/* ***************************************************
* Function: handle_timeout
* ***************************************************
* This function is called whenever there is a timeout. Unless we
* are in the TIME_WAIT state, I retransmit all the packets starting
* from the beginning of the window.
* The RTO is also doubled when there is a retransmission as described
* in K&R.
*/
static void handle_timeout(mysocket_t sd, context_t *ctx)
{
if (ctx->connection_state==CSTATE_TIME_WAIT){
ctx->connection_state = CSTATE_CLOSED;
ctx->done = true;
return;
}
our_dprintf("TIMEOUT waiting for seq:%d\n", ctx->seq_base);
assert(ctx->sbuffer.num_entries>0 || !DEBUG);
assert(ctx->sbuffer.start->next!=NULL || !DEBUG);
struct p_entry *curr = ctx->sbuffer.start->next;
ctx->rto= MIN(ctx->rto*2, MAX_RTO);
/* Retransmit all packets */
while (curr){
struct tcphdr *hdr = (struct tcphdr*)curr->packet;
if (curr->num_transmits>=MAX_RT_TRIES){
our_dprintf("MAX NUMBER OF TRIES REACHED KILLING CONNECTION !!!!\n\n");
ctx->done = true;
errno = ETIMEDOUT;
return;
}
hdr->th_ack = ctx->last_ack_sent;
curr->num_transmits+=1; /* increase counter */
gettimeofday(&(curr->tstart),NULL);
network_send(sd, hdr, curr->packet_size);
curr = curr->next;
our_dprintf("Retransmitting Seq:%d with Len:%d New RTO:%f\n",
hdr->th_seq, ctx->sbuffer.start->next->packet_size, ctx->rto);
}
}
/* ***************************************************
* Function: passive_init
* ***************************************************
* Passive node waits for a SYN packet to arrive, it then
* sends an SYN_ACK using another helper function (below)
*/
static bool passive_init(mysocket_t sd, context_t *ctx)
{
ctx->connection_state = CSTATE_LISTEN;
struct tcphdr* syn_packet = (struct tcphdr *)calloc(1,
(TH_MAX_OFFSET*sizeof(uint32_t))+STCP_MSS);
/* Listen for a connection request */
while (true){
stcp_wait_for_event(sd, NETWORK_DATA, NULL);
network_recv(sd, syn_packet);
if (syn_packet->th_flags == TH_SYN){
break;
}
}
our_dprintf("PASSIVE - RCVD SYN with seq: %d\n", syn_packet->th_seq);
/* Prepare SYN_ACK*/
syn_packet->th_ack = syn_packet->th_seq + 1;
syn_packet->th_seq = ctx->initial_sequence_num;
syn_packet->th_off = TH_MIN_OFFSET;
syn_packet->th_flags = TH_SYN | TH_ACK;
syn_packet->th_win = RWIN;
/*Update connection state variables */
ctx->last_ack_sent = syn_packet->th_ack;
ctx->nxt_seq_num = ctx->initial_sequence_num + 1;
ctx->connection_state = CSTATE_SYN_RCVD;
ctx->seq_base = ctx->nxt_seq_num;
our_dprintf("PASSIVE - SEND SYN_ACK Packet with seq: %d and ack: %d \n",
syn_packet->th_seq, syn_packet->th_ack);
bool success = send_syn_ack(sd, ctx, syn_packet);
free(syn_packet);
return success;
}
/* ***************************************************
* Function: handle_ack
* ***************************************************
* We received an ACK. Check the special case that we received
* a duplicate SYN_ACK and if so, send an ACK back (this is the only
* ACK packet that requires an ACK to be sent back). Then check if the
* ACK falls within the sender window and if so, estimate the new rto
* (using helper function below), remove everything upto that sequence
* number from the window. Finally, check to see if this is a FIN ACK
* and update state variables.
*/
static void handle_ack(struct tcphdr* hdr, mysocket_t sd, context_t* ctx)
{
our_dprintf("Ack:%d received - Prior Window Bottom:%d - Window Top: %d\n",
hdr->th_ack, ctx->seq_base, ctx->nxt_seq_num);
if (hdr->th_flags & TH_SYN) {
/* Received a duplicate SYN_ACK during init - can only happen first time around for client */
assert(((hdr->th_seq == ctx->last_ack_sent-1) &&
(hdr->th_ack==ctx->initial_sequence_num+1)) || !DEBUG);
if((hdr->th_seq == ctx->last_ack_sent-1) &&
(hdr->th_ack==ctx->initial_sequence_num+1)){
send_ack(sd,ctx);
return;
}
}
if (!((hdr->th_ack <= ctx->nxt_seq_num) && (hdr->th_ack > ctx->seq_base))) {
our_dprintf("Ack outside window. Throw Away!\n");
return;
}
/* ACK INSIDE WINDOW - HANDLE IT */
estimate_rto(ctx, hdr->th_ack); /* check if we can get a new RTO*/
ctx->seq_base = hdr->th_ack; /* new window bottom */
remove_until_seq(ctx); /* remove everything upto the new window bottom (cumulative acks)*/
/* Check to see if we got ACK for FIN. If so update state variables*/
if (hdr->th_ack == ctx->fin_ack) {
if (ctx->connection_state == CSTATE_FIN_WAIT1) {
ctx->connection_state = CSTATE_FIN_WAIT2;
}
else if (ctx->connection_state == CSTATE_LAST_ACK) {
assert((ctx->nxt_seq_num==ctx->seq_base) || !DEBUG);
ctx->connection_state = CSTATE_CLOSED;
ctx->done = 1;
}
}
}
/* ***************************************************
* Function: active_init
* ***************************************************
* Initiate the active side connection. Send the SYN packet,
* wait for the SYN_ACK and then send the final SYN.
