void tcpStateFinWait2(Socket *socket, TcpHeader *segment,
const NetBuffer *buffer, size_t offset, size_t length)
{
//Debug message
TRACE_DEBUG("TCP FSM: FIN-WAIT-2 state\r\n");
//First check sequence number
if(tcpCheckSequenceNumber(socket, segment, length))
return;
//Check the RST bit
if(segment->flags & TCP_FLAG_RST)
{
//Switch to the CLOSED state
tcpChangeState(socket, TCP_STATE_CLOSED);
//Return immediately
return;
}
//Check the SYN bit
if(tcpCheckSyn(socket, segment, length))
return;
//Check the ACK field
if(tcpCheckAck(socket, segment, length))
return;
//Process the segment text
if(length > 0)
tcpProcessSegmentData(socket, segment, buffer, offset, length);
//Check the FIN bit
if(segment->flags & TCP_FLAG_FIN)
{
//The FIN can only be acknowledged if all the segment data
//has been successfully transferred to the receive buffer
if(socket->rcvNxt == (segment->seqNum + length))
{
//Advance RCV.NXT over the FIN
socket->rcvNxt++;
//Send an acknowledgement for the FIN
tcpSendSegment(socket, TCP_FLAG_ACK, socket->sndNxt, socket->rcvNxt, 0, FALSE);
//Release previously allocated resources
tcpDeleteControlBlock(socket);
//Start the 2MSL timer
tcpTimerStart(&socket->timeWaitTimer, TCP_2MSL_TIMER);
//Switch to the TIME_WAIT state
tcpChangeState(socket, TCP_STATE_TIME_WAIT);
}
}
}
void tcpStateTimeWait(Socket *socket, TcpHeader *segment, size_t length)
{
//Debug message
TRACE_DEBUG("TCP FSM: TIME-WAIT state\r\n");
//First check sequence number
if(tcpCheckSequenceNumber(socket, segment, length))
return;
//Check the RST bit
if(segment->flags & TCP_FLAG_RST)
{
//Enter CLOSED state
tcpChangeState(socket, TCP_STATE_CLOSED);
//Dispose the socket if the user does not have the ownership anymore
if(!socket->ownedFlag)
{
//Delete the TCB
tcpDeleteControlBlock(socket);
//Mark the socket as closed
socket->type = SOCKET_TYPE_UNUSED;
}
//Return immediately
return;
}
//Check the SYN bit
if(tcpCheckSyn(socket, segment, length))
return;
//If the ACK bit is off drop the segment and return
if(!(segment->flags & TCP_FLAG_ACK))
return;
//The only thing that can arrive in this state is a retransmission
//of the remote FIN. Acknowledge it and restart the 2 MSL timeout
if(segment->flags & TCP_FLAG_FIN)
{
//Send an acknowledgement for the FIN
tcpSendSegment(socket, TCP_FLAG_ACK, socket->sndNxt, socket->rcvNxt, 0, FALSE);
//Restart the 2MSL timer
tcpTimerStart(&socket->timeWaitTimer, TCP_2MSL_TIMER);
}
}
void tcpStateClosing(Socket *socket, TcpHeader *segment, size_t length)
{
//Debug message
TRACE_DEBUG("TCP FSM: CLOSING state\r\n");
//First check sequence number
if(tcpCheckSequenceNumber(socket, segment, length))
return;
//Check the RST bit
if(segment->flags & TCP_FLAG_RST)
{
//Enter CLOSED state
tcpChangeState(socket, TCP_STATE_CLOSED);
//Return immediately
return;
}
//Check the SYN bit
if(tcpCheckSyn(socket, segment, length))
return;
//Check the ACK field
if(tcpCheckAck(socket, segment, length))
return;
//If the ACK acknowledges our FIN then enter the TIME-WAIT
//state, otherwise ignore the segment
if(segment->ackNum == socket->sndNxt)
{
//Release previously allocated resources
tcpDeleteControlBlock(socket);
//Start the 2MSL timer
tcpTimerStart(&socket->timeWaitTimer, TCP_2MSL_TIMER);
//Switch to the TIME-WAIT state
tcpChangeState(socket, TCP_STATE_TIME_WAIT);
}
}
error_t tcpSend(Socket *socket, const uint8_t *data,
size_t length, size_t *written, uint_t flags)
{
uint_t n;
uint_t totalLength;
uint_t event;
//Check whether the socket is in the listening state
if(socket->state == TCP_STATE_LISTEN)
return ERROR_NOT_CONNECTED;
//Actual number of bytes written
totalLength = 0;
//Send as much data as possible
do
{
//Wait until there is more room in the send buffer
event = tcpWaitForEvents(socket, SOCKET_EVENT_TX_READY, socket->timeout);
//A timeout exception occurred?
if(event != SOCKET_EVENT_TX_READY)
return ERROR_TIMEOUT;
//Check current TCP state
switch(socket->state)
{
//ESTABLISHED or CLOSE-WAIT state?
