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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 #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                 debug(" data=");
  90                 for(int i = sizeof hdr; i < len; i++) {
  91                         const char *data = pkt;
  92                         debug("%c", data[i] >= 32 ? data[i] : '.');
  93                 }
  94         }
  95
  96         debug("\n");
  97 }
  98 #else
  99 #define debug(...)
 100 #define print_packet(...)
 101 #endif
 102
 103 static void set_state(struct utcp_connection *c, enum state state) {
 104         c->state = state;
 105         if(state == ESTABLISHED)
 106                 timerclear(&c->conn_timeout);
 107         debug("%p new state: %s\n", c->utcp, strstate[state]);
 108 }
 109
 110 static bool fin_wanted(struct utcp_connection *c, uint32_t seq) {
 111         if(seq != c->snd.last)
 112                 return false;
 113         switch(c->state) {
 114         case FIN_WAIT_1:
 115         case CLOSING:
 116         case LAST_ACK:
 117                 return true;
 118         default:
 119                 return false;
 120         }
 121 }
 122
 123 static inline void list_connections(struct utcp *utcp) {
 124         debug("%p has %d connections:\n", utcp, utcp->nconnections);
 125         for(int i = 0; i < utcp->nconnections; i++)
 126                 debug("  %u -> %u state %s\n", utcp->connections[i]->src, utcp->connections[i]->dst, strstate[utcp->connections[i]->state]);
 127 }
 128
 129 static int32_t seqdiff(uint32_t a, uint32_t b) {
 130         return a - b;
 131 }
 132
 133 // Buffer functions
 134 // TODO: convert to ringbuffers to avoid memmove() operations.
 135
 136 // Store data into the buffer
 137 static ssize_t buffer_put_at(struct buffer *buf, size_t offset, const void *data, size_t len) {
 138         if(buf->maxsize <= buf->used)
 139                 return 0;
 140
 141         debug("buffer_put_at %zu %zu %zu\n", buf->used, offset, len);
 142
 143         size_t required = offset + len;
 144         if(required > buf->maxsize) {
 145                 if(offset >= buf->maxsize)
 146                         return 0;
 147                 abort();
 148                 len = buf->maxsize - offset;
 149                 required = buf->maxsize;
 150         }
 151
 152         if(required > buf->size) {
 153                 size_t newsize = buf->size;
 154                 if(!newsize) {
 155                         newsize = required;
 156                 } else {
 157                         do {
 158                                 newsize *= 2;
 159                         } while(newsize < buf->used + len);
 160                 }
 161                 if(newsize > buf->maxsize)
 162                         newsize = buf->maxsize;
 163                 char *newdata = realloc(buf->data, newsize);
 164                 if(!newdata)
 165                         return -1;
 166                 buf->data = newdata;
 167                 buf->size = newsize;
 168         }
 169
 170         memcpy(buf->data + offset, data, len);
 171         if(required > buf->used)
 172                 buf->used = required;
 173         return len;
 174 }
 175
 176 static ssize_t buffer_put(struct buffer *buf, const void *data, size_t len) {
 177         return buffer_put_at(buf, buf->used, data, len);
 178 }
 179
 180 // Get data from the buffer. data can be NULL.
 181 static ssize_t buffer_get(struct buffer *buf, void *data, size_t len) {
 182         if(len > buf->used)
 183                 len = buf->used;
 184         if(data)
 185                 memcpy(data, buf->data, len);
 186         if(len < buf->used)
 187                 memmove(buf->data, buf->data + len, buf->used - len);
 188         buf->used -= len;
 189         return len;
 190 }
 191
 192 // Copy data from the buffer without removing it.
 193 static ssize_t buffer_copy(struct buffer *buf, void *data, size_t offset, size_t len) {
 194         if(offset >= buf->used)
 195                 return 0;
 196         if(offset + len > buf->used)
 197                 len = buf->used - offset;
 198         memcpy(data, buf->data + offset, len);
 199         return len;
 200 }
 201
 202 static bool buffer_init(struct buffer *buf, uint32_t len, uint32_t maxlen) {
 203         memset(buf, 0, sizeof *buf);
 204         if(len) {
 205                 buf->data = malloc(len);
 206                 if(!buf->data)
 207                         return false;
 208         }
 209         buf->size = len;
 210         buf->maxsize = maxlen;
 211         return true;
 212 }
 213
 214 static void buffer_exit(struct buffer *buf) {
 215         free(buf->data);
 216         memset(buf, 0, sizeof *buf);
 217 }
 218
 219 static uint32_t buffer_free(const struct buffer *buf) {
 220         return buf->maxsize - buf->used;
 221 }
 222
 223 // Connections are stored in a sorted list.
 224 // This gives O(log(N)) lookup time, O(N log(N)) insertion time and O(N) deletion time.
