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 #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->utcp = utcp;
 185
 186         // Add it to the sorted list of connections
 187
 188         utcp->connections[utcp->nconnections++] = c;
 189         qsort(utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 190
 191         return c;
 192 }
 193
 194 struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
 195         struct utcp_connection *c = allocate_connection(utcp, 0, dst);
 196         if(!c)
 197                 return NULL;
 198
 199         c->recv = recv;
 200
 201         struct hdr hdr;
 202
 203         hdr.src = c->src;
 204         hdr.dst = c->dst;
 205         hdr.seq = c->snd.iss;
 206         hdr.ack = 0;
 207         hdr.ctl = SYN;
 208         hdr.wnd = c->rcv.wnd;
 209
 210         set_state(c, SYN_SENT);
 211
 212         print_packet(utcp, "send", &hdr, sizeof hdr);
 213         utcp->send(utcp, &hdr, sizeof hdr);
 214
 215         gettimeofday(&c->conn_timeout, NULL);
 216         c->conn_timeout.tv_sec += utcp->timeout;
 217
 218         return c;
 219 }
 220
 221 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 222         if(c->reapable || c->state != SYN_RECEIVED) {
 223                 debug("Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
 224                 return;
 225         }
 226
 227         debug("%p accepted, %p %p\n", c, recv, priv);
 228         c->recv = recv;
 229         c->priv = priv;
 230         set_state(c, ESTABLISHED);
 231 }
 232
 233 ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 234         if(c->reapable) {
 235                 debug("Error: send() called on closed connection %p\n", c);
 236                 errno = EBADF;
 237                 return -1;
 238         }
 239
 240         switch(c->state) {
 241         case CLOSED:
 242         case LISTEN:
 243         case SYN_SENT:
 244         case SYN_RECEIVED:
 245                 debug("Error: send() called on unconnected connection %p\n", c);
 246                 errno = ENOTCONN;
 247                 return -1;
 248         case ESTABLISHED:
 249         case CLOSE_WAIT:
 250                 break;
 251         case FIN_WAIT_1:
 252         case FIN_WAIT_2:
 253         case CLOSING:
 254         case LAST_ACK:
 255         case TIME_WAIT:
 256                 debug("Error: send() called on closing connection %p\n", c);
 257                 errno = EPIPE;
 258                 return -1;
 259         }
 260
 261         // Add data to send buffer
 262
 263         if(!len)
 264                 return 0;
 265
 266         if(!data) {
 267                 errno = EFAULT;
 268                 return -1;
 269         }
 270
 271         uint32_t bufused = seqdiff(c->snd.nxt, c->snd.una);
 272
 273         /* Check our send buffer.
 274          * - If it's big enough, just put the data in there.
 275          * - If not, decide whether to enlarge if possible.
 276          * - Cap len so it doesn't overflow our buffer.
