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   1 /*
   2     utcp.c -- Userspace TCP
   3     Copyright (C) 2014 Guus Sliepen <guus@tinc-vpn.org>
   4
   5     This program is free software; you can redistribute it and/or modify
   6     it under the terms of the GNU General Public License as published by
   7     the Free Software Foundation; either version 2 of the License, or
   8     (at your option) any later version.
   9
  10     This program is distributed in the hope that it will be useful,
  11     but WITHOUT ANY WARRANTY; without even the implied warranty of
  12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13     GNU General Public License for more details.
  14
  15     You should have received a copy of the GNU General Public License along
  16     with this program; if not, write to the Free Software Foundation, Inc.,
  17     51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  18 */
  19
  20 #define _GNU_SOURCE
  21
  22 #include <errno.h>
  23 #include <stdio.h>
  24 #include <stdlib.h>
  25 #include <stdint.h>
  26 #include <stdbool.h>
  27 #include <string.h>
  28 #include <unistd.h>
  29 #include <sys/time.h>
  30 #include <sys/socket.h>
  31
  32 #include "utcp_priv.h"
  33
  34 static void set_state(struct utcp_connection *c, enum state state) {
  35         c->state = state;
  36         if(state == ESTABLISHED)
  37                 timerclear(&c->conn_timeout);
  38         fprintf(stderr, "%p new state: %s\n", c->utcp, strstate[state]);
  39 }
  40
  41 static void print_packet(struct utcp *utcp, const char *dir, const void *pkt, size_t len) {
  42         struct hdr hdr;
  43         if(len < sizeof hdr) {
  44                 fprintf(stderr, "%p %s: short packet (%zu bytes)\n", utcp, dir, len);
  45                 return;
  46         }
  47
  48         memcpy(&hdr, pkt, sizeof hdr);
  49         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);
  50         if(hdr.ctl & SYN)
  51                 fprintf(stderr, "SYN");
  52         if(hdr.ctl & RST)
  53                 fprintf(stderr, "RST");
  54         if(hdr.ctl & FIN)
  55                 fprintf(stderr, "FIN");
  56         if(hdr.ctl & ACK)
  57                 fprintf(stderr, "ACK");
  58
  59         if(len > sizeof hdr) {
  60                 fprintf(stderr, " data=");
  61                 for(int i = sizeof hdr; i < len; i++) {
  62                         const char *data = pkt;
  63                         fprintf(stderr, "%c", data[i] >= 32 ? data[i] : '.');
  64                 }
  65         }
  66
  67         fprintf(stderr, "\n");
  68 }
  69
  70 static inline void list_connections(struct utcp *utcp) {
  71         fprintf(stderr, "%p has %d connections:\n", utcp, utcp->nconnections);
  72         for(int i = 0; i < utcp->nconnections; i++)
  73                 fprintf(stderr, "  %u -> %u state %s\n", utcp->connections[i]->src, utcp->connections[i]->dst, strstate[utcp->connections[i]->state]);
  74 }
  75
  76 // Connections are stored in a sorted list.
  77 // This gives O(log(N)) lookup time, O(N log(N)) insertion time and O(N) deletion time.
