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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 iss;
  96         } snd;
  97
  98         struct {
  99                 uint32_t nxt;
 100                 uint32_t wnd;
 101                 uint32_t irs;
 102         } rcv;
 103
 104         utcp_recv_t recv;
 105
 106         struct timeval conn_timeout;
 107         struct timeval rtrx_timeout;
 108
 109         char *sndbuf;
 110         uint32_t sndbufsize;
 111 };
 112
 113 struct utcp {
 114         void *priv;
 115
 116         utcp_accept_t accept;
 117         utcp_pre_accept_t pre_accept;
 118         utcp_send_t send;
 119
 120         uint16_t mtu;
 121         int timeout;
 122
 123         struct utcp_connection **connections;
 124         int nconnections;
 125         int nallocated;
 126 };
 127
 128 static void set_state(struct utcp_connection *c, enum state state) {
 129         c->state = state;
 130         if(state == ESTABLISHED)
 131                 timerclear(&c->conn_timeout);
 132         fprintf(stderr, "%p new state: %s\n", c->utcp, strstate[state]);
 133 }
 134
 135 static void print_packet(struct utcp *utcp, const char *dir, const void *pkt, size_t len) {
 136         struct hdr hdr;
 137         if(len < sizeof hdr) {
 138                 fprintf(stderr, "%p %s: short packet (%zu bytes)\n", utcp, dir, len);
 139                 return;
 140         }
 141
 142         memcpy(&hdr, pkt, sizeof hdr);
 143         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);
 144         if(hdr.ctl & SYN)
 145                 fprintf(stderr, "SYN");
 146         if(hdr.ctl & RST)
 147                 fprintf(stderr, "RST");
 148         if(hdr.ctl & FIN)
 149                 fprintf(stderr, "FIN");
 150         if(hdr.ctl & ACK)
 151                 fprintf(stderr, "ACK");
 152
 153         if(len > sizeof hdr) {
 154                 fprintf(stderr, " data=");
 155                 for(int i = sizeof hdr; i < len; i++) {
 156                         const char *data = pkt;
 157                         fprintf(stderr, "%c", data[i] >= 32 ? data[i] : '.');
 158                 }
 159         }
 160
 161         fprintf(stderr, "\n");
 162 }
 163
 164 static inline void list_connections(struct utcp *utcp) {
 165         fprintf(stderr, "%p has %d connections:\n", utcp, utcp->nconnections);
 166         for(int i = 0; i < utcp->nconnections; i++)
 167                 fprintf(stderr, "  %u -> %u state %s\n", utcp->connections[i]->src, utcp->connections[i]->dst, strstate[utcp->connections[i]->state]);
 168 }
 169
 170 // Connections are stored in a sorted list.
 171 // This gives O(log(N)) lookup time, O(N log(N)) insertion time and O(N) deletion time.
