2 utcp.c -- Userspace TCP
3 Copyright (C) 2014-2017 Guus Sliepen <guus@tinc-vpn.org>
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.
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.
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.
31 #include <sys/socket.h>
33 #include "utcp_priv.h"
48 #define timersub(a, b, r)\
50 (r)->tv_sec = (a)->tv_sec - (b)->tv_sec;\
51 (r)->tv_usec = (a)->tv_usec - (b)->tv_usec;\
53 (r)->tv_sec--, (r)->tv_usec += USEC_PER_SEC;\
57 static inline size_t max(size_t a, size_t b) {
64 static void debug(const char *format, ...) {
67 vfprintf(stderr, format, ap);
71 static void print_packet(struct utcp *utcp, const char *dir, const void *pkt, size_t len) {
74 if(len < sizeof(hdr)) {
75 debug("%p %s: short packet (%lu bytes)\n", utcp, dir, (unsigned long)len);
79 memcpy(&hdr, pkt, sizeof(hdr));
80 debug("%p %s: len=%lu, src=%u dst=%u seq=%u ack=%u wnd=%u aux=%x ctl=", utcp, dir, (unsigned long)len, hdr.src, hdr.dst, hdr.seq, hdr.ack, hdr.wnd, hdr.aux);
98 if(len > sizeof(hdr)) {
99 uint32_t datalen = len - sizeof(hdr);
100 const uint8_t *data = (uint8_t *)pkt + sizeof(hdr);
101 char str[datalen * 2 + 1];
104 for(uint32_t i = 0; i < datalen; i++) {
105 *p++ = "0123456789ABCDEF"[data[i] >> 4];
106 *p++ = "0123456789ABCDEF"[data[i] & 15];
111 debug(" data=%s", str);
117 #define debug(...) do {} while(0)
118 #define print_packet(...) do {} while(0)
121 static void set_state(struct utcp_connection *c, enum state state) {
124 if(state == ESTABLISHED) {
125 timerclear(&c->conn_timeout);
128 debug("%p new state: %s\n", c->utcp, strstate[state]);
131 static bool fin_wanted(struct utcp_connection *c, uint32_t seq) {
132 if(seq != c->snd.last) {
147 static bool is_reliable(struct utcp_connection *c) {
148 return c->flags & UTCP_RELIABLE;
151 static int32_t seqdiff(uint32_t a, uint32_t b) {
156 // TODO: convert to ringbuffers to avoid memmove() operations.
158 // Store data into the buffer
159 static ssize_t buffer_put_at(struct buffer *buf, size_t offset, const void *data, size_t len) {
160 debug("buffer_put_at %lu %lu %lu\n", (unsigned long)buf->used, (unsigned long)offset, (unsigned long)len);
162 size_t required = offset + len;
164 if(required > buf->maxsize) {
165 if(offset >= buf->maxsize) {
169 len = buf->maxsize - offset;
170 required = buf->maxsize;
173 if(required > buf->size) {
174 size_t newsize = buf->size;
181 } while(newsize < required);
184 if(newsize > buf->maxsize) {
185 newsize = buf->maxsize;
188 char *newdata = realloc(buf->data, newsize);
198 memcpy(buf->data + offset, data, len);
200 if(required > buf->used) {
201 buf->used = required;
207 static ssize_t buffer_put(struct buffer *buf, const void *data, size_t len) {
208 return buffer_put_at(buf, buf->used, data, len);
211 // Get data from the buffer. data can be NULL.
212 static ssize_t buffer_get(struct buffer *buf, void *data, size_t len) {
213 if(len > buf->used) {
218 memcpy(data, buf->data, len);
221 if(len < buf->used) {
222 memmove(buf->data, buf->data + len, buf->used - len);
229 // Copy data from the buffer without removing it.
230 static ssize_t buffer_copy(struct buffer *buf, void *data, size_t offset, size_t len) {
231 if(offset >= buf->used) {
235 if(offset + len > buf->used) {
236 len = buf->used - offset;
239 memcpy(data, buf->data + offset, len);
243 static bool buffer_init(struct buffer *buf, uint32_t len, uint32_t maxlen) {
244 memset(buf, 0, sizeof(*buf));
247 buf->data = malloc(len);
255 buf->maxsize = maxlen;
259 static void buffer_exit(struct buffer *buf) {
261 memset(buf, 0, sizeof(*buf));
264 static uint32_t buffer_free(const struct buffer *buf) {
265 return buf->maxsize - buf->used;
268 // Connections are stored in a sorted list.
269 // This gives O(log(N)) lookup time, O(N log(N)) insertion time and O(N) deletion time.
