git.meshlink.io Git - utcp/blob - utcp.c

   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         int timeout;
 126
 127         struct utcp_connection **connections;
 128         int nconnections;
 129         int nallocated;
 130 };
 131
 132 static void set_state(struct utcp_connection *c, enum state state) {
 133         c->state = state;
 134         if(state == ESTABLISHED)
 135                 timerclear(&c->conn_timeout);
 136         fprintf(stderr, "%p new state: %s\n", c->utcp, strstate[state]);
 137 }
 138
 139 static void print_packet(const void *pkt, size_t len) {
 140         struct hdr hdr;
 141         if(len < sizeof hdr) {
 142                 fprintf(stderr, "short packet (%zu bytes)\n", len);
 143                 return;
 144         }
 145
 146         memcpy(&hdr, pkt, sizeof hdr);
 147         fprintf (stderr, "src=%u dst=%u seq=%u ack=%u wnd=%u ctl=", hdr.src, hdr.dst, hdr.seq, hdr.ack, hdr.wnd);
 148         if(hdr.ctl & SYN)
 149                 fprintf(stderr, "SYN");
 150         if(hdr.ctl & RST)
 151                 fprintf(stderr, "RST");
 152         if(hdr.ctl & FIN)
 153                 fprintf(stderr, "FIN");
 154         if(hdr.ctl & ACK)
 155                 fprintf(stderr, "ACK");
 156
 157         if(len > sizeof hdr) {
 158                 fprintf(stderr, " data=");
 159                 for(int i = sizeof hdr; i < len; i++) {
 160                         const char *data = pkt;
 161                         fprintf(stderr, "%c", data[i] >= 32 ? data[i] : '.');
 162                 }
 163         }
 164
 165         fprintf(stderr, "\n");
 166 }
 167
 168 static inline void list_connections(struct utcp *utcp) {
 169         fprintf(stderr, "%p has %d connections:\n", utcp, utcp->nconnections);
 170         for(int i = 0; i < utcp->nconnections; i++)
 171                 fprintf(stderr, "  %u -> %u state %s\n", utcp->connections[i]->src, utcp->connections[i]->dst, strstate[utcp->connections[i]->state]);
 172 }
 173
 174 // Connections are stored in a sorted list.
 175 // This gives O(log(N)) lookup time, O(N log(N)) insertion time and O(N) deletion time.
 176
 177 static int compare(const void *va, const void *vb) {
 178         const struct utcp_connection *a = *(struct utcp_connection **)va;
 179         const struct utcp_connection *b = *(struct utcp_connection **)vb;
 180         if(!a->src || !b->src)
 181                 abort();
 182         int c = (int)a->src - (int)b->src;
 183         if(c)
 184                 return c;
 185         c = (int)a->dst - (int)b->dst;
 186         return c;
 187 }
 188
 189 static struct utcp_connection *find_connection(const struct utcp *utcp, uint16_t src, uint16_t dst) {
 190         if(!utcp->nconnections)
 191                 return NULL;
 192         struct utcp_connection key = {
 193                 .src = src,
 194                 .dst = dst,
 195         }, *keyp = &key;
 196         struct utcp_connection **match = bsearch(&keyp, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 197         return match ? *match : NULL;
 198 }
 199
 200 static void free_connection(struct utcp_connection *c) {
 201         struct utcp *utcp = c->utcp;
 202         struct utcp_connection **cp = bsearch(&c, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 203         if(!cp)
 204                 abort();
 205
 206         int i = cp - utcp->connections;
 207         memmove(cp + i, cp + i + 1, (utcp->nconnections - i - 1) * sizeof *cp);
 208         utcp->nconnections--;
 209
 210         free(c);
 211 }
 212
 213 static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t src, uint16_t dst) {
 214         // Check whether this combination of src and dst is free
 215
 216         if(src) {
 217                 if(find_connection(utcp, src, dst)) {
 218                         errno = EADDRINUSE;
 219                         return NULL;
 220                 }
 221         } else { // If src == 0, generate a random port number with the high bit set
 222                 if(utcp->nconnections >= 32767) {
 223                         errno = ENOMEM;
 224                         return NULL;
 225                 }
 226                 src = rand() | 0x8000;
 227                 while(find_connection(utcp, src, dst))
