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   1 /*
   2     utcp.c -- Userspace TCP
   3     Copyright (C) 2014 Guus Sliepen <guus@tinc-vpn.org>
   4
   5     This program is free software; you can redistribute it and/or modify
   6     it under the terms of the GNU General Public License as published by
   7     the Free Software Foundation; either version 2 of the License, or
   8     (at your option) any later version.
   9
  10     This program is distributed in the hope that it will be useful,
  11     but WITHOUT ANY WARRANTY; without even the implied warranty of
  12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13     GNU General Public License for more details.
  14
  15     You should have received a copy of the GNU General Public License along
  16     with this program; if not, write to the Free Software Foundation, Inc.,
  17     51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  18 */
  19
  20 #define _GNU_SOURCE
  21
  22 #include <errno.h>
  23 #include <stdio.h>
  24 #include <stdlib.h>
  25 #include <stdint.h>
  26 #include <stdbool.h>
  27 #include <string.h>
  28 #include <unistd.h>
  29 #include <sys/time.h>
  30 #include <sys/socket.h>
  31
  32 #define UTCP_INTERNAL
  33 #include "utcp.h"
  34
  35 #define PREP(l) char pkt[(l) + sizeof struct hdr]; struct hdr *hdr = &pkt;
  36
  37 #define SYN 1
  38 #define ACK 2
  39 #define FIN 4
  40 #define RST 8
  41
  42 struct hdr {
  43         uint16_t src; // Source port
  44         uint16_t dst; // Destination port
  45         uint32_t seq; // Sequence number
  46         uint32_t ack; // Acknowledgement number
  47         uint32_t wnd; // Window size
  48         uint16_t ctl; // Flags (SYN, ACK, FIN, RST)
  49         uint16_t aux; // other stuff
  50 };
  51
  52 enum state {
  53         CLOSED,
  54         LISTEN,
  55         SYN_SENT,
  56         SYN_RECEIVED,
  57         ESTABLISHED,
  58         FIN_WAIT_1,
  59         FIN_WAIT_2,
  60         CLOSE_WAIT,
  61         CLOSING,
  62         LAST_ACK,
  63         TIME_WAIT
  64 };
  65
  66 const char *strstate[] = {
  67         "CLOSED",
  68         "LISTEN",
  69         "SYN_SENT",
  70         "SYN_RECEIVED",
  71         "ESTABLISHED",
  72         "FIN_WAIT_1",
  73         "FIN_WAIT_2",
  74         "CLOSE_WAIT",
  75         "CLOSING",
  76         "LAST_ACK",
  77         "TIME_WAIT"
  78 };
  79
  80 struct utcp_connection {
  81         void *priv;
  82         struct utcp *utcp;
  83         bool reapable;
  84
  85         uint16_t src;
  86         uint16_t dst;
  87         enum state state;
  88
  89         // The following two structures form the TCB
  90
  91         struct {
  92                 uint32_t una;
  93                 uint32_t nxt;
  94                 uint32_t wnd;
  95                 uint32_t up;
  96                 uint32_t wl1;
  97                 uint32_t wl2;
  98                 uint32_t iss;
  99         } snd;
 100
 101         struct {
 102                 uint32_t nxt;
 103                 uint32_t wnd;
 104                 uint32_t up;
 105                 uint32_t irs;
 106         } rcv;
 107
 108         utcp_recv_t recv;
 109
 110         struct timeval conn_timeout;
 111         struct timeval rtrx_timeout;
 112
 113         char *sndbuf;
 114         uint32_t sndbufsize;
 115 };
 116
 117 struct utcp {
 118         void *priv;
 119
 120         utcp_accept_t accept;
 121         utcp_pre_accept_t pre_accept;
 122         utcp_send_t send;
 123
 124         uint16_t mtu;
 125         int timeout;
 126
 127         struct utcp_connection **connections;
 128         int nconnections;
 129         int nallocated;
 130 };
 131
 132 static void set_state(struct utcp_connection *c, enum state state) {
 133         c->state = state;
 134         if(state == ESTABLISHED)
 135                 timerclear(&c->conn_timeout);
 136         fprintf(stderr, "%p new state: %s\n", c->utcp, strstate[state]);
 137 }
 138
 139 static void print_packet(struct utcp *utcp, const char *dir, const void *pkt, size_t len) {
 140         struct hdr hdr;
 141         if(len < sizeof hdr) {
 142                 fprintf(stderr, "%p %s: short packet (%zu bytes)\n", utcp, dir, len);
 143                 return;
