git.meshlink.io Git - utcp/blob - utcp.c

   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 <assert.h>
  23 #include <errno.h>
  24 #include <stdio.h>
  25 #include <stdlib.h>
  26 #include <stdint.h>
  27 #include <stdbool.h>
  28 #include <string.h>
  29 #include <unistd.h>
  30 #include <sys/time.h>
  31 #include <sys/socket.h>
  32
  33 #include "utcp_priv.h"
  34
  35 #ifndef EBADMSG
  36 #define EBADMSG         104
  37 #endif
  38
  39 #ifndef SHUT_RDWR
  40 #define SHUT_RDWR 2
  41 #endif
  42
  43 #ifdef poll
  44 #undef poll
  45 #endif
  46
  47 #ifndef timersub
  48 #define timersub(a, b, r) do {\
  49         (r)->tv_sec = (a)->tv_sec - (b)->tv_sec;\
  50         (r)->tv_usec = (a)->tv_usec - (b)->tv_usec;\
  51         if((r)->tv_usec < 0)\
  52                 (r)->tv_sec--, (r)->tv_usec += 1000000;\
  53 } while (0)
  54 #endif
  55
  56 #ifdef UTCP_DEBUG
  57 #include <stdarg.h>
  58
  59 static void debug(const char *format, ...) {
  60         va_list ap;
  61         va_start(ap, format);
  62         vfprintf(stderr, format, ap);
  63         va_end(ap);
  64 }
  65
  66 static void print_packet(struct utcp *utcp, const char *dir, const void *pkt, size_t len) {
  67         struct hdr hdr;
  68         if(len < sizeof hdr) {
  69                 debug("%p %s: short packet (%zu bytes)\n", utcp, dir, len);
  70                 return;
  71         }
  72
  73         memcpy(&hdr, pkt, sizeof hdr);
  74         fprintf (stderr, "%p %s: len=%zu, src=%u dst=%u seq=%u ack=%u wnd=%u ctl=", utcp, dir, len, hdr.src, hdr.dst, hdr.seq, hdr.ack, hdr.wnd);
  75         if(hdr.ctl & SYN)
  76                 debug("SYN");
  77         if(hdr.ctl & RST)
  78                 debug("RST");
  79         if(hdr.ctl & FIN)
  80                 debug("FIN");
  81         if(hdr.ctl & ACK)
  82                 debug("ACK");
  83
  84         if(len > sizeof hdr) {
  85                 debug(" data=");
  86                 for(int i = sizeof hdr; i < len; i++) {
  87                         const char *data = pkt;
  88                         debug("%c", data[i] >= 32 ? data[i] : '.');
  89                 }
  90         }
  91
  92         debug("\n");
  93 }
  94 #else
  95 #define debug(...)
  96 #define print_packet(...)
  97 #endif
  98
  99 static void set_state(struct utcp_connection *c, enum state state) {
 100         c->state = state;
 101         if(state == ESTABLISHED)
 102                 timerclear(&c->conn_timeout);
 103         debug("%p new state: %s\n", c->utcp, strstate[state]);
 104 }
 105
 106 static inline void list_connections(struct utcp *utcp) {
 107         debug("%p has %d connections:\n", utcp, utcp->nconnections);
 108         for(int i = 0; i < utcp->nconnections; i++)
 109                 debug("  %u -> %u state %s\n", utcp->connections[i]->src, utcp->connections[i]->dst, strstate[utcp->connections[i]->state]);
 110 }
 111
 112 static int32_t seqdiff(uint32_t a, uint32_t b) {
 113         return a - b;
 114 }
 115
 116 // Buffer functions
 117 // TODO: convert to ringbuffers to avoid memmove() operations.
 118
 119 // Store data into the buffer
 120 static ssize_t buffer_put(struct buffer *buf, const void *data, size_t len) {
 121         if(buf->maxsize <= buf->used)
 122                 return 0;
 123         if(len > buf->maxsize - buf->used)
 124                 len = buf->maxsize - buf->used;
 125         if(len > buf->size - buf->used) {
 126                 size_t newsize = buf->size;
 127                 do {
 128                         newsize *= 2;
 129                 } while(newsize < buf->used + len);
 130                 if(newsize > buf->maxsize)
 131                         newsize = buf->maxsize;
 132                 char *newdata = realloc(buf->data, newsize);
 133                 if(!newdata)
 134                         return -1;
 135                 buf->data = newdata;
 136                 buf->size = newsize;
 137         }
 138         memcpy(buf->data + buf->used, data, len);
 139         buf->used += len;
 140         return len;
 141 }
 142
 143 // Get data from the buffer. data can be NULL.
 144 static ssize_t buffer_get(struct buffer *buf, void *data, size_t len) {
 145         if(len > buf->used)
 146                 len = buf->used;
 147         if(data)
 148                 memcpy(data, buf->data, len);
 149         if(len < buf->used)
 150                 memmove(buf->data, buf->data + len, buf->used - len);
 151         buf->used -= len;
 152         return len;
 153 }
 154
 155 // Copy data from the buffer without removing it.