271 static int compare(const void *va, const void *vb) {
274 const struct utcp_connection *a = *(struct utcp_connection **)va;
275 const struct utcp_connection *b = *(struct utcp_connection **)vb;
278 assert(a->src && b->src);
280 int c = (int)a->src - (int)b->src;
286 c = (int)a->dst - (int)b->dst;
290 static struct utcp_connection *find_connection(const struct utcp *utcp, uint16_t src, uint16_t dst) {
291 if(!utcp->nconnections) {
295 struct utcp_connection key = {
299 struct utcp_connection **match = bsearch(&keyp, utcp->connections, utcp->nconnections, sizeof(*utcp->connections), compare);
300 return match ? *match : NULL;
303 static void free_connection(struct utcp_connection *c) {
304 struct utcp *utcp = c->utcp;
305 struct utcp_connection **cp = bsearch(&c, utcp->connections, utcp->nconnections, sizeof(*utcp->connections), compare);
309 int i = cp - utcp->connections;
310 memmove(cp, cp + 1, (utcp->nconnections - i - 1) * sizeof(*cp));
311 utcp->nconnections--;
313 buffer_exit(&c->rcvbuf);
314 buffer_exit(&c->sndbuf);
318 static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t src, uint16_t dst) {
319 // Check whether this combination of src and dst is free
322 if(find_connection(utcp, src, dst)) {
326 } else { // If src == 0, generate a random port number with the high bit set
327 if(utcp->nconnections >= 32767) {
332 src = rand() | 0x8000;
334 while(find_connection(utcp, src, dst)) {
339 // Allocate memory for the new connection
341 if(utcp->nconnections >= utcp->nallocated) {
342 if(!utcp->nallocated) {
343 utcp->nallocated = 4;
345 utcp->nallocated *= 2;
348 struct utcp_connection **new_array = realloc(utcp->connections, utcp->nallocated * sizeof(*utcp->connections));
354 utcp->connections = new_array;
357 struct utcp_connection *c = calloc(1, sizeof(*c));
363 if(!buffer_init(&c->sndbuf, DEFAULT_SNDBUFSIZE, DEFAULT_MAXSNDBUFSIZE)) {
368 if(!buffer_init(&c->rcvbuf, DEFAULT_RCVBUFSIZE, DEFAULT_MAXRCVBUFSIZE)) {
369 buffer_exit(&c->sndbuf);
374 // Fill in the details
383 c->snd.una = c->snd.iss;
384 c->snd.nxt = c->snd.iss + 1;
385 c->rcv.wnd = utcp->mtu;
386 c->snd.last = c->snd.nxt;
387 c->snd.cwnd = utcp->mtu;
390 // Add it to the sorted list of connections
392 utcp->connections[utcp->nconnections++] = c;
393 qsort(utcp->connections, utcp->nconnections, sizeof(*utcp->connections), compare);
398 static inline uint32_t absdiff(uint32_t a, uint32_t b) {
406 // Update RTT variables. See RFC 6298.
407 static void update_rtt(struct utcp_connection *c, uint32_t rtt) {
409 debug("invalid rtt\n");
413 struct utcp *utcp = c->utcp;
417 utcp->rttvar = rtt / 2;
418 utcp->rto = rtt + max(2 * rtt, CLOCK_GRANULARITY);
420 utcp->rttvar = (utcp->rttvar * 3 + absdiff(utcp->srtt, rtt)) / 4;
421 utcp->srtt = (utcp->srtt * 7 + rtt) / 8;
422 utcp->rto = utcp->srtt + max(utcp->rttvar, CLOCK_GRANULARITY);
425 if(utcp->rto > MAX_RTO) {
429 debug("rtt %u srtt %u rttvar %u rto %u\n", rtt, utcp->srtt, utcp->rttvar, utcp->rto);
432 static void start_retransmit_timer(struct utcp_connection *c) {
433 gettimeofday(&c->rtrx_timeout, NULL);
434 c->rtrx_timeout.tv_usec += c->utcp->rto;
436 while(c->rtrx_timeout.tv_usec >= 1000000) {
437 c->rtrx_timeout.tv_usec -= 1000000;
438 c->rtrx_timeout.tv_sec++;
441 debug("timeout set to %lu.%06lu (%u)\n", c->rtrx_timeout.tv_sec, c->rtrx_timeout.tv_usec, c->utcp->rto);
444 static void stop_retransmit_timer(struct utcp_connection *c) {
445 timerclear(&c->rtrx_timeout);
446 debug("timeout cleared\n");
449 struct utcp_connection *utcp_connect_ex(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv, uint32_t flags) {
450 struct utcp_connection *c = allocate_connection(utcp, 0, dst);
456 assert((flags & ~0x1f) == 0);
467 pkt.hdr.src = c->src;
468 pkt.hdr.dst = c->dst;
469 pkt.hdr.seq = c->snd.iss;
471 pkt.hdr.wnd = c->rcv.wnd;
473 pkt.hdr.aux = 0x0101;
477 pkt.init[3] = flags & 0x7;
479 set_state(c, SYN_SENT);
481 print_packet(utcp, "send", &pkt, sizeof(pkt));
482 utcp->send(utcp, &pkt, sizeof(pkt));
484 gettimeofday(&c->conn_timeout, NULL);
