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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 #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->snd.last = c->snd.nxt;
 185         c->snd.cwnd = utcp->mtu;
 186         c->utcp = utcp;
 187
 188         // Add it to the sorted list of connections
 189
 190         utcp->connections[utcp->nconnections++] = c;
 191         qsort(utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 192
 193         return c;
 194 }
 195
 196 struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
 197         struct utcp_connection *c = allocate_connection(utcp, 0, dst);
 198         if(!c)
 199                 return NULL;
 200
 201         c->recv = recv;
 202
 203         struct hdr hdr;
 204
 205         hdr.src = c->src;
 206         hdr.dst = c->dst;
 207         hdr.seq = c->snd.iss;
 208         hdr.ack = 0;
 209         hdr.ctl = SYN;
 210         hdr.wnd = c->rcv.wnd;
 211
 212         set_state(c, SYN_SENT);
 213
 214         print_packet(utcp, "send", &hdr, sizeof hdr);
 215         utcp->send(utcp, &hdr, sizeof hdr);
 216
 217         gettimeofday(&c->conn_timeout, NULL);
 218         c->conn_timeout.tv_sec += utcp->timeout;
 219
 220         return c;
 221 }
 222
 223 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 224         if(c->reapable || c->state != SYN_RECEIVED) {
 225                 debug("Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
 226                 return;
 227         }
 228
 229         debug("%p accepted, %p %p\n", c, recv, priv);
 230         c->recv = recv;
 231         c->priv = priv;
 232         set_state(c, ESTABLISHED);
 233 }
 234
 235 static void ack(struct utcp_connection *c, bool sendatleastone) {
 236         uint32_t left = seqdiff(c->snd.last, c->snd.nxt);
 237         int32_t cwndleft = c->snd.cwnd - seqdiff(c->snd.nxt, c->snd.una);
 238         char *data = c->sndbuf + seqdiff(c->snd.nxt, c->snd.una);
 239
 240         if(cwndleft <= 0)
 241                 cwndleft = 0;
 242
 243         if(cwndleft < left)
 244                 left = cwndleft;
 245
 246         if(!left && !sendatleastone)
 247                 return;
 248
 249         struct {
 250                 struct hdr hdr;
 251                 char data[c->utcp->mtu];
 252         } pkt;
 253
 254         pkt.hdr.src = c->src;
 255         pkt.hdr.dst = c->dst;
 256         pkt.hdr.ack = c->rcv.nxt;
 257         pkt.hdr.wnd = c->snd.wnd;
 258         pkt.hdr.ctl = ACK;
 259
 260         do {
 261                 uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
 262                 pkt.hdr.seq = c->snd.nxt;
 263
 264                 memcpy(pkt.data, data, seglen);
 265
 266                 c->snd.nxt += seglen;
 267                 data += seglen;
 268                 left -= seglen;
 269
 270                 print_packet(c->utcp, "send", &pkt, sizeof pkt.hdr + seglen);
 271                 c->utcp->send(c->utcp, &pkt, sizeof pkt.hdr + seglen);
 272         } while(left);
 273 }
 274
 275 ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 276         if(c->reapable) {
 277                 debug("Error: send() called on closed connection %p\n", c);
 278                 errno = EBADF;
 279                 return -1;
 280         }
 281
 282         switch(c->state) {
 283         case CLOSED:
 284         case LISTEN:
 285         case SYN_SENT:
 286         case SYN_RECEIVED:
 287                 debug("Error: send() called on unconnected connection %p\n", c);
 288                 errno = ENOTCONN;
 289                 return -1;
 290         case ESTABLISHED:
 291         case CLOSE_WAIT:
 292                 break;
 293         case FIN_WAIT_1:
 294         case FIN_WAIT_2:
 295         case CLOSING:
 296         case LAST_ACK:
 297         case TIME_WAIT:
 298                 debug("Error: send() called on closing connection %p\n", c);
 299                 errno = EPIPE;
 300                 return -1;
 301         }
 302
 303         // Add data to send buffer
 304
 305         if(!len)
 306                 return 0;
 307
 308         if(!data) {
 309                 errno = EFAULT;
 310                 return -1;
 311         }
 312
 313         uint32_t bufused = seqdiff(c->snd.nxt, c->snd.una);
 314
 315         /* Check our send buffer.