  78
  79 static int compare(const void *va, const void *vb) {
  80         const struct utcp_connection *a = *(struct utcp_connection **)va;
  81         const struct utcp_connection *b = *(struct utcp_connection **)vb;
  82         if(!a->src || !b->src)
  83                 abort();
  84         int c = (int)a->src - (int)b->src;
  85         if(c)
  86                 return c;
  87         c = (int)a->dst - (int)b->dst;
  88         return c;
  89 }
  90
  91 static struct utcp_connection *find_connection(const struct utcp *utcp, uint16_t src, uint16_t dst) {
  92         if(!utcp->nconnections)
  93                 return NULL;
  94         struct utcp_connection key = {
  95                 .src = src,
  96                 .dst = dst,
  97         }, *keyp = &key;
  98         struct utcp_connection **match = bsearch(&keyp, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
  99         return match ? *match : NULL;
 100 }
 101
 102 static void free_connection(struct utcp_connection *c) {
 103         struct utcp *utcp = c->utcp;
 104         struct utcp_connection **cp = bsearch(&c, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 105         if(!cp)
 106                 abort();
 107
 108         int i = cp - utcp->connections;
 109         memmove(cp + i, cp + i + 1, (utcp->nconnections - i - 1) * sizeof *cp);
 110         utcp->nconnections--;
 111
 112         free(c);
 113 }
 114
 115 static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t src, uint16_t dst) {
 116         // Check whether this combination of src and dst is free
 117
 118         if(src) {
 119                 if(find_connection(utcp, src, dst)) {
 120                         errno = EADDRINUSE;
 121                         return NULL;
 122                 }
 123         } else { // If src == 0, generate a random port number with the high bit set
 124                 if(utcp->nconnections >= 32767) {
 125                         errno = ENOMEM;
 126                         return NULL;
 127                 }
 128                 src = rand() | 0x8000;
 129                 while(find_connection(utcp, src, dst))
 130                         src++;
 131         }
 132
 133         // Allocate memory for the new connection
 134
 135         if(utcp->nconnections >= utcp->nallocated) {
 136                 if(!utcp->nallocated)
 137                         utcp->nallocated = 4;
 138                 else
 139                         utcp->nallocated *= 2;
 140                 struct utcp_connection **new_array = realloc(utcp->connections, utcp->nallocated * sizeof *utcp->connections);
 141                 if(!new_array) {
 142                         errno = ENOMEM;
 143                         return NULL;
 144                 }
 145                 utcp->connections = new_array;
 146         }
 147
 148         struct utcp_connection *c = calloc(1, sizeof *c);
 149         if(!c) {
 150                 errno = ENOMEM;
 151                 return NULL;
 152         }
 153
 154         // Fill in the details
 155
 156         c->src = src;
 157         c->dst = dst;
 158         c->snd.iss = rand();
 159         c->snd.una = c->snd.iss;
 160         c->snd.nxt = c->snd.iss + 1;
 161         c->rcv.wnd = utcp->mtu;
 162         c->utcp = utcp;
 163         c->sndbufsize = 65536;
 164         c->sndbuf = malloc(c->sndbufsize);
 165         if(!c->sndbuf)
 166                 c->sndbufsize = 0;
 167
 168         // Add it to the sorted list of connections
 169
 170         utcp->connections[utcp->nconnections++] = c;
 171         qsort(utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 172
 173         return c;
 174 }
 175
 176 struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
 177         struct utcp_connection *c = allocate_connection(utcp, 0, dst);
 178         if(!c)
 179                 return NULL;
 180
 181         c->recv = recv;
 182
 183         struct hdr hdr;
 184
 185         hdr.src = c->src;
 186         hdr.dst = c->dst;
 187         hdr.seq = c->snd.iss;
 188         hdr.ack = 0;
 189         hdr.ctl = SYN;
 190         hdr.wnd = c->rcv.wnd;
 191
 192         set_state(c, SYN_SENT);
 193
 194         print_packet(utcp, "send", &hdr, sizeof hdr);
 195         utcp->send(utcp, &hdr, sizeof hdr);
 196
 197         gettimeofday(&c->conn_timeout, NULL);
 198         c->conn_timeout.tv_sec += utcp->timeout;
 199
 200         return c;
 201 }
 202
 203 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 204         if(c->reapable || c->state != SYN_RECEIVED) {
 205                 fprintf(stderr, "Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
 206                 return;
 207         }
 208
 209         fprintf(stderr, "%p accepted, %p %p\n", c, recv, priv);
 210         c->recv = recv;
 211         c->priv = priv;
 212         set_state(c, ESTABLISHED);
 213 }
 214
 215 ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 216         if(c->reapable) {
 217                 fprintf(stderr, "Error: send() called on closed connection %p\n", c);
 218                 errno = EBADF;
 219                 return -1;
 220         }
 221
 222         switch(c->state) {
 223         case CLOSED:
 224         case LISTEN:
 225         case SYN_SENT:
 226         case SYN_RECEIVED:
 227                 fprintf(stderr, "Error: send() called on unconnected connection %p\n", c);
 228                 errno = ENOTCONN;
 229                 return -1;
 230         case ESTABLISHED:
 231         case CLOSE_WAIT:
 232                 break;
 233         case FIN_WAIT_1:
 234         case FIN_WAIT_2:
 235         case CLOSING:
 236         case LAST_ACK:
 237         case TIME_WAIT:
 238                 fprintf(stderr, "Error: send() called on closing connection %p\n", c);
 239                 errno = EPIPE;
 240                 return -1;
 241         }
 242
 243         // Add data to send buffer
 244
 245         if(!len)
 246                 return 0;
 247
 248         if(!data) {
 249                 errno = EFAULT;
 250                 return -1;
 251         }
 252
 253         uint32_t bufused = c->snd.nxt - c->snd.una;
 254
 255         /* Check our send buffer.