*/
static bool active_init(mysocket_t sd, context_t *ctx)
{
struct tcphdr* syn_packet = (struct tcphdr *)calloc(1,(TH_MAX_OFFSET*sizeof(uint32_t)) + STCP_MSS);
if (!sendrcv_syn(sd, ctx, syn_packet)) {
return false; /* Timeout waiting for SYN_ACK*/
}
ctx->connection_state = CSTATE_SYN_SENT;
our_dprintf("Active - RVCD SYN_ACK Seq: %d, ACK: %d \n", syn_packet->th_seq, syn_packet->th_ack);
ctx->recv_win = MIN(syn_packet->th_win, CWIN);
/* Send final ACK ---- Prepare Headers */
syn_packet->th_ack = syn_packet->th_seq + 1;
syn_packet->th_seq = ctx->nxt_seq_num;
syn_packet->th_flags = TH_ACK;
syn_packet->th_off = TH_MIN_OFFSET;
syn_packet->th_win = RWIN;
our_dprintf("Active - Sending Final ACK Seq: %d, ACK: %d \n", syn_packet->th_seq, syn_packet->th_ack);
network_send(sd, syn_packet, (TH_MIN_OFFSET*sizeof(uint32_t)));
/* Update connection state variables */
ctx->seq_base = ctx->nxt_seq_num;
ctx->last_ack_sent = syn_packet->th_ack;
free(syn_packet);
return true;
}
/* ***************************************************
* Function: send_syn_ack
* ***************************************************
* Passive node calls this to send SYN_ACK and wait for
* the final ACK packet. It tries a total of 6 times before
* giving up.
*/
static bool send_syn_ack(mysocket_t sd, context_t *ctx, struct tcphdr* syn_packet)
{
struct tcphdr* ack_packet = (struct tcphdr *)calloc(1,(TH_MAX_OFFSET*sizeof(uint32_t))+STCP_MSS);
unsigned int event;
bool success = false;
int num_tries = 1;
struct timeval tstart;
gettimeofday(&tstart, NULL); /*Start the timer */
network_send(sd, syn_packet, (TH_MIN_OFFSET*sizeof(uint32_t)));
while((num_tries < MAX_RT_TRIES) && !success){
event = wait_for_event(sd, NETWORK_DATA, ctx, tstart);
if (event & NETWORK_DATA) {
network_recv(sd, ack_packet);
our_dprintf("Passive (ACK waiting): Ack: %d, Seq:%d, Next Seq:%d, Last Ack Sent: %d\n",
ack_packet->th_ack, ack_packet->th_seq, ctx->nxt_seq_num, ctx->last_ack_sent);
success = ((ack_packet->th_flags == TH_ACK) &&
(ack_packet->th_ack == ctx->nxt_seq_num));
}
else if (event==TIMEOUT){
our_dprintf("Passive Final INIT ACK not Received TIMEOUT!\n");
num_tries+=1;
gettimeofday(&tstart, NULL);
our_dprintf("PASSIVE - SEND SYN_ACK Packet with seq: %d and ack: %d \n",
syn_packet->th_seq, syn_packet->th_ack);
network_send(sd, syn_packet, (TH_MIN_OFFSET*sizeof(uint32_t)));
}
}
if (success){
our_dprintf("PASSIVE - RCVD Last Ack Packet has seq: %d and ack: %d \n",
ack_packet->th_seq, ack_packet->th_ack);
ctx->recv_win = MIN(syn_packet->th_win, CWIN);
}
free(ack_packet);
return success;
}
/* ***************************************************
* Function: handle_app_data
* ***************************************************
* The application has new data to be sent out. First make sure that
* there is some space in the window. Get maximum amount of data from
* the application, added it to the sender's buffer, and send it across
* the network.
*/
static void handle_app_data(mysocket_t sd, context_t *ctx)
{
size_t bytes_in_transit = ctx->nxt_seq_num - ctx->seq_base;
size_t win_space = ctx->recv_win - bytes_in_transit;
if (win_space>0){
char *pkt = (char *)calloc(1,(TH_MIN_OFFSET*sizeof(uint32_t)) + STCP_MSS);
struct tcphdr* hdr = (struct tcphdr*)pkt;
hdr->th_off = TH_MIN_OFFSET;
hdr->th_seq = ctx->nxt_seq_num;
hdr->th_flags = 0;
hdr->th_win = RWIN;
/* Pick the minimum between space in the window and MSS */
size_t data_max = MIN(STCP_MSS, win_space);
size_t len = stcp_app_recv(sd, pkt + TCP_DATA_START(hdr), data_max);
ctx->nxt_seq_num += len; /*add len to obtain nxt_seq_num to be used */
add_to_send_buffer(ctx, pkt, (TH_MIN_OFFSET*sizeof(uint32_t)) + len);
our_dprintf("Sending packet with seq: %d of size: %d\n",
hdr->th_seq,(TH_MIN_OFFSET*sizeof(uint32_t)) + len);
network_send(sd, pkt, (TH_MIN_OFFSET*sizeof(uint32_t)) + len);
free(pkt);
}
else {
our_dprintf(".");
}
}
int handle_cstate_fin_wait_2(mysocket_t sd, context_t * ctx){
int ret = 0;
unsigned int event;
our_dprintf("in CSTATE_FIN_WAIT_2\n");
event = stcp_wait_for_event(sd, NETWORK_DATA | TIMEOUT, NULL);
/* check whether it was the network, app, or a close request */
uint8_t buff[MAX_WINDOW_SIZE + sizeof(struct tcphdr)];
if (event & NETWORK_DATA) {
/* there was network data received */
size_t recd;
recd = stcp_network_recv(sd, buff, MAX_WINDOW_SIZE);
if (recd == 0) {
our_dprintf("bad network recv\n");
return -1;
}
struct tcphdr * tcp_packet = (struct tcphdr *) buff;
if (tcp_packet->th_flags & TH_FIN){
/* if fin */
ctx->recd_last_byte_recd++;
ctx->recd_last_byte_read++;
ctx->recd_next_byte_expected++;
send_syn_ack_fin(sd, ctx, SEND_ACK, 0, ctx->recd_next_byte_expected);
ctx->connection_state = CSTATE_TIME_WAIT;
}
}
return ret;
}
/* ***************************************************
* Function: control_wait
* ***************************************************
* This function determines the right event to wait for based on window size
* and connection state.