 316          * - If it's big enough, just put the data in there.
 317          * - If not, decide whether to enlarge if possible.
 318          * - Cap len so it doesn't overflow our buffer.
 319          */
 320
 321         if(len > c->sndbufsize - bufused && c->sndbufsize < c->maxsndbufsize) {
 322                 uint32_t newbufsize;
 323                 if(c->sndbufsize > c->maxsndbufsize / 2)
 324                         newbufsize = c->maxsndbufsize;
 325                 else
 326                         newbufsize = c->sndbufsize * 2;
 327                 char *newbuf = realloc(c->sndbuf, newbufsize);
 328                 if(newbuf) {
 329                         c->sndbuf = newbuf;
 330                         c->sndbufsize = newbufsize;
 331                 }
 332         }
 333
 334         if(len > c->sndbufsize - bufused)
 335                 len = c->sndbufsize - bufused;
 336
 337         if(!len) {
 338                 errno == EWOULDBLOCK;
 339                 return 0;
 340         }
 341
 342         memcpy(c->sndbuf + bufused, data, len);
 343         c->snd.last += len;
 344
 345         ack(c, false);
 346         return len;
 347 }
 348
 349 static void swap_ports(struct hdr *hdr) {
 350         uint16_t tmp = hdr->src;
 351         hdr->src = hdr->dst;
 352         hdr->dst = tmp;
 353 }
 354
 355 int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 356         if(!utcp) {
 357                 errno = EFAULT;
 358                 return -1;
 359         }
 360
 361         if(!len)
 362                 return 0;
 363
 364         if(!data) {
 365                 errno = EFAULT;
 366                 return -1;
 367         }
 368
 369         print_packet(utcp, "recv", data, len);
 370
 371         // Drop packets smaller than the header
 372
 373         struct hdr hdr;
 374         if(len < sizeof hdr) {
 375                 errno = EBADMSG;
 376                 return -1;
 377         }
 378
 379         // Make a copy from the potentially unaligned data to a struct hdr
 380
 381         memcpy(&hdr, data, sizeof hdr);
 382         data += sizeof hdr;
 383         len -= sizeof hdr;
 384
 385         // Drop packets with an unknown CTL flag
 386
 387         if(hdr.ctl & ~(SYN | ACK | RST | FIN)) {
 388                 errno = EBADMSG;
 389                 return -1;
 390         }
 391
 392         // Try to match the packet to an existing connection
 393
 394         struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
 395
 396         // Is it for a new connection?
 397
 398         if(!c) {
 399                 // Ignore RST packets
 400
 401                 if(hdr.ctl & RST)
 402                         return 0;
 403
 404                 // Is it a SYN packet and are we LISTENing?
 405
 406                 if(hdr.ctl & SYN && !(hdr.ctl & ACK) && utcp->accept) {
 407                         // If we don't want to accept it, send a RST back
 408                         if((utcp->pre_accept && !utcp->pre_accept(utcp, hdr.dst))) {
 409                                 len = 1;
 410                                 goto reset;
 411                         }
 412
 413                         // Try to allocate memory, otherwise send a RST back
 414                         c = allocate_connection(utcp, hdr.dst, hdr.src);
 415                         if(!c) {
 416                                 len = 1;
 417                                 goto reset;
 418                         }
 419
 420                         // Return SYN+ACK, go to SYN_RECEIVED state
 421                         c->snd.wnd = hdr.wnd;
 422                         c->rcv.irs = hdr.seq;
 423                         c->rcv.nxt = c->rcv.irs + 1;
 424                         set_state(c, SYN_RECEIVED);
 425
 426                         hdr.dst = c->dst;
 427                         hdr.src = c->src;
 428                         hdr.ack = c->rcv.irs + 1;
 429                         hdr.seq = c->snd.iss;
 430                         hdr.ctl = SYN | ACK;
 431                         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 432                         utcp->send(utcp, &hdr, sizeof hdr);
 433                 } else {
 434                         // No, we don't want your packets, send a RST back
 435                         len = 1;
 436                         goto reset;
 437                 }
 438
 439                 return 0;
 440         }
 441
 442         debug("%p state %s\n", c->utcp, strstate[c->state]);
 443
 444         // In case this is for a CLOSED connection, ignore the packet.