 228                         src++;
 229         }
 230
 231         // Allocate memory for the new connection
 232
 233         if(utcp->nconnections >= utcp->nallocated) {
 234                 if(!utcp->nallocated)
 235                         utcp->nallocated = 4;
 236                 else
 237                         utcp->nallocated *= 2;
 238                 struct utcp_connection **new_array = realloc(utcp->connections, utcp->nallocated * sizeof *utcp->connections);
 239                 if(!new_array) {
 240                         errno = ENOMEM;
 241                         return NULL;
 242                 }
 243                 utcp->connections = new_array;
 244         }
 245
 246         struct utcp_connection *c = calloc(1, sizeof *c);
 247         if(!c) {
 248                 errno = ENOMEM;
 249                 return NULL;
 250         }
 251
 252         // Fill in the details
 253
 254         c->src = src;
 255         c->dst = dst;
 256         c->snd.iss = rand();
 257         c->snd.una = c->snd.iss;
 258         c->snd.nxt = c->snd.iss + 1;
 259         c->rcv.wnd = utcp->mtu;
 260         c->utcp = utcp;
 261         c->sndbufsize = 65536;
 262         c->sndbuf = malloc(c->sndbufsize);
 263         if(!c->sndbuf)
 264                 c->sndbufsize = 0;
 265
 266         // Add it to the sorted list of connections
 267
 268         utcp->connections[utcp->nconnections++] = c;
 269         qsort(utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 270
 271         return c;
 272 }
 273
 274 struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
 275         struct utcp_connection *c = allocate_connection(utcp, 0, dst);
 276         if(!c)
 277                 return NULL;
 278
 279         c->recv = recv;
 280
 281         struct hdr hdr;
 282
 283         hdr.src = c->src;
 284         hdr.dst = c->dst;
 285         hdr.seq = c->snd.iss;
 286         hdr.ack = 0;
 287         hdr.ctl = SYN;
 288         hdr.wnd = c->rcv.wnd;
 289
 290         set_state(c, SYN_SENT);
 291
 292         utcp->send(utcp, &hdr, sizeof hdr);
 293
 294         gettimeofday(&c->conn_timeout, NULL);
 295         c->conn_timeout.tv_sec += utcp->timeout;
 296
 297         return c;
 298 }
 299
 300 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 301         if(c->reapable || c->state != SYN_RECEIVED) {
 302                 fprintf(stderr, "Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
 303                 return;
 304         }
 305
 306         fprintf(stderr, "%p accepted, %p %p\n", c, recv, priv);
 307         c->recv = recv;
 308         c->priv = priv;
 309         set_state(c, ESTABLISHED);
 310 }
 311
 312 ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 313         if(c->reapable) {
 314                 fprintf(stderr, "Error: send() called on closed connection %p\n", c);
 315                 errno = EBADF;
 316                 return -1;
 317         }
 318
 319         switch(c->state) {
 320         case CLOSED:
 321         case LISTEN:
 322         case SYN_SENT:
 323         case SYN_RECEIVED:
 324                 fprintf(stderr, "Error: send() called on unconnected connection %p\n", c);
 325                 errno = ENOTCONN;
 326                 return -1;
 327         case ESTABLISHED:
 328         case CLOSE_WAIT:
 329                 break;
 330         case FIN_WAIT_1:
 331         case FIN_WAIT_2:
 332         case CLOSING:
 333         case LAST_ACK:
 334         case TIME_WAIT:
 335                 fprintf(stderr, "Error: send() called on closing connection %p\n", c);
 336                 errno = EPIPE;
 337                 return -1;
 338         }
 339
 340         // Add data to send buffer
 341
 342         if(!len)
 343                 return 0;
 344
 345         if(!data) {
 346                 errno = EFAULT;
 347                 return -1;
 348         }
 349
 350         uint32_t bufused = c->snd.nxt - c->snd.una;
 351
 352         if(len > c->sndbufsize - bufused)
 353                 len = c->sndbufsize - bufused;
 354
 355         memcpy(c->sndbuf + (c->snd.nxt - c->snd.una), data, len);
 356
 357         // Send segments
 358
 359         struct {
 360                 struct hdr hdr;
 361                 char data[c->utcp->mtu];
 362         } pkt;