* If the window is full, then we don't wait for application data as we know
* we can't send any.
* If there are bytes outstanding (not-acked), then we need to wait using a timeout
* value.
* If we are TIME_WAIT state, then we set the RTO to the TIME_WAIT_VALUE and only accept
* network data (i.e. FIN that need to be acknowledged).
*/
unsigned int control_wait(mysocket_t sd, context_t *ctx, bool fin_retry)
{
unsigned int event = 0;
size_t bytes_in_transit = ctx->nxt_seq_num - ctx->seq_base;
size_t win_space = ctx->recv_win - bytes_in_transit;
unsigned int wait_flags = NETWORK_DATA | APP_CLOSE_REQUESTED;
if (win_space >0 && !fin_retry) {
wait_flags |= APP_DATA;
}
/* Is there something in flight? */
if (bytes_in_transit > 0) {
assert((ctx->sbuffer.num_entries>0) || !DEBUG);
our_dprintf("Waiting with RTO for Seq:%d \n", ctx->seq_base);
event = wait_with_rto(sd, wait_flags, ctx);
}
else if (ctx->connection_state==CSTATE_TIME_WAIT) {
ctx->rto = TIME_WAIT_VALUE;
struct timeval current_time;
gettimeofday(¤t_time, NULL);
our_dprintf("IN TIME WAIT!!!\n");
event = wait_for_event(sd, NETWORK_DATA, ctx,current_time);
}
else {
/* No unacked packets... take your sweet time*/
event = stcp_wait_for_event(sd, ANY_EVENT, NULL);
}
return event;
}
int handle_cstate_est_send(mysocket_t sd, context_t * ctx){
//our_dprintf("*IN EST SEND\n");
size_t eff_wind = calc_eff_window(ctx);
size_t max_to_send = MIN(eff_wind, STCP_MSS);
if (max_to_send == 0) {
//our_dprintf("window too small to send min(%u, %u) \n", eff_wind, STCP_MSS);
return 0;
}
//our_dprintf("max to send %u\n", max_to_send);
/* receive data from app */
size_t recd_app;
uint8_t buff[max_to_send];
recd_app = stcp_app_recv(sd, buff, max_to_send);
/* construct header */
uint32_t header_size = sizeof(struct tcphdr);
uint8_t header_buf[header_size];
memset(header_buf, 0, header_size);
struct tcphdr * tcp_header = ( struct tcphdr *) header_buf;
tcp_header->th_seq = htonl(ctx->sent_last_byte_sent + 1);
tcp_header->th_flags |= TH_SYN;
tcp_header->th_off = 5; /* no options, data begins 20 bytes into packet */
/* set adv window size */
tcp_header->th_win = htons(calc_adv_wind(ctx));
ctx->sent_adv_window = calc_adv_wind(ctx);
/* copy the data into the tcp buffer */
uint32_t wind_index = ((ctx->sent_last_byte_written + 1)
- ctx->initial_sequence_num) % MAX_WINDOW_SIZE;
our_dprintf("window index %u\n", wind_index);
/* we're wrapping the buffer */
if (wind_index + recd_app > MAX_WINDOW_SIZE) {
size_t delta = MAX_WINDOW_SIZE - wind_index;
our_dprintf("wrapping the buffer\n");
/* fill the end of the buffer */
memcpy(ctx->send_wind + wind_index, buff, delta);
/* restart at the beginning of the buffer */
memcpy(ctx->send_wind, buff+delta, recd_app - delta);
stcp_network_send(sd, header_buf, header_size, ctx->send_wind + wind_index, delta,
ctx->send_wind, recd_app - delta, NULL);
} else {
/* don't need to wrap the buffer */
our_dprintf("not wrapping the buffer\n");
memcpy(ctx->send_wind + wind_index, buff, recd_app);
stcp_network_send(sd, header_buf, header_size, (ctx->send_wind + wind_index), recd_app, NULL);
}
ctx->sent_last_byte_sent += recd_app;
ctx->sent_last_byte_written += recd_app;
return 0;
}
int handle_cstate_fin_wait_1(mysocket_t sd, context_t * ctx){
int ret = 0;
unsigned int event;
our_dprintf("in CSTATE_FIN_WAIT_1\n");
event = stcp_wait_for_event(sd, NETWORK_DATA | TIMEOUT, NULL);
/* check whether it was the network, app, or a close request */
uint8_t buff[MAX_WINDOW_SIZE + sizeof(struct tcphdr)];
if (event & NETWORK_DATA) {
/* there was network data received */
size_t recd;
recd = stcp_network_recv(sd, buff, MAX_WINDOW_SIZE);
if (recd == 0) {
our_dprintf("bad network recv\n");
return -1;
}
struct tcphdr * tcp_packet = (struct tcphdr *) buff;
if (tcp_packet->th_flags & (TH_ACK | TH_FIN)) {
/* if ack + fin */
if (ntohl(tcp_packet->th_ack) < ctx->sent_last_byte_acked || ntohl(tcp_packet->th_ack) > ctx->sent_last_byte_written+1){
our_dprintf("bad ack, expected %u, received %u. returning \n", ctx->sent_last_byte_sent+1, tcp_packet->th_ack);
return -1;
}
ctx->sent_last_byte_acked = ntohl(tcp_packet->th_ack);
ctx->recd_last_byte_recd++;
ctx->recd_last_byte_read++;
ctx->recd_next_byte_expected++;
send_syn_ack_fin(sd, ctx, SEND_ACK, 0, ctx->recd_next_byte_expected);
ctx->connection_state = CSTATE_TIME_WAIT;
} else if (tcp_packet->th_flags & TH_ACK){
/* ack received */
