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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 <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 static inline size_t max(size_t a, size_t b) {
  57         return a > b ? a : b;
  58 }
  59
  60 #ifdef UTCP_DEBUG
  61 #include <stdarg.h>
  62
  63 static void debug(const char *format, ...) {
  64         va_list ap;
  65         va_start(ap, format);
  66         vfprintf(stderr, format, ap);
  67         va_end(ap);
  68 }
  69
  70 static void print_packet(struct utcp *utcp, const char *dir, const void *pkt, size_t len) {
  71         struct hdr hdr;
  72         if(len < sizeof hdr) {
  73                 debug("%p %s: short packet (%zu bytes)\n", utcp, dir, len);
  74                 return;
  75         }
  76
  77         memcpy(&hdr, pkt, sizeof hdr);
  78         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);
  79         if(hdr.ctl & SYN)
  80                 debug("SYN");
  81         if(hdr.ctl & RST)
  82                 debug("RST");
  83         if(hdr.ctl & FIN)
  84                 debug("FIN");
  85         if(hdr.ctl & ACK)
  86                 debug("ACK");
  87
  88         if(len > sizeof hdr) {
  89                 uint32_t datalen = len - sizeof hdr;
  90                 uint8_t *str = malloc((datalen << 1) + 7);
  91                 if(!str) {
  92                         debug("out of memory");
  93                         return;
  94                 }
  95                 memcpy(str, " data=", 6);
  96                 uint8_t *strptr = str + 6;
  97                 const uint8_t *data = pkt;
  98                 const uint8_t *dataend = data + datalen;
  99
 100                 while(data != dataend) {
 101                         *strptr = (*data >> 4) > 9? (*data >> 4) + 55 : (*data >> 4) + 48;
 102                         ++strptr;
 103                         *strptr = (*data & 0xf) > 9? (*data & 0xf) + 55 : (*data & 0xf) + 48;
 104                         ++strptr;
 105                         ++data;
 106                 }
 107                 *strptr = 0;
 108
 109                 debug(str);
 110                 free(str);
 111         }
 112
 113         debug("\n");
 114 }
 115 #else
 116 #define debug(...)
 117 #define print_packet(...)
 118 #endif
 119
 120 static void set_state(struct utcp_connection *c, enum state state) {
 121         c->state = state;
 122         if(state == ESTABLISHED)
 123                 timerclear(&c->conn_timeout);
 124         debug("%p new state: %s\n", c->utcp, strstate[state]);
 125 }
 126
 127 static bool fin_wanted(struct utcp_connection *c, uint32_t seq) {
 128         if(seq != c->snd.last)
 129                 return false;
 130         switch(c->state) {
 131         case FIN_WAIT_1:
 132         case CLOSING:
 133         case LAST_ACK:
 134                 return true;
 135         default:
 136                 return false;
 137         }
 138 }
 139
 140 static inline void list_connections(struct utcp *utcp) {
 141         debug("%p has %d connections:\n", utcp, utcp->nconnections);
 142         for(int i = 0; i < utcp->nconnections; i++)
 143                 debug("  %u -> %u state %s\n", utcp->connections[i]->src, utcp->connections[i]->dst, strstate[utcp->connections[i]->state]);
 144 }
 145
 146 static int32_t seqdiff(uint32_t a, uint32_t b) {
 147         return a - b;
 148 }
 149
 150 // Buffer functions
 151 // TODO: convert to ringbuffers to avoid memmove() operations.
 152
 153 // Store data into the buffer
 154 static ssize_t buffer_put_at(struct buffer *buf, size_t offset, const void *data, size_t len) {
 155         if(buf->maxsize <= buf->used)
 156                 return 0;
 157
 158         debug("buffer_put_at %zu %zu %zu\n", buf->used, offset, len);
 159
 160         size_t required = offset + len;
 161         if(required > buf->maxsize) {
 162                 if(offset >= buf->maxsize)
 163                         return 0;
 164                 abort();
 165                 len = buf->maxsize - offset;
 166                 required = buf->maxsize;
 167         }
 168
 169         if(required > buf->size) {
 170                 size_t newsize = buf->size;
 171                 if(!newsize) {
 172                         newsize = required;
 173                 } else {
 174                         do {
 175                                 newsize *= 2;
 176                         } while(newsize < buf->used + len);
 177                 }
 178                 if(newsize > buf->maxsize)
 179                         newsize = buf->maxsize;
 180                 char *newdata = realloc(buf->data, newsize);
 181                 if(!newdata)
 182                         return -1;
 183                 buf->data = newdata;
 184                 buf->size = newsize;
 185         }
 186
 187         memcpy(buf->data + offset, data, len);
 188         if(required > buf->used)
 189                 buf->used = required;
 190         return len;
 191 }
 192
 193 static ssize_t buffer_put(struct buffer *buf, const void *data, size_t len) {
 194         return buffer_put_at(buf, buf->used, data, len);
 195 }
 196
 197 // Get data from the buffer. data can be NULL.
 198 static ssize_t buffer_get(struct buffer *buf, void *data, size_t len) {
 199         if(len > buf->used)
 200                 len = buf->used;
 201         if(data)
 202                 memcpy(data, buf->data, len);
 203         if(len < buf->used)
 204                 memmove(buf->data, buf->data + len, buf->used - len);
 205         buf->used -= len;
 206         return len;
 207 }
 208
 209 // Copy data from the buffer without removing it.
 210 static ssize_t buffer_copy(struct buffer *buf, void *data, size_t offset, size_t len) {
 211         if(offset >= buf->used)
 212                 return 0;
 213         if(offset + len > buf->used)
 214                 len = buf->used - offset;
 215         memcpy(data, buf->data + offset, len);
 216         return len;
 217 }
 218
 219 static bool buffer_init(struct buffer *buf, uint32_t len, uint32_t maxlen) {
 220         memset(buf, 0, sizeof *buf);
 221         if(len) {
 222                 buf->data = malloc(len);
 223                 if(!buf->data)
 224                         return false;
 225         }
 226         buf->size = len;
 227         buf->maxsize = maxlen;
 228         return true;
 229 }
 230
 231 static void buffer_exit(struct buffer *buf) {
 232         free(buf->data);
 233         memset(buf, 0, sizeof *buf);
 234 }
 235
 236 static uint32_t buffer_free(const struct buffer *buf) {
 237         return buf->maxsize - buf->used;
 238 }
 239
 240 // Connections are stored in a sorted list.
 241 // This gives O(log(N)) lookup time, O(N log(N)) insertion time and O(N) deletion time.