 363
 364         pkt.hdr.src = c->src;
 365         pkt.hdr.dst = c->dst;
 366         pkt.hdr.ack = c->rcv.nxt;
 367         pkt.hdr.wnd = c->snd.wnd;
 368         pkt.hdr.ctl = ACK;
 369
 370         uint32_t left = len;
 371
 372         while(left) {
 373                 uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
 374                 pkt.hdr.seq = c->snd.nxt;
 375
 376                 memcpy(pkt.data, data, seglen);
 377
 378                 c->snd.nxt += seglen;
 379                 data += seglen;
 380                 left -= seglen;
 381
 382                 c->utcp->send(c->utcp, &pkt, sizeof pkt.hdr + seglen);
 383         }
 384
 385         fprintf(stderr, "len=%zu\n", len);
 386         return len;
 387 }
 388
 389 static void swap_ports(struct hdr *hdr) {
 390         uint16_t tmp = hdr->src;
 391         hdr->src = hdr->dst;
 392         hdr->dst = tmp;
 393 }
 394
 395 static int32_t seqdiff(uint32_t a, uint32_t b) {
 396         return a - b;
 397 }
 398
 399 int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 400         if(!utcp) {
 401                 errno = EFAULT;
 402                 return -1;
 403         }
 404
 405         if(!len)
 406                 return 0;
 407
 408         if(!data) {
 409                 errno = EFAULT;
 410                 return -1;
 411         }
 412
 413         fprintf(stderr, "%p got: ", utcp);
 414         print_packet(data, len);
 415
 416         struct hdr hdr;
 417         if(len < sizeof hdr) {
 418                 errno = EBADMSG;
 419                 return -1;
 420         }
 421
 422         memcpy(&hdr, data, sizeof hdr);
 423         data += sizeof hdr;
 424         len -= sizeof hdr;
 425
 426         if(hdr.ctl & ~(SYN | ACK | RST | FIN)) {
 427                 errno = EBADMSG;
 428                 return -1;
 429         }
 430
 431         //list_connections(utcp);
 432
 433         struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
 434
 435         // Is it for a new connection?
 436
 437         if(!c) {
 438                 if(hdr.ctl & RST)
 439                         return 0;
 440
 441                 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
 442                         // Return SYN+ACK
 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                         utcp->send(utcp, &hdr, sizeof hdr);
 454                         return 0;
 455                 } else { // CLOSED
 456                         len = 1;
 457                         goto reset;
 458                 }
 459         }
 460
 461         fprintf(stderr, "%p state %s\n", c->utcp, strstate[c->state]);
 462
 463         if(c->state == CLOSED) {
 464                 fprintf(stderr, "Error: packet recv()d on closed connection %p\n", c);
 465                 errno = EBADF;
 466                 return -1;
 467         }
 468
 469         // It is for an existing connection.
 470
 471         if(c->state == SYN_SENT) {
 472                 if(hdr.ctl & ACK) {
 473                         if(seqdiff(hdr.ack, c->snd.iss) <= 0 || seqdiff(hdr.ack, c->snd.nxt) > 0) {
 474                                 fprintf(stderr, "Invalid ACK, %u %u %u\n", hdr.ack, c->snd.iss, c->snd.nxt);
 475                                 goto reset;
 476                         }
 477                 }
 478                 if(hdr.ctl & RST) {
 479                         if(!(hdr.ctl & ACK))
 480                                 return 0;
 481                         set_state(c, CLOSED);
 482                         errno = ECONNREFUSED;
 483                         if(c->recv)
 484                                 c->recv(c, NULL, 0);
 485                         return 0;
 486                 }
 487                 if(hdr.ctl & SYN) {
 488                         c->dst = hdr.src;
 489                         c->rcv.nxt = hdr.seq + 1;
 490                         c->rcv.irs = hdr.seq;
 491                         c->snd.wnd = hdr.wnd;
 492
 493                         if(hdr.ctl & ACK)
 494                                 c->snd.una = hdr.ack;
 495                         if(seqdiff(c->snd.una, c->snd.iss) > 0) {
 496                                 set_state(c, ESTABLISHED);
 497                                 // TODO: signal app?