485 c->conn_timeout.tv_sec += utcp->timeout;
487 start_retransmit_timer(c);
492 struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
493 return utcp_connect_ex(utcp, dst, recv, priv, UTCP_TCP);
496 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
497 if(c->reapable || c->state != SYN_RECEIVED) {
498 debug("Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
502 debug("%p accepted, %p %p\n", c, recv, priv);
505 set_state(c, ESTABLISHED);
508 static void ack(struct utcp_connection *c, bool sendatleastone) {
509 int32_t left = seqdiff(c->snd.last, c->snd.nxt);
510 int32_t cwndleft = c->snd.cwnd - seqdiff(c->snd.nxt, c->snd.una);
511 debug("cwndleft = %d\n", cwndleft);
519 if(cwndleft < left) {
523 if(!left && !sendatleastone) {
532 pkt = malloc(sizeof(pkt->hdr) + c->utcp->mtu);
538 pkt->hdr.src = c->src;
539 pkt->hdr.dst = c->dst;
540 pkt->hdr.ack = c->rcv.nxt;
541 pkt->hdr.wnd = c->snd.wnd;
546 uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
547 pkt->hdr.seq = c->snd.nxt;
549 buffer_copy(&c->sndbuf, pkt->data, seqdiff(c->snd.nxt, c->snd.una), seglen);
551 c->snd.nxt += seglen;
554 if(seglen && fin_wanted(c, c->snd.nxt)) {
559 if(!c->rtt_start.tv_sec) {
560 // Start RTT measurement
561 gettimeofday(&c->rtt_start, NULL);
562 c->rtt_seq = pkt->hdr.seq + seglen;
563 debug("Starting RTT measurement, expecting ack %u\n", c->rtt_seq);
566 print_packet(c->utcp, "send", pkt, sizeof(pkt->hdr) + seglen);
567 c->utcp->send(c->utcp, pkt, sizeof(pkt->hdr) + seglen);
573 ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
575 debug("Error: send() called on closed connection %p\n", c);
583 debug("Error: send() called on unconnected connection %p\n", c);
598 debug("Error: send() called on closing connection %p\n", c);
603 // Exit early if we have nothing to send.
614 // Check if we need to be able to buffer all data
616 if(c->flags & UTCP_NO_PARTIAL) {
617 if(len > buffer_free(&c->sndbuf)) {
618 if(len > c->sndbuf.maxsize) {
628 // Add data to send buffer.
630 if(is_reliable(c) || (c->state != SYN_SENT && c->state != SYN_RECEIVED)) {
631 len = buffer_put(&c->sndbuf, data, len);
645 // Don't send anything yet if the connection has not fully established yet
647 if(c->state == SYN_SENT || c->state == SYN_RECEIVED) {
653 if(!is_reliable(c)) {
654 c->snd.una = c->snd.nxt = c->snd.last;
655 buffer_get(&c->sndbuf, NULL, c->sndbuf.used);
658 if(is_reliable(c) && !timerisset(&c->rtrx_timeout)) {
659 start_retransmit_timer(c);
662 if(is_reliable(c) && !timerisset(&c->conn_timeout)) {
663 gettimeofday(&c->conn_timeout, NULL);
664 c->conn_timeout.tv_sec += c->utcp->timeout;
670 static void swap_ports(struct hdr *hdr) {
671 uint16_t tmp = hdr->src;
676 static void retransmit(struct utcp_connection *c) {
677 if(c->state == CLOSED || c->snd.last == c->snd.una) {
678 debug("Retransmit() called but nothing to retransmit!\n");
679 stop_retransmit_timer(c);
683 struct utcp *utcp = c->utcp;
690 pkt = malloc(sizeof(pkt->hdr) + c->utcp->mtu);
696 pkt->hdr.src = c->src;
697 pkt->hdr.dst = c->dst;
698 pkt->hdr.wnd = c->rcv.wnd;
703 // Send our SYN again
704 pkt->hdr.seq = c->snd.iss;
707 pkt->hdr.aux = 0x0101;
711 pkt->data[3] = c->flags & 0x7;
712 print_packet(c->utcp, "rtrx", pkt, sizeof(pkt->hdr) + 4);
713 utcp->send(utcp, pkt, sizeof(pkt->hdr) + 4);
718 pkt->hdr.seq = c->snd.nxt;
719 pkt->hdr.ack = c->rcv.nxt;
720 pkt->hdr.ctl = SYN | ACK;
721 print_packet(c->utcp, "rtrx", pkt, sizeof(pkt->hdr));
722 utcp->send(utcp, pkt, sizeof(pkt->hdr));
730 // Send unacked data again.
731 pkt->hdr.seq = c->snd.una;
732 pkt->hdr.ack = c->rcv.nxt;
734 uint32_t len = seqdiff(c->snd.last, c->snd.una);
736 if(len > utcp->mtu) {
740 if(fin_wanted(c, c->snd.una + len)) {
745 c->snd.nxt = c->snd.una + len;
746 c->snd.cwnd = utcp->mtu; // reduce cwnd on retransmit
747 buffer_copy(&c->sndbuf, pkt->data, 0, len);
748 print_packet(c->utcp, "rtrx", pkt, sizeof(pkt->hdr) + len);
749 utcp->send(utcp, pkt, sizeof(pkt->hdr) + len);
756 // We shouldn't need to retransmit anything in this state.
