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 bool fin_wanted(struct utcp_connection *c, uint32_t seq) {
 107         if(seq != c->snd.last)
 108                 return false;
 109         switch(c->state) {
 110         case FIN_WAIT_1:
 111         case CLOSING:
 112         case LAST_ACK:
 113                 return true;
 114         default:
 115                 return false;
 116         }
 117 }
 118
 119 static inline void list_connections(struct utcp *utcp) {
 120         debug("%p has %d connections:\n", utcp, utcp->nconnections);
 121         for(int i = 0; i < utcp->nconnections; i++)
 122                 debug("  %u -> %u state %s\n", utcp->connections[i]->src, utcp->connections[i]->dst, strstate[utcp->connections[i]->state]);
 123 }
 124
 125 static int32_t seqdiff(uint32_t a, uint32_t b) {
 126         return a - b;
 127 }
 128
 129 // Buffer functions
 130 // TODO: convert to ringbuffers to avoid memmove() operations.
 131
 132 // Store data into the buffer
 133 static ssize_t buffer_put_at(struct buffer *buf, size_t offset, const void *data, size_t len) {
 134         if(buf->maxsize <= buf->used)
 135                 return 0;
 136
 137         debug("buffer_put_at %zu %zu %zu\n", buf->used, offset, len);
 138
 139         size_t required = offset + len;
 140         if(required > buf->maxsize) {
 141                 if(offset >= buf->maxsize)
 142                         return 0;
 143                 abort();
 144                 len = buf->maxsize - offset;
 145                 required = buf->maxsize;
 146         }
 147
 148         if(required > buf->size) {
 149                 size_t newsize = buf->size;
 150                 if(!newsize) {
 151                         newsize = required;
 152                 } else {
 153                         do {
 154                                 newsize *= 2;
 155                         } while(newsize < buf->used + len);
 156                 }
 157                 if(newsize > buf->maxsize)
 158                         newsize = buf->maxsize;
 159                 char *newdata = realloc(buf->data, newsize);
 160                 if(!newdata)
 161                         return -1;
 162                 buf->data = newdata;
 163                 buf->size = newsize;
 164         }
 165
 166         memcpy(buf->data + offset, data, len);
 167         if(required > buf->used)
 168                 buf->used = required;
 169         return len;
 170 }
 171
 172 static ssize_t buffer_put(struct buffer *buf, const void *data, size_t len) {
 173         return buffer_put_at(buf, buf->used, data, len);
 174 }
 175
 176 // Get data from the buffer. data can be NULL.
 177 static ssize_t buffer_get(struct buffer *buf, void *data, size_t len) {
 178         if(len > buf->used)
 179                 len = buf->used;
 180         if(data)
 181                 memcpy(data, buf->data, len);
 182         if(len < buf->used)
 183                 memmove(buf->data, buf->data + len, buf->used - len);
 184         buf->used -= len;
 185         return len;
 186 }
 187
 188 // Copy data from the buffer without removing it.
 189 static ssize_t buffer_copy(struct buffer *buf, void *data, size_t offset, size_t len) {
 190         if(offset >= buf->used)
 191                 return 0;
 192         if(offset + len > buf->used)
 193                 len = buf->used - offset;
 194         memcpy(data, buf->data + offset, len);
 195         return len;
 196 }
 197
 198 static bool buffer_init(struct buffer *buf, uint32_t len, uint32_t maxlen) {
 199         memset(buf, 0, sizeof *buf);
 200         if(len) {
 201                 buf->data = malloc(len);
 202                 if(!buf->data)
 203                         return false;
 204         }
 205         buf->size = len;
 206         buf->maxsize = maxlen;
 207         return true;
 208 }
 209
 210 static void buffer_exit(struct buffer *buf) {
 211         free(buf->data);
 212         memset(buf, 0, sizeof *buf);
 213 }
 214
 215 static uint32_t buffer_free(const struct buffer *buf) {
 216         return buf->maxsize - buf->used;
 217 }
 218
 219 // Connections are stored in a sorted list.
 220 // This gives O(log(N)) lookup time, O(N log(N)) insertion time and O(N) deletion time.