 498                                 swap_ports(&hdr);
 499                                 hdr.seq = c->snd.nxt;
 500                                 hdr.ack = c->rcv.nxt;
 501                                 hdr.ctl = ACK;
 502                         } else {
 503                                 set_state(c, SYN_RECEIVED);
 504                                 swap_ports(&hdr);
 505                                 hdr.seq = c->snd.iss;
 506                                 hdr.ack = c->rcv.nxt;
 507                                 hdr.ctl = SYN | ACK;
 508                         }
 509                         utcp->send(utcp, &hdr, sizeof hdr);
 510                         // TODO: queue any data?
 511                 }
 512
 513                 return 0;
 514         }
 515
 516         bool acceptable;
 517
 518         if(len == 0)
 519                 if(c->rcv.wnd == 0)
 520                         acceptable = hdr.seq == c->rcv.nxt;
 521                 else
 522                         acceptable = (hdr.seq >= c->rcv.nxt && hdr.seq < c->rcv.nxt + c->rcv.wnd);
 523         else
 524                 if(c->rcv.wnd == 0)
 525                         acceptable = false;
 526                 else
 527                         acceptable = (hdr.seq >= c->rcv.nxt && hdr.seq < c->rcv.nxt + c->rcv.wnd)
 528                                 || (hdr.seq + len - 1 >= c->rcv.nxt && hdr.seq + len - 1 < c->rcv.nxt + c->rcv.wnd);
 529
 530         if(!acceptable) {
 531                 fprintf(stderr, "Packet not acceptable, %u %u %u %zu\n", hdr.seq, c->rcv.nxt, c->rcv.wnd, len);
 532                 if(hdr.ctl & RST)
 533                         return 0;
 534                 goto ack_and_drop;
 535         }
 536
 537         c->snd.wnd = hdr.wnd;
 538
 539         // TODO: check whether segment really starts at rcv.nxt, otherwise trim it.
 540
 541         if(hdr.ctl & RST) {
 542                 switch(c->state) {
 543                 case SYN_RECEIVED:
 544                         // TODO: delete connection?
 545                         break;
 546                 case ESTABLISHED:
 547                 case FIN_WAIT_1:
 548                 case FIN_WAIT_2:
 549                 case CLOSE_WAIT:
 550                         set_state(c, CLOSED);
 551                         errno = ECONNRESET;
 552                         if(c->recv)
 553                                 c->recv(c, NULL, 0);
 554                         break;
 555                 case CLOSING:
 556                 case LAST_ACK:
 557                 case TIME_WAIT:
 558                         // TODO: delete connection?
 559                         break;
 560                 default:
 561                         // TODO: wtf?
 562                         return 0;
 563                 }
 564                 set_state(c, CLOSED);
 565                 return 0;
 566         }
 567
 568         if(hdr.ctl & SYN) {
 569                 switch(c->state) {
 570                 case SYN_RECEIVED:
 571                 case ESTABLISHED:
 572                 case FIN_WAIT_1:
 573                 case FIN_WAIT_2:
 574                 case CLOSE_WAIT:
 575                 case CLOSING:
 576                 case LAST_ACK:
 577                 case TIME_WAIT:
 578                         set_state(c, CLOSED);
 579                         errno = ECONNRESET;
 580                         if(c->recv)
 581                                 c->recv(c, NULL, 0);
 582                         goto reset;
 583                         break;
 584                 default:
 585                         // TODO: wtf?