760 stop_retransmit_timer(c);
764 start_retransmit_timer(c);
767 if(utcp->rto > MAX_RTO) {
771 c->rtt_start.tv_sec = 0; // invalidate RTT timer
777 /* Update receive buffer and SACK entries after consuming data.
781 * |.....0000..1111111111.....22222......3333|
784 * 0..3 represent the SACK entries. The ^ indicates up to which point we want
785 * to remove data from the receive buffer. The idea is to substract "len"
786 * from the offset of all the SACK entries, and then remove/cut down entries
787 * that are shifted to before the start of the receive buffer.
789 * There are three cases:
790 * - the SACK entry is after ^, in that case just change the offset.
791 * - the SACK entry starts before and ends after ^, so we have to
792 * change both its offset and size.
793 * - the SACK entry is completely before ^, in that case delete it.
795 static void sack_consume(struct utcp_connection *c, size_t len) {
796 debug("sack_consume %lu\n", (unsigned long)len);
798 if(len > c->rcvbuf.used) {
799 debug("All SACK entries consumed");
804 buffer_get(&c->rcvbuf, NULL, len);
806 for(int i = 0; i < NSACKS && c->sacks[i].len;) {
807 if(len < c->sacks[i].offset) {
808 c->sacks[i].offset -= len;
810 } else if(len < c->sacks[i].offset + c->sacks[i].len) {
811 c->sacks[i].len -= len - c->sacks[i].offset;
812 c->sacks[i].offset = 0;
816 memmove(&c->sacks[i], &c->sacks[i + 1], (NSACKS - 1 - i) * sizeof(c->sacks)[i]);
817 c->sacks[NSACKS - 1].len = 0;
825 for(int i = 0; i < NSACKS && c->sacks[i].len; i++) {
826 debug("SACK[%d] offset %u len %u\n", i, c->sacks[i].offset, c->sacks[i].len);
830 static void handle_out_of_order(struct utcp_connection *c, uint32_t offset, const void *data, size_t len) {
831 debug("out of order packet, offset %u\n", offset);
832 // Packet loss or reordering occured. Store the data in the buffer.
833 ssize_t rxd = buffer_put_at(&c->rcvbuf, offset, data, len);
835 if(rxd < 0 || (size_t)rxd < len) {
839 // Make note of where we put it.
840 for(int i = 0; i < NSACKS; i++) {
841 if(!c->sacks[i].len) { // nothing to merge, add new entry
842 debug("New SACK entry %d\n", i);
843 c->sacks[i].offset = offset;
844 c->sacks[i].len = rxd;
846 } else if(offset < c->sacks[i].offset) {
847 if(offset + rxd < c->sacks[i].offset) { // insert before
848 if(!c->sacks[NSACKS - 1].len) { // only if room left
849 debug("Insert SACK entry at %d\n", i);
850 memmove(&c->sacks[i + 1], &c->sacks[i], (NSACKS - i - 1) * sizeof(c->sacks)[i]);
851 c->sacks[i].offset = offset;
852 c->sacks[i].len = rxd;
854 debug("SACK entries full, dropping packet\n");
859 debug("Merge with start of SACK entry at %d\n", i);
860 c->sacks[i].offset = offset;
863 } else if(offset <= c->sacks[i].offset + c->sacks[i].len) {
864 if(offset + rxd > c->sacks[i].offset + c->sacks[i].len) { // merge
865 debug("Merge with end of SACK entry at %d\n", i);
866 c->sacks[i].len = offset + rxd - c->sacks[i].offset;
867 // TODO: handle potential merge with next entry
874 for(int i = 0; i < NSACKS && c->sacks[i].len; i++) {
875 debug("SACK[%d] offset %u len %u\n", i, c->sacks[i].offset, c->sacks[i].len);
879 static void handle_in_order(struct utcp_connection *c, const void *data, size_t len) {
880 // Check if we can process out-of-order data now.
881 if(c->sacks[0].len && len >= c->sacks[0].offset) { // TODO: handle overlap with second SACK
882 debug("incoming packet len %lu connected with SACK at %u\n", (unsigned long)len, c->sacks[0].offset);
883 buffer_put_at(&c->rcvbuf, 0, data, len); // TODO: handle return value
884 len = max(len, c->sacks[0].offset + c->sacks[0].len);
885 data = c->rcvbuf.data;
889 ssize_t rxd = c->recv(c, data, len);
891 if(rxd < 0 || (size_t)rxd != len) {
892 // TODO: handle the application not accepting all data.
