2 utcp.c -- Userspace TCP
3 Copyright (C) 2014 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) do {\
49 (r)->tv_sec = (a)->tv_sec - (b)->tv_sec;\
50 (r)->tv_usec = (a)->tv_usec - (b)->tv_usec;\
52 (r)->tv_sec--, (r)->tv_usec += 1000000;\
59 static void debug(const char *format, ...) {
62 vfprintf(stderr, format, ap);
66 static void print_packet(struct utcp *utcp, const char *dir, const void *pkt, size_t len) {
68 if(len < sizeof hdr) {
69 debug("%p %s: short packet (%zu bytes)\n", utcp, dir, len);
73 memcpy(&hdr, pkt, sizeof hdr);
74 fprintf (stderr, "%p %s: len=%zu, src=%u dst=%u seq=%u ack=%u wnd=%u ctl=", utcp, dir, len, hdr.src, hdr.dst, hdr.seq, hdr.ack, hdr.wnd);
84 if(len > sizeof hdr) {
86 for(int i = sizeof hdr; i < len; i++) {
87 const char *data = pkt;
88 debug("%c", data[i] >= 32 ? data[i] : '.');
96 #define print_packet(...)
99 static void set_state(struct utcp_connection *c, enum state state) {
101 if(state == ESTABLISHED)
102 timerclear(&c->conn_timeout);
103 debug("%p new state: %s\n", c->utcp, strstate[state]);
106 static bool fin_wanted(struct utcp_connection *c, uint32_t seq) {
107 if(seq != c->snd.last)
119 static inline void list_connections(struct utcp *utcp) {
120 debug("%p has %d connections:\n", utcp, utcp->nconnections);
121 for(int i = 0; i < utcp->nconnections; i++)
122 debug(" %u -> %u state %s\n", utcp->connections[i]->src, utcp->connections[i]->dst, strstate[utcp->connections[i]->state]);
125 static int32_t seqdiff(uint32_t a, uint32_t b) {
130 // TODO: convert to ringbuffers to avoid memmove() operations.
132 // Store data into the buffer
133 static ssize_t buffer_put(struct buffer *buf, const void *data, size_t len) {
134 if(buf->maxsize <= buf->used)
136 if(len > buf->maxsize - buf->used)
137 len = buf->maxsize - buf->used;
138 if(len > buf->size - buf->used) {
139 size_t newsize = buf->size;
142 } while(newsize < buf->used + len);
143 if(newsize > buf->maxsize)
144 newsize = buf->maxsize;
145 char *newdata = realloc(buf->data, newsize);
151 memcpy(buf->data + buf->used, data, len);
156 // Get data from the buffer. data can be NULL.
157 static ssize_t buffer_get(struct buffer *buf, void *data, size_t len) {
161 memcpy(data, buf->data, len);
163 memmove(buf->data, buf->data + len, buf->used - len);
168 // Copy data from the buffer without removing it.
169 static ssize_t buffer_copy(struct buffer *buf, void *data, size_t offset, size_t len) {
170 if(offset >= buf->used)
172 if(offset + len > buf->used)
173 len = buf->used - offset;
174 memcpy(data, buf->data + offset, len);
178 static bool buffer_init(struct buffer *buf, uint32_t len, uint32_t maxlen) {
179 memset(buf, 0, sizeof *buf);
180 buf->data = malloc(len);
184 buf->maxsize = maxlen;
188 static void buffer_exit(struct buffer *buf) {
190 memset(buf, 0, sizeof *buf);
193 static uint32_t buffer_free(const struct buffer *buf) {
194 return buf->maxsize - buf->used;
197 // Connections are stored in a sorted list.
198 // This gives O(log(N)) lookup time, O(N log(N)) insertion time and O(N) deletion time.