 445         // TODO: make it so incoming packets can never match a CLOSED connection.
 446
 447         if(c->state == CLOSED)
 448                 return 0;
 449
 450         // It is for an existing connection.
 451
 452         // 1. Drop invalid packets.
 453
 454         // 1a. Drop packets that should not happen in our current state.
 455
 456         switch(c->state) {
 457         case SYN_SENT:
 458         case SYN_RECEIVED:
 459         case ESTABLISHED:
 460         case FIN_WAIT_1:
 461         case FIN_WAIT_2:
 462         case CLOSE_WAIT:
 463         case CLOSING:
 464         case LAST_ACK:
 465         case TIME_WAIT:
 466                 break;
 467         default:
 468                 abort();
 469         }
 470
 471         // 1b. Drop packets with a sequence number not in our receive window.
 472
 473         bool acceptable;
 474
 475         if(c->state == SYN_SENT)
 476                 acceptable = true;
 477
 478         // TODO: handle packets overlapping c->rcv.nxt.
 479 #if 0
 480         // Only use this when accepting out-of-order packets.
 481         else if(len == 0)
 482                 if(c->rcv.wnd == 0)
 483                         acceptable = hdr.seq == c->rcv.nxt;
 484                 else
 485                         acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0);
 486         else
 487                 if(c->rcv.wnd == 0)
 488                         // We don't accept data when the receive window is zero.
 489                         acceptable = false;
 490                 else
 491                         // Both start and end of packet must be within the receive window
 492                         acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0)
 493                                 || (seqdiff(hdr.seq + len + 1, c->rcv.nxt) >= 0 && seqdiff(hdr.seq + len - 1, c->rcv.nxt + c->rcv.wnd) < 0);
 494 #else
 495         if(c->state != SYN_SENT)
 496                 acceptable = hdr.seq == c->rcv.nxt;
 497 #endif
 498
 499         if(!acceptable) {
 500                 debug("Packet not acceptable, %u  <= %u + %zu < %u\n", c->rcv.nxt, hdr.seq, len, c->rcv.nxt + c->rcv.wnd);
 501                 // Ignore unacceptable RST packets.
 502                 if(hdr.ctl & RST)
 503                         return 0;
 504                 // Otherwise, send an ACK back in the hope things improve.
 505                 goto ack;
 506         }
 507
 508         c->snd.wnd = hdr.wnd; // TODO: move below
 509
 510         // 1c. Drop packets with an invalid ACK.
 511         // ackno should not roll back, and it should also not be bigger than snd.nxt.
 512
 513         if(hdr.ctl & ACK && (seqdiff(hdr.ack, c->snd.nxt) > 0 || seqdiff(hdr.ack, c->snd.una) < 0)) {
 514                 debug("Packet ack seqno out of range, %u %u %u\n", hdr.ack, c->snd.una, c->snd.nxt);
 515                 // Ignore unacceptable RST packets.
 516                 if(hdr.ctl & RST)
 517                         return 0;
 518                 goto reset;
 519         }
 520
 521         // 2. Handle RST packets
 522
 523         if(hdr.ctl & RST) {
 524                 switch(c->state) {
 525                 case SYN_SENT:
 526                         if(!(hdr.ctl & ACK))
 527                                 return 0;
 528                         // The peer has refused our connection.
 529                         set_state(c, CLOSED);
 530                         errno = ECONNREFUSED;
 531                         if(c->recv)
 532                                 c->recv(c, NULL, 0);
 533                         return 0;
 534                 case SYN_RECEIVED:
 535                         if(hdr.ctl & ACK)
 536                                 return 0;
 537                         // We haven't told the application about this connection yet. Silently delete.
 538                         free_connection(c);
 539                         return 0;
 540                 case ESTABLISHED:
 541                 case FIN_WAIT_1:
 542                 case FIN_WAIT_2:
 543                 case CLOSE_WAIT:
 544                         if(hdr.ctl & ACK)
 545                                 return 0;
 546                         // The peer has aborted our connection.