 144         }
 145
 146         memcpy(&hdr, pkt, sizeof hdr);
 147         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);
 148         if(hdr.ctl & SYN)
 149                 fprintf(stderr, "SYN");
 150         if(hdr.ctl & RST)
 151                 fprintf(stderr, "RST");
 152         if(hdr.ctl & FIN)
 153                 fprintf(stderr, "FIN");
 154         if(hdr.ctl & ACK)
 155                 fprintf(stderr, "ACK");
 156
 157         if(len > sizeof hdr) {
 158                 fprintf(stderr, " data=");
 159                 for(int i = sizeof hdr; i < len; i++) {
 160                         const char *data = pkt;
 161                         fprintf(stderr, "%c", data[i] >= 32 ? data[i] : '.');
 162                 }
 163         }
 164
 165         fprintf(stderr, "\n");
 166 }
 167
 168 static inline void list_connections(struct utcp *utcp) {
 169         fprintf(stderr, "%p has %d connections:\n", utcp, utcp->nconnections);
 170         for(int i = 0; i < utcp->nconnections; i++)
 171                 fprintf(stderr, "  %u -> %u state %s\n", utcp->connections[i]->src, utcp->connections[i]->dst, strstate[utcp->connections[i]->state]);
 172 }
 173
 174 // Connections are stored in a sorted list.
 175 // This gives O(log(N)) lookup time, O(N log(N)) insertion time and O(N) deletion time.
 176
 177 static int compare(const void *va, const void *vb) {
 178         const struct utcp_connection *a = *(struct utcp_connection **)va;
 179         const struct utcp_connection *b = *(struct utcp_connection **)vb;
 180         if(!a->src || !b->src)
 181                 abort();
 182         int c = (int)a->src - (int)b->src;
 183         if(c)
 184                 return c;
 185         c = (int)a->dst - (int)b->dst;
 186         return c;
 187 }
 188
 189 static struct utcp_connection *find_connection(const struct utcp *utcp, uint16_t src, uint16_t dst) {
 190         if(!utcp->nconnections)
 191                 return NULL;
 192         struct utcp_connection key = {
 193                 .src = src,
 194                 .dst = dst,
 195         }, *keyp = &key;
 196         struct utcp_connection **match = bsearch(&keyp, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 197         return match ? *match : NULL;
 198 }
 199
 200 static void free_connection(struct utcp_connection *c) {
 201         struct utcp *utcp = c->utcp;
 202         struct utcp_connection **cp = bsearch(&c, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 203         if(!cp)
 204                 abort();
 205
 206         int i = cp - utcp->connections;
 207         memmove(cp + i, cp + i + 1, (utcp->nconnections - i - 1) * sizeof *cp);
 208         utcp->nconnections--;
 209
 210         free(c);
 211 }
 212
 213 static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t src, uint16_t dst) {
 214         // Check whether this combination of src and dst is free
 215
 216         if(src) {
 217                 if(find_connection(utcp, src, dst)) {
 218                         errno = EADDRINUSE;
 219                         return NULL;
 220                 }
 221         } else { // If src == 0, generate a random port number with the high bit set
 222                 if(utcp->nconnections >= 32767) {
 223                         errno = ENOMEM;
 224                         return NULL;
 225                 }
 226                 src = rand() | 0x8000;
 227                 while(find_connection(utcp, src, dst))
 228                         src++;
 229         }
 230
 231         // Allocate memory for the new connection
 232
 233         if(utcp->nconnections >= utcp->nallocated) {
 234                 if(!utcp->nallocated)
 235                         utcp->nallocated = 4;
 236                 else
 237                         utcp->nallocated *= 2;
 238                 struct utcp_connection **new_array = realloc(utcp->connections, utcp->nallocated * sizeof *utcp->connections);
 239                 if(!new_array) {
 240                         errno = ENOMEM;
 241                         return NULL;
 242                 }
 243                 utcp->connections = new_array;
 244         }
 245
 246         struct utcp_connection *c = calloc(1, sizeof *c);
 247         if(!c) {