200 static int compare(const void *va, const void *vb) {
203 const struct utcp_connection *a = *(struct utcp_connection **)va;
204 const struct utcp_connection *b = *(struct utcp_connection **)vb;
207 assert(a->src && b->src);
209 int c = (int)a->src - (int)b->src;
212 c = (int)a->dst - (int)b->dst;
216 static struct utcp_connection *find_connection(const struct utcp *utcp, uint16_t src, uint16_t dst) {
217 if(!utcp->nconnections)
219 struct utcp_connection key = {
223 struct utcp_connection **match = bsearch(&keyp, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
224 return match ? *match : NULL;
227 static void free_connection(struct utcp_connection *c) {
228 struct utcp *utcp = c->utcp;
229 struct utcp_connection **cp = bsearch(&c, utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
233 int i = cp - utcp->connections;
234 memmove(cp, cp + 1, (utcp->nconnections - i - 1) * sizeof *cp);
235 utcp->nconnections--;
237 buffer_exit(&c->sndbuf);
241 static struct utcp_connection *allocate_connection(struct utcp *utcp, uint16_t src, uint16_t dst) {
242 // Check whether this combination of src and dst is free
245 if(find_connection(utcp, src, dst)) {
249 } else { // If src == 0, generate a random port number with the high bit set
250 if(utcp->nconnections >= 32767) {
254 src = rand() | 0x8000;
255 while(find_connection(utcp, src, dst))
259 // Allocate memory for the new connection
261 if(utcp->nconnections >= utcp->nallocated) {
262 if(!utcp->nallocated)
263 utcp->nallocated = 4;
265 utcp->nallocated *= 2;
266 struct utcp_connection **new_array = realloc(utcp->connections, utcp->nallocated * sizeof *utcp->connections);
269 utcp->connections = new_array;
272 struct utcp_connection *c = calloc(1, sizeof *c);
276 if(!buffer_init(&c->sndbuf, DEFAULT_SNDBUFSIZE, DEFAULT_MAXSNDBUFSIZE)) {
281 // Fill in the details
286 c->snd.una = c->snd.iss;
287 c->snd.nxt = c->snd.iss + 1;
288 c->rcv.wnd = utcp->mtu;
289 c->snd.last = c->snd.nxt;
290 c->snd.cwnd = utcp->mtu;
293 // Add it to the sorted list of connections
295 utcp->connections[utcp->nconnections++] = c;
296 qsort(utcp->connections, utcp->nconnections, sizeof *utcp->connections, compare);
301 struct utcp_connection *utcp_connect(struct utcp *utcp, uint16_t dst, utcp_recv_t recv, void *priv) {
302 struct utcp_connection *c = allocate_connection(utcp, 0, dst);
313 hdr.seq = c->snd.iss;
315 hdr.wnd = c->rcv.wnd;
319 set_state(c, SYN_SENT);
321 print_packet(utcp, "send", &hdr, sizeof hdr);
322 utcp->send(utcp, &hdr, sizeof hdr);
324 gettimeofday(&c->conn_timeout, NULL);
325 c->conn_timeout.tv_sec += utcp->timeout;
330 void utcp_accept(struct utcp_connection *c, utcp_recv_t recv, void *priv) {
331 if(c->reapable || c->state != SYN_RECEIVED) {
332 debug("Error: accept() called on invalid connection %p in state %s\n", c, strstate[c->state]);
336 debug("%p accepted, %p %p\n", c, recv, priv);
339 set_state(c, ESTABLISHED);
342 static void ack(struct utcp_connection *c, bool sendatleastone) {
343 int32_t left = seqdiff(c->snd.last, c->snd.nxt);
344 int32_t cwndleft = c->snd.cwnd - seqdiff(c->snd.nxt, c->snd.una);
354 if(!left && !sendatleastone)
362 pkt = malloc(sizeof pkt->hdr + c->utcp->mtu);
366 pkt->hdr.src = c->src;
367 pkt->hdr.dst = c->dst;
368 pkt->hdr.ack = c->rcv.nxt;
369 pkt->hdr.wnd = c->snd.wnd;
