-
Notifications
You must be signed in to change notification settings - Fork 0
/
transport.c
514 lines (420 loc) · 18.8 KB
/
transport.c
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
/*
* transport.c
*
* CS244a HW#3 (Reliable Transport)
*
* This file implements the STCP layer that sits between the
* mysocket and network layers. You are required to fill in the STCP
* functionality in this file.
*
*/
#include <stdio.h>
#include <stdarg.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include "mysock.h"
#include "stcp_api.h"
#include "transport.h"
#include <time.h>
#include <arpa/inet.h>
#define MAX_SEND_WINDOW_SIZE 3027
#define MAX_RECV_WINDOW_SIZE 3027
#define MIN_CWND_SIZE 3027
#define MAX_PAYLOAD_SIZE 536
#define MAX_SIZE 556
enum {
CSTATE_ESTABLISHED,
CSTATE_CLOSED,
CSTATE_LISTEN,
CSTATE_SYN_SENT,
CSTATE_SYN_RCVD,
CSTATE_FIN_WAIT_1,
CSTATE_FIN_WAIT_1a,
CSTATE_FIN_WAIT_1b,
CSTATE_FIN_WAIT_2,
CSTATE_CLOSE_WAIT,
CSTATE_LAST_ACK,
CSTATE_CLOSING
}; /* obviously you should have more states */
/* this structure is global to a mysocket descriptor */
typedef struct
{
bool_t done; /* TRUE once connection is closed */
int connection_state; /* state of the connection (established, etc.) */
tcp_seq initial_sequence_num;
/* any other connection-wide global variables go here */
/* Variables on our end */
tcp_seq max_ACK_rcvd;
uint16_t our_wndw;
tcp_seq nxt_seqnum;
/* Variables on the other end */
tcp_seq nxt_exp; /* used to keep track of what the other side is expecting and what we are expecting from them */
uint16_t other_wndw;
} context_t;
static void generate_initial_seq_num(context_t *ctx);
tcphdr *create_tcphdr(uint8_t th_flag, context_t *ctx);
void send_packet(mysocket_t sd, context_t *ctx, uint8_t th_flag);
void est_handshake(mysocket_t sd, context_t *ctx);
static void control_loop(mysocket_t sd, context_t *ctx);
void end_handshake(mysocket_t sd, context_t *ctx);
void update_wndw(context_t *ctx, tcphdr *tcp_hdr);
/* 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;
ctx = (context_t *) calloc(1, sizeof(context_t));
assert(ctx);
generate_initial_seq_num(ctx);
/* 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.
*/
if (is_active) {
ctx->nxt_seqnum = ctx->initial_sequence_num;
send_packet(sd, ctx, TH_SYN);
ctx->connection_state = CSTATE_SYN_SENT;
}
else {
ctx->nxt_seqnum = ctx->initial_sequence_num;
ctx->connection_state = CSTATE_LISTEN;
}
ctx->our_wndw = MAX_SEND_WINDOW_SIZE;
ctx->other_wndw = MAX_RECV_WINDOW_SIZE; /* Will be updated when first packet arrives */
printf("establishing handshake\n");
est_handshake(sd, ctx);
if (ctx->connection_state != CSTATE_ESTABLISHED)
fprintf(stderr, "CSTATE not established!\n");
stcp_unblock_application(sd);
control_loop(sd, ctx);
printf("done\n");
/* do any cleanup here */
free(ctx);
}
tcphdr *create_tcphdr(uint8_t th_flag, context_t *ctx)
{
tcphdr *ret = (tcphdr *) calloc(sizeof(tcphdr), 1);
assert(ret);
ret->th_seq = htonl(ctx->nxt_seqnum);
ret->th_flags = th_flag;
ret->th_ack = (th_flag & TH_ACK) ? htonl(ctx->nxt_exp) : 0;
ret->th_win = htons(MAX_SEND_WINDOW_SIZE);
ret->th_off = 5;
return ret;
}
/* specifically for sending TH_ACK/TH_SYN/TH_FIN */
void send_packet(mysocket_t sd, context_t *ctx, uint8_t th_flag)
{
tcphdr *tcp_hdr = create_tcphdr(th_flag, ctx);