 248                 errno = ENOMEM;
 249                 return NULL;
 250         }
 251
 252         // Fill in the details
 253
 254         c->src = src;
 255         c->dst = dst;
 256         c->snd.iss = rand();
 257         c->snd.una = c->snd.iss;
 258         c->snd.nxt = c->snd.iss + 1;
 259         c->rcv.wnd = utcp->mtu;
 260         c->utcp = utcp;
 261         c->sndbufsize = 65536;
 262         c->sndbuf = malloc(c->sndbufsize);
 263         if(!c->sndbuf)
 264                 c->sndbufsize = 0;
 265
 266         // Add it to the sorted list of connections
 267
 268         utcp->connections[utcp->nconnections++] = c;
 269         qsort(utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 270
 271         return c;
 272 }
 273
 274 struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
 275         struct utcp_connection *c = allocate_connection(utcp, 0, dst);
 276         if(!c)
 277                 return NULL;
 278
 279         c->recv = recv;
 280
 281         struct hdr hdr;
 282
 283         hdr.src = c->src;
 284         hdr.dst = c->dst;
 285         hdr.seq = c->snd.iss;
 286         hdr.ack = 0;
 287         hdr.ctl = SYN;
 288         hdr.wnd = c->rcv.wnd;
 289
 290         set_state(c, SYN_SENT);
 291
 292         print_packet(utcp, "send", &hdr, sizeof hdr);
 293         utcp->send(utcp, &hdr, sizeof hdr);
 294
 295         gettimeofday(&c->conn_timeout, NULL);
 296         c->conn_timeout.tv_sec += utcp->timeout;
 297
 298         return c;
 299 }
 300
 301 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 302         if(c->reapable || c->state != SYN_RECEIVED) {
 303                 fprintf(stderr, "Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
 304                 return;
 305         }
 306
 307         fprintf(stderr, "%p accepted, %p %p\n", c, recv, priv);
 308         c->recv = recv;
 309         c->priv = priv;
 310         set_state(c, ESTABLISHED);
 311 }
 312
 313 ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 314         if(c->reapable) {
 315                 fprintf(stderr, "Error: send() called on closed connection %p\n", c);
 316                 errno = EBADF;
 317                 return -1;
 318         }
 319
 320         switch(c->state) {
 321         case CLOSED:
 322         case LISTEN:
 323         case SYN_SENT:
 324         case SYN_RECEIVED:
 325                 fprintf(stderr, "Error: send() called on unconnected connection %p\n", c);
 326                 errno = ENOTCONN;
 327                 return -1;
 328         case ESTABLISHED:
 329         case CLOSE_WAIT:
 330                 break;
 331         case FIN_WAIT_1:
 332         case FIN_WAIT_2:
 333         case CLOSING:
 334         case LAST_ACK:
 335         case TIME_WAIT:
 336                 fprintf(stderr, "Error: send() called on closing connection %p\n", c);
 337                 errno = EPIPE;
 338                 return -1;
 339         }
 340
 341         // Add data to send buffer
 342
 343         if(!len)
 344                 return 0;
 345
 346         if(!data) {
 347                 errno = EFAULT;
 348                 return -1;
 349         }
 350
 351         uint32_t bufused = c->snd.nxt - c->snd.una;
 352
 353         if(len > c->sndbufsize - bufused)
 354                 len = c->sndbufsize - bufused;
 355
 356         memcpy(c->sndbuf + (c->snd.nxt - c->snd.una), data, len);
 357
 358         // Send segments
 359
 360         struct {
 361                 struct hdr hdr;
 362                 char data[c->utcp->mtu];
 363         } pkt;
 364
 365         pkt.hdr.src = c->src;
 366         pkt.hdr.dst = c->dst;
 367         pkt.hdr.ack = c->rcv.nxt;
 368         pkt.hdr.wnd = c->snd.wnd;
 369         pkt.hdr.ctl = ACK;
 370
 371         uint32_t left = len;
 372
 373         while(left) {
 374                 uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
 375                 pkt.hdr.seq = c->snd.nxt;
 376
 377                 memcpy(pkt.data, data, seglen);
 378
 379                 c->snd.nxt += seglen;
 380                 data += seglen;
 381                 left -= seglen;
 382
 383                 print_packet(c->utcp, "send", &pkt, sizeof pkt.hdr + seglen);
 384                 c->utcp->send(c->utcp, &pkt, sizeof pkt.hdr + seglen);