374 uint32_t seglen = left > c->utcp->mtu ? c->utcp->mtu : left;
375 pkt->hdr.seq = c->snd.nxt;
377 buffer_copy(&c->sndbuf, pkt->data, seqdiff(c->snd.nxt, c->snd.una), seglen);
379 c->snd.nxt += seglen;
382 if(seglen && fin_wanted(c, c->snd.nxt)) {
387 print_packet(c->utcp, "send", pkt, sizeof pkt->hdr + seglen);
388 c->utcp->send(c->utcp, pkt, sizeof pkt->hdr + seglen);
394 ssize_t utcp_send(struct utcp_connection *c, const void *data, size_t len) {
396 debug("Error: send() called on closed connection %p\n", c);
406 debug("Error: send() called on unconnected connection %p\n", c);
417 debug("Error: send() called on closing connection %p\n", c);
422 // Add data to send buffer
432 len = buffer_put(&c->sndbuf, data, len);
443 static void swap_ports(struct hdr *hdr) {
444 uint16_t tmp = hdr->src;
449 static void retransmit(struct utcp_connection *c) {
450 if(c->state == CLOSED || c->snd.nxt == c->snd.una)
453 struct utcp *utcp = c->utcp;
460 pkt = malloc(sizeof pkt->hdr + c->utcp->mtu);
464 pkt->hdr.src = c->src;
465 pkt->hdr.dst = c->dst;
469 // Send our SYN again
470 pkt->hdr.seq = c->snd.iss;
472 pkt->hdr.wnd = c->rcv.wnd;
474 print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr);
475 utcp->send(utcp, pkt, sizeof pkt->hdr);
480 pkt->hdr.seq = c->snd.nxt;
481 pkt->hdr.ack = c->rcv.nxt;
482 pkt->hdr.ctl = SYN | ACK;
483 print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr);
484 utcp->send(utcp, pkt, sizeof pkt->hdr);
492 // Send unacked data again.
493 pkt->hdr.seq = c->snd.una;
494 pkt->hdr.ack = c->rcv.nxt;
496 uint32_t len = seqdiff(c->snd.last, c->snd.una);
499 if(fin_wanted(c, c->snd.una + len)) {
503 buffer_copy(&c->sndbuf, pkt->data, 0, len);
504 print_packet(c->utcp, "rtrx", pkt, sizeof pkt->hdr + len);
505 utcp->send(utcp, pkt, sizeof pkt->hdr + len);
512 // We shouldn't need to retransmit anything in this state.
516 timerclear(&c->rtrx_timeout);
524 ssize_t utcp_recv(struct utcp *utcp, const void *data, size_t len) {
538 print_packet(utcp, "recv", data, len);
540 // Drop packets smaller than the header
543 if(len < sizeof hdr) {
548 // Make a copy from the potentially unaligned data to a struct hdr
550 memcpy(&hdr, data, sizeof hdr);
554 // Drop packets with an unknown CTL flag
556 if(hdr.ctl & ~(SYN | ACK | RST | FIN)) {
561 // Try to match the packet to an existing connection
563 struct utcp_connection *c = find_connection(utcp, hdr.dst, hdr.src);
565 // Is it for a new connection?
568 // Ignore RST packets
573 // Is it a SYN packet and are we LISTENing?
575 if(hdr.ctl & SYN && !(hdr.ctl & ACK) && utcp->accept) {
576 // If we don't want to accept it, send a RST back
577 if((utcp->pre_accept && !utcp->pre_accept(utcp, hdr.dst))) {
582 // Try to allocate memory, otherwise send a RST back
583 c = allocate_connection(utcp, hdr.dst, hdr.src);
589 // Return SYN+ACK, go to SYN_RECEIVED state
590 c->snd.wnd = hdr.wnd;
591 c->rcv.irs = hdr.seq;
592 c->rcv.nxt = c->rcv.irs + 1;
593 set_state(c, SYN_RECEIVED);
597 hdr.ack = c->rcv.irs + 1;
598 hdr.seq = c->snd.iss;
600 print_packet(c->utcp, "send", &hdr, sizeof hdr);
601 utcp->send(utcp, &hdr, sizeof hdr);
603 // No, we don't want your packets, send a RST back
611 debug("%p state %s\n", c->utcp, strstate[c->state]);
613 // In case this is for a CLOSED connection, ignore the packet.
