void tcpStateSynReceived(Socket *socket, TcpHeader *segment,
const NetBuffer *buffer, size_t offset, size_t length)
{
//Debug message
TRACE_DEBUG("TCP FSM: SYN-RECEIVED state\r\n");
//First check sequence number
if(tcpCheckSequenceNumber(socket, segment, length))
return;
//Check the RST bit
if(segment->flags & TCP_FLAG_RST)
{
//Return to CLOSED state
tcpChangeState(socket, TCP_STATE_CLOSED);
//Number of times TCP connections have made a direct transition to the
//CLOSED state from either the SYN-SENT state or the SYN-RECEIVED state
MIB2_INC_COUNTER32(mib2Base.tcpGroup.tcpAttemptFails, 1);
//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;
//Make sure the acknowledgment number is valid
if(segment->ackNum != socket->sndNxt)
{
//If the segment acknowledgment is not acceptable, form a reset
//segment and send it
tcpSendSegment(socket, TCP_FLAG_RST, segment->ackNum, 0, 0, FALSE);
//Drop the segment and return
return;
}
//Update the send window before entering ESTABLISHED state (see RFC 1122 4.2.2.20)
socket->sndWnd = segment->window;
socket->sndWl1 = segment->seqNum;
socket->sndWl2 = segment->ackNum;
//Maximum send window it has seen so far on the connection
socket->maxSndWnd = segment->window;
//Enter ESTABLISHED state
tcpChangeState(socket, TCP_STATE_ESTABLISHED);
//And continue processing...
tcpStateEstablished(socket, segment, buffer, offset, length);
}
error_t tcpAbort(Socket *socket)
{
error_t error;
//Check current state
switch(socket->state)
{
//SYN-RECEIVED, ESTABLISHED, FIN-WAIT-1
//FIN-WAIT-2 or CLOSE-WAIT state?
case TCP_STATE_SYN_RECEIVED:
case TCP_STATE_ESTABLISHED:
case TCP_STATE_FIN_WAIT_1:
case TCP_STATE_FIN_WAIT_2:
case TCP_STATE_CLOSE_WAIT:
//Send a reset segment
error = tcpSendSegment(socket, TCP_FLAG_RST, socket->sndNxt, 0, 0, FALSE);
//Enter CLOSED state
tcpChangeState(socket, TCP_STATE_CLOSED);
//Delete TCB
tcpDeleteControlBlock(socket);
//Mark the socket as closed
socket->type = SOCKET_TYPE_UNUSED;
//Return status code
return error;
//TIME-WAIT state?
case TCP_STATE_TIME_WAIT:
#if (TCP_2MSL_TIMER > 0)
//The user doe not own the socket anymore...
socket->ownedFlag = FALSE;
//TCB will be deleted and socket will be closed
//when the 2MSL timer will elapse
return NO_ERROR;
#else
//Enter CLOSED state
tcpChangeState(socket, TCP_STATE_CLOSED);
//Delete TCB
tcpDeleteControlBlock(socket);
//Mark the socket as closed
socket->type = SOCKET_TYPE_UNUSED;
//No error to report
return NO_ERROR;
#endif
//Any other state?
default:
//Enter CLOSED state
tcpChangeState(socket, TCP_STATE_CLOSED);
//Delete TCB
tcpDeleteControlBlock(socket);
//Mark the socket as closed
socket->type = SOCKET_TYPE_UNUSED;
//No error to report
return NO_ERROR;
}
}
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 tcpStateEstablished(Socket *socket, TcpHeader *segment,
const NetBuffer *buffer, size_t offset, size_t length)
{
uint_t flags = 0;
//Debug message
TRACE_DEBUG("TCP FSM: ESTABLISHED 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);
//Number of times TCP connections have made a direct transition to the
//CLOSED state from either the ESTABLISHED state or the CLOSE-WAIT state
MIB2_INC_COUNTER32(mib2Base.tcpGroup.tcpEstabResets, 1);
//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);
//Switch to the CLOSE-WAIT state
tcpChangeState(socket, TCP_STATE_CLOSE_WAIT);
}
}
#if (TCP_CONGEST_CONTROL_SUPPORT == ENABLED)
//Duplicate AK received?