 242
 243 static int compare(const void *va, const void *vb) {
 244         assert(va && vb);
 245
 246         const struct utcp_connection *a = *(struct utcp_connection **)va;
 247         const struct utcp_connection *b = *(struct utcp_connection **)vb;
 248
 249         assert(a && b);
 250         assert(a->src && b->src);
 251
 252         int c = (int)a->src - (int)b->src;
 253         if(c)
 254                 return c;
 255         c = (int)a->dst - (int)b->dst;
 256         return c;
 257 }
 258
 259 static struct utcp_connection *find_connection(const struct utcp *utcp, uint16_t src, uint16_t dst) {
 260         if(!utcp->nconnections)
 261                 return NULL;
 262         struct utcp_connection key = {
 263                 .src = src,
 264                 .dst = dst,
 265         }, *keyp = &key;
 266         struct utcp_connection **match = bsearch(&keyp, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 267         return match ? *match : NULL;
 268 }
 269
 270 static void free_connection(struct utcp_connection *c) {
 271         struct utcp *utcp = c->utcp;
 272         struct utcp_connection **cp = bsearch(&c, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 273
 274         assert(cp);
 275
 276         int i = cp - utcp->connections;
 277         memmove(cp, cp + 1, (utcp->nconnections - i - 1) * sizeof *cp);
 278         utcp->nconnections--;
 279
 280         buffer_exit(&c->rcvbuf);
 281         buffer_exit(&c->sndbuf);
 282         free(c);
 283 }
 284
 285 static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t src, uint16_t dst) {
 286         // Check whether this combination of src and dst is free
 287
 288         if(src) {
 289                 if(find_connection(utcp, src, dst)) {
 290                         errno = EADDRINUSE;
 291                         return NULL;
 292                 }
 293         } else { // If src == 0, generate a random port number with the high bit set
 294                 if(utcp->nconnections >= 32767) {
 295                         errno = ENOMEM;
 296                         return NULL;
 297                 }
 298                 src = rand() | 0x8000;
 299                 while(find_connection(utcp, src, dst))
 300                         src++;
 301         }
 302
 303         // Allocate memory for the new connection
 304
 305         if(utcp->nconnections >= utcp->nallocated) {
 306                 if(!utcp->nallocated)
 307                         utcp->nallocated = 4;
 308                 else
 309                         utcp->nallocated *= 2;
 310                 struct utcp_connection **new_array = realloc(utcp->connections, utcp->nallocated * sizeof *utcp->connections);
 311                 if(!new_array)
 312                         return NULL;
 313                 utcp->connections = new_array;
 314         }
 315
 316         struct utcp_connection *c = calloc(1, sizeof *c);
 317         if(!c)
 318                 return NULL;
 319
 320         if(!buffer_init(&c->sndbuf, DEFAULT_SNDBUFSIZE, DEFAULT_MAXSNDBUFSIZE)) {
 321                 free(c);
 322                 return NULL;
 323         }
 324
 325         if(!buffer_init(&c->rcvbuf, DEFAULT_RCVBUFSIZE, DEFAULT_MAXRCVBUFSIZE)) {
 326                 buffer_exit(&c->sndbuf);
 327                 free(c);
 328                 return NULL;
 329         }
 330
 331         // Fill in the details
 332
 333         c->src = src;
 334         c->dst = dst;
 335 #ifdef UTCP_DEBUG
 336         c->snd.iss = 0;
 337 #else
 338         c->snd.iss = rand();
 339 #endif
 340         c->snd.una = c->snd.iss;
 341         c->snd.nxt = c->snd.iss + 1;
 342         c->rcv.wnd = utcp->mtu;
 343         c->snd.last = c->snd.nxt;
 344         c->snd.cwnd = utcp->mtu;
 345         c->utcp = utcp;
 346
 347         // Add it to the sorted list of connections
 348
 349         utcp->connections[utcp->nconnections++] = c;
 350         qsort(utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 351
 352         return c;
 353 }
 354
 355 // Update RTT variables. See RFC 6298.
 356 static void update_rtt(struct utcp_connection *c, uint32_t rtt) {
 357         if(!rtt) {
 358                 debug("invalid rtt\n");
 359                 return;
 360         }
 361
 362         struct utcp *utcp = c->utcp;
 363
 364         if(!utcp->srtt) {
 365                 utcp->srtt = rtt;
 366                 utcp->rttvar = rtt / 2;
 367                 utcp->rto = rtt + max(2 * rtt, CLOCK_GRANULARITY);
 368         } else {
 369                 utcp->rttvar = (utcp->rttvar * 3 + abs(utcp->srtt - rtt)) / 4;
 370                 utcp->srtt = (utcp->srtt * 7 + rtt) / 8;
 371                 utcp->rto = utcp->srtt + max(utcp->rttvar, CLOCK_GRANULARITY);
 372         }
 373
 374         if(utcp->rto > MAX_RTO)
 375                 utcp->rto = MAX_RTO;
 376
 377         debug("rtt %u srtt %u rttvar %u rto %u\n", rtt, utcp->srtt, utcp->rttvar, utcp->rto);
 378 }
 379
 380 static void start_retransmit_timer(struct utcp_connection *c) {
 381         gettimeofday(&c->rtrx_timeout, NULL);
 382         c->rtrx_timeout.tv_usec += c->utcp->rto;
 383         while(c->rtrx_timeout.tv_usec >= 1000000) {
 384                 c->rtrx_timeout.tv_usec -= 1000000;
 385                 c->rtrx_timeout.tv_sec++;
 386         }
 387         debug("timeout set to %lu.%06lu (%u)\n", c->rtrx_timeout.tv_sec, c->rtrx_timeout.tv_usec, c->utcp->rto);
 388 }
 389
 390 static void stop_retransmit_timer(struct utcp_connection *c) {
 391         timerclear(&c->rtrx_timeout);
 392         debug("timeout cleared\n");
 393 }
 394
 395 struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
 396         struct utcp_connection *c = allocate_connection(utcp, 0, dst);
 397         if(!c)
 398                 return NULL;
 399
 400         c->recv = recv;
 401         c->priv = priv;
 402
 403         struct hdr hdr;
 404
 405         hdr.src = c->src;
 406         hdr.dst = c->dst;
 407         hdr.seq = c->snd.iss;
 408         hdr.ack = 0;
 409         hdr.wnd = c->rcv.wnd;
 410         hdr.ctl = SYN;
 411         hdr.aux = 0;
 412
 413         set_state(c, SYN_SENT);
 414
 415         print_packet(utcp, "send", &hdr, sizeof hdr);
 416         utcp->send(utcp, &hdr, sizeof hdr);
 417
 418         gettimeofday(&c->conn_timeout, NULL);
 419         c->conn_timeout.tv_sec += utcp->timeout;
 420
 421         return c;
 422 }
 423
 424 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 425         if(c->reapable || c->state != SYN_RECEIVED) {
 426                 debug("Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
 427                 return;
 428         }
 429
 430         debug("%p accepted, %p %p\n", c, recv, priv);
 431         c->recv = recv;
 432         c->priv = priv;
 433         set_state(c, ESTABLISHED);
 434 }
 435