printf("sending: th_seq: %d\nth_ack: %d\nth_flags: %u\n", ntohl(tcp_hdr->th_seq), ntohl(tcp_hdr->th_ack), tcp_hdr->th_flags);
if (stcp_network_send(sd, tcp_hdr, sizeof(tcphdr), NULL) < (int) sizeof(tcphdr)) {
fprintf(stderr, "send_packet failed to send entirety of packet\n");
}
ctx->other_wndw -= sizeof(tcphdr);
ctx->nxt_seqnum++; /* expecting a ack with this seqnum */
if (th_flag & TH_ACK)
ctx->nxt_exp++; /* expecting seqnum of next received packet to be this (set during handshake) */
free(tcp_hdr);
}
void est_handshake(mysocket_t sd, context_t *ctx)
{
stcp_event_type_t flag;
ssize_t rcvd;
tcphdr *tcp_hdr;
while (ctx->connection_state == CSTATE_SYN_SENT || ctx->connection_state == CSTATE_SYN_RCVD || ctx->connection_state == CSTATE_LISTEN) {
/* APP has been blocked */
flag = (stcp_event_type_t) stcp_wait_for_event(sd, NETWORK_DATA, NULL);
if (flag == NETWORK_DATA) {
char buf[MAX_SIZE];
rcvd = stcp_network_recv(sd, buf, MAX_SIZE);
tcp_hdr = (tcphdr *) buf;
switch (ctx->connection_state) {
case CSTATE_LISTEN:
if (tcp_hdr->th_flags & TH_SYN) {
ctx->nxt_exp = ntohl(tcp_hdr->th_seq) + rcvd - tcp_hdr->th_off * 4 + 1;
update_wndw(ctx, tcp_hdr);
send_packet(sd, ctx, TH_ACK | TH_SYN);
ctx->connection_state = CSTATE_SYN_RCVD;
}
break;
case CSTATE_SYN_SENT:
if (tcp_hdr->th_flags & TH_SYN) {
ctx->nxt_exp = ntohl(tcp_hdr->th_seq) + rcvd - tcp_hdr->th_off * 4 + 1;
ctx->connection_state = CSTATE_SYN_RCVD;
if (tcp_hdr->th_flags & TH_ACK && ntohl(tcp_hdr->th_ack) == ctx->nxt_seqnum) {
ctx->max_ACK_rcvd = ntohl(tcp_hdr->th_ack);
ctx->nxt_seqnum++;
ctx->connection_state = CSTATE_ESTABLISHED;
send_packet(sd, ctx, TH_ACK);
update_wndw(ctx, tcp_hdr);
break;
}
send_packet(sd, ctx, TH_ACK | TH_SYN);
update_wndw(ctx, tcp_hdr);
}
break;
case CSTATE_SYN_RCVD:
if (tcp_hdr->th_flags & TH_ACK && ntohl(tcp_hdr->th_ack) == ctx->nxt_seqnum) {
ctx->nxt_exp = ntohl(tcp_hdr->th_seq) + rcvd - tcp_hdr->th_off * 4 + 1;
ctx->max_ACK_rcvd = ntohl(tcp_hdr->th_ack);
ctx->nxt_seqnum++;
update_wndw(ctx, tcp_hdr);
ctx->connection_state = CSTATE_ESTABLISHED;
}/* Here, the sliding window does not play any role yet. later an ACK will be accepted if it its > last recieved ack */
break;
default:
printf("Invalid state\n");
break;
}
}
else
printf("Flag is not NETWORK_DATA!\n");
}
}
/* generate random initial sequence number for an STCP connection */
static void generate_initial_seq_num(context_t *ctx)
{
assert(ctx);
srand(time(NULL));
#ifdef FIXED_INITNUM
/* please don't change this! */
ctx->initial_sequence_num = 1;
#else
/* you have to fill this up */
ctx->initial_sequence_num = rand() % 256;
#endif
}
/* 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);
while (!ctx->done)
{
unsigned int event;
event = stcp_wait_for_event(sd, ANY_EVENT, NULL);
char buf[MAX_SIZE];
size_t bytes_rcvd;
uint16_t load_size;
int len;
tcphdr *tcp_hdr;
uint8_t *temp;
switch (event) {
case NETWORK_DATA:
bytes_rcvd = stcp_network_recv(sd, buf, MAX_SIZE);
tcp_hdr = (tcphdr *) buf;
load_size = bytes_rcvd - tcp_hdr->th_off * 4;
update_wndw(ctx, tcp_hdr);
// ERROR CHECKING
printf("recieved\n");
printf("th_flags on packet: %u\n", tcp_hdr->th_flags);
printf("acknowledging (should be > max_ACK_rcvd: %d\n", ntohl(tcp_hdr->th_ack));