if(socket->dupAckCount > 0)
flags = SOCKET_FLAG_NO_DELAY;
#endif
//The Nagle algorithm should be implemented to coalesce
//short segments (refer to RFC 1122 4.2.3.4)
tcpNagleAlgo(socket, flags);
}
void tcpStateSynSent(Socket *socket, TcpHeader *segment, size_t length)
{
TcpOption *option;
//Debug message
TRACE_DEBUG("TCP FSM: SYN-SENT state\r\n");
//Check the ACK bit
if(segment->flags & TCP_FLAG_ACK)
{
//Make sure the acknowledgment number is valid
if(segment->ackNum != socket->sndNxt)
{
//Send a reset segment unless the RST bit is set
if(!(segment->flags & TCP_FLAG_RST))
tcpSendSegment(socket, TCP_FLAG_RST, segment->ackNum, 0, 0, FALSE);
//Drop the segment and return
return;
}
}
//Check the RST bit
if(segment->flags & TCP_FLAG_RST)
{
//Make sure the ACK is acceptable
if(segment->flags & TCP_FLAG_ACK)
{
//Enter CLOSED state
tcpChangeState(socket, TCP_STATE_CLOSED);
//Number of times TCP connections have made a direct transition to the
//CLOSED state from either the SYN-SENT state or the SYN-RECEIVED state
MIB2_INC_COUNTER32(mib2Base.tcpGroup.tcpAttemptFails, 1);
}
//Drop the segment and return
return;
}
//Check the SYN bit
if(segment->flags & TCP_FLAG_SYN)
{
//Save initial receive sequence number
socket->irs = segment->seqNum;
//Initialize RCV.NXT pointer
socket->rcvNxt = segment->seqNum + 1;
//If there is an ACK, SND.UNA should be advanced to equal SEG.ACK
if(segment->flags & TCP_FLAG_ACK)
socket->sndUna = segment->ackNum;
//Compute retransmission timeout
tcpComputeRto(socket);
//Any segments on the retransmission queue which are thereby
//acknowledged should be removed
tcpUpdateRetransmitQueue(socket);
//Get the maximum segment size
option = tcpGetOption(segment, TCP_OPTION_MAX_SEGMENT_SIZE);
//Specified option found?
if(option != NULL && option->length == 4)
{
//Retrieve MSS value
memcpy(&socket->mss, option->value, 2);
//Convert from network byte order to host byte order
socket->mss = ntohs(socket->mss);
//Debug message
TRACE_DEBUG("Remote host MSS = %" PRIu16 "\r\n", socket->mss);
//Make sure that the MSS advertised by the peer is acceptable
socket->mss = MIN(socket->mss, TCP_MAX_MSS);
socket->mss = MAX(socket->mss, TCP_MIN_MSS);
}
#if (TCP_CONGEST_CONTROL_SUPPORT == ENABLED)
//Initial congestion window
socket->cwnd = MIN(TCP_INITIAL_WINDOW * socket->mss, socket->txBufferSize);
#endif
//Check whether our SYN has been acknowledged (SND.UNA > ISS)
if(TCP_CMP_SEQ(socket->sndUna, socket->iss) > 0)
{
//Update the send window before entering ESTABLISHED state (see RFC 1122 4.2.2.20)
socket->sndWnd = segment->window;
socket->sndWl1 = segment->seqNum;
socket->sndWl2 = segment->ackNum;
//Maximum send window it has seen so far on the connection
socket->maxSndWnd = segment->window;
//Form an ACK segment and send it
tcpSendSegment(socket, TCP_FLAG_ACK, socket->sndNxt, socket->rcvNxt, 0, FALSE);
//Switch to the ESTABLISHED state
tcpChangeState(socket, TCP_STATE_ESTABLISHED);
}
else
{
//Form an SYN ACK segment and send it
tcpSendSegment(socket, TCP_FLAG_SYN | TCP_FLAG_ACK, socket->iss, socket->rcvNxt, 0, TRUE);
//Enter SYN-RECEIVED state
tcpChangeState(socket, TCP_STATE_SYN_RECEIVED);
}
}
}
error_t tcpShutdown(Socket *socket, uint_t how)
{
error_t error;
uint_t event;
//Disable transmission?
