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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 #define UTCP_INTERNAL
  33 #include "utcp.h"
  34
  35 #define PREP(l) char pkt[(l) + sizeof struct hdr]; struct hdr *hdr = &pkt;
  36
  37 #define SYN 1
  38 #define ACK 2
  39 #define FIN 4
  40 #define RST 8
  41
  42 struct hdr {
  43         uint16_t src; // Source port
  44         uint16_t dst; // Destination port
  45         uint32_t seq; // Sequence number
  46         uint32_t ack; // Acknowledgement number
  47         uint32_t wnd; // Window size
  48         uint16_t ctl; // Flags (SYN, ACK, FIN, RST)
  49         uint16_t aux; // other stuff
  50 };
  51
  52 enum state {
  53         CLOSED,
  54         LISTEN,
  55         SYN_SENT,
  56         SYN_RECEIVED,
  57         ESTABLISHED,
  58         FIN_WAIT_1,
  59         FIN_WAIT_2,
  60         CLOSE_WAIT,
  61         CLOSING,
  62         LAST_ACK,
  63         TIME_WAIT
  64 };
  65
  66 const char *strstate[] = {
  67         "CLOSED",
  68         "LISTEN",
  69         "SYN_SENT",
  70         "SYN_RECEIVED",
  71         "ESTABLISHED",
  72         "FIN_WAIT_1",
  73         "FIN_WAIT_2",
  74         "CLOSE_WAIT",
  75         "CLOSING",
  76         "LAST_ACK",
  77         "TIME_WAIT"
  78 };
  79
  80 struct utcp_connection {
  81         void *priv;
  82         struct utcp *utcp;
  83         bool reapable;
  84
  85         uint16_t src;
  86         uint16_t dst;
  87         enum state state;
  88
  89         // The following two structures form the TCB
  90
  91         struct {
  92                 uint32_t una;
  93                 uint32_t nxt;
  94                 uint32_t wnd;
  95                 uint32_t up;
  96                 uint32_t wl1;
  97                 uint32_t wl2;
  98                 uint32_t iss;
  99         } snd;
 100
 101         struct {
 102                 uint32_t nxt;
 103                 uint32_t wnd;
 104                 uint32_t up;
 105                 uint32_t irs;
 106         } rcv;
 107
 108         utcp_recv_t recv;
 109
 110         struct timeval conn_timeout;
 111         struct timeval rtrx_timeout;
 112
 113         char *sndbuf;
 114         uint32_t sndbufsize;
 115 };
 116
 117 struct utcp {
 118         void *priv;
 119
 120         utcp_accept_t accept;
 121         utcp_pre_accept_t pre_accept;
 122         utcp_send_t send;
 123
 124         uint16_t mtu;
 125
 126         struct utcp_connection **connections;
 127         int nconnections;
 128         int nallocated;
 129         int gap;
 130 };
 131
 132 static void set_state(struct utcp_connection *c, enum state state) {
 133         c->state = state;
 134         fprintf(stderr, "%p new state: %s\n", c->utcp, strstate[state]);
 135 }
 136
 137 static void print_packet(void *pkt, size_t len) {
 138         struct hdr hdr;
 139         if(len < sizeof hdr) {
 140                 fprintf(stderr, "short packet (%zu bytes)\n", len);
 141                 return;
 142         }
 143
 144         memcpy(&hdr, pkt, sizeof hdr);
 145         fprintf (stderr, "src=%u dst=%u seq=%u ack=%u wnd=%u ctl=", hdr.src, hdr.dst, hdr.seq, hdr.ack, hdr.wnd);
 146         if(hdr.ctl & SYN)
 147                 fprintf(stderr, "SYN");
 148         if(hdr.ctl & RST)
 149                 fprintf(stderr, "RST");
 150         if(hdr.ctl & FIN)
 151                 fprintf(stderr, "FIN");
 152         if(hdr.ctl & ACK)
 153                 fprintf(stderr, "ACK");
 154
 155         if(len > sizeof hdr) {
 156                 fprintf(stderr, " data=");
 157                 for(int i = sizeof hdr; i < len; i++) {
 158                         char *data = pkt;
 159                         fprintf(stderr, "%c", data[i] >= 32 ? data[i] : '.');
 160                 }
 161         }
 162
 163         fprintf(stderr, "\n");
 164 }
 165
 166 static void list_connections(struct utcp *utcp) {
 167         fprintf(stderr, "%p has %d connections:\n", utcp, utcp->nconnections);
 168         for(int i = 0; i < utcp->nconnections; i++)
 169                 fprintf(stderr, "  %u -> %u state %s\n", utcp->connections[i]->src, utcp->connections[i]->dst, strstate[utcp->connections[i]->state]);
 170 }
 171
 172 // Connections are stored in a sorted list.