 277          */
 278
 279         if(len > c->sndbufsize - bufused && c->sndbufsize < c->maxsndbufsize) {
 280                 if(c->sndbufsize > c->maxsndbufsize / 2)
 281                         c->sndbufsize = c->maxsndbufsize;
 282                 else
 283                         c->sndbufsize *= 2;
 284                 c->sndbuf = realloc(c->sndbuf, c->sndbufsize);
 285         }
 286
 287         if(len > c->sndbufsize - bufused)
 288                 len = c->sndbufsize - bufused;
 289
 290         if(!len) {
 291                 errno == EWOULDBLOCK;
 292                 return 0;
 293         }
 294
 295         memcpy(c->sndbuf + bufused, data, len);
 296
 297         // Send segments
 298
 299         struct {
 300                 struct hdr hdr;
 301                 char data[c->utcp->mtu];
 302         } pkt;
 303
 304         pkt.hdr.src = c->src;
 305         pkt.hdr.dst = c->dst;
 306         pkt.hdr.ack = c->rcv.nxt;
 307         pkt.hdr.wnd = c->snd.wnd;
 308         pkt.hdr.ctl = ACK;
 309
 310         uint32_t left = len;
 311
 312         while(left) {
 313                 uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
 314                 pkt.hdr.seq = c->snd.nxt;
 315
 316                 memcpy(pkt.data, data, seglen);
 317
 318                 c->snd.nxt += seglen;
 319                 data += seglen;
 320                 left -= seglen;
 321
 322                 print_packet(c->utcp, "send", &pkt, sizeof pkt.hdr + seglen);
 323                 c->utcp->send(c->utcp, &pkt, sizeof pkt.hdr + seglen);
 324         }
 325
 326         fprintf(stderr, "len=%zu\n", len);
 327         return len;
 328 }
 329
 330 static void swap_ports(struct hdr *hdr) {
 331         uint16_t tmp = hdr->src;
 332         hdr->src = hdr->dst;
 333         hdr->dst = tmp;
 334 }
 335
 336 int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 337         if(!utcp) {
 338                 errno = EFAULT;
 339                 return -1;
 340         }
 341
 342         if(!len)
 343                 return 0;
 344
 345         if(!data) {
 346                 errno = EFAULT;
 347                 return -1;
 348         }
 349
 350         print_packet(utcp, "recv", data, len);
 351
 352         // Drop packets smaller than the header
 353
 354         struct hdr hdr;
 355         if(len < sizeof hdr) {
 356                 errno = EBADMSG;
 357                 return -1;
 358         }
 359
 360         // Make a copy from the potentially unaligned data to a struct hdr
 361
 362         memcpy(&hdr, data, sizeof hdr);
 363         data += sizeof hdr;
 364         len -= sizeof hdr;
 365
 366         // Drop packets with an unknown CTL flag
 367
 368         if(hdr.ctl & ~(SYN | ACK | RST | FIN)) {
 369                 errno = EBADMSG;
 370                 return -1;
 371         }
 372
 373         // Try to match the packet to an existing connection
 374
 375         struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
 376
 377         // Is it for a new connection?
 378
 379         if(!c) {
 380                 // Ignore RST packets
 381
 382                 if(hdr.ctl & RST)
 383                         return 0;
 384
 385                 // Is it a SYN packet and are we LISTENing?
 386
 387                 if(hdr.ctl & SYN && !(hdr.ctl & ACK) && utcp->accept) {
 388                         // If we don't want to accept it, send a RST back
 389                         if((utcp->pre_accept && !utcp->pre_accept(utcp, hdr.dst))) {
 390                                 len = 1;
 391                                 goto reset;
 392                         }
 393
 394                         // Try to allocate memory, otherwise send a RST back
 395                         c = allocate_connection(utcp, hdr.dst, hdr.src);
 396                         if(!c) {
 397                                 len = 1;
 398                                 goto reset;
 399                         }
 400
 401                         // Return SYN+ACK, go to SYN_RECEIVED state
 402                         c->snd.wnd = hdr.wnd;
 403                         c->rcv.irs = hdr.seq;
 404                         c->rcv.nxt = c->rcv.irs + 1;
 405                         set_state(c, SYN_RECEIVED);
 406
 407                         hdr.dst = c->dst;
 408                         hdr.src = c->src;
 409                         hdr.ack = c->rcv.irs + 1;
 410                         hdr.seq = c->snd.iss;
 411                         hdr.ctl = SYN | ACK;
 412                         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 413                         utcp->send(utcp, &hdr, sizeof hdr);
 414                 } else {
 415                         // No, we don't want your packets, send a RST back
 416                         len = 1;
 417                         goto reset;
 418                 }
 419
 420                 return 0;
 421         }
 422
 423         debug("%p state %s\n", c->utcp, strstate[c->state]);
 424
 425         // In case this is for a CLOSED connection, ignore the packet.
 426         // TODO: make it so incoming packets can never match a CLOSED connection.
 427
 428         if(c->state == CLOSED)
 429                 return 0;
 430
 431         // It is for an existing connection.
 432
 433         // 1. Drop invalid packets.
 434
 435         // 1a. Drop packets that should not happen in our current state.
