like to notify the app when we are halfway to that point.
const uint32_t kIdealRefillSize = (m_sbuf_len + m_rbuf_len) / 2;
if (m_bWriteEnable &&
static_cast<uint32_t>(m_sbuf.GetBuffered()) < kIdealRefillSize) {
m_bWriteEnable = false;
if (m_notify) {
m_notify->OnTcpWriteable(this);
}
// notify(evWrite);
}
// Conditions were acks must be sent:
// 1) Segment is too old (they missed an ACK) (immediately)
// 2) Segment is too new (we missed a segment) (immediately)
// 3) Segment has data (so we need to ACK!) (delayed)
// ... so the only time we don't need to ACK, is an empty segment that points
// to rcv_nxt!
SendFlags sflags = sfNone;
if (seg.seq != m_rcv_nxt) {
sflags = sfImmediateAck; // (Fast Recovery)
} else if (seg.len != 0) {
if (m_ack_delay == 0) {
sflags = sfImmediateAck;
} else {
sflags = sfDelayedAck;
}
}
#if _DEBUGMSG >= _DBG_NORMAL
if (sflags == sfImmediateAck) {
if (seg.seq > m_rcv_nxt) {
RTC_LOG_F(LS_INFO) << "too new";
} else if (seg.seq + seg.len <= m_rcv_nxt) {
RTC_LOG_F(LS_INFO) << "too old";
}
}
#endif // _DEBUGMSG
// Adjust the incoming segment to fit our receive buffer
if (seg.seq < m_rcv_nxt) {
uint32_t nAdjust = m_rcv_nxt - seg.seq;
if (nAdjust < seg.len) {
seg.seq += nAdjust;
seg.data += nAdjust;
seg.len -= nAdjust;
} else {
seg.len = 0;
}
}
size_t available_space = 0;
m_rbuf.GetWriteRemaining(&available_space);
if ((seg.seq + seg.len - m_rcv_nxt) >
static_cast<uint32_t>(available_space)) {
uint32_t nAdjust =
seg.seq + seg.len - m_rcv_nxt - static_cast<uint32_t>(available_space);
if (nAdjust < seg.len) {
seg.len -= nAdjust;
} else {
seg.len = 0;
}
}
bool bIgnoreData = (seg.flags & FLAG_CTL) || (m_shutdown != SD_NONE);
bool bNewData = false;
if (seg.len > 0) {
bool bRecover = false;
if (bIgnoreData) {
if (seg.seq == m_rcv_nxt) {
m_rcv_nxt += seg.len;
// If we received a data segment out of order relative to a control
// segment, then we wrote it into the receive buffer at an offset (see
// "WriteOffset") below. So we need to advance the position in the
// buffer to avoid corrupting data. See bugs.webrtc.org/9208
//
// We advance the position in the buffer by N bytes by acting like we
// wrote N bytes and then immediately read them. We can only do this if
// there's not already data ready to read, but this should always be
// true in the problematic scenario, since control frames are always
// sent first in the stream.
if (m_rbuf.GetBuffered() == 0) {
m_rbuf.ConsumeWriteBuffer(seg.len);
m_rbuf.ConsumeReadData(seg.len);
// After shifting the position in the buffer, we may have
// out-of-order packets ready to be recovered.
bRecover = true;
}
}
} else {
uint32_t nOffset = seg.seq - m_rcv_nxt;
if (!m_rbuf.WriteOffset(seg.data, seg.len, nOffset, NULL)) {
// Ignore incoming packets outside of the receive window.
return false;
}
if (seg.seq == m_rcv_nxt) {
m_rbuf.ConsumeWriteBuffer(seg.len);
m_rcv_nxt += seg.len;
m_rcv_wnd -= seg.len;
bNewData = true;
// May be able to recover packets previously received out-of-order
// now.