 225
 226 static int compare(const void *va, const void *vb) {
 227         assert(va && vb);
 228
 229         const struct utcp_connection *a = *(struct utcp_connection **)va;
 230         const struct utcp_connection *b = *(struct utcp_connection **)vb;
 231
 232         assert(a && b);
 233         assert(a->src && b->src);
 234
 235         int c = (int)a->src - (int)b->src;
 236         if(c)
 237                 return c;
 238         c = (int)a->dst - (int)b->dst;
 239         return c;
 240 }
 241
 242 static struct utcp_connection *find_connection(const struct utcp *utcp, uint16_t src, uint16_t dst) {
 243         if(!utcp->nconnections)
 244                 return NULL;
 245         struct utcp_connection key = {
 246                 .src = src,
 247                 .dst = dst,
 248         }, *keyp = &key;
 249         struct utcp_connection **match = bsearch(&keyp, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 250         return match ? *match : NULL;
 251 }
 252
 253 static void free_connection(struct utcp_connection *c) {
 254         struct utcp *utcp = c->utcp;
 255         struct utcp_connection **cp = bsearch(&c, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 256
 257         assert(cp);
 258
 259         int i = cp - utcp->connections;
 260         memmove(cp, cp + 1, (utcp->nconnections - i - 1) * sizeof *cp);
 261         utcp->nconnections--;
 262
 263         buffer_exit(&c->sndbuf);
 264         free(c);
 265 }
 266
 267 static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t src, uint16_t dst) {
 268         // Check whether this combination of src and dst is free
 269
 270         if(src) {
 271                 if(find_connection(utcp, src, dst)) {
 272                         errno = EADDRINUSE;
 273                         return NULL;
 274                 }
 275         } else { // If src == 0, generate a random port number with the high bit set
 276                 if(utcp->nconnections >= 32767) {
 277                         errno = ENOMEM;
 278                         return NULL;
 279                 }
 280                 src = rand() | 0x8000;
 281                 while(find_connection(utcp, src, dst))
 282                         src++;
 283         }
 284
 285         // Allocate memory for the new connection
 286
 287         if(utcp->nconnections >= utcp->nallocated) {
 288                 if(!utcp->nallocated)
 289                         utcp->nallocated = 4;
 290                 else
 291                         utcp->nallocated *= 2;
 292                 struct utcp_connection **new_array = realloc(utcp->connections, utcp->nallocated * sizeof *utcp->connections);
 293                 if(!new_array)
 294                         return NULL;
 295                 utcp->connections = new_array;
 296         }
 297
 298         struct utcp_connection *c = calloc(1, sizeof *c);
 299         if(!c)
 300                 return NULL;
 301
 302         if(!buffer_init(&c->sndbuf, DEFAULT_SNDBUFSIZE, DEFAULT_MAXSNDBUFSIZE)) {
 303                 free(c);
 304                 return NULL;
 305         }
 306
 307         if(!buffer_init(&c->rcvbuf, DEFAULT_RCVBUFSIZE, DEFAULT_MAXRCVBUFSIZE)) {
 308                 free(c);
 309                 return NULL;
 310         }
 311
 312         // Fill in the details
 313
 314         c->src = src;
 315         c->dst = dst;
 316 #ifdef UTCP_DEBUG
 317         c->snd.iss = 0;
 318 #else
 319         c->snd.iss = rand();
 320 #endif
 321         c->snd.una = c->snd.iss;
 322         c->snd.nxt = c->snd.iss + 1;
 323         c->rcv.wnd = utcp->mtu;
 324         c->snd.last = c->snd.nxt;
 325         c->snd.cwnd = utcp->mtu;
 326         c->utcp = utcp;
 327
 328         // Add it to the sorted list of connections
 329
 330         utcp->connections[utcp->nconnections++] = c;
 331         qsort(utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
 332
 333         return c;
 334 }
 335
 336 struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
 337         struct utcp_connection *c = allocate_connection(utcp, 0, dst);
 338         if(!c)
 339                 return NULL;
 340
 341         c->recv = recv;
 342         c->priv = priv;
 343
 344         struct hdr hdr;
 345
 346         hdr.src = c->src;
 347         hdr.dst = c->dst;
 348         hdr.seq = c->snd.iss;
 349         hdr.ack = 0;
 350         hdr.wnd = c->rcv.wnd;
 351         hdr.ctl = SYN;
 352         hdr.aux = 0;
 353
 354         set_state(c, SYN_SENT);
 355
 356         print_packet(utcp, "send", &hdr, sizeof hdr);
 357         utcp->send(utcp, &hdr, sizeof hdr);
 358
 359         gettimeofday(&c->conn_timeout, NULL);
 360         c->conn_timeout.tv_sec += utcp->timeout;
 361
 362         return c;
 363 }
 364
 365 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
 366         if(c->reapable || c->state != SYN_RECEIVED) {
 367                 debug("Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
 368                 return;
 369         }
 370
 371         debug("%p accepted, %p %p\n", c, recv, priv);
 372         c->recv = recv;
 373         c->priv = priv;
 374         set_state(c, ESTABLISHED);
 375 }
 376
 377 static void ack(struct utcp_connection *c, bool sendatleastone) {
 378         int32_t left = seqdiff(c->snd.last, c->snd.nxt);
 379         int32_t cwndleft = c->snd.cwnd - seqdiff(c->snd.nxt, c->snd.una);
 380         debug("cwndleft = %d\n", cwndleft);
 381
 382         assert(left >= 0);
 383
 384         if(cwndleft <= 0)
 385                 cwndleft = 0;
 386
 387         if(cwndleft < left)
 388                 left = cwndleft;
 389
 390         if(!left && !sendatleastone)
 391                 return;
 392
 393         struct {
 394                 struct hdr hdr;
 395                 char data[];
 396         } *pkt;
 397
 398         pkt = malloc(sizeof pkt->hdr + c->utcp->mtu);
 399         if(!pkt)
 400                 return;
 401
 402         pkt->hdr.src = c->src;
 403         pkt->hdr.dst = c->dst;
 404         pkt->hdr.ack = c->rcv.nxt;
 405         pkt->hdr.wnd = c->snd.wnd;
 406         pkt->hdr.ctl = ACK;
 407         pkt->hdr.aux = 0;
 408
 409         do {
 410                 uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
 411                 pkt->hdr.seq = c->snd.nxt;
 412
 413                 buffer_copy(&c->sndbuf, pkt->data, seqdiff(c->snd.nxt, c->snd.una), seglen);
 414
 415                 c->snd.nxt += seglen;
 416                 left -= seglen;
 417
 418                 if(seglen && fin_wanted(c, c->snd.nxt)) {
 419                         seglen--;
 420                         pkt->hdr.ctl |= FIN;
 421                 }