 256          * - If it's big enough, just put the data in there.
 257          * - If not, decide whether to enlarge. (TODO, now we just always enlarge)
 258          * - Cap len so it doesn't overflow our buffer.
 259          */
 260
 261         if(len > c->sndbufsize - bufused) {
 262                 c->sndbufsize *= 2;
 263                 c->sndbuf = realloc(c->sndbuf, c->sndbufsize);
 264         }
 265
 266         if(len > c->sndbufsize - bufused)
 267                 len = c->sndbufsize - bufused;
 268
 269         if(!len) {
 270                 errno == EWOULDBLOCK;
 271                 return 0;
 272         }
 273
 274         memcpy(c->sndbuf + bufused, data, len);
 275
 276         // Send segments
 277
 278         struct {
 279                 struct hdr hdr;
 280                 char data[c->utcp->mtu];
 281         } pkt;
 282
 283         pkt.hdr.src = c->src;
 284         pkt.hdr.dst = c->dst;
 285         pkt.hdr.ack = c->rcv.nxt;
 286         pkt.hdr.wnd = c->snd.wnd;
 287         pkt.hdr.ctl = ACK;
 288
 289         uint32_t left = len;
 290
 291         while(left) {
 292                 uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
 293                 pkt.hdr.seq = c->snd.nxt;
 294
 295                 memcpy(pkt.data, data, seglen);
 296
 297                 c->snd.nxt += seglen;
 298                 data += seglen;
 299                 left -= seglen;
 300
 301                 print_packet(c->utcp, "send", &pkt, sizeof pkt.hdr + seglen);
 302                 c->utcp->send(c->utcp, &pkt, sizeof pkt.hdr + seglen);
 303         }
 304
 305         fprintf(stderr, "len=%zu\n", len);
 306         return len;
 307 }
 308
 309 static void swap_ports(struct hdr *hdr) {
 310         uint16_t tmp = hdr->src;
 311         hdr->src = hdr->dst;
 312         hdr->dst = tmp;
 313 }
 314
 315 static int32_t seqdiff(uint32_t a, uint32_t b) {
 316         return a - b;
 317 }
 318
 319 int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 320         if(!utcp) {
 321                 errno = EFAULT;
 322                 return -1;
 323         }
 324
 325         if(!len)
 326                 return 0;
 327
 328         if(!data) {
 329                 errno = EFAULT;
 330                 return -1;
 331         }
 332
 333         print_packet(utcp, "recv", data, len);
 334
 335         // Drop packets smaller than the header
 336
 337         struct hdr hdr;
 338         if(len < sizeof hdr) {
 339                 errno = EBADMSG;
 340                 return -1;
 341         }
 342
 343         // Make a copy from the potentially unaligned data to a struct hdr
 344
 345         memcpy(&hdr, data, sizeof hdr);
 346         data += sizeof hdr;
 347         len -= sizeof hdr;
 348
 349         // Drop packets with an unknown CTL flag
 350
 351         if(hdr.ctl & ~(SYN | ACK | RST | FIN)) {
 352                 errno = EBADMSG;
 353                 return -1;
 354         }
 355
 356         // Try to match the packet to an existing connection
 357
 358         struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
 359
 360         // Is it for a new connection?