 172
 173 static int compare(const void *va, const void *vb) {
 174         const struct utcp_connection *a = *(struct utcp_connection **)va;
 175         const struct utcp_connection *b = *(struct utcp_connection **)vb;
 176         if(!a->src || !b->src)
 177                 abort();
 178         int c = (int)a->src - (int)b->src;
 179         if(c)
 180                 return c;
 181         c = (int)a->dst - (int)b->dst;
 182         return c;
 183 }
 184
 185 static struct utcp_connection *find_connection(const struct utcp *utcp, uint16_t src, uint16_t dst) {
 186         if(!utcp->nconnections)
 187                 return NULL;
 188         struct utcp_connection key = {
 189                 .src = src,
 190                 .dst = dst,
 191         }, *keyp = &key;
 192         struct utcp_connection **match = bsearch(&keyp, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 193         return match ? *match : NULL;
 194 }
 195
 196 static void free_connection(struct utcp_connection *c) {
 197         struct utcp *utcp = c->utcp;
 198         struct utcp_connection **cp = bsearch(&c, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 199         if(!cp)
 200                 abort();
 201
 202         int i = cp - utcp->connections;
 203         memmove(cp + i, cp + i + 1, (utcp->nconnections - i - 1) * sizeof *cp);
 204         utcp->nconnections--;
 205
 206         free(c);
 207 }
 208
 209 static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t src, uint16_t dst) {
 210         // Check whether this combination of src and dst is free
 211
 212         if(src) {
 213                 if(find_connection(utcp, src, dst)) {
 214                         errno = EADDRINUSE;
 215                         return NULL;
 216                 }
 217         } else { // If src == 0, generate a random port number with the high bit set
 218                 if(utcp->nconnections >= 32767) {
 219                         errno = ENOMEM;
 220                         return NULL;
 221                 }
 222                 src = rand() | 0x8000;
 223                 while(find_connection(utcp, src, dst))
 224                         src++;
 225         }
 226
 227         // Allocate memory for the new connection
 228
 229         if(utcp->nconnections >= utcp->nallocated) {
 230                 if(!utcp->nallocated)
 231                         utcp->nallocated = 4;
 232                 else
 233                         utcp->nallocated *= 2;
 234                 struct utcp_connection **new_array = realloc(utcp->connections, utcp->nallocated * sizeof *utcp->connections);
 235                 if(!new_array) {
 236                         errno = ENOMEM;
 237                         return NULL;
 238                 }
 239                 utcp->connections = new_array;
 240         }
 241
 242         struct utcp_connection *c = calloc(1, sizeof *c);
 243         if(!c) {
 244                 errno = ENOMEM;
 245                 return NULL;
 246         }
 247
 248         // Fill in the details
 249
 250         c->src = src;
 251         c->dst = dst;
 252         c->snd.iss = rand();
 253         c->snd.una = c->snd.iss;
 254         c->snd.nxt = c->snd.iss + 1;
 255         c->rcv.wnd = utcp->mtu;
 256         c->utcp = utcp;
 257         c->sndbufsize = 65536;
 258         c->sndbuf = malloc(c->sndbufsize);
 259         if(!c->sndbuf)
 260                 c->sndbufsize = 0;
 261
 262         // Add it to the sorted list of connections
 263
 264         utcp->connections[utcp->nconnections++] = c;
 265         qsort(utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 266
 267         return c;
 268 }
 269
 270 struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
 271         struct utcp_connection *c = allocate_connection(utcp, 0, dst);
 272         if(!c)
 273                 return NULL;
 274
 275         c->recv = recv;
 276
 277         struct hdr hdr;
 278
 279         hdr.src = c->src;
 280         hdr.dst = c->dst;
 281         hdr.seq = c->snd.iss;
 282         hdr.ack = 0;
 283         hdr.ctl = SYN;
 284         hdr.wnd = c->rcv.wnd;
 285
 286         set_state(c, SYN_SENT);
 287
 288         print_packet(utcp, "send", &hdr, sizeof hdr);
 289         utcp->send(utcp, &hdr, sizeof hdr);
 290
 291         gettimeofday(&c->conn_timeout, NULL);
 292         c->conn_timeout.tv_sec += utcp->timeout;
 293
 294         return c;
 295 }
 296
 297 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 298         if(c->reapable || c->state != SYN_RECEIVED) {