 173 // This gives O(log(N)) lookup time, O(N log(N)) insertion time and O(N) deletion time.
 174
 175 static int compare(const void *va, const void *vb) {
 176         const struct utcp_connection *a = *(struct utcp_connection **)va;
 177         const struct utcp_connection *b = *(struct utcp_connection **)vb;
 178         if(!a->src || !b->src)
 179                 abort();
 180         int c = (int)a->src - (int)b->src;
 181         if(c)
 182                 return c;
 183         c = (int)a->dst - (int)b->dst;
 184         return c;
 185 }
 186
 187 static struct utcp_connection *find_connection(const struct utcp *utcp, uint16_t src, uint16_t dst) {
 188         if(!utcp->nconnections)
 189                 return NULL;
 190         struct utcp_connection key = {
 191                 .src = src,
 192                 .dst = dst,
 193         }, *keyp = &key;
 194         struct utcp_connection **match = bsearch(&keyp, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 195         return match ? *match : NULL;
 196 }
 197
 198 static void free_connection(struct utcp_connection *c) {
 199         struct utcp *utcp = c->utcp;
 200         struct utcp_connection **cp = bsearch(&c, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 201         if(!cp)
 202                 abort();
 203
 204         int i = cp - utcp->connections;
 205         memmove(cp + i, cp + i + 1, (utcp->nconnections - i - 1) * sizeof *cp);
 206         utcp->nconnections--;
 207
 208         free(c);
 209 }
 210
 211 static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t src, uint16_t dst) {
 212         // Check whether this combination of src and dst is free
 213
 214         if(src) {
 215                 if(find_connection(utcp, src, dst)) {
 216                         errno = EADDRINUSE;
 217                         return NULL;
 218                 }
 219         } else { // If src == 0, generate a random port number with the high bit set
 220                 if(utcp->nconnections >= 32767) {
 221                         errno = ENOMEM;
 222                         return NULL;
 223                 }
 224                 src = rand() | 0x8000;
 225                 while(find_connection(utcp, src, dst))
 226                         src++;
 227         }
 228
 229         // Allocate memory for the new connection
 230
 231         if(utcp->nconnections >= utcp->nallocated) {
 232                 if(!utcp->nallocated)
 233                         utcp->nallocated = 4;
 234                 else
 235                         utcp->nallocated *= 2;
 236                 struct utcp_connection **new_array = realloc(utcp->connections, utcp->nallocated * sizeof *utcp->connections);
 237                 if(!new_array) {
 238                         errno = ENOMEM;
 239                         return NULL;
 240                 }
 241                 utcp->connections = new_array;
 242         }
 243
 244         struct utcp_connection *c = calloc(1, sizeof *c);
 245         if(!c) {
 246                 errno = ENOMEM;
 247                 return NULL;
 248         }
 249
 250         // Fill in the details
 251
 252         c->src = src;
 253         c->dst = dst;
 254         c->snd.iss = rand();
 255         c->snd.una = c->snd.iss;
 256         c->snd.nxt = c->snd.iss + 1;
 257         c->rcv.wnd = utcp->mtu;
 258         c->utcp = utcp;
 259
 260         // Add it to the sorted list of connections
 261
 262         utcp->connections[utcp->nconnections++] = c;
 263         qsort(utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 264
 265         return c;
 266 }
 267
 268 struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
 269         struct utcp_connection *c = allocate_connection(utcp, 0, dst);
 270         if(!c)
 271                 return NULL;
 272
 273         c->recv = recv;
 274
 275         struct hdr hdr;
 276
 277         hdr.src = c->src;
 278         hdr.dst = c->dst;
 279         hdr.seq = c->snd.iss;
 280         hdr.ack = 0;
 281         hdr.ctl = SYN;
 282         hdr.wnd = c->rcv.wnd;
 283
 284         set_state(c, SYN_SENT);
 285
 286         utcp->send(utcp, &hdr, sizeof hdr);
 287
 288         // Set timeout?