 547                         set_state(c, CLOSED);
 548                         errno = ECONNRESET;
 549                         if(c->recv)
 550                                 c->recv(c, NULL, 0);
 551                         return 0;
 552                 case CLOSING:
 553                 case LAST_ACK:
 554                 case TIME_WAIT:
 555                         if(hdr.ctl & ACK)
 556                                 return 0;
 557                         // As far as the application is concerned, the connection has already been closed.
 558                         // If it has called utcp_close() already, we can immediately free this connection.
 559                         if(c->reapable) {
 560                                 free_connection(c);
 561                                 return 0;
 562                         }
 563                         // Otherwise, immediately move to the CLOSED state.
 564                         set_state(c, CLOSED);
 565                         return 0;
 566                 default:
 567                         abort();
 568                 }
 569         }
 570
 571         // 3. Advance snd.una
 572
 573         uint32_t advanced = seqdiff(hdr.ack, c->snd.una);
 574         c->snd.una = hdr.ack;
 575
 576         if(advanced) {
 577                 debug("%p advanced %u\n", utcp, advanced);
 578                 // Make room in the send buffer.
 579                 // TODO: try to avoid memmoving too much. Circular buffer?
 580                 uint32_t left = seqdiff(c->snd.nxt, hdr.ack);
 581                 if(left)
 582                         memmove(c->sndbuf, c->sndbuf + advanced, left);
 583                 c->dupack = 0;
 584                 c->snd.cwnd += utcp->mtu;
 585                 if(c->snd.cwnd > c->maxsndbufsize)
 586                         c->snd.cwnd = c->maxsndbufsize;
 587         } else {
 588                 if(!len) {
 589                         c->dupack++;
 590                         if(c->dupack >= 3) {
 591                                 debug("Triplicate ACK\n");
 592                                 abort();
 593                         }
 594                 }
 595         }
 596
 597         // 4. Update timers
 598
 599         if(advanced) {
 600                 timerclear(&c->conn_timeout); // It should be set anew in utcp_timeout() if c->snd.una != c->snd.nxt.
 601                 if(c->snd.una == c->snd.nxt)
 602                         timerclear(&c->rtrx_timeout);
 603         }
 604
 605         // 5. Process SYN stuff
 606
 607         if(hdr.ctl & SYN) {
 608                 switch(c->state) {
 609                 case SYN_SENT:
 610                         // This is a SYNACK. It should always have ACKed the SYN.
 611                         if(!advanced)
 612                                 goto reset;
 613                         c->rcv.irs = hdr.seq;
 614                         c->rcv.nxt = hdr.seq;
 615                         set_state(c, ESTABLISHED);
 616                         // TODO: notify application of this somehow.
 617                         break;
 618                 case SYN_RECEIVED:
 619                 case ESTABLISHED:
 620                 case FIN_WAIT_1:
 621                 case FIN_WAIT_2:
 622                 case CLOSE_WAIT:
 623                 case CLOSING:
 624                 case LAST_ACK:
 625                 case TIME_WAIT:
 626                         // Ehm, no. We should never receive a second SYN.
 627                         goto reset;
 628                 default:
 629                         abort();
 630                 }
 631
 632                 // SYN counts as one sequence number
 633                 c->rcv.nxt++;
 634         }
 635
 636         // 6. Process new data
 637
 638         if(c->state == SYN_RECEIVED) {
 639                 // This is the ACK after the SYNACK. It should always have ACKed the SYNACK.
 640                 if(!advanced)
 641                         goto reset;
 642
 643                 // Are we still LISTENing?
 644                 if(utcp->accept)
 645                         utcp->accept(c, c->src);
 646
 647                 if(c->state != ESTABLISHED) {
 648                         set_state(c, CLOSED);
 649                         c->reapable = true;
 650                         goto reset;
 651                 }
 652         }
 653
 654         if(len) {
 655                 switch(c->state) {
 656                 case SYN_SENT:
 657                 case SYN_RECEIVED:
 658                         // This should never happen.