 422
 423                 print_packet(c->utcp, "send", pkt, sizeof pkt->hdr + seglen);
 424                 c->utcp->send(c->utcp, pkt, sizeof pkt->hdr + seglen);
 425         } while(left);
 426
 427         free(pkt);
 428 }
 429
 430 ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
 431         if(c->reapable) {
 432                 debug("Error: send() called on closed connection %p\n", c);
 433                 errno = EBADF;
 434                 return -1;
 435         }
 436
 437         switch(c->state) {
 438         case CLOSED:
 439         case LISTEN:
 440         case SYN_SENT:
 441         case SYN_RECEIVED:
 442                 debug("Error: send() called on unconnected connection %p\n", c);
 443                 errno = ENOTCONN;
 444                 return -1;
 445         case ESTABLISHED:
 446         case CLOSE_WAIT:
 447                 break;
 448         case FIN_WAIT_1:
 449         case FIN_WAIT_2:
 450         case CLOSING:
 451         case LAST_ACK:
 452         case TIME_WAIT:
 453                 debug("Error: send() called on closing connection %p\n", c);
 454                 errno = EPIPE;
 455                 return -1;
 456         }
 457
 458         // Add data to send buffer
 459
 460         if(!len)
 461                 return 0;
 462
 463         if(!data) {
 464                 errno = EFAULT;
 465                 return -1;
 466         }
 467
 468         len = buffer_put(&c->sndbuf, data, len);
 469         if(len <= 0) {
 470                 errno = EWOULDBLOCK;
 471                 return 0;
 472         }
 473
 474         c->snd.last += len;
 475         ack(c, false);
 476         return len;
 477 }
 478
 479 static void swap_ports(struct hdr *hdr) {
 480         uint16_t tmp = hdr->src;
 481         hdr->src = hdr->dst;
 482         hdr->dst = tmp;
 483 }
 484
 485 static void retransmit(struct utcp_connection *c) {
 486         if(c->state == CLOSED || c->snd.nxt == c->snd.una)
 487                 return;
 488
 489         struct utcp *utcp = c->utcp;
 490
 491         struct {
 492                 struct hdr hdr;
 493                 char data[];
 494         } *pkt;
 495
 496         pkt = malloc(sizeof pkt->hdr + c->utcp->mtu);
 497         if(!pkt)
 498                 return;
 499
 500         pkt->hdr.src = c->src;
 501         pkt->hdr.dst = c->dst;
 502
 503         switch(c->state) {
 504                 case SYN_SENT:
 505                         // Send our SYN again
 506                         pkt->hdr.seq = c->snd.iss;
 507                         pkt->hdr.ack = 0;
 508                         pkt->hdr.wnd = c->rcv.wnd;
 509                         pkt->hdr.ctl = SYN;
 510                         print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr);
 511                         utcp->send(utcp, pkt, sizeof pkt->hdr);
 512                         break;
 513
 514                 case SYN_RECEIVED:
 515                         // Send SYNACK again
 516                         pkt->hdr.seq = c->snd.nxt;
 517                         pkt->hdr.ack = c->rcv.nxt;
 518                         pkt->hdr.ctl = SYN | ACK;
 519                         print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr);
 520                         utcp->send(utcp, pkt, sizeof pkt->hdr);
 521                         break;
 522
 523                 case ESTABLISHED:
 524                 case FIN_WAIT_1:
 525                 case CLOSE_WAIT:
 526                 case CLOSING:
 527                 case LAST_ACK:
 528                         // Send unacked data again.
 529                         pkt->hdr.seq = c->snd.una;
 530                         pkt->hdr.ack = c->rcv.nxt;
 531                         pkt->hdr.ctl = ACK;
 532                         uint32_t len = seqdiff(c->snd.last, c->snd.una);
 533                         if(len > utcp->mtu)
 534                                 len = utcp->mtu;
 535                         if(fin_wanted(c, c->snd.una + len)) {
 536                                 len--;
 537                                 pkt->hdr.ctl |= FIN;
 538                         }
 539                         c->snd.nxt = c->snd.una + len;
 540                         c->snd.cwnd = utcp->mtu; // reduce cwnd on retransmit
 541                         buffer_copy(&c->sndbuf, pkt->data, 0, len);
 542                         print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr + len);
 543                         utcp->send(utcp, pkt, sizeof pkt->hdr + len);
 544                         break;
 545
 546                 case CLOSED:
 547                 case LISTEN:
 548                 case TIME_WAIT:
 549                 case FIN_WAIT_2:
 550                         // We shouldn't need to retransmit anything in this state.
 551 #ifdef UTCP_DEBUG
 552                         abort();
 553 #endif
 554                         timerclear(&c->rtrx_timeout);
 555                         break;
 556         }
 557
 558         free(pkt);
 559 }
 560
 561 // Update receive buffer and SACK entries after consuming data.
 562 static void sack_consume(struct utcp_connection *c, size_t len) {
 563         debug("sack_consume %zu\n", len);
 564         if(len > c->rcvbuf.used)
 565                 abort();
 566
 567         buffer_get(&c->rcvbuf, NULL, len);
 568
 569         for(int i = 0; i < NSACKS && c->sacks[i].len; ) {
 570                 if(len < c->sacks[i].offset) {
 571                         c->sacks[i].offset -= len;
 572                         i++;
 573                 } else if(len < c->sacks[i].offset + c->sacks[i].len) {
 574                         c->sacks[i].offset = 0;
 575                         c->sacks[i].len -= len - c->sacks[i].offset;
 576                         i++;
 577                 } else {
 578                         if(i < NSACKS - 1) {
 579                                 memmove(&c->sacks[i], &c->sacks[i + 1], (NSACKS - 1 - i) * sizeof c->sacks[i]);
 580                                 c->sacks[i + 1].len = 0;
 581                         } else {
 582                                 c->sacks[i].len = 0;
 583                                 break;
 584                         }
 585                 }
 586         }
 587
 588         for(int i = 0; i < NSACKS && c->sacks[i].len; i++)
 589                 debug("SACK[%d] offset %u len %u\n", i, c->sacks[i].offset, c->sacks[i].len);
 590 }
 591
 592 static void handle_out_of_order(struct utcp_connection *c, uint32_t offset, const void *data, size_t len) {
 593         debug("out of order packet, offset %u\n", offset);
 594         // Packet loss or reordering occured. Store the data in the buffer.