 299                 fprintf(stderr, "Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
 300                 return;
 301         }
 302
 303         fprintf(stderr, "%p accepted, %p %p\n", c, recv, priv);
 304         c->recv = recv;
 305         c->priv = priv;
 306         set_state(c, ESTABLISHED);
 307 }
 308
 309 ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 310         if(c->reapable) {
 311                 fprintf(stderr, "Error: send() called on closed connection %p\n", c);
 312                 errno = EBADF;
 313                 return -1;
 314         }
 315
 316         switch(c->state) {
 317         case CLOSED:
 318         case LISTEN:
 319         case SYN_SENT:
 320         case SYN_RECEIVED:
 321                 fprintf(stderr, "Error: send() called on unconnected connection %p\n", c);
 322                 errno = ENOTCONN;
 323                 return -1;
 324         case ESTABLISHED:
 325         case CLOSE_WAIT:
 326                 break;
 327         case FIN_WAIT_1:
 328         case FIN_WAIT_2:
 329         case CLOSING:
 330         case LAST_ACK:
 331         case TIME_WAIT:
 332                 fprintf(stderr, "Error: send() called on closing connection %p\n", c);
 333                 errno = EPIPE;
 334                 return -1;
 335         }
 336
 337         // Add data to send buffer
 338
 339         if(!len)
 340                 return 0;
 341
 342         if(!data) {
 343                 errno = EFAULT;
 344                 return -1;
 345         }
 346
 347         uint32_t bufused = c->snd.nxt - c->snd.una;
 348
 349         if(len > c->sndbufsize - bufused)
 350                 len = c->sndbufsize - bufused;
 351
 352         memcpy(c->sndbuf + (c->snd.nxt - c->snd.una), data, len);
 353
 354         // Send segments
 355
 356         struct {
 357                 struct hdr hdr;
 358                 char data[c->utcp->mtu];
 359         } pkt;
 360
 361         pkt.hdr.src = c->src;
 362         pkt.hdr.dst = c->dst;
 363         pkt.hdr.ack = c->rcv.nxt;
 364         pkt.hdr.wnd = c->snd.wnd;
 365         pkt.hdr.ctl = ACK;
 366
 367         uint32_t left = len;
 368
 369         while(left) {
 370                 uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
 371                 pkt.hdr.seq = c->snd.nxt;
 372
 373                 memcpy(pkt.data, data, seglen);
 374
 375                 c->snd.nxt += seglen;
 376                 data += seglen;
 377                 left -= seglen;
 378
 379                 print_packet(c->utcp, "send", &pkt, sizeof pkt.hdr + seglen);
 380                 c->utcp->send(c->utcp, &pkt, sizeof pkt.hdr + seglen);
 381         }
 382
 383         fprintf(stderr, "len=%zu\n", len);
 384         return len;
 385 }
 386
 387 static void swap_ports(struct hdr *hdr) {
 388         uint16_t tmp = hdr->src;
 389         hdr->src = hdr->dst;
 390         hdr->dst = tmp;
 391 }
 392
 393 static int32_t seqdiff(uint32_t a, uint32_t b) {
 394         return a - b;
 395 }
 396
 397 int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 398         if(!utcp) {
 399                 errno = EFAULT;
 400                 return -1;
 401         }
 402
 403         if(!len)
 404                 return 0;
 405
 406         if(!data) {
 407                 errno = EFAULT;
 408                 return -1;
 409         }
 410
 411         print_packet(utcp, "recv", data, len);
 412
 413         // Drop packets smaller than the header
 414
 415         struct hdr hdr;
 416         if(len < sizeof hdr) {
 417                 errno = EBADMSG;
 418                 return -1;
 419         }
 420
 421         // Make a copy from the potentially unaligned data to a struct hdr
 422
 423         memcpy(&hdr, data, sizeof hdr);
 424         data += sizeof hdr;
 425         len -= sizeof hdr;
 426
 427         // Drop packets with an unknown CTL flag
 428
 429         if(hdr.ctl & ~(SYN | ACK | RST | FIN)) {
 430                 errno = EBADMSG;
 431                 return -1;
 432         }
 433
 434         // Try to match the packet to an existing connection
 435
 436         struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
 437
 438         // Is it for a new connection?
 439
 440         if(!c) {
 441                 // Ignore RST packets
 442
 443                 if(hdr.ctl & RST)
 444                         return 0;
 445
 446                 // Is it a SYN packet and are we LISTENing?
