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   1 /*
   2     utcp.c -- Userspace TCP
   3     Copyright (C) 2014 Guus Sliepen <guus@tinc-vpn.org>
   4
   5     This program is free software; you can redistribute it and/or modify
   6     it under the terms of the GNU General Public License as published by
   7     the Free Software Foundation; either version 2 of the License, or
   8     (at your option) any later version.
   9
  10     This program is distributed in the hope that it will be useful,
  11     but WITHOUT ANY WARRANTY; without even the implied warranty of
  12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13     GNU General Public License for more details.
  14
  15     You should have received a copy of the GNU General Public License along
  16     with this program; if not, write to the Free Software Foundation, Inc.,
  17     51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  18 */
  19
  20 #define _GNU_SOURCE
  21
  22 #include <errno.h>
  23 #include <stdio.h>
  24 #include <stdlib.h>
  25 #include <stdint.h>
  26 #include <stdbool.h>
  27 #include <string.h>
  28 #include <unistd.h>
  29 #include <sys/time.h>
  30 #include <sys/socket.h>
  31
  32 #include "utcp_priv.h"
  33
  34 #ifdef UTCP_DEBUG
  35 #include <stdarg.h>
  36
  37 static void debug(const char *format, ...) {
  38         va_list ap;
  39         va_start(ap, format);
  40         vfprintf(stderr, format, ap);
  41         va_end(ap);
  42 }
  43
  44 static void print_packet(struct utcp *utcp, const char *dir, const void *pkt, size_t len) {
  45         struct hdr hdr;
  46         if(len < sizeof hdr) {
  47                 debug("%p %s: short packet (%zu bytes)\n", utcp, dir, len);
  48                 return;
  49         }
  50
  51         memcpy(&hdr, pkt, sizeof hdr);
  52         fprintf (stderr, "%p %s: src=%u dst=%u seq=%u ack=%u wnd=%u ctl=", utcp, dir, hdr.src, hdr.dst, hdr.seq, hdr.ack, hdr.wnd);
  53         if(hdr.ctl & SYN)
  54                 debug("SYN");
  55         if(hdr.ctl & RST)
  56                 debug("RST");
  57         if(hdr.ctl & FIN)
  58                 debug("FIN");
  59         if(hdr.ctl & ACK)
  60                 debug("ACK");
  61
  62         if(len > sizeof hdr) {
  63                 debug(" data=");
  64                 for(int i = sizeof hdr; i < len; i++) {
  65                         const char *data = pkt;
  66                         debug("%c", data[i] >= 32 ? data[i] : '.');
  67                 }
  68         }
  69
  70         debug("\n");
  71 }
  72 #else
  73 #define debug(...)
  74 #define print_packet(...)
  75 #endif
  76
  77 static void set_state(struct utcp_connection *c, enum state state) {
  78         c->state = state;
  79         if(state == ESTABLISHED)
  80                 timerclear(&c->conn_timeout);
  81         debug("%p new state: %s\n", c->utcp, strstate[state]);
  82 }
  83
  84 static inline void list_connections(struct utcp *utcp) {
  85         debug("%p has %d connections:\n", utcp, utcp->nconnections);
  86         for(int i = 0; i < utcp->nconnections; i++)
  87                 debug("  %u -> %u state %s\n", utcp->connections[i]->src, utcp->connections[i]->dst, strstate[utcp->connections[i]->state]);
  88 }
  89
  90 static int32_t seqdiff(uint32_t a, uint32_t b) {
  91         return a - b;
  92 }
  93
  94 // Connections are stored in a sorted list.
  95 // This gives O(log(N)) lookup time, O(N log(N)) insertion time and O(N) deletion time.
