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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 static int32_t seqdiff(uint32_t a, uint32_t b) {
  77         return a - b;
  78 }
  79
  80 // Connections are stored in a sorted list.
  81 // This gives O(log(N)) lookup time, O(N log(N)) insertion time and O(N) deletion time.
  82
  83 static int compare(const void *va, const void *vb) {
  84         const struct utcp_connection *a = *(struct utcp_connection **)va;
  85         const struct utcp_connection *b = *(struct utcp_connection **)vb;
  86         if(!a->src || !b->src)
  87                 abort();
  88         int c = (int)a->src - (int)b->src;
  89         if(c)
  90                 return c;
  91         c = (int)a->dst - (int)b->dst;
  92         return c;
  93 }
  94
  95 static struct utcp_connection *find_connection(const struct utcp *utcp, uint16_t src, uint16_t dst) {
  96         if(!utcp->nconnections)
  97                 return NULL;
  98         struct utcp_connection key = {
  99                 .src = src,
 100                 .dst = dst,
 101         }, *keyp = &key;
 102         struct utcp_connection **match = bsearch(&keyp, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 103         return match ? *match : NULL;
 104 }
 105
 106 static void free_connection(struct utcp_connection *c) {
 107         struct utcp *utcp = c->utcp;
 108         struct utcp_connection **cp = bsearch(&c, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 109         if(!cp)
 110                 abort();
 111
 112         int i = cp - utcp->connections;
 113         memmove(cp + i, cp + i + 1, (utcp->nconnections - i - 1) * sizeof *cp);
 114         utcp->nconnections--;
 115
 116         free(c);
 117 }
 118
 119 static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t src, uint16_t dst) {
 120         // Check whether this combination of src and dst is free
 121
 122         if(src) {
 123                 if(find_connection(utcp, src, dst)) {
 124                         errno = EADDRINUSE;
 125                         return NULL;
 126                 }
 127         } else { // If src == 0, generate a random port number with the high bit set
 128                 if(utcp->nconnections >= 32767) {
 129                         errno = ENOMEM;
 130                         return NULL;
 131                 }
 132                 src = rand() | 0x8000;
 133                 while(find_connection(utcp, src, dst))
 134                         src++;
 135         }
 136
 137         // Allocate memory for the new connection
 138
 139         if(utcp->nconnections >= utcp->nallocated) {
 140                 if(!utcp->nallocated)
 141                         utcp->nallocated = 4;
 142                 else
 143                         utcp->nallocated *= 2;
 144                 struct utcp_connection **new_array = realloc(utcp->connections, utcp->nallocated * sizeof *utcp->connections);
 145                 if(!new_array)
 146                         return NULL;
 147                 utcp->connections = new_array;
 148         }
 149
 150         struct utcp_connection *c = calloc(1, sizeof *c);
 151         if(!c)
 152                 return NULL;
 153
 154         c->sndbufsize = DEFAULT_SNDBUFSIZE;
 155         c->maxsndbufsize = DEFAULT_MAXSNDBUFSIZE;
 156         c->sndbuf = malloc(c->sndbufsize);
 157         if(!c->sndbuf) {
 158                 free(c);
 159                 return NULL;
 160         }
 161
 162         // Fill in the details
 163
 164         c->src = src;
 165         c->dst = dst;
 166         c->snd.iss = rand();
 167         c->snd.una = c->snd.iss;
 168         c->snd.nxt = c->snd.iss + 1;
 169         c->rcv.wnd = utcp->mtu;
 170         c->utcp = utcp;
 171
 172         // Add it to the sorted list of connections
 173
 174         utcp->connections[utcp->nconnections++] = c;
 175         qsort(utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 176
 177         return c;
 178 }
 179
 180 struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
 181         struct utcp_connection *c = allocate_connection(utcp, 0, dst);
 182         if(!c)
 183                 return NULL;
 184