printf("max_ACK_rcvd: %d\n", ctx->max_ACK_rcvd);
printf("ctx->nxt_seqnum : %d\n", ctx->nxt_seqnum);
printf("tcp_hdr->th_seq: %d\n", ntohl(tcp_hdr->th_seq));
printf("load_size: %d\n", load_size);
printf("ctx->nxt_exp : %d\n", ctx->nxt_exp);
/* Reliable mode: Packet should be as expected, or in extraordinary circumstances: old data is retransmitted with new data */
if ((ntohl(tcp_hdr->th_seq) == ctx->nxt_exp) || (ntohl(tcp_hdr->th_ack) > ctx->max_ACK_rcvd && ntohl(tcp_hdr->th_ack) <= ctx->nxt_seqnum) || (ntohl(tcp_hdr->th_seq) + load_size >= ctx->nxt_exp && ntohl(tcp_hdr->th_seq) + load_size <= ctx->nxt_exp + ctx->our_wndw)) {
/* check if typical packet, check if valid ACK, check if packet falls within our window */
/* concatenate recieved old data */
if (ntohl(tcp_hdr->th_seq) + tcp_hdr->th_off * 4 < ctx->nxt_exp) {
load_size -= (ctx->nxt_exp - ntohl(tcp_hdr->th_seq) - tcp_hdr->th_off * 4);
}
/* Pure TCP packet */
if (load_size == 0) {
ctx->nxt_exp++;
if (tcp_hdr->th_flags & TH_FIN) {
if (ctx->connection_state == CSTATE_FIN_WAIT_1 || ctx->connection_state == CSTATE_FIN_WAIT_1b) {
printf("ending sequence\n");
ctx->connection_state = CSTATE_FIN_WAIT_1a;
end_handshake(sd, ctx);
break;
}
else if (ctx->connection_state == CSTATE_FIN_WAIT_2) {
printf("ending sequence\n");
end_handshake(sd, ctx);
}
printf("server acks fin\n");
send_packet(sd, ctx, TH_ACK);
ctx->connection_state = CSTATE_CLOSE_WAIT;
stcp_fin_received(sd);
}
}
else if (load_size > 0) { /* Payload exists */
/* Pointer to the payload */
temp = (((uint8_t *) tcp_hdr) + tcp_hdr->th_off * 4);
/* Take care of the extraordinary circumstance */
if ((ntohl(tcp_hdr->th_seq) + tcp_hdr->th_off * 4 < ctx->nxt_exp)) {
temp = (((uint8_t *) tcp_hdr) + (ctx->nxt_exp - ntohl(tcp_hdr->th_seq)));
}
ctx->nxt_exp += load_size;
send_packet(sd, ctx, TH_ACK);
stcp_app_send(sd, temp, load_size);
/* TH_FIN is piggybacked */
if (tcp_hdr->th_flags & TH_FIN) {
if (ctx->connection_state == CSTATE_FIN_WAIT_1 || ctx->connection_state == CSTATE_FIN_WAIT_1b) {
printf("ending sequence\n");
ctx->connection_state = CSTATE_FIN_WAIT_1a;
end_handshake(sd, ctx);
break;
}
else if (ctx->connection_state == CSTATE_FIN_WAIT_2) {
printf("ending sequence\n");
end_handshake(sd, ctx);
}
/* Already ACKED! */
ctx->connection_state = CSTATE_CLOSE_WAIT;
stcp_fin_received(sd);
}
}
if (tcp_hdr->th_flags & TH_ACK && ntohl(tcp_hdr->th_ack) > ctx->max_ACK_rcvd && ntohl(tcp_hdr->th_ack) <= ctx->nxt_seqnum) {
ctx->max_ACK_rcvd = ntohl(tcp_hdr->th_ack);
ctx->nxt_seqnum++;
/* All payload packets has been acked; recieving ack for TH_FIN */
if (ntohl(tcp_hdr->th_ack) == ctx->nxt_seqnum && (ctx->connection_state == CSTATE_FIN_WAIT_1)) {
printf("client recieving ACK for FIN\n");
ctx->nxt_exp = ntohl(tcp_hdr->th_seq) + 1; /* not accounted for if load_size == 0 */
ctx->connection_state = CSTATE_FIN_WAIT_1b;
end_handshake(sd,ctx);
break;
}
}
}
/* re-send ack for oustanding packets */
else if (ntohl(tcp_hdr->th_seq) != ctx->nxt_exp) {
ctx->nxt_exp--;
send_packet(sd, ctx, TH_ACK);
}
break;
case APP_DATA:
len = (ctx->other_wndw < MAX_SIZE - sizeof(tcphdr)) ? ctx->other_wndw : MAX_SIZE - sizeof(tcphdr);
printf("app data\n");
bytes_rcvd = stcp_app_recv(sd, buf, len);
tcp_hdr = (tcphdr *) calloc(sizeof(tcphdr) + bytes_rcvd, 1);