 221
 222 static int compare(const void *va, const void *vb) {
 223         assert(va && vb);
 224
 225         const struct utcp_connection *a = *(struct utcp_connection **)va;
 226         const struct utcp_connection *b = *(struct utcp_connection **)vb;
 227
 228         assert(a && b);
 229         assert(a->src && b->src);
 230
 231         int c = (int)a->src - (int)b->src;
 232         if(c)
 233                 return c;
 234         c = (int)a->dst - (int)b->dst;
 235         return c;
 236 }
 237
 238 static struct utcp_connection *find_connection(const struct utcp *utcp, uint16_t src, uint16_t dst) {
 239         if(!utcp->nconnections)
 240                 return NULL;
 241         struct utcp_connection key = {
 242                 .src = src,
 243                 .dst = dst,
 244         }, *keyp = &key;
 245         struct utcp_connection **match = bsearch(&keyp, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 246         return match ? *match : NULL;
 247 }
 248
 249 static void free_connection(struct utcp_connection *c) {
 250         struct utcp *utcp = c->utcp;
 251         struct utcp_connection **cp = bsearch(&c, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 252
 253         assert(cp);
 254
 255         int i = cp - utcp->connections;
 256         memmove(cp, cp + 1, (utcp->nconnections - i - 1) * sizeof *cp);
 257         utcp->nconnections--;
 258
 259         buffer_exit(&c->sndbuf);
 260         free(c);
 261 }
 262
 263 static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t src, uint16_t dst) {
 264         // Check whether this combination of src and dst is free
 265
 266         if(src) {
 267                 if(find_connection(utcp, src, dst)) {
 268                         errno = EADDRINUSE;
 269                         return NULL;
 270                 }
 271         } else { // If src == 0, generate a random port number with the high bit set
 272                 if(utcp->nconnections >= 32767) {
 273                         errno = ENOMEM;
 274                         return NULL;
 275                 }
 276                 src = rand() | 0x8000;
 277                 while(find_connection(utcp, src, dst))
 278                         src++;
 279         }
 280
 281         // Allocate memory for the new connection
 282
 283         if(utcp->nconnections >= utcp->nallocated) {
 284                 if(!utcp->nallocated)
 285                         utcp->nallocated = 4;
 286                 else
 287                         utcp->nallocated *= 2;
 288                 struct utcp_connection **new_array = realloc(utcp->connections, utcp->nallocated * sizeof *utcp->connections);
 289                 if(!new_array)
 290                         return NULL;
 291                 utcp->connections = new_array;
 292         }
 293
 294         struct utcp_connection *c = calloc(1, sizeof *c);
 295         if(!c)
 296                 return NULL;
 297
 298         if(!buffer_init(&c->sndbuf, DEFAULT_SNDBUFSIZE, DEFAULT_MAXSNDBUFSIZE)) {
 299                 free(c);
 300                 return NULL;
 301         }
 302
 303         // Fill in the details
 304
 305         c->src = src;
 306         c->dst = dst;
 307 #ifdef UTCP_DEBUG
 308 #warning debugging
 309         c->snd.iss = 0;
 310 #else
 311         c->snd.iss = rand();
 312 #endif
 313         c->snd.una = c->snd.iss;
 314         c->snd.nxt = c->snd.iss + 1;
 315         c->rcv.wnd = utcp->mtu;
 316         c->snd.last = c->snd.nxt;
 317         c->snd.cwnd = utcp->mtu;
 318         c->utcp = utcp;
 319
 320         // Add it to the sorted list of connections
 321
 322         utcp->connections[utcp->nconnections++] = c;
 323         qsort(utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 324
 325         return c;
 326 }
 327
 328 struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
 329         struct utcp_connection *c = allocate_connection(utcp, 0, dst);
 330         if(!c)
 331                 return NULL;
 332
 333         c->recv = recv;
 334         c->priv = priv;
 335
 336         struct hdr hdr;
 337
 338         hdr.src = c->src;
 339         hdr.dst = c->dst;
 340         hdr.seq = c->snd.iss;
 341         hdr.ack = 0;
 342         hdr.wnd = c->rcv.wnd;
 343         hdr.ctl = SYN;
 344         hdr.aux = 0;
 345
 346         set_state(c, SYN_SENT);
 347
 348         print_packet(utcp, "send", &hdr, sizeof hdr);
 349         utcp->send(utcp, &hdr, sizeof hdr);
 350
 351         gettimeofday(&c->conn_timeout, NULL);
 352         c->conn_timeout.tv_sec += utcp->timeout;
 353
 354         return c;
 355 }
 356
 357 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 358         if(c->reapable || c->state != SYN_RECEIVED) {
 359                 debug("Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
 360                 return;
 361         }
 362
 363         debug("%p accepted, %p %p\n", c, recv, priv);
 364         c->recv = recv;
 365         c->priv = priv;
 366         set_state(c, ESTABLISHED);
 367 }
 368
 369 static void ack(struct utcp_connection *c, bool sendatleastone) {
 370         int32_t left = seqdiff(c->snd.last, c->snd.nxt);
 371         int32_t cwndleft = c->snd.cwnd - seqdiff(c->snd.nxt, c->snd.una);
 372
 373         assert(left >= 0);
 374
 375         if(cwndleft <= 0)
 376                 cwndleft = 0;
 377
 378         if(cwndleft < left)
 379                 left = cwndleft;
 380
 381         if(!left && !sendatleastone)
 382                 return;
 383
 384         struct {
 385                 struct hdr hdr;
 386                 char data[];