 385         }
 386
 387         fprintf(stderr, "len=%zu\n", len);
 388         return len;
 389 }
 390
 391 static void swap_ports(struct hdr *hdr) {
 392         uint16_t tmp = hdr->src;
 393         hdr->src = hdr->dst;
 394         hdr->dst = tmp;
 395 }
 396
 397 static int32_t seqdiff(uint32_t a, uint32_t b) {
 398         return a - b;
 399 }
 400
 401 int utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 402         if(!utcp) {
 403                 errno = EFAULT;
 404                 return -1;
 405         }
 406
 407         if(!len)
 408                 return 0;
 409
 410         if(!data) {
 411                 errno = EFAULT;
 412                 return -1;
 413         }
 414
 415         print_packet(utcp, "recv", data, len);
 416
 417         struct hdr hdr;
 418         if(len < sizeof hdr) {
 419                 errno = EBADMSG;
 420                 return -1;
 421         }
 422
 423         memcpy(&hdr, data, sizeof hdr);
 424         data += sizeof hdr;
 425         len -= sizeof hdr;
 426
 427         if(hdr.ctl & ~(SYN | ACK | RST | FIN)) {
 428                 errno = EBADMSG;
 429                 return -1;
 430         }
 431
 432         //list_connections(utcp);
 433
 434         struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
 435
 436         // Is it for a new connection?
 437
 438         if(!c) {
 439                 if(hdr.ctl & RST)
 440                         return 0;
 441
 442                 if(hdr.ctl & SYN && !(hdr.ctl & ACK) && utcp->accept && (!utcp->pre_accept || utcp->pre_accept(utcp, hdr.dst)) && (c = allocate_connection(utcp, hdr.dst, hdr.src))) { // LISTEN
 443                         // Return SYN+ACK
 444                         c->snd.wnd = hdr.wnd;
 445                         c->rcv.irs = hdr.seq;
 446                         c->rcv.nxt = c->rcv.irs + 1;
 447                         set_state(c, SYN_RECEIVED);
 448
 449                         hdr.dst = c->dst;
 450                         hdr.src = c->src;
 451                         hdr.ack = c->rcv.irs + 1;
 452                         hdr.seq = c->snd.iss;
 453                         hdr.ctl = SYN | ACK;
 454                         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 455                         utcp->send(utcp, &hdr, sizeof hdr);
 456                         return 0;
 457                 } else { // CLOSED
 458                         len = 1;
 459                         goto reset;
 460                 }
 461         }
 462
 463         fprintf(stderr, "%p state %s\n", c->utcp, strstate[c->state]);
 464
 465         if(c->state == CLOSED) {
 466                 fprintf(stderr, "Error: packet recv()d on closed connection %p\n", c);
 467                 errno = EBADF;
 468                 return -1;
 469         }
 470
 471         // It is for an existing connection.
 472
 473         if(c->state == SYN_SENT) {
 474                 if(hdr.ctl & ACK) {
 475                         if(seqdiff(hdr.ack, c->snd.iss) <= 0 || seqdiff(hdr.ack, c->snd.nxt) > 0) {
 476                                 fprintf(stderr, "Invalid ACK, %u %u %u\n", hdr.ack, c->snd.iss, c->snd.nxt);
 477                                 goto reset;
 478                         }
 479                 }
 480                 if(hdr.ctl & RST) {
 481                         if(!(hdr.ctl & ACK))
 482                                 return 0;
 483                         set_state(c, CLOSED);
 484                         errno = ECONNREFUSED;
 485                         if(c->recv)
 486                                 c->recv(c, NULL, 0);
 487                         return 0;
 488                 }
 489                 if(hdr.ctl & SYN) {
 490                         c->dst = hdr.src;
 491                         c->rcv.nxt = hdr.seq + 1;
 492                         c->rcv.irs = hdr.seq;
 493                         c->snd.wnd = hdr.wnd;
 494
 495                         if(hdr.ctl & ACK)
 496                                 c->snd.una = hdr.ack;
 497                         if(seqdiff(c->snd.una, c->snd.iss) > 0) {
 498                                 set_state(c, ESTABLISHED);
 499                                 // TODO: signal app?