memcpy(tcp_hdr + 1, buf, bytes_rcvd);
tcp_hdr->th_seq = htonl(ctx->nxt_seqnum);
tcp_hdr->th_win = htons(MAX_SEND_WINDOW_SIZE);
tcp_hdr->th_off = 5;
printf("sending: th_seq: %d\nth_ack: %d\nth_flags: %u\n", ntohl(tcp_hdr->th_seq), ntohl(tcp_hdr->th_ack), tcp_hdr->th_flags);
if (stcp_network_send(sd, tcp_hdr, sizeof(tcphdr) + bytes_rcvd, NULL) < (int) (sizeof(tcphdr) + bytes_rcvd)) {
fprintf(stderr, "send_packet failed to send entirety of packet\n");
}
free(tcp_hdr);
ctx->other_wndw -= sizeof(tcphdr) + bytes_rcvd;
ctx->nxt_seqnum += bytes_rcvd;
break;
case APP_CLOSE_REQUESTED:
printf("close requested\n");
end_handshake(sd, ctx);
break;
default:
break;
}
}
}
void end_handshake(mysocket_t sd, context_t *ctx)
{
tcphdr *tcp_hdr;
char buf[MAX_SIZE];
do {
switch (ctx->connection_state) {
case CSTATE_ESTABLISHED:
printf("client sends FIN\n");
send_packet(sd, ctx, TH_FIN);
ctx->connection_state = CSTATE_FIN_WAIT_1;
return;
case CSTATE_FIN_WAIT_1a:
printf("recieved FIN after sent FIN\n");
stcp_fin_received(sd);
send_packet(sd, ctx, TH_ACK);
ctx->connection_state = CSTATE_CLOSING;
break;
case CSTATE_FIN_WAIT_1b:
printf("recieved ACK after sent FIN\n");
ctx->connection_state = CSTATE_FIN_WAIT_2;
return;
case CSTATE_FIN_WAIT_2:
printf("Recieved final FIN\n");
stcp_fin_received(sd);
send_packet(sd, ctx, TH_ACK);
ctx->connection_state = CSTATE_CLOSED;
break;
case CSTATE_CLOSING:
printf("Recieved final ACK\n");
if (tcp_hdr->th_flags & TH_ACK && ntohl(tcp_hdr->th_ack) == ctx->nxt_seqnum) {
update_wndw(ctx, tcp_hdr);
ctx->nxt_exp++;
ctx->max_ACK_rcvd = ntohl(tcp_hdr->th_ack);
ctx->nxt_seqnum++;
ctx->connection_state = CSTATE_CLOSED;
}
break;
case CSTATE_CLOSE_WAIT:
printf("Final FIN sent\n");
send_packet(sd, ctx, TH_FIN);
ctx->connection_state = CSTATE_LAST_ACK;
break;
case CSTATE_LAST_ACK:
printf("Final ack recieved (last ack)\nth_ack: %d\n", ntohl(tcp_hdr->th_ack));
printf("ctx seqnum : %d\n", ctx->nxt_seqnum);
printf("th_flags: %u\n", tcp_hdr->th_flags);
if (tcp_hdr->th_flags & TH_ACK && ntohl(tcp_hdr->th_ack) == ctx->nxt_seqnum) {
update_wndw(ctx, tcp_hdr);
ctx->nxt_exp++;
ctx->max_ACK_rcvd = ntohl(tcp_hdr->th_ack);
ctx->nxt_seqnum++;
ctx->connection_state = CSTATE_CLOSED;
send_packet(sd, ctx, TH_ACK);
}
break;
default:
break;
}
if (ctx->connection_state != CSTATE_CLOSED) {
stcp_wait_for_event(sd, NETWORK_DATA, NULL);
stcp_network_recv(sd, buf, MAX_SIZE);
tcp_hdr = (tcphdr *) buf;
}
} while (ctx->connection_state != CSTATE_CLOSED);
ctx->done = TRUE;
}
void update_wndw(context_t *ctx, tcphdr *tcp_hdr)
{
ctx->other_wndw = (ntohs(tcp_hdr->th_win) > MAX_SEND_WINDOW_SIZE) ? MAX_SEND_WINDOW_SIZE : (ntohs(tcp_hdr->th_win));
}
/**********************************************************************/
/* our_dprintf
*
* Send a formatted message to stdout.
*
* format A printf-style format string.
*
* This function is equivalent to a printf, but may be
* changed to log errors to a file if desired.
*
* Calls to this function are generated by the dprintf amd
* dperror macros in transport.h
*/
void our_dprintf(const char *format,...)
{
va_list argptr;
char buffer[1024];
assert(format);
va_start(argptr, format);
vsnprintf(buffer, sizeof(buffer), format, argptr);
va_end(argptr);
fputs(buffer, stdout);
fflush(stdout);
}