if(how == SOCKET_SD_SEND || how == SOCKET_SD_BOTH)
{
//Check current state
switch(socket->state)
{
//CLOSED or LISTEN state?
case TCP_STATE_CLOSED:
case TCP_STATE_LISTEN:
//Connection does not exist
return ERROR_NOT_CONNECTED;
//SYN-RECEIVED or ESTABLISHED state?
case TCP_STATE_SYN_RECEIVED:
case TCP_STATE_ESTABLISHED:
//Flush the send buffer
error = tcpSend(socket, NULL, 0, NULL, SOCKET_FLAG_NO_DELAY);
//Any error to report?
if(error) return error;
//Make sure all the data has been sent out
event = tcpWaitForEvents(socket, SOCKET_EVENT_TX_DONE, socket->timeout);
//Timeout error?
if(event != SOCKET_EVENT_TX_DONE)
return ERROR_TIMEOUT;
//Send a FIN segment
error = tcpSendSegment(socket, TCP_FLAG_FIN | TCP_FLAG_ACK,
socket->sndNxt, socket->rcvNxt, 0, TRUE);
//Failed to send FIN segment?
if(error) return error;
//Sequence number expected to be received
socket->sndNxt++;
//Switch to the FIN-WAIT1 state
tcpChangeState(socket, TCP_STATE_FIN_WAIT_1);
//Wait for the FIN to be acknowledged
event = tcpWaitForEvents(socket, SOCKET_EVENT_TX_SHUTDOWN, socket->timeout);
//Timeout interval elapsed?
if(event != SOCKET_EVENT_TX_SHUTDOWN)
return ERROR_TIMEOUT;
//Continue processing...
break;
//CLOSE-WAIT state?
case TCP_STATE_CLOSE_WAIT:
//Flush the send buffer
error = tcpSend(socket, NULL, 0, NULL, SOCKET_FLAG_NO_DELAY);
//Any error to report?
if(error) return error;
//Make sure all the data has been sent out
event = tcpWaitForEvents(socket, SOCKET_EVENT_TX_DONE, socket->timeout);
//Timeout error?
if(event != SOCKET_EVENT_TX_DONE)
return ERROR_TIMEOUT;
//Send a FIN segment
error = tcpSendSegment(socket, TCP_FLAG_FIN | TCP_FLAG_ACK,
socket->sndNxt, socket->rcvNxt, 0, TRUE);
//Failed to send FIN segment?
if(error) return error;
//Sequence number expected to be received
socket->sndNxt++;
//Switch to the LAST-ACK state
tcpChangeState(socket, TCP_STATE_LAST_ACK);
//Wait for the FIN to be acknowledged
event = tcpWaitForEvents(socket, SOCKET_EVENT_TX_SHUTDOWN, socket->timeout);
//Timeout interval elapsed?
if(event != SOCKET_EVENT_TX_SHUTDOWN)
return ERROR_TIMEOUT;
//Continue processing...
break;
//SYN-SENT, FIN-WAIT-1, FIN-WAIT-2, CLOSING,
//TIME-WAIT or LAST-ACK state?
default:
//Continue processing...
break;
}
}
//Disable reception?
if(how == SOCKET_SD_RECEIVE || how == SOCKET_SD_BOTH)
{
//Check current state
switch(socket->state)
{
//CLOSED or LISTEN state?
case TCP_STATE_CLOSED:
case TCP_STATE_LISTEN:
//Connection does not exist
return ERROR_NOT_CONNECTED;
//SYN-SENT, SYN-RECEIVED, ESTABLISHED, FIN-WAIT-1 or FIN-WAIT-2 state?