 659                         abort();
 660                 case ESTABLISHED:
 661                 case FIN_WAIT_1:
 662                 case FIN_WAIT_2:
 663                         break;
 664                 case CLOSE_WAIT:
 665                 case CLOSING:
 666                 case LAST_ACK:
 667                 case TIME_WAIT:
 668                         // Ehm no, We should never receive more data after a FIN.
 669                         goto reset;
 670                 default:
 671                         abort();
 672                 }
 673
 674                 int rxd;
 675
 676                 if(c->recv) {
 677                         rxd = c->recv(c, data, len);
 678                         if(rxd < 0)
 679                                 rxd = 0;
 680                         else if(rxd > len)
 681                                 rxd = len; // Bad application, bad!
 682                 } else {
 683                         rxd = len;
 684                 }
 685
 686                 c->rcv.nxt += len;
 687         }
 688
 689         // 7. Process FIN stuff
 690
 691         if(hdr.ctl & FIN) {
 692                 switch(c->state) {
 693                 case SYN_SENT:
 694                 case SYN_RECEIVED:
 695                         // This should never happen.
 696                         abort();
 697                 case ESTABLISHED:
 698                         set_state(c, CLOSE_WAIT);
 699                         break;
 700                 case FIN_WAIT_1:
 701                         set_state(c, CLOSING);
 702                         break;
 703                 case FIN_WAIT_2:
 704                         set_state(c, TIME_WAIT);
 705                         break;
 706                 case CLOSE_WAIT:
 707                 case CLOSING:
 708                 case LAST_ACK:
 709                 case TIME_WAIT:
 710                         // Ehm, no. We should never receive a second FIN.
 711                         goto reset;
 712                 default:
 713                         abort();
 714                 }
 715
 716                 // FIN counts as one sequence number
 717                 c->rcv.nxt++;
 718
 719                 // Inform the application that the peer closed the connection.
 720                 if(c->recv) {
 721                         errno = 0;
 722                         c->recv(c, NULL, 0);
 723                 }
 724         }
 725
 726         if(!len && !advanced)
 727                 return 0;
 728
 729         if(!len && !(hdr.ctl & SYN) && !(hdr.ctl & FIN))
 730                 return 0;
 731
 732 ack:
 733         ack(c, true);
 734         return 0;
 735
 736 reset:
 737         swap_ports(&hdr);
 738         hdr.wnd = 0;
 739         if(hdr.ctl & ACK) {
 740                 hdr.seq = hdr.ack;
 741                 hdr.ctl = RST;
 742         } else {
 743                 hdr.ack = hdr.seq + len;
 744                 hdr.seq = 0;
 745                 hdr.ctl = RST | ACK;
 746         }
 747         print_packet(utcp, "send", &hdr, sizeof hdr);
 748         utcp->send(utcp, &hdr, sizeof hdr);
 749         return 0;
 750
 751 }
 752
 753 int utcp_shutdown(struct utcp_connection *c, int dir) {
 754         debug("%p shutdown %d\n", c->utcp, dir);
 755         if(!c) {
 756                 errno = EFAULT;
 757                 return -1;
 758         }
 759
 760         if(c->reapable) {
 761                 debug("Error: shutdown() called on closed connection %p\n", c);
 762                 errno = EBADF;
 763                 return -1;
 764         }
 765
 766         // TODO: handle dir
 767
 768         switch(c->state) {
 769         case CLOSED:
 770                 return 0;
 771         case LISTEN:
 772         case SYN_SENT:
 773                 set_state(c, CLOSED);
 774                 return 0;
 775
 776         case SYN_RECEIVED:
 777         case ESTABLISHED:
 778                 set_state(c, FIN_WAIT_1);
 779                 break;
 780         case FIN_WAIT_1:
 781         case FIN_WAIT_2:
 782                 return 0;
 783         case CLOSE_WAIT:
 784                 set_state(c, CLOSING);
 785                 break;
 786
 787         case CLOSING:
 788         case LAST_ACK:
 789         case TIME_WAIT:
 790                 return 0;
 791         }
 792
 793         // Send FIN
 794
 795         struct hdr hdr;
 796
 797         hdr.src = c->src;
 798         hdr.dst = c->dst;
 799         hdr.seq = c->snd.nxt;
 800         hdr.ack = c->rcv.nxt;