if (ntohl(tcp_packet->th_ack) < ctx->sent_last_byte_acked || ntohl(tcp_packet->th_ack) > ctx->sent_last_byte_written+1){
our_dprintf("bad ack, expected %u, received %u. returning \n", ctx->sent_last_byte_sent+1, tcp_packet->th_ack);
return -1;
}
ctx->sent_last_byte_acked = ntohl(tcp_packet->th_ack);
//our_dprintf("*** got an ack %u\n", ctx->sent_last_byte_acked);
ctx->connection_state = CSTATE_FIN_WAIT_2;
} else if (tcp_packet->th_flags & TH_FIN){
/* else if fin */
ctx->recd_last_byte_recd++;
ctx->recd_last_byte_read++;
ctx->recd_next_byte_expected++;
send_syn_ack_fin(sd, ctx, SEND_ACK, 0, ctx->recd_next_byte_expected);
ctx->connection_state = CSTATE_CLOSING;
}
}
return ret;
}
int handle_cstate_close_wait(mysocket_t sd, context_t * ctx){
int ret = 0;
unsigned int event;
our_dprintf("in CSTATE_CLOSE_WAIT\n");
struct timespec wait_time;
time_t curtime;
curtime = time(0);
//our_dprintf("curtime = %u\n", curtime);
wait_time.tv_sec = curtime + 240; /* wait atleast 2 lifetimes */
wait_time.tv_nsec = 0;
event = stcp_wait_for_event(sd, APP_CLOSE_REQUESTED | TIMEOUT, &wait_time);
/* check whether it was the network, app, or a close request */
if (event & APP_CLOSE_REQUESTED) {
/* there was network data received */
send_syn_ack_fin(sd, ctx, SEND_FIN, 0, 0);
ctx->connection_state = CSTATE_LAST_ACK;
}
return ret;
}
int open_tcp_conn(mysocket_t sd, context_t * ctx, bool_t is_active) {
/* make sure the state is closed before we try to open it */
assert(ctx->connection_state == CSTATE_CLOSED);
while (ctx->connection_state != CSTATE_ESTABLISHED &&
ctx->connection_state != CSTATE_FIN_WAIT_1 ) {
switch(ctx->connection_state) {
case CSTATE_CLOSED:
/* connection is closed */
handle_cstate_closed(sd, ctx, is_active);
break;
case CSTATE_LISTEN:
/* listening */
handle_cstate_listen(sd, ctx);
break;
case CSTATE_SYN_RCVD:
/* syn has been received */
handle_cstate_syn_rcvd(sd, ctx);
break;
case CSTATE_SYN_SENT:
/* syn has been sent */
handle_cstate_syn_sent(sd, ctx);
break;
default:
/* shouldn't happen */
our_dprintf("bad open tcp conn state\n");
assert(0);
break;
}
}
return 0;
}
/* ***************************************************
* Function: transport_init
* ***************************************************
* initialise the transport layer, and start the main loop, handling
* any data from the peer or the application. this function should not
* return until the connection is closed.
*/
void transport_init(mysocket_t sd, bool_t is_active)
{
context_t *ctx = init_ctx(is_active);
bool success = false;
if (is_active) {
success = active_init(sd, ctx);
}
else {
success = passive_init(sd, ctx);
}
if (success){
ctx->connection_state = CSTATE_ESTABLISHED;
stcp_unblock_application(sd);
control_loop(sd, ctx);
}
else {
errno = ETIMEDOUT;
stcp_unblock_application(sd);
}
teardown_resources(ctx);
/* Wait for potential pending processes in
* other side (this is to fix a bug in the starter code) */
sleep(1);
our_dprintf("Exiting Loop!\n");
}
/* ***************************************************
* Function: control_loop
* ***************************************************
* control_loop() is the main STCP loop; it repeatedly waits for one of the
* following to happen:
* - incoming data from the peer
* - new data from the application (via mywrite())
* - the socket to be closed (via myclose())
* - a timeout
*/
static void control_loop(mysocket_t sd, context_t *ctx)
{
assert(ctx);
unsigned int event = 0;
bool fin_retry = false; /* TRUE = APP_CLOSE_REQUESTED but window was full */
while (!ctx->done)
{
size_t bytes_in_transit = ctx->nxt_seq_num - ctx->seq_base;
size_t win_space = ctx->recv_win - bytes_in_transit;
event = control_wait(sd, ctx, fin_retry);
if (event & NETWORK_DATA) {
handle_network_data(sd, ctx);
}
if ((event & APP_DATA) && !fin_retry) {
handle_app_data(sd, ctx);
}
if (event == TIMEOUT){
handle_timeout(sd, ctx);
}
if ((event & APP_CLOSE_REQUESTED) || fin_retry) {
if (win_space>0){
send_fin(sd, ctx);
fin_retry = false;
}
else {
our_dprintf("App requested FIN but window is full\n");
fin_retry = true;
}
}
}
}
/* ***************************************************
* Function: handle_fin
* ***************************************************
* This function is called when we receive a FIN (or actually
* when we process a FIN in-order from the receive buffer). It
* simply updates the states variables and calls stcp_fin_received.