 436
 437         switch(c->state) {
 438         case SYN_SENT:
 439         case SYN_RECEIVED:
 440         case ESTABLISHED:
 441         case FIN_WAIT_1:
 442         case FIN_WAIT_2:
 443         case CLOSE_WAIT:
 444         case CLOSING:
 445         case LAST_ACK:
 446         case TIME_WAIT:
 447                 break;
 448         default:
 449                 abort();
 450         }
 451
 452         // 1b. Drop packets with a sequence number not in our receive window.
 453
 454         bool acceptable;
 455
 456         if(c->state == SYN_SENT)
 457                 acceptable = true;
 458
 459         // TODO: handle packets overlapping c->rcv.nxt.
 460 #if 0
 461         // Only use this when accepting out-of-order packets.
 462         else if(len == 0)
 463                 if(c->rcv.wnd == 0)
 464                         acceptable = hdr.seq == c->rcv.nxt;
 465                 else
 466                         acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0);
 467         else
 468                 if(c->rcv.wnd == 0)
 469                         // We don't accept data when the receive window is zero.
 470                         acceptable = false;
 471                 else
 472                         // Both start and end of packet must be within the receive window
 473                         acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0)
 474                                 || (seqdiff(hdr.seq + len + 1, c->rcv.nxt) >= 0 && seqdiff(hdr.seq + len - 1, c->rcv.nxt + c->rcv.wnd) < 0);
 475 #else
 476         if(c->state != SYN_SENT)
 477                 acceptable = hdr.seq == c->rcv.nxt;
 478 #endif
 479
 480         if(!acceptable) {
 481                 debug("Packet not acceptable, %u  <= %u + %zu < %u\n", c->rcv.nxt, hdr.seq, len, c->rcv.nxt + c->rcv.wnd);
 482                 // Ignore unacceptable RST packets.
 483                 if(hdr.ctl & RST)
 484                         return 0;
 485                 // Otherwise, send an ACK back in the hope things improve.
 486                 goto ack;
 487         }
 488
 489         c->snd.wnd = hdr.wnd; // TODO: move below
 490
 491         // 1c. Drop packets with an invalid ACK.
 492         // ackno should not roll back, and it should also not be bigger than snd.nxt.
 493
 494         if(hdr.ctl & ACK && (seqdiff(hdr.ack, c->snd.nxt) > 0 || seqdiff(hdr.ack, c->snd.una) < 0)) {
 495                 debug("Packet ack seqno out of range, %u %u %u\n", hdr.ack, c->snd.una, c->snd.nxt);
 496                 // Ignore unacceptable RST packets.
 497                 if(hdr.ctl & RST)
 498                         return 0;
 499                 goto reset;
 500         }
 501
 502         // 2. Handle RST packets
 503
 504         if(hdr.ctl & RST) {
 505                 switch(c->state) {
 506                 case SYN_SENT:
 507                         if(!(hdr.ctl & ACK))
 508                                 return 0;
 509                         // The peer has refused our connection.
 510                         set_state(c, CLOSED);
 511                         errno = ECONNREFUSED;
 512                         if(c->recv)
 513                                 c->recv(c, NULL, 0);
 514                         return 0;
 515                 case SYN_RECEIVED:
 516                         if(hdr.ctl & ACK)
 517                                 return 0;
 518                         // We haven't told the application about this connection yet. Silently delete.
 519                         free_connection(c);
 520                         return 0;
 521                 case ESTABLISHED:
 522                 case FIN_WAIT_1:
 523                 case FIN_WAIT_2:
 524                 case CLOSE_WAIT:
 525                         if(hdr.ctl & ACK)
 526                                 return 0;
 527                         // The peer has aborted our connection.
 528                         set_state(c, CLOSED);
 529                         errno = ECONNRESET;
 530                         if(c->recv)
 531                                 c->recv(c, NULL, 0);
 532                         return 0;
 533                 case CLOSING:
 534                 case LAST_ACK:
 535                 case TIME_WAIT:
 536                         if(hdr.ctl & ACK)
 537                                 return 0;
 538                         // As far as the application is concerned, the connection has already been closed.