case TCP_STATE_SYN_SENT:
case TCP_STATE_SYN_RECEIVED:
case TCP_STATE_ESTABLISHED:
case TCP_STATE_FIN_WAIT_1:
case TCP_STATE_FIN_WAIT_2:
//Wait for a FIN to be received
event = tcpWaitForEvents(socket, SOCKET_EVENT_RX_SHUTDOWN, socket->timeout);
//Timeout interval elapsed?
if(event != SOCKET_EVENT_RX_SHUTDOWN)
return ERROR_TIMEOUT;
//A FIN segment has been received
break;
//CLOSING, TIME-WAIT, CLOSE-WAIT or LAST-ACK state?
default:
//A FIN segment has already been received
break;
}
}
//Successful operation
return NO_ERROR;
}
Socket *tcpAccept(Socket *socket, IpAddr *clientIpAddr, uint16_t *clientPort)
{
error_t error;
Socket *newSocket;
TcpSynQueueItem *queueItem;
//Ensure the socket was previously placed in the listening state
if(tcpGetState(socket) != TCP_STATE_LISTEN)
return NULL;
//Enter critical section
osAcquireMutex(&socketMutex);
//Wait for an connection attempt
while(1)
{
//The SYN queue is empty?
if(!socket->synQueue)
{
//Set the events the application is interested in
socket->eventMask = SOCKET_EVENT_RX_READY;
//Reset the event object
osResetEvent(&socket->event);
//Leave critical section
osReleaseMutex(&socketMutex);
//Wait until a SYN message is received from a client
osWaitForEvent(&socket->event, socket->timeout);
//Enter critical section
osAcquireMutex(&socketMutex);
}
//Check whether the queue is still empty
if(!socket->synQueue)
{
//Timeout error
newSocket = NULL;
//Exit immediately
break;
}
//Point to the first item in the receive queue
queueItem = socket->synQueue;
//Return the client IP address and port number
if(clientIpAddr)
*clientIpAddr = queueItem->srcAddr;
if(clientPort)
*clientPort = queueItem->srcPort;
//Leave critical section
osReleaseMutex(&socketMutex);
//Create a new socket to handle the incoming connection request
newSocket = socketOpen(SOCKET_TYPE_STREAM, SOCKET_IP_PROTO_TCP);
//Enter critical section
osAcquireMutex(&socketMutex);
//Socket successfully created?
if(newSocket != NULL)
{
//The user owns the socket
newSocket->ownedFlag = TRUE;
//Inherit settings from the listening socket
newSocket->txBufferSize = socket->txBufferSize;
newSocket->rxBufferSize = socket->rxBufferSize;
//Number of chunks that comprise the TX and the RX buffers
newSocket->txBuffer.maxChunkCount = arraysize(newSocket->txBuffer.chunk);
newSocket->rxBuffer.maxChunkCount = arraysize(newSocket->rxBuffer.chunk);
//Allocate transmit buffer
error = netBufferSetLength((NetBuffer *) &newSocket->txBuffer, newSocket->txBufferSize);
//Check status code
if(!error)
{
//Allocate receive buffer
error = netBufferSetLength((NetBuffer *) &newSocket->rxBuffer, newSocket->rxBufferSize);
}
//Transmit and receive buffers successfully allocated?