 387         } *pkt;
 388
 389         pkt = malloc(sizeof pkt->hdr + c->utcp->mtu);
 390         if(!pkt)
 391                 return;
 392
 393         pkt->hdr.src = c->src;
 394         pkt->hdr.dst = c->dst;
 395         pkt->hdr.ack = c->rcv.nxt;
 396         pkt->hdr.wnd = c->snd.wnd;
 397         pkt->hdr.ctl = ACK;
 398         pkt->hdr.aux = 0;
 399
 400         do {
 401                 uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
 402                 pkt->hdr.seq = c->snd.nxt;
 403
 404                 buffer_copy(&c->sndbuf, pkt->data, seqdiff(c->snd.nxt, c->snd.una), seglen);
 405
 406                 c->snd.nxt += seglen;
 407                 left -= seglen;
 408
 409                 if(seglen && fin_wanted(c, c->snd.nxt)) {
 410                         seglen--;
 411                         pkt->hdr.ctl |= FIN;
 412                 }
 413
 414                 print_packet(c->utcp, "send", pkt, sizeof pkt->hdr + seglen);
 415                 c->utcp->send(c->utcp, pkt, sizeof pkt->hdr + seglen);
 416         } while(left);
 417
 418         free(pkt);
 419 }
 420
 421 ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 422         if(c->reapable) {
 423                 debug("Error: send() called on closed connection %p\n", c);
 424                 errno = EBADF;
 425                 return -1;
 426         }
 427
 428         switch(c->state) {
 429         case CLOSED:
 430         case LISTEN:
 431         case SYN_SENT:
 432         case SYN_RECEIVED:
 433                 debug("Error: send() called on unconnected connection %p\n", c);
 434                 errno = ENOTCONN;
 435                 return -1;
 436         case ESTABLISHED:
 437         case CLOSE_WAIT:
 438                 break;
 439         case FIN_WAIT_1:
 440         case FIN_WAIT_2:
 441         case CLOSING:
 442         case LAST_ACK:
 443         case TIME_WAIT:
 444                 debug("Error: send() called on closing connection %p\n", c);
 445                 errno = EPIPE;
 446                 return -1;
 447         }
 448
 449         // Add data to send buffer
 450
 451         if(!len)
 452                 return 0;
 453
 454         if(!data) {
 455                 errno = EFAULT;
 456                 return -1;
 457         }
 458
 459         len = buffer_put(&c->sndbuf, data, len);
 460         if(len <= 0) {
 461                 errno = EWOULDBLOCK;
 462                 return 0;
 463         }
 464
 465         c->snd.last += len;
 466         ack(c, false);
 467         return len;
 468 }
 469
 470 static void swap_ports(struct hdr *hdr) {
 471         uint16_t tmp = hdr->src;
 472         hdr->src = hdr->dst;
 473         hdr->dst = tmp;
 474 }
 475
 476 static void retransmit(struct utcp_connection *c) {
 477         if(c->state == CLOSED || c->snd.nxt == c->snd.una)
 478                 return;
 479
 480         struct utcp *utcp = c->utcp;
 481
 482         struct {
 483                 struct hdr hdr;
 484                 char data[];
 485         } *pkt;
 486
 487         pkt = malloc(sizeof pkt->hdr + c->utcp->mtu);
 488         if(!pkt)
 489                 return;
 490
 491         pkt->hdr.src = c->src;
 492         pkt->hdr.dst = c->dst;
 493
 494         switch(c->state) {
 495                 case SYN_SENT:
 496                         // Send our SYN again
 497                         pkt->hdr.seq = c->snd.iss;
 498                         pkt->hdr.ack = 0;
 499                         pkt->hdr.wnd = c->rcv.wnd;
 500                         pkt->hdr.ctl = SYN;
 501                         print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr);
 502                         utcp->send(utcp, pkt, sizeof pkt->hdr);
 503                         break;
 504
 505                 case SYN_RECEIVED:
 506                         // Send SYNACK again
 507                         pkt->hdr.seq = c->snd.nxt;
 508                         pkt->hdr.ack = c->rcv.nxt;
 509                         pkt->hdr.ctl = SYN | ACK;
 510                         print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr);
 511                         utcp->send(utcp, pkt, sizeof pkt->hdr);
 512                         break;
 513
 514                 case ESTABLISHED:
 515                 case FIN_WAIT_1:
 516                 case CLOSE_WAIT:
 517                 case CLOSING:
 518                 case LAST_ACK:
 519                         // Send unacked data again.
 520                         pkt->hdr.seq = c->snd.una;
 521                         pkt->hdr.ack = c->rcv.nxt;
 522                         pkt->hdr.ctl = ACK;
 523                         uint32_t len = seqdiff(c->snd.last, c->snd.una);
 524                         if(len > utcp->mtu)
 525                                 len = utcp->mtu;
 526                         if(fin_wanted(c, c->snd.una + len)) {
 527                                 len--;
 528                                 pkt->hdr.ctl |= FIN;
 529                         }
 530                         c->snd.nxt = c->snd.una + len;
 531                         buffer_copy(&c->sndbuf, pkt->data, 0, len);
 532                         print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr + len);
 533                         utcp->send(utcp, pkt, sizeof pkt->hdr + len);
 534                         break;
 535
 536                 case CLOSED:
 537                 case LISTEN:
 538                 case TIME_WAIT:
 539                 case FIN_WAIT_2:
 540                         // We shouldn't need to retransmit anything in this state.