 185         c->recv = recv;
 186
 187         struct hdr hdr;
 188
 189         hdr.src = c->src;
 190         hdr.dst = c->dst;
 191         hdr.seq = c->snd.iss;
 192         hdr.ack = 0;
 193         hdr.ctl = SYN;
 194         hdr.wnd = c->rcv.wnd;
 195
 196         set_state(c, SYN_SENT);
 197
 198         print_packet(utcp, "send", &hdr, sizeof hdr);
 199         utcp->send(utcp, &hdr, sizeof hdr);
 200
 201         gettimeofday(&c->conn_timeout, NULL);
 202         c->conn_timeout.tv_sec += utcp->timeout;
 203
 204         return c;
 205 }
 206
 207 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 208         if(c->reapable || c->state != SYN_RECEIVED) {
 209                 fprintf(stderr, "Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
 210                 return;
 211         }
 212
 213         fprintf(stderr, "%p accepted, %p %p\n", c, recv, priv);
 214         c->recv = recv;
 215         c->priv = priv;
 216         set_state(c, ESTABLISHED);
 217 }
 218
 219 ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 220         if(c->reapable) {
 221                 fprintf(stderr, "Error: send() called on closed connection %p\n", c);
 222                 errno = EBADF;
 223                 return -1;
 224         }
 225
 226         switch(c->state) {
 227         case CLOSED:
 228         case LISTEN:
 229         case SYN_SENT:
 230         case SYN_RECEIVED:
 231                 fprintf(stderr, "Error: send() called on unconnected connection %p\n", c);
 232                 errno = ENOTCONN;
 233                 return -1;
 234         case ESTABLISHED:
 235         case CLOSE_WAIT:
 236                 break;
 237         case FIN_WAIT_1:
 238         case FIN_WAIT_2:
 239         case CLOSING:
 240         case LAST_ACK:
 241         case TIME_WAIT:
 242                 fprintf(stderr, "Error: send() called on closing connection %p\n", c);
 243                 errno = EPIPE;
 244                 return -1;
 245         }
 246
 247         // Add data to send buffer
 248
 249         if(!len)
 250                 return 0;
 251
 252         if(!data) {
 253                 errno = EFAULT;
 254                 return -1;
 255         }
 256
 257         uint32_t bufused = seqdiff(c->snd.nxt, c->snd.una);
 258
 259         /* Check our send buffer.
 260          * - If it's big enough, just put the data in there.
 261          * - If not, decide whether to enlarge if possible.
 262          * - Cap len so it doesn't overflow our buffer.
 263          */
 264
 265         if(len > c->sndbufsize - bufused && c->sndbufsize < c->maxsndbufsize) {
 266                 if(c->sndbufsize > c->maxsndbufsize / 2)
 267                         c->sndbufsize = c->maxsndbufsize;
 268                 else
 269                         c->sndbufsize *= 2;
 270                 c->sndbuf = realloc(c->sndbuf, c->sndbufsize);
 271         }
 272
 273         if(len > c->sndbufsize - bufused)
 274                 len = c->sndbufsize - bufused;
 275
 276         if(!len) {
 277                 errno == EWOULDBLOCK;
 278                 return 0;
 279         }
 280
 281         memcpy(c->sndbuf + bufused, data, len);
 282
 283         // Send segments
 284
 285         struct {
 286                 struct hdr hdr;
 287                 char data[c->utcp->mtu];
 288         } pkt;
 289
 290         pkt.hdr.src = c->src;
 291         pkt.hdr.dst = c->dst;
 292         pkt.hdr.ack = c->rcv.nxt;
 293         pkt.hdr.wnd = c->snd.wnd;
 294         pkt.hdr.ctl = ACK;
 295
 296         uint32_t left = len;
 297
 298         while(left) {
 299                 uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
 300                 pkt.hdr.seq = c->snd.nxt;
 301
 302                 memcpy(pkt.data, data, seglen);
 303
 304                 c->snd.nxt += seglen;
 305                 data += seglen;
 306                 left -= seglen;
 307
 308                 print_packet(c->utcp, "send", &pkt, sizeof pkt.hdr + seglen);
 309                 c->utcp->send(c->utcp, &pkt, sizeof pkt.hdr + seglen);
 310         }
 311
 312         fprintf(stderr, "len=%zu\n", len);
 313         return len;
 314 }
 315
 316 static void swap_ports(struct hdr *hdr) {