 156 static ssize_t buffer_copy(struct buffer *buf, void *data, size_t offset, size_t len) {
 157         if(offset >= buf->used)
 158                 return 0;
 159         if(offset + len > buf->used)
 160                 len = buf->used - offset;
 161         memcpy(data, buf->data + offset, len);
 162         return len;
 163 }
 164
 165 static bool buffer_init(struct buffer *buf, uint32_t len, uint32_t maxlen) {
 166         memset(buf, 0, sizeof *buf);
 167         buf->data = malloc(len);
 168         if(!len)
 169                 return false;
 170         buf->size = len;
 171         buf->maxsize = maxlen;
 172         return true;
 173 }
 174
 175 static void buffer_exit(struct buffer *buf) {
 176         free(buf->data);
 177         memset(buf, 0, sizeof *buf);
 178 }
 179
 180 static uint32_t buffer_free(const struct buffer *buf) {
 181         return buf->maxsize - buf->used;
 182 }
 183
 184 // Connections are stored in a sorted list.
 185 // This gives O(log(N)) lookup time, O(N log(N)) insertion time and O(N) deletion time.
 186
 187 static int compare(const void *va, const void *vb) {
 188         assert(va && vb);
 189
 190         const struct utcp_connection *a = *(struct utcp_connection **)va;
 191         const struct utcp_connection *b = *(struct utcp_connection **)vb;
 192
 193         assert(a && b);
 194         assert(a->src && b->src);
 195
 196         int c = (int)a->src - (int)b->src;
 197         if(c)
 198                 return c;
 199         c = (int)a->dst - (int)b->dst;
 200         return c;
 201 }
 202
 203 static struct utcp_connection *find_connection(const struct utcp *utcp, uint16_t src, uint16_t dst) {
 204         if(!utcp->nconnections)
 205                 return NULL;
 206         struct utcp_connection key = {
 207                 .src = src,
 208                 .dst = dst,
 209         }, *keyp = &key;
 210         struct utcp_connection **match = bsearch(&keyp, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 211         return match ? *match : NULL;
 212 }
 213
 214 static void free_connection(struct utcp_connection *c) {
 215         struct utcp *utcp = c->utcp;
 216         struct utcp_connection **cp = bsearch(&c, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 217
 218         assert(cp);
 219
 220         int i = cp - utcp->connections;
 221         memmove(cp, cp + 1, (utcp->nconnections - i - 1) * sizeof *cp);
 222         utcp->nconnections--;
 223
 224         buffer_exit(&c->sndbuf);
 225         free(c);
 226 }
 227
 228 static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t src, uint16_t dst) {
 229         // Check whether this combination of src and dst is free
 230
 231         if(src) {
 232                 if(find_connection(utcp, src, dst)) {
 233                         errno = EADDRINUSE;
 234                         return NULL;
 235                 }
 236         } else { // If src == 0, generate a random port number with the high bit set
 237                 if(utcp->nconnections >= 32767) {
 238                         errno = ENOMEM;
 239                         return NULL;
 240                 }
 241                 src = rand() | 0x8000;
 242                 while(find_connection(utcp, src, dst))
 243                         src++;
 244         }
 245
 246         // Allocate memory for the new connection
 247
 248         if(utcp->nconnections >= utcp->nallocated) {
 249                 if(!utcp->nallocated)
 250                         utcp->nallocated = 4;
 251                 else
 252                         utcp->nallocated *= 2;
 253                 struct utcp_connection **new_array = realloc(utcp->connections, utcp->nallocated * sizeof *utcp->connections);
 254                 if(!new_array)
 255                         return NULL;
 256                 utcp->connections = new_array;
 257         }
 258
 259         struct utcp_connection *c = calloc(1, sizeof *c);
 260         if(!c)
 261                 return NULL;
 262
 263         if(!buffer_init(&c->sndbuf, DEFAULT_SNDBUFSIZE, DEFAULT_MAXSNDBUFSIZE)) {
 264                 free(c);
 265                 return NULL;
 266         }
 267
 268         // Fill in the details
 269
 270         c->src = src;
 271         c->dst = dst;
 272         c->snd.iss = rand();
 273         c->snd.una = c->snd.iss;
 274         c->snd.nxt = c->snd.iss + 1;
 275         c->rcv.wnd = utcp->mtu;
 276         c->snd.last = c->snd.nxt;
 277         c->snd.cwnd = utcp->mtu;
 278         c->utcp = utcp;
 279
 280         // Add it to the sorted list of connections
 281
 282         utcp->connections[utcp->nconnections++] = c;
 283         qsort(utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 284
 285         return c;
 286 }
 287
 288 struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
 289         struct utcp_connection *c = allocate_connection(utcp, 0, dst);
 290         if(!c)
 291                 return NULL;
 292
 293         c->recv = recv;
 294         c->priv = priv;
 295
 296         struct hdr hdr;
 297
 298         hdr.src = c->src;
 299         hdr.dst = c->dst;
 300         hdr.seq = c->snd.iss;
 301         hdr.ack = 0;
 302         hdr.wnd = c->rcv.wnd;
 303         hdr.ctl = SYN;
 304         hdr.aux = 0;
 305
 306         set_state(c, SYN_SENT);
 307
 308         print_packet(utcp, "send", &hdr, sizeof hdr);