if(!error)
{
//Bind the newly created socket to the appropriate interface
newSocket->interface = queueItem->interface;
//Bind the socket to the specified address
newSocket->localIpAddr = queueItem->destAddr;
newSocket->localPort = socket->localPort;
//Save the port number and the IP address of the remote host
newSocket->remoteIpAddr = queueItem->srcAddr;
newSocket->remotePort = queueItem->srcPort;
//Save the maximum segment size
newSocket->mss = queueItem->mss;
//Initialize TCP control block
newSocket->iss = netGetRand();
newSocket->irs = queueItem->isn;
newSocket->sndUna = newSocket->iss;
newSocket->sndNxt = newSocket->iss + 1;
newSocket->rcvNxt = newSocket->irs + 1;
newSocket->rcvUser = 0;
newSocket->rcvWnd = newSocket->rxBufferSize;
//Default retransmission timeout
newSocket->rto = TCP_INITIAL_RTO;
#if (TCP_CONGESTION_CONTROL_SUPPORT == ENABLED)
//Initial congestion window
newSocket->cwnd = MIN(TCP_INITIAL_WINDOW * newSocket->mss, newSocket->txBufferSize);
//Slow start threshold should be set arbitrarily high
newSocket->ssthresh = UINT16_MAX;
#endif
//Send a SYN ACK control segment
error = tcpSendSegment(newSocket, TCP_FLAG_SYN | TCP_FLAG_ACK,
newSocket->iss, newSocket->rcvNxt, 0, TRUE);
//TCP segment successfully sent?
if(!error)
{
//Remove the item from the SYN queue
socket->synQueue = queueItem->next;
//Deallocate memory buffer
memPoolFree(queueItem);
//Update the state of events
tcpUpdateEvents(socket);
//The connection state should be changed to SYN-RECEIVED
tcpChangeState(newSocket, TCP_STATE_SYN_RECEIVED);
//We are done...
break;
}
}
//Dispose the socket
tcpAbort(newSocket);
}
//Debug message
TRACE_WARNING("Cannot accept TCP connection!\r\n");
//Remove the item from the SYN queue
socket->synQueue = queueItem->next;
//Deallocate memory buffer
memPoolFree(queueItem);
//Wait for the next connection attempt
}
//Leave critical section
osReleaseMutex(&socketMutex);
//Return a handle to the newly created socket
return newSocket;
}
error_t tcpConnect(Socket *socket)
{
error_t error;
uint_t event;
//Socket already connected?
if(socket->state != TCP_STATE_CLOSED)
return ERROR_ALREADY_CONNECTED;
//The user owns the socket
socket->ownedFlag = TRUE;
//Number of chunks that comprise the TX and the RX buffers
socket->txBuffer.maxChunkCount = arraysize(socket->txBuffer.chunk);
socket->rxBuffer.maxChunkCount = arraysize(socket->rxBuffer.chunk);
//Allocate transmit buffer
error = netBufferSetLength((NetBuffer *) &socket->txBuffer, socket->txBufferSize);
//Allocate receive buffer
if(!error)
error = netBufferSetLength((NetBuffer *) &socket->rxBuffer, socket->rxBufferSize);
//Failed to allocate memory?
if(error)
{
//Free any previously allocated memory
tcpDeleteControlBlock(socket);
//Report an error to the caller
return error;
}
//Default MSS value
socket->mss = MIN(TCP_DEFAULT_MSS, TCP_MAX_MSS);
//An initial send sequence number is selected
socket->iss = netGetRand();
//Initialize TCP control block
socket->sndUna = socket->iss;
socket->sndNxt = socket->iss + 1;
socket->rcvUser = 0;
socket->rcvWnd = socket->rxBufferSize;
//Default retransmission timeout
socket->rto = TCP_INITIAL_RTO;
//Send a SYN segment
error = tcpSendSegment(socket, TCP_FLAG_SYN, socket->iss, 0, 0, TRUE);
//Failed to send TCP segment?
if(error) return error;
//Switch to the SYN-SENT state
tcpChangeState(socket, TCP_STATE_SYN_SENT);
//Wait for the connection to be established
event = tcpWaitForEvents(socket, SOCKET_EVENT_CONNECTED |
SOCKET_EVENT_CLOSED, socket->timeout);
//Connection successfully established?
if(event == SOCKET_EVENT_CONNECTED)
return NO_ERROR;
//Failed to establish connection?
else if(event == SOCKET_EVENT_CLOSED)
return ERROR_CONNECTION_FAILED;
//Timeout exception?
else
return ERROR_TIMEOUT;
}
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);
}
