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