bRecover = true;
} else {
#if _DEBUGMSG >= _DBG_NORMAL
RTC_LOG(LS_INFO) << "Saving " << seg.len << " bytes (" << seg.seq
<< " -> " << seg.seq + seg.len << ")";
#endif // _DEBUGMSG
RSegment rseg;
rseg.seq = seg.seq;
rseg.len = seg.len;
RList::iterator it = m_rlist.begin();
while ((it != m_rlist.end()) && (it->seq < rseg.seq)) {
++it;
}
m_rlist.insert(it, rseg);
}
}
if (bRecover) {
RList::iterator it = m_rlist.begin();
while ((it != m_rlist.end()) && (it->seq <= m_rcv_nxt)) {
if (it->seq + it->len > m_rcv_nxt) {
sflags = sfImmediateAck; // (Fast Recovery)
uint32_t nAdjust = (it->seq + it->len) - m_rcv_nxt;
#if _DEBUGMSG >= _DBG_NORMAL
RTC_LOG(LS_INFO) << "Recovered " << nAdjust << " bytes (" << m_rcv_nxt
<< " -> " << m_rcv_nxt + nAdjust << ")";
#endif // _DEBUGMSG
m_rbuf.ConsumeWriteBuffer(nAdjust);
m_rcv_nxt += nAdjust;
m_rcv_wnd -= nAdjust;
bNewData = true;
}
it = m_rlist.erase(it);
}
}
}
attemptSend(sflags);
// If we have new data, notify the user
if (bNewData && m_bReadEnable) {
m_bReadEnable = false;
if (m_notify) {
m_notify->OnTcpReadable(this);
}
// notify(evRead);
}
return true;
}
bool PseudoTcp::transmit(const SList::iterator& seg, uint32_t now) {
if (seg->xmit >= ((m_state == TCP_ESTABLISHED) ? 15 : 30)) {
RTC_LOG_F(LS_VERBOSE) << "too many retransmits";
return false;
}
uint32_t nTransmit = std::min(seg->len, m_mss);
while (true) {
uint32_t seq = seg->seq;
uint8_t flags = (seg->bCtrl ? FLAG_CTL : 0);
IPseudoTcpNotify::WriteResult wres =
packet(seq, flags, seg->seq - m_snd_una, nTransmit);
if (wres == IPseudoTcpNotify::WR_SUCCESS)
break;
if (wres == IPseudoTcpNotify::WR_FAIL) {
RTC_LOG_F(LS_VERBOSE) << "packet failed";
return false;
}
RTC_DCHECK(wres == IPseudoTcpNotify::WR_TOO_LARGE);
while (true) {
if (PACKET_MAXIMUMS[m_msslevel + 1] == 0) {
RTC_LOG_F(LS_VERBOSE) << "MTU too small";
return false;
}
// !?! We need to break up all outstanding and pending packets and then
// retransmit!?!
m_mss = PACKET_MAXIMUMS[++m_msslevel] - PACKET_OVERHEAD;
m_cwnd = 2 * m_mss; // I added this... haven't researched actual formula
if (m_mss < nTransmit) {
nTransmit = m_mss;
break;
}
}
#if _DEBUGMSG >= _DBG_NORMAL
RTC_LOG(LS_INFO) << "Adjusting mss to " << m_mss << " bytes";
#endif // _DEBUGMSG
}
if (nTransmit < seg->len) {
RTC_LOG_F(LS_VERBOSE) << "mss reduced to " << m_mss;
SSegment subseg(seg->seq + nTransmit, seg->len - nTransmit, seg->bCtrl);
// subseg.tstamp = seg->tstamp;
subseg.xmit = seg->xmit;
seg->len = nTransmit;
SList::iterator next = seg;
m_slist.insert(++next, subseg);
}
if (seg->xmit == 0) {
m_snd_nxt += seg->len;
}
seg->xmit += 1;
// seg->tstamp = now;
if (m_rto_base == 0) {
m_rto_base = now;
}
return true;
}
void PseudoTcp::attemptSend(SendFlags sflags) {
uint32_t now = Now();
if (rtc::TimeDiff32(now, m_lastsend) > static_cast<long>(m_rx_rto)) {
m_cwnd = m_mss;
}
#if _DEBUGMSG
bool bFirst = true;
#endif // _DEBUGMSG
while (true) {
uint32_t cwnd = m_cwnd;
if ((m_dup_acks == 1) || (m_dup_acks == 2)) { // Limited Transmit
cwnd += m_dup_acks * m_mss;
}
uint32_t nWindow = std::min(m_snd_wnd, cwnd);
uint32_t nInFlight = m_snd_nxt - m_snd_una;
uint32_t nUseable = (nInFlight < nWindow) ? (nWindow - nInFlight) : 0;