*
*/
static void handle_fin(mysocket_t sd, context_t *ctx)
{
size_t bytes_in_transit = ctx->nxt_seq_num - ctx->seq_base;
our_dprintf("FIN PACKET RECEIVED. ACK SEN. Window Start:%d Window End:%d\n",
ctx->seq_base, ctx->nxt_seq_num);
/* This is a special case, we sent a FIN first but we received another
* FIN before we got an ACK for the first FIN. If this is the case, I just
* treat that second FIN as an ACK for the first FIN (though this would not be
* necessarily true if both sides were to send FINs simulatenously). We were
* not asked to deal with simulatenous shut-down so I just do it this clean
* way */
if (ctx->connection_state == CSTATE_FIN_WAIT1) {
assert(((ctx->seq_base + 1) == ctx->nxt_seq_num) || !DEBUG);
ctx->seq_base = ctx->nxt_seq_num;
remove_until_seq(ctx);
ctx->connection_state = CSTATE_TIME_WAIT;
}
else if (ctx->connection_state == CSTATE_FIN_WAIT2) {
assert(bytes_in_transit==0 || !DEBUG);
ctx->connection_state = CSTATE_TIME_WAIT;
}
else {
assert(ctx->connection_state = CSTATE_ESTABLISHED || !DEBUG);
assert(bytes_in_transit==0 || !DEBUG);
ctx->connection_state = CSTATE_CLOSE_WAIT;
}
stcp_fin_received(sd);
}
int handle_cstate_listen(mysocket_t sd, context_t * ctx) {
int ret = 0;
unsigned int event;
our_dprintf("in CSTATE_LISTEN\n");
event = stcp_wait_for_event(sd, ANY_EVENT, NULL);
/* check whether it was the network, app, or a close request */
if (event & NETWORK_DATA) {
/* there was network data received */
size_t recd;
recd = stcp_network_recv(sd, ctx->recv_wind, MAX_WINDOW_SIZE);
if (recd == 0) {
our_dprintf("bad network recv\n");
return -1;
}
struct tcphdr * tcp_packet = (struct tcphdr *) ctx->recv_wind;
//size_t recd_app = recd - 4 * tcp_packet->th_off;
if (tcp_packet->th_flags & TH_SYN){
/* syn received */
ctx->initial_recd_seq_num = ntohl(tcp_packet->th_seq);
ctx->recd_last_byte_recd = ctx->initial_recd_seq_num;
ctx->recd_next_byte_expected = ctx->recd_last_byte_recd + 1;
ctx->recd_adv_window = ntohs(tcp_packet->th_win);
send_syn_ack_fin(sd, ctx, SEND_SYN | SEND_ACK,
ctx->initial_sequence_num, ctx->recd_next_byte_expected);
ctx->connection_state = CSTATE_SYN_RCVD;
}
}
if (event & APP_DATA) {
/* the application has requested that data be sent */
send_syn_ack_fin(sd, ctx, SEND_SYN, ctx->initial_sequence_num, 0);
ctx->connection_state = CSTATE_SYN_SENT;
}
if (event & APP_CLOSE_REQUESTED) {
/* the application has requested that the conn be closed */
ctx->connection_state = CSTATE_CLOSED;
}
return ret;
}
int handle_cstate_syn_rcvd(mysocket_t sd, context_t * ctx) {
int ret = 0;
unsigned int event;
our_dprintf("in CSTATE_SYN_RCVD\n");
event = stcp_wait_for_event(sd, NETWORK_DATA | APP_CLOSE_REQUESTED | TIMEOUT, NULL);
/* check whether it was the network, app, or a close request */
if (event & NETWORK_DATA) {
/* there was network data received */
size_t recd;
recd = stcp_network_recv(sd, ctx->recv_wind, MAX_WINDOW_SIZE);
if (recd == 0) {
our_dprintf("bad network recv\n");
return -1;
}
struct tcphdr * tcp_packet = (struct tcphdr *) ctx->recv_wind;
if (tcp_packet->th_flags & TH_ACK){
/* ack received */
if (ntohl(tcp_packet->th_ack) < ctx->sent_last_byte_acked || ntohl(tcp_packet->th_ack) > ctx->sent_last_byte_written+1){
our_dprintf("bad ack, expected %u, received %u. returning \n", ctx->sent_last_byte_sent+1, tcp_packet->th_ack);
return -1;
}
ctx->sent_last_byte_acked = ntohl(tcp_packet->th_ack);
ctx->recd_adv_window = ntohs(tcp_packet->th_win);
//our_dprintf("*** got ack %u, got adv window %u\n", ctx->sent_last_byte_acked, ctx->recd_adv_window);
ctx->connection_state = CSTATE_ESTABLISHED;
}
}
if (event & APP_CLOSE_REQUESTED) {
/* the application has requested that the conn be closed */
ctx->connection_state = CSTATE_FIN_WAIT_1;
close_tcp_conn(sd, ctx);
}
return ret;
}
/* ***************************************************
* Function: add_to_recv_buffer
* ***************************************************
* This function simply adds a packet (if its a valid packet, defined
* by the next function) to the receiver buffer. It searches the receiver
* buffer for the right place to put the file. The receive buffer is always
* kept in anscending order of sequence numbers.
*/
static void add_to_recv_buffer(context_t *ctx, char* pkt, size_t len)
{
tcp_seq target_seq = ((struct tcphdr *)pkt)->th_seq;
size_t data_len = len - TCP_DATA_START(pkt);
if (!is_valid_entry(ctx,target_seq, data_len)){
our_dprintf("Invalid incoming packet - dropping!\n");
return;
}
struct window* win = &(ctx->rbuffer);
assert((win->end->next==NULL) || !DEBUG);
/* Create a new link list entry */
struct p_entry* new_entry = (struct p_entry*)calloc(1,sizeof(struct p_entry));
new_entry->packet = (char *)calloc(1, len);
memcpy(new_entry->packet, pkt, len);
new_entry->packet_size = len;
tcp_seq curr_seq;
struct p_entry* prev = win->start;
struct p_entry* curr = win->start->next;
bool inserted = false;
/* Search for the right place to add this sequence */
while(curr) {
curr_seq = ((struct tcphdr *)curr->packet)->th_seq;
if (target_seq < curr_seq) {
/* Place found */
inserted = true;
new_entry->next = curr;
prev->next = new_entry;
break;
}
prev = curr;
curr = curr->next;
}
/* Add to the end of the list if not added before */
if (!inserted){
new_entry->next = NULL;
win->end->next = new_entry;
win->end = win->end->next;
}
win->num_entries+=1;
our_dprintf("Added Recv: %d to receive buffer\n", ((struct tcphdr*)pkt)->th_seq);
}
/* ***************************************************
* Function: is_valid_entry
* ***************************************************
* Determines if an incoming packet "fits" in the receive buffer.