 317         uint16_t tmp = hdr->src;
 318         hdr->src = hdr->dst;
 319         hdr->dst = tmp;
 320 }
 321
 322 int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 323         if(!utcp) {
 324                 errno = EFAULT;
 325                 return -1;
 326         }
 327
 328         if(!len)
 329                 return 0;
 330
 331         if(!data) {
 332                 errno = EFAULT;
 333                 return -1;
 334         }
 335
 336         print_packet(utcp, "recv", data, len);
 337
 338         // Drop packets smaller than the header
 339
 340         struct hdr hdr;
 341         if(len < sizeof hdr) {
 342                 errno = EBADMSG;
 343                 return -1;
 344         }
 345
 346         // Make a copy from the potentially unaligned data to a struct hdr
 347
 348         memcpy(&hdr, data, sizeof hdr);
 349         data += sizeof hdr;
 350         len -= sizeof hdr;
 351
 352         // Drop packets with an unknown CTL flag
 353
 354         if(hdr.ctl & ~(SYN | ACK | RST | FIN)) {
 355                 errno = EBADMSG;
 356                 return -1;
 357         }
 358
 359         // Try to match the packet to an existing connection
 360
 361         struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
 362
 363         // Is it for a new connection?
 364
 365         if(!c) {
 366                 // Ignore RST packets
 367
 368                 if(hdr.ctl & RST)
 369                         return 0;
 370
 371                 // Is it a SYN packet and are we LISTENing?
 372
 373                 if(hdr.ctl & SYN && !(hdr.ctl & ACK) && utcp->accept) {
 374                         // If we don't want to accept it, send a RST back
 375                         if((utcp->pre_accept && !utcp->pre_accept(utcp, hdr.dst))) {
 376                                 len = 1;
 377                                 goto reset;
 378                         }
 379
 380                         // Try to allocate memory, otherwise send a RST back
 381                         c = allocate_connection(utcp, hdr.dst, hdr.src);
 382                         if(!c) {
 383                                 len = 1;
 384                                 goto reset;
 385                         }
 386
 387                         // Return SYN+ACK, go to SYN_RECEIVED state
 388                         c->snd.wnd = hdr.wnd;
 389                         c->rcv.irs = hdr.seq;
 390                         c->rcv.nxt = c->rcv.irs + 1;
 391                         set_state(c, SYN_RECEIVED);
 392
 393                         hdr.dst = c->dst;
 394                         hdr.src = c->src;
 395                         hdr.ack = c->rcv.irs + 1;
 396                         hdr.seq = c->snd.iss;
 397                         hdr.ctl = SYN | ACK;
 398                         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 399                         utcp->send(utcp, &hdr, sizeof hdr);
 400                 } else {
 401                         // No, we don't want your packets, send a RST back
 402                         len = 1;
 403                         goto reset;
 404                 }
 405
 406                 return 0;
 407         }
 408
 409         fprintf(stderr, "%p state %s\n", c->utcp, strstate[c->state]);
 410
 411         // In case this is for a CLOSED connection, ignore the packet.
 412         // TODO: make it so incoming packets can never match a CLOSED connection.
 413
 414         if(c->state == CLOSED)
 415                 return 0;
 416
 417         // It is for an existing connection.
 418
 419         // 1. Drop invalid packets.
 420
 421         // 1a. Drop packets that should not happen in our current state.
 422
 423         switch(c->state) {
 424         case SYN_SENT:
 425         case SYN_RECEIVED:
 426         case ESTABLISHED:
 427         case FIN_WAIT_1:
 428         case FIN_WAIT_2:
 429         case CLOSE_WAIT:
 430         case CLOSING:
 431         case LAST_ACK:
 432         case TIME_WAIT:
 433                 break;
 434         default:
 435                 abort();
 436         }
 437
 438         // 1b. Drop packets with a sequence number not in our receive window.