 309         utcp->send(utcp, &hdr, sizeof hdr);
 310
 311         gettimeofday(&c->conn_timeout, NULL);
 312         c->conn_timeout.tv_sec += utcp->timeout;
 313
 314         return c;
 315 }
 316
 317 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 318         if(c->reapable || c->state != SYN_RECEIVED) {
 319                 debug("Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
 320                 return;
 321         }
 322
 323         debug("%p accepted, %p %p\n", c, recv, priv);
 324         c->recv = recv;
 325         c->priv = priv;
 326         set_state(c, ESTABLISHED);
 327 }
 328
 329 static void ack(struct utcp_connection *c, bool sendatleastone) {
 330         int32_t left = seqdiff(c->snd.last, c->snd.nxt);
 331         int32_t cwndleft = c->snd.cwnd - seqdiff(c->snd.nxt, c->snd.una);
 332
 333         assert(left >= 0);
 334
 335         if(cwndleft <= 0)
 336                 cwndleft = 0;
 337
 338         if(cwndleft < left)
 339                 left = cwndleft;
 340
 341         if(!left && !sendatleastone)
 342                 return;
 343
 344         struct {
 345                 struct hdr hdr;
 346                 char data[];
 347         } *pkt;
 348
 349         pkt = malloc(sizeof pkt->hdr + c->utcp->mtu);
 350         if(!pkt->data)
 351                 return;
 352
 353         pkt->hdr.src = c->src;
 354         pkt->hdr.dst = c->dst;
 355         pkt->hdr.ack = c->rcv.nxt;
 356         pkt->hdr.wnd = c->snd.wnd;
 357         pkt->hdr.ctl = ACK;
 358         pkt->hdr.aux = 0;
 359
 360         do {
 361                 uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
 362                 pkt->hdr.seq = c->snd.nxt;
 363
 364                 buffer_copy(&c->sndbuf, pkt->data, seqdiff(c->snd.nxt, c->snd.una), seglen);
 365
 366                 c->snd.nxt += seglen;
 367                 left -= seglen;
 368
 369                 if(c->state != ESTABLISHED && !left && seglen) {
 370                         switch(c->state) {
 371                         case FIN_WAIT_1:
 372                         case CLOSING:
 373                                 seglen--;
 374                                 pkt->hdr.ctl |= FIN;
 375                                 break;
 376                         default:
 377                                 break;
 378                         }
 379                 }
 380
 381                 print_packet(c->utcp, "send", pkt, sizeof pkt->hdr + seglen);
 382                 c->utcp->send(c->utcp, pkt, sizeof pkt->hdr + seglen);
 383         } while(left);
 384
 385         free(pkt);
 386 }
 387
 388 ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 389         if(c->reapable) {
 390                 debug("Error: send() called on closed connection %p\n", c);
 391                 errno = EBADF;
 392                 return -1;
 393         }
 394
 395         switch(c->state) {
 396         case CLOSED:
 397         case LISTEN:
 398         case SYN_SENT:
 399         case SYN_RECEIVED:
 400                 debug("Error: send() called on unconnected connection %p\n", c);
 401                 errno = ENOTCONN;
 402                 return -1;
 403         case ESTABLISHED:
 404         case CLOSE_WAIT:
 405                 break;
 406         case FIN_WAIT_1:
 407         case FIN_WAIT_2:
 408         case CLOSING:
 409         case LAST_ACK:
 410         case TIME_WAIT:
 411                 debug("Error: send() called on closing connection %p\n", c);
 412                 errno = EPIPE;
 413                 return -1;
 414         }
 415
 416         // Add data to send buffer
 417
 418         if(!len)
 419                 return 0;
 420
 421         if(!data) {
 422                 errno = EFAULT;
 423                 return -1;
 424         }
 425
 426         len = buffer_put(&c->sndbuf, data, len);
 427         if(len <= 0) {
 428                 errno = EWOULDBLOCK;
 429                 return 0;
 430         }
 431
 432         c->snd.last += len;
 433         ack(c, false);
 434         return len;
 435 }
 436
 437 static void swap_ports(struct hdr *hdr) {
 438         uint16_t tmp = hdr->src;
 439         hdr->src = hdr->dst;
 440         hdr->dst = tmp;
 441 }
 442
 443 static void retransmit(struct utcp_connection *c) {
 444         if(c->state == CLOSED || c->snd.nxt == c->snd.una)
 445                 return;
 446
 447         struct utcp *utcp = c->utcp;
 448
 449         struct {
 450                 struct hdr hdr;
 451                 char data[];
 452         } *pkt;
 453
 454         pkt = malloc(sizeof pkt->hdr + c->utcp->mtu);
 455         if(!pkt)
 456                 return;
 457
 458         pkt->hdr.src = c->src;
 459         pkt->hdr.dst = c->dst;
 460
 461         switch(c->state) {
 462                 case LISTEN:
 463                         // TODO: this should not happen
 464                         break;
 465
 466                 case SYN_SENT:
 467                         pkt->hdr.seq = c->snd.iss;
 468                         pkt->hdr.ack = 0;
 469                         pkt->hdr.wnd = c->rcv.wnd;
 470                         pkt->hdr.ctl = SYN;
 471                         print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr);
 472                         utcp->send(utcp, pkt, sizeof pkt->hdr);
 473                         break;