 447
 448                 if(hdr.ctl & SYN && !(hdr.ctl & ACK) && utcp->accept) {
 449                         // If we don't want to accept it, send a RST back
 450                         if((utcp->pre_accept && !utcp->pre_accept(utcp, hdr.dst))) {
 451                                 len = 1;
 452                                 goto reset;
 453                         }
 454
 455                         // Try to allocate memory, otherwise send a RST back
 456                         c = allocate_connection(utcp, hdr.dst, hdr.src);
 457                         if(!c) {
 458                                 len = 1;
 459                                 goto reset;
 460                         }
 461
 462                         // Return SYN+ACK, go to SYN_RECEIVED state
 463                         c->snd.wnd = hdr.wnd;
 464                         c->rcv.irs = hdr.seq;
 465                         c->rcv.nxt = c->rcv.irs + 1;
 466                         set_state(c, SYN_RECEIVED);
 467
 468                         hdr.dst = c->dst;
 469                         hdr.src = c->src;
 470                         hdr.ack = c->rcv.irs + 1;
 471                         hdr.seq = c->snd.iss;
 472                         hdr.ctl = SYN | ACK;
 473                         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 474                         utcp->send(utcp, &hdr, sizeof hdr);
 475                 } else {
 476                         // No, we don't want your packets, send a RST back
 477                         len = 1;
 478                         goto reset;
 479                 }
 480
 481                 return 0;
 482         }
 483
 484         fprintf(stderr, "%p state %s\n", c->utcp, strstate[c->state]);
 485
 486         // In case this is for a CLOSED connection, ignore the packet.
 487         // TODO: make it so incoming packets can never match a CLOSED connection.
 488
 489         if(c->state == CLOSED)
 490                 return 0;
 491
 492         // It is for an existing connection.
 493
 494         // 1. Drop invalid packets.
 495
 496         // 1a. Drop packets that should not happen in our current state.
 497
 498         switch(c->state) {
 499         case SYN_SENT:
 500         case SYN_RECEIVED:
 501         case ESTABLISHED:
 502         case FIN_WAIT_1:
 503         case FIN_WAIT_2:
 504         case CLOSE_WAIT:
 505         case CLOSING:
 506         case LAST_ACK:
 507         case TIME_WAIT:
 508                 break;
 509         default:
 510                 abort();
 511         }
 512
 513         // 1b. Drop packets with a sequence number not in our receive window.
 514
 515         bool acceptable;
 516
 517         if(c->state == SYN_SENT)
 518                 acceptable = true;
 519
 520         // TODO: handle packets overlapping c->rcv.nxt.
 521 #if 0
 522         // Only use this when accepting out-of-order packets.
 523         else if(len == 0)
 524                 if(c->rcv.wnd == 0)
 525                         acceptable = hdr.seq == c->rcv.nxt;
 526                 else
 527                         acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0);
 528         else
 529                 if(c->rcv.wnd == 0)
 530                         // We don't accept data when the receive window is zero.
 531                         acceptable = false;
 532                 else
 533                         // Both start and end of packet must be within the receive window
 534                         acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0)
 535                                 || (seqdiff(hdr.seq + len + 1, c->rcv.nxt) >= 0 && seqdiff(hdr.seq + len - 1, c->rcv.nxt + c->rcv.wnd) < 0);
 536 #else
 537         if(c->state != SYN_SENT)
 538                 acceptable = hdr.seq == c->rcv.nxt;
 539 #endif
 540
 541         if(!acceptable) {
 542                 fprintf(stderr, "Packet not acceptable, %u  <= %u + %zu < %u\n", c->rcv.nxt, hdr.seq, len, c->rcv.nxt + c->rcv.wnd);
 543                 // Ignore unacceptable RST packets.
 544                 if(hdr.ctl & RST)
 545                         return 0;
 546                 // Otherwise, send an ACK back in the hope things improve.
 547                 goto ack;
 548         }
 549
 550         c->snd.wnd = hdr.wnd; // TODO: move below
 551
 552         // 1c. Drop packets with an invalid ACK.
 553         // ackno should not roll back, and it should also not be bigger than snd.nxt.
 554
 555         if(hdr.ctl & ACK && (seqdiff(hdr.ack, c->snd.nxt) > 0 || seqdiff(hdr.ack, c->snd.una) < 0)) {
 556                 fprintf(stderr, "Packet ack seqno out of range, %u %u %u\n", hdr.ack, c->snd.una, c->snd.nxt);
 557                 // Ignore unacceptable RST packets.