* The following conditions must be sastified.
* 1.) The incoming sequence number better be greater than or equal to
* the last ack we sent out, otherwise we already have the data.
* 2.) The incoming sequence number cannot be identical to any sequence
* number in the receive buffer. This just means we have a duplicate
* packet so no need to store it.
* 3.) If the packet fits between sequence X and sequence Y, its length
* better not be large enough to overlap with Y, and the length of X
* better not be large enough to overlap with the packet's sequence.
* This means the packet is trying to overwrite data and I simply drop it.
*/
static bool is_valid_entry(context_t* ctx, tcp_seq target_seq, size_t data_len)
{
if (target_seq< ctx->last_ack_sent){
our_dprintf("Received Packet Outside receiver window with seq: %d\n", target_seq);
return false;
}
struct p_entry* prev = ctx->rbuffer.start;
struct p_entry* curr = ctx->rbuffer.start->next;
while(curr) {
tcp_seq curr_seq = ((struct tcphdr *)curr->packet)->th_seq;
if (target_seq==curr_seq){
our_dprintf("Received Duplicate Packet with seq: %d\n", target_seq);
return false;
}
else if (target_seq < curr_seq) {
if (curr->next){
tcp_seq next_seq = ((struct tcphdr *)curr->next->packet)->th_seq;
if ( (target_seq + data_len) > next_seq) {
our_dprintf("Packet overwriting 1!!! TARGET SEQ:%d DATA_LEN:%d NEXT_SEQ:%d CURR SEQ:%d\n",
target_seq, data_len, curr_seq);
assert(!DEBUG);
return false;
}
}
if (prev!=ctx->rbuffer.start) {
tcp_seq prev_seq = ((struct tcphdr *)prev->packet)->th_seq;
size_t prev_len = prev->packet_size - TCP_DATA_START(prev->packet);
if ((target_seq>prev_seq) && ((prev_seq + prev_len) > target_seq)){
our_dprintf("Packet overwriting 2!!! PREV SEQ:%d PREV_LEN:%d TARGET_SEQ:%d CURR SEQ:%d\n",
prev_seq, prev_len, target_seq, curr_seq);
assert(!DEBUG);
return false;
}
}
}
prev = curr;
curr = curr->next;
}
return true;
}
int handle_cstate_closed(mysocket_t sd, context_t * ctx, bool_t is_active) {
int ret = 0;
our_dprintf("in CSTATE_CLOSED\n");
if (is_active) {
send_syn_ack_fin(sd, ctx, SEND_SYN, ctx->initial_sequence_num, 0);
ctx->connection_state = CSTATE_SYN_SENT;
} else {
ctx->connection_state = CSTATE_LISTEN;
}
return ret;
}
/* ***************************************************
* Function: send_ack
* ***************************************************
* Small helper function for preparing an ACK packet and sending
* it to the network.
*/
static void send_ack(mysocket_t sd, context_t* ctx)
{
struct tcphdr *ack_pkt = (struct tcphdr *)calloc(1, (TH_MIN_OFFSET*sizeof(uint32_t)));
ack_pkt->th_flags = TH_ACK;
ack_pkt->th_ack = ctx->last_ack_sent;
ack_pkt->th_seq = ctx->nxt_seq_num;
our_dprintf("Sending ack: %d with seq: %d\n", ack_pkt->th_ack, ack_pkt->th_seq);
ack_pkt->th_win = RWIN;
ack_pkt->th_off = TH_MIN_OFFSET;
network_send(sd, ack_pkt, TH_MIN_OFFSET*sizeof(uint32_t));
free(ack_pkt);
}
int close_tcp_conn(mysocket_t sd, context_t * ctx) {
while(ctx->connection_state != CSTATE_CLOSED) {
switch (ctx->connection_state) {
case CSTATE_FIN_WAIT_1:
/* first fin wait state */
handle_cstate_fin_wait_1(sd, ctx);
break;
case CSTATE_FIN_WAIT_2:
/* second fin wait state */
handle_cstate_fin_wait_2(sd, ctx);
break;
case CSTATE_CLOSING:
/* currently closing */
handle_cstate_closing(sd, ctx);
break;
case CSTATE_TIME_WAIT:
/* waiting timeout */
handle_cstate_time_wait(sd, ctx);
break;
case CSTATE_CLOSE_WAIT:
/* close wait state */
handle_cstate_close_wait(sd, ctx);
break;
case CSTATE_LAST_ACK:
/* last ack */
handle_cstate_last_ack(sd, ctx);
break;
default:
/* shouldn't happen */
our_dprintf("bad close ctcp state\n");
assert(0);
}
}
ctx->done = TRUE;
our_dprintf("ALL DONE\n");
return 0;
}
/* ***************************************************
* Function: sendrcv_syn
* ***************************************************
* Helper function for active-side network initiation.
