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   1 /*
   2     utcp.c -- Userspace TCP
   3     Copyright (C) 2014 Guus Sliepen <guus@tinc-vpn.org>
   4
   5     This program is free software; you can redistribute it and/or modify
   6     it under the terms of the GNU General Public License as published by
   7     the Free Software Foundation; either version 2 of the License, or
   8     (at your option) any later version.
   9
  10     This program is distributed in the hope that it will be useful,
  11     but WITHOUT ANY WARRANTY; without even the implied warranty of
  12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13     GNU General Public License for more details.
  14
  15     You should have received a copy of the GNU General Public License along
  16     with this program; if not, write to the Free Software Foundation, Inc.,
  17     51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  18 */
  19
  20 #define _GNU_SOURCE
  21
  22 #include <errno.h>
  23 #include <stdio.h>
  24 #include <stdlib.h>
  25 #include <stdint.h>
  26 #include <stdbool.h>
  27 #include <string.h>
  28 #include <unistd.h>
  29 #include <sys/time.h>
  30 #include <sys/socket.h>
  31
  32 #define UTCP_INTERNAL
  33 #include "utcp.h"
  34
  35 #define PREP(l) char pkt[(l) + sizeof struct hdr]; struct hdr *hdr = &pkt;
  36
  37 #define SYN 1
  38 #define ACK 2
  39 #define FIN 4
  40 #define RST 8
  41
  42 struct hdr {
  43         uint16_t src; // Source port
  44         uint16_t dst; // Destination port
  45         uint32_t seq; // Sequence number
  46         uint32_t ack; // Acknowledgement number
  47         uint32_t wnd; // Window size
  48         uint16_t ctl; // Flags (SYN, ACK, FIN, RST)
  49         uint16_t aux; // other stuff
  50 };
  51
  52 enum state {
  53         CLOSED,
  54         LISTEN,
  55         SYN_SENT,
  56         SYN_RECEIVED,
  57         ESTABLISHED,
  58         FIN_WAIT_1,
  59         FIN_WAIT_2,
  60         CLOSE_WAIT,
  61         CLOSING,
  62         LAST_ACK,
  63         TIME_WAIT
  64 };
  65
  66 const char *strstate[] = {
  67         "CLOSED",
  68         "LISTEN",
  69         "SYN_SENT",
  70         "SYN_RECEIVED",
  71         "ESTABLISHED",
  72         "FIN_WAIT_1",
  73         "FIN_WAIT_2",
  74         "CLOSE_WAIT",
  75         "CLOSING",
  76         "LAST_ACK",
  77         "TIME_WAIT"
  78 };
  79
  80 struct utcp_connection {
  81         void *priv;
  82         struct utcp *utcp;
  83         bool reapable;
  84
  85         uint16_t src;
  86         uint16_t dst;
  87         enum state state;
  88
  89         // The following two structures form the TCB
  90
  91         struct {
  92                 uint32_t una;
  93                 uint32_t nxt;
  94                 uint32_t wnd;
  95                 uint32_t up;
  96                 uint32_t wl1;
  97                 uint32_t wl2;
  98                 uint32_t iss;
  99         } snd;
 100
 101         struct {
 102                 uint32_t nxt;
 103                 uint32_t wnd;
 104                 uint32_t up;
 105                 uint32_t irs;
 106         } rcv;
 107
 108         utcp_recv_t recv;
 109
 110         struct timeval conn_timeout;
 111         struct timeval rtrx_timeout;
 112
 113         char *sndbuf;
 114         uint32_t sndbufsize;
 115 };
 116
 117 struct utcp {
 118         void *priv;
 119
 120         utcp_accept_t accept;
 121         utcp_pre_accept_t pre_accept;
 122         utcp_send_t send;
 123
 124         uint16_t mtu;
 125         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                 break;
 601         case ESTABLISHED:
 602         case CLOSE_WAIT:
 603                 if(seqdiff(hdr.ack, c->snd.una) < 0)
 604                         return 0;
 605                 if(seqdiff(hdr.ack, c->snd.nxt) > 0)
 606                         goto ack_and_drop;
 607                 if(seqdiff(hdr.ack, c->snd.una) > 0 && seqdiff(hdr.ack, c->snd.nxt) <= 0) {
 608                         c->snd.una = hdr.ack;
 609                         if(seqdiff(c->snd.wl1, hdr.seq) < 0 || (c->snd.wl1 == hdr.seq && seqdiff(c->snd.wl2, hdr.ack) <= 0)) {
 610                                 c->snd.wnd = hdr.wnd;
 611                                 c->snd.wl1 = hdr.seq;
 612                                 c->snd.wl2 = hdr.ack;
 613                         }
 614                 }
 615                 break;
 616         case FIN_WAIT_1:
 617                 if(hdr.ack == c->snd.nxt)
 618                         set_state(c, FIN_WAIT_2);
 619                 break;
 620         case FIN_WAIT_2:
 621                 // TODO: If nothing left to send, close.