 595         ssize_t rxd = buffer_put_at(&c->rcvbuf, offset, data, len);
 596         if(rxd < len)
 597                 abort();
 598
 599         // Make note of where we put it.
 600         for(int i = 0; i < NSACKS; i++) {
 601                 if(!c->sacks[i].len) { // nothing to merge, add new entry
 602                         debug("New SACK entry %d\n", i);
 603                         c->sacks[i].offset = offset;
 604                         c->sacks[i].len = rxd;
 605                         break;
 606                 } else if(offset < c->sacks[i].offset) {
 607                         if(offset + rxd < c->sacks[i].offset) { // insert before
 608                                 if(!c->sacks[NSACKS - 1].len) { // only if room left
 609                                         debug("Insert SACK entry at %d\n", i);
 610                                         memmove(&c->sacks[i + 1], &c->sacks[i], (NSACKS - i - 1) * sizeof c->sacks[i]);
 611                                         c->sacks[i].offset = offset;
 612                                         c->sacks[i].len = rxd;
 613                                 }
 614                                 break;
 615                         } else { // merge
 616                                 debug("Merge with start of SACK entry at %d\n", i);
 617                                 c->sacks[i].offset = offset;
 618                                 break;
 619                         }
 620                 } else if(offset <= c->sacks[i].offset + c->sacks[i].len) {
 621                         if(offset + rxd > c->sacks[i].offset + c->sacks[i].len) { // merge
 622                                 debug("Merge with end of SACK entry at %d\n", i);
 623                                 c->sacks[i].len = offset + rxd - c->sacks[i].offset;
 624                                 // TODO: handle potential merge with next entry
 625                         }
 626                         break;
 627                 }
 628         }
 629
 630         for(int i = 0; i < NSACKS && c->sacks[i].len; i++)
 631                 debug("SACK[%d] offset %u len %u\n", i, c->sacks[i].offset, c->sacks[i].len);
 632 }
 633
 634 static void handle_in_order(struct utcp_connection *c, const void *data, size_t len) {
 635         // Check if we can process out-of-order data now.
 636         if(c->sacks[0].len && len >= c->sacks[0].offset) { // TODO: handle overlap with second SACK
 637                 debug("incoming packet len %zu connected with SACK at %u\n", len, c->sacks[0].offset);
 638                 buffer_put_at(&c->rcvbuf, 0, data, len); // TODO: handle return value
 639                 len = max(len, c->sacks[0].offset + c->sacks[0].len);
 640                 data = c->rcvbuf.data;
 641         }
 642
 643         if(c->recv) {
 644                 ssize_t rxd = c->recv(c, data, len);
 645                 if(rxd != len) {
 646                         // TODO: handle the application not accepting all data.
 647                         abort();
 648                 }
 649         }
 650
 651         if(c->rcvbuf.used)
 652                 sack_consume(c, len);
 653
 654         c->rcv.nxt += len;
 655 }
 656
 657
 658 static void handle_incoming_data(struct utcp_connection *c, uint32_t seq, const void *data, size_t len) {
 659         uint32_t offset = seqdiff(seq, c->rcv.nxt);
 660         if(offset + len > c->rcvbuf.maxsize)
 661                 abort();
 662
 663         if(offset)
 664                 handle_out_of_order(c, offset, data, len);
 665         else
 666                 handle_in_order(c, data, len);
 667 }
 668
 669
 670 ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
 671         if(!utcp) {
 672                 errno = EFAULT;
 673                 return -1;
 674         }
 675
 676         if(!len)
 677                 return 0;
 678
 679         if(!data) {
 680                 errno = EFAULT;
 681                 return -1;
 682         }
 683
 684         print_packet(utcp, "recv", data, len);
 685
 686         // Drop packets smaller than the header
 687
 688         struct hdr hdr;
 689         if(len < sizeof hdr) {
 690                 errno = EBADMSG;
 691                 return -1;
 692         }
 693
 694         // Make a copy from the potentially unaligned data to a struct hdr
 695
 696         memcpy(&hdr, data, sizeof hdr);
 697         data += sizeof hdr;
 698         len -= sizeof hdr;
 699
 700         // Drop packets with an unknown CTL flag
 701
 702         if(hdr.ctl & ~(SYN | ACK | RST | FIN)) {
 703                 errno = EBADMSG;
 704                 return -1;
 705         }
 706
 707         // Try to match the packet to an existing connection
 708
 709         struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
 710
 711         // Is it for a new connection?
 712
 713         if(!c) {
 714                 // Ignore RST packets
 715
 716                 if(hdr.ctl & RST)
 717                         return 0;
 718
 719                 // Is it a SYN packet and are we LISTENing?
 720
 721                 if(hdr.ctl & SYN && !(hdr.ctl & ACK) && utcp->accept) {
 722                         // If we don't want to accept it, send a RST back
 723                         if((utcp->pre_accept && !utcp->pre_accept(utcp, hdr.dst))) {
 724                                 len = 1;
 725                                 goto reset;
 726                         }
 727
 728                         // Try to allocate memory, otherwise send a RST back
 729                         c = allocate_connection(utcp, hdr.dst, hdr.src);
 730                         if(!c) {
 731                                 len = 1;
 732                                 goto reset;
 733                         }
 734
 735                         // Return SYN+ACK, go to SYN_RECEIVED state
 736                         c->snd.wnd = hdr.wnd;
 737                         c->rcv.irs = hdr.seq;
 738                         c->rcv.nxt = c->rcv.irs + 1;
 739                         set_state(c, SYN_RECEIVED);
 740
 741                         hdr.dst = c->dst;
 742                         hdr.src = c->src;
 743                         hdr.ack = c->rcv.irs + 1;
 744                         hdr.seq = c->snd.iss;
 745                         hdr.ctl = SYN | ACK;
 746                         print_packet(c->utcp, "send", &hdr, sizeof hdr);
 747                         utcp->send(utcp, &hdr, sizeof hdr);
 748                 } else {
 749                         // No, we don't want your packets, send a RST back
 750                         len = 1;
 751                         goto reset;
 752                 }
 753
 754                 return 0;
 755         }
 756
 757         debug("%p state %s\n", c->utcp, strstate[c->state]);
 758
 759         // In case this is for a CLOSED connection, ignore the packet.