case TCP_STATE_ESTABLISHED:
case TCP_STATE_CLOSE_WAIT:
//The send buffer is now available for writing
break;
//LAST-ACK, FIN-WAIT-1, FIN-WAIT-2, CLOSING or TIME-WAIT state?
case TCP_STATE_LAST_ACK:
case TCP_STATE_FIN_WAIT_1:
case TCP_STATE_FIN_WAIT_2:
case TCP_STATE_CLOSING:
case TCP_STATE_TIME_WAIT:
//The connection is being closed
return ERROR_CONNECTION_CLOSING;
//CLOSED state?
default:
//The connection was reset by remote side?
return (socket->resetFlag) ? ERROR_CONNECTION_RESET : ERROR_NOT_CONNECTED;
}
//Determine the actual number of bytes in the send buffer
n = socket->sndUser + socket->sndNxt - socket->sndUna;
//Exit immediately if the transmission buffer is full (sanity check)
if(n >= socket->txBufferSize)
return ERROR_FAILURE;
//Number of bytes available for writing
n = socket->txBufferSize - n;
//Calculate the number of bytes to copy at a time
n = MIN(n, length - totalLength);
//Any data to copy?
if(n > 0)
{
//Copy user data to send buffer
tcpWriteTxBuffer(socket, socket->sndNxt + socket->sndUser, data, n);
//Update the number of data buffered but not yet sent
socket->sndUser += n;
//Advance data pointer
data += n;
//Update byte counter
totalLength += n;
//Total number of data that have been written
if(written != NULL)
*written = totalLength;
//Update TX events
tcpUpdateEvents(socket);
//To avoid a deadlock, it is necessary to have a timeout to force
//transmission of data, overriding the SWS avoidance algorithm. In
//practice, this timeout should seldom occur (see RFC 1122 4.2.3.4)
if(socket->sndUser == n)
tcpTimerStart(&socket->overrideTimer, TCP_OVERRIDE_TIMEOUT);
}
//The Nagle algorithm should be implemented to coalesce
//short segments (refer to RFC 1122 4.2.3.4)
tcpNagleAlgo(socket, flags);
//Send as much data as possible
} while(totalLength < length);
//The SOCKET_FLAG_WAIT_ACK flag causes the function to
//wait for acknowledgement from the remote side
if(flags & SOCKET_FLAG_WAIT_ACK)
{
//Wait for the data to be acknowledged
event = tcpWaitForEvents(socket, SOCKET_EVENT_TX_ACKED, socket->timeout);
//A timeout exception occurred?
if(event != SOCKET_EVENT_TX_ACKED)
return ERROR_TIMEOUT;
//The connection was closed before an acknowledgement was received?
if(socket->state != TCP_STATE_ESTABLISHED && socket->state != TCP_STATE_CLOSE_WAIT)
return ERROR_NOT_CONNECTED;
}
//Successful write operation
return NO_ERROR;
}
void tcpTick(void)
{
error_t error;
uint_t i;
uint_t n;
uint_t u;
//Enter critical section
osAcquireMutex(&socketMutex);
//Loop through opened sockets
for(i = 0; i < SOCKET_MAX_COUNT; i++)
{
//Shortcut to the current socket
Socket *socket = socketTable + i;
//Check socket type
if(socket->type != SOCKET_TYPE_STREAM)
continue;
//Check the current state of the TCP state machine
if(socket->state == TCP_STATE_CLOSED)
continue;
//Is there any packet in the retransmission queue?
if(socket->retransmitQueue != NULL)
{
//Retransmission timeout?
if(tcpTimerElapsed(&socket->retransmitTimer))
{
//When a TCP sender detects segment loss using the retransmission
//timer and the given segment has not yet been resent by way of
//the retransmission timer, the value of ssthresh must be updated
if(!socket->retransmitCount)
{
//Amount of data that has been sent but not yet acknowledged
uint_t flightSize = socket->sndNxt - socket->sndUna;
//Adjust ssthresh value
socket->ssthresh = MAX(flightSize / 2, 2 * socket->mss);
}
//Furthermore, upon a timeout cwnd must be set to no more than
//the loss window, LW, which equals 1 full-sized segment
socket->cwnd = MIN(TCP_LOSS_WINDOW * socket->mss, socket->txBufferSize);
//Make sure the maximum number of retransmissions has not been reached
if(socket->retransmitCount < TCP_MAX_RETRIES)
{
//Debug message
TRACE_INFO("%s: TCP segment retransmission #%u (%u data bytes)...\r\n",
formatSystemTime(osGetSystemTime(), NULL), socket->retransmitCount + 1,
socket->retransmitQueue->length);
//Retransmit the earliest segment that has not been
//acknowledged by the TCP receiver
tcpRetransmitSegment(socket);
//Use exponential back-off algorithm to calculate the new RTO
socket->rto = MIN(socket->rto * 2, TCP_MAX_RTO);
//Restart retransmission timer
tcpTimerStart(&socket->retransmitTimer, socket->rto);
//Increment retransmission counter
socket->retransmitCount++;
}
else
{
//The maximum number of retransmissions has been exceeded
tcpChangeState(socket, TCP_STATE_CLOSED);
//Turn off the retransmission timer
tcpTimerStop(&socket->retransmitTimer);
}
//TCP must use Karn's algorithm for taking RTT samples. That is, RTT
//samples must not be made using segments that were retransmitted
socket->rttBusy = FALSE;
}
}
//Check the current state of the TCP state machine
if(socket->state == TCP_STATE_CLOSED)
continue;
//The persist timer is used when the remote host advertises
//a window size of zero
if(!socket->sndWnd && socket->wndProbeInterval)
{
//Time to send a new probe?