 541 #ifdef UTCP_DEBUG
 542                         abort();
 543 #endif
 544                         timerclear(&c->rtrx_timeout);
 545                         break;
 546         }
 547
 548         free(pkt);
 549 }
 550
 551
 552 ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 553         if(!utcp) {
 554                 errno = EFAULT;
 555                 return -1;
 556         }
 557
 558         if(!len)
 559                 return 0;
 560
 561         if(!data) {
 562                 errno = EFAULT;
 563                 return -1;
 564         }
 565
 566         print_packet(utcp, "recv", data, len);
 567
 568         // Drop packets smaller than the header
 569
 570         struct hdr hdr;
 571         if(len < sizeof hdr) {
 572                 errno = EBADMSG;
 573                 return -1;
 574         }
 575
 576         // Make a copy from the potentially unaligned data to a struct hdr
 577
 578         memcpy(&hdr, data, sizeof hdr);
 579         data += sizeof hdr;
 580         len -= sizeof hdr;
 581
 582         // Drop packets with an unknown CTL flag
 583
 584         if(hdr.ctl & ~(SYN | ACK | RST | FIN)) {
 585                 errno = EBADMSG;
 586                 return -1;
 587         }
 588
 589         // Try to match the packet to an existing connection
 590
 591         struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
 592
 593         // Is it for a new connection?
 594
 595         if(!c) {
 596                 // Ignore RST packets
 597
 598                 if(hdr.ctl & RST)
 599                         return 0;
 600
 601                 // Is it a SYN packet and are we LISTENing?
 602
 603                 if(hdr.ctl & SYN && !(hdr.ctl & ACK) && utcp->accept) {
 604                         // If we don't want to accept it, send a RST back
 605                         if((utcp->pre_accept && !utcp->pre_accept(utcp, hdr.dst))) {
 606                                 len = 1;
 607                                 goto reset;
 608                         }
 609
 610                         // Try to allocate memory, otherwise send a RST back
 611                         c = allocate_connection(utcp, hdr.dst, hdr.src);
 612                         if(!c) {
 613                                 len = 1;
 614                                 goto reset;
 615                         }
 616
 617                         // Return SYN+ACK, go to SYN_RECEIVED state
 618                         c->snd.wnd = hdr.wnd;
 619                         c->rcv.irs = hdr.seq;
 620                         c->rcv.nxt = c->rcv.irs + 1;
 621                         set_state(c, SYN_RECEIVED);
 622
 623                         hdr.dst = c->dst;
 624                         hdr.src = c->src;
 625                         hdr.ack = c->rcv.irs + 1;
 626                         hdr.seq = c->snd.iss;
 627                         hdr.ctl = SYN | ACK;
 628                         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 629                         utcp->send(utcp, &hdr, sizeof hdr);
 630                 } else {
 631                         // No, we don't want your packets, send a RST back
 632                         len = 1;
 633                         goto reset;
 634                 }
 635
 636                 return 0;
 637         }
 638
 639         debug("%p state %s\n", c->utcp, strstate[c->state]);
 640
 641         // In case this is for a CLOSED connection, ignore the packet.
 642         // TODO: make it so incoming packets can never match a CLOSED connection.
 643
 644         if(c->state == CLOSED)
 645                 return 0;
 646
 647         // It is for an existing connection.
 648
 649         uint32_t prevrcvnxt = c->rcv.nxt;
 650
 651         // 1. Drop invalid packets.
 652
 653         // 1a. Drop packets that should not happen in our current state.
 654
 655         switch(c->state) {
 656         case SYN_SENT:
 657         case SYN_RECEIVED:
 658         case ESTABLISHED:
 659         case FIN_WAIT_1:
 660         case FIN_WAIT_2:
 661         case CLOSE_WAIT:
 662         case CLOSING:
 663         case LAST_ACK:
 664         case TIME_WAIT:
 665                 break;
 666         default:
 667 #ifdef UTCP_DEBUG
 668                 abort();
 669 #endif
 670                 break;
 671         }
 672
 673         // 1b. Drop packets with a sequence number not in our receive window.
 674
 675         bool acceptable;
 676
 677         if(c->state == SYN_SENT)
 678                 acceptable = true;
 679
 680         // TODO: handle packets overlapping c->rcv.nxt.
 681 #if 0
 682         // Only use this when accepting out-of-order packets.
 683         else if(len == 0)
 684                 if(c->rcv.wnd == 0)
 685                         acceptable = hdr.seq == c->rcv.nxt;
 686                 else
 687                         acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0);
 688         else
 689                 if(c->rcv.wnd == 0)
 690                         // We don't accept data when the receive window is zero.
 691                         acceptable = false;
 692                 else
 693                         // Both start and end of packet must be within the receive window
 694                         acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0)
 695                                 || (seqdiff(hdr.seq + len + 1, c->rcv.nxt) >= 0 && seqdiff(hdr.seq + len - 1, c->rcv.nxt + c->rcv.wnd) < 0);
 696 #else
 697         if(c->state != SYN_SENT)
 698                 acceptable = hdr.seq == c->rcv.nxt;
 699 #endif
 700
 701         if(!acceptable) {
 702                 debug("Packet not acceptable, %u <= %u + %zu < %u\n", c->rcv.nxt, hdr.seq, len, c->rcv.nxt + c->rcv.wnd);
 703                 // Ignore unacceptable RST packets.
 704                 if(hdr.ctl & RST)
 705                         return 0;
 706                 // Otherwise, send an ACK back in the hope things improve.