 760         // TODO: make it so incoming packets can never match a CLOSED connection.
 761
 762         if(c->state == CLOSED)
 763                 return 0;
 764
 765         // It is for an existing connection.
 766
 767         uint32_t prevrcvnxt = c->rcv.nxt;
 768
 769         // 1. Drop invalid packets.
 770
 771         // 1a. Drop packets that should not happen in our current state.
 772
 773         switch(c->state) {
 774         case SYN_SENT:
 775         case SYN_RECEIVED:
 776         case ESTABLISHED:
 777         case FIN_WAIT_1:
 778         case FIN_WAIT_2:
 779         case CLOSE_WAIT:
 780         case CLOSING:
 781         case LAST_ACK:
 782         case TIME_WAIT:
 783                 break;
 784         default:
 785 #ifdef UTCP_DEBUG
 786                 abort();
 787 #endif
 788                 break;
 789         }
 790
 791         // 1b. Drop packets with a sequence number not in our receive window.
 792
 793         bool acceptable;
 794
 795         if(c->state == SYN_SENT)
 796                 acceptable = true;
 797
 798         // TODO: handle packets overlapping c->rcv.nxt.
 799 #if 1
 800         // Only use this when accepting out-of-order packets.
 801         else if(len == 0)
 802                 acceptable = seqdiff(hdr.seq, c->rcv.nxt) >= 0;
 803         else
 804                 acceptable = seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt) + len <= c->rcvbuf.maxsize;
 805 #else
 806         if(c->state != SYN_SENT)
 807                 acceptable = hdr.seq == c->rcv.nxt;
 808 #endif
 809
 810         if(!acceptable) {
 811                 debug("Packet not acceptable, %u <= %u + %zu < %u\n", c->rcv.nxt, hdr.seq, len, c->rcv.nxt + c->rcvbuf.maxsize);
 812                 // Ignore unacceptable RST packets.
 813                 if(hdr.ctl & RST)
 814                         return 0;
 815                 // Otherwise, send an ACK back in the hope things improve.
 816                 ack(c, true);
 817                 return 0;
 818         }
 819
 820         c->snd.wnd = hdr.wnd; // TODO: move below
 821
 822         // 1c. Drop packets with an invalid ACK.
 823         // ackno should not roll back, and it should also not be bigger than what we ever could have sent
 824         // (= snd.una + c->sndbuf.used).
 825
 826         if(hdr.ctl & ACK &&
 827                         ((seqdiff(hdr.ack, c->snd.una + c->sndbuf.used) > 0 &&
 828                           seqdiff(hdr.ack, c->snd.nxt) > 0) // TODO: simplify this if
 829                          || seqdiff(hdr.ack, c->snd.una) < 0)) {
 830                 debug("Packet ack seqno out of range, %u <= %u < %u\n", c->snd.una, hdr.ack, c->snd.una + c->sndbuf.used);
 831                 // Ignore unacceptable RST packets.
 832                 if(hdr.ctl & RST)
 833                         return 0;
 834                 goto reset;
 835         }
 836
 837         // 2. Handle RST packets
 838
 839         if(hdr.ctl & RST) {
 840                 switch(c->state) {
 841                 case SYN_SENT:
 842                         if(!(hdr.ctl & ACK))
 843                                 return 0;
 844                         // The peer has refused our connection.
 845                         set_state(c, CLOSED);
 846                         errno = ECONNREFUSED;
 847                         if(c->recv)
 848                                 c->recv(c, NULL, 0);
 849                         return 0;
 850                 case SYN_RECEIVED:
 851                         if(hdr.ctl & ACK)
 852                                 return 0;
 853                         // We haven't told the application about this connection yet. Silently delete.
 854                         free_connection(c);
 855                         return 0;
 856                 case ESTABLISHED:
 857                 case FIN_WAIT_1:
 858                 case FIN_WAIT_2:
 859                 case CLOSE_WAIT:
 860                         if(hdr.ctl & ACK)
 861                                 return 0;
 862                         // The peer has aborted our connection.
 863                         set_state(c, CLOSED);
 864                         errno = ECONNRESET;
 865                         if(c->recv)
 866                                 c->recv(c, NULL, 0);
 867                         return 0;
 868                 case CLOSING:
 869                 case LAST_ACK:
 870                 case TIME_WAIT:
 871                         if(hdr.ctl & ACK)
 872                                 return 0;
 873                         // As far as the application is concerned, the connection has already been closed.
 874                         // If it has called utcp_close() already, we can immediately free this connection.
 875                         if(c->reapable) {
 876                                 free_connection(c);
 877                                 return 0;
 878                         }
 879                         // Otherwise, immediately move to the CLOSED state.
 880                         set_state(c, CLOSED);
 881                         return 0;
 882                 default:
 883 #ifdef UTCP_DEBUG
 884                         abort();
 885 #endif
 886                         break;
 887                 }
 888         }
 889
 890         // 3. Advance snd.una
 891
 892         uint32_t advanced = seqdiff(hdr.ack, c->snd.una);
 893         prevrcvnxt = c->rcv.nxt;
 894
 895         if(advanced) {
 896                 int32_t data_acked = advanced;
 897
 898                 switch(c->state) {
 899                         case SYN_SENT:
 900                         case SYN_RECEIVED:
 901                                 data_acked--;
 902                                 break;
 903                         // TODO: handle FIN as well.