 500                                 swap_ports(&hdr);
 501                                 hdr.seq = c->snd.nxt;
 502                                 hdr.ack = c->rcv.nxt;
 503                                 hdr.ctl = ACK;
 504                         } else {
 505                                 set_state(c, SYN_RECEIVED);
 506                                 swap_ports(&hdr);
 507                                 hdr.seq = c->snd.iss;
 508                                 hdr.ack = c->rcv.nxt;
 509                                 hdr.ctl = SYN | ACK;
 510                         }
 511                         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 512                         utcp->send(utcp, &hdr, sizeof hdr);
 513                         // TODO: queue any data?
 514                 }
 515
 516                 return 0;
 517         }
 518
 519         bool acceptable;
 520
 521         if(len == 0)
 522                 if(c->rcv.wnd == 0)
 523                         acceptable = hdr.seq == c->rcv.nxt;
 524                 else
 525                         acceptable = (hdr.seq >= c->rcv.nxt && hdr.seq < c->rcv.nxt + c->rcv.wnd);
 526         else
 527                 if(c->rcv.wnd == 0)
 528                         acceptable = false;
 529                 else
 530                         acceptable = (hdr.seq >= c->rcv.nxt && hdr.seq < c->rcv.nxt + c->rcv.wnd)
 531                                 || (hdr.seq + len - 1 >= c->rcv.nxt && hdr.seq + len - 1 < c->rcv.nxt + c->rcv.wnd);
 532
 533         if(!acceptable) {
 534                 fprintf(stderr, "Packet not acceptable, %u %u %u %zu\n", hdr.seq, c->rcv.nxt, c->rcv.wnd, len);
 535                 if(hdr.ctl & RST)
 536                         return 0;
 537                 goto ack_and_drop;
 538         }
 539
 540         c->snd.wnd = hdr.wnd;
 541
 542         // TODO: check whether segment really starts at rcv.nxt, otherwise trim it.
 543
 544         if(hdr.ctl & RST) {
 545                 switch(c->state) {
 546                 case SYN_RECEIVED:
 547                         // TODO: delete connection?
 548                         break;
 549                 case ESTABLISHED:
 550                 case FIN_WAIT_1:
 551                 case FIN_WAIT_2:
 552                 case CLOSE_WAIT:
 553                         set_state(c, CLOSED);
 554                         errno = ECONNRESET;
 555                         if(c->recv)
 556                                 c->recv(c, NULL, 0);
 557                         break;
 558                 case CLOSING:
 559                 case LAST_ACK:
 560                 case TIME_WAIT:
 561                         // TODO: delete connection?
 562                         break;
 563                 default:
 564                         // TODO: wtf?
 565                         return 0;
 566                 }
 567                 set_state(c, CLOSED);
 568                 return 0;
 569         }
 570
 571         if(hdr.ctl & SYN) {
 572                 switch(c->state) {
 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                         set_state(c, CLOSED);
 582                         errno = ECONNRESET;
 583                         if(c->recv)
 584                                 c->recv(c, NULL, 0);
 585                         goto reset;
 586                         break;
 587                 default:
 588                         // TODO: wtf?