 707                 ack(c, true);
 708                 return 0;
 709         }
 710
 711         c->snd.wnd = hdr.wnd; // TODO: move below
 712
 713         // 1c. Drop packets with an invalid ACK.
 714         // ackno should not roll back, and it should also not be bigger than snd.nxt.
 715
 716         if(hdr.ctl & ACK && (seqdiff(hdr.ack, c->snd.nxt) > 0 || seqdiff(hdr.ack, c->snd.una) < 0)) {
 717                 debug("Packet ack seqno out of range, %u %u %u\n", hdr.ack, c->snd.una, c->snd.nxt);
 718                 // Ignore unacceptable RST packets.
 719                 if(hdr.ctl & RST)
 720                         return 0;
 721                 goto reset;
 722         }
 723
 724         // 2. Handle RST packets
 725
 726         if(hdr.ctl & RST) {
 727                 switch(c->state) {
 728                 case SYN_SENT:
 729                         if(!(hdr.ctl & ACK))
 730                                 return 0;
 731                         // The peer has refused our connection.
 732                         set_state(c, CLOSED);
 733                         errno = ECONNREFUSED;
 734                         if(c->recv)
 735                                 c->recv(c, NULL, 0);
 736                         return 0;
 737                 case SYN_RECEIVED:
 738                         if(hdr.ctl & ACK)
 739                                 return 0;
 740                         // We haven't told the application about this connection yet. Silently delete.
 741                         free_connection(c);
 742                         return 0;
 743                 case ESTABLISHED:
 744                 case FIN_WAIT_1:
 745                 case FIN_WAIT_2:
 746                 case CLOSE_WAIT:
 747                         if(hdr.ctl & ACK)
 748                                 return 0;
 749                         // The peer has aborted our connection.
 750                         set_state(c, CLOSED);
 751                         errno = ECONNRESET;
 752                         if(c->recv)
 753                                 c->recv(c, NULL, 0);
 754                         return 0;
 755                 case CLOSING:
 756                 case LAST_ACK:
 757                 case TIME_WAIT:
 758                         if(hdr.ctl & ACK)
 759                                 return 0;
 760                         // As far as the application is concerned, the connection has already been closed.
 761                         // If it has called utcp_close() already, we can immediately free this connection.
 762                         if(c->reapable) {
 763                                 free_connection(c);
 764                                 return 0;
 765                         }
 766                         // Otherwise, immediately move to the CLOSED state.
 767                         set_state(c, CLOSED);
 768                         return 0;
 769                 default:
 770 #ifdef UTCP_DEBUG
 771                         abort();
 772 #endif
 773                         break;
 774                 }
 775         }
 776
 777         // 3. Advance snd.una
 778
 779         uint32_t advanced = seqdiff(hdr.ack, c->snd.una);
 780         prevrcvnxt = c->rcv.nxt;
 781
 782         if(advanced) {
 783                 int32_t data_acked = advanced;
 784
 785                 switch(c->state) {
 786                         case SYN_SENT:
 787                         case SYN_RECEIVED:
 788                                 data_acked--;
 789                                 break;
 790                         // TODO: handle FIN as well.
 791                         default:
 792                                 break;
 793                 }
 794
 795                 assert(data_acked >= 0);
 796
 797                 int32_t bufused = seqdiff(c->snd.last, c->snd.una);
 798                 assert(data_acked <= bufused);
 799
 800                 if(data_acked)
 801                         buffer_get(&c->sndbuf, NULL, data_acked);
 802
 803                 c->snd.una = hdr.ack;
 804
 805                 c->dupack = 0;
 806                 c->snd.cwnd += utcp->mtu;
 807                 if(c->snd.cwnd > c->sndbuf.maxsize)
 808                         c->snd.cwnd = c->sndbuf.maxsize;
 809
 810                 // Check if we have sent a FIN that is now ACKed.
 811                 switch(c->state) {
 812                 case FIN_WAIT_1:
 813                         if(c->snd.una == c->snd.last)
 814                                 set_state(c, FIN_WAIT_2);
 815                         break;
 816                 case CLOSING:
 817                         if(c->snd.una == c->snd.last) {
 818                                 gettimeofday(&c->conn_timeout, NULL);
 819                                 c->conn_timeout.tv_sec += 60;
 820                                 set_state(c, TIME_WAIT);
 821                         }
 822                         break;
 823                 default:
 824                         break;
 825                 }
 826         } else {
 827                 if(!len) {
 828                         c->dupack++;
 829                         if(c->dupack == 3) {
 830                                 debug("Triplicate ACK\n");
 831                                 //TODO: Resend one packet and go to fast recovery mode. See RFC 6582.
 832                                 //We do a very simple variant here; reset the nxt pointer to the last acknowledged packet from the peer.
 833                                 //This will cause us to start retransmitting, but at the same speed as the incoming ACKs arrive,
 834                                 //thus preventing a drop in speed.
 835                                 c->snd.nxt = c->snd.una;
 836                         }
 837                 }
 838         }
 839
 840         // 4. Update timers
 841
 842         if(advanced) {
 843                 timerclear(&c->conn_timeout); // It will be set anew in utcp_timeout() if c->snd.una != c->snd.nxt.