 436 static void ack(struct utcp_connection *c, bool sendatleastone) {
 437         int32_t left = seqdiff(c->snd.last, c->snd.nxt);
 438         int32_t cwndleft = c->snd.cwnd - seqdiff(c->snd.nxt, c->snd.una);
 439         debug("cwndleft = %d\n", cwndleft);
 440
 441         assert(left >= 0);
 442
 443         if(cwndleft <= 0)
 444                 cwndleft = 0;
 445
 446         if(cwndleft < left)
 447                 left = cwndleft;
 448
 449         if(!left && !sendatleastone)
 450                 return;
 451
 452         struct {
 453                 struct hdr hdr;
 454                 char data[];
 455         } *pkt;
 456
 457         pkt = malloc(sizeof pkt->hdr + c->utcp->mtu);
 458         if(!pkt)
 459                 return;
 460
 461         pkt->hdr.src = c->src;
 462         pkt->hdr.dst = c->dst;
 463         pkt->hdr.ack = c->rcv.nxt;
 464         pkt->hdr.wnd = c->snd.wnd;
 465         pkt->hdr.ctl = ACK;
 466         pkt->hdr.aux = 0;
 467
 468         do {
 469                 uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
 470                 pkt->hdr.seq = c->snd.nxt;
 471
 472                 buffer_copy(&c->sndbuf, pkt->data, seqdiff(c->snd.nxt, c->snd.una), seglen);
 473
 474                 c->snd.nxt += seglen;
 475                 left -= seglen;
 476
 477                 if(seglen && fin_wanted(c, c->snd.nxt)) {
 478                         seglen--;
 479                         pkt->hdr.ctl |= FIN;
 480                 }
 481
 482                 if(!c->rtt_start.tv_sec) {
 483                         // Start RTT measurement
 484                         gettimeofday(&c->rtt_start, NULL);
 485                         c->rtt_seq = pkt->hdr.seq + seglen;
 486                         debug("Starting RTT measurement, expecting ack %u\n", c->rtt_seq);
 487                 }
 488
 489                 print_packet(c->utcp, "send", pkt, sizeof pkt->hdr + seglen);
 490                 c->utcp->send(c->utcp, pkt, sizeof pkt->hdr + seglen);
 491         } while(left);
 492
 493         free(pkt);
 494 }
 495
 496 ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 497         if(c->reapable) {
 498                 debug("Error: send() called on closed connection %p\n", c);
 499                 errno = EBADF;
 500                 return -1;
 501         }
 502
 503         switch(c->state) {
 504         case CLOSED:
 505         case LISTEN:
 506         case SYN_SENT:
 507         case SYN_RECEIVED:
 508                 debug("Error: send() called on unconnected connection %p\n", c);
 509                 errno = ENOTCONN;
 510                 return -1;
 511         case ESTABLISHED:
 512         case CLOSE_WAIT:
 513                 break;
 514         case FIN_WAIT_1:
 515         case FIN_WAIT_2:
 516         case CLOSING:
 517         case LAST_ACK:
 518         case TIME_WAIT:
 519                 debug("Error: send() called on closing connection %p\n", c);
 520                 errno = EPIPE;
 521                 return -1;
 522         }
 523
 524         // Add data to send buffer
 525
 526         if(!len)
 527                 return 0;
 528
 529         if(!data) {
 530                 errno = EFAULT;
 531                 return -1;
 532         }
 533
 534         len = buffer_put(&c->sndbuf, data, len);
 535         if(len <= 0) {
 536                 errno = EWOULDBLOCK;
 537                 return 0;
 538         }
 539
 540         c->snd.last += len;
 541         ack(c, false);
 542         if(!timerisset(&c->rtrx_timeout))
 543                 start_retransmit_timer(c);
 544         return len;
 545 }
 546
 547 static void swap_ports(struct hdr *hdr) {
 548         uint16_t tmp = hdr->src;
 549         hdr->src = hdr->dst;
 550         hdr->dst = tmp;
 551 }
 552
 553 static void retransmit(struct utcp_connection *c) {
 554         if(c->state == CLOSED || c->snd.last == c->snd.una) {
 555                 debug("Retransmit() called but nothing to retransmit!\n");
 556                 stop_retransmit_timer(c);
 557                 return;
 558         }
 559
 560         struct utcp *utcp = c->utcp;
 561
 562         struct {
 563                 struct hdr hdr;
 564                 char data[];
 565         } *pkt;
 566
 567         pkt = malloc(sizeof pkt->hdr + c->utcp->mtu);
 568         if(!pkt)
 569                 return;
 570
 571         pkt->hdr.src = c->src;
 572         pkt->hdr.dst = c->dst;
 573         pkt->hdr.wnd = c->rcv.wnd;
 574         pkt->hdr.aux = 0;
 575
 576         switch(c->state) {
 577                 case SYN_SENT:
 578                         // Send our SYN again
 579                         pkt->hdr.seq = c->snd.iss;
 580                         pkt->hdr.ack = 0;
 581                         pkt->hdr.ctl = SYN;
 582                         print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr);
 583                         utcp->send(utcp, pkt, sizeof pkt->hdr);
 584                         break;
 585
 586                 case SYN_RECEIVED:
 587                         // Send SYNACK again
 588                         pkt->hdr.seq = c->snd.nxt;
 589                         pkt->hdr.ack = c->rcv.nxt;
 590                         pkt->hdr.ctl = SYN | ACK;
 591                         print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr);
 592                         utcp->send(utcp, pkt, sizeof pkt->hdr);
 593                         break;
 594
 595                 case ESTABLISHED:
 596                 case FIN_WAIT_1:
 597                 case CLOSE_WAIT:
 598                 case CLOSING:
 599                 case LAST_ACK:
 600                         // Send unacked data again.
 601                         pkt->hdr.seq = c->snd.una;
 602                         pkt->hdr.ack = c->rcv.nxt;
 603                         pkt->hdr.ctl = ACK;
 604                         uint32_t len = seqdiff(c->snd.last, c->snd.una);
 605                         if(len > utcp->mtu)
 606                                 len = utcp->mtu;
 607                         if(fin_wanted(c, c->snd.una + len)) {
 608                                 len--;
 609                                 pkt->hdr.ctl |= FIN;
 610                         }
 611                         c->snd.nxt = c->snd.una + len;
 612                         c->snd.cwnd = utcp->mtu; // reduce cwnd on retransmit
 613                         buffer_copy(&c->sndbuf, pkt->data, 0, len);
 614                         print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr + len);
 615                         utcp->send(utcp, pkt, sizeof pkt->hdr + len);
 616                         break;
 617
 618                 case CLOSED:
 619                 case LISTEN:
 620                 case TIME_WAIT:
 621                 case FIN_WAIT_2:
 622                         // We shouldn't need to retransmit anything in this state.