 586                         return 0;
 587                 }
 588         }
 589
 590         if(!(hdr.ctl & ACK))
 591                 return 0;
 592
 593         switch(c->state) {
 594         case SYN_RECEIVED:
 595                 if(seqdiff(hdr.ack, c->snd.una) >= 0 && seqdiff(hdr.ack, c->snd.nxt) <= 0)
 596                         c->utcp->accept(c, hdr.dst);
 597
 598                 if(c->state != ESTABLISHED)
 599                         goto reset;
 600
 601                 c->snd.una = hdr.ack;
 602                 break;
 603         case ESTABLISHED:
 604         case CLOSE_WAIT:
 605                 if(seqdiff(hdr.ack, c->snd.una) < 0)
 606                         return 0;
 607                 if(seqdiff(hdr.ack, c->snd.nxt) > 0)
 608                         goto ack_and_drop;
 609                 if(seqdiff(hdr.ack, c->snd.una) > 0 && seqdiff(hdr.ack, c->snd.nxt) <= 0) {
 610                         c->snd.una = hdr.ack;
 611                         if(seqdiff(c->snd.wl1, hdr.seq) < 0 || (c->snd.wl1 == hdr.seq && seqdiff(c->snd.wl2, hdr.ack) <= 0)) {
 612                                 c->snd.wnd = hdr.wnd;
 613                                 c->snd.wl1 = hdr.seq;
 614                                 c->snd.wl2 = hdr.ack;
 615                         }
 616                 }
 617                 break;
 618         case FIN_WAIT_1:
 619                 if(hdr.ack == c->snd.nxt)
 620                         set_state(c, FIN_WAIT_2);
 621                 break;
 622         case FIN_WAIT_2:
 623                 // TODO: If nothing left to send, close.
 624                 break;
 625         case CLOSING:
 626                 if(hdr.ack == c->snd.nxt) {
 627                         set_state(c, TIME_WAIT);
 628                 }
 629                 break;
 630         case LAST_ACK:
 631                 if(hdr.ack == c->snd.nxt) {
 632                         set_state(c, CLOSED);
 633                 }
 634                 return 0;
 635         case TIME_WAIT:
 636                 // TODO: retransmission of remote FIN, ACK and restart 2 MSL timeout
 637                 break;
 638         default:
 639                 goto reset;
 640         }
 641
 642         // Process data
 643
 644         switch(c->state) {
 645         case ESTABLISHED:
 646         case FIN_WAIT_1:
 647         case FIN_WAIT_2:
 648                 // TODO: process the data, see page 74
 649                 break;
 650         case CLOSE_WAIT:
 651         case CLOSING:
 652         case LAST_ACK:
 653         case TIME_WAIT:
 654                 break;
 655         default:
 656                 abort();
 657         }
 658
 659         if(hdr.ctl & FIN) {
 660                 switch(c->state) {
 661                 case CLOSED:
 662                 case LISTEN:
 663                 case SYN_SENT:
 664                         return 0;
 665                 case SYN_RECEIVED:
 666                 case ESTABLISHED:
 667                         set_state(c, CLOSE_WAIT);
 668                         c->rcv.nxt++;
 669                         goto ack_and_drop;
 670                 case FIN_WAIT_1:
 671                         set_state(c, CLOSING);
 672                         c->rcv.nxt++;
 673                         goto ack_and_drop;
 674                 case FIN_WAIT_2:
 675                         set_state(c, TIME_WAIT);
 676                         c->rcv.nxt++;
 677                         goto ack_and_drop;
 678                 case CLOSE_WAIT:
 679                 case CLOSING:
 680                 case LAST_ACK:
 681                 case TIME_WAIT:
 682                         break;
 683                 default:
 684                         abort();
 685                 }
 686         }
 687
 688         // Process the data
 689
 690         if(len && c->recv) {
 691                 c->recv(c, data, len);
 692                 c->rcv.nxt += len;
 693                 goto ack_and_drop;
 694         }
 695
 696         return 0;
 697
 698 reset:
 699         swap_ports(&hdr);
 700         hdr.wnd = 0;
 701         if(hdr.ctl & ACK) {
 702                 hdr.seq = hdr.ack;
 703                 hdr.ctl = RST;
 704         } else {
 705                 hdr.ack = hdr.seq + len;
 706                 hdr.seq = 0;
 707                 hdr.ctl = RST | ACK;
 708         }
 709         utcp->send(utcp, &hdr, sizeof hdr);