 558                 if(hdr.ctl & RST)
 559                         return 0;
 560                 goto reset;
 561         }
 562
 563         // 2. Handle RST packets
 564
 565         if(hdr.ctl & RST) {
 566                 switch(c->state) {
 567                 case SYN_SENT:
 568                         if(!(hdr.ctl & ACK))
 569                                 return 0;
 570                         // The peer has refused our connection.
 571                         set_state(c, CLOSED);
 572                         errno = ECONNREFUSED;
 573                         if(c->recv)
 574                                 c->recv(c, NULL, 0);
 575                         return 0;
 576                 case SYN_RECEIVED:
 577                         if(hdr.ctl & ACK)
 578                                 return 0;
 579                         // We haven't told the application about this connection yet. Silently delete.
 580                         free_connection(c);
 581                         return 0;
 582                 case ESTABLISHED:
 583                 case FIN_WAIT_1:
 584                 case FIN_WAIT_2:
 585                 case CLOSE_WAIT:
 586                         if(hdr.ctl & ACK)
 587                                 return 0;
 588                         // The peer has aborted our connection.
 589                         set_state(c, CLOSED);
 590                         errno = ECONNRESET;
 591                         if(c->recv)
 592                                 c->recv(c, NULL, 0);
 593                         return 0;
 594                 case CLOSING:
 595                 case LAST_ACK:
 596                 case TIME_WAIT:
 597                         if(hdr.ctl & ACK)
 598                                 return 0;
 599                         // As far as the application is concerned, the connection has already been closed.
 600                         // If it has called utcp_close() already, we can immediately free this connection.
 601                         if(c->reapable) {
 602                                 free_connection(c);
 603                                 return 0;
 604                         }
 605                         // Otherwise, immediately move to the CLOSED state.
 606                         set_state(c, CLOSED);
 607                         return 0;
 608                 default:
 609                         abort();
 610                 }
 611         }
 612
 613         // 3. Advance snd.una
 614
 615         uint32_t advanced = seqdiff(hdr.ack, c->snd.una);
 616         c->snd.una = hdr.ack;
 617
 618         if(advanced) {
 619                 fprintf(stderr, "%p advanced %u\n", utcp, advanced);
 620                 // Make room in the send buffer.
 621                 // TODO: try to avoid memmoving too much. Circular buffer?
 622                 uint32_t left = seqdiff(c->snd.nxt, hdr.ack);
 623                 if(left)
 624                         memmove(c->sndbuf, c->sndbuf + advanced, left);
 625         }
 626
 627         // 4. Update timers
 628
 629         if(advanced) {
 630                 timerclear(&c->conn_timeout); // It should be set anew in utcp_timeout() if c->snd.una != c->snd.nxt.
 631                 if(c->snd.una == c->snd.nxt)
 632                         timerclear(&c->rtrx_timeout);
 633         }
 634
 635         // 5. Process SYN stuff
 636
 637         if(hdr.ctl & SYN) {
 638                 switch(c->state) {
 639                 case SYN_SENT:
 640                         // This is a SYNACK. It should always have ACKed the SYN.
 641                         if(!advanced)
 642                                 goto reset;
 643                         c->rcv.irs = hdr.seq;
 644                         c->rcv.nxt = hdr.seq;
 645                         set_state(c, ESTABLISHED);
 646                         // TODO: notify application of this somehow.
 647                         break;
 648                 case SYN_RECEIVED:
 649                 case ESTABLISHED:
 650                 case FIN_WAIT_1:
 651                 case FIN_WAIT_2:
 652                 case CLOSE_WAIT:
 653                 case CLOSING:
 654                 case LAST_ACK:
 655                 case TIME_WAIT:
 656                         // Ehm, no. We should never receive a second SYN.