 623 #ifdef UTCP_DEBUG
 624                         abort();
 625 #endif
 626                         stop_retransmit_timer(c);
 627                         goto cleanup;
 628         }
 629
 630         start_retransmit_timer(c);
 631         utcp->rto *= 2;
 632         if(utcp->rto > MAX_RTO)
 633                 utcp->rto = MAX_RTO;
 634         c->rtt_start.tv_sec = 0; // invalidate RTT timer
 635
 636 cleanup:
 637         free(pkt);
 638 }
 639
 640 /* Update receive buffer and SACK entries after consuming data.
 641  *
 642  * Situation:
 643  *
 644  * |.....0000..1111111111.....22222......3333|
 645  * |---------------^
 646  *
 647  * 0..3 represent the SACK entries. The ^ indicates up to which point we want
 648  * to remove data from the receive buffer. The idea is to substract "len"
 649  * from the offset of all the SACK entries, and then remove/cut down entries
 650  * that are shifted to before the start of the receive buffer.
 651  *
 652  * There are three cases:
 653  * - the SACK entry is after ^, in that case just change the offset.
 654  * - the SACK entry starts before and ends after ^, so we have to
 655  *   change both its offset and size.
 656  * - the SACK entry is completely before ^, in that case delete it.
 657  */
 658 static void sack_consume(struct utcp_connection *c, size_t len) {
 659         debug("sack_consume %zu\n", len);
 660         if(len > c->rcvbuf.used)
 661                 abort();
 662
 663         buffer_get(&c->rcvbuf, NULL, len);
 664
 665         for(int i = 0; i < NSACKS && c->sacks[i].len; ) {
 666                 if(len < c->sacks[i].offset) {
 667                         c->sacks[i].offset -= len;
 668                         i++;
 669                 } else if(len < c->sacks[i].offset + c->sacks[i].len) {
 670                         c->sacks[i].len -= len - c->sacks[i].offset;
 671                         c->sacks[i].offset = 0;
 672                         i++;
 673                 } else {
 674                         if(i < NSACKS - 1) {
 675                                 memmove(&c->sacks[i], &c->sacks[i + 1], (NSACKS - 1 - i) * sizeof c->sacks[i]);
 676                                 c->sacks[NSACKS - 1].len = 0;
 677                         } else {
 678                                 c->sacks[i].len = 0;
 679                                 break;
 680                         }
 681                 }
 682         }
 683
 684         for(int i = 0; i < NSACKS && c->sacks[i].len; i++)
 685                 debug("SACK[%d] offset %u len %u\n", i, c->sacks[i].offset, c->sacks[i].len);
 686 }
 687
 688 static void handle_out_of_order(struct utcp_connection *c, uint32_t offset, const void *data, size_t len) {
 689         debug("out of order packet, offset %u\n", offset);
 690         // Packet loss or reordering occured. Store the data in the buffer.
 691         ssize_t rxd = buffer_put_at(&c->rcvbuf, offset, data, len);
 692         if(rxd < len)
 693                 abort();
 694
 695         // Make note of where we put it.
 696         for(int i = 0; i < NSACKS; i++) {
 697                 if(!c->sacks[i].len) { // nothing to merge, add new entry
 698                         debug("New SACK entry %d\n", i);
 699                         c->sacks[i].offset = offset;
 700                         c->sacks[i].len = rxd;
 701                         break;
 702                 } else if(offset < c->sacks[i].offset) {
 703                         if(offset + rxd < c->sacks[i].offset) { // insert before
 704                                 if(!c->sacks[NSACKS - 1].len) { // only if room left
 705                                         debug("Insert SACK entry at %d\n", i);
 706                                         memmove(&c->sacks[i + 1], &c->sacks[i], (NSACKS - i - 1) * sizeof c->sacks[i]);
 707                                         c->sacks[i].offset = offset;
 708                                         c->sacks[i].len = rxd;
 709                                 }
 710                                 break;
 711                         } else { // merge
 712                                 debug("Merge with start of SACK entry at %d\n", i);
 713                                 c->sacks[i].offset = offset;
 714                                 break;
 715                         }
 716                 } else if(offset <= c->sacks[i].offset + c->sacks[i].len) {
 717                         if(offset + rxd > c->sacks[i].offset + c->sacks[i].len) { // merge
 718                                 debug("Merge with end of SACK entry at %d\n", i);
 719                                 c->sacks[i].len = offset + rxd - c->sacks[i].offset;
 720                                 // TODO: handle potential merge with next entry
 721                         }
 722                         break;
 723                 }
 724         }
 725
 726         for(int i = 0; i < NSACKS && c->sacks[i].len; i++)
 727                 debug("SACK[%d] offset %u len %u\n", i, c->sacks[i].offset, c->sacks[i].len);
 728 }
 729
 730 static void handle_in_order(struct utcp_connection *c, const void *data, size_t len) {
 731         // Check if we can process out-of-order data now.
 732         if(c->sacks[0].len && len >= c->sacks[0].offset) { // TODO: handle overlap with second SACK
 733                 debug("incoming packet len %zu connected with SACK at %u\n", len, c->sacks[0].offset);
 734                 buffer_put_at(&c->rcvbuf, 0, data, len); // TODO: handle return value
 735                 len = max(len, c->sacks[0].offset + c->sacks[0].len);
 736                 data = c->rcvbuf.data;
 737         }
 738
 739         if(c->recv) {
 740                 ssize_t rxd = c->recv(c, data, len);
 741                 if(rxd != len) {
 742                         // TODO: handle the application not accepting all data.