 289
 290         return c;
 291 }
 292
 293 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 294         if(c->reapable || c->state != SYN_RECEIVED) {
 295                 fprintf(stderr, "Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
 296                 return;
 297         }
 298
 299         fprintf(stderr, "%p accepted, %p %p\n", c, recv, priv);
 300         c->recv = recv;
 301         c->priv = priv;
 302         set_state(c, ESTABLISHED);
 303 }
 304
 305 int utcp_send(struct utcp_connection *c, void *data, size_t len) {
 306         if(c->reapable) {
 307                 fprintf(stderr, "Error: send() called on closed connection %p\n", c);
 308                 errno = EBADF;
 309                 return -1;
 310         }
 311
 312         switch(c->state) {
 313         case CLOSED:
 314         case LISTEN:
 315         case SYN_SENT:
 316         case SYN_RECEIVED:
 317                 fprintf(stderr, "Error: send() called on unconnected connection %p\n", c);
 318                 errno = ENOTCONN;
 319                 return -1;
 320         case ESTABLISHED:
 321         case CLOSE_WAIT:
 322                 break;
 323         case FIN_WAIT_1:
 324         case FIN_WAIT_2:
 325         case CLOSING:
 326         case LAST_ACK:
 327         case TIME_WAIT:
 328                 fprintf(stderr, "Error: send() called on closing connection %p\n", c);
 329                 errno = EPIPE;
 330                 return -1;
 331         }
 332
 333         if(!len)
 334                 return 0;
 335
 336         if(!data) {
 337                 errno = EFAULT;
 338                 return -1;
 339         }
 340
 341
 342         struct {
 343                 struct hdr hdr;
 344                 char data[len];
 345         } pkt;
 346
 347         pkt.hdr.src = c->src;
 348         pkt.hdr.dst = c->dst;
 349         pkt.hdr.seq = c->snd.nxt;
 350         pkt.hdr.ack = c->rcv.nxt;
 351         pkt.hdr.wnd = c->snd.wnd;
 352         pkt.hdr.ctl = ACK;
 353
 354         memcpy(pkt.data, data, len);
 355
 356         c->snd.nxt += len;
 357
 358         c->utcp->send(c->utcp, &pkt, sizeof pkt.hdr + len);
 359         //
 360         // Can we add it to the send window?
 361
 362         // Do we need to kick some timers?
 363
 364         return 0;
 365 }
 366
 367 static void swap_ports(struct hdr *hdr) {
 368         uint16_t tmp = hdr->src;
 369         hdr->src = hdr->dst;
 370         hdr->dst = tmp;
 371 }
 372
 373 int utcp_recv(struct utcp *utcp, void *data, size_t len) {
 374         if(!utcp) {
 375                 errno = EFAULT;
 376                 return -1;
 377         }
 378
 379         if(!len)
 380                 return 0;
 381
 382         if(!data) {
 383                 errno = EFAULT;
 384                 return -1;
 385         }
 386
 387         fprintf(stderr, "%p got: ", utcp);
 388         print_packet(data, len);
 389
 390         struct hdr hdr;
 391         if(len < sizeof hdr) {
 392                 errno = EBADMSG;
 393                 return -1;
 394         }
 395
 396         memcpy(&hdr, data, sizeof hdr);
 397         data += sizeof hdr;
 398         len -= sizeof hdr;
 399
 400         if(hdr.ctl & ~(SYN | ACK | RST | FIN)) {
 401                 errno = EBADMSG;
 402                 return -1;
 403         }
 404
 405         //list_connections(utcp);
 406
 407         struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
 408
 409         // Is it for a new connection?