 474
 475                 case SYN_RECEIVED:
 476                         pkt->hdr.seq = c->snd.nxt;
 477                         pkt->hdr.ack = c->rcv.nxt;
 478                         pkt->hdr.ctl = SYN | ACK;
 479                         print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr);
 480                         utcp->send(utcp, pkt, sizeof pkt->hdr);
 481                         break;
 482
 483                 case ESTABLISHED:
 484                 case FIN_WAIT_1:
 485                         pkt->hdr.seq = c->snd.una;
 486                         pkt->hdr.ack = c->rcv.nxt;
 487                         pkt->hdr.ctl = ACK;
 488                         uint32_t len = seqdiff(c->snd.nxt, c->snd.una);
 489                         fprintf(stderr, "retransmit %u %u %u\n", pkt->hdr.seq, pkt->hdr.ack, len);
 490                         if(c->state == FIN_WAIT_1)
 491                                 len--;
 492                         if(len > utcp->mtu)
 493                                 len = utcp->mtu;
 494                         else {
 495                                 if(c->state == FIN_WAIT_1)
 496                                         pkt->hdr.ctl |= FIN;
 497                         }
 498                         buffer_copy(&c->sndbuf, pkt->data, 0, len);
 499                         print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr + len);
 500                         utcp->send(utcp, pkt, sizeof pkt->hdr + len);
 501                         break;
 502
 503                 default:
 504                         // TODO: implement
 505                         abort();
 506         }
 507
 508         free(pkt);
 509 }
 510
 511
 512 ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 513         if(!utcp) {
 514                 errno = EFAULT;
 515                 return -1;
 516         }
 517
 518         if(!len)
 519                 return 0;
 520
 521         if(!data) {
 522                 errno = EFAULT;
 523                 return -1;
 524         }
 525
 526         print_packet(utcp, "recv", data, len);
 527
 528         // Drop packets smaller than the header
 529
 530         struct hdr hdr;
 531         if(len < sizeof hdr) {
 532                 errno = EBADMSG;
 533                 return -1;
 534         }
 535
 536         // Make a copy from the potentially unaligned data to a struct hdr
 537
 538         memcpy(&hdr, data, sizeof hdr);
 539         data += sizeof hdr;
 540         len -= sizeof hdr;
 541
 542         // Drop packets with an unknown CTL flag
 543
 544         if(hdr.ctl & ~(SYN | ACK | RST | FIN)) {
 545                 errno = EBADMSG;
 546                 return -1;
 547         }
 548
 549         // Try to match the packet to an existing connection
 550
 551         struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
 552
 553         // Is it for a new connection?
 554
 555         if(!c) {
 556                 // Ignore RST packets
 557
 558                 if(hdr.ctl & RST)
 559                         return 0;
 560
 561                 // Is it a SYN packet and are we LISTENing?
 562
 563                 if(hdr.ctl & SYN && !(hdr.ctl & ACK) && utcp->accept) {
 564                         // If we don't want to accept it, send a RST back
 565                         if((utcp->pre_accept && !utcp->pre_accept(utcp, hdr.dst))) {
 566                                 len = 1;
 567                                 goto reset;
 568                         }
 569
 570                         // Try to allocate memory, otherwise send a RST back
 571                         c = allocate_connection(utcp, hdr.dst, hdr.src);
 572                         if(!c) {
 573                                 len = 1;
 574                                 goto reset;
 575                         }
 576
 577                         // Return SYN+ACK, go to SYN_RECEIVED state
 578                         c->snd.wnd = hdr.wnd;
 579                         c->rcv.irs = hdr.seq;
 580                         c->rcv.nxt = c->rcv.irs + 1;
 581                         set_state(c, SYN_RECEIVED);
 582
 583                         hdr.dst = c->dst;
 584                         hdr.src = c->src;
 585                         hdr.ack = c->rcv.irs + 1;
 586                         hdr.seq = c->snd.iss;
 587                         hdr.ctl = SYN | ACK;
 588                         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 589                         utcp->send(utcp, &hdr, sizeof hdr);
 590                 } else {
 591                         // No, we don't want your packets, send a RST back
 592                         len = 1;
 593                         goto reset;
 594                 }
 595
 596                 return 0;
 597         }
 598
 599         debug("%p state %s\n", c->utcp, strstate[c->state]);
 600
 601         // In case this is for a CLOSED connection, ignore the packet.
 602         // TODO: make it so incoming packets can never match a CLOSED connection.
 603
 604         if(c->state == CLOSED)
 605                 return 0;
 606
 607         // It is for an existing connection.
 608
 609         uint32_t prevrcvnxt = c->rcv.nxt;
 610
 611         // 1. Drop invalid packets.
 612
 613         // 1a. Drop packets that should not happen in our current state.