 904                         default:
 905                                 break;
 906                 }
 907
 908                 assert(data_acked >= 0);
 909
 910                 int32_t bufused = seqdiff(c->snd.last, c->snd.una);
 911                 assert(data_acked <= bufused);
 912
 913                 if(data_acked)
 914                         buffer_get(&c->sndbuf, NULL, data_acked);
 915
 916                 // Also advance snd.nxt if possible
 917                 if(seqdiff(c->snd.nxt, hdr.ack) < 0)
 918                         c->snd.nxt = hdr.ack;
 919
 920                 c->snd.una = hdr.ack;
 921
 922                 c->dupack = 0;
 923                 c->snd.cwnd += utcp->mtu;
 924                 if(c->snd.cwnd > c->sndbuf.maxsize)
 925                         c->snd.cwnd = c->sndbuf.maxsize;
 926
 927                 // Check if we have sent a FIN that is now ACKed.
 928                 switch(c->state) {
 929                 case FIN_WAIT_1:
 930                         if(c->snd.una == c->snd.last)
 931                                 set_state(c, FIN_WAIT_2);
 932                         break;
 933                 case CLOSING:
 934                         if(c->snd.una == c->snd.last) {
 935                                 gettimeofday(&c->conn_timeout, NULL);
 936                                 c->conn_timeout.tv_sec += 60;
 937                                 set_state(c, TIME_WAIT);
 938                         }
 939                         break;
 940                 default:
 941                         break;
 942                 }
 943         } else {
 944                 if(!len) {
 945                         c->dupack++;
 946                         if(c->dupack == 3) {
 947                                 debug("Triplicate ACK\n");
 948                                 //TODO: Resend one packet and go to fast recovery mode. See RFC 6582.
 949                                 //We do a very simple variant here; reset the nxt pointer to the last acknowledged packet from the peer.
 950                                 //Reset the congestion window so we wait for ACKs.
 951                                 c->snd.nxt = c->snd.una;
 952                                 c->snd.cwnd = utcp->mtu;
 953                         }
 954                 }
 955         }
 956
 957         // 4. Update timers
 958
 959         if(advanced) {
 960                 timerclear(&c->conn_timeout); // It will be set anew in utcp_timeout() if c->snd.una != c->snd.nxt.
 961                 if(c->snd.una == c->snd.nxt)
 962                         timerclear(&c->rtrx_timeout);
 963         }
 964
 965         // 5. Process SYN stuff
 966
 967         if(hdr.ctl & SYN) {
 968                 switch(c->state) {
 969                 case SYN_SENT:
 970                         // This is a SYNACK. It should always have ACKed the SYN.
 971                         if(!advanced)
 972                                 goto reset;
 973                         c->rcv.irs = hdr.seq;
 974                         c->rcv.nxt = hdr.seq;
 975                         set_state(c, ESTABLISHED);
 976                         // TODO: notify application of this somehow.
 977                         break;
 978                 case SYN_RECEIVED:
 979                 case ESTABLISHED:
 980                 case FIN_WAIT_1:
 981                 case FIN_WAIT_2:
 982                 case CLOSE_WAIT:
 983                 case CLOSING:
 984                 case LAST_ACK:
 985                 case TIME_WAIT:
 986                         // Ehm, no. We should never receive a second SYN.
 987                         goto reset;
 988                 default:
 989 #ifdef UTCP_DEBUG
 990                         abort();
 991 #endif
 992                         return 0;
 993                 }
 994
 995                 // SYN counts as one sequence number
 996                 c->rcv.nxt++;
 997         }
 998
 999         // 6. Process new data
1000
1001         if(c->state == SYN_RECEIVED) {
1002                 // This is the ACK after the SYNACK. It should always have ACKed the SYNACK.
1003                 if(!advanced)
1004                         goto reset;
1005
1006                 // Are we still LISTENing?
1007                 if(utcp->accept)
1008                         utcp->accept(c, c->src);
1009
1010                 if(c->state != ESTABLISHED) {
1011                         set_state(c, CLOSED);
1012                         c->reapable = true;
1013                         goto reset;
1014                 }
1015         }
1016
1017         if(len) {
1018                 switch(c->state) {
1019                 case SYN_SENT:
1020                 case SYN_RECEIVED:
1021                         // This should never happen.
1022 #ifdef UTCP_DEBUG
1023                         abort();
1024 #endif
1025                         return 0;
1026                 case ESTABLISHED:
1027                 case FIN_WAIT_1:
1028                 case FIN_WAIT_2:
1029                         break;
1030                 case CLOSE_WAIT:
1031                 case CLOSING:
1032                 case LAST_ACK:
1033                 case TIME_WAIT:
1034                         // Ehm no, We should never receive more data after a FIN.
1035                         goto reset;
1036                 default:
1037 #ifdef UTCP_DEBUG
1038                         abort();
1039 #endif
1040                         return 0;
1041                 }
1042
1043                 handle_incoming_data(c, hdr.seq, data, len);
1044         }
1045
1046         // 7. Process FIN stuff
1047
1048         if((hdr.ctl & FIN) && hdr.seq + len == c->rcv.nxt) {
1049                 switch(c->state) {
1050                 case SYN_SENT:
1051                 case SYN_RECEIVED:
1052                         // This should never happen.
1053 #ifdef UTCP_DEBUG
1054                         abort();
1055 #endif
1056                         break;
1057                 case ESTABLISHED:
1058                         set_state(c, CLOSE_WAIT);
1059                         break;
1060                 case FIN_WAIT_1:
1061                         set_state(c, CLOSING);
1062                         break;
1063                 case FIN_WAIT_2:
1064                         gettimeofday(&c->conn_timeout, NULL);
1065                         c->conn_timeout.tv_sec += 60;
1066                         set_state(c, TIME_WAIT);
1067                         break;
1068                 case CLOSE_WAIT:
1069                 case CLOSING:
1070                 case LAST_ACK:
1071                 case TIME_WAIT:
1072                         // Ehm, no. We should never receive a second FIN.
1073                         goto reset;
1074                 default:
1075 #ifdef UTCP_DEBUG
1076                         abort();
1077 #endif
1078                         break;
1079                 }
1080
1081                 // FIN counts as one sequence number
1082                 c->rcv.nxt++;
1083                 len++;
1084
1085                 // Inform the application that the peer closed the connection.