614 // TODO: make it so incoming packets can never match a CLOSED connection.
616 if(c->state == CLOSED)
619 // It is for an existing connection.
621 uint32_t prevrcvnxt = c->rcv.nxt;
623 // 1. Drop invalid packets.
625 // 1a. Drop packets that should not happen in our current state.
645 // 1b. Drop packets with a sequence number not in our receive window.
649 if(c->state == SYN_SENT)
652 // TODO: handle packets overlapping c->rcv.nxt.
654 // Only use this when accepting out-of-order packets.
657 acceptable = hdr.seq == c->rcv.nxt;
659 acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0);
662 // We don't accept data when the receive window is zero.
665 // Both start and end of packet must be within the receive window
666 acceptable = (seqdiff(hdr.seq, c->rcv.nxt) >= 0 && seqdiff(hdr.seq, c->rcv.nxt + c->rcv.wnd) < 0)
667 || (seqdiff(hdr.seq + len + 1, c->rcv.nxt) >= 0 && seqdiff(hdr.seq + len - 1, c->rcv.nxt + c->rcv.wnd) < 0);
669 if(c->state != SYN_SENT)
670 acceptable = hdr.seq == c->rcv.nxt;
674 debug("Packet not acceptable, %u <= %u + %zu < %u\n", c->rcv.nxt, hdr.seq, len, c->rcv.nxt + c->rcv.wnd);
675 // Ignore unacceptable RST packets.
678 // Otherwise, send an ACK back in the hope things improve.
683 c->snd.wnd = hdr.wnd; // TODO: move below
685 // 1c. Drop packets with an invalid ACK.
686 // ackno should not roll back, and it should also not be bigger than snd.nxt.
688 if(hdr.ctl & ACK && (seqdiff(hdr.ack, c->snd.nxt) > 0 || seqdiff(hdr.ack, c->snd.una) < 0)) {
689 debug("Packet ack seqno out of range, %u %u %u\n", hdr.ack, c->snd.una, c->snd.nxt);
690 // Ignore unacceptable RST packets.
696 // 2. Handle RST packets
703 // The peer has refused our connection.
704 set_state(c, CLOSED);
705 errno = ECONNREFUSED;
712 // We haven't told the application about this connection yet. Silently delete.
721 // The peer has aborted our connection.
722 set_state(c, CLOSED);
732 // As far as the application is concerned, the connection has already been closed.
733 // If it has called utcp_close() already, we can immediately free this connection.
738 // Otherwise, immediately move to the CLOSED state.
739 set_state(c, CLOSED);
749 // 3. Advance snd.una
751 uint32_t advanced = seqdiff(hdr.ack, c->snd.una);
752 prevrcvnxt = c->rcv.nxt;
755 int32_t data_acked = advanced;
762 // TODO: handle FIN as well.
767 assert(data_acked >= 0);
769 int32_t bufused = seqdiff(c->snd.last, c->snd.una);
770 assert(data_acked <= bufused);
773 buffer_get(&c->sndbuf, NULL, data_acked);
775 c->snd.una = hdr.ack;
778 c->snd.cwnd += utcp->mtu;
779 if(c->snd.cwnd > c->sndbuf.maxsize)
780 c->snd.cwnd = c->sndbuf.maxsize;
782 // Check if we have sent a FIN that is now ACKed.
785 if(c->snd.una == c->snd.last)
786 set_state(c, FIN_WAIT_2);
789 if(c->snd.una == c->snd.last) {
790 gettimeofday(&c->conn_timeout, NULL);
791 c->conn_timeout.tv_sec += 60;
792 set_state(c, TIME_WAIT);
802 debug("Triplicate ACK\n");
803 //TODO: Resend one packet and go to fast recovery mode. See RFC 6582.