 410
 411         if(!c) {
 412                 if(hdr.ctl & RST)
 413                         return 0;
 414
 415                 if(hdr.ctl & SYN && !(hdr.ctl & ACK) && utcp->accept && (!utcp->pre_accept || utcp->pre_accept(utcp, hdr.dst)) && (c = allocate_connection(utcp, hdr.dst, hdr.src))) { // LISTEN
 416                         // Return SYN+ACK
 417                         c->snd.wnd = hdr.wnd;
 418                         c->rcv.irs = hdr.seq;
 419                         c->rcv.nxt = c->rcv.irs + 1;
 420                         set_state(c, SYN_RECEIVED);
 421
 422                         hdr.dst = c->dst;
 423                         hdr.src = c->src;
 424                         hdr.ack = c->rcv.irs + 1;
 425                         hdr.seq = c->snd.iss;
 426                         hdr.ctl = SYN | ACK;
 427                         utcp->send(utcp, &hdr, sizeof hdr);
 428                         return 0;
 429                 } else { // CLOSED
 430                         len = 1;
 431                         goto reset;
 432                 }
 433         }
 434
 435         fprintf(stderr, "%p state %s\n", c->utcp, strstate[c->state]);
 436
 437         if(c->state == CLOSED) {
 438                 fprintf(stderr, "Error: packet recv()d on closed connection %p\n", c);
 439                 errno = EBADF;
 440                 return -1;
 441         }
 442
 443         // It is for an existing connection.
 444
 445         if(c->state == SYN_SENT) {
 446                 if(hdr.ctl & ACK) {
 447                         if(hdr.ack <= c->snd.iss || hdr.ack > c->snd.nxt) {
 448                                 fprintf(stderr, "Invalid ACK, %u %u %u\n", hdr.ack, c->snd.iss, c->snd.nxt);
 449                                 goto reset;
 450                         }
 451                 }
 452                 if(hdr.ctl & RST) {
 453                         if(!(hdr.ctl & ACK))
 454                                 return 0;
 455                         set_state(c, CLOSED);
 456                         errno = ECONNREFUSED;
 457                         c->recv(c, NULL, 0);
 458                         return 0;
 459                 }
 460                 if(hdr.ctl & SYN) {
 461                         c->dst = hdr.src;
 462                         c->rcv.nxt = hdr.seq + 1;
 463                         c->rcv.irs = hdr.seq;
 464                         c->snd.wnd = hdr.wnd;
 465
 466                         if(hdr.ctl & ACK)
 467                                 c->snd.una = hdr.ack;
 468                         if(c->snd.una > c->snd.iss) {
 469                                 set_state(c, ESTABLISHED);
 470                                 // TODO: signal app?
 471                                 swap_ports(&hdr);
 472                                 hdr.seq = c->snd.nxt;
 473                                 hdr.ack = c->rcv.nxt;
 474                                 hdr.ctl = ACK;
 475                         } else {
 476                                 set_state(c, SYN_RECEIVED);
 477                                 swap_ports(&hdr);
 478                                 hdr.seq = c->snd.iss;
 479                                 hdr.ack = c->rcv.nxt;
 480                                 hdr.ctl = SYN | ACK;
 481                         }
 482                         utcp->send(utcp, &hdr, sizeof hdr);
 483                         // TODO: queue any data?