  96
  97 static int compare(const void *va, const void *vb) {
  98         const struct utcp_connection *a = *(struct utcp_connection **)va;
  99         const struct utcp_connection *b = *(struct utcp_connection **)vb;
 100         if(!a->src || !b->src)
 101                 abort();
 102         int c = (int)a->src - (int)b->src;
 103         if(c)
 104                 return c;
 105         c = (int)a->dst - (int)b->dst;
 106         return c;
 107 }
 108
 109 static struct utcp_connection *find_connection(const struct utcp *utcp, uint16_t src, uint16_t dst) {
 110         if(!utcp->nconnections)
 111                 return NULL;
 112         struct utcp_connection key = {
 113                 .src = src,
 114                 .dst = dst,
 115         }, *keyp = &key;
 116         struct utcp_connection **match = bsearch(&keyp, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 117         return match ? *match : NULL;
 118 }
 119
 120 static void free_connection(struct utcp_connection *c) {
 121         struct utcp *utcp = c->utcp;
 122         struct utcp_connection **cp = bsearch(&c, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 123         if(!cp)
 124                 abort();
 125
 126         int i = cp - utcp->connections;
 127         memmove(cp + i, cp + i + 1, (utcp->nconnections - i - 1) * sizeof *cp);
 128         utcp->nconnections--;
 129
 130         free(c);
 131 }
 132
 133 static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t src, uint16_t dst) {
 134         // Check whether this combination of src and dst is free
 135
 136         if(src) {
 137                 if(find_connection(utcp, src, dst)) {
 138                         errno = EADDRINUSE;
 139                         return NULL;
 140                 }
 141         } else { // If src == 0, generate a random port number with the high bit set
 142                 if(utcp->nconnections >= 32767) {
 143                         errno = ENOMEM;
 144                         return NULL;
 145                 }
 146                 src = rand() | 0x8000;
 147                 while(find_connection(utcp, src, dst))
 148                         src++;
 149         }
 150
 151         // Allocate memory for the new connection
 152
 153         if(utcp->nconnections >= utcp->nallocated) {
 154                 if(!utcp->nallocated)
 155                         utcp->nallocated = 4;
 156                 else
 157                         utcp->nallocated *= 2;
 158                 struct utcp_connection **new_array = realloc(utcp->connections, utcp->nallocated * sizeof *utcp->connections);
 159                 if(!new_array)
 160                         return NULL;
 161                 utcp->connections = new_array;
 162         }
 163
 164         struct utcp_connection *c = calloc(1, sizeof *c);
 165         if(!c)
 166                 return NULL;
 167
 168         c->sndbufsize = DEFAULT_SNDBUFSIZE;
 169         c->maxsndbufsize = DEFAULT_MAXSNDBUFSIZE;
 170         c->sndbuf = malloc(c->sndbufsize);
 171         if(!c->sndbuf) {
 172                 free(c);
 173                 return NULL;
 174         }
 175
 176         // Fill in the details
 177
 178         c->src = src;
 179         c->dst = dst;
 180         c->snd.iss = rand();
 181         c->snd.una = c->snd.iss;
 182         c->snd.nxt = c->snd.iss + 1;
 183         c->rcv.wnd = utcp->mtu;
 184         c->snd.last = c->snd.nxt;
 185         c->snd.cwnd = utcp->mtu;
 186         c->utcp = utcp;
 187
 188         // Add it to the sorted list of connections
 189
 190         utcp->connections[utcp->nconnections++] = c;
 191         qsort(utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 192
 193         return c;
 194 }
 195
 196 struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
 197         struct utcp_connection *c = allocate_connection(utcp, 0, dst);
 198         if(!c)
 199                 return NULL;
 200
 201         c->recv = recv;
 202
 203         struct hdr hdr;
 204
 205         hdr.src = c->src;
 206         hdr.dst = c->dst;
 207         hdr.seq = c->snd.iss;
 208         hdr.ack = 0;
 209         hdr.ctl = SYN;
 210         hdr.wnd = c->rcv.wnd;
 211
 212         set_state(c, SYN_SENT);
 213
 214         print_packet(utcp, "send", &hdr, sizeof hdr);
 215         utcp->send(utcp, &hdr, sizeof hdr);
 216
 217         gettimeofday(&c->conn_timeout, NULL);
 218         c->conn_timeout.tv_sec += utcp->timeout;
 219
 220         return c;
 221 }
 222
 223 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 224         if(c->reapable || c->state != SYN_RECEIVED) {
 225                 debug("Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
 226                 return;
 227         }
 228
 229         debug("%p accepted, %p %p\n", c, recv, priv);
 230         c->recv = recv;
 231         c->priv = priv;
 232         set_state(c, ESTABLISHED);
 233 }
 234
 235 static void ack(struct utcp_connection *c, bool sendatleastone) {
 236         int32_t left = seqdiff(c->snd.last, c->snd.nxt);
 237         int32_t cwndleft = c->snd.cwnd - seqdiff(c->snd.nxt, c->snd.una);
 238         char *data = c->sndbuf + seqdiff(c->snd.nxt, c->snd.una);
 239
 240         fprintf(stderr, "ack, left=%d, cwndleft=%d, sendatleastone=%d\n", left, cwndleft, sendatleastone);
 241         if(left < 0)
 242                 abort();
 243
 244         if(cwndleft <= 0)
 245                 cwndleft = 0;
 246
 247         if(cwndleft < left)
 248                 left = cwndleft;
 249