 361
 362         if(!c) {
 363                 // Ignore RST packets
 364
 365                 if(hdr.ctl & RST)
 366                         return 0;
 367
 368                 // Is it a SYN packet and are we LISTENing?
 369
 370                 if(hdr.ctl & SYN && !(hdr.ctl & ACK) && utcp->accept) {
 371                         // If we don't want to accept it, send a RST back
 372                         if((utcp->pre_accept && !utcp->pre_accept(utcp, hdr.dst))) {
 373                                 len = 1;
 374                                 goto reset;
 375                         }
 376
 377                         // Try to allocate memory, otherwise send a RST back
 378                         c = allocate_connection(utcp, hdr.dst, hdr.src);
 379                         if(!c) {
 380                                 len = 1;
 381                                 goto reset;
 382                         }
 383
 384                         // Return SYN+ACK, go to SYN_RECEIVED state
 385                         c->snd.wnd = hdr.wnd;
 386                         c->rcv.irs = hdr.seq;
 387                         c->rcv.nxt = c->rcv.irs + 1;
 388                         set_state(c, SYN_RECEIVED);
 389
 390                         hdr.dst = c->dst;
 391                         hdr.src = c->src;
 392                         hdr.ack = c->rcv.irs + 1;
 393                         hdr.seq = c->snd.iss;
 394                         hdr.ctl = SYN | ACK;
 395                         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 396                         utcp->send(utcp, &hdr, sizeof hdr);
 397                 } else {
 398                         // No, we don't want your packets, send a RST back
 399                         len = 1;
 400                         goto reset;
 401                 }
 402
 403                 return 0;
 404         }
 405
 406         fprintf(stderr, "%p state %s\n", c->utcp, strstate[c->state]);
 407
 408         // In case this is for a CLOSED connection, ignore the packet.
 409         // TODO: make it so incoming packets can never match a CLOSED connection.
 410
 411         if(c->state == CLOSED)
 412                 return 0;
 413
 414         // It is for an existing connection.
 415
 416         // 1. Drop invalid packets.
 417
 418         // 1a. Drop packets that should not happen in our current state.
 419
 420         switch(c->state) {
 421         case SYN_SENT:
 422         case SYN_RECEIVED:
 423         case ESTABLISHED:
 424         case FIN_WAIT_1:
 425         case FIN_WAIT_2:
 426         case CLOSE_WAIT:
 427         case CLOSING:
 428         case LAST_ACK:
 429         case TIME_WAIT:
 430                 break;
 431         default:
 432                 abort();
 433         }
 434
 435         // 1b. Drop packets with a sequence number not in our receive window.
 436
 437         bool acceptable;
 438
 439         if(c->state == SYN_SENT)
 440                 acceptable = true;
 441
 442         // TODO: handle packets overlapping c->rcv.nxt.
 443 #if 0
 444         // Only use this when accepting out-of-order packets.
 445         else if(len == 0)
 446                 if(c->rcv.wnd == 0)
 447                         acceptable = hdr.seq == c->rcv.nxt;
 448                 else
 449                         acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0);
 450         else
 451                 if(c->rcv.wnd == 0)
 452                         // We don't accept data when the receive window is zero.
 453                         acceptable = false;
 454                 else
 455                         // Both start and end of packet must be within the receive window
 456                         acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0)
 457                                 || (seqdiff(hdr.seq + len + 1, c->rcv.nxt) >= 0 && seqdiff(hdr.seq + len - 1, c->rcv.nxt + c->rcv.wnd) < 0);
 458 #else
 459         if(c->state != SYN_SENT)
 460                 acceptable = hdr.seq == c->rcv.nxt;
 461 #endif
 462
 463         if(!acceptable) {
 464                 fprintf(stderr, "Packet not acceptable, %u  <= %u + %zu < %u\n", c->rcv.nxt, hdr.seq, len, c->rcv.nxt + c->rcv.wnd);
 465                 // Ignore unacceptable RST packets.
 466                 if(hdr.ctl & RST)
 467                         return 0;
 468                 // Otherwise, send an ACK back in the hope things improve.
 469                 goto ack;
 470         }
 471
 472         c->snd.wnd = hdr.wnd; // TODO: move below
 473
 474         // 1c. Drop packets with an invalid ACK.