 614
 615         switch(c->state) {
 616         case SYN_SENT:
 617         case SYN_RECEIVED:
 618         case ESTABLISHED:
 619         case FIN_WAIT_1:
 620         case FIN_WAIT_2:
 621         case CLOSE_WAIT:
 622         case CLOSING:
 623         case LAST_ACK:
 624         case TIME_WAIT:
 625                 break;
 626         default:
 627                 abort();
 628         }
 629
 630         // 1b. Drop packets with a sequence number not in our receive window.
 631
 632         bool acceptable;
 633
 634         if(c->state == SYN_SENT)
 635                 acceptable = true;
 636
 637         // TODO: handle packets overlapping c->rcv.nxt.
 638 #if 0
 639         // Only use this when accepting out-of-order packets.
 640         else if(len == 0)
 641                 if(c->rcv.wnd == 0)
 642                         acceptable = hdr.seq == c->rcv.nxt;
 643                 else
 644                         acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0);
 645         else
 646                 if(c->rcv.wnd == 0)
 647                         // We don't accept data when the receive window is zero.
 648                         acceptable = false;
 649                 else
 650                         // Both start and end of packet must be within the receive window
 651                         acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0)
 652                                 || (seqdiff(hdr.seq + len + 1, c->rcv.nxt) >= 0 && seqdiff(hdr.seq + len - 1, c->rcv.nxt + c->rcv.wnd) < 0);
 653 #else
 654         if(c->state != SYN_SENT)
 655                 acceptable = hdr.seq == c->rcv.nxt;
 656 #endif
 657
 658         if(!acceptable) {
 659                 debug("Packet not acceptable, %u <= %u + %zu < %u\n", c->rcv.nxt, hdr.seq, len, c->rcv.nxt + c->rcv.wnd);
 660                 // Ignore unacceptable RST packets.
 661                 if(hdr.ctl & RST)
 662                         return 0;
 663                 // Otherwise, send an ACK back in the hope things improve.
 664                 ack(c, true);
 665                 return 0;
 666         }
 667
 668         c->snd.wnd = hdr.wnd; // TODO: move below
 669
 670         // 1c. Drop packets with an invalid ACK.
 671         // ackno should not roll back, and it should also not be bigger than snd.nxt.
 672
 673         if(hdr.ctl & ACK && (seqdiff(hdr.ack, c->snd.nxt) > 0 || seqdiff(hdr.ack, c->snd.una) < 0)) {
 674                 debug("Packet ack seqno out of range, %u %u %u\n", hdr.ack, c->snd.una, c->snd.nxt);
 675                 // Ignore unacceptable RST packets.
 676                 if(hdr.ctl & RST)
 677                         return 0;
 678                 goto reset;
 679         }
 680
 681         // 2. Handle RST packets
 682
 683         if(hdr.ctl & RST) {
 684                 switch(c->state) {
 685                 case SYN_SENT:
 686                         if(!(hdr.ctl & ACK))
 687                                 return 0;
 688                         // The peer has refused our connection.
 689                         set_state(c, CLOSED);
 690                         errno = ECONNREFUSED;
 691                         if(c->recv)
 692                                 c->recv(c, NULL, 0);
 693                         return 0;
 694                 case SYN_RECEIVED:
 695                         if(hdr.ctl & ACK)
 696                                 return 0;
 697                         // We haven't told the application about this connection yet. Silently delete.
 698                         free_connection(c);
 699                         return 0;
 700                 case ESTABLISHED:
 701                 case FIN_WAIT_1:
 702                 case FIN_WAIT_2:
 703                 case CLOSE_WAIT:
 704                         if(hdr.ctl & ACK)
 705                                 return 0;
 706                         // The peer has aborted our connection.
 707                         set_state(c, CLOSED);
 708                         errno = ECONNRESET;
 709                         if(c->recv)
 710                                 c->recv(c, NULL, 0);
 711                         return 0;
 712                 case CLOSING:
 713                 case LAST_ACK:
 714                 case TIME_WAIT:
 715                         if(hdr.ctl & ACK)
 716                                 return 0;
 717                         // As far as the application is concerned, the connection has already been closed.
 718                         // If it has called utcp_close() already, we can immediately free this connection.
 719                         if(c->reapable) {
 720                                 free_connection(c);
 721                                 return 0;
 722                         }
 723                         // Otherwise, immediately move to the CLOSED state.
 724                         set_state(c, CLOSED);
 725                         return 0;
 726                 default:
 727                         abort();
 728                 }
 729         }
 730
 731         // 3. Advance snd.una
 732
 733         uint32_t advanced = seqdiff(hdr.ack, c->snd.una);
 734         prevrcvnxt = c->rcv.nxt;
 735
 736         if(advanced) {
 737                 int32_t data_acked = advanced;
 738
 739                 switch(c->state) {
 740                         case SYN_SENT:
 741                         case SYN_RECEIVED:
 742                                 data_acked--;
 743                                 break;
 744                         // TODO: handle FIN as well.