898 sack_consume(c, len);
905 static void handle_incoming_data(struct utcp_connection *c, uint32_t seq, const void *data, size_t len) {
906 if(!is_reliable(c)) {
907 c->recv(c, data, len);
908 c->rcv.nxt = seq + len;
912 uint32_t offset = seqdiff(seq, c->rcv.nxt);
914 if(offset + len > c->rcvbuf.maxsize) {
919 handle_out_of_order(c, offset, data, len);
921 handle_in_order(c, data, len);
926 ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
927 const uint8_t *ptr = data;
943 print_packet(utcp, "recv", data, len);
945 // Drop packets smaller than the header
949 if(len < sizeof(hdr)) {
954 // Make a copy from the potentially unaligned data to a struct hdr
956 memcpy(&hdr, ptr, sizeof(hdr));
960 // Drop packets with an unknown CTL flag
962 if(hdr.ctl & ~(SYN | ACK | RST | FIN)) {
967 // Check for auxiliary headers
969 const uint8_t *init = NULL;
971 uint16_t aux = hdr.aux;
974 size_t auxlen = 4 * (aux >> 8) & 0xf;
975 uint8_t auxtype = aux & 0xff;
984 if(!(hdr.ctl & SYN) || auxlen != 4) {
1000 if(!(aux & 0x800)) {
1009 memcpy(&aux, ptr, 2);
1014 bool has_data = len || (hdr.ctl & (SYN | FIN));
1016 // Try to match the packet to an existing connection
1018 struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
1020 // Is it for a new connection?
1023 // Ignore RST packets
1029 // Is it a SYN packet and are we LISTENing?
1031 if(hdr.ctl & SYN && !(hdr.ctl & ACK) && utcp->accept) {
1032 // If we don't want to accept it, send a RST back
1033 if((utcp->pre_accept && !utcp->pre_accept(utcp, hdr.dst))) {
1038 // Try to allocate memory, otherwise send a RST back
1039 c = allocate_connection(utcp, hdr.dst, hdr.src);
1046 // Parse auxilliary information
1053 c->flags = init[3] & 0x7;
1055 c->flags = UTCP_TCP;
1058 // Return SYN+ACK, go to SYN_RECEIVED state
1059 c->snd.wnd = hdr.wnd;
1060 c->rcv.irs = hdr.seq;
1061 c->rcv.nxt = c->rcv.irs + 1;
1062 set_state(c, SYN_RECEIVED);
1069 pkt.hdr.src = c->src;
1070 pkt.hdr.dst = c->dst;
1071 pkt.hdr.ack = c->rcv.irs + 1;
1072 pkt.hdr.seq = c->snd.iss;
1073 pkt.hdr.wnd = c->rcv.wnd;
1074 pkt.hdr.ctl = SYN | ACK;
1077 pkt.hdr.aux = 0x0101;
1081 pkt.data[3] = c->flags & 0x7;
1082 print_packet(c->utcp, "send", &pkt, sizeof(hdr) + 4);
1083 utcp->send(utcp, &pkt, sizeof(hdr) + 4);
1086 print_packet(c->utcp, "send", &pkt, sizeof(hdr));
1087 utcp->send(utcp, &pkt, sizeof(hdr));
1090 // No, we don't want your packets, send a RST back
1098 debug("%p state %s\n", c->utcp, strstate[c->state]);
1100 // In case this is for a CLOSED connection, ignore the packet.
1101 // TODO: make it so incoming packets can never match a CLOSED connection.
1103 if(c->state == CLOSED) {
1104 debug("Got packet for closed connection\n");
1108 // It is for an existing connection.
1110 // 1. Drop invalid packets.
1112 // 1a. Drop packets that should not happen in our current state.
1133 // 1b. Discard data that is not in our receive window.
1135 if(is_reliable(c)) {
1138 if(c->state == SYN_SENT) {
1140 } else if(len == 0) {
1141 acceptable = seqdiff(hdr.seq, c->rcv.nxt) >= 0;
1143 int32_t rcv_offset = seqdiff(hdr.seq, c->rcv.nxt);
1145 // cut already accepted front overlapping
1146 if(rcv_offset < 0) {
1147 acceptable = len > (size_t) - rcv_offset;
1152 hdr.seq -= rcv_offset;
1155 acceptable = seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt) + len <= c->rcvbuf.maxsize;
1160 debug("Packet not acceptable, %u <= %u + %lu < %u\n", c->rcv.nxt, hdr.seq, (unsigned long)len, c->rcv.nxt + c->rcvbuf.maxsize);
1162 // Ignore unacceptable RST packets.
1167 // Otherwise, continue processing.
1172 c->snd.wnd = hdr.wnd; // TODO: move below
1174 // 1c. Drop packets with an invalid ACK.
1175 // ackno should not roll back, and it should also not be bigger than what we ever could have sent
1176 // (= snd.una + c->sndbuf.used).
1178 if(!is_reliable(c)) {
1179 if(hdr.ack != c->snd.last && c->state >= ESTABLISHED) {
1180 hdr.ack = c->snd.una;
1184 if(hdr.ctl & ACK && (seqdiff(hdr.ack, c->snd.last) > 0 || seqdiff(hdr.ack, c->snd.una) < 0)) {
1185 debug("Packet ack seqno out of range, %u <= %u < %u\n", c->snd.una, hdr.ack, c->snd.una + c->sndbuf.used);
1187 // Ignore unacceptable RST packets.