 475         // ackno should not roll back, and it should also not be bigger than snd.nxt.
 476
 477         if(hdr.ctl & ACK && (seqdiff(hdr.ack, c->snd.nxt) > 0 || seqdiff(hdr.ack, c->snd.una) < 0)) {
 478                 fprintf(stderr, "Packet ack seqno out of range, %u %u %u\n", hdr.ack, c->snd.una, c->snd.nxt);
 479                 // Ignore unacceptable RST packets.
 480                 if(hdr.ctl & RST)
 481                         return 0;
 482                 goto reset;
 483         }
 484
 485         // 2. Handle RST packets
 486
 487         if(hdr.ctl & RST) {
 488                 switch(c->state) {
 489                 case SYN_SENT:
 490                         if(!(hdr.ctl & ACK))
 491                                 return 0;
 492                         // The peer has refused our connection.
 493                         set_state(c, CLOSED);
 494                         errno = ECONNREFUSED;
 495                         if(c->recv)
 496                                 c->recv(c, NULL, 0);
 497                         return 0;
 498                 case SYN_RECEIVED:
 499                         if(hdr.ctl & ACK)
 500                                 return 0;
 501                         // We haven't told the application about this connection yet. Silently delete.
 502                         free_connection(c);
 503                         return 0;
 504                 case ESTABLISHED:
 505                 case FIN_WAIT_1:
 506                 case FIN_WAIT_2:
 507                 case CLOSE_WAIT:
 508                         if(hdr.ctl & ACK)
 509                                 return 0;
 510                         // The peer has aborted our connection.
 511                         set_state(c, CLOSED);
 512                         errno = ECONNRESET;
 513                         if(c->recv)
 514                                 c->recv(c, NULL, 0);
 515                         return 0;
 516                 case CLOSING:
 517                 case LAST_ACK:
 518                 case TIME_WAIT:
 519                         if(hdr.ctl & ACK)
 520                                 return 0;
 521                         // As far as the application is concerned, the connection has already been closed.
 522                         // If it has called utcp_close() already, we can immediately free this connection.
 523                         if(c->reapable) {
 524                                 free_connection(c);
 525                                 return 0;
 526                         }
 527                         // Otherwise, immediately move to the CLOSED state.
 528                         set_state(c, CLOSED);
 529                         return 0;
 530                 default:
 531                         abort();
 532                 }
 533         }
 534
 535         // 3. Advance snd.una
 536
 537         uint32_t advanced = seqdiff(hdr.ack, c->snd.una);
 538         c->snd.una = hdr.ack;
 539
 540         if(advanced) {
 541                 fprintf(stderr, "%p advanced %u\n", utcp, advanced);
 542                 // Make room in the send buffer.
 543                 // TODO: try to avoid memmoving too much. Circular buffer?
 544                 uint32_t left = seqdiff(c->snd.nxt, hdr.ack);
 545                 if(left)
 546                         memmove(c->sndbuf, c->sndbuf + advanced, left);
 547         }
 548
 549         // 4. Update timers
 550
 551         if(advanced) {
 552                 timerclear(&c->conn_timeout); // It should be set anew in utcp_timeout() if c->snd.una != c->snd.nxt.
 553                 if(c->snd.una == c->snd.nxt)
 554                         timerclear(&c->rtrx_timeout);
 555         }
 556
 557         // 5. Process SYN stuff
 558
 559         if(hdr.ctl & SYN) {
 560                 switch(c->state) {
 561                 case SYN_SENT:
 562                         // This is a SYNACK. It should always have ACKed the SYN.
 563                         if(!advanced)
 564                                 goto reset;
 565                         c->rcv.irs = hdr.seq;
 566                         c->rcv.nxt = hdr.seq;
 567                         set_state(c, ESTABLISHED);
 568                         // TODO: notify application of this somehow.
 569                         break;
 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                         // Ehm, no. We should never receive a second SYN.