 539                         // If it has called utcp_close() already, we can immediately free this connection.
 540                         if(c->reapable) {
 541                                 free_connection(c);
 542                                 return 0;
 543                         }
 544                         // Otherwise, immediately move to the CLOSED state.
 545                         set_state(c, CLOSED);
 546                         return 0;
 547                 default:
 548                         abort();
 549                 }
 550         }
 551
 552         // 3. Advance snd.una
 553
 554         uint32_t advanced = seqdiff(hdr.ack, c->snd.una);
 555         c->snd.una = hdr.ack;
 556
 557         if(advanced) {
 558                 debug("%p advanced %u\n", utcp, advanced);
 559                 // Make room in the send buffer.
 560                 // TODO: try to avoid memmoving too much. Circular buffer?
 561                 uint32_t left = seqdiff(c->snd.nxt, hdr.ack);
 562                 if(left)
 563                         memmove(c->sndbuf, c->sndbuf + advanced, left);
 564         }
 565
 566         // 4. Update timers
 567
 568         if(advanced) {
 569                 timerclear(&c->conn_timeout); // It should be set anew in utcp_timeout() if c->snd.una != c->snd.nxt.
 570                 if(c->snd.una == c->snd.nxt)
 571                         timerclear(&c->rtrx_timeout);
 572         }
 573
 574         // 5. Process SYN stuff
 575
 576         if(hdr.ctl & SYN) {
 577                 switch(c->state) {
 578                 case SYN_SENT:
 579                         // This is a SYNACK. It should always have ACKed the SYN.
 580                         if(!advanced)
 581                                 goto reset;
 582                         c->rcv.irs = hdr.seq;
 583                         c->rcv.nxt = hdr.seq;
 584                         set_state(c, ESTABLISHED);
 585                         // TODO: notify application of this somehow.
 586                         break;
 587                 case SYN_RECEIVED:
 588                 case ESTABLISHED:
 589                 case FIN_WAIT_1:
 590                 case FIN_WAIT_2:
 591                 case CLOSE_WAIT:
 592                 case CLOSING:
 593                 case LAST_ACK:
 594                 case TIME_WAIT:
 595                         // Ehm, no. We should never receive a second SYN.
 596                         goto reset;
 597                 default:
 598                         abort();
 599                 }
 600
 601                 // SYN counts as one sequence number
 602                 c->rcv.nxt++;
 603         }
 604
 605         // 6. Process new data
 606
 607         if(c->state == SYN_RECEIVED) {
 608                 // This is the ACK after the SYNACK. It should always have ACKed the SYNACK.
 609                 if(!advanced)
 610                         goto reset;
 611
 612                 // Are we still LISTENing?
 613                 if(utcp->accept)
 614                         utcp->accept(c, c->src);
 615
 616                 if(c->state != ESTABLISHED) {
 617                         set_state(c, CLOSED);
 618                         c->reapable = true;
 619                         goto reset;
 620                 }
 621         }
 622
 623         if(len) {
 624                 switch(c->state) {
 625                 case SYN_SENT:
 626                 case SYN_RECEIVED:
 627                         // This should never happen.
 628                         abort();
 629                 case ESTABLISHED:
 630                 case FIN_WAIT_1:
 631                 case FIN_WAIT_2:
 632                         break;
 633                 case CLOSE_WAIT:
 634                 case CLOSING:
 635                 case LAST_ACK:
 636                 case TIME_WAIT:
 637                         // Ehm no, We should never receive more data after a FIN.
 638                         goto reset;
 639                 default:
 640                         abort();
 641                 }
 642
 643                 int rxd;
 644
 645                 if(c->recv) {
 646                         rxd = c->recv(c, data, len);
 647                         if(rxd < 0)
 648                                 rxd = 0;
 649                         else if(rxd > len)
 650                                 rxd = len; // Bad application, bad!