1195 // 2. Handle RST packets
1200 if(!(hdr.ctl & ACK)) {
1204 // The peer has refused our connection.
1205 set_state(c, CLOSED);
1206 errno = ECONNREFUSED;
1209 c->recv(c, NULL, 0);
1212 if(c->poll && !c->reapable) {
1223 // We haven't told the application about this connection yet. Silently delete.
1235 // The peer has aborted our connection.
1236 set_state(c, CLOSED);
1240 c->recv(c, NULL, 0);
1243 if(c->poll && !c->reapable) {
1256 // As far as the application is concerned, the connection has already been closed.
1257 // If it has called utcp_close() already, we can immediately free this connection.
1263 // Otherwise, immediately move to the CLOSED state.
1264 set_state(c, CLOSED);
1277 if(!(hdr.ctl & ACK)) {
1282 // 3. Advance snd.una
1284 advanced = seqdiff(hdr.ack, c->snd.una);
1288 if(c->rtt_start.tv_sec) {
1289 if(c->rtt_seq == hdr.ack) {
1290 struct timeval now, diff;
1291 gettimeofday(&now, NULL);
1292 timersub(&now, &c->rtt_start, &diff);
1293 update_rtt(c, diff.tv_sec * 1000000 + diff.tv_usec);
1294 c->rtt_start.tv_sec = 0;
1295 } else if(c->rtt_seq < hdr.ack) {
1296 debug("Cancelling RTT measurement: %u < %u\n", c->rtt_seq, hdr.ack);
1297 c->rtt_start.tv_sec = 0;
1301 int32_t data_acked = advanced;
1309 // TODO: handle FIN as well.
1314 assert(data_acked >= 0);
1316 int32_t bufused = seqdiff(c->snd.last, c->snd.una);
1317 assert(data_acked <= bufused);
1320 buffer_get(&c->sndbuf, NULL, data_acked);
1323 // Also advance snd.nxt if possible
1324 if(seqdiff(c->snd.nxt, hdr.ack) < 0) {
1325 c->snd.nxt = hdr.ack;
1328 c->snd.una = hdr.ack;
1331 c->snd.cwnd += utcp->mtu;
1333 if(c->snd.cwnd > c->sndbuf.maxsize) {
1334 c->snd.cwnd = c->sndbuf.maxsize;
1337 // Check if we have sent a FIN that is now ACKed.
1340 if(c->snd.una == c->snd.last) {
1341 set_state(c, FIN_WAIT_2);
1347 if(c->snd.una == c->snd.last) {
1348 gettimeofday(&c->conn_timeout, NULL);
1349 c->conn_timeout.tv_sec += 60;
1350 set_state(c, TIME_WAIT);
1359 if(!len && is_reliable(c)) {
1362 if(c->dupack == 3) {
1363 debug("Triplicate ACK\n");
1364 //TODO: Resend one packet and go to fast recovery mode. See RFC 6582.
1365 //We do a very simple variant here; reset the nxt pointer to the last acknowledged packet from the peer.
1366 //Reset the congestion window so we wait for ACKs.
1367 c->snd.nxt = c->snd.una;
1368 c->snd.cwnd = utcp->mtu;
1369 start_retransmit_timer(c);
1377 if(c->snd.una == c->snd.last) {
1378 stop_retransmit_timer(c);
1379 timerclear(&c->conn_timeout);
1380 } else if(is_reliable(c)) {
1381 start_retransmit_timer(c);
1382 gettimeofday(&c->conn_timeout, NULL);
1383 c->conn_timeout.tv_sec += utcp->timeout;
1388 // 5. Process SYN stuff
1394 // This is a SYNACK. It should always have ACKed the SYN.
1399 c->rcv.irs = hdr.seq;
1400 c->rcv.nxt = hdr.seq;
1404 set_state(c, FIN_WAIT_1);
1406 set_state(c, ESTABLISHED);
1409 // TODO: notify application of this somehow.
1420 // Ehm, no. We should never receive a second SYN.
1430 // SYN counts as one sequence number
1434 // 6. Process new data
1436 if(c->state == SYN_RECEIVED) {
1437 // This is the ACK after the SYNACK. It should always have ACKed the SYNACK.
1442 // Are we still LISTENing?
1444 utcp->accept(c, c->src);
1447 if(c->state != ESTABLISHED) {
1448 set_state(c, CLOSED);
1458 // This should never happen.
1473 // Ehm no, We should never receive more data after a FIN.
1483 handle_incoming_data(c, hdr.seq, ptr, len);
1486 // 7. Process FIN stuff
1488 if((hdr.ctl & FIN) && (!is_reliable(c) || hdr.seq + len == c->rcv.nxt)) {
1492 // This should never happen.
1499 set_state(c, CLOSE_WAIT);
1503 set_state(c, CLOSING);
1507 gettimeofday(&c->conn_timeout, NULL);
1508 c->conn_timeout.tv_sec += 60;
1509 set_state(c, TIME_WAIT);
1516 // Ehm, no. We should never receive a second FIN.