 439
 440         bool acceptable;
 441
 442         if(c->state == SYN_SENT)
 443                 acceptable = true;
 444
 445         // TODO: handle packets overlapping c->rcv.nxt.
 446 #if 0
 447         // Only use this when accepting out-of-order packets.
 448         else if(len == 0)
 449                 if(c->rcv.wnd == 0)
 450                         acceptable = hdr.seq == c->rcv.nxt;
 451                 else
 452                         acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0);
 453         else
 454                 if(c->rcv.wnd == 0)
 455                         // We don't accept data when the receive window is zero.
 456                         acceptable = false;
 457                 else
 458                         // Both start and end of packet must be within the receive window
 459                         acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0)
 460                                 || (seqdiff(hdr.seq + len + 1, c->rcv.nxt) >= 0 && seqdiff(hdr.seq + len - 1, c->rcv.nxt + c->rcv.wnd) < 0);
 461 #else
 462         if(c->state != SYN_SENT)
 463                 acceptable = hdr.seq == c->rcv.nxt;
 464 #endif
 465
 466         if(!acceptable) {
 467                 fprintf(stderr, "Packet not acceptable, %u  <= %u + %zu < %u\n", c->rcv.nxt, hdr.seq, len, c->rcv.nxt + c->rcv.wnd);
 468                 // Ignore unacceptable RST packets.
 469                 if(hdr.ctl & RST)
 470                         return 0;
 471                 // Otherwise, send an ACK back in the hope things improve.
 472                 goto ack;
 473         }
 474
 475         c->snd.wnd = hdr.wnd; // TODO: move below
 476
 477         // 1c. Drop packets with an invalid ACK.
 478         // ackno should not roll back, and it should also not be bigger than snd.nxt.
 479
 480         if(hdr.ctl & ACK && (seqdiff(hdr.ack, c->snd.nxt) > 0 || seqdiff(hdr.ack, c->snd.una) < 0)) {
 481                 fprintf(stderr, "Packet ack seqno out of range, %u %u %u\n", hdr.ack, c->snd.una, c->snd.nxt);
 482                 // Ignore unacceptable RST packets.
 483                 if(hdr.ctl & RST)
 484                         return 0;
 485                 goto reset;
 486         }
 487
 488         // 2. Handle RST packets
 489
 490         if(hdr.ctl & RST) {
 491                 switch(c->state) {
 492                 case SYN_SENT:
 493                         if(!(hdr.ctl & ACK))
 494                                 return 0;
 495                         // The peer has refused our connection.
 496                         set_state(c, CLOSED);
 497                         errno = ECONNREFUSED;
 498                         if(c->recv)
 499                                 c->recv(c, NULL, 0);
 500                         return 0;
 501                 case SYN_RECEIVED:
 502                         if(hdr.ctl & ACK)
 503                                 return 0;
 504                         // We haven't told the application about this connection yet. Silently delete.
 505                         free_connection(c);
 506                         return 0;
 507                 case ESTABLISHED:
 508                 case FIN_WAIT_1:
 509                 case FIN_WAIT_2:
 510                 case CLOSE_WAIT:
 511                         if(hdr.ctl & ACK)
 512                                 return 0;
 513                         // The peer has aborted our connection.
 514                         set_state(c, CLOSED);
 515                         errno = ECONNRESET;
 516                         if(c->recv)
 517                                 c->recv(c, NULL, 0);
 518                         return 0;
 519                 case CLOSING:
 520                 case LAST_ACK:
 521                 case TIME_WAIT:
 522                         if(hdr.ctl & ACK)
 523                                 return 0;
 524                         // As far as the application is concerned, the connection has already been closed.
 525                         // If it has called utcp_close() already, we can immediately free this connection.