 844                 if(c->snd.una == c->snd.nxt)
 845                         timerclear(&c->rtrx_timeout);
 846         }
 847
 848         // 5. Process SYN stuff
 849
 850         if(hdr.ctl & SYN) {
 851                 switch(c->state) {
 852                 case SYN_SENT:
 853                         // This is a SYNACK. It should always have ACKed the SYN.
 854                         if(!advanced)
 855                                 goto reset;
 856                         c->rcv.irs = hdr.seq;
 857                         c->rcv.nxt = hdr.seq;
 858                         set_state(c, ESTABLISHED);
 859                         // TODO: notify application of this somehow.
 860                         break;
 861                 case SYN_RECEIVED:
 862                 case ESTABLISHED:
 863                 case FIN_WAIT_1:
 864                 case FIN_WAIT_2:
 865                 case CLOSE_WAIT:
 866                 case CLOSING:
 867                 case LAST_ACK:
 868                 case TIME_WAIT:
 869                         // Ehm, no. We should never receive a second SYN.
 870                         goto reset;
 871                 default:
 872 #ifdef UTCP_DEBUG
 873                         abort();
 874 #endif
 875                         return 0;
 876                 }
 877
 878                 // SYN counts as one sequence number
 879                 c->rcv.nxt++;
 880         }
 881
 882         // 6. Process new data
 883
 884         if(c->state == SYN_RECEIVED) {
 885                 // This is the ACK after the SYNACK. It should always have ACKed the SYNACK.
 886                 if(!advanced)
 887                         goto reset;
 888
 889                 // Are we still LISTENing?
 890                 if(utcp->accept)
 891                         utcp->accept(c, c->src);
 892
 893                 if(c->state != ESTABLISHED) {
 894                         set_state(c, CLOSED);
 895                         c->reapable = true;
 896                         goto reset;
 897                 }
 898         }
 899
 900         if(len) {
 901                 switch(c->state) {
 902                 case SYN_SENT:
 903                 case SYN_RECEIVED:
 904                         // This should never happen.
 905 #ifdef UTCP_DEBUG
 906                         abort();
 907 #endif
 908                         return 0;
 909                 case ESTABLISHED:
 910                 case FIN_WAIT_1:
 911                 case FIN_WAIT_2:
 912                         break;
 913                 case CLOSE_WAIT:
 914                 case CLOSING:
 915                 case LAST_ACK:
 916                 case TIME_WAIT:
 917                         // Ehm no, We should never receive more data after a FIN.
 918                         goto reset;
 919                 default:
 920 #ifdef UTCP_DEBUG
 921                         abort();
 922 #endif
 923                         return 0;
 924                 }
 925
 926                 ssize_t rxd;
 927
 928                 if(c->recv) {
 929                         rxd = c->recv(c, data, len);
 930                         if(rxd != len) {
 931                                 // TODO: once we have a receive buffer, handle the application not accepting all data.
 932                                 abort();
 933                         }
 934                         if(rxd < 0)
 935                                 rxd = 0;
 936                         else if(rxd > len)
 937                                 rxd = len; // Bad application, bad!
 938                 } else {
 939                         rxd = len;
 940                 }
 941
 942                 c->rcv.nxt += len;
 943         }
 944
 945         // 7. Process FIN stuff
 946
 947         if(hdr.ctl & FIN) {
 948                 switch(c->state) {
 949                 case SYN_SENT:
 950                 case SYN_RECEIVED:
 951                         // This should never happen.
 952 #ifdef UTCP_DEBUG
 953                         abort();
 954 #endif
 955                         break;
 956                 case ESTABLISHED:
 957                         set_state(c, CLOSE_WAIT);
 958                         break;
 959                 case FIN_WAIT_1:
 960                         set_state(c, CLOSING);
 961                         break;
 962                 case FIN_WAIT_2:
 963                         gettimeofday(&c->conn_timeout, NULL);
 964                         c->conn_timeout.tv_sec += 60;
 965                         set_state(c, TIME_WAIT);
 966                         break;
 967                 case CLOSE_WAIT:
 968                 case CLOSING:
 969                 case LAST_ACK:
 970                 case TIME_WAIT:
 971                         // Ehm, no. We should never receive a second FIN.
 972                         goto reset;
 973                 default:
 974 #ifdef UTCP_DEBUG
 975                         abort();
 976 #endif
 977                         break;
 978                 }
 979
 980                 // FIN counts as one sequence number
 981                 c->rcv.nxt++;
 982                 len++;
 983
 984                 // Inform the application that the peer closed the connection.