 250         if(!left && !sendatleastone)
 251                 return;
 252
 253         struct {
 254                 struct hdr hdr;
 255                 char data[c->utcp->mtu];
 256         } pkt;
 257
 258         pkt.hdr.src = c->src;
 259         pkt.hdr.dst = c->dst;
 260         pkt.hdr.ack = c->rcv.nxt;
 261         pkt.hdr.wnd = c->snd.wnd;
 262         pkt.hdr.ctl = ACK;
 263
 264         do {
 265                 uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
 266                 pkt.hdr.seq = c->snd.nxt;
 267
 268                 memcpy(pkt.data, data, seglen);
 269
 270                 c->snd.nxt += seglen;
 271                 data += seglen;
 272                 left -= seglen;
 273
 274                 if(c->state != ESTABLISHED && !left && seglen) {
 275                         switch(c->state) {
 276                         case FIN_WAIT_1:
 277                         case CLOSING:
 278                                 seglen--;
 279                                 pkt.hdr.ctl |= FIN;
 280                                 break;
 281                         default:
 282                                 break;
 283                         }
 284                 }
 285
 286                 print_packet(c->utcp, "send", &pkt, sizeof pkt.hdr + seglen);
 287                 c->utcp->send(c->utcp, &pkt, sizeof pkt.hdr + seglen);
 288         } while(left);
 289 }
 290
 291 ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 292         if(c->reapable) {
 293                 debug("Error: send() called on closed connection %p\n", c);
 294                 errno = EBADF;
 295                 return -1;
 296         }
 297
 298         switch(c->state) {
 299         case CLOSED:
 300         case LISTEN:
 301         case SYN_SENT:
 302         case SYN_RECEIVED:
 303                 debug("Error: send() called on unconnected connection %p\n", c);
 304                 errno = ENOTCONN;
 305                 return -1;
 306         case ESTABLISHED:
 307         case CLOSE_WAIT:
 308                 break;
 309         case FIN_WAIT_1:
 310         case FIN_WAIT_2:
 311         case CLOSING:
 312         case LAST_ACK:
 313         case TIME_WAIT:
 314                 debug("Error: send() called on closing connection %p\n", c);
 315                 errno = EPIPE;
 316                 return -1;
 317         }
 318
 319         // Add data to send buffer
 320
 321         if(!len)
 322                 return 0;
 323
 324         if(!data) {
 325                 errno = EFAULT;
 326                 return -1;
 327         }
 328
 329         uint32_t bufused = seqdiff(c->snd.nxt, c->snd.una);
 330
 331         /* Check our send buffer.
 332          * - If it's big enough, just put the data in there.
 333          * - If not, decide whether to enlarge if possible.
 334          * - Cap len so it doesn't overflow our buffer.
 335          */
 336
 337         if(len > c->sndbufsize - bufused && c->sndbufsize < c->maxsndbufsize) {
 338                 uint32_t newbufsize;
 339                 if(c->sndbufsize > c->maxsndbufsize / 2)
 340                         newbufsize = c->maxsndbufsize;
 341                 else
 342                         newbufsize = c->sndbufsize * 2;
 343                 if(bufused + len > newbufsize) {
 344                         if(bufused + len > c->maxsndbufsize)
 345                                 newbufsize = c->maxsndbufsize;
 346                         else
 347                                 newbufsize = bufused + len;
 348                 }
 349                 char *newbuf = realloc(c->sndbuf, newbufsize);
 350                 if(newbuf) {
 351                         c->sndbuf = newbuf;
 352                         c->sndbufsize = newbufsize;
 353                 }
 354         }
 355
 356         if(len > c->sndbufsize - bufused)
 357                 len = c->sndbufsize - bufused;
 358
 359         if(!len) {
 360                 errno == EWOULDBLOCK;
 361                 return 0;
 362         }
 363
 364         memcpy(c->sndbuf + bufused, data, len);
 365         c->snd.last += len;
 366
 367         ack(c, false);
 368         return len;
 369 }
 370
 371 static void swap_ports(struct hdr *hdr) {
 372         uint16_t tmp = hdr->src;
 373         hdr->src = hdr->dst;
 374         hdr->dst = tmp;
 375 }
 376
 377 int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 378         if(!utcp) {
 379                 errno = EFAULT;
 380                 return -1;
 381         }
 382
 383         if(!len)
 384                 return 0;
 385
 386         if(!data) {
 387                 errno = EFAULT;
 388                 return -1;
 389         }
 390
 391         print_packet(utcp, "recv", data, len);
 392
 393         // Drop packets smaller than the header
 394
 395         struct hdr hdr;
 396         if(len < sizeof hdr) {
 397                 errno = EBADMSG;
 398                 return -1;
 399         }
 400
 401         // Make a copy from the potentially unaligned data to a struct hdr
 402
 403         memcpy(&hdr, data, sizeof hdr);
 404         data += sizeof hdr;
 405         len -= sizeof hdr;
 406
 407         // Drop packets with an unknown CTL flag
 408
 409         if(hdr.ctl & ~(SYN | ACK | RST | FIN)) {
 410                 errno = EBADMSG;
 411                 return -1;
 412         }
 413
 414         // Try to match the packet to an existing connection
 415
 416         struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
 417
 418         // Is it for a new connection?