 526                         if(c->reapable) {
 527                                 free_connection(c);
 528                                 return 0;
 529                         }
 530                         // Otherwise, immediately move to the CLOSED state.
 531                         set_state(c, CLOSED);
 532                         return 0;
 533                 default:
 534                         abort();
 535                 }
 536         }
 537
 538         // 3. Advance snd.una
 539
 540         uint32_t advanced = seqdiff(hdr.ack, c->snd.una);
 541         c->snd.una = hdr.ack;
 542
 543         if(advanced) {
 544                 fprintf(stderr, "%p advanced %u\n", utcp, advanced);
 545                 // Make room in the send buffer.
 546                 // TODO: try to avoid memmoving too much. Circular buffer?
 547                 uint32_t left = seqdiff(c->snd.nxt, hdr.ack);
 548                 if(left)
 549                         memmove(c->sndbuf, c->sndbuf + advanced, left);
 550         }
 551
 552         // 4. Update timers
 553
 554         if(advanced) {
 555                 timerclear(&c->conn_timeout); // It should be set anew in utcp_timeout() if c->snd.una != c->snd.nxt.
 556                 if(c->snd.una == c->snd.nxt)
 557                         timerclear(&c->rtrx_timeout);
 558         }
 559
 560         // 5. Process SYN stuff
 561
 562         if(hdr.ctl & SYN) {
 563                 switch(c->state) {
 564                 case SYN_SENT:
 565                         // This is a SYNACK. It should always have ACKed the SYN.
 566                         if(!advanced)
 567                                 goto reset;
 568                         c->rcv.irs = hdr.seq;
 569                         c->rcv.nxt = hdr.seq;
 570                         set_state(c, ESTABLISHED);
 571                         // TODO: notify application of this somehow.
 572                         break;
 573                 case SYN_RECEIVED:
 574                 case ESTABLISHED:
 575                 case FIN_WAIT_1:
 576                 case FIN_WAIT_2:
 577                 case CLOSE_WAIT:
 578                 case CLOSING:
 579                 case LAST_ACK:
 580                 case TIME_WAIT:
 581                         // Ehm, no. We should never receive a second SYN.
 582                         goto reset;
 583                 default:
 584                         abort();
 585                 }
 586
 587                 // SYN counts as one sequence number
 588                 c->rcv.nxt++;
 589         }
 590
 591         // 6. Process new data
 592
 593         if(c->state == SYN_RECEIVED) {
 594                 // This is the ACK after the SYNACK. It should always have ACKed the SYNACK.
 595                 if(!advanced)
 596                         goto reset;
 597
 598                 // Are we still LISTENing?
 599                 if(utcp->accept)
 600                         utcp->accept(c, c->src);
 601
 602                 if(c->state != ESTABLISHED) {
 603                         set_state(c, CLOSED);
 604                         c->reapable = true;
 605                         goto reset;
 606                 }
 607         }
 608
 609         if(len) {
 610                 switch(c->state) {
 611                 case SYN_SENT:
 612                 case SYN_RECEIVED:
 613                         // This should never happen.
 614                         abort();
 615                 case ESTABLISHED:
 616                 case FIN_WAIT_1:
 617                 case FIN_WAIT_2:
 618                         break;
 619                 case CLOSE_WAIT:
 620                 case CLOSING:
 621                 case LAST_ACK:
 622                 case TIME_WAIT:
 623                         // Ehm no, We should never receive more data after a FIN.
 624                         goto reset;
 625                 default:
 626                         abort();
 627                 }
 628
 629                 int rxd;
 630
 631                 if(c->recv) {
 632                         rxd = c->recv(c, data, len);
 633                         if(rxd < 0)
 634                                 rxd = 0;
 635                         else if(rxd > len)
 636                                 rxd = len; // Bad application, bad!
 637                 } else {
 638                         rxd = len;
 639                 }
 640
 641                 c->rcv.nxt += len;
 642         }
 643
 644         // 7. Process FIN stuff
 645
 646         if(hdr.ctl & FIN) {
 647                 switch(c->state) {
 648                 case SYN_SENT:
 649                 case SYN_RECEIVED:
 650                         // This should never happen.