* It sends the SYN packet and waits for the right SYN_ACK
*/
static bool sendrcv_syn(mysocket_t sd, context_t *ctx, struct tcphdr* in_packet)
{
/* Set SYN Headers */
struct tcphdr* out_packet = (struct tcphdr *)calloc(1,(TH_MIN_OFFSET*sizeof(uint32_t)));
out_packet->th_ack = 0;
out_packet->th_seq = ctx->initial_sequence_num;
out_packet->th_flags = TH_SYN;
out_packet->th_off = TH_MIN_OFFSET;
out_packet->th_win = RWIN;
ctx->nxt_seq_num = ctx->initial_sequence_num + 1; /* SYN Packet = 1 byte */
our_dprintf("Active Sending SYN. Seq:%d\n", out_packet->th_seq);
unsigned int event;
bool success = false;
int num_tries = 1;
struct timeval tstart;
gettimeofday(&tstart,NULL); /*start the timer */
network_send(sd, out_packet, (TH_MIN_OFFSET*sizeof(uint32_t)));
/* Try sending the SYN a total of 6 times before giving up */
while ((num_tries < MAX_RT_TRIES) && !success){
event = wait_for_event(sd, NETWORK_DATA, ctx, tstart);
if (event & NETWORK_DATA) {
network_recv(sd, in_packet);
/* Check to see if we got the right SYN_ACK */
success = ((in_packet->th_flags & (TH_SYN | TH_ACK)) &&
(in_packet->th_ack == ctx->nxt_seq_num));
}
else if (event==TIMEOUT){
our_dprintf("Active - SYN TIMEOUT!, no SYN_ACK!\n");
gettimeofday(&tstart,NULL);
num_tries+=1;
our_dprintf("Active Resending SYN. Seq:%d\n", out_packet->th_seq);
network_send(sd, out_packet, (TH_MIN_OFFSET*sizeof(uint32_t)));
}
}
free(out_packet);
return success;
}
int handle_cstate_last_ack(mysocket_t sd, context_t * ctx){
int ret = 0;
unsigned int event;
our_dprintf("in CSTATE_LAST_ACK\n");
event = stcp_wait_for_event(sd, NETWORK_DATA | TIMEOUT, NULL);
/* check whether it was the network, app, or a close request */
uint8_t buff[MAX_WINDOW_SIZE + sizeof(struct tcphdr)];
if (event & NETWORK_DATA) {
/* there was network data received */
size_t recd;
recd = stcp_network_recv(sd, buff, MAX_WINDOW_SIZE);
if (recd == 0) {
our_dprintf("bad network recv\n");
return -1;
}
struct tcphdr * tcp_packet = (struct tcphdr *) buff;
if (tcp_packet->th_flags & TH_ACK){
/* if ack */
if (ntohl(tcp_packet->th_ack) < ctx->sent_last_byte_acked || ntohl(tcp_packet->th_ack) > ctx->sent_last_byte_written+1){
our_dprintf("bad ack, expected %u, received %u. returning \n", ctx->sent_last_byte_sent+1, tcp_packet->th_ack);
return -1;
}
//our_dprintf("*** got an ack %u\n", ctx->sent_last_byte_acked);
ctx->sent_last_byte_acked = ntohl(tcp_packet->th_ack);
ctx->connection_state = CSTATE_CLOSED;
}
}
return ret;
}
/* ***************************************************
* Function: handle_network_data
* ***************************************************
* A packet has arrived. If its an ACK packet, call a helper
* function that deals with acks. If the packet has data or it's
* a FIN packet, then add the packet to the receiver buffer only
* if it fits in the receiving window. If it doesn't fit,
* drop the packet. If it fits, send an acknowledgement.
*/
static void handle_network_data(mysocket_t sd, context_t *ctx)
{
char *pkt = (char *)calloc(1, (TH_MAX_OFFSET*sizeof(uint32_t)) + STCP_MSS);
size_t total_length = network_recv(sd, pkt);
struct tcphdr* hdr = (struct tcphdr *)pkt;
ctx->recv_win = MIN(hdr->th_win, CWIN);
if (hdr->th_flags & TH_ACK) {
handle_ack(hdr, sd, ctx);
}
size_t data_length = total_length - TCP_DATA_START(hdr);
if (data_length>0 || (hdr->th_flags & TH_FIN)) {
our_dprintf("Received %d bytes of data with seq: %d, last ack sent: %d\n",
data_length, hdr->th_seq, ctx->last_ack_sent);
/* Does the packet fit in the receiving window?*/
if ((hdr->th_seq + data_length)<=(ctx->last_ack_sent + RWIN)) {
add_to_recv_buffer(ctx, pkt, total_length);
if (hdr->th_seq == ctx->last_ack_sent){
/* The packet arrived in order. We can remove all in-order
* packets from the receive buffer now */
our_dprintf("Packet In Order. Handling buffer\n");
handle_recv_buffer(sd, ctx);
}
else {
if (hdr->th_seq > ctx->last_ack_sent) {
our_dprintf("This packet is out of order. Adding to recv buffer\n");
}
}
send_ack(sd, ctx);
}
else {
our_dprintf("Packet outside receiver buffer. Dropping!!!\n");
}
}
free(pkt);
}
/* ***************************************************
* Function: handle_recv_buffer
* ***************************************************
* This function is called whenever we get the next packet
* we are expecting from the sender in-order. It iterates
* through the receive buffer sending packets to the application
* for consumption. When a packet is consumed, it is freed and
* removed from the buffer. The loop stops as soon as we see
* that the next packet is not in order or when we have emptied out
* the buffer entirely (whichever happens first).
*/
static void handle_recv_buffer(mysocket_t sd, context_t *ctx)
{
struct window* win = &(ctx->rbuffer);
struct p_entry* curr = win->start->next;
assert(curr || !DEBUG);
tcp_seq next_seq, curr_seq;
size_t data_len;
bool is_fin = false;
bool stop_loop = false;
/* Iterate through all entries in the receive buffer */
while (win->num_entries>0 && !stop_loop) {
data_len = curr->packet_size - TCP_DATA_START(curr->packet);
curr_seq = ((struct tcphdr *)curr->packet)->th_seq;
/* Special case, FIN packet in receive buffer */
is_fin = (((struct tcphdr *)curr->packet)->th_flags & TH_FIN);
if (is_fin){
assert(curr->next==NULL || !DEBUG);
ctx->last_ack_sent+=1;
if (data_len>0) {
/* FIN packet with data. Send data to app */
stcp_app_send(sd, curr->packet + TCP_DATA_START(curr->packet), data_len);
}
handle_fin(sd, ctx); /* Call helper function */
break;
}
our_dprintf("Sending packet with Seq: %d to application \n", curr_seq);
ctx->last_ack_sent = curr_seq + data_len;
stcp_app_send(sd, curr->packet + TCP_DATA_START(curr->packet), data_len);
/* Have we reached the end of the buffer?*/
if (curr->next){
/* No, exit only if next sequence is not in order */
next_seq = ((struct tcphdr *)curr->next->packet)->th_seq;
if ((data_len + curr_seq)!=next_seq){
stop_loop = true;
}
}
/* Update pointers and free memory */
win->start->next = curr->next;
if (win->end == curr){
win->end = win->start;
}
free(curr->packet);
free(curr);
curr = win->start->next;
win->num_entries-=1;
}
}
/* ***************************************************
* Function: add_to_send_buffer
* ***************************************************
* A data/fin packet is being sent out. This function adds that packet
* to the sender's window (end of link list) in case it timeouts and
* needs to be retransmitted. It records the time the packet was sent.