if(tcpTimerElapsed(&socket->persistTimer))
{
//Make sure the maximum number of retransmissions has not been reached
if(socket->wndProbeCount < TCP_MAX_RETRIES)
{
//Debug message
TRACE_INFO("%s: TCP zero window probe #%u...\r\n",
formatSystemTime(osGetSystemTime(), NULL), socket->wndProbeCount + 1);
//Zero window probes usually have the sequence number one less than expected
tcpSendSegment(socket, TCP_FLAG_ACK, socket->sndNxt - 1, socket->rcvNxt, 0, FALSE);
//The interval between successive probes should be increased exponentially
socket->wndProbeInterval = MIN(socket->wndProbeInterval * 2, TCP_MAX_PROBE_INTERVAL);
//Restart the persist timer
tcpTimerStart(&socket->persistTimer, socket->wndProbeInterval);
//Increment window probe counter
socket->wndProbeCount++;
}
else
{
//Enter CLOSED state
tcpChangeState(socket, TCP_STATE_CLOSED);
}
}
}
//To avoid a deadlock, it is necessary to have a timeout to force
//transmission of data, overriding the SWS avoidance algorithm. In
//practice, this timeout should seldom occur (see RFC 1122 4.2.3.4)
if(socket->state == TCP_STATE_ESTABLISHED || socket->state == TCP_STATE_CLOSE_WAIT)
{
//The override timeout occurred?
if(socket->sndUser && tcpTimerElapsed(&socket->overrideTimer))
{
//The amount of data that can be sent at any given time is
//limited by the receiver window and the congestion window
n = MIN(socket->sndWnd, socket->cwnd);
n = MIN(n, socket->txBufferSize);
//Retrieve the size of the usable window
u = n - (socket->sndNxt - socket->sndUna);
//Send as much data as possible
while(socket->sndUser > 0)
{
//The usable window size may become zero or negative,
//preventing packet transmission
if((int_t) u <= 0) break;
//Calculate the number of bytes to send at a time
n = MIN(u, socket->sndUser);
n = MIN(n, socket->mss);
//Send TCP segment
error = tcpSendSegment(socket, TCP_FLAG_PSH | TCP_FLAG_ACK,
socket->sndNxt, socket->rcvNxt, n, TRUE);
//Failed to send TCP segment?
if(error) break;
//Advance SND.NXT pointer
socket->sndNxt += n;
//Adjust the number of bytes buffered but not yet sent
socket->sndUser -= n;
}
//Check whether the transmitter can accept more data
tcpUpdateEvents(socket);
//Restart override timer if necessary
if(socket->sndUser > 0)
tcpTimerStart(&socket->overrideTimer, TCP_OVERRIDE_TIMEOUT);
}
}
//The FIN-WAIT-2 timer prevents the connection
//from staying in the FIN-WAIT-2 state forever
if(socket->state == TCP_STATE_FIN_WAIT_2)
{
//Maximum FIN-WAIT-2 time has elapsed?
if(tcpTimerElapsed(&socket->finWait2Timer))
{
//Debug message
TRACE_WARNING("TCP FIN-WAIT-2 timer elapsed...\r\n");
//Enter CLOSED state
tcpChangeState(socket, TCP_STATE_CLOSED);
}
}
//TIME-WAIT timer
if(socket->state == TCP_STATE_TIME_WAIT)
{
//2MSL time has elapsed?
if(tcpTimerElapsed(&socket->timeWaitTimer))
{
//Debug message
TRACE_WARNING("TCP 2MSL timer elapsed (socket %u)...\r\n", i);
//Enter CLOSED state
tcpChangeState(socket, TCP_STATE_CLOSED);
//Dispose the socket if the user does not have the ownership anymore
if(!socket->ownedFlag)
{
//Delete the TCB
tcpDeleteControlBlock(socket);
//Mark the socket as closed
socket->type = SOCKET_TYPE_UNUSED;
}
}
}
}
//Leave critical section
osReleaseMutex(&socketMutex);
}