1526 // FIN counts as one sequence number
1530 // Inform the application that the peer closed its end of the connection.
1533 c->recv(c, NULL, 0);
1537 // Now we send something back if:
1538 // - we received data, so we have to send back an ACK
1539 // -> sendatleastone = true
1540 // - or we got an ack, so we should maybe send a bit more data
1541 // -> sendatleastone = false
1543 if(is_reliable(c) || hdr.ctl & SYN || hdr.ctl & FIN) {
1558 hdr.ack = hdr.seq + len;
1560 hdr.ctl = RST | ACK;
1563 print_packet(utcp, "send", &hdr, sizeof(hdr));
1564 utcp->send(utcp, &hdr, sizeof(hdr));
1569 int utcp_shutdown(struct utcp_connection *c, int dir) {
1570 debug("%p shutdown %d at %u\n", c ? c->utcp : NULL, dir, c ? c->snd.last : 0);
1578 debug("Error: shutdown() called on closed connection %p\n", c);
1583 if(!(dir == UTCP_SHUT_RD || dir == UTCP_SHUT_WR || dir == UTCP_SHUT_RDWR)) {
1588 // TCP does not have a provision for stopping incoming packets.
1589 // The best we can do is to just ignore them.
1590 if(dir == UTCP_SHUT_RD || dir == UTCP_SHUT_RDWR) {
1594 // The rest of the code deals with shutting down writes.
1595 if(dir == UTCP_SHUT_RD) {
1599 // Only process shutting down writes once.
1617 set_state(c, FIN_WAIT_1);
1625 set_state(c, CLOSING);
1638 if(!timerisset(&c->rtrx_timeout)) {
1639 start_retransmit_timer(c);
1645 static bool reset_connection(struct utcp_connection *c) {
1652 debug("Error: abort() called on closed connection %p\n", c);
1669 set_state(c, CLOSED);
1677 set_state(c, CLOSED);
1687 hdr.seq = c->snd.nxt;
1692 print_packet(c->utcp, "send", &hdr, sizeof(hdr));
1693 c->utcp->send(c->utcp, &hdr, sizeof(hdr));
1697 // Closes all the opened connections
1698 void utcp_abort_all_connections(struct utcp *utcp) {
1704 for(int i = 0; i < utcp->nconnections; i++) {
1705 struct utcp_connection *c = utcp->connections[i];
1707 if(c->reapable || c->state == CLOSED) {
1711 utcp_recv_t old_recv = c->recv;
1712 utcp_poll_t old_poll = c->poll;
1714 reset_connection(c);
1718 old_recv(c, NULL, 0);
1721 if(old_poll && !c->reapable) {
1730 int utcp_close(struct utcp_connection *c) {
1731 if(utcp_shutdown(c, SHUT_RDWR) && errno != ENOTCONN) {
1741 int utcp_abort(struct utcp_connection *c) {
1742 if(!reset_connection(c)) {
1751 * One call to this function will loop through all connections,
1752 * checking if something needs to be resent or not.
1753 * The return value is the time to the next timeout in milliseconds,
1754 * or maybe a negative value if the timeout is infinite.
1756 struct timeval utcp_timeout(struct utcp *utcp) {
1758 gettimeofday(&now, NULL);
1759 struct timeval next = {now.tv_sec + 3600, now.tv_usec};
1761 for(int i = 0; i < utcp->nconnections; i++) {
1762 struct utcp_connection *c = utcp->connections[i];
1768 // delete connections that have been utcp_close()d.