 985                 if(c->recv) {
 986                         errno = 0;
 987                         c->recv(c, NULL, 0);
 988                 }
 989         }
 990
 991         // Now we send something back if:
 992         // - we advanced rcv.nxt (ie, we got some data that needs to be ACKed)
 993         //   -> sendatleastone = true
 994         // - or we got an ack, so we should maybe send a bit more data
 995         //   -> sendatleastone = false
 996
 997 ack:
 998         ack(c, prevrcvnxt != c->rcv.nxt);
 999         return 0;
1000
1001 reset:
1002         swap_ports(&hdr);
1003         hdr.wnd = 0;
1004         if(hdr.ctl & ACK) {
1005                 hdr.seq = hdr.ack;
1006                 hdr.ctl = RST;
1007         } else {
1008                 hdr.ack = hdr.seq + len;
1009                 hdr.seq = 0;
1010                 hdr.ctl = RST | ACK;
1011         }
1012         print_packet(utcp, "send", &hdr, sizeof hdr);
1013         utcp->send(utcp, &hdr, sizeof hdr);
1014         return 0;
1015
1016 }
1017
1018 int utcp_shutdown(struct utcp_connection *c, int dir) {
1019         debug("%p shutdown %d at %u\n", c ? c->utcp : NULL, dir, c ? c->snd.last : 0);
1020         if(!c) {
1021                 errno = EFAULT;
1022                 return -1;
1023         }
1024
1025         if(c->reapable) {
1026                 debug("Error: shutdown() called on closed connection %p\n", c);
1027                 errno = EBADF;
1028                 return -1;
1029         }
1030
1031         if(!(dir == UTCP_SHUT_RD || dir == UTCP_SHUT_WR || dir == UTCP_SHUT_RDWR)) {
1032                 errno = EINVAL;
1033                 return -1;
1034         }
1035
1036         // TCP does not have a provision for stopping incoming packets.
1037         // The best we can do is to just ignore them.
1038         if(dir == UTCP_SHUT_RD || dir == UTCP_SHUT_RDWR)
1039                 c->recv = NULL;
1040
1041         // The rest of the code deals with shutting down writes.
1042         if(dir == UTCP_SHUT_RD)
1043                 return 0;
1044
1045         switch(c->state) {
1046         case CLOSED:
1047         case LISTEN:
1048                 errno = ENOTCONN;
1049                 return -1;
1050
1051         case SYN_SENT:
1052                 set_state(c, CLOSED);
1053                 return 0;
1054
1055         case SYN_RECEIVED:
1056         case ESTABLISHED:
1057                 set_state(c, FIN_WAIT_1);
1058                 break;
1059         case FIN_WAIT_1:
1060         case FIN_WAIT_2:
1061                 return 0;
1062         case CLOSE_WAIT:
1063                 set_state(c, CLOSING);
1064                 break;
1065
1066         case CLOSING:
1067         case LAST_ACK:
1068         case TIME_WAIT:
1069                 return 0;
1070         }
1071
1072         c->snd.last++;
1073
1074         ack(c, false);
1075         return 0;
1076 }
1077
1078 int utcp_close(struct utcp_connection *c) {
1079         if(utcp_shutdown(c, SHUT_RDWR))
1080                 return -1;
1081         c->recv = NULL;
1082         c->poll = NULL;
1083         c->reapable = true;
1084         return 0;
1085 }
1086
1087 int utcp_abort(struct utcp_connection *c) {
1088         if(!c) {
1089                 errno = EFAULT;
1090                 return -1;
1091         }
1092
1093         if(c->reapable) {
1094                 debug("Error: abort() called on closed connection %p\n", c);
1095                 errno = EBADF;
1096                 return -1;
1097         }
1098
1099         c->recv = NULL;
1100         c->poll = NULL;
1101         c->reapable = true;
1102
1103         switch(c->state) {
1104         case CLOSED:
1105                 return 0;
1106         case LISTEN:
1107         case SYN_SENT:
1108         case CLOSING:
1109         case LAST_ACK:
1110         case TIME_WAIT:
1111                 set_state(c, CLOSED);
1112                 return 0;
1113
1114         case SYN_RECEIVED:
1115         case ESTABLISHED:
1116         case FIN_WAIT_1:
1117         case FIN_WAIT_2:
1118         case CLOSE_WAIT:
1119                 set_state(c, CLOSED);
1120                 break;
1121         }
1122
1123         // Send RST
1124
1125         struct hdr hdr;
1126
1127         hdr.src = c->src;
1128         hdr.dst = c->dst;
1129         hdr.seq = c->snd.nxt;
1130         hdr.ack = 0;
1131         hdr.wnd = 0;
1132         hdr.ctl = RST;
1133
1134         print_packet(c->utcp, "send", &hdr, sizeof hdr);
1135         c->utcp->send(c->utcp, &hdr, sizeof hdr);
1136         return 0;
1137 }
1138
1139 /* Handle timeouts.
1140  * One call to this function will loop through all connections,
1141  * checking if something needs to be resent or not.
1142  * The return value is the time to the next timeout in milliseconds,
1143  * or maybe a negative value if the timeout is infinite.