 419
 420         if(!c) {
 421                 // Ignore RST packets
 422
 423                 if(hdr.ctl & RST)
 424                         return 0;
 425
 426                 // Is it a SYN packet and are we LISTENing?
 427
 428                 if(hdr.ctl & SYN && !(hdr.ctl & ACK) && utcp->accept) {
 429                         // If we don't want to accept it, send a RST back
 430                         if((utcp->pre_accept && !utcp->pre_accept(utcp, hdr.dst))) {
 431                                 len = 1;
 432                                 goto reset;
 433                         }
 434
 435                         // Try to allocate memory, otherwise send a RST back
 436                         c = allocate_connection(utcp, hdr.dst, hdr.src);
 437                         if(!c) {
 438                                 len = 1;
 439                                 goto reset;
 440                         }
 441
 442                         // Return SYN+ACK, go to SYN_RECEIVED state
 443                         c->snd.wnd = hdr.wnd;
 444                         c->rcv.irs = hdr.seq;
 445                         c->rcv.nxt = c->rcv.irs + 1;
 446                         set_state(c, SYN_RECEIVED);
 447
 448                         hdr.dst = c->dst;
 449                         hdr.src = c->src;
 450                         hdr.ack = c->rcv.irs + 1;
 451                         hdr.seq = c->snd.iss;
 452                         hdr.ctl = SYN | ACK;
 453                         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 454                         utcp->send(utcp, &hdr, sizeof hdr);
 455                 } else {
 456                         // No, we don't want your packets, send a RST back
 457                         len = 1;
 458                         goto reset;
 459                 }
 460
 461                 return 0;
 462         }
 463
 464         debug("%p state %s\n", c->utcp, strstate[c->state]);
 465
 466         // In case this is for a CLOSED connection, ignore the packet.
 467         // TODO: make it so incoming packets can never match a CLOSED connection.
 468
 469         if(c->state == CLOSED)
 470                 return 0;
 471
 472         // It is for an existing connection.
 473
 474         // 1. Drop invalid packets.
 475
 476         // 1a. Drop packets that should not happen in our current state.
 477
 478         switch(c->state) {
 479         case SYN_SENT:
 480         case SYN_RECEIVED:
 481         case ESTABLISHED:
 482         case FIN_WAIT_1:
 483         case FIN_WAIT_2:
 484         case CLOSE_WAIT:
 485         case CLOSING:
 486         case LAST_ACK:
 487         case TIME_WAIT:
 488                 break;
 489         default:
 490                 abort();
 491         }
 492
 493         // 1b. Drop packets with a sequence number not in our receive window.
 494
 495         bool acceptable;
 496
 497         if(c->state == SYN_SENT)
 498                 acceptable = true;
 499
 500         // TODO: handle packets overlapping c->rcv.nxt.
 501 #if 0
 502         // Only use this when accepting out-of-order packets.
 503         else if(len == 0)
 504                 if(c->rcv.wnd == 0)
 505                         acceptable = hdr.seq == c->rcv.nxt;
 506                 else
 507                         acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0);
 508         else
 509                 if(c->rcv.wnd == 0)
 510                         // We don't accept data when the receive window is zero.
 511                         acceptable = false;
 512                 else
 513                         // Both start and end of packet must be within the receive window
 514                         acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0)
 515                                 || (seqdiff(hdr.seq + len + 1, c->rcv.nxt) >= 0 && seqdiff(hdr.seq + len - 1, c->rcv.nxt + c->rcv.wnd) < 0);
 516 #else
 517         if(c->state != SYN_SENT)
 518                 acceptable = hdr.seq == c->rcv.nxt;
 519 #endif
 520
 521         if(!acceptable) {
 522                 debug("Packet not acceptable, %u  <= %u + %zu < %u\n", c->rcv.nxt, hdr.seq, len, c->rcv.nxt + c->rcv.wnd);
 523                 // Ignore unacceptable RST packets.
 524                 if(hdr.ctl & RST)
 525                         return 0;
 526                 // Otherwise, send an ACK back in the hope things improve.