 710         return 0;
 711
 712 ack_and_drop:
 713         swap_ports(&hdr);
 714         hdr.seq = c->snd.nxt;
 715         hdr.ack = c->rcv.nxt;
 716         hdr.ctl = ACK;
 717         utcp->send(utcp, &hdr, sizeof hdr);
 718         if(c->state == CLOSE_WAIT || c->state == TIME_WAIT) {
 719                 errno = 0;
 720                 if(c->recv)
 721                         c->recv(c, NULL, 0);
 722         }
 723         return 0;
 724 }
 725
 726 int utcp_shutdown(struct utcp_connection *c, int dir) {
 727         if(!c) {
 728                 errno = EFAULT;
 729                 return -1;
 730         }
 731
 732         if(c->reapable) {
 733                 fprintf(stderr, "Error: shutdown() called on closed connection %p\n", c);
 734                 errno = EBADF;
 735                 return -1;
 736         }
 737
 738         // TODO: handle dir
 739
 740         switch(c->state) {
 741         case CLOSED:
 742                 return 0;
 743         case LISTEN:
 744         case SYN_SENT:
 745                 set_state(c, CLOSED);
 746                 return 0;
 747
 748         case SYN_RECEIVED:
 749         case ESTABLISHED:
 750                 set_state(c, FIN_WAIT_1);
 751                 break;
 752         case FIN_WAIT_1:
 753         case FIN_WAIT_2:
 754                 return 0;
 755         case CLOSE_WAIT:
 756                 set_state(c, LAST_ACK);
 757                 break;
 758
 759         case CLOSING:
 760         case LAST_ACK:
 761         case TIME_WAIT:
 762                 return 0;
 763         }
 764
 765         // Send FIN
 766
 767         struct hdr hdr;
 768
 769         hdr.src = c->src;
 770         hdr.dst = c->dst;
 771         hdr.seq = c->snd.nxt;
 772         hdr.ack = c->rcv.nxt;
 773         hdr.wnd = c->snd.wnd;
 774         hdr.ctl = FIN | ACK;
 775
 776         c->snd.nxt += 1;
 777
 778         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 779         return 0;
 780 }
 781
 782 int utcp_close(struct utcp_connection *c) {
 783         if(utcp_shutdown(c, SHUT_RDWR))
 784                 return -1;
 785         c->reapable = true;
 786         return 0;
 787 }
 788
 789 int utcp_abort(struct utcp_connection *c) {
 790         if(!c) {
 791                 errno = EFAULT;
 792                 return -1;
 793         }
 794
 795         if(c->reapable) {
 796                 fprintf(stderr, "Error: abort() called on closed connection %p\n", c);
 797                 errno = EBADF;
 798                 return -1;
 799         }
 800
 801         c->reapable = true;
 802
 803         switch(c->state) {
 804         case CLOSED:
 805                 return 0;
 806         case LISTEN:
 807         case SYN_SENT:
 808         case CLOSING:
 809         case LAST_ACK:
 810         case TIME_WAIT:
 811                 set_state(c, CLOSED);
 812                 return 0;
 813
 814         case SYN_RECEIVED:
 815         case ESTABLISHED:
 816         case FIN_WAIT_1:
 817         case FIN_WAIT_2:
 818         case CLOSE_WAIT:
 819                 set_state(c, CLOSED);
 820                 break;
 821         }
 822
 823         // Send RST
 824
 825         struct hdr hdr;
 826
 827         hdr.src = c->src;
 828         hdr.dst = c->dst;
 829         hdr.seq = c->snd.nxt;
 830         hdr.ack = 0;
 831         hdr.wnd = 0;
 832         hdr.ctl = RST;
 833
 834         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 835         return 0;
 836 }
 837
 838 static void retransmit(struct utcp_connection *c) {
 839         if(c->state == CLOSED || c->snd.nxt == c->snd.una)
 840                 return;
 841
 842         struct utcp *utcp = c->utcp;
 843
 844         struct {
 845                 struct hdr hdr;
 846                 char data[c->utcp->mtu];
 847         } pkt;
 848
 849         pkt.hdr.src = c->src;
 850         pkt.hdr.dst = c->dst;
 851
 852         switch(c->state) {
 853                 case LISTEN:
 854                         // TODO: this should not happen
 855                         break;
 856
 857                 case SYN_SENT:
 858                         pkt.hdr.seq = c->snd.iss;
 859                         pkt.hdr.ack = 0;
 860                         pkt.hdr.wnd = c->rcv.wnd;
 861                         pkt.hdr.ctl = SYN;