 657                         goto reset;
 658                 default:
 659                         abort();
 660                 }
 661
 662                 // SYN counts as one sequence number
 663                 c->rcv.nxt++;
 664         }
 665
 666         // 6. Process new data
 667
 668         if(c->state == SYN_RECEIVED) {
 669                 // This is the ACK after the SYNACK. It should always have ACKed the SYNACK.
 670                 if(!advanced)
 671                         goto reset;
 672
 673                 // Are we still LISTENing?
 674                 if(utcp->accept)
 675                         utcp->accept(c, c->src);
 676
 677                 if(c->state != ESTABLISHED) {
 678                         set_state(c, CLOSED);
 679                         c->reapable = true;
 680                         goto reset;
 681                 }
 682         }
 683
 684         if(len) {
 685                 switch(c->state) {
 686                 case SYN_SENT:
 687                 case SYN_RECEIVED:
 688                         // This should never happen.
 689                         abort();
 690                 case ESTABLISHED:
 691                 case FIN_WAIT_1:
 692                 case FIN_WAIT_2:
 693                         break;
 694                 case CLOSE_WAIT:
 695                 case CLOSING:
 696                 case LAST_ACK:
 697                 case TIME_WAIT:
 698                         // Ehm no, We should never receive more data after a FIN.
 699                         goto reset;
 700                 default:
 701                         abort();
 702                 }
 703
 704                 int rxd;
 705
 706                 if(c->recv) {
 707                         rxd = c->recv(c, data, len);
 708                         if(rxd < 0)
 709                                 rxd = 0;
 710                         else if(rxd > len)
 711                                 rxd = len; // Bad application, bad!
 712                 } else {
 713                         rxd = len;
 714                 }
 715
 716                 c->rcv.nxt += len;
 717         }
 718
 719         // 7. Process FIN stuff
 720
 721         if(hdr.ctl & FIN) {
 722                 switch(c->state) {
 723                 case SYN_SENT:
 724                 case SYN_RECEIVED:
 725                         // This should never happen.
 726                         abort();
 727                 case ESTABLISHED:
 728                         set_state(c, CLOSE_WAIT);
 729                         break;
 730                 case FIN_WAIT_1:
 731                         set_state(c, CLOSING);
 732                         break;
 733                 case FIN_WAIT_2:
 734                         set_state(c, TIME_WAIT);
 735                         break;
 736                 case CLOSE_WAIT:
 737                 case CLOSING:
 738                 case LAST_ACK:
 739                 case TIME_WAIT:
 740                         // Ehm, no. We should never receive a second FIN.
 741                         goto reset;
 742                 default:
 743                         abort();
 744                 }
 745
 746                 // FIN counts as one sequence number
 747                 c->rcv.nxt++;
 748
 749                 // Inform the application that the peer closed the connection.
 750                 if(c->recv) {
 751                         errno = 0;
 752                         c->recv(c, NULL, 0);
 753                 }
 754         }
 755
 756         if(!len && !advanced)
 757                 return 0;
 758
 759         if(!len && !(hdr.ctl & SYN) && !(hdr.ctl & FIN))
 760                 return 0;
 761
 762 ack:
 763         hdr.src = c->src;
 764         hdr.dst = c->dst;
 765         hdr.seq = c->snd.nxt;
 766         hdr.ack = c->rcv.nxt;
 767         hdr.ctl = ACK;
 768         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 769         utcp->send(utcp, &hdr, sizeof hdr);
 770         return 0;
 771
 772 reset:
 773         swap_ports(&hdr);
 774         hdr.wnd = 0;
 775         if(hdr.ctl & ACK) {
 776                 hdr.seq = hdr.ack;
 777                 hdr.ctl = RST;
 778         } else {
 779                 hdr.ack = hdr.seq + len;
 780                 hdr.seq = 0;
 781                 hdr.ctl = RST | ACK;
 782         }
 783         print_packet(utcp, "send", &hdr, sizeof hdr);
 784         utcp->send(utcp, &hdr, sizeof hdr);
 785         return 0;
 786
 787 }
 788
 789 int utcp_shutdown(struct utcp_connection *c, int dir) {
 790         fprintf(stderr, "%p shutdown %d\n", c->utcp, dir);
 791         if(!c) {
 792                 errno = EFAULT;
 793                 return -1;
 794         }
 795
 796         if(c->reapable) {
 797                 fprintf(stderr, "Error: shutdown() called on closed connection %p\n", c);
 798                 errno = EBADF;
 799                 return -1;
 800         }
 801