 527                 goto ack;
 528         }
 529
 530         c->snd.wnd = hdr.wnd; // TODO: move below
 531
 532         // 1c. Drop packets with an invalid ACK.
 533         // ackno should not roll back, and it should also not be bigger than snd.nxt.
 534
 535         if(hdr.ctl & ACK && (seqdiff(hdr.ack, c->snd.nxt) > 0 || seqdiff(hdr.ack, c->snd.una) < 0)) {
 536                 debug("Packet ack seqno out of range, %u %u %u\n", hdr.ack, c->snd.una, c->snd.nxt);
 537                 // Ignore unacceptable RST packets.
 538                 if(hdr.ctl & RST)
 539                         return 0;
 540                 goto reset;
 541         }
 542
 543         // 2. Handle RST packets
 544
 545         if(hdr.ctl & RST) {
 546                 switch(c->state) {
 547                 case SYN_SENT:
 548                         if(!(hdr.ctl & ACK))
 549                                 return 0;
 550                         // The peer has refused our connection.
 551                         set_state(c, CLOSED);
 552                         errno = ECONNREFUSED;
 553                         if(c->recv)
 554                                 c->recv(c, NULL, 0);
 555                         return 0;
 556                 case SYN_RECEIVED:
 557                         if(hdr.ctl & ACK)
 558                                 return 0;
 559                         // We haven't told the application about this connection yet. Silently delete.
 560                         free_connection(c);
 561                         return 0;
 562                 case ESTABLISHED:
 563                 case FIN_WAIT_1:
 564                 case FIN_WAIT_2:
 565                 case CLOSE_WAIT:
 566                         if(hdr.ctl & ACK)
 567                                 return 0;
 568                         // The peer has aborted our connection.
 569                         set_state(c, CLOSED);
 570                         errno = ECONNRESET;
 571                         if(c->recv)
 572                                 c->recv(c, NULL, 0);
 573                         return 0;
 574                 case CLOSING:
 575                 case LAST_ACK:
 576                 case TIME_WAIT:
 577                         if(hdr.ctl & ACK)
 578                                 return 0;
 579                         // As far as the application is concerned, the connection has already been closed.
 580                         // If it has called utcp_close() already, we can immediately free this connection.
 581                         if(c->reapable) {
 582                                 free_connection(c);
 583                                 return 0;
 584                         }
 585                         // Otherwise, immediately move to the CLOSED state.
 586                         set_state(c, CLOSED);
 587                         return 0;
 588                 default:
 589                         abort();
 590                 }
 591         }
 592
 593         // 3. Advance snd.una
 594
 595         uint32_t advanced = seqdiff(hdr.ack, c->snd.una);
 596         c->snd.una = hdr.ack;
 597
 598         if(advanced) {
 599                 debug("%p advanced %u\n", utcp, advanced);
 600                 // Make room in the send buffer.
 601                 // TODO: try to avoid memmoving too much. Circular buffer?
 602                 uint32_t left = seqdiff(c->snd.nxt, hdr.ack);
 603                 if(left)
 604                         memmove(c->sndbuf, c->sndbuf + advanced, left);
 605                 c->dupack = 0;
 606                 c->snd.cwnd += utcp->mtu;
 607                 if(c->snd.cwnd > c->maxsndbufsize)
 608                         c->snd.cwnd = c->maxsndbufsize;
 609                 debug("%p increasing cwnd to %u\n", utcp, c->snd.cwnd);
 610
 611                 // Check if we have sent a FIN that is now ACKed.
 612                 switch(c->state) {
 613                 case FIN_WAIT_1:
 614                         if(c->snd.una == c->snd.last)
 615                                 set_state(c, FIN_WAIT_2);
 616                         break;
 617                 case CLOSING:
 618                         if(c->snd.una == c->snd.last) {
 619                                 gettimeofday(&c->conn_timeout, NULL);
 620                                 c->conn_timeout.tv_sec += 60;
 621                                 set_state(c, TIME_WAIT);
 622                         }
 623                         break;
 624                 default:
 625                         break;
 626                 }
 627         } else {
 628                 if(!len) {
 629                         c->dupack++;
 630                         if(c->dupack >= 3) {
 631                                 debug("Triplicate ACK\n");
 632                                 abort();
 633                         }
 634                 }
 635         }
 636
 637         // 4. Update timers
 638
 639         if(advanced) {
 640                 timerclear(&c->conn_timeout); // It should be set anew in utcp_timeout() if c->snd.una != c->snd.nxt.
 641                 if(c->snd.una == c->snd.nxt)
 642                         timerclear(&c->rtrx_timeout);
 643         }
 644
 645         // 5. Process SYN stuff
 646
 647         if(hdr.ctl & SYN) {
 648                 switch(c->state) {
 649                 case SYN_SENT:
 650                         // This is a SYNACK. It should always have ACKed the SYN.