 801         hdr.wnd = c->snd.wnd;
 802         hdr.ctl = FIN | ACK;
 803
 804         c->snd.nxt += 1;
 805
 806         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 807         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 808         return 0;
 809 }
 810
 811 int utcp_close(struct utcp_connection *c) {
 812         if(utcp_shutdown(c, SHUT_RDWR))
 813                 return -1;
 814         c->reapable = true;
 815         return 0;
 816 }
 817
 818 int utcp_abort(struct utcp_connection *c) {
 819         if(!c) {
 820                 errno = EFAULT;
 821                 return -1;
 822         }
 823
 824         if(c->reapable) {
 825                 debug("Error: abort() called on closed connection %p\n", c);
 826                 errno = EBADF;
 827                 return -1;
 828         }
 829
 830         c->reapable = true;
 831
 832         switch(c->state) {
 833         case CLOSED:
 834                 return 0;
 835         case LISTEN:
 836         case SYN_SENT:
 837         case CLOSING:
 838         case LAST_ACK:
 839         case TIME_WAIT:
 840                 set_state(c, CLOSED);
 841                 return 0;
 842
 843         case SYN_RECEIVED:
 844         case ESTABLISHED:
 845         case FIN_WAIT_1:
 846         case FIN_WAIT_2:
 847         case CLOSE_WAIT:
 848                 set_state(c, CLOSED);
 849                 break;
 850         }
 851
 852         // Send RST
 853
 854         struct hdr hdr;
 855
 856         hdr.src = c->src;
 857         hdr.dst = c->dst;
 858         hdr.seq = c->snd.nxt;
 859         hdr.ack = 0;
 860         hdr.wnd = 0;
 861         hdr.ctl = RST;
 862
 863         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 864         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 865         return 0;
 866 }
 867
 868 static void retransmit(struct utcp_connection *c) {
 869         if(c->state == CLOSED || c->snd.nxt == c->snd.una)
 870                 return;
 871
 872         struct utcp *utcp = c->utcp;
 873
 874         struct {
 875                 struct hdr hdr;
 876                 char data[c->utcp->mtu];
 877         } pkt;
 878
 879         pkt.hdr.src = c->src;
 880         pkt.hdr.dst = c->dst;
 881
 882         switch(c->state) {
 883                 case LISTEN:
 884                         // TODO: this should not happen
 885                         break;
 886
 887                 case SYN_SENT:
 888                         pkt.hdr.seq = c->snd.iss;
 889                         pkt.hdr.ack = 0;
 890                         pkt.hdr.wnd = c->rcv.wnd;
 891                         pkt.hdr.ctl = SYN;
 892                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr);
 893                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 894                         break;
 895
 896                 case SYN_RECEIVED:
 897                         pkt.hdr.seq = c->snd.nxt;
 898                         pkt.hdr.ack = c->rcv.nxt;
 899                         pkt.hdr.ctl = SYN | ACK;
 900                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr);
 901                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 902                         break;
 903
 904                 case ESTABLISHED:
 905                 case FIN_WAIT_1:
 906                         pkt.hdr.seq = c->snd.una;
 907                         pkt.hdr.ack = c->rcv.nxt;
 908                         pkt.hdr.ctl = ACK;
 909                         uint32_t len = seqdiff(c->snd.nxt, c->snd.una);
 910                         if(c->state == FIN_WAIT_1)
 911                                 len--;
 912                         if(len > utcp->mtu)
 913                                 len = utcp->mtu;
 914                         else {
 915                                 if(c->state == FIN_WAIT_1)
 916                                         pkt.hdr.ctl |= FIN;
 917                         }
 918                         memcpy(pkt.data, c->sndbuf, len);
 919                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr + len);
 920                         utcp->send(utcp, &pkt, sizeof pkt.hdr + len);
 921                         break;
 922
 923                 default:
 924                         // TODO: implement
 925                         abort();
 926         }
 927 }
 928
 929 /* Handle timeouts.
 930  * One call to this function will loop through all connections,
 931  * checking if something needs to be resent or not.