 745                         default:
 746                                 break;
 747                 }
 748
 749                 assert(data_acked >= 0);
 750
 751                 int32_t bufused = seqdiff(c->snd.last, c->snd.una);
 752                 assert(data_acked <= bufused);
 753
 754                 if(data_acked)
 755                         buffer_get(&c->sndbuf, NULL, data_acked);
 756
 757                 c->snd.una = hdr.ack;
 758
 759                 c->dupack = 0;
 760                 c->snd.cwnd += utcp->mtu;
 761                 if(c->snd.cwnd > c->sndbuf.maxsize)
 762                         c->snd.cwnd = c->sndbuf.maxsize;
 763
 764                 // Check if we have sent a FIN that is now ACKed.
 765                 switch(c->state) {
 766                 case FIN_WAIT_1:
 767                         if(c->snd.una == c->snd.last)
 768                                 set_state(c, FIN_WAIT_2);
 769                         break;
 770                 case CLOSING:
 771                         if(c->snd.una == c->snd.last) {
 772                                 gettimeofday(&c->conn_timeout, NULL);
 773                                 c->conn_timeout.tv_sec += 60;
 774                                 set_state(c, TIME_WAIT);
 775                         }
 776                         break;
 777                 default:
 778                         break;
 779                 }
 780         } else {
 781                 if(!len) {
 782                         c->dupack++;
 783                         if(c->dupack == 3) {
 784                                 debug("Triplicate ACK\n");
 785                                 fprintf(stderr, "Triplicate ACK\n");
 786                                 //TODO: Resend one packet and go to fast recovery mode. See RFC 6582.
 787                                 //We do a very simple variant here; reset the nxt pointer to the last acknowledged packet from the peer.
 788                                 //This will cause us to start retransmitting, but at the same speed as the incoming ACKs arrive,
 789                                 //thus preventing a drop in speed.
 790                                 c->snd.nxt = c->snd.una;
 791                         }
 792                 }
 793         }
 794
 795         // 4. Update timers
 796
 797         if(advanced) {
 798                 timerclear(&c->conn_timeout); // It will be set anew in utcp_timeout() if c->snd.una != c->snd.nxt.
 799                 if(c->snd.una == c->snd.nxt)
 800                         timerclear(&c->rtrx_timeout);
 801         }
 802
 803         // 5. Process SYN stuff
 804
 805         if(hdr.ctl & SYN) {
 806                 switch(c->state) {
 807                 case SYN_SENT:
 808                         // This is a SYNACK. It should always have ACKed the SYN.
 809                         if(!advanced)
 810                                 goto reset;
 811                         c->rcv.irs = hdr.seq;
 812                         c->rcv.nxt = hdr.seq;
 813                         set_state(c, ESTABLISHED);
 814                         // TODO: notify application of this somehow.
 815                         break;
 816                 case SYN_RECEIVED:
 817                 case ESTABLISHED:
 818                 case FIN_WAIT_1:
 819                 case FIN_WAIT_2:
 820                 case CLOSE_WAIT:
 821                 case CLOSING:
 822                 case LAST_ACK:
 823                 case TIME_WAIT:
 824                         // Ehm, no. We should never receive a second SYN.
 825                         goto reset;
 826                 default:
 827                         abort();
 828                 }
 829
 830                 // SYN counts as one sequence number
 831                 c->rcv.nxt++;
 832         }
 833
 834         // 6. Process new data
 835
 836         if(c->state == SYN_RECEIVED) {
 837                 // This is the ACK after the SYNACK. It should always have ACKed the SYNACK.
 838                 if(!advanced)
 839                         goto reset;
 840
 841                 // Are we still LISTENing?
 842                 if(utcp->accept)
 843                         utcp->accept(c, c->src);
 844
 845                 if(c->state != ESTABLISHED) {
 846                         set_state(c, CLOSED);
 847                         c->reapable = true;
 848                         goto reset;
 849                 }
 850         }
 851
 852         if(len) {
 853                 switch(c->state) {
 854                 case SYN_SENT:
 855                 case SYN_RECEIVED:
 856                         // This should never happen.
 857                         abort();
 858                 case ESTABLISHED:
 859                 case FIN_WAIT_1:
 860                 case FIN_WAIT_2:
 861                         break;
 862                 case CLOSE_WAIT:
 863                 case CLOSING:
 864                 case LAST_ACK:
 865                 case TIME_WAIT:
 866                         // Ehm no, We should never receive more data after a FIN.
 867                         goto reset;
 868                 default:
 869                         abort();
 870                 }
 871
 872                 ssize_t rxd;
 873
 874                 if(c->recv) {
 875                         rxd = c->recv(c, data, len);
 876                         if(rxd != len) {
 877                                 // TODO: once we have a receive buffer, handle the application not accepting all data.
 878                                 abort();
 879                         }
 880                         if(rxd < 0)
 881                                 rxd = 0;
 882                         else if(rxd > len)
 883                                 rxd = len; // Bad application, bad!
 884                 } else {
 885                         rxd = len;
 886                 }
 887
 888                 c->rcv.nxt += len;
 889         }
 890
 891         // 7. Process FIN stuff
 892
 893         if(hdr.ctl & FIN) {
 894                 switch(c->state) {
 895                 case SYN_SENT:
 896                 case SYN_RECEIVED:
 897                         // This should never happen.