 579                         goto reset;
 580                 default:
 581                         abort();
 582                 }
 583
 584                 // SYN counts as one sequence number
 585                 c->rcv.nxt++;
 586         }
 587
 588         // 6. Process new data
 589
 590         if(c->state == SYN_RECEIVED) {
 591                 // This is the ACK after the SYNACK. It should always have ACKed the SYNACK.
 592                 if(!advanced)
 593                         goto reset;
 594
 595                 // Are we still LISTENing?
 596                 if(utcp->accept)
 597                         utcp->accept(c, c->src);
 598
 599                 if(c->state != ESTABLISHED) {
 600                         set_state(c, CLOSED);
 601                         c->reapable = true;
 602                         goto reset;
 603                 }
 604         }
 605
 606         if(len) {
 607                 switch(c->state) {
 608                 case SYN_SENT:
 609                 case SYN_RECEIVED:
 610                         // This should never happen.
 611                         abort();
 612                 case ESTABLISHED:
 613                 case FIN_WAIT_1:
 614                 case FIN_WAIT_2:
 615                         break;
 616                 case CLOSE_WAIT:
 617                 case CLOSING:
 618                 case LAST_ACK:
 619                 case TIME_WAIT:
 620                         // Ehm no, We should never receive more data after a FIN.
 621                         goto reset;
 622                 default:
 623                         abort();
 624                 }
 625
 626                 int rxd;
 627
 628                 if(c->recv) {
 629                         rxd = c->recv(c, data, len);
 630                         if(rxd < 0)
 631                                 rxd = 0;
 632                         else if(rxd > len)
 633                                 rxd = len; // Bad application, bad!
 634                 } else {
 635                         rxd = len;
 636                 }
 637
 638                 c->rcv.nxt += len;
 639         }
 640
 641         // 7. Process FIN stuff
 642
 643         if(hdr.ctl & FIN) {
 644                 switch(c->state) {
 645                 case SYN_SENT:
 646                 case SYN_RECEIVED:
 647                         // This should never happen.
 648                         abort();
 649                 case ESTABLISHED:
 650                         set_state(c, CLOSE_WAIT);
 651                         break;
 652                 case FIN_WAIT_1:
 653                         set_state(c, CLOSING);
 654                         break;
 655                 case FIN_WAIT_2:
 656                         set_state(c, TIME_WAIT);
 657                         break;
 658                 case CLOSE_WAIT:
 659                 case CLOSING:
 660                 case LAST_ACK:
 661                 case TIME_WAIT:
 662                         // Ehm, no. We should never receive a second FIN.
 663                         goto reset;
 664                 default:
 665                         abort();
 666                 }
 667
 668                 // FIN counts as one sequence number
 669                 c->rcv.nxt++;
 670
 671                 // Inform the application that the peer closed the connection.
 672                 if(c->recv) {
 673                         errno = 0;
 674                         c->recv(c, NULL, 0);
 675                 }
 676         }
 677
 678         if(!len && !advanced)
 679                 return 0;
 680
 681         if(!len && !(hdr.ctl & SYN) && !(hdr.ctl & FIN))
 682                 return 0;
 683
 684 ack:
 685         hdr.src = c->src;
 686         hdr.dst = c->dst;
 687         hdr.seq = c->snd.nxt;
 688         hdr.ack = c->rcv.nxt;
 689         hdr.ctl = ACK;
 690         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 691         utcp->send(utcp, &hdr, sizeof hdr);
 692         return 0;
 693
 694 reset:
 695         swap_ports(&hdr);
 696         hdr.wnd = 0;
 697         if(hdr.ctl & ACK) {
 698                 hdr.seq = hdr.ack;
 699                 hdr.ctl = RST;
 700         } else {
 701                 hdr.ack = hdr.seq + len;
 702                 hdr.seq = 0;
 703                 hdr.ctl = RST | ACK;
 704         }
 705         print_packet(utcp, "send", &hdr, sizeof hdr);
 706         utcp->send(utcp, &hdr, sizeof hdr);
 707         return 0;
 708
 709 }
 710
 711 int utcp_shutdown(struct utcp_connection *c, int dir) {
 712         fprintf(stderr, "%p shutdown %d\n", c->utcp, dir);
 713         if(!c) {
 714                 errno = EFAULT;
 715                 return -1;
 716         }
 717
 718         if(c->reapable) {
 719                 fprintf(stderr, "Error: shutdown() called on closed connection %p\n", c);
 720                 errno = EBADF;
 721                 return -1;
 722         }
 723
 724         // TODO: handle dir
 725
 726         switch(c->state) {
 727         case CLOSED:
 728                 return 0;
 729         case LISTEN:
 730         case SYN_SENT:
 731                 set_state(c, CLOSED);
 732                 return 0;
 733
 734         case SYN_RECEIVED:
 735         case ESTABLISHED:
 736                 set_state(c, FIN_WAIT_1);
 737                 break;
 738         case FIN_WAIT_1:
 739         case FIN_WAIT_2:
 740                 return 0;
 741         case CLOSE_WAIT:
 742                 set_state(c, CLOSING);
 743                 break;
 744
 745         case CLOSING:
 746         case LAST_ACK:
 747         case TIME_WAIT:
 748                 return 0;
 749         }
 750
 751         // Send FIN
 752
 753         struct hdr hdr;
 754
 755         hdr.src = c->src;
 756         hdr.dst = c->dst;
 757         hdr.seq = c->snd.nxt;
 758         hdr.ack = c->rcv.nxt;
 759         hdr.wnd = c->snd.wnd;
 760         hdr.ctl = FIN | ACK;
 761
 762         c->snd.nxt += 1;
 763
 764         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 765         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 766         return 0;
 767 }
 768
 769 int utcp_close(struct utcp_connection *c) {
 770         if(utcp_shutdown(c, SHUT_RDWR))
 771                 return -1;
 772         c->reapable = true;
 773         return 0;
 774 }
 775
 776 int utcp_abort(struct utcp_connection *c) {
 777         if(!c) {
 778                 errno = EFAULT;
 779                 return -1;
 780         }
 781
 782         if(c->reapable) {
 783                 fprintf(stderr, "Error: abort() called on closed connection %p\n", c);
 784                 errno = EBADF;
 785                 return -1;
 786         }
 787
 788         c->reapable = true;
 789
 790         switch(c->state) {
 791         case CLOSED:
 792                 return 0;
 793         case LISTEN:
 794         case SYN_SENT:
 795         case CLOSING:
 796         case LAST_ACK:
 797         case TIME_WAIT:
 798                 set_state(c, CLOSED);
 799                 return 0;
 800
 801         case SYN_RECEIVED:
 802         case ESTABLISHED:
 803         case FIN_WAIT_1:
 804         case FIN_WAIT_2:
 805         case CLOSE_WAIT:
 806                 set_state(c, CLOSED);
 807                 break;
 808         }
 809
 810         // Send RST
 811
 812         struct hdr hdr;
 813
 814         hdr.src = c->src;
 815         hdr.dst = c->dst;
 816         hdr.seq = c->snd.nxt;
 817         hdr.ack = 0;
 818         hdr.wnd = 0;
 819         hdr.ctl = RST;
 820
 821         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 822         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 823         return 0;
 824 }
 825
 826 static void retransmit(struct utcp_connection *c) {
 827         if(c->state == CLOSED || c->snd.nxt == c->snd.una)
 828                 return;
 829
 830         struct utcp *utcp = c->utcp;
 831
 832         struct {
 833                 struct hdr hdr;
 834                 char data[c->utcp->mtu];
 835         } pkt;
 836
 837         pkt.hdr.src = c->src;
 838         pkt.hdr.dst = c->dst;
 839
 840         switch(c->state) {
 841                 case LISTEN:
 842                         // TODO: this should not happen
 843                         break;
 844
 845                 case SYN_SENT:
 846                         pkt.hdr.seq = c->snd.iss;
 847                         pkt.hdr.ack = 0;
 848                         pkt.hdr.wnd = c->rcv.wnd;
 849                         pkt.hdr.ctl = SYN;
 850                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr);
 851                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 852                         break;
 853
 854                 case SYN_RECEIVED:
 855                         pkt.hdr.seq = c->snd.nxt;
 856                         pkt.hdr.ack = c->rcv.nxt;
 857                         pkt.hdr.ctl = SYN | ACK;
 858                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr);
 859                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 860                         break;
 861
 862                 case ESTABLISHED:
 863                 case FIN_WAIT_1:
 864                         pkt.hdr.seq = c->snd.una;
 865                         pkt.hdr.ack = c->rcv.nxt;
 866                         pkt.hdr.ctl = ACK;
 867                         uint32_t len = seqdiff(c->snd.nxt, c->snd.una);
 868                         if(c->state == FIN_WAIT_1)
 869                                 len--;
 870                         if(len > utcp->mtu)
 871                                 len = utcp->mtu;
 872                         else {
 873                                 if(c->state == FIN_WAIT_1)
 874                                         pkt.hdr.ctl |= FIN;
 875                         }
 876                         memcpy(pkt.data, c->sndbuf, len);
 877                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr + len);
 878                         utcp->send(utcp, &pkt, sizeof pkt.hdr + len);
 879                         break;
 880
 881                 default:
 882                         // TODO: implement
 883                         abort();
 884         }
 885 }
 886
 887 /* Handle timeouts.