 743                         abort();
 744                 }
 745         }
 746
 747         if(c->rcvbuf.used)
 748                 sack_consume(c, len);
 749
 750         c->rcv.nxt += len;
 751 }
 752
 753
 754 static void handle_incoming_data(struct utcp_connection *c, uint32_t seq, const void *data, size_t len) {
 755         uint32_t offset = seqdiff(seq, c->rcv.nxt);
 756         if(offset + len > c->rcvbuf.maxsize)
 757                 abort();
 758
 759         if(offset)
 760                 handle_out_of_order(c, offset, data, len);
 761         else
 762                 handle_in_order(c, data, len);
 763 }
 764
 765
 766 ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 767         if(!utcp) {
 768                 errno = EFAULT;
 769                 return -1;
 770         }
 771
 772         if(!len)
 773                 return 0;
 774
 775         if(!data) {
 776                 errno = EFAULT;
 777                 return -1;
 778         }
 779
 780         print_packet(utcp, "recv", data, len);
 781
 782         // Drop packets smaller than the header
 783
 784         struct hdr hdr;
 785         if(len < sizeof hdr) {
 786                 errno = EBADMSG;
 787                 return -1;
 788         }
 789
 790         // Make a copy from the potentially unaligned data to a struct hdr
 791
 792         memcpy(&hdr, data, sizeof hdr);
 793         data += sizeof hdr;
 794         len -= sizeof hdr;
 795
 796         // Drop packets with an unknown CTL flag
 797
 798         if(hdr.ctl & ~(SYN | ACK | RST | FIN)) {
 799                 errno = EBADMSG;
 800                 return -1;
 801         }
 802
 803         // Try to match the packet to an existing connection
 804
 805         struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
 806
 807         // Is it for a new connection?
 808
 809         if(!c) {
 810                 // Ignore RST packets
 811
 812                 if(hdr.ctl & RST)
 813                         return 0;
 814
 815                 // Is it a SYN packet and are we LISTENing?
 816
 817                 if(hdr.ctl & SYN && !(hdr.ctl & ACK) && utcp->accept) {
 818                         // If we don't want to accept it, send a RST back
 819                         if((utcp->pre_accept && !utcp->pre_accept(utcp, hdr.dst))) {
 820                                 len = 1;
 821                                 goto reset;
 822                         }
 823
 824                         // Try to allocate memory, otherwise send a RST back
 825                         c = allocate_connection(utcp, hdr.dst, hdr.src);
 826                         if(!c) {
 827                                 len = 1;
 828                                 goto reset;
 829                         }
 830
 831                         // Return SYN+ACK, go to SYN_RECEIVED state
 832                         c->snd.wnd = hdr.wnd;
 833                         c->rcv.irs = hdr.seq;
 834                         c->rcv.nxt = c->rcv.irs + 1;
 835                         set_state(c, SYN_RECEIVED);
 836
 837                         hdr.dst = c->dst;
 838                         hdr.src = c->src;
 839                         hdr.ack = c->rcv.irs + 1;
 840                         hdr.seq = c->snd.iss;
 841                         hdr.ctl = SYN | ACK;
 842                         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 843                         utcp->send(utcp, &hdr, sizeof hdr);
 844                 } else {
 845                         // No, we don't want your packets, send a RST back
 846                         len = 1;
 847                         goto reset;
 848                 }
 849
 850                 return 0;
 851         }
 852
 853         debug("%p state %s\n", c->utcp, strstate[c->state]);
 854
 855         // In case this is for a CLOSED connection, ignore the packet.
 856         // TODO: make it so incoming packets can never match a CLOSED connection.
 857
 858         if(c->state == CLOSED)
 859                 return 0;
 860
 861         // It is for an existing connection.
 862
 863         uint32_t prevrcvnxt = c->rcv.nxt;
 864
 865         // 1. Drop invalid packets.
 866
 867         // 1a. Drop packets that should not happen in our current state.
 868
 869         switch(c->state) {
 870         case SYN_SENT:
 871         case SYN_RECEIVED:
 872         case ESTABLISHED:
 873         case FIN_WAIT_1:
 874         case FIN_WAIT_2:
 875         case CLOSE_WAIT:
 876         case CLOSING:
 877         case LAST_ACK:
 878         case TIME_WAIT:
 879                 break;
 880         default:
 881 #ifdef UTCP_DEBUG
 882                 abort();
 883 #endif
 884                 break;
 885         }
 886
 887         // 1b. Drop packets with a sequence number not in our receive window.
 888
 889         bool acceptable;
 890
 891         if(c->state == SYN_SENT)
 892                 acceptable = true;
 893         else if(len == 0)
 894                 acceptable = seqdiff(hdr.seq, c->rcv.nxt) >= 0;
 895         else {
 896                 int32_t rcv_offset = seqdiff(hdr.seq, c->rcv.nxt);
 897
 898                 // cut already accepted front overlapping
 899                 if(rcv_offset < 0) {
 900                         acceptable = rcv_offset + len >= 0;
 901                         if(acceptable) {
 902                                 data -= rcv_offset;
 903                                 len += rcv_offset;
 904                         }
 905                 }
 906
 907                 acceptable = seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt) + len <= c->rcvbuf.maxsize;
 908         }
 909
 910         if(!acceptable) {
 911                 debug("Packet not acceptable, %u <= %u + %zu < %u\n", c->rcv.nxt, hdr.seq, len, c->rcv.nxt + c->rcvbuf.maxsize);
 912                 // Ignore unacceptable RST packets.
 913                 if(hdr.ctl & RST)
 914                         return 0;
 915                 // Otherwise, send an ACK back in the hope things improve.
 916                 ack(c, true);
 917                 return 0;
 918         }
 919
 920         c->snd.wnd = hdr.wnd; // TODO: move below
 921
 922         // 1c. Drop packets with an invalid ACK.
 923         // ackno should not roll back, and it should also not be bigger than what we ever could have sent
 924         // (= snd.una + c->sndbuf.used).
 925
 926         if(hdr.ctl & ACK && (seqdiff(hdr.ack, c->snd.last) > 0 || seqdiff(hdr.ack, c->snd.una) < 0)) {
 927                 debug("Packet ack seqno out of range, %u <= %u < %u\n", c->snd.una, hdr.ack, c->snd.una + c->sndbuf.used);
 928                 // Ignore unacceptable RST packets.
 929                 if(hdr.ctl & RST)
 930                         return 0;
 931                 goto reset;
 932         }
 933
 934         // 2. Handle RST packets
 935
 936         if(hdr.ctl & RST) {
 937                 switch(c->state) {
 938                 case SYN_SENT:
 939                         if(!(hdr.ctl & ACK))
 940                                 return 0;
 941                         // The peer has refused our connection.
 942                         set_state(c, CLOSED);
 943                         errno = ECONNREFUSED;
 944                         if(c->recv)
 945                                 c->recv(c, NULL, 0);
 946                         return 0;
 947                 case SYN_RECEIVED:
 948                         if(hdr.ctl & ACK)
 949                                 return 0;
 950                         // We haven't told the application about this connection yet. Silently delete.
 951                         free_connection(c);
 952                         return 0;
 953                 case ESTABLISHED:
 954                 case FIN_WAIT_1:
 955                 case FIN_WAIT_2:
 956                 case CLOSE_WAIT:
 957                         if(hdr.ctl & ACK)
 958                                 return 0;
 959                         // The peer has aborted our connection.