 651                         abort();
 652                 case ESTABLISHED:
 653                         set_state(c, CLOSE_WAIT);
 654                         break;
 655                 case FIN_WAIT_1:
 656                         set_state(c, CLOSING);
 657                         break;
 658                 case FIN_WAIT_2:
 659                         set_state(c, TIME_WAIT);
 660                         break;
 661                 case CLOSE_WAIT:
 662                 case CLOSING:
 663                 case LAST_ACK:
 664                 case TIME_WAIT:
 665                         // Ehm, no. We should never receive a second FIN.
 666                         goto reset;
 667                 default:
 668                         abort();
 669                 }
 670
 671                 // FIN counts as one sequence number
 672                 c->rcv.nxt++;
 673
 674                 // Inform the application that the peer closed the connection.
 675                 if(c->recv) {
 676                         errno = 0;
 677                         c->recv(c, NULL, 0);
 678                 }
 679         }
 680
 681         if(!len && !advanced)
 682                 return 0;
 683
 684         if(!len && !(hdr.ctl & SYN) && !(hdr.ctl & FIN))
 685                 return 0;
 686
 687 ack:
 688         hdr.src = c->src;
 689         hdr.dst = c->dst;
 690         hdr.seq = c->snd.nxt;
 691         hdr.ack = c->rcv.nxt;
 692         hdr.ctl = ACK;
 693         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 694         utcp->send(utcp, &hdr, sizeof hdr);
 695         return 0;
 696
 697 reset:
 698         swap_ports(&hdr);
 699         hdr.wnd = 0;
 700         if(hdr.ctl & ACK) {
 701                 hdr.seq = hdr.ack;
 702                 hdr.ctl = RST;
 703         } else {
 704                 hdr.ack = hdr.seq + len;
 705                 hdr.seq = 0;
 706                 hdr.ctl = RST | ACK;
 707         }
 708         print_packet(utcp, "send", &hdr, sizeof hdr);
 709         utcp->send(utcp, &hdr, sizeof hdr);
 710         return 0;
 711
 712 }
 713
 714 int utcp_shutdown(struct utcp_connection *c, int dir) {
 715         fprintf(stderr, "%p shutdown %d\n", c->utcp, dir);
 716         if(!c) {
 717                 errno = EFAULT;
 718                 return -1;
 719         }
 720
 721         if(c->reapable) {
 722                 fprintf(stderr, "Error: shutdown() called on closed connection %p\n", c);
 723                 errno = EBADF;
 724                 return -1;
 725         }
 726
 727         // TODO: handle dir
 728
 729         switch(c->state) {
 730         case CLOSED:
 731                 return 0;
 732         case LISTEN:
 733         case SYN_SENT:
 734                 set_state(c, CLOSED);
 735                 return 0;
 736
 737         case SYN_RECEIVED:
 738         case ESTABLISHED:
 739                 set_state(c, FIN_WAIT_1);
 740                 break;
 741         case FIN_WAIT_1:
 742         case FIN_WAIT_2:
 743                 return 0;
 744         case CLOSE_WAIT:
 745                 set_state(c, CLOSING);
 746                 break;
 747
 748         case CLOSING:
 749         case LAST_ACK:
 750         case TIME_WAIT:
 751                 return 0;
 752         }
 753
 754         // Send FIN
 755
 756         struct hdr hdr;
 757
 758         hdr.src = c->src;
 759         hdr.dst = c->dst;
 760         hdr.seq = c->snd.nxt;
 761         hdr.ack = c->rcv.nxt;
 762         hdr.wnd = c->snd.wnd;
 763         hdr.ctl = FIN | ACK;
 764
 765         c->snd.nxt += 1;
 766
 767         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 768         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 769         return 0;
 770 }
 771
 772 int utcp_close(struct utcp_connection *c) {
 773         if(utcp_shutdown(c, SHUT_RDWR))
 774                 return -1;
 775         c->reapable = true;
 776         return 0;
 777 }
 778
 779 int utcp_abort(struct utcp_connection *c) {
 780         if(!c) {
 781                 errno = EFAULT;