 888  * One call to this function will loop through all connections,
 889  * checking if something needs to be resent or not.
 890  * The return value is the time to the next timeout in milliseconds,
 891  * or maybe a negative value if the timeout is infinite.
 892  */
 893 int utcp_timeout(struct utcp *utcp) {
 894         struct timeval now;
 895         gettimeofday(&now, NULL);
 896         struct timeval next = {now.tv_sec + 3600, now.tv_usec};
 897
 898         for(int i = 0; i < utcp->nconnections; i++) {
 899                 struct utcp_connection *c = utcp->connections[i];
 900                 if(!c)
 901                         continue;
 902
 903                 if(c->state == CLOSED) {
 904                         if(c->reapable) {
 905                                 fprintf(stderr, "Reaping %p\n", c);
 906                                 free_connection(c);
 907                                 i--;
 908                         }
 909                         continue;
 910                 }
 911
 912                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &now, <)) {
 913                         errno = ETIMEDOUT;
 914                         c->state = CLOSED;
 915                         if(c->recv)
 916                                 c->recv(c, NULL, 0);
 917                         continue;
 918                 }
 919
 920                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &now, <)) {
 921                         retransmit(c);
 922                 }
 923
 924                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <))
 925                         next = c->conn_timeout;
 926
 927                 if(c->snd.nxt != c->snd.una) {
 928                         c->rtrx_timeout = now;
 929                         c->rtrx_timeout.tv_sec++;
 930                 } else {
 931                         timerclear(&c->rtrx_timeout);
 932                 }
 933
 934                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <))
 935                         next = c->rtrx_timeout;
 936         }
 937
 938         struct timeval diff;
 939         timersub(&next, &now, &diff);
 940         if(diff.tv_sec < 0)
 941                 return 0;
 942         return diff.tv_sec * 1000 + diff.tv_usec / 1000;
 943 }
 944
 945 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
 946         struct utcp *utcp = calloc(1, sizeof *utcp);
 947         if(!utcp)
 948                 return NULL;
 949
 950         if(!send) {
 951                 errno = EFAULT;
 952                 return NULL;
 953         }
 954
 955         utcp->accept = accept;
 956         utcp->pre_accept = pre_accept;
 957         utcp->send = send;
 958         utcp->priv = priv;
 959         utcp->mtu = 1000;
 960         utcp->timeout = 60;
 961
 962         return utcp;
 963 }
 964
 965 void utcp_exit(struct utcp *utcp) {
 966         if(!utcp)
 967                 return;
 968         for(int i = 0; i < utcp->nconnections; i++)
 969                 free_connection(utcp->connections[i]);
 970         free(utcp);
 971 }
 972
 973 void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
 974         // TODO: handle overhead of the header
 975         utcp->mtu = mtu;
 976 }
 977
 978 int utcp_set_connection_timeout(struct utcp *u, int timeout) {
 979         int prev = u->timeout;
 980         u->timeout = timeout;
 981         return prev;
 982 }