 589                         return 0;
 590                 }
 591         }
 592
 593         if(!(hdr.ctl & ACK))
 594                 return 0;
 595
 596         switch(c->state) {
 597         case SYN_RECEIVED:
 598                 if(seqdiff(hdr.ack, c->snd.una) >= 0 && seqdiff(hdr.ack, c->snd.nxt) <= 0)
 599                         c->utcp->accept(c, hdr.dst);
 600
 601                 if(c->state != ESTABLISHED)
 602                         goto reset;
 603
 604                 c->snd.una = hdr.ack;
 605                 break;
 606         case ESTABLISHED:
 607         case CLOSE_WAIT:
 608                 if(seqdiff(hdr.ack, c->snd.una) < 0)
 609                         return 0;
 610                 if(seqdiff(hdr.ack, c->snd.nxt) > 0)
 611                         goto ack_and_drop;
 612                 if(seqdiff(hdr.ack, c->snd.una) > 0 && seqdiff(hdr.ack, c->snd.nxt) <= 0) {
 613                         c->snd.una = hdr.ack;
 614                         if(seqdiff(c->snd.wl1, hdr.seq) < 0 || (c->snd.wl1 == hdr.seq && seqdiff(c->snd.wl2, hdr.ack) <= 0)) {
 615                                 c->snd.wnd = hdr.wnd;
 616                                 c->snd.wl1 = hdr.seq;
 617                                 c->snd.wl2 = hdr.ack;
 618                         }
 619                 }
 620                 break;
 621         case FIN_WAIT_1:
 622                 if(hdr.ack == c->snd.nxt)
 623                         set_state(c, FIN_WAIT_2);
 624                 break;
 625         case FIN_WAIT_2:
 626                 // TODO: If nothing left to send, close.
 627                 break;
 628         case CLOSING:
 629                 if(hdr.ack == c->snd.nxt) {
 630                         set_state(c, TIME_WAIT);
 631                 }
 632                 break;
 633         case LAST_ACK:
 634                 if(hdr.ack == c->snd.nxt) {
 635                         set_state(c, CLOSED);
 636                 }
 637                 return 0;
 638         case TIME_WAIT:
 639                 // TODO: retransmission of remote FIN, ACK and restart 2 MSL timeout
 640                 break;
 641         default:
 642                 goto reset;
 643         }
 644
 645         // Process data
 646
 647         switch(c->state) {
 648         case ESTABLISHED:
 649         case FIN_WAIT_1:
 650         case FIN_WAIT_2:
 651                 // TODO: process the data, see page 74
 652                 break;
 653         case CLOSE_WAIT:
 654         case CLOSING:
 655         case LAST_ACK:
 656         case TIME_WAIT:
 657                 break;
 658         default:
 659                 abort();
 660         }
 661
 662         if(hdr.ctl & FIN) {
 663                 switch(c->state) {
 664                 case CLOSED:
 665                 case LISTEN:
 666                 case SYN_SENT:
 667                         return 0;
 668                 case SYN_RECEIVED:
 669                 case ESTABLISHED:
 670                         set_state(c, CLOSE_WAIT);
 671                         c->rcv.nxt++;
 672                         goto ack_and_drop;
 673                 case FIN_WAIT_1:
 674                         set_state(c, CLOSING);
 675                         c->rcv.nxt++;
 676                         goto ack_and_drop;
 677                 case FIN_WAIT_2:
 678                         set_state(c, TIME_WAIT);
 679                         c->rcv.nxt++;
 680                         goto ack_and_drop;
 681                 case CLOSE_WAIT:
 682                 case CLOSING:
 683                 case LAST_ACK:
 684                 case TIME_WAIT:
 685                         break;
 686                 default:
 687                         abort();
 688                 }
 689         }
 690
 691         // Process the data
 692
 693         if(len && c->recv) {
 694                 c->recv(c, data, len);
 695                 c->rcv.nxt += len;
 696                 goto ack_and_drop;
 697         }
 698
 699         return 0;
 700
 701 reset:
 702         swap_ports(&hdr);
 703         hdr.wnd = 0;
 704         if(hdr.ctl & ACK) {
 705                 hdr.seq = hdr.ack;
 706                 hdr.ctl = RST;
 707         } else {
 708                 hdr.ack = hdr.seq + len;
 709                 hdr.seq = 0;
 710                 hdr.ctl = RST | ACK;
 711         }
 712         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 713         utcp->send(utcp, &hdr, sizeof hdr);
 714         return 0;
 715
 716 ack_and_drop:
 717         swap_ports(&hdr);
 718         hdr.seq = c->snd.nxt;
 719         hdr.ack = c->rcv.nxt;
 720         hdr.ctl = ACK;
 721         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 722         utcp->send(utcp, &hdr, sizeof hdr);
 723         if(c->state == CLOSE_WAIT || c->state == TIME_WAIT) {
 724                 errno = 0;
 725                 if(c->recv)
 726                         c->recv(c, NULL, 0);
 727         }
 728         return 0;
 729 }
 730
 731 int utcp_shutdown(struct utcp_connection *c, int dir) {
 732         if(!c) {
 733                 errno = EFAULT;
 734                 return -1;
 735         }
 736
 737         if(c->reapable) {
 738                 fprintf(stderr, "Error: shutdown() called on closed connection %p\n", c);
 739                 errno = EBADF;
 740                 return -1;
 741         }
 742
 743         // TODO: handle dir
 744
 745         switch(c->state) {
 746         case CLOSED:
 747                 return 0;
 748         case LISTEN:
 749         case SYN_SENT:
 750                 set_state(c, CLOSED);
 751                 return 0;
 752
 753         case SYN_RECEIVED:
 754         case ESTABLISHED:
 755                 set_state(c, FIN_WAIT_1);
 756                 break;
 757         case FIN_WAIT_1:
 758         case FIN_WAIT_2:
 759                 return 0;
 760         case CLOSE_WAIT:
 761                 set_state(c, LAST_ACK);
 762                 break;
 763
 764         case CLOSING:
 765         case LAST_ACK:
 766         case TIME_WAIT:
 767                 return 0;
 768         }
 769
 770         // Send FIN
 771
 772         struct hdr hdr;
 773
 774         hdr.src = c->src;
 775         hdr.dst = c->dst;
 776         hdr.seq = c->snd.nxt;
 777         hdr.ack = c->rcv.nxt;
 778         hdr.wnd = c->snd.wnd;
 779         hdr.ctl = FIN | ACK;
 780
 781         c->snd.nxt += 1;
 782
 783         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 784         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 785         return 0;
 786 }
 787
 788 int utcp_close(struct utcp_connection *c) {
 789         if(utcp_shutdown(c, SHUT_RDWR))
 790                 return -1;
 791         c->reapable = true;
 792         return 0;
 793 }
 794
 795 int utcp_abort(struct utcp_connection *c) {
 796         if(!c) {
 797                 errno = EFAULT;
 798                 return -1;
 799         }
 800
 801         if(c->reapable) {
 802                 fprintf(stderr, "Error: abort() called on closed connection %p\n", c);
 803                 errno = EBADF;
 804                 return -1;
 805         }
 806
 807         c->reapable = true;
 808
 809         switch(c->state) {
 810         case CLOSED:
 811                 return 0;
 812         case LISTEN:
 813         case SYN_SENT:
 814         case CLOSING:
 815         case LAST_ACK:
 816         case TIME_WAIT:
 817                 set_state(c, CLOSED);
 818                 return 0;
 819
 820         case SYN_RECEIVED:
 821         case ESTABLISHED:
 822         case FIN_WAIT_1:
 823         case FIN_WAIT_2:
 824         case CLOSE_WAIT:
 825                 set_state(c, CLOSED);
 826                 break;
 827         }
 828
 829         // Send RST
 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 = 0;
 837         hdr.wnd = 0;
 838         hdr.ctl = RST;
 839
 840         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 841         c->utcp->send(c->utcp, &hdr, sizeof hdr);
 842         return 0;
 843 }
 844
 845 static void retransmit(struct utcp_connection *c) {
 846         if(c->state == CLOSED || c->snd.nxt == c->snd.una)
 847                 return;
 848
 849         struct utcp *utcp = c->utcp;
 850
 851         struct {
 852                 struct hdr hdr;
 853                 char data[c->utcp->mtu];
 854         } pkt;
 855
 856         pkt.hdr.src = c->src;
 857         pkt.hdr.dst = c->dst;
 858
 859         switch(c->state) {
 860                 case LISTEN:
 861                         // TODO: this should not happen
 862                         break;
 863
 864                 case SYN_SENT:
 865                         pkt.hdr.seq = c->snd.iss;
 866                         pkt.hdr.ack = 0;
 867                         pkt.hdr.wnd = c->rcv.wnd;
 868                         pkt.hdr.ctl = SYN;
 869                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr);
 870                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 871                         break;