 782                 return -1;
 783         }
 784
 785         if(c->reapable) {
 786                 fprintf(stderr, "Error: abort() called on closed connection %p\n", c);
 787                 errno = EBADF;
 788                 return -1;
 789         }
 790
 791         c->reapable = true;
 792
 793         switch(c->state) {
 794         case CLOSED:
 795                 return 0;
 796         case LISTEN:
 797         case SYN_SENT:
 798         case CLOSING:
 799         case LAST_ACK:
 800         case TIME_WAIT:
 801                 set_state(c, CLOSED);
 802                 return 0;
 803
 804         case SYN_RECEIVED:
 805         case ESTABLISHED:
 806         case FIN_WAIT_1:
 807         case FIN_WAIT_2:
 808         case CLOSE_WAIT:
 809                 set_state(c, CLOSED);
 810                 break;
 811         }
 812
 813         // Send RST
 814
 815         struct hdr hdr;
 816
 817         hdr.src = c->src;
 818         hdr.dst = c->dst;
 819         hdr.seq = c->snd.nxt;
 820         hdr.ack = 0;
 821         hdr.wnd = 0;
 822         hdr.ctl = RST;
 823
 824         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 825         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 826         return 0;
 827 }
 828
 829 static void retransmit(struct utcp_connection *c) {
 830         if(c->state == CLOSED || c->snd.nxt == c->snd.una)
 831                 return;
 832
 833         struct utcp *utcp = c->utcp;
 834
 835         struct {
 836                 struct hdr hdr;
 837                 char data[c->utcp->mtu];
 838         } pkt;
 839
 840         pkt.hdr.src = c->src;
 841         pkt.hdr.dst = c->dst;
 842
 843         switch(c->state) {
 844                 case LISTEN:
 845                         // TODO: this should not happen
 846                         break;
 847
 848                 case SYN_SENT:
 849                         pkt.hdr.seq = c->snd.iss;
 850                         pkt.hdr.ack = 0;
 851                         pkt.hdr.wnd = c->rcv.wnd;
 852                         pkt.hdr.ctl = SYN;
 853                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr);
 854                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 855                         break;
 856
 857                 case SYN_RECEIVED:
 858                         pkt.hdr.seq = c->snd.nxt;
 859                         pkt.hdr.ack = c->rcv.nxt;
 860                         pkt.hdr.ctl = SYN | ACK;
 861                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr);
 862                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 863                         break;
 864
 865                 case ESTABLISHED:
 866                 case FIN_WAIT_1:
 867                         pkt.hdr.seq = c->snd.una;
 868                         pkt.hdr.ack = c->rcv.nxt;
 869                         pkt.hdr.ctl = ACK;
 870                         uint32_t len = seqdiff(c->snd.nxt, c->snd.una);
 871                         if(c->state == FIN_WAIT_1)
 872                                 len--;
 873                         if(len > utcp->mtu)
 874                                 len = utcp->mtu;
 875                         else {
 876                                 if(c->state == FIN_WAIT_1)
 877                                         pkt.hdr.ctl |= FIN;
 878                         }
 879                         memcpy(pkt.data, c->sndbuf, len);
 880                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr + len);
 881                         utcp->send(utcp, &pkt, sizeof pkt.hdr + len);
 882                         break;
 883
 884                 default:
 885                         // TODO: implement
 886                         abort();
 887         }
 888 }
 889
 890 /* Handle timeouts.
 891  * One call to this function will loop through all connections,
 892  * checking if something needs to be resent or not.
 893  * The return value is the time to the next timeout in milliseconds,
 894  * or maybe a negative value if the timeout is infinite.