 960                         set_state(c, CLOSED);
 961                         errno = ECONNRESET;
 962                         if(c->recv)
 963                                 c->recv(c, NULL, 0);
 964                         return 0;
 965                 case CLOSING:
 966                 case LAST_ACK:
 967                 case TIME_WAIT:
 968                         if(hdr.ctl & ACK)
 969                                 return 0;
 970                         // As far as the application is concerned, the connection has already been closed.
 971                         // If it has called utcp_close() already, we can immediately free this connection.
 972                         if(c->reapable) {
 973                                 free_connection(c);
 974                                 return 0;
 975                         }
 976                         // Otherwise, immediately move to the CLOSED state.
 977                         set_state(c, CLOSED);
 978                         return 0;
 979                 default:
 980 #ifdef UTCP_DEBUG
 981                         abort();
 982 #endif
 983                         break;
 984                 }
 985         }
 986
 987         // 3. Advance snd.una
 988
 989         uint32_t advanced = seqdiff(hdr.ack, c->snd.una);
 990         prevrcvnxt = c->rcv.nxt;
 991
 992         if(advanced) {
 993                 // RTT measurement
 994                 if(c->rtt_start.tv_sec) {
 995                         if(c->rtt_seq == hdr.ack) {
 996                                 struct timeval now, diff;
 997                                 gettimeofday(&now, NULL);
 998                                 timersub(&now, &c->rtt_start, &diff);
 999                                 update_rtt(c, diff.tv_sec * 1000000 + diff.tv_usec);
1000                                 c->rtt_start.tv_sec = 0;
1001                         } else if(c->rtt_seq < hdr.ack) {
1002                                 debug("Cancelling RTT measurement: %u < %u\n", c->rtt_seq, hdr.ack);
1003                                 c->rtt_start.tv_sec = 0;
1004                         }
1005                 }
1006
1007                 int32_t data_acked = advanced;
1008
1009                 switch(c->state) {
1010                         case SYN_SENT:
1011                         case SYN_RECEIVED:
1012                                 data_acked--;
1013                                 break;
1014                         // TODO: handle FIN as well.
1015                         default:
1016                                 break;
1017                 }
1018
1019                 assert(data_acked >= 0);
1020
1021                 int32_t bufused = seqdiff(c->snd.last, c->snd.una);
1022                 assert(data_acked <= bufused);
1023
1024                 if(data_acked)
1025                         buffer_get(&c->sndbuf, NULL, data_acked);
1026
1027                 // Also advance snd.nxt if possible
1028                 if(seqdiff(c->snd.nxt, hdr.ack) < 0)
1029                         c->snd.nxt = hdr.ack;
1030
1031                 c->snd.una = hdr.ack;
1032
1033                 c->dupack = 0;
1034                 c->snd.cwnd += utcp->mtu;
1035                 if(c->snd.cwnd > c->sndbuf.maxsize)
1036                         c->snd.cwnd = c->sndbuf.maxsize;
1037
1038                 // Check if we have sent a FIN that is now ACKed.
1039                 switch(c->state) {
1040                 case FIN_WAIT_1:
1041                         if(c->snd.una == c->snd.last)
1042                                 set_state(c, FIN_WAIT_2);
1043                         break;
1044                 case CLOSING:
1045                         if(c->snd.una == c->snd.last) {
1046                                 gettimeofday(&c->conn_timeout, NULL);
1047                                 c->conn_timeout.tv_sec += 60;
1048                                 set_state(c, TIME_WAIT);
1049                         }
1050                         break;
1051                 default:
1052                         break;
1053                 }
1054         } else {
1055                 if(!len) {
1056                         c->dupack++;
1057                         if(c->dupack == 3) {
1058                                 debug("Triplicate ACK\n");
1059                                 //TODO: Resend one packet and go to fast recovery mode. See RFC 6582.
1060                                 //We do a very simple variant here; reset the nxt pointer to the last acknowledged packet from the peer.
1061                                 //Reset the congestion window so we wait for ACKs.
1062                                 c->snd.nxt = c->snd.una;
1063                                 c->snd.cwnd = utcp->mtu;
1064                                 start_retransmit_timer(c);
1065                         }
1066                 }
1067         }
1068
1069         // 4. Update timers
1070
1071         if(advanced) {
1072                 timerclear(&c->conn_timeout); // It will be set anew in utcp_timeout() if c->snd.una != c->snd.nxt.
1073                 if(c->snd.una == c->snd.last)
1074                         stop_retransmit_timer(c);
1075                 else
1076                         start_retransmit_timer(c);
1077         }
1078
1079         // 5. Process SYN stuff
1080
1081         if(hdr.ctl & SYN) {
1082                 switch(c->state) {
1083                 case SYN_SENT:
1084                         // This is a SYNACK. It should always have ACKed the SYN.
1085                         if(!advanced)
1086                                 goto reset;
1087                         c->rcv.irs = hdr.seq;
1088                         c->rcv.nxt = hdr.seq;
1089                         set_state(c, ESTABLISHED);
1090                         // TODO: notify application of this somehow.
1091                         break;
1092                 case SYN_RECEIVED:
1093                 case ESTABLISHED:
1094                 case FIN_WAIT_1:
1095                 case FIN_WAIT_2:
1096                 case CLOSE_WAIT:
1097                 case CLOSING:
1098                 case LAST_ACK:
1099                 case TIME_WAIT:
1100                         // Ehm, no. We should never receive a second SYN.
1101                         goto reset;
1102                 default:
1103 #ifdef UTCP_DEBUG
1104                         abort();
1105 #endif
1106                         return 0;
1107                 }
1108
1109                 // SYN counts as one sequence number
1110                 c->rcv.nxt++;
1111         }
1112
1113         // 6. Process new data
1114
1115         if(c->state == SYN_RECEIVED) {
1116                 // This is the ACK after the SYNACK. It should always have ACKed the SYNACK.
1117                 if(!advanced)
1118                         goto reset;
1119
1120                 // Are we still LISTENing?
1121                 if(utcp->accept)
1122                         utcp->accept(c, c->src);
1123
1124                 if(c->state != ESTABLISHED) {
1125                         set_state(c, CLOSED);
1126                         c->reapable = true;
1127                         goto reset;
1128                 }
1129         }
1130
1131         if(len) {
1132                 switch(c->state) {
1133                 case SYN_SENT:
1134                 case SYN_RECEIVED:
1135                         // This should never happen.
1136 #ifdef UTCP_DEBUG
1137                         abort();
1138 #endif
1139                         return 0;
1140                 case ESTABLISHED:
1141                 case FIN_WAIT_1:
1142                 case FIN_WAIT_2:
1143                         break;
1144                 case CLOSE_WAIT:
1145                 case CLOSING:
1146                 case LAST_ACK:
1147                 case TIME_WAIT:
1148                         // Ehm no, We should never receive more data after a FIN.