1086                 if(c->recv) {
1087                         errno = 0;
1088                         c->recv(c, NULL, 0);
1089                 }
1090         }
1091
1092         // Now we send something back if:
1093         // - we advanced rcv.nxt (ie, we got some data that needs to be ACKed)
1094         //   -> sendatleastone = true
1095         // - or we got an ack, so we should maybe send a bit more data
1096         //   -> sendatleastone = false
1097
1098 ack:
1099         ack(c, prevrcvnxt != c->rcv.nxt);
1100         return 0;
1101
1102 reset:
1103         swap_ports(&hdr);
1104         hdr.wnd = 0;
1105         if(hdr.ctl & ACK) {
1106                 hdr.seq = hdr.ack;
1107                 hdr.ctl = RST;
1108         } else {
1109                 hdr.ack = hdr.seq + len;
1110                 hdr.seq = 0;
1111                 hdr.ctl = RST | ACK;
1112         }
1113         print_packet(utcp, "send", &hdr, sizeof hdr);
1114         utcp->send(utcp, &hdr, sizeof hdr);
1115         return 0;
1116
1117 }
1118
1119 int utcp_shutdown(struct utcp_connection *c, int dir) {
1120         debug("%p shutdown %d at %u\n", c ? c->utcp : NULL, dir, c ? c->snd.last : 0);
1121         if(!c) {
1122                 errno = EFAULT;
1123                 return -1;
1124         }
1125
1126         if(c->reapable) {
1127                 debug("Error: shutdown() called on closed connection %p\n", c);
1128                 errno = EBADF;
1129                 return -1;
1130         }
1131
1132         if(!(dir == UTCP_SHUT_RD || dir == UTCP_SHUT_WR || dir == UTCP_SHUT_RDWR)) {
1133                 errno = EINVAL;
1134                 return -1;
1135         }
1136
1137         // TCP does not have a provision for stopping incoming packets.
1138         // The best we can do is to just ignore them.
1139         if(dir == UTCP_SHUT_RD || dir == UTCP_SHUT_RDWR)
1140                 c->recv = NULL;
1141
1142         // The rest of the code deals with shutting down writes.
1143         if(dir == UTCP_SHUT_RD)
1144                 return 0;
1145
1146         switch(c->state) {
1147         case CLOSED:
1148         case LISTEN:
1149                 errno = ENOTCONN;
1150                 return -1;
1151
1152         case SYN_SENT:
1153                 set_state(c, CLOSED);
1154                 return 0;
1155
1156         case SYN_RECEIVED:
1157         case ESTABLISHED:
1158                 set_state(c, FIN_WAIT_1);
1159                 break;
1160         case FIN_WAIT_1:
1161         case FIN_WAIT_2:
1162                 return 0;
1163         case CLOSE_WAIT:
1164                 set_state(c, CLOSING);
1165                 break;
1166
1167         case CLOSING:
1168         case LAST_ACK:
1169         case TIME_WAIT:
1170                 return 0;
1171         }
1172
1173         c->snd.last++;
1174
1175         ack(c, false);
1176         return 0;
1177 }
1178
1179 int utcp_close(struct utcp_connection *c) {
1180         if(utcp_shutdown(c, SHUT_RDWR))
1181                 return -1;
1182         c->recv = NULL;
1183         c->poll = NULL;
1184         c->reapable = true;
1185         return 0;
1186 }
1187
1188 int utcp_abort(struct utcp_connection *c) {
1189         if(!c) {
1190                 errno = EFAULT;
1191                 return -1;
1192         }
1193
1194         if(c->reapable) {
1195                 debug("Error: abort() called on closed connection %p\n", c);
1196                 errno = EBADF;
1197                 return -1;
1198         }
1199
1200         c->recv = NULL;
1201         c->poll = NULL;
1202         c->reapable = true;
1203
1204         switch(c->state) {
1205         case CLOSED:
1206                 return 0;
1207         case LISTEN:
1208         case SYN_SENT:
1209         case CLOSING:
1210         case LAST_ACK:
1211         case TIME_WAIT:
1212                 set_state(c, CLOSED);
1213                 return 0;
1214
1215         case SYN_RECEIVED:
1216         case ESTABLISHED:
1217         case FIN_WAIT_1:
1218         case FIN_WAIT_2:
1219         case CLOSE_WAIT:
1220                 set_state(c, CLOSED);
1221                 break;
1222         }
1223
1224         // Send RST
1225
1226         struct hdr hdr;
1227
1228         hdr.src = c->src;
1229         hdr.dst = c->dst;
1230         hdr.seq = c->snd.nxt;
1231         hdr.ack = 0;
1232         hdr.wnd = 0;
1233         hdr.ctl = RST;
1234
1235         print_packet(c->utcp, "send", &hdr, sizeof hdr);
1236         c->utcp->send(c->utcp, &hdr, sizeof hdr);
1237         return 0;
1238 }
1239
1240 /* Handle timeouts.
1241  * One call to this function will loop through all connections,
1242  * checking if something needs to be resent or not.
1243  * The return value is the time to the next timeout in milliseconds,
1244  * or maybe a negative value if the timeout is infinite.