 651                 } else {
 652                         rxd = len;
 653                 }
 654
 655                 c->rcv.nxt += len;
 656         }
 657
 658         // 7. Process FIN stuff
 659
 660         if(hdr.ctl & FIN) {
 661                 switch(c->state) {
 662                 case SYN_SENT:
 663                 case SYN_RECEIVED:
 664                         // This should never happen.
 665                         abort();
 666                 case ESTABLISHED:
 667                         set_state(c, CLOSE_WAIT);
 668                         break;
 669                 case FIN_WAIT_1:
 670                         set_state(c, CLOSING);
 671                         break;
 672                 case FIN_WAIT_2:
 673                         set_state(c, TIME_WAIT);
 674                         break;
 675                 case CLOSE_WAIT:
 676                 case CLOSING:
 677                 case LAST_ACK:
 678                 case TIME_WAIT:
 679                         // Ehm, no. We should never receive a second FIN.
 680                         goto reset;
 681                 default:
 682                         abort();
 683                 }
 684
 685                 // FIN counts as one sequence number
 686                 c->rcv.nxt++;
 687
 688                 // Inform the application that the peer closed the connection.
 689                 if(c->recv) {
 690                         errno = 0;
 691                         c->recv(c, NULL, 0);
 692                 }
 693         }
 694
 695         if(!len && !advanced)
 696                 return 0;
 697
 698         if(!len && !(hdr.ctl & SYN) && !(hdr.ctl & FIN))
 699                 return 0;
 700
 701 ack:
 702         hdr.src = c->src;
 703         hdr.dst = c->dst;
 704         hdr.seq = c->snd.nxt;
 705         hdr.ack = c->rcv.nxt;
 706         hdr.ctl = ACK;
 707         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 708         utcp->send(utcp, &hdr, sizeof hdr);
 709         return 0;
 710
 711 reset:
 712         swap_ports(&hdr);
 713         hdr.wnd = 0;
 714         if(hdr.ctl & ACK) {
 715                 hdr.seq = hdr.ack;
 716                 hdr.ctl = RST;
 717         } else {
 718                 hdr.ack = hdr.seq + len;
 719                 hdr.seq = 0;
 720                 hdr.ctl = RST | ACK;
 721         }
 722         print_packet(utcp, "send", &hdr, sizeof hdr);
 723         utcp->send(utcp, &hdr, sizeof hdr);
 724         return 0;
 725
 726 }
 727
 728 int utcp_shutdown(struct utcp_connection *c, int dir) {
 729         debug("%p shutdown %d\n", c->utcp, dir);
 730         if(!c) {
 731                 errno = EFAULT;
 732                 return -1;
 733         }
 734
 735         if(c->reapable) {
 736                 debug("Error: shutdown() called on closed connection %p\n", c);
 737                 errno = EBADF;
 738                 return -1;
 739         }
 740
 741         // TODO: handle dir
 742
 743         switch(c->state) {
 744         case CLOSED:
 745                 return 0;
 746         case LISTEN:
 747         case SYN_SENT:
 748                 set_state(c, CLOSED);
 749                 return 0;
 750
 751         case SYN_RECEIVED:
 752         case ESTABLISHED:
 753                 set_state(c, FIN_WAIT_1);
 754                 break;
 755         case FIN_WAIT_1:
 756         case FIN_WAIT_2:
 757                 return 0;
 758         case CLOSE_WAIT:
 759                 set_state(c, CLOSING);
 760                 break;
 761
 762         case CLOSING:
 763         case LAST_ACK:
 764         case TIME_WAIT:
 765                 return 0;
 766         }
 767
 768         // Send FIN
 769
 770         struct hdr hdr;
 771
 772         hdr.src = c->src;
 773         hdr.dst = c->dst;
 774         hdr.seq = c->snd.nxt;
 775         hdr.ack = c->rcv.nxt;
 776         hdr.wnd = c->snd.wnd;
 777         hdr.ctl = FIN | ACK;
 778
 779         c->snd.nxt += 1;
 780
 781         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 782         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 783         return 0;
 784 }
 785
 786 int utcp_close(struct utcp_connection *c) {
 787         if(utcp_shutdown(c, SHUT_RDWR))