 872
 873                 case SYN_RECEIVED:
 874                         pkt.hdr.seq = c->snd.nxt;
 875                         pkt.hdr.ack = c->rcv.nxt;
 876                         pkt.hdr.ctl = SYN | ACK;
 877                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr);
 878                         utcp->send(utcp, &pkt, sizeof pkt.hdr);
 879                         break;
 880
 881                 case ESTABLISHED:
 882                         pkt.hdr.seq = c->snd.una;
 883                         pkt.hdr.ack = c->rcv.nxt;
 884                         pkt.hdr.ctl = ACK;
 885                         uint32_t len = seqdiff(c->snd.nxt, c->snd.una);
 886                         if(len > utcp->mtu)
 887                                 len = utcp->mtu;
 888                         memcpy(pkt.data, c->sndbuf, len);
 889                         print_packet(c->utcp, "rtrx", &pkt, sizeof pkt.hdr + len);
 890                         utcp->send(utcp, &pkt, sizeof pkt.hdr + len);
 891                         break;
 892
 893                 default:
 894                         // TODO: implement
 895                         abort();
 896         }
 897 }
 898
 899 /* Handle timeouts.
 900  * One call to this function will loop through all connections,
 901  * checking if something needs to be resent or not.
 902  * The return value is the time to the next timeout in milliseconds,
 903  * or maybe a negative value if the timeout is infinite.
 904  */
 905 int utcp_timeout(struct utcp *utcp) {
 906         struct timeval now;
 907         gettimeofday(&now, NULL);
 908         struct timeval next = {now.tv_sec + 3600, now.tv_usec};
 909
 910         for(int i = 0; i < utcp->nconnections; i++) {
 911                 struct utcp_connection *c = utcp->connections[i];
 912                 if(!c)
 913                         continue;
 914
 915                 if(c->state == CLOSED) {
 916                         if(c->reapable) {
 917                                 fprintf(stderr, "Reaping %p\n", c);
 918                                 free_connection(c);
 919                                 i--;
 920                         }
 921                         continue;
 922                 }
 923
 924                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &now, <)) {
 925                         errno = ETIMEDOUT;
 926                         c->state = CLOSED;
 927                         if(c->recv)
 928                                 c->recv(c, NULL, 0);
 929                         continue;
 930                 }
 931
 932                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &now, <)) {
 933                         retransmit(c);
 934                 }
 935
 936                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <))
 937                         next = c->conn_timeout;
 938
 939                 if(c->snd.nxt != c->snd.una) {
 940                         c->rtrx_timeout = now;
 941                         c->rtrx_timeout.tv_sec++;
 942                 } else {
 943                         timerclear(&c->rtrx_timeout);
 944                 }
 945
 946                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <))
 947                         next = c->rtrx_timeout;
 948         }
 949
 950         struct timeval diff;
 951         timersub(&next, &now, &diff);
 952         if(diff.tv_sec < 0)
 953                 return 0;
 954         return diff.tv_sec * 1000 + diff.tv_usec / 1000;
 955 }
 956
 957 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
 958         struct utcp *utcp = calloc(1, sizeof *utcp);
 959         if(!utcp)
 960                 return NULL;
 961
 962         if(!send) {
 963                 errno = EFAULT;
 964                 return NULL;
 965         }
 966
 967         utcp->accept = accept;
 968         utcp->pre_accept = pre_accept;
 969         utcp->send = send;
 970         utcp->priv = priv;
 971         utcp->mtu = 1000;
 972         utcp->timeout = 60;
 973
 974         return utcp;
 975 }
 976
 977 void utcp_exit(struct utcp *utcp) {
 978         if(!utcp)
 979                 return;
 980         for(int i = 0; i < utcp->nconnections; i++)
 981                 free_connection(utcp->connections[i]);
 982         free(utcp);
 983 }
 984
 985 int utcp_set_connection_timeout(struct utcp *u, int timeout) {
 986         int prev = u->timeout;
 987         u->timeout = timeout;
 988         return prev;
 989 }