 484                 }
 485
 486                 return 0;
 487         }
 488
 489         bool acceptable;
 490
 491         if(len == 0)
 492                 if(c->rcv.wnd == 0)
 493                         acceptable = hdr.seq == c->rcv.nxt;
 494                 else
 495                         acceptable = (hdr.seq >= c->rcv.nxt && hdr.seq < c->rcv.nxt + c->rcv.wnd);
 496         else
 497                 if(c->rcv.wnd == 0)
 498                         acceptable = false;
 499                 else
 500                         acceptable = (hdr.seq >= c->rcv.nxt && hdr.seq < c->rcv.nxt + c->rcv.wnd)
 501                                 || (hdr.seq + len - 1 >= c->rcv.nxt && hdr.seq + len - 1 < c->rcv.nxt + c->rcv.wnd);
 502
 503         if(!acceptable) {
 504                 fprintf(stderr, "Packet not acceptable, %u %u %u %zu\n", hdr.seq, c->rcv.nxt, c->rcv.wnd, len);
 505                 if(hdr.ctl & RST)
 506                         return 0;
 507                 goto ack_and_drop;
 508         }
 509
 510         c->snd.wnd = hdr.wnd;
 511
 512         // TODO: check whether segment really starts at rcv.nxt, otherwise trim it.
 513
 514         if(hdr.ctl & RST) {
 515                 switch(c->state) {
 516                 case SYN_RECEIVED:
 517                         // TODO: delete connection?
 518                         break;
 519                 case ESTABLISHED:
 520                 case FIN_WAIT_1:
 521                 case FIN_WAIT_2:
 522                 case CLOSE_WAIT:
 523                         set_state(c, CLOSED);
 524                         errno = ECONNRESET;
 525                         c->recv(c, NULL, 0);
 526                         break;
 527                 case CLOSING:
 528                 case LAST_ACK:
 529                 case TIME_WAIT:
 530                         // TODO: delete connection?
 531                         break;
 532                 default:
 533                         // TODO: wtf?
 534                         return 0;
 535                 }
 536                 set_state(c, CLOSED);
 537                 return 0;
 538         }
 539
 540         if(hdr.ctl & SYN) {
 541                 switch(c->state) {
 542                 case SYN_RECEIVED:
 543                 case ESTABLISHED:
 544                 case FIN_WAIT_1:
 545                 case FIN_WAIT_2:
 546                 case CLOSE_WAIT:
 547                 case CLOSING:
 548                 case LAST_ACK:
 549                 case TIME_WAIT:
 550                         set_state(c, CLOSED);
 551                         errno = ECONNRESET;
 552                         c->recv(c, NULL, 0);
 553                         goto reset;
 554                         break;
 555                 default:
 556                         // TODO: wtf?
 557                         return 0;
 558                 }
 559         }
 560
 561         if(!(hdr.ctl & ACK))
 562                 return 0;
 563
 564         switch(c->state) {
 565         case SYN_RECEIVED:
 566                 if(hdr.ack >= c->snd.una && hdr.ack <= c->snd.nxt)
 567                         c->utcp->accept(c, hdr.dst);
 568
 569                 if(c->state != ESTABLISHED)
 570                         goto reset;
 571                 break;
 572         case ESTABLISHED:
 573         case CLOSE_WAIT:
 574                 if(hdr.ack < c->snd.una)
 575                         return 0;
 576                 if(hdr.ack > c->snd.nxt)
 577                         goto ack_and_drop;
 578                 if(hdr.ack > c->snd.una && hdr.ack <= c->snd.nxt) {
 579                         c->snd.una = hdr.ack;
 580                         if(c->snd.wl1 < hdr.seq || (c->snd.wl1 == hdr.seq && c->snd.wl2 <= hdr.ack)) {
 581                                 c->snd.wnd = hdr.wnd;
 582                                 c->snd.wl1 = hdr.seq;
 583                                 c->snd.wl2 = hdr.ack;
 584                         }
 585                 }
 586                 break;
 587         case FIN_WAIT_1:
 588                 if(hdr.ack == c->snd.nxt)
 589                         set_state(c, FIN_WAIT_2);
 590                 break;
 591         case FIN_WAIT_2:
 592                 // TODO: If nothing left to send, close.