size_t snd_buffered = m_sbuf.GetBuffered();
uint32_t nAvailable =
std::min(static_cast<uint32_t>(snd_buffered) - nInFlight, m_mss);
if (nAvailable > nUseable) {
if (nUseable * 4 < nWindow) {
// RFC 813 - avoid SWS
nAvailable = 0;
} else {
nAvailable = nUseable;
}
}
#if _DEBUGMSG >= _DBG_VERBOSE
if (bFirst) {
size_t available_space = 0;
m_sbuf.GetWriteRemaining(&available_space);
bFirst = false;
RTC_LOG(LS_INFO) << "[cwnd: " << m_cwnd << " nWindow: " << nWindow
<< " nInFlight: " << nInFlight
<< " nAvailable: " << nAvailable
<< " nQueued: " << snd_buffered
<< " nEmpty: " << available_space
<< " ssthresh: " << m_ssthresh << "]";
}
#endif // _DEBUGMSG
if (nAvailable == 0) {
if (sflags == sfNone)
return;
// If this is an immediate ack, or the second delayed ack
if ((sflags == sfImmediateAck) || m_t_ack) {
packet(m_snd_nxt, 0, 0, 0);
} else {
m_t_ack = Now();
}
return;
}
// Nagle's algorithm.
// If there is data already in-flight, and we haven't a full segment of
// data ready to send then hold off until we get more to send, or the
// in-flight data is acknowledged.
if (m_use_nagling && (m_snd_nxt > m_snd_una) && (nAvailable < m_mss)) {
return;
}
// Find the next segment to transmit
SList::iterator it = m_slist.begin();
while (it->xmit > 0) {
++it;
RTC_DCHECK(it != m_slist.end());
}
SList::iterator seg = it;
// If the segment is too large, break it into two
if (seg->len > nAvailable) {
SSegment subseg(seg->seq + nAvailable, seg->len - nAvailable, seg->bCtrl);
seg->len = nAvailable;
m_slist.insert(++it, subseg);
}
if (!transmit(seg, now)) {
RTC_LOG_F(LS_VERBOSE) << "transmit failed";
// TODO(?): consider closing socket
return;
}
sflags = sfNone;
}
}
void PseudoTcp::closedown(uint32_t err) {
RTC_LOG(LS_INFO) << "State: TCP_CLOSED";
m_state = TCP_CLOSED;
if (m_notify) {
m_notify->OnTcpClosed(this, err);
}
// notify(evClose, err);
}
void PseudoTcp::adjustMTU() {
// Determine our current mss level, so that we can adjust appropriately later
for (m_msslevel = 0; PACKET_MAXIMUMS[m_msslevel + 1] > 0; ++m_msslevel) {
if (static_cast<uint16_t>(PACKET_MAXIMUMS[m_msslevel]) <= m_mtu_advise) {
break;
}
}
m_mss = m_mtu_advise - PACKET_OVERHEAD;
// !?! Should we reset m_largest here?
#if _DEBUGMSG >= _DBG_NORMAL
RTC_LOG(LS_INFO) << "Adjusting mss to " << m_mss << " bytes";
#endif // _DEBUGMSG
// Enforce minimums on ssthresh and cwnd
m_ssthresh = std::max(m_ssthresh, 2 * m_mss);
m_cwnd = std::max(m_cwnd, m_mss);
}
bool PseudoTcp::isReceiveBufferFull() const {
size_t available_space = 0;
m_rbuf.GetWriteRemaining(&available_space);
return !available_space;
}
void PseudoTcp::disableWindowScale() {
m_support_wnd_scale = false;
}
void PseudoTcp::queueConnectMessage() {
rtc::ByteBufferWriter buf;
buf.WriteUInt8(CTL_CONNECT);
if (m_support_wnd_scale) {
buf.WriteUInt8(TCP_OPT_WND_SCALE);
buf.WriteUInt8(1);
buf.WriteUInt8(m_rwnd_scale);
}
m_snd_wnd = static_cast<uint32_t>(buf.Length());
queue(reinterpret_cast<const char*>(buf.Data()),
static_cast<uint32_t>(buf.Length()), true);
}
void PseudoTcp::parseOptions(const char* data, uint32_t len) {
std::set<uint8_t> options_specified;
// See http://www.freesoft.org/CIE/Course/Section4/8.htm for
// parsing the options list.