 895  */
 896 int utcp_timeout(struct utcp *utcp) {
 897         struct timeval now;
 898         gettimeofday(&now, NULL);
 899         struct timeval next = {now.tv_sec + 3600, now.tv_usec};
 900
 901         for(int i = 0; i < utcp->nconnections; i++) {
 902                 struct utcp_connection *c = utcp->connections[i];
 903                 if(!c)
 904                         continue;
 905
 906                 if(c->state == CLOSED) {
 907                         if(c->reapable) {
 908                                 fprintf(stderr, "Reaping %p\n", c);
 909                                 free_connection(c);
 910                                 i--;
 911                         }
 912                         continue;
 913                 }
 914
 915                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &now, <)) {
 916                         errno = ETIMEDOUT;
 917                         c->state = CLOSED;
 918                         if(c->recv)
 919                                 c->recv(c, NULL, 0);
 920                         continue;
 921                 }
 922
 923                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &now, <)) {
 924                         retransmit(c);
 925                 }
 926
 927                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <))
 928                         next = c->conn_timeout;
 929
 930                 if(c->snd.nxt != c->snd.una) {
 931                         c->rtrx_timeout = now;
 932                         c->rtrx_timeout.tv_sec++;
 933                 } else {
 934                         timerclear(&c->rtrx_timeout);
 935                 }
 936
 937                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <))
 938                         next = c->rtrx_timeout;
 939         }
 940
 941         struct timeval diff;
 942         timersub(&next, &now, &diff);
 943         if(diff.tv_sec < 0)
 944                 return 0;
 945         return diff.tv_sec * 1000 + diff.tv_usec / 1000;
 946 }
 947
 948 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
 949         struct utcp *utcp = calloc(1, sizeof *utcp);
 950         if(!utcp)
 951                 return NULL;
 952
 953         if(!send) {
 954                 errno = EFAULT;
 955                 return NULL;
 956         }
 957
 958         utcp->accept = accept;
 959         utcp->pre_accept = pre_accept;
 960         utcp->send = send;
 961         utcp->priv = priv;
 962         utcp->mtu = 1000;
 963         utcp->timeout = 60;
 964
 965         return utcp;
 966 }
 967
 968 void utcp_exit(struct utcp *utcp) {
 969         if(!utcp)
 970                 return;
 971         for(int i = 0; i < utcp->nconnections; i++)
 972                 free_connection(utcp->connections[i]);
 973         free(utcp);
 974 }
 975
 976 uint16_t utcp_get_mtu(struct utcp *utcp) {
 977         return utcp->mtu;
 978 }
 979
 980 void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
 981         // TODO: handle overhead of the header
 982         utcp->mtu = mtu;
 983 }
 984
 985 int utcp_get_user_timeout(struct utcp *u) {
 986         return u->timeout;
 987 }
 988
 989 void utcp_set_user_timeout(struct utcp *u, int timeout) {
 990         u->timeout = timeout;
 991 }
 992
 993 size_t utcp_get_sndbuf(struct utcp_connection *c) {
 994         return c->maxsndbufsize;
 995 }
 996
 997 void utcp_set_sndbuf(struct utcp_connection *c, size_t size) {
 998         c->maxsndbufsize = size;
 999         if(c->maxsndbufsize != size)
1000                 c->maxsndbufsize = -1;
1001 }
1002
1003 bool utcp_get_nodelay(struct utcp_connection *c) {
1004         return c->nodelay;
1005 }
1006
1007 void utcp_set_nodelay(struct utcp_connection *c, bool nodelay) {
1008         c->nodelay = nodelay;
1009 }
1010
1011 bool utcp_get_keepalive(struct utcp_connection *c) {
1012         return c->keepalive;
1013 }
1014
1015 void utcp_set_keepalive(struct utcp_connection *c, bool keepalive) {
1016         c->keepalive = keepalive;
1017 }
1018
1019 size_t utcp_get_outq(struct utcp_connection *c) {
1020         return seqdiff(c->snd.nxt, c->snd.una);
1021 }