 622                 break;
 623         case CLOSING:
 624                 if(hdr.ack == c->snd.nxt) {
 625                         set_state(c, TIME_WAIT);
 626                 }
 627                 break;
 628         case LAST_ACK:
 629                 if(hdr.ack == c->snd.nxt) {
 630                         set_state(c, CLOSED);
 631                 }
 632                 return 0;
 633         case TIME_WAIT:
 634                 // TODO: retransmission of remote FIN, ACK and restart 2 MSL timeout
 635                 break;
 636         default:
 637                 goto reset;
 638         }
 639
 640         // Process data
 641
 642         switch(c->state) {
 643         case ESTABLISHED:
 644         case FIN_WAIT_1:
 645         case FIN_WAIT_2:
 646                 // TODO: process the data, see page 74
 647                 break;
 648         case CLOSE_WAIT:
 649         case CLOSING:
 650         case LAST_ACK:
 651         case TIME_WAIT:
 652                 break;
 653         default:
 654                 abort();
 655         }
 656
 657         if(hdr.ctl & FIN) {
 658                 switch(c->state) {
 659                 case CLOSED:
 660                 case LISTEN:
 661                 case SYN_SENT:
 662                         return 0;
 663                 case SYN_RECEIVED:
 664                 case ESTABLISHED:
 665                         set_state(c, CLOSE_WAIT);
 666                         c->rcv.nxt++;
 667                         goto ack_and_drop;
 668                 case FIN_WAIT_1:
 669                         set_state(c, CLOSING);
 670                         c->rcv.nxt++;
 671                         goto ack_and_drop;
 672                 case FIN_WAIT_2:
 673                         set_state(c, TIME_WAIT);
 674                         c->rcv.nxt++;
 675                         goto ack_and_drop;
 676                 case CLOSE_WAIT:
 677                 case CLOSING:
 678                 case LAST_ACK:
 679                 case TIME_WAIT:
 680                         break;
 681                 default:
 682                         abort();
 683                 }
 684         }
 685
 686         // Process the data
 687
 688         if(len && c->recv) {
 689                 c->recv(c, data, len);
 690                 c->rcv.nxt += len;
 691                 goto ack_and_drop;
 692         }
 693
 694         return 0;
 695
 696 reset:
 697         swap_ports(&hdr);
 698         hdr.wnd = 0;
 699         if(hdr.ctl & ACK) {
 700                 hdr.seq = hdr.ack;
 701                 hdr.ctl = RST;
 702         } else {
 703                 hdr.ack = hdr.seq + len;
 704                 hdr.seq = 0;
 705                 hdr.ctl = RST | ACK;
 706         }
 707         utcp->send(utcp, &hdr, sizeof hdr);
 708         return 0;
 709
 710 ack_and_drop:
 711         swap_ports(&hdr);
 712         hdr.seq = c->snd.nxt;
 713         hdr.ack = c->rcv.nxt;
 714         hdr.ctl = ACK;
 715         utcp->send(utcp, &hdr, sizeof hdr);
 716         if(c->state == CLOSE_WAIT || c->state == TIME_WAIT) {
 717                 errno = 0;
 718                 if(c->recv)
 719                         c->recv(c, NULL, 0);
 720         }
 721         return 0;
 722 }
 723
 724 int utcp_shutdown(struct utcp_connection *c, int dir) {
 725         if(!c) {
 726                 errno = EFAULT;
 727                 return -1;
 728         }
 729
 730         if(c->reapable) {
 731                 fprintf(stderr, "Error: shutdown() called on closed connection %p\n", c);
 732                 errno = EBADF;
 733                 return -1;
 734         }
 735
 736         // TODO: handle dir
 737
 738         switch(c->state) {
 739         case CLOSED:
 740                 return 0;
 741         case LISTEN:
 742         case SYN_SENT:
 743                 set_state(c, CLOSED);
 744                 return 0;
 745
 746         case SYN_RECEIVED:
 747         case ESTABLISHED:
 748                 set_state(c, FIN_WAIT_1);
 749                 break;
 750         case FIN_WAIT_1:
 751         case FIN_WAIT_2:
 752                 return 0;
 753         case CLOSE_WAIT:
 754                 set_state(c, LAST_ACK);
 755                 break;
 756
 757         case CLOSING:
 758         case LAST_ACK:
 759         case TIME_WAIT:
 760                 return 0;
 761         }
 762
 763         // Send FIN
 764
 765         struct hdr hdr;
 766
 767         hdr.src = c->src;
 768         hdr.dst = c->dst;
 769         hdr.seq = c->snd.nxt;
 770         hdr.ack = c->rcv.nxt;
 771         hdr.wnd = c->snd.wnd;
 772         hdr.ctl = FIN | ACK;
 773
 774         c->snd.nxt += 1;
 775
 776         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 777         return 0;
 778 }
 779
 780 int utcp_close(struct utcp_connection *c) {
 781         if(utcp_shutdown(c, SHUT_RDWR))
 782                 return -1;
 783         c->reapable = true;
 784         return 0;
 785 }
 786
 787 int utcp_abort(struct utcp_connection *c) {
 788         if(!c) {
 789                 errno = EFAULT;
 790                 return -1;
 791         }
 792
 793         if(c->reapable) {
 794                 fprintf(stderr, "Error: abort() called on closed connection %p\n", c);
 795                 errno = EBADF;
 796                 return -1;
 797         }
 798
 799         c->reapable = true;
 800
 801         switch(c->state) {
 802         case CLOSED:
 803                 return 0;
 804         case LISTEN:
 805         case SYN_SENT:
 806         case CLOSING:
 807         case LAST_ACK:
 808         case TIME_WAIT:
 809                 set_state(c, CLOSED);
 810                 return 0;
 811
 812         case SYN_RECEIVED:
 813         case ESTABLISHED:
 814         case FIN_WAIT_1:
 815         case FIN_WAIT_2:
 816         case CLOSE_WAIT:
 817                 set_state(c, CLOSED);
 818                 break;
 819         }
 820
 821         // Send RST
 822
 823         struct hdr hdr;
 824
 825         hdr.src = c->src;
 826         hdr.dst = c->dst;
 827         hdr.seq = c->snd.nxt;
 828         hdr.ack = 0;
 829         hdr.wnd = 0;
 830         hdr.ctl = RST;
 831
 832         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 833         return 0;
 834 }
 835
 836 static void retransmit(struct utcp_connection *c) {
 837         if(c->state == CLOSED || c->snd.nxt == c->snd.una)
 838                 return;
 839
 840         struct utcp *utcp = c->utcp;
 841
 842         struct {
 843                 struct hdr hdr;
 844                 char data[c->utcp->mtu];
 845         } pkt;
 846
 847         pkt.hdr.src = c->src;
 848         pkt.hdr.dst = c->dst;
 849
 850         switch(c->state) {
 851                 case LISTEN:
 852                         // TODO: this should not happen
 853                         break;
 854
 855                 case SYN_SENT:
 856                         pkt.hdr.seq = c->snd.iss;
 857                         pkt.hdr.ack = 0;
 858                         pkt.hdr.wnd = c->rcv.wnd;
 859                         pkt.hdr.ctl = SYN;
 860                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 861                         break;
 862
 863                 case SYN_RECEIVED:
 864                         pkt.hdr.seq = c->snd.nxt;
 865                         pkt.hdr.ack = c->rcv.nxt;
 866                         pkt.hdr.ctl = SYN | ACK;
 867                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 868                         break;
 869
 870                 case ESTABLISHED:
 871                         pkt.hdr.seq = c->snd.una;
 872                         pkt.hdr.ack = c->rcv.nxt;
 873                         pkt.hdr.ctl = ACK;
 874                         uint32_t len = seqdiff(c->snd.nxt, c->snd.una);
 875                         if(len > utcp->mtu)
 876                                 len = utcp->mtu;
 877                         memcpy(pkt.data, c->sndbuf, 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 int utcp_set_connection_timeout(struct utcp *u, int timeout) {
 974         int prev = u->timeout;
 975         u->timeout = timeout;
 976         return prev;
 977 }