 593                 break;
 594         case CLOSING:
 595                 if(hdr.ack == c->snd.nxt) {
 596                         set_state(c, TIME_WAIT);
 597                 }
 598                 break;
 599         case LAST_ACK:
 600                 if(hdr.ack == c->snd.nxt) {
 601                         set_state(c, CLOSED);
 602                 }
 603                 return 0;
 604         case TIME_WAIT:
 605                 // TODO: retransmission of remote FIN, ACK and restart 2 MSL timeout
 606                 break;
 607         default:
 608                 goto reset;
 609         }
 610
 611         // Process data
 612
 613         switch(c->state) {
 614         case ESTABLISHED:
 615         case FIN_WAIT_1:
 616         case FIN_WAIT_2:
 617                 // TODO: process the data, see page 74
 618                 break;
 619         case CLOSE_WAIT:
 620         case CLOSING:
 621         case LAST_ACK:
 622         case TIME_WAIT:
 623                 break;
 624         default:
 625                 abort();
 626         }
 627
 628         if(hdr.ctl & FIN) {
 629                 switch(c->state) {
 630                 case CLOSED:
 631                 case LISTEN:
 632                 case SYN_SENT:
 633                         return 0;
 634                 case SYN_RECEIVED:
 635                 case ESTABLISHED:
 636                         set_state(c, CLOSE_WAIT);
 637                         c->rcv.nxt++;
 638                         goto ack_and_drop;
 639                 case FIN_WAIT_1:
 640                         set_state(c, CLOSING);
 641                         c->rcv.nxt++;
 642                         goto ack_and_drop;
 643                 case FIN_WAIT_2:
 644                         set_state(c, TIME_WAIT);
 645                         c->rcv.nxt++;
 646                         goto ack_and_drop;
 647                 case CLOSE_WAIT:
 648                 case CLOSING:
 649                 case LAST_ACK:
 650                 case TIME_WAIT:
 651                         break;
 652                 default:
 653                         abort();
 654                 }
 655         }
 656
 657         // Process the data
 658
 659         if(len && c->recv) {
 660                 c->recv(c, data, len);
 661                 c->rcv.nxt += len;
 662                 goto ack_and_drop;
 663         }
 664
 665         return 0;
 666
 667 reset:
 668         swap_ports(&hdr);
 669         hdr.wnd = 0;
 670         if(hdr.ctl & ACK) {
 671                 hdr.seq = hdr.ack;
 672                 hdr.ctl = RST;
 673         } else {
 674                 hdr.ack = hdr.seq + len;
 675                 hdr.seq = 0;
 676                 hdr.ctl = RST | ACK;
 677         }
 678         utcp->send(utcp, &hdr, sizeof hdr);
 679         return 0;
 680
 681 ack_and_drop:
 682         swap_ports(&hdr);
 683         hdr.seq = c->snd.nxt;
 684         hdr.ack = c->rcv.nxt;
 685         hdr.ctl = ACK;
 686         utcp->send(utcp, &hdr, sizeof hdr);
 687         if(c->state == CLOSE_WAIT || c->state == TIME_WAIT) {
 688                 errno = 0;
 689                 c->recv(c, NULL, 0);
 690         }
 691         return 0;
 692 }
 693
 694 int utcp_shutdown(struct utcp_connection *c, int dir) {
 695         if(!c) {
 696                 errno = EFAULT;
 697                 return -1;
 698         }
 699
 700         if(c->reapable) {
 701                 fprintf(stderr, "Error: shutdown() called on closed connection %p\n", c);
 702                 errno = EBADF;
 703                 return -1;
 704         }
 705
 706         // TODO: handle dir
 707
 708         switch(c->state) {
 709         case CLOSED:
 710                 return 0;
 711         case LISTEN:
 712         case SYN_SENT:
 713                 set_state(c, CLOSED);
 714                 return 0;
 715
 716         case SYN_RECEIVED:
 717         case ESTABLISHED:
 718                 set_state(c, FIN_WAIT_1);
 719                 break;
 720         case FIN_WAIT_1:
 721         case FIN_WAIT_2:
 722                 return 0;
 723         case CLOSE_WAIT:
 724                 set_state(c, LAST_ACK);
 725                 break;
 726
 727         case CLOSING:
 728         case LAST_ACK:
 729         case TIME_WAIT:
 730                 return 0;
 731         }
 732
 733         // Send FIN
 734
 735         struct hdr hdr;
 736
 737         hdr.src = c->src;
 738         hdr.dst = c->dst;
 739         hdr.seq = c->snd.nxt;
 740         hdr.ack = c->rcv.nxt;
 741         hdr.wnd = c->snd.wnd;
 742         hdr.ctl = FIN | ACK;
 743
 744         c->snd.nxt += 1;
 745
 746         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 747         return 0;
 748 }
 749
 750 int utcp_close(struct utcp_connection *c) {
 751         if(utcp_shutdown(c, SHUT_RDWR))
 752                 return -1;
 753         c->reapable = true;
 754         return 0;
 755 }
 756
 757 int utcp_abort(struct utcp_connection *c) {
 758         if(!c) {
 759                 errno = EFAULT;
 760                 return -1;
 761         }
 762
 763         if(c->reapable) {
 764                 fprintf(stderr, "Error: abort() called on closed connection %p\n", c);
 765                 errno = EBADF;
 766                 return -1;
 767         }
 768
 769         c->reapable = true;
 770
 771         switch(c->state) {
 772         case CLOSED:
 773                 return 0;
 774         case LISTEN:
 775         case SYN_SENT:
 776         case CLOSING:
 777         case LAST_ACK:
 778         case TIME_WAIT:
 779                 set_state(c, CLOSED);
 780                 return 0;
 781
 782         case SYN_RECEIVED:
 783         case ESTABLISHED:
 784         case FIN_WAIT_1:
 785         case FIN_WAIT_2:
 786         case CLOSE_WAIT:
 787                 set_state(c, CLOSED);
 788                 break;
 789         }
 790
 791         // Send RST
 792
 793         struct hdr hdr;
 794
 795         hdr.src = c->src;
 796         hdr.dst = c->dst;
 797         hdr.seq = c->snd.nxt;
 798         hdr.ack = 0;
 799         hdr.wnd = 0;
 800         hdr.ctl = RST;
 801
 802         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 803         return 0;
 804 }
 805
 806 void utcp_timeout(struct utcp *utcp) {
 807         struct timeval now;
 808         gettimeofday(&now, NULL);
 809
 810         for(int i = 0; i < utcp->nconnections; i++) {
 811                 struct utcp_connection *c = utcp->connections[i];
 812                 if(!c)
 813                         continue;
 814
 815                 if(c->reapable) {
 816                         fprintf(stderr, "Reaping %p\n", c);
 817                         free_connection(c);
 818                         continue;
 819                 }
 820
 821                 if(c->state == CLOSED)
 822                         return;
 823
 824                 if(c->conn_timeout.tv_sec && timercmp(&c->conn_timeout, &now, <)) {
 825                         if(!c->reapable) {
 826                                 errno = ETIMEDOUT;
 827                                 c->recv(c, NULL, 0);
 828                         }
 829                         c->state = CLOSED;
 830                         return;
 831                 }
 832
 833                 if(c->rtrx_timeout.tv_sec && timercmp(&c->rtrx_timeout, &now, <)) {
 834                         // TODO: retransmit stuff;
 835                 }
 836         }
 837 }
 838
 839 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
 840         struct utcp *utcp = calloc(1, sizeof *utcp);
 841         if(!utcp)
 842                 return NULL;
 843
 844         utcp->accept = accept;
 845         utcp->pre_accept = pre_accept;
 846         utcp->send = send;
 847         utcp->priv = priv;
 848         utcp->gap = -1;
 849         utcp->mtu = 1000;
 850
 851         return utcp;
 852 }
 853
 854 void utcp_exit(struct utcp *utcp) {
 855         if(!utcp)
 856                 return;
 857         for(int i = 0; i < utcp->nconnections; i++)
 858                 free_connection(utcp->connections[i]);
 859         free(utcp);
 860 }