 651                         if(!advanced)
 652                                 goto reset;
 653                         c->rcv.irs = hdr.seq;
 654                         c->rcv.nxt = hdr.seq;
 655                         set_state(c, ESTABLISHED);
 656                         // TODO: notify application of this somehow.
 657                         break;
 658                 case SYN_RECEIVED:
 659                 case ESTABLISHED:
 660                 case FIN_WAIT_1:
 661                 case FIN_WAIT_2:
 662                 case CLOSE_WAIT:
 663                 case CLOSING:
 664                 case LAST_ACK:
 665                 case TIME_WAIT:
 666                         // Ehm, no. We should never receive a second SYN.
 667                         goto reset;
 668                 default:
 669                         abort();
 670                 }
 671
 672                 // SYN counts as one sequence number
 673                 c->rcv.nxt++;
 674         }
 675
 676         // 6. Process new data
 677
 678         if(c->state == SYN_RECEIVED) {
 679                 // This is the ACK after the SYNACK. It should always have ACKed the SYNACK.
 680                 if(!advanced)
 681                         goto reset;
 682
 683                 // Are we still LISTENing?
 684                 if(utcp->accept)
 685                         utcp->accept(c, c->src);
 686
 687                 if(c->state != ESTABLISHED) {
 688                         set_state(c, CLOSED);
 689                         c->reapable = true;
 690                         goto reset;
 691                 }
 692         }
 693
 694         if(len) {
 695                 switch(c->state) {
 696                 case SYN_SENT:
 697                 case SYN_RECEIVED:
 698                         // This should never happen.
 699                         abort();
 700                 case ESTABLISHED:
 701                 case FIN_WAIT_1:
 702                 case FIN_WAIT_2:
 703                         break;
 704                 case CLOSE_WAIT:
 705                 case CLOSING:
 706                 case LAST_ACK:
 707                 case TIME_WAIT:
 708                         // Ehm no, We should never receive more data after a FIN.
 709                         goto reset;
 710                 default:
 711                         abort();
 712                 }
 713
 714                 int rxd;
 715
 716                 if(c->recv) {
 717                         rxd = c->recv(c, data, len);
 718                         if(rxd < 0)
 719                                 rxd = 0;
 720                         else if(rxd > len)
 721                                 rxd = len; // Bad application, bad!
 722                 } else {
 723                         rxd = len;
 724                 }
 725
 726                 c->rcv.nxt += len;
 727         }
 728
 729         // 7. Process FIN stuff
 730
 731         if(hdr.ctl & FIN) {
 732                 switch(c->state) {
 733                 case SYN_SENT:
 734                 case SYN_RECEIVED:
 735                         // This should never happen.
 736                         abort();
 737                 case ESTABLISHED:
 738                         set_state(c, CLOSE_WAIT);
 739                         break;
 740                 case FIN_WAIT_1:
 741                         set_state(c, CLOSING);
 742                         break;
 743                 case FIN_WAIT_2:
 744                         gettimeofday(&c->conn_timeout, NULL);
 745                         c->conn_timeout.tv_sec += 60;
 746                         set_state(c, TIME_WAIT);
 747                         break;
 748                 case CLOSE_WAIT:
 749                 case CLOSING:
 750                 case LAST_ACK:
 751                 case TIME_WAIT:
 752                         // Ehm, no. We should never receive a second FIN.
 753                         goto reset;
 754                 default:
 755                         abort();
 756                 }
 757
 758                 // FIN counts as one sequence number
 759                 c->rcv.nxt++;
 760
 761                 // Inform the application that the peer closed the connection.