 788                 return -1;
 789         c->reapable = true;
 790         return 0;
 791 }
 792
 793 int utcp_abort(struct utcp_connection *c) {
 794         if(!c) {
 795                 errno = EFAULT;
 796                 return -1;
 797         }
 798
 799         if(c->reapable) {
 800                 debug("Error: abort() called on closed connection %p\n", c);
 801                 errno = EBADF;
 802                 return -1;
 803         }
 804
 805         c->reapable = true;
 806
 807         switch(c->state) {
 808         case CLOSED:
 809                 return 0;
 810         case LISTEN:
 811         case SYN_SENT:
 812         case CLOSING:
 813         case LAST_ACK:
 814         case TIME_WAIT:
 815                 set_state(c, CLOSED);
 816                 return 0;
 817
 818         case SYN_RECEIVED:
 819         case ESTABLISHED:
 820         case FIN_WAIT_1:
 821         case FIN_WAIT_2:
 822         case CLOSE_WAIT:
 823                 set_state(c, CLOSED);
 824                 break;
 825         }
 826
 827         // Send RST
 828
 829         struct hdr hdr;
 830
 831         hdr.src = c->src;
 832         hdr.dst = c->dst;
 833         hdr.seq = c->snd.nxt;
 834         hdr.ack = 0;
 835         hdr.wnd = 0;
 836         hdr.ctl = RST;
 837
 838         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 839         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 840         return 0;
 841 }
 842
 843 static void retransmit(struct utcp_connection *c) {
 844         if(c->state == CLOSED || c->snd.nxt == c->snd.una)
 845                 return;
 846
 847         struct utcp *utcp = c->utcp;
 848
 849         struct {
 850                 struct hdr hdr;
 851                 char data[c->utcp->mtu];
 852         } pkt;
 853
 854         pkt.hdr.src = c->src;
 855         pkt.hdr.dst = c->dst;
 856
 857         switch(c->state) {
 858                 case LISTEN:
 859                         // TODO: this should not happen
 860                         break;
 861
 862                 case SYN_SENT:
 863                         pkt.hdr.seq = c->snd.iss;
 864                         pkt.hdr.ack = 0;
 865                         pkt.hdr.wnd = c->rcv.wnd;
 866                         pkt.hdr.ctl = SYN;
 867                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr);
 868                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 869                         break;
 870
 871                 case SYN_RECEIVED:
 872                         pkt.hdr.seq = c->snd.nxt;
 873                         pkt.hdr.ack = c->rcv.nxt;
 874                         pkt.hdr.ctl = SYN | ACK;
 875                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr);
 876                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 877                         break;
 878
 879                 case ESTABLISHED:
 880                 case FIN_WAIT_1:
 881                         pkt.hdr.seq = c->snd.una;
 882                         pkt.hdr.ack = c->rcv.nxt;
 883                         pkt.hdr.ctl = ACK;
 884                         uint32_t len = seqdiff(c->snd.nxt, c->snd.una);
 885                         if(c->state == FIN_WAIT_1)
 886                                 len--;
 887                         if(len > utcp->mtu)
 888                                 len = utcp->mtu;
 889                         else {
 890                                 if(c->state == FIN_WAIT_1)
 891                                         pkt.hdr.ctl |= FIN;
 892                         }
 893                         memcpy(pkt.data, c->sndbuf, len);
 894                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr + len);
 895                         utcp->send(utcp, &pkt, sizeof pkt.hdr + len);
 896                         break;
 897
 898                 default:
 899                         // TODO: implement
 900                         abort();
 901         }
 902 }
 903
 904 /* Handle timeouts.
 905  * One call to this function will loop through all connections,
 906  * checking if something needs to be resent or not.
 907  * The return value is the time to the next timeout in milliseconds,
 908  * or maybe a negative value if the timeout is infinite.