 862                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 863                         break;
 864
 865                 case SYN_RECEIVED:
 866                         pkt.hdr.seq = c->snd.nxt;
 867                         pkt.hdr.ack = c->rcv.nxt;
 868                         pkt.hdr.ctl = SYN | ACK;
 869                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 870                         break;
 871
 872                 case ESTABLISHED:
 873                         pkt.hdr.seq = c->snd.una;
 874                         pkt.hdr.ack = c->rcv.nxt;
 875                         pkt.hdr.ctl = ACK;
 876                         uint32_t len = seqdiff(c->snd.nxt, c->snd.una);
 877                         if(len > utcp->mtu)
 878                                 len = utcp->mtu;
 879                         memcpy(pkt.data, c->sndbuf, len);
 880                         utcp->send(utcp, &pkt, sizeof pkt.hdr + len);
 881                         break;
 882
 883                 default:
 884                         // TODO: implement
 885                         abort();
 886         }
 887 }
 888
 889 /* Handle timeouts.
 890  * One call to this function will loop through all connections,
 891  * checking if something needs to be resent or not.
 892  * The return value is the time to the next timeout in milliseconds,
 893  * or maybe a negative value if the timeout is infinite.
 894  */
 895 int utcp_timeout(struct utcp *utcp) {
 896         struct timeval now;
 897         gettimeofday(&now, NULL);
 898         struct timeval next = {now.tv_sec + 3600, now.tv_usec};
 899
 900         for(int i = 0; i < utcp->nconnections; i++) {
 901                 struct utcp_connection *c = utcp->connections[i];
 902                 if(!c)
 903                         continue;
 904
 905                 if(c->state == CLOSED) {
 906                         if(c->reapable) {
 907                                 fprintf(stderr, "Reaping %p\n", c);
 908                                 free_connection(c);
 909                                 i--;
 910                         }
 911                         continue;
 912                 }
 913
 914                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &now, <)) {
 915                         errno = ETIMEDOUT;
 916                         c->state = CLOSED;
 917                         if(c->recv)
 918                                 c->recv(c, NULL, 0);
 919                         continue;
 920                 }
 921
 922                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &now, <)) {
 923                         retransmit(c);
 924                 }
 925
 926                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <))
 927                         next = c->conn_timeout;
 928
 929                 if(c->snd.nxt != c->snd.una) {
 930                         c->rtrx_timeout = now;
 931                         c->rtrx_timeout.tv_sec++;
 932                 } else {
 933                         timerclear(&c->rtrx_timeout);
 934                 }
 935
 936                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <))
 937                         next = c->rtrx_timeout;
 938         }
 939
 940         struct timeval diff;
 941         timersub(&next, &now, &diff);
 942         if(diff.tv_sec < 0)
 943                 return 0;
 944         return diff.tv_sec * 1000 + diff.tv_usec / 1000;
 945 }
 946
 947 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
 948         struct utcp *utcp = calloc(1, sizeof *utcp);
 949         if(!utcp)
 950                 return NULL;
 951
 952         if(!send) {
 953                 errno = EFAULT;
 954                 return NULL;
 955         }
 956
 957         utcp->accept = accept;
 958         utcp->pre_accept = pre_accept;
 959         utcp->send = send;
 960         utcp->priv = priv;
 961         utcp->mtu = 1000;
 962         utcp->timeout = 60;
 963
 964         return utcp;
 965 }
 966
 967 void utcp_exit(struct utcp *utcp) {
 968         if(!utcp)
 969                 return;
 970         for(int i = 0; i < utcp->nconnections; i++)
 971                 free_connection(utcp->connections[i]);
 972         free(utcp);
 973 }
 974
 975 int utcp_set_connection_timeout(struct utcp *u, int timeout) {
 976         int prev = u->timeout;
 977         u->timeout = timeout;
 978         return prev;
 979 }