 802         // TODO: handle dir
 803
 804         switch(c->state) {
 805         case CLOSED:
 806                 return 0;
 807         case LISTEN:
 808         case SYN_SENT:
 809                 set_state(c, CLOSED);
 810                 return 0;
 811
 812         case SYN_RECEIVED:
 813         case ESTABLISHED:
 814                 set_state(c, FIN_WAIT_1);
 815                 break;
 816         case FIN_WAIT_1:
 817         case FIN_WAIT_2:
 818                 return 0;
 819         case CLOSE_WAIT:
 820                 set_state(c, CLOSING);
 821                 break;
 822
 823         case CLOSING:
 824         case LAST_ACK:
 825         case TIME_WAIT:
 826                 return 0;
 827         }
 828
 829         // Send FIN
 830
 831         struct hdr hdr;
 832
 833         hdr.src = c->src;
 834         hdr.dst = c->dst;
 835         hdr.seq = c->snd.nxt;
 836         hdr.ack = c->rcv.nxt;
 837         hdr.wnd = c->snd.wnd;
 838         hdr.ctl = FIN | ACK;
 839
 840         c->snd.nxt += 1;
 841
 842         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 843         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 844         return 0;
 845 }
 846
 847 int utcp_close(struct utcp_connection *c) {
 848         if(utcp_shutdown(c, SHUT_RDWR))
 849                 return -1;
 850         c->reapable = true;
 851         return 0;
 852 }
 853
 854 int utcp_abort(struct utcp_connection *c) {
 855         if(!c) {
 856                 errno = EFAULT;
 857                 return -1;
 858         }
 859
 860         if(c->reapable) {
 861                 fprintf(stderr, "Error: abort() called on closed connection %p\n", c);
 862                 errno = EBADF;
 863                 return -1;
 864         }
 865
 866         c->reapable = true;
 867
 868         switch(c->state) {
 869         case CLOSED:
 870                 return 0;
 871         case LISTEN:
 872         case SYN_SENT:
 873         case CLOSING:
 874         case LAST_ACK:
 875         case TIME_WAIT:
 876                 set_state(c, CLOSED);
 877                 return 0;
 878
 879         case SYN_RECEIVED:
 880         case ESTABLISHED:
 881         case FIN_WAIT_1:
 882         case FIN_WAIT_2:
 883         case CLOSE_WAIT:
 884                 set_state(c, CLOSED);
 885                 break;
 886         }
 887
 888         // Send RST
 889
 890         struct hdr hdr;
 891
 892         hdr.src = c->src;
 893         hdr.dst = c->dst;
 894         hdr.seq = c->snd.nxt;
 895         hdr.ack = 0;
 896         hdr.wnd = 0;
 897         hdr.ctl = RST;
 898
 899         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 900         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 901         return 0;
 902 }
 903
 904 static void retransmit(struct utcp_connection *c) {
 905         if(c->state == CLOSED || c->snd.nxt == c->snd.una)
 906                 return;
 907
 908         struct utcp *utcp = c->utcp;
 909
 910         struct {
 911                 struct hdr hdr;
 912                 char data[c->utcp->mtu];
 913         } pkt;
 914
 915         pkt.hdr.src = c->src;
 916         pkt.hdr.dst = c->dst;
 917
 918         switch(c->state) {
 919                 case LISTEN:
 920                         // TODO: this should not happen
 921                         break;
 922
 923                 case SYN_SENT:
 924                         pkt.hdr.seq = c->snd.iss;
 925                         pkt.hdr.ack = 0;
 926                         pkt.hdr.wnd = c->rcv.wnd;
 927                         pkt.hdr.ctl = SYN;
 928                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr);
 929                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 930                         break;
 931
 932                 case SYN_RECEIVED:
 933                         pkt.hdr.seq = c->snd.nxt;
 934                         pkt.hdr.ack = c->rcv.nxt;
 935                         pkt.hdr.ctl = SYN | ACK;
 936                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr);
 937                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 938                         break;
 939
 940                 case ESTABLISHED:
 941                         pkt.hdr.seq = c->snd.una;
 942                         pkt.hdr.ack = c->rcv.nxt;
 943                         pkt.hdr.ctl = ACK;
 944                         uint32_t len = seqdiff(c->snd.nxt, c->snd.una);
 945                         if(len > utcp->mtu)
 946                                 len = utcp->mtu;
 947                         memcpy(pkt.data, c->sndbuf, len);
 948                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr + len);
 949                         utcp->send(utcp, &pkt, sizeof pkt.hdr + len);
 950                         break;
 951
 952                 default:
 953                         // TODO: implement
 954                         abort();
 955         }
 956 }
 957
 958 /* Handle timeouts.