 909  */
 910 int utcp_timeout(struct utcp *utcp) {
 911         struct timeval now;
 912         gettimeofday(&now, NULL);
 913         struct timeval next = {now.tv_sec + 3600, now.tv_usec};
 914
 915         for(int i = 0; i < utcp->nconnections; i++) {
 916                 struct utcp_connection *c = utcp->connections[i];
 917                 if(!c)
 918                         continue;
 919
 920                 if(c->state == CLOSED) {
 921                         if(c->reapable) {
 922                                 debug("Reaping %p\n", c);
 923                                 free_connection(c);
 924                                 i--;
 925                         }
 926                         continue;
 927                 }
 928
 929                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &now, <)) {
 930                         errno = ETIMEDOUT;
 931                         c->state = CLOSED;
 932                         if(c->recv)
 933                                 c->recv(c, NULL, 0);
 934                         continue;
 935                 }
 936
 937                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &now, <)) {
 938                         retransmit(c);
 939                 }
 940
 941                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <))
 942                         next = c->conn_timeout;
 943
 944                 if(c->snd.nxt != c->snd.una) {
 945                         c->rtrx_timeout = now;
 946                         c->rtrx_timeout.tv_sec++;
 947                 } else {
 948                         timerclear(&c->rtrx_timeout);
 949                 }
 950
 951                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <))
 952                         next = c->rtrx_timeout;
 953         }
 954
 955         struct timeval diff;
 956         timersub(&next, &now, &diff);
 957         if(diff.tv_sec < 0)
 958                 return 0;
 959         return diff.tv_sec * 1000 + diff.tv_usec / 1000;
 960 }
 961
 962 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
 963         struct utcp *utcp = calloc(1, sizeof *utcp);
 964         if(!utcp)
 965                 return NULL;
 966
 967         if(!send) {
 968                 errno = EFAULT;
 969                 return NULL;
 970         }
 971
 972         utcp->accept = accept;
 973         utcp->pre_accept = pre_accept;
 974         utcp->send = send;
 975         utcp->priv = priv;
 976         utcp->mtu = 1000;
 977         utcp->timeout = 60;
 978
 979         return utcp;
 980 }
 981
 982 void utcp_exit(struct utcp *utcp) {
 983         if(!utcp)
 984                 return;
 985         for(int i = 0; i < utcp->nconnections; i++)
 986                 free_connection(utcp->connections[i]);
 987         free(utcp);
 988 }
 989
 990 uint16_t utcp_get_mtu(struct utcp *utcp) {
 991         return utcp->mtu;
 992 }
 993
 994 void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
 995         // TODO: handle overhead of the header
 996         utcp->mtu = mtu;
 997 }
 998
 999 int utcp_get_user_timeout(struct utcp *u) {
1000         return u->timeout;
1001 }
1002
1003 void utcp_set_user_timeout(struct utcp *u, int timeout) {
1004         u->timeout = timeout;
1005 }
1006
1007 size_t utcp_get_sndbuf(struct utcp_connection *c) {
1008         return c->maxsndbufsize;
1009 }
1010
1011 void utcp_set_sndbuf(struct utcp_connection *c, size_t size) {
1012         c->maxsndbufsize = size;
1013         if(c->maxsndbufsize != size)
1014                 c->maxsndbufsize = -1;
1015 }
1016
1017 bool utcp_get_nodelay(struct utcp_connection *c) {
1018         return c->nodelay;
1019 }
1020
1021 void utcp_set_nodelay(struct utcp_connection *c, bool nodelay) {
1022         c->nodelay = nodelay;
1023 }
1024
1025 bool utcp_get_keepalive(struct utcp_connection *c) {
1026         return c->keepalive;
1027 }
1028
1029 void utcp_set_keepalive(struct utcp_connection *c, bool keepalive) {
1030         c->keepalive = keepalive;
1031 }
1032
1033 size_t utcp_get_outq(struct utcp_connection *c) {
1034         return seqdiff(c->snd.nxt, c->snd.una);
1035 }