 762                 if(c->recv) {
 763                         errno = 0;
 764                         c->recv(c, NULL, 0);
 765                 }
 766         }
 767
 768         if(!len && !advanced)
 769                 return 0;
 770
 771         if(!len && !(hdr.ctl & SYN) && !(hdr.ctl & FIN))
 772                 return 0;
 773
 774 ack:
 775         ack(c, true);
 776         return 0;
 777
 778 reset:
 779         swap_ports(&hdr);
 780         hdr.wnd = 0;
 781         if(hdr.ctl & ACK) {
 782                 hdr.seq = hdr.ack;
 783                 hdr.ctl = RST;
 784         } else {
 785                 hdr.ack = hdr.seq + len;
 786                 hdr.seq = 0;
 787                 hdr.ctl = RST | ACK;
 788         }
 789         print_packet(utcp, "send", &hdr, sizeof hdr);
 790         utcp->send(utcp, &hdr, sizeof hdr);
 791         return 0;
 792
 793 }
 794
 795 int utcp_shutdown(struct utcp_connection *c, int dir) {
 796         debug("%p shutdown %d\n", c->utcp, dir);
 797         if(!c) {
 798                 errno = EFAULT;
 799                 return -1;
 800         }
 801
 802         if(c->reapable) {
 803                 debug("Error: shutdown() called on closed connection %p\n", c);
 804                 errno = EBADF;
 805                 return -1;
 806         }
 807
 808         // TODO: handle dir
 809
 810         switch(c->state) {
 811         case CLOSED:
 812                 return 0;
 813         case LISTEN:
 814         case SYN_SENT:
 815                 set_state(c, CLOSED);
 816                 return 0;
 817
 818         case SYN_RECEIVED:
 819         case ESTABLISHED:
 820                 set_state(c, FIN_WAIT_1);
 821                 break;
 822         case FIN_WAIT_1:
 823         case FIN_WAIT_2:
 824                 return 0;
 825         case CLOSE_WAIT:
 826                 set_state(c, CLOSING);
 827                 break;
 828
 829         case CLOSING:
 830         case LAST_ACK:
 831         case TIME_WAIT:
 832                 return 0;
 833         }
 834
 835         c->snd.last++;
 836
 837         ack(c, false);
 838         return 0;
 839 }
 840
 841 int utcp_close(struct utcp_connection *c) {
 842         if(utcp_shutdown(c, SHUT_RDWR))
 843                 return -1;
 844         c->reapable = true;
 845         return 0;
 846 }
 847
 848 int utcp_abort(struct utcp_connection *c) {
 849         if(!c) {
 850                 errno = EFAULT;
 851                 return -1;
 852         }
 853
 854         if(c->reapable) {
 855                 debug("Error: abort() called on closed connection %p\n", c);
 856                 errno = EBADF;
 857                 return -1;
 858         }
 859
 860         c->reapable = true;
 861
 862         switch(c->state) {
 863         case CLOSED:
 864                 return 0;
 865         case LISTEN:
 866         case SYN_SENT:
 867         case CLOSING:
 868         case LAST_ACK:
 869         case TIME_WAIT:
 870                 set_state(c, CLOSED);
 871                 return 0;
 872
 873         case SYN_RECEIVED:
 874         case ESTABLISHED:
 875         case FIN_WAIT_1:
 876         case FIN_WAIT_2:
 877         case CLOSE_WAIT:
 878                 set_state(c, CLOSED);
 879                 break;
 880         }
 881
 882         // Send RST
 883
 884         struct hdr hdr;
 885
 886         hdr.src = c->src;
 887         hdr.dst = c->dst;
 888         hdr.seq = c->snd.nxt;
 889         hdr.ack = 0;
 890         hdr.wnd = 0;
 891         hdr.ctl = RST;
 892
 893         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 894         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 895         return 0;
 896 }
 897
 898 static void retransmit(struct utcp_connection *c) {
 899         if(c->state == CLOSED || c->snd.nxt == c->snd.una)
 900                 return;
 901
 902         struct utcp *utcp = c->utcp;
 903
 904         struct {
 905                 struct hdr hdr;
 906                 char data[c->utcp->mtu];
 907         } pkt;
 908
 909         pkt.hdr.src = c->src;
 910         pkt.hdr.dst = c->dst;
 911
 912         switch(c->state) {
 913                 case LISTEN:
 914                         // TODO: this should not happen
 915                         break;
 916
 917                 case SYN_SENT:
 918                         pkt.hdr.seq = c->snd.iss;
 919                         pkt.hdr.ack = 0;
 920                         pkt.hdr.wnd = c->rcv.wnd;
 921                         pkt.hdr.ctl = SYN;
 922                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr);
 923                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 924                         break;
 925
 926                 case SYN_RECEIVED:
 927                         pkt.hdr.seq = c->snd.nxt;
 928                         pkt.hdr.ack = c->rcv.nxt;
 929                         pkt.hdr.ctl = SYN | ACK;
 930                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr);
 931                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 932                         break;
 933
 934                 case ESTABLISHED:
 935                 case FIN_WAIT_1:
 936                         pkt.hdr.seq = c->snd.una;
 937                         pkt.hdr.ack = c->rcv.nxt;
 938                         pkt.hdr.ctl = ACK;
 939                         uint32_t len = seqdiff(c->snd.nxt, c->snd.una);
 940                         if(c->state == FIN_WAIT_1)
 941                                 len--;
 942                         if(len > utcp->mtu)
 943                                 len = utcp->mtu;
 944                         else {
 945                                 if(c->state == FIN_WAIT_1)
 946                                         pkt.hdr.ctl |= FIN;
 947                         }
 948                         memcpy(pkt.data, c->sndbuf, len);
 949                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr + len);
 950                         utcp->send(utcp, &pkt, sizeof pkt.hdr + len);
 951                         break;
 952
 953                 default:
 954                         // TODO: implement
 955                         abort();
 956         }
 957 }
 958
 959 /* Handle timeouts.