 959  * One call to this function will loop through all connections,
 960  * checking if something needs to be resent or not.
 961  * The return value is the time to the next timeout in milliseconds,
 962  * or maybe a negative value if the timeout is infinite.
 963  */
 964 int utcp_timeout(struct utcp *utcp) {
 965         struct timeval now;
 966         gettimeofday(&now, NULL);
 967         struct timeval next = {now.tv_sec + 3600, now.tv_usec};
 968
 969         for(int i = 0; i < utcp->nconnections; i++) {
 970                 struct utcp_connection *c = utcp->connections[i];
 971                 if(!c)
 972                         continue;
 973
 974                 if(c->state == CLOSED) {
 975                         if(c->reapable) {
 976                                 fprintf(stderr, "Reaping %p\n", c);
 977                                 free_connection(c);
 978                                 i--;
 979                         }
 980                         continue;
 981                 }
 982
 983                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &now, <)) {
 984                         errno = ETIMEDOUT;
 985                         c->state = CLOSED;
 986                         if(c->recv)
 987                                 c->recv(c, NULL, 0);
 988                         continue;
 989                 }
 990
 991                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &now, <)) {
 992                         retransmit(c);
 993                 }
 994
 995                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <))
 996                         next = c->conn_timeout;
 997
 998                 if(c->snd.nxt != c->snd.una) {
 999                         c->rtrx_timeout = now;
1000                         c->rtrx_timeout.tv_sec++;
1001                 } else {
1002                         timerclear(&c->rtrx_timeout);
1003                 }
1004
1005                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <))
1006                         next = c->rtrx_timeout;
1007         }
1008
1009         struct timeval diff;
1010         timersub(&next, &now, &diff);
1011         if(diff.tv_sec < 0)
1012                 return 0;
1013         return diff.tv_sec * 1000 + diff.tv_usec / 1000;
1014 }
1015
1016 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
1017         struct utcp *utcp = calloc(1, sizeof *utcp);
1018         if(!utcp)
1019                 return NULL;
1020
1021         if(!send) {
1022                 errno = EFAULT;
1023                 return NULL;
1024         }
1025
1026         utcp->accept = accept;
1027         utcp->pre_accept = pre_accept;
1028         utcp->send = send;
1029         utcp->priv = priv;
1030         utcp->mtu = 1000;
1031         utcp->timeout = 60;
1032
1033         return utcp;
1034 }
1035
1036 void utcp_exit(struct utcp *utcp) {
1037         if(!utcp)
1038                 return;
1039         for(int i = 0; i < utcp->nconnections; i++)
1040                 free_connection(utcp->connections[i]);
1041         free(utcp);
1042 }
1043
1044 int utcp_set_connection_timeout(struct utcp *u, int timeout) {
1045         int prev = u->timeout;
1046         u->timeout = timeout;
1047         return prev;
1048 }