 932  * The return value is the time to the next timeout in milliseconds,
 933  * or maybe a negative value if the timeout is infinite.
 934  */
 935 int utcp_timeout(struct utcp *utcp) {
 936         struct timeval now;
 937         gettimeofday(&now, NULL);
 938         struct timeval next = {now.tv_sec + 3600, now.tv_usec};
 939
 940         for(int i = 0; i < utcp->nconnections; i++) {
 941                 struct utcp_connection *c = utcp->connections[i];
 942                 if(!c)
 943                         continue;
 944
 945                 if(c->state == CLOSED) {
 946                         if(c->reapable) {
 947                                 debug("Reaping %p\n", c);
 948                                 free_connection(c);
 949                                 i--;
 950                         }
 951                         continue;
 952                 }
 953
 954                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &now, <)) {
 955                         errno = ETIMEDOUT;
 956                         c->state = CLOSED;
 957                         if(c->recv)
 958                                 c->recv(c, NULL, 0);
 959                         continue;
 960                 }
 961
 962                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &now, <)) {
 963                         retransmit(c);
 964                 }
 965
 966                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <))
 967                         next = c->conn_timeout;
 968
 969                 if(c->snd.nxt != c->snd.una) {
 970                         c->rtrx_timeout = now;
 971                         c->rtrx_timeout.tv_sec++;
 972                 } else {
 973                         timerclear(&c->rtrx_timeout);
 974                 }
 975
 976                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <))
 977                         next = c->rtrx_timeout;
 978         }
 979
 980         struct timeval diff;
 981         timersub(&next, &now, &diff);
 982         if(diff.tv_sec < 0)
 983                 return 0;
 984         return diff.tv_sec * 1000 + diff.tv_usec / 1000;
 985 }
 986
 987 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
 988         struct utcp *utcp = calloc(1, sizeof *utcp);
 989         if(!utcp)
 990                 return NULL;
 991
 992         if(!send) {
 993                 errno = EFAULT;
 994                 return NULL;
 995         }
 996
 997         utcp->accept = accept;
 998         utcp->pre_accept = pre_accept;
 999         utcp->send = send;
1000         utcp->priv = priv;
1001         utcp->mtu = 1000;
1002         utcp->timeout = 60;
1003
1004         return utcp;
1005 }
1006
1007 void utcp_exit(struct utcp *utcp) {
1008         if(!utcp)
1009                 return;
1010         for(int i = 0; i < utcp->nconnections; i++)
1011                 free_connection(utcp->connections[i]);
1012         free(utcp);
1013 }
1014
1015 uint16_t utcp_get_mtu(struct utcp *utcp) {
1016         return utcp->mtu;
1017 }
1018
1019 void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
1020         // TODO: handle overhead of the header
1021         utcp->mtu = mtu;
1022 }
1023
1024 int utcp_get_user_timeout(struct utcp *u) {
1025         return u->timeout;
1026 }
1027
1028 void utcp_set_user_timeout(struct utcp *u, int timeout) {
1029         u->timeout = timeout;
1030 }
1031
1032 size_t utcp_get_sndbuf(struct utcp_connection *c) {
1033         return c->maxsndbufsize;
1034 }
1035
1036 void utcp_set_sndbuf(struct utcp_connection *c, size_t size) {
1037         c->maxsndbufsize = size;
1038         if(c->maxsndbufsize != size)
1039                 c->maxsndbufsize = -1;
1040 }
1041
1042 bool utcp_get_nodelay(struct utcp_connection *c) {
1043         return c->nodelay;
1044 }
1045
1046 void utcp_set_nodelay(struct utcp_connection *c, bool nodelay) {
1047         c->nodelay = nodelay;
1048 }
1049
1050 bool utcp_get_keepalive(struct utcp_connection *c) {
1051         return c->keepalive;
1052 }
1053
1054 void utcp_set_keepalive(struct utcp_connection *c, bool keepalive) {
1055         c->keepalive = keepalive;
1056 }
1057
1058 size_t utcp_get_outq(struct utcp_connection *c) {
1059         return seqdiff(c->snd.nxt, c->snd.una);
1060 }