1769 if(c->state == CLOSED) {
1771 debug("Reaping %p\n", c);
1779 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &now, <)) {
1784 c->recv(c, NULL, 0);
1787 if(c->poll && !c->reapable) {
1794 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &now, <)) {
1795 debug("retransmit()\n");
1800 if((c->state == ESTABLISHED || c->state == CLOSE_WAIT)) {
1801 uint32_t len = buffer_free(&c->sndbuf);
1806 } else if(c->state == CLOSED) {
1811 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <)) {
1812 next = c->conn_timeout;
1815 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <)) {
1816 next = c->rtrx_timeout;
1820 struct timeval diff;
1822 timersub(&next, &now, &diff);
1827 bool utcp_is_active(struct utcp *utcp) {
1832 for(int i = 0; i < utcp->nconnections; i++)
1833 if(utcp->connections[i]->state != CLOSED && utcp->connections[i]->state != TIME_WAIT) {
1840 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
1846 struct utcp *utcp = calloc(1, sizeof(*utcp));
1852 utcp->accept = accept;
1853 utcp->pre_accept = pre_accept;
1856 utcp->mtu = DEFAULT_MTU;
1857 utcp->timeout = DEFAULT_USER_TIMEOUT; // sec
1858 utcp->rto = START_RTO; // usec
1863 void utcp_exit(struct utcp *utcp) {
1868 for(int i = 0; i < utcp->nconnections; i++) {
1869 struct utcp_connection *c = utcp->connections[i];
1873 c->recv(c, NULL, 0);
1876 if(c->poll && !c->reapable) {
1881 buffer_exit(&c->rcvbuf);
1882 buffer_exit(&c->sndbuf);
1886 free(utcp->connections);
1890 uint16_t utcp_get_mtu(struct utcp *utcp) {
1891 return utcp ? utcp->mtu : 0;
1894 void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
1895 // TODO: handle overhead of the header
1901 void utcp_reset_timers(struct utcp *utcp) {
1906 struct timeval now, then;
1908 gettimeofday(&now, NULL);
1912 then.tv_sec += utcp->timeout;
1914 for(int i = 0; i < utcp->nconnections; i++) {
1915 struct utcp_connection *c = utcp->connections[i];
1921 c->rtrx_timeout = now;
1922 c->conn_timeout = then;
1923 c->rtt_start.tv_sec = 0;
1926 if(utcp->rto > START_RTO) {
1927 utcp->rto = START_RTO;
1931 int utcp_get_user_timeout(struct utcp *u) {
1932 return u ? u->timeout : 0;
1935 void utcp_set_user_timeout(struct utcp *u, int timeout) {
1937 u->timeout = timeout;
1941 size_t utcp_get_sndbuf(struct utcp_connection *c) {
1942 return c ? c->sndbuf.maxsize : 0;
1945 size_t utcp_get_sndbuf_free(struct utcp_connection *c) {
1955 return buffer_free(&c->sndbuf);
1962 void utcp_set_sndbuf(struct utcp_connection *c, size_t size) {
1967 c->sndbuf.maxsize = size;
1969 if(c->sndbuf.maxsize != size) {
1970 c->sndbuf.maxsize = -1;
1974 size_t utcp_get_rcvbuf(struct utcp_connection *c) {
1975 return c ? c->rcvbuf.maxsize : 0;
1978 size_t utcp_get_rcvbuf_free(struct utcp_connection *c) {
1979 if(c && (c->state == ESTABLISHED || c->state == CLOSE_WAIT)) {
1980 return buffer_free(&c->rcvbuf);
1986 void utcp_set_rcvbuf(struct utcp_connection *c, size_t size) {
1991 c->rcvbuf.maxsize = size;
1993 if(c->rcvbuf.maxsize != size) {
1994 c->rcvbuf.maxsize = -1;
1998 size_t utcp_get_sendq(struct utcp_connection *c) {
1999 return c->sndbuf.used;
2002 size_t utcp_get_recvq(struct utcp_connection *c) {
2003 return c->rcvbuf.used;
2006 bool utcp_get_nodelay(struct utcp_connection *c) {
2007 return c ? c->nodelay : false;
2010 void utcp_set_nodelay(struct utcp_connection *c, bool nodelay) {
2012 c->nodelay = nodelay;
2016 bool utcp_get_keepalive(struct utcp_connection *c) {
2017 return c ? c->keepalive : false;
2020 void utcp_set_keepalive(struct utcp_connection *c, bool keepalive) {
2022 c->keepalive = keepalive;
2026 size_t utcp_get_outq(struct utcp_connection *c) {
2027 return c ? seqdiff(c->snd.nxt, c->snd.una) : 0;
2030 void utcp_set_recv_cb(struct utcp_connection *c, utcp_recv_t recv) {
2036 void utcp_set_poll_cb(struct utcp_connection *c, utcp_poll_t poll) {
2042 void utcp_set_accept_cb(struct utcp *utcp, utcp_accept_t accept, utcp_pre_accept_t pre_accept) {
2044 utcp->accept = accept;
2045 utcp->pre_accept = pre_accept;
2049 void utcp_expect_data(struct utcp_connection *c, bool expect) {
2050 if(!c || c->reapable) {
2054 if(!(c->state == ESTABLISHED || c->state == FIN_WAIT_1 || c->state == FIN_WAIT_2)) {
2059 // If we expect data, start the connection timer.
2060 if(!timerisset(&c->conn_timeout)) {
2061 gettimeofday(&c->conn_timeout, NULL);
2062 c->conn_timeout.tv_sec += c->utcp->timeout;
2065 // If we want to cancel expecting data, only clear the timer when there is no unACKed data.
2066 if(c->snd.una == c->snd.last) {
2067 timerclear(&c->conn_timeout);
2072 void utcp_offline(struct utcp *utcp, bool offline) {
2073 for(int i = 0; i < utcp->nconnections; i++) {
2074 struct utcp_connection *c = utcp->connections[i];
2077 utcp_expect_data(c, offline);
2079 // If we are online again, reset the retransmission timers, but keep the connection timeout as it is,
2080 // to prevent peers toggling online/offline state frequently from keeping connections alive
2081 // if there is no progress in sending actual data.
2083 gettimeofday(&utcp->connections[i]->rtrx_timeout, NULL);
2084 utcp->connections[i]->rtt_start.tv_sec = 0;
2089 if(!offline && utcp->rto > START_RTO) {
2090 utcp->rto = START_RTO;