 898                         abort();
 899                 case ESTABLISHED:
 900                         set_state(c, CLOSE_WAIT);
 901                         break;
 902                 case FIN_WAIT_1:
 903                         set_state(c, CLOSING);
 904                         break;
 905                 case FIN_WAIT_2:
 906                         gettimeofday(&c->conn_timeout, NULL);
 907                         c->conn_timeout.tv_sec += 60;
 908                         set_state(c, TIME_WAIT);
 909                         break;
 910                 case CLOSE_WAIT:
 911                 case CLOSING:
 912                 case LAST_ACK:
 913                 case TIME_WAIT:
 914                         // Ehm, no. We should never receive a second FIN.
 915                         goto reset;
 916                 default:
 917                         abort();
 918                 }
 919
 920                 // FIN counts as one sequence number
 921                 c->rcv.nxt++;
 922                 len++;
 923
 924                 // Inform the application that the peer closed the connection.
 925                 if(c->recv) {
 926                         errno = 0;
 927                         c->recv(c, NULL, 0);
 928                 }
 929         }
 930
 931         // Now we send something back if:
 932         // - we advanced rcv.nxt (ie, we got some data that needs to be ACKed)
 933         //   -> sendatleastone = true
 934         // - or we got an ack, so we should maybe send a bit more data
 935         //   -> sendatleastone = false
 936
 937 ack:
 938         ack(c, prevrcvnxt != c->rcv.nxt);
 939         return 0;
 940
 941 reset:
 942         swap_ports(&hdr);
 943         hdr.wnd = 0;
 944         if(hdr.ctl & ACK) {
 945                 hdr.seq = hdr.ack;
 946                 hdr.ctl = RST;
 947         } else {
 948                 hdr.ack = hdr.seq + len;
 949                 hdr.seq = 0;
 950                 hdr.ctl = RST | ACK;
 951         }
 952         print_packet(utcp, "send", &hdr, sizeof hdr);
 953         utcp->send(utcp, &hdr, sizeof hdr);
 954         return 0;
 955
 956 }
 957
 958 int utcp_shutdown(struct utcp_connection *c, int dir) {
 959         debug("%p shutdown %d\n", c ? c->utcp : NULL, dir);
 960         if(!c) {
 961                 errno = EFAULT;
 962                 return -1;
 963         }
 964
 965         if(c->reapable) {
 966                 debug("Error: shutdown() called on closed connection %p\n", c);
 967                 errno = EBADF;
 968                 return -1;
 969         }
 970
 971         // TODO: handle dir
 972
 973         switch(c->state) {
 974         case CLOSED:
 975                 return 0;
 976         case LISTEN:
 977         case SYN_SENT:
 978                 set_state(c, CLOSED);
 979                 return 0;
 980
 981         case SYN_RECEIVED:
 982         case ESTABLISHED:
 983                 set_state(c, FIN_WAIT_1);
 984                 break;
 985         case FIN_WAIT_1:
 986         case FIN_WAIT_2:
 987                 return 0;
 988         case CLOSE_WAIT:
 989                 set_state(c, CLOSING);
 990                 break;
 991
 992         case CLOSING:
 993         case LAST_ACK:
 994         case TIME_WAIT:
 995                 return 0;
 996         }
 997
 998         c->snd.last++;
 999
1000         ack(c, false);
1001         return 0;
1002 }
1003
1004 int utcp_close(struct utcp_connection *c) {
1005         if(utcp_shutdown(c, SHUT_RDWR))
1006                 return -1;
1007         c->recv = NULL;
1008         c->poll = NULL;
1009         c->reapable = true;
1010         return 0;
1011 }
1012
1013 int utcp_abort(struct utcp_connection *c) {
1014         if(!c) {
1015                 errno = EFAULT;
1016                 return -1;
1017         }
1018
1019         if(c->reapable) {
1020                 debug("Error: abort() called on closed connection %p\n", c);
1021                 errno = EBADF;
1022                 return -1;
1023         }
1024
1025         c->recv = NULL;
1026         c->poll = NULL;
1027         c->reapable = true;
1028
1029         switch(c->state) {
1030         case CLOSED:
1031                 return 0;
1032         case LISTEN:
1033         case SYN_SENT:
1034         case CLOSING:
1035         case LAST_ACK:
1036         case TIME_WAIT:
1037                 set_state(c, CLOSED);
1038                 return 0;
1039
1040         case SYN_RECEIVED:
1041         case ESTABLISHED:
1042         case FIN_WAIT_1:
1043         case FIN_WAIT_2:
1044         case CLOSE_WAIT:
1045                 set_state(c, CLOSED);
1046                 break;
1047         }
1048
1049         // Send RST
1050
1051         struct hdr hdr;
1052
1053         hdr.src = c->src;
1054         hdr.dst = c->dst;
1055         hdr.seq = c->snd.nxt;
1056         hdr.ack = 0;
1057         hdr.wnd = 0;
1058         hdr.ctl = RST;
1059
1060         print_packet(c->utcp, "send", &hdr, sizeof hdr);
1061         c->utcp->send(c->utcp, &hdr, sizeof hdr);
1062         return 0;
1063 }
1064
1065 /* Handle timeouts.