1149                         goto reset;
1150                 default:
1151 #ifdef UTCP_DEBUG
1152                         abort();
1153 #endif
1154                         return 0;
1155                 }
1156
1157                 handle_incoming_data(c, hdr.seq, data, len);
1158         }
1159
1160         // 7. Process FIN stuff
1161
1162         if((hdr.ctl & FIN) && hdr.seq + len == c->rcv.nxt) {
1163                 switch(c->state) {
1164                 case SYN_SENT:
1165                 case SYN_RECEIVED:
1166                         // This should never happen.
1167 #ifdef UTCP_DEBUG
1168                         abort();
1169 #endif
1170                         break;
1171                 case ESTABLISHED:
1172                         set_state(c, CLOSE_WAIT);
1173                         break;
1174                 case FIN_WAIT_1:
1175                         set_state(c, CLOSING);
1176                         break;
1177                 case FIN_WAIT_2:
1178                         gettimeofday(&c->conn_timeout, NULL);
1179                         c->conn_timeout.tv_sec += 60;
1180                         set_state(c, TIME_WAIT);
1181                         break;
1182                 case CLOSE_WAIT:
1183                 case CLOSING:
1184                 case LAST_ACK:
1185                 case TIME_WAIT:
1186                         // Ehm, no. We should never receive a second FIN.
1187                         goto reset;
1188                 default:
1189 #ifdef UTCP_DEBUG
1190                         abort();
1191 #endif
1192                         break;
1193                 }
1194
1195                 // FIN counts as one sequence number
1196                 c->rcv.nxt++;
1197                 len++;
1198
1199                 // Inform the application that the peer closed the connection.
1200                 if(c->recv) {
1201                         errno = 0;
1202                         c->recv(c, NULL, 0);
1203                 }
1204         }
1205
1206         // Now we send something back if:
1207         // - we advanced rcv.nxt (ie, we got some data that needs to be ACKed)
1208         //   -> sendatleastone = true
1209         // - or we got an ack, so we should maybe send a bit more data
1210         //   -> sendatleastone = false
1211
1212         ack(c, len || prevrcvnxt != c->rcv.nxt);
1213         return 0;
1214
1215 reset:
1216         swap_ports(&hdr);
1217         hdr.wnd = 0;
1218         if(hdr.ctl & ACK) {
1219                 hdr.seq = hdr.ack;
1220                 hdr.ctl = RST;
1221         } else {
1222                 hdr.ack = hdr.seq + len;
1223                 hdr.seq = 0;
1224                 hdr.ctl = RST | ACK;
1225         }
1226         print_packet(utcp, "send", &hdr, sizeof hdr);
1227         utcp->send(utcp, &hdr, sizeof hdr);
1228         return 0;
1229
1230 }
1231
1232 int utcp_shutdown(struct utcp_connection *c, int dir) {
1233         debug("%p shutdown %d at %u\n", c ? c->utcp : NULL, dir, c ? c->snd.last : 0);
1234         if(!c) {
1235                 errno = EFAULT;
1236                 return -1;
1237         }
1238
1239         if(c->reapable) {
1240                 debug("Error: shutdown() called on closed connection %p\n", c);
1241                 errno = EBADF;
1242                 return -1;
1243         }
1244
1245         if(!(dir == UTCP_SHUT_RD || dir == UTCP_SHUT_WR || dir == UTCP_SHUT_RDWR)) {
1246                 errno = EINVAL;
1247                 return -1;
1248         }
1249
1250         // TCP does not have a provision for stopping incoming packets.
1251         // The best we can do is to just ignore them.
1252         if(dir == UTCP_SHUT_RD || dir == UTCP_SHUT_RDWR)
1253                 c->recv = NULL;
1254
1255         // The rest of the code deals with shutting down writes.
1256         if(dir == UTCP_SHUT_RD)
1257                 return 0;
1258
1259         switch(c->state) {
1260         case CLOSED:
1261         case LISTEN:
1262                 errno = ENOTCONN;
1263                 return -1;
1264
1265         case SYN_SENT:
1266                 set_state(c, CLOSED);
1267                 return 0;
1268
1269         case SYN_RECEIVED:
1270         case ESTABLISHED:
1271                 set_state(c, FIN_WAIT_1);
1272                 break;
1273         case FIN_WAIT_1:
1274         case FIN_WAIT_2:
1275                 return 0;
1276         case CLOSE_WAIT:
1277                 set_state(c, CLOSING);
1278                 break;
1279
1280         case CLOSING:
1281         case LAST_ACK:
1282         case TIME_WAIT:
1283                 return 0;
1284         }
1285
1286         c->snd.last++;
1287
1288         ack(c, false);
1289         if(!timerisset(&c->rtrx_timeout))
1290                 start_retransmit_timer(c);
1291         return 0;
1292 }
1293
1294 int utcp_close(struct utcp_connection *c) {
1295         if(utcp_shutdown(c, SHUT_RDWR))
1296                 return -1;
1297         c->recv = NULL;
1298         c->poll = NULL;
1299         c->reapable = true;
1300         return 0;
1301 }
1302
1303 int utcp_abort(struct utcp_connection *c) {
1304         if(!c) {
1305                 errno = EFAULT;
1306                 return -1;
1307         }
1308
1309         if(c->reapable) {
1310                 debug("Error: abort() called on closed connection %p\n", c);
1311                 errno = EBADF;
1312                 return -1;
1313         }
1314
1315         c->recv = NULL;
1316         c->poll = NULL;
1317         c->reapable = true;
1318
1319         switch(c->state) {
1320         case CLOSED:
1321                 return 0;
1322         case LISTEN:
1323         case SYN_SENT:
1324         case CLOSING:
1325         case LAST_ACK:
1326         case TIME_WAIT:
1327                 set_state(c, CLOSED);
1328                 return 0;
1329
1330         case SYN_RECEIVED:
1331         case ESTABLISHED:
1332         case FIN_WAIT_1:
1333         case FIN_WAIT_2:
1334         case CLOSE_WAIT:
1335                 set_state(c, CLOSED);
1336                 break;
1337         }
1338
1339         // Send RST
1340
1341         struct hdr hdr;
1342
1343         hdr.src = c->src;
1344         hdr.dst = c->dst;
1345         hdr.seq = c->snd.nxt;
1346         hdr.ack = 0;
1347         hdr.wnd = 0;
1348         hdr.ctl = RST;
1349
1350         print_packet(c->utcp, "send", &hdr, sizeof hdr);
1351         c->utcp->send(c->utcp, &hdr, sizeof hdr);
1352         return 0;
1353 }
1354
1355 /* Handle timeouts.
1356  * One call to this function will loop through all connections,
1357  * checking if something needs to be resent or not.