 960  * One call to this function will loop through all connections,
 961  * checking if something needs to be resent or not.
 962  * The return value is the time to the next timeout in milliseconds,
 963  * or maybe a negative value if the timeout is infinite.
 964  */
 965 int utcp_timeout(struct utcp *utcp) {
 966         struct timeval now;
 967         gettimeofday(&now, NULL);
 968         struct timeval next = {now.tv_sec + 3600, now.tv_usec};
 969
 970         for(int i = 0; i < utcp->nconnections; i++) {
 971                 struct utcp_connection *c = utcp->connections[i];
 972                 if(!c)
 973                         continue;
 974
 975                 if(c->state == CLOSED) {
 976                         if(c->reapable) {
 977                                 debug("Reaping %p\n", c);
 978                                 free_connection(c);
 979                                 i--;
 980                         }
 981                         continue;
 982                 }
 983
 984                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &now, <)) {
 985                         errno = ETIMEDOUT;
 986                         c->state = CLOSED;
 987                         if(c->recv)
 988                                 c->recv(c, NULL, 0);
 989                         continue;
 990                 }
 991
 992                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &now, <)) {
 993                         retransmit(c);
 994                 }
 995
 996                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <))
 997                         next = c->conn_timeout;
 998
 999                 if(c->snd.nxt != c->snd.una) {
1000                         c->rtrx_timeout = now;
1001                         c->rtrx_timeout.tv_sec++;
1002                 } else {
1003                         timerclear(&c->rtrx_timeout);
1004                 }
1005
1006                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <))
1007                         next = c->rtrx_timeout;
1008         }
1009
1010         struct timeval diff;
1011         timersub(&next, &now, &diff);
1012         if(diff.tv_sec < 0)
1013                 return 0;
1014         return diff.tv_sec * 1000 + diff.tv_usec / 1000;
1015 }
1016
1017 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
1018         struct utcp *utcp = calloc(1, sizeof *utcp);
1019         if(!utcp)
1020                 return NULL;
1021
1022         if(!send) {
1023                 errno = EFAULT;
1024                 return NULL;
1025         }
1026
1027         utcp->accept = accept;
1028         utcp->pre_accept = pre_accept;
1029         utcp->send = send;
1030         utcp->priv = priv;
1031         utcp->mtu = 1000;
1032         utcp->timeout = 60;
1033
1034         return utcp;
1035 }
1036
1037 void utcp_exit(struct utcp *utcp) {
1038         if(!utcp)
1039                 return;
1040         for(int i = 0; i < utcp->nconnections; i++)
1041                 free_connection(utcp->connections[i]);
1042         free(utcp);
1043 }
1044
1045 uint16_t utcp_get_mtu(struct utcp *utcp) {
1046         return utcp->mtu;
1047 }
1048
1049 void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
1050         // TODO: handle overhead of the header
1051         utcp->mtu = mtu;
1052 }
1053
1054 int utcp_get_user_timeout(struct utcp *u) {
1055         return u->timeout;
1056 }
1057
1058 void utcp_set_user_timeout(struct utcp *u, int timeout) {
1059         u->timeout = timeout;
1060 }
1061
1062 size_t utcp_get_sndbuf(struct utcp_connection *c) {
1063         return c->maxsndbufsize;
1064 }
1065
1066 void utcp_set_sndbuf(struct utcp_connection *c, size_t size) {
1067         c->maxsndbufsize = size;
1068         if(c->maxsndbufsize != size)
1069                 c->maxsndbufsize = -1;
1070 }
1071
1072 bool utcp_get_nodelay(struct utcp_connection *c) {
1073         return c->nodelay;
1074 }
1075
1076 void utcp_set_nodelay(struct utcp_connection *c, bool nodelay) {
1077         c->nodelay = nodelay;
1078 }
1079
1080 bool utcp_get_keepalive(struct utcp_connection *c) {
1081         return c->keepalive;
1082 }
1083
1084 void utcp_set_keepalive(struct utcp_connection *c, bool keepalive) {
1085         c->keepalive = keepalive;
1086 }
1087
1088 size_t utcp_get_outq(struct utcp_connection *c) {
1089         return seqdiff(c->snd.nxt, c->snd.una);
1090 }