1245  */
1246 struct timeval utcp_timeout(struct utcp *utcp) {
1247         struct timeval now;
1248         gettimeofday(&now, NULL);
1249         struct timeval next = {now.tv_sec + 3600, now.tv_usec};
1250
1251         for(int i = 0; i < utcp->nconnections; i++) {
1252                 struct utcp_connection *c = utcp->connections[i];
1253                 if(!c)
1254                         continue;
1255
1256                 if(c->state == CLOSED) {
1257                         if(c->reapable) {
1258                                 debug("Reaping %p\n", c);
1259                                 free_connection(c);
1260                                 i--;
1261                         }
1262                         continue;
1263                 }
1264
1265                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &now, <)) {
1266                         errno = ETIMEDOUT;
1267                         c->state = CLOSED;
1268                         if(c->recv)
1269                                 c->recv(c, NULL, 0);
1270                         continue;
1271                 }
1272
1273                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &now, <)) {
1274                         retransmit(c);
1275                 }
1276
1277                 if(c->poll && buffer_free(&c->sndbuf) && (c->state == ESTABLISHED || c->state == CLOSE_WAIT))
1278                         c->poll(c, buffer_free(&c->sndbuf));
1279
1280                 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <))
1281                         next = c->conn_timeout;
1282
1283                 if(c->snd.nxt != c->snd.una) {
1284                         c->rtrx_timeout = now;
1285                         c->rtrx_timeout.tv_sec++;
1286                 } else {
1287                         timerclear(&c->rtrx_timeout);
1288                 }
1289
1290                 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <))
1291                         next = c->rtrx_timeout;
1292         }
1293
1294         struct timeval diff;
1295         timersub(&next, &now, &diff);
1296         return diff;
1297 }
1298
1299 bool utcp_is_active(struct utcp *utcp) {
1300         if(!utcp)
1301                 return false;
1302
1303         for(int i = 0; i < utcp->nconnections; i++)
1304                 if(utcp->connections[i]->state != CLOSED && utcp->connections[i]->state != TIME_WAIT)
1305                         return true;
1306
1307         return false;
1308 }
1309
1310 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
1311         if(!send) {
1312                 errno = EFAULT;
1313                 return NULL;
1314         }
1315
1316         struct utcp *utcp = calloc(1, sizeof *utcp);
1317         if(!utcp)
1318                 return NULL;
1319
1320         utcp->accept = accept;
1321         utcp->pre_accept = pre_accept;
1322         utcp->send = send;
1323         utcp->priv = priv;
1324         utcp->mtu = DEFAULT_MTU;
1325         utcp->timeout = DEFAULT_USER_TIMEOUT; // s
1326
1327         return utcp;
1328 }
1329
1330 void utcp_exit(struct utcp *utcp) {
1331         if(!utcp)
1332                 return;
1333         for(int i = 0; i < utcp->nconnections; i++) {
1334                 if(!utcp->connections[i]->reapable)
1335                         debug("Warning, freeing unclosed connection %p\n", utcp->connections[i]);
1336                 buffer_exit(&utcp->connections[i]->sndbuf);
1337                 free(utcp->connections[i]);
1338         }
1339         free(utcp->connections);
1340         free(utcp);
1341 }
1342
1343 uint16_t utcp_get_mtu(struct utcp *utcp) {
1344         return utcp ? utcp->mtu : 0;
1345 }
1346
1347 void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
1348         // TODO: handle overhead of the header
1349         if(utcp)
1350                 utcp->mtu = mtu;
1351 }
1352
1353 int utcp_get_user_timeout(struct utcp *u) {
1354         return u ? u->timeout : 0;
1355 }
1356
1357 void utcp_set_user_timeout(struct utcp *u, int timeout) {
1358         if(u)
1359                 u->timeout = timeout;
1360 }
1361
1362 size_t utcp_get_sndbuf(struct utcp_connection *c) {
1363         return c ? c->sndbuf.maxsize : 0;
1364 }
1365
1366 size_t utcp_get_sndbuf_free(struct utcp_connection *c) {
1367         if(c && (c->state == ESTABLISHED || c->state == CLOSE_WAIT))
1368                 return buffer_free(&c->sndbuf);
1369         else
1370                 return 0;
1371 }
1372
1373 void utcp_set_sndbuf(struct utcp_connection *c, size_t size) {
1374         if(!c)
1375                 return;
1376         c->sndbuf.maxsize = size;
1377         if(c->sndbuf.maxsize != size)
1378                 c->sndbuf.maxsize = -1;
1379 }
1380
1381 size_t utcp_get_rcvbuf(struct utcp_connection *c) {
1382         return c ? c->rcvbuf.maxsize : 0;
1383 }
1384
1385 size_t utcp_get_rcvbuf_free(struct utcp_connection *c) {
1386         if(c && (c->state == ESTABLISHED || c->state == CLOSE_WAIT))
1387                 return buffer_free(&c->rcvbuf);
1388         else
1389                 return 0;
1390 }
1391
1392 void utcp_set_rcvbuf(struct utcp_connection *c, size_t size) {
1393         if(!c)
1394                 return;
1395         c->rcvbuf.maxsize = size;
1396         if(c->rcvbuf.maxsize != size)
1397                 c->rcvbuf.maxsize = -1;
1398 }
1399
1400 bool utcp_get_nodelay(struct utcp_connection *c) {
1401         return c ? c->nodelay : false;
1402 }
1403
1404 void utcp_set_nodelay(struct utcp_connection *c, bool nodelay) {
1405         if(c)
1406                 c->nodelay = nodelay;
1407 }
1408
1409 bool utcp_get_keepalive(struct utcp_connection *c) {
1410         return c ? c->keepalive : false;
1411 }
1412
1413 void utcp_set_keepalive(struct utcp_connection *c, bool keepalive) {
1414         if(c)
1415                 c->keepalive = keepalive;
1416 }
1417
1418 size_t utcp_get_outq(struct utcp_connection *c) {
1419         return c ? seqdiff(c->snd.nxt, c->snd.una) : 0;
1420 }
1421
1422 void utcp_set_recv_cb(struct utcp_connection *c, utcp_recv_t recv) {
1423         if(c)
1424                 c->recv = recv;
1425 }
1426
1427 void utcp_set_poll_cb(struct utcp_connection *c, utcp_poll_t poll) {
1428         if(c)
1429                 c->poll = poll;
1430 }
1431
1432 void utcp_set_accept_cb(struct utcp *utcp, utcp_accept_t accept, utcp_pre_accept_t pre_accept) {
1433         if(utcp) {
1434                 utcp->accept = accept;
1435                 utcp->pre_accept = pre_accept;
1436         }
1437 }