1358  * The return value is the time to the next timeout in milliseconds,
1359  * or maybe a negative value if the timeout is infinite.
1360  */
1361 struct timeval utcp_timeout(struct utcp *utcp) {
1362         struct timeval now;
1363         gettimeofday(&now, NULL);
1364         struct timeval next = {now.tv_sec + 3600, now.tv_usec};
1365
1366         for(int i = 0; i < utcp->nconnections; i++) {
1367                 struct utcp_connection *c = utcp->connections[i];
1368                 if(!c)
1369                         continue;
1370
1371                 // delete connections that have been utcp_close()d.
1372                 if(c->state == CLOSED) {
1373                         if(c->reapable) {
1374                                 debug("Reaping %p\n", c);
1375                                 free_connection(c);
1376                                 i--;
1377                         }
1378                         continue;
1379                 }
1380
1381                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &now, <)) {
1382                         errno = ETIMEDOUT;
1383                         c->state = CLOSED;
1384                         if(c->recv)
1385                                 c->recv(c, NULL, 0);
1386                         continue;
1387                 }
1388
1389                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &now, <)) {
1390                         debug("retransmit()\n");
1391                         retransmit(c);
1392                 }
1393
1394                 if(c->poll && buffer_free(&c->sndbuf) && (c->state == ESTABLISHED || c->state == CLOSE_WAIT))
1395                         c->poll(c, buffer_free(&c->sndbuf));
1396
1397                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <))
1398                         next = c->conn_timeout;
1399
1400                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <))
1401                         next = c->rtrx_timeout;
1402         }
1403
1404         struct timeval diff;
1405         timersub(&next, &now, &diff);
1406         return diff;
1407 }
1408
1409 bool utcp_is_active(struct utcp *utcp) {
1410         if(!utcp)
1411                 return false;
1412
1413         for(int i = 0; i < utcp->nconnections; i++)
1414                 if(utcp->connections[i]->state != CLOSED && utcp->connections[i]->state != TIME_WAIT)
1415                         return true;
1416
1417         return false;
1418 }
1419
1420 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
1421         if(!send) {
1422                 errno = EFAULT;
1423                 return NULL;
1424         }
1425
1426         struct utcp *utcp = calloc(1, sizeof *utcp);
1427         if(!utcp)
1428                 return NULL;
1429
1430         utcp->accept = accept;
1431         utcp->pre_accept = pre_accept;
1432         utcp->send = send;
1433         utcp->priv = priv;
1434         utcp->mtu = DEFAULT_MTU;
1435         utcp->timeout = DEFAULT_USER_TIMEOUT; // s
1436         utcp->rto = START_RTO; // us
1437
1438         return utcp;
1439 }
1440
1441 void utcp_exit(struct utcp *utcp) {
1442         if(!utcp)
1443                 return;
1444         for(int i = 0; i < utcp->nconnections; i++) {
1445                 if(!utcp->connections[i]->reapable)
1446                         debug("Warning, freeing unclosed connection %p\n", utcp->connections[i]);
1447                 buffer_exit(&utcp->connections[i]->rcvbuf);
1448                 buffer_exit(&utcp->connections[i]->sndbuf);
1449                 free(utcp->connections[i]);
1450         }
1451         free(utcp->connections);
1452         free(utcp);
1453 }
1454
1455 uint16_t utcp_get_mtu(struct utcp *utcp) {
1456         return utcp ? utcp->mtu : 0;
1457 }
1458
1459 void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
1460         // TODO: handle overhead of the header
1461         if(utcp)
1462                 utcp->mtu = mtu;
1463 }
1464
1465 int utcp_get_user_timeout(struct utcp *u) {
1466         return u ? u->timeout : 0;
1467 }
1468
1469 void utcp_set_user_timeout(struct utcp *u, int timeout) {
1470         if(u)
1471                 u->timeout = timeout;
1472 }
1473
1474 size_t utcp_get_sndbuf(struct utcp_connection *c) {
1475         return c ? c->sndbuf.maxsize : 0;
1476 }
1477
1478 size_t utcp_get_sndbuf_free(struct utcp_connection *c) {
1479         if(c && (c->state == ESTABLISHED || c->state == CLOSE_WAIT))
1480                 return buffer_free(&c->sndbuf);
1481         else
1482                 return 0;
1483 }
1484
1485 void utcp_set_sndbuf(struct utcp_connection *c, size_t size) {
1486         if(!c)
1487                 return;
1488         c->sndbuf.maxsize = size;
1489         if(c->sndbuf.maxsize != size)
1490                 c->sndbuf.maxsize = -1;
1491 }
1492
1493 size_t utcp_get_rcvbuf(struct utcp_connection *c) {
1494         return c ? c->rcvbuf.maxsize : 0;
1495 }
1496
1497 size_t utcp_get_rcvbuf_free(struct utcp_connection *c) {
1498         if(c && (c->state == ESTABLISHED || c->state == CLOSE_WAIT))
1499                 return buffer_free(&c->rcvbuf);
1500         else
1501                 return 0;
1502 }
1503
1504 void utcp_set_rcvbuf(struct utcp_connection *c, size_t size) {
1505         if(!c)
1506                 return;
1507         c->rcvbuf.maxsize = size;
1508         if(c->rcvbuf.maxsize != size)
1509                 c->rcvbuf.maxsize = -1;
1510 }
1511
1512 bool utcp_get_nodelay(struct utcp_connection *c) {
1513         return c ? c->nodelay : false;
1514 }
1515
1516 void utcp_set_nodelay(struct utcp_connection *c, bool nodelay) {
1517         if(c)
1518                 c->nodelay = nodelay;
1519 }
1520
1521 bool utcp_get_keepalive(struct utcp_connection *c) {
1522         return c ? c->keepalive : false;
1523 }
1524
1525 void utcp_set_keepalive(struct utcp_connection *c, bool keepalive) {
1526         if(c)
1527                 c->keepalive = keepalive;
1528 }
1529
1530 size_t utcp_get_outq(struct utcp_connection *c) {
1531         return c ? seqdiff(c->snd.nxt, c->snd.una) : 0;
1532 }
1533
1534 void utcp_set_recv_cb(struct utcp_connection *c, utcp_recv_t recv) {
1535         if(c)
1536                 c->recv = recv;
1537 }
1538
1539 void utcp_set_poll_cb(struct utcp_connection *c, utcp_poll_t poll) {
1540         if(c)
1541                 c->poll = poll;
1542 }
1543
1544 void utcp_set_accept_cb(struct utcp *utcp, utcp_accept_t accept, utcp_pre_accept_t pre_accept) {
1545         if(utcp) {
1546                 utcp->accept = accept;
1547                 utcp->pre_accept = pre_accept;
1548         }
1549 }