rtc::ByteBufferReader buf(
rtc::MakeArrayView(reinterpret_cast<const uint8_t*>(data), len));
while (buf.Length()) {
uint8_t kind = TCP_OPT_EOL;
buf.ReadUInt8(&kind);
if (kind == TCP_OPT_EOL) {
// End of option list.
break;
} else if (kind == TCP_OPT_NOOP) {
// No op.
continue;
}
// Length of this option.
RTC_DCHECK(len != 0);
uint8_t opt_len = 0;
buf.ReadUInt8(&opt_len);
// Content of this option.
if (opt_len <= buf.Length()) {
applyOption(kind, reinterpret_cast<const char*>(buf.Data()), opt_len);
buf.Consume(opt_len);
} else {
RTC_LOG(LS_ERROR) << "Invalid option length received.";
return;
}
options_specified.insert(kind);
}
if (options_specified.find(TCP_OPT_WND_SCALE) == options_specified.end()) {
RTC_LOG(LS_WARNING) << "Peer doesn't support window scaling";
if (m_rwnd_scale > 0) {
// Peer doesn't support TCP options and window scaling.
// Revert receive buffer size to default value.
resizeReceiveBuffer(DEFAULT_RCV_BUF_SIZE);
m_swnd_scale = 0;
}
}
}
void PseudoTcp::applyOption(char kind, const char* data, uint32_t len) {
if (kind == TCP_OPT_MSS) {
RTC_LOG(LS_WARNING) << "Peer specified MSS option which is not supported.";
// TODO(?): Implement.
} else if (kind == TCP_OPT_WND_SCALE) {
// Window scale factor.
// http://www.ietf.org/rfc/rfc1323.txt
if (len != 1) {
RTC_LOG_F(LS_WARNING) << "Invalid window scale option received.";
return;
}
applyWindowScaleOption(data[0]);
}
}
void PseudoTcp::applyWindowScaleOption(uint8_t scale_factor) {
m_swnd_scale = scale_factor;
}
void PseudoTcp::resizeSendBuffer(uint32_t new_size) {
m_sbuf_len = new_size;
m_sbuf.SetCapacity(new_size);
}
void PseudoTcp::resizeReceiveBuffer(uint32_t new_size) {
uint8_t scale_factor = 0;
// Determine the scale factor such that the scaled window size can fit
// in a 16-bit unsigned integer.
while (new_size > 0xFFFF) {
++scale_factor;
new_size >>= 1;
}
// Determine the proper size of the buffer.
new_size <<= scale_factor;
bool result = m_rbuf.SetCapacity(new_size);
// Make sure the new buffer is large enough to contain data in the old
// buffer. This should always be true because this method is called either
// before connection is established or when peers are exchanging connect
// messages.