1066  * One call to this function will loop through all connections,
1067  * checking if something needs to be resent or not.
1068  * The return value is the time to the next timeout in milliseconds,
1069  * or maybe a negative value if the timeout is infinite.
1070  */
1071 struct timeval utcp_timeout(struct utcp *utcp) {
1072         struct timeval now;
1073         gettimeofday(&now, NULL);
1074         struct timeval next = {now.tv_sec + 3600, now.tv_usec};
1075
1076         for(int i = 0; i < utcp->nconnections; i++) {
1077                 struct utcp_connection *c = utcp->connections[i];
1078                 if(!c)
1079                         continue;
1080
1081                 if(c->state == CLOSED) {
1082                         if(c->reapable) {
1083                                 debug("Reaping %p\n", c);
1084                                 free_connection(c);
1085                                 i--;
1086                         }
1087                         continue;
1088                 }
1089
1090                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &now, <)) {
1091                         errno = ETIMEDOUT;
1092                         c->state = CLOSED;
1093                         if(c->recv)
1094                                 c->recv(c, NULL, 0);
1095                         continue;
1096                 }
1097
1098                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &now, <)) {
1099                         retransmit(c);
1100                 }
1101
1102                 if(c->poll && buffer_free(&c->sndbuf) && (c->state == ESTABLISHED || c->state == CLOSE_WAIT))
1103                         c->poll(c, buffer_free(&c->sndbuf));
1104
1105                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <))
1106                         next = c->conn_timeout;
1107
1108                 if(c->snd.nxt != c->snd.una) {
1109                         c->rtrx_timeout = now;
1110                         c->rtrx_timeout.tv_sec++;
1111                 } else {
1112                         timerclear(&c->rtrx_timeout);
1113                 }
1114
1115                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <))
1116                         next = c->rtrx_timeout;
1117         }
1118
1119         struct timeval diff;
1120         timersub(&next, &now, &diff);
1121         return diff;
1122 }
1123
1124 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
1125         struct utcp *utcp = calloc(1, sizeof *utcp);
1126         if(!utcp)
1127                 return NULL;
1128
1129         if(!send) {
1130                 errno = EFAULT;
1131                 return NULL;
1132         }
1133
1134         utcp->accept = accept;
1135         utcp->pre_accept = pre_accept;
1136         utcp->send = send;
1137         utcp->priv = priv;
1138         utcp->mtu = 1000;
1139         utcp->timeout = 60;
1140
1141         return utcp;
1142 }
1143
1144 void utcp_exit(struct utcp *utcp) {
1145         if(!utcp)
1146                 return;
1147         for(int i = 0; i < utcp->nconnections; i++) {
1148                 if(!utcp->connections[i]->reapable)
1149                         debug("Warning, freeing unclosed connection %p\n", utcp->connections[i]);
1150                 buffer_exit(&utcp->connections[i]->sndbuf);
1151                 free(utcp->connections[i]);
1152         }
1153         free(utcp->connections);
1154         free(utcp);
1155 }
1156
1157 uint16_t utcp_get_mtu(struct utcp *utcp) {
1158         return utcp->mtu;
1159 }
1160
1161 void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
1162         // TODO: handle overhead of the header
1163         utcp->mtu = mtu;
1164 }
1165
1166 int utcp_get_user_timeout(struct utcp *u) {
1167         return u->timeout;
1168 }
1169
1170 void utcp_set_user_timeout(struct utcp *u, int timeout) {
1171         u->timeout = timeout;
1172 }
1173
1174 size_t utcp_get_sndbuf(struct utcp_connection *c) {
1175         return c->sndbuf.maxsize;
1176 }
1177
1178 size_t utcp_get_sndbuf_free(struct utcp_connection *c) {
1179         return buffer_free(&c->sndbuf);
1180 }
1181
1182 void utcp_set_sndbuf(struct utcp_connection *c, size_t size) {
1183         c->sndbuf.maxsize = size;
1184         if(c->sndbuf.maxsize != size)
1185                 c->sndbuf.maxsize = -1;
1186 }
1187
1188 bool utcp_get_nodelay(struct utcp_connection *c) {
1189         return c->nodelay;
1190 }
1191
1192 void utcp_set_nodelay(struct utcp_connection *c, bool nodelay) {
1193         c->nodelay = nodelay;
1194 }
1195
1196 bool utcp_get_keepalive(struct utcp_connection *c) {
1197         return c->keepalive;
1198 }
1199
1200 void utcp_set_keepalive(struct utcp_connection *c, bool keepalive) {
1201         c->keepalive = keepalive;
1202 }
1203
1204 size_t utcp_get_outq(struct utcp_connection *c) {
1205         return seqdiff(c->snd.nxt, c->snd.una);
1206 }
1207
1208 void utcp_set_recv_cb(struct utcp_connection *c, utcp_recv_t recv) {
1209         c->recv = recv;
1210 }
1211
1212 void utcp_set_poll_cb(struct utcp_connection *c, utcp_poll_t poll) {
1213         c->poll = poll;
1214 }