1144  */
1145 struct timeval utcp_timeout(struct utcp *utcp) {
1146         struct timeval now;
1147         gettimeofday(&now, NULL);
1148         struct timeval next = {now.tv_sec + 3600, now.tv_usec};
1149
1150         for(int i = 0; i < utcp->nconnections; i++) {
1151                 struct utcp_connection *c = utcp->connections[i];
1152                 if(!c)
1153                         continue;
1154
1155                 if(c->state == CLOSED) {
1156                         if(c->reapable) {
1157                                 debug("Reaping %p\n", c);
1158                                 free_connection(c);
1159                                 i--;
1160                         }
1161                         continue;
1162                 }
1163
1164                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &now, <)) {
1165                         errno = ETIMEDOUT;
1166                         c->state = CLOSED;
1167                         if(c->recv)
1168                                 c->recv(c, NULL, 0);
1169                         continue;
1170                 }
1171
1172                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &now, <)) {
1173                         retransmit(c);
1174                 }
1175
1176                 if(c->poll && buffer_free(&c->sndbuf) && (c->state == ESTABLISHED || c->state == CLOSE_WAIT))
1177                         c->poll(c, buffer_free(&c->sndbuf));
1178
1179                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <))
1180                         next = c->conn_timeout;
1181
1182                 if(c->snd.nxt != c->snd.una) {
1183                         c->rtrx_timeout = now;
1184                         c->rtrx_timeout.tv_sec++;
1185                 } else {
1186                         timerclear(&c->rtrx_timeout);
1187                 }
1188
1189                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <))
1190                         next = c->rtrx_timeout;
1191         }
1192
1193         struct timeval diff;
1194         timersub(&next, &now, &diff);
1195         return diff;
1196 }
1197
1198 bool utcp_is_active(struct utcp *utcp) {
1199         if(!utcp)
1200                 return false;
1201
1202         for(int i = 0; i < utcp->nconnections; i++)
1203                 if(utcp->connections[i]->state != CLOSED && utcp->connections[i]->state != TIME_WAIT)
1204                         return true;
1205
1206         return false;
1207 }
1208
1209 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
1210         struct utcp *utcp = calloc(1, sizeof *utcp);
1211         if(!utcp)
1212                 return NULL;
1213
1214         if(!send) {
1215                 errno = EFAULT;
1216                 return NULL;
1217         }
1218
1219         utcp->accept = accept;
1220         utcp->pre_accept = pre_accept;
1221         utcp->send = send;
1222         utcp->priv = priv;
1223         utcp->mtu = 1000;
1224         utcp->timeout = 60;
1225
1226         return utcp;
1227 }
1228
1229 void utcp_exit(struct utcp *utcp) {
1230         if(!utcp)
1231                 return;
1232         for(int i = 0; i < utcp->nconnections; i++) {
1233                 if(!utcp->connections[i]->reapable)
1234                         debug("Warning, freeing unclosed connection %p\n", utcp->connections[i]);
1235                 buffer_exit(&utcp->connections[i]->sndbuf);
1236                 free(utcp->connections[i]);
1237         }
1238         free(utcp->connections);
1239         free(utcp);
1240 }
1241
1242 uint16_t utcp_get_mtu(struct utcp *utcp) {
1243         return utcp ? utcp->mtu : 0;
1244 }
1245
1246 void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
1247         // TODO: handle overhead of the header
1248         if(utcp)
1249                 utcp->mtu = mtu;
1250 }
1251
1252 int utcp_get_user_timeout(struct utcp *u) {
1253         return u ? u->timeout : 0;
1254 }
1255
1256 void utcp_set_user_timeout(struct utcp *u, int timeout) {
1257         if(u)
1258                 u->timeout = timeout;
1259 }
1260
1261 size_t utcp_get_sndbuf(struct utcp_connection *c) {
1262         return c ? c->sndbuf.maxsize : 0;
1263 }
1264
1265 size_t utcp_get_sndbuf_free(struct utcp_connection *c) {
1266         if(c && (c->state == ESTABLISHED || c->state == CLOSE_WAIT))
1267                 return buffer_free(&c->sndbuf);
1268         else
1269                 return 0;
1270 }
1271
1272 void utcp_set_sndbuf(struct utcp_connection *c, size_t size) {
1273         if(!c)
1274                 return;
1275         c->sndbuf.maxsize = size;
1276         if(c->sndbuf.maxsize != size)
1277                 c->sndbuf.maxsize = -1;
1278 }
1279
1280 bool utcp_get_nodelay(struct utcp_connection *c) {
1281         return c ? c->nodelay : false;
1282 }
1283
1284 void utcp_set_nodelay(struct utcp_connection *c, bool nodelay) {
1285         if(c)
1286                 c->nodelay = nodelay;
1287 }
1288
1289 bool utcp_get_keepalive(struct utcp_connection *c) {
1290         return c ? c->keepalive : false;
1291 }
1292
1293 void utcp_set_keepalive(struct utcp_connection *c, bool keepalive) {
1294         if(c)
1295                 c->keepalive = keepalive;
1296 }
1297
1298 size_t utcp_get_outq(struct utcp_connection *c) {
1299         return c ? seqdiff(c->snd.nxt, c->snd.una) : 0;
1300 }
1301
1302 void utcp_set_recv_cb(struct utcp_connection *c, utcp_recv_t recv) {
1303         if(c)
1304                 c->recv = recv;
1305 }
1306
1307 void utcp_set_poll_cb(struct utcp_connection *c, utcp_poll_t poll) {
1308         if(c)
1309                 c->poll = poll;
1310 }
1311
1312 void utcp_set_accept_cb(struct utcp *utcp, utcp_accept_t accept, utcp_pre_accept_t pre_accept) {
1313         if(utcp) {
1314                 utcp->accept = accept;
1315                 utcp->pre_accept = pre_accept;
1316         }
1317 }