RTC_DCHECK(result);
m_rbuf_len = new_size;
m_rwnd_scale = scale_factor;
m_ssthresh = new_size;
size_t available_space = 0;
m_rbuf.GetWriteRemaining(&available_space);
m_rcv_wnd = static_cast<uint32_t>(available_space);
}
PseudoTcp::LockedFifoBuffer::LockedFifoBuffer(size_t size)
: buffer_(new char[size]),
buffer_length_(size),
data_length_(0),
read_position_(0) {}
PseudoTcp::LockedFifoBuffer::~LockedFifoBuffer() {}
size_t PseudoTcp::LockedFifoBuffer::GetBuffered() const {
webrtc::MutexLock lock(&mutex_);
return data_length_;
}
bool PseudoTcp::LockedFifoBuffer::SetCapacity(size_t size) {
webrtc::MutexLock lock(&mutex_);
if (data_length_ > size)
return false;
if (size != buffer_length_) {
char* buffer = new char[size];
const size_t copy = data_length_;
const size_t tail_copy = std::min(copy, buffer_length_ - read_position_);
memcpy(buffer, &buffer_[read_position_], tail_copy);
memcpy(buffer + tail_copy, &buffer_[0], copy - tail_copy);
buffer_.reset(buffer);
read_position_ = 0;
buffer_length_ = size;
}
return true;
}
bool PseudoTcp::LockedFifoBuffer::ReadOffset(void* buffer,
size_t bytes,
size_t offset,
size_t* bytes_read) {
webrtc::MutexLock lock(&mutex_);
return ReadOffsetLocked(buffer, bytes, offset, bytes_read);
}
bool PseudoTcp::LockedFifoBuffer::WriteOffset(const void* buffer,
size_t bytes,
size_t offset,
size_t* bytes_written) {
webrtc::MutexLock lock(&mutex_);
return WriteOffsetLocked(buffer, bytes, offset, bytes_written);
}
bool PseudoTcp::LockedFifoBuffer::Read(void* buffer,
size_t bytes,
size_t* bytes_read) {
webrtc::MutexLock lock(&mutex_);
size_t copy = 0;
if (!ReadOffsetLocked(buffer, bytes, 0, &copy))
return false;
// If read was successful then adjust the read position and number of
// bytes buffered.
read_position_ = (read_position_ + copy) % buffer_length_;
data_length_ -= copy;
if (bytes_read)
*bytes_read = copy;
return true;
}
bool PseudoTcp::LockedFifoBuffer::Write(const void* buffer,
size_t bytes,
size_t* bytes_written) {
webrtc::MutexLock lock(&mutex_);
size_t copy = 0;
if (!WriteOffsetLocked(buffer, bytes, 0, &copy))
return false;
// If write was successful then adjust the number of readable bytes.
data_length_ += copy;
if (bytes_written) {
*bytes_written = copy;
}
return true;
}
void PseudoTcp::LockedFifoBuffer::ConsumeReadData(size_t size) {
webrtc::MutexLock lock(&mutex_);
RTC_DCHECK(size <= data_length_);
read_position_ = (read_position_ + size) % buffer_length_;
data_length_ -= size;
}
void PseudoTcp::LockedFifoBuffer::ConsumeWriteBuffer(size_t size) {
webrtc::MutexLock lock(&mutex_);
RTC_DCHECK(size <= buffer_length_ - data_length_);
data_length_ += size;
}
bool PseudoTcp::LockedFifoBuffer::GetWriteRemaining(size_t* size) const {
webrtc::MutexLock lock(&mutex_);
*size = buffer_length_ - data_length_;
return true;
}
bool PseudoTcp::LockedFifoBuffer::ReadOffsetLocked(void* buffer,
size_t bytes,
size_t offset,
size_t* bytes_read) {
if (offset >= data_length_)
return false;
const size_t available = data_length_ - offset;
const size_t read_position = (read_position_ + offset) % buffer_length_;
const size_t copy = std::min(bytes, available);
const size_t tail_copy = std::min(copy, buffer_length_ - read_position);
char* const p = static_cast<char*>(buffer);
memcpy(p, &buffer_[read_position], tail_copy);
memcpy(p + tail_copy, &buffer_[0], copy - tail_copy);
if (bytes_read)
*bytes_read = copy;
return true;
}
bool PseudoTcp::LockedFifoBuffer::WriteOffsetLocked(const void* buffer,
size_t bytes,
size_t offset,
size_t* bytes_written) {
if (data_length_ + offset >= buffer_length_)
return false;
const size_t available = buffer_length_ - data_length_ - offset;
const size_t write_position =
(read_position_ + data_length_ + offset) % buffer_length_;
const size_t copy = std::min(bytes, available);
const size_t tail_copy = std::min(copy, buffer_length_ - write_position);
const char* const p = static_cast<const char*>(buffer);
memcpy(&buffer_[write_position], p, tail_copy);
memcpy(&buffer_[0], p + tail_copy, copy - tail_copy);
if (bytes_written)
*bytes_written = copy;
return true;
}
} // namespace cricket