*/
static void add_to_send_buffer(context_t* ctx, char* pkt, size_t len)
{
struct window* win = &(ctx->sbuffer);
assert((win->end->next==NULL) || !DEBUG);
struct p_entry* new_entry = (struct p_entry*)calloc(1,sizeof(struct p_entry));
new_entry->packet = (char *)calloc(1, len);
memcpy(new_entry->packet, pkt, len);
new_entry->packet_size = len;
new_entry->next = NULL;
new_entry->num_transmits = 1;
gettimeofday(&(new_entry->tstart), NULL);
win->end->next = new_entry; /* Attach to the end of the list */
win->end = win->end->next; /* Update the end of the list */
win->num_entries+=1; /* Add 1 to the number of entries */
assert(win->start->next || !DEBUG);
our_dprintf("Added Seq: %d to send buffer\n", ((struct tcphdr*)pkt)->th_seq);
}
/* initialise the transport layer, and start the main loop, handling
* any data from the peer or the application. this function should not
* return until the connection is closed.
*/
void transport_init(mysocket_t sd, bool_t is_active)
{
context_t *ctx;
int res;
ctx = (context_t *) calloc(1, sizeof(context_t));
assert(ctx);
generate_initial_seq_num(ctx);
ctx->connection_state = CSTATE_CLOSED;
ctx->send_wind = (uint8_t *) malloc(MAX_WINDOW_SIZE);
memset(ctx->send_wind, 0, MAX_WINDOW_SIZE);
ctx->recv_wind = (uint8_t *) malloc(MAX_WINDOW_SIZE);
memset(ctx->recv_wind, 0, MAX_WINDOW_SIZE);
res = open_tcp_conn(sd, ctx, is_active);
/* XXX: you should send a SYN packet here if is_active, or wait for one
* to arrive if !is_active. after the handshake completes, unblock the
* application with stcp_unblock_application(sd). you may also use
* this to communicate an error condition back to the application, e.g.
* if connection fails; to do so, just set errno appropriately (e.g. to
* ECONNREFUSED, etc.) before calling the function.
*/
stcp_unblock_application(sd);
if (ctx->connection_state == CSTATE_ESTABLISHED){
control_loop(sd, ctx);
} else if (ctx->connection_state == CSTATE_FIN_WAIT_1){
close_tcp_conn(sd, ctx);
} else if (ctx->connection_state == CSTATE_CLOSED) {
;
}else {
our_dprintf("bad state in transport init");
assert(0);
}
/* do any cleanup here */
free(ctx->send_wind);
free(ctx->recv_wind);
free(ctx);
}
/* ***************************************************
* Function: remove_until_seq
* ***************************************************
* When we receive an ACK, this is the function we call to
* remove all entries up to the new/updated bottom of the
* send window.
*/
static void remove_until_seq(context_t* ctx)
{
struct window* win = &(ctx->sbuffer);
assert((win->start->next!=NULL) || !DEBUG);
assert((win->num_entries>0) || !DEBUG);
while (win->num_entries>0){
struct p_entry* victim = win->start->next;
tcp_seq sequence = ((struct tcphdr*)(victim->packet))->th_seq;
if (sequence>=ctx->seq_base) break;
our_dprintf("Removing Seq: %d from sender's buffer\n",
((struct tcphdr*)victim->packet)->th_seq);
if (victim==win->end) {
win->end = win->start;
}
win->start->next = win->start->next->next;
win->num_entries-=1;
free(victim->packet);
free(victim);
}
}
/* ***************************************************
* Function: send_fin
* ***************************************************
* The application has requested to be closed and there
* is at least 1 byte of room in the window. This function
* prepares a fin packet, adds it to the send buffer, and
* sends it. It also updates the connection state.
*/
static void send_fin(mysocket_t sd, context_t *ctx)
{
our_dprintf("App requested close there is space in window... SENDING FIN\n");
struct tcphdr* fin_pkt = (struct tcphdr *)calloc(1,TH_MIN_OFFSET*sizeof(uint32_t));
fin_pkt->th_seq = ctx->nxt_seq_num;
ctx->fin_ack = fin_pkt->th_seq + 1;
ctx->nxt_seq_num += 1; /*FIN = 1 byte of data */
fin_pkt->th_off = TH_MIN_OFFSET;
fin_pkt->th_flags = TH_FIN;
fin_pkt->th_win = RWIN;
/* Update State variables depending on previous state */
if (ctx->connection_state == CSTATE_ESTABLISHED ) {
ctx->connection_state = CSTATE_FIN_WAIT1;
}
else {
assert(ctx->connection_state == CSTATE_CLOSE_WAIT || !DEBUG);
ctx->connection_state = CSTATE_LAST_ACK;
}
add_to_send_buffer(ctx, (char *)fin_pkt, (TH_MIN_OFFSET*sizeof(uint32_t)));
network_send(sd, fin_pkt, TH_MIN_OFFSET*sizeof(uint32_t));
free(fin_pkt);
}