804 //We do a very simple variant here; reset the nxt pointer to the last acknowledged packet from the peer.
805 //This will cause us to start retransmitting, but at the same speed as the incoming ACKs arrive,
806 //thus preventing a drop in speed.
807 c->snd.nxt = c->snd.una;
815 timerclear(&c->conn_timeout); // It will be set anew in utcp_timeout() if c->snd.una != c->snd.nxt.
816 if(c->snd.una == c->snd.nxt)
817 timerclear(&c->rtrx_timeout);
820 // 5. Process SYN stuff
825 // This is a SYNACK. It should always have ACKed the SYN.
828 c->rcv.irs = hdr.seq;
829 c->rcv.nxt = hdr.seq;
830 set_state(c, ESTABLISHED);
831 // TODO: notify application of this somehow.
841 // Ehm, no. We should never receive a second SYN.
850 // SYN counts as one sequence number
854 // 6. Process new data
856 if(c->state == SYN_RECEIVED) {
857 // This is the ACK after the SYNACK. It should always have ACKed the SYNACK.
861 // Are we still LISTENing?
863 utcp->accept(c, c->src);
865 if(c->state != ESTABLISHED) {
866 set_state(c, CLOSED);
876 // This should never happen.
889 // Ehm no, We should never receive more data after a FIN.
901 rxd = c->recv(c, data, len);
903 // TODO: once we have a receive buffer, handle the application not accepting all data.
909 rxd = len; // Bad application, bad!
917 // 7. Process FIN stuff
923 // This should never happen.
929 set_state(c, CLOSE_WAIT);
932 set_state(c, CLOSING);
935 gettimeofday(&c->conn_timeout, NULL);
936 c->conn_timeout.tv_sec += 60;
937 set_state(c, TIME_WAIT);
943 // Ehm, no. We should never receive a second FIN.
952 // FIN counts as one sequence number
956 // Inform the application that the peer closed the connection.
963 // Now we send something back if:
964 // - we advanced rcv.nxt (ie, we got some data that needs to be ACKed)
965 // -> sendatleastone = true
966 // - or we got an ack, so we should maybe send a bit more data
967 // -> sendatleastone = false
970 ack(c, prevrcvnxt != c->rcv.nxt);
980 hdr.ack = hdr.seq + len;
984 print_packet(utcp, "send", &hdr, sizeof hdr);
985 utcp->send(utcp, &hdr, sizeof hdr);
990 int utcp_shutdown(struct utcp_connection *c, int dir) {
991 debug("%p shutdown %d at %u\n", c ? c->utcp : NULL, dir, c->snd.last);
998 debug("Error: shutdown() called on closed connection %p\n", c);
1003 if(!(dir == UTCP_SHUT_RD || dir == UTCP_SHUT_WR || dir == UTCP_SHUT_RDWR)) {
1008 // TCP does not have a provision for stopping incoming packets.
1009 // The best we can do is to just ignore them.
1010 if(dir == UTCP_SHUT_RD || dir == UTCP_SHUT_RDWR)
1013 // The rest of the code deals with shutting down writes.
1014 if(dir == UTCP_SHUT_RD)
1024 set_state(c, CLOSED);
1029 set_state(c, FIN_WAIT_1);
1035 set_state(c, CLOSING);
1050 int utcp_close(struct utcp_connection *c) {
1051 if(utcp_shutdown(c, SHUT_RDWR))
1059 int utcp_abort(struct utcp_connection *c) {
1066 debug("Error: abort() called on closed connection %p\n", c);
1083 set_state(c, CLOSED);
1091 set_state(c, CLOSED);
1101 hdr.seq = c->snd.nxt;
1106 print_packet(c->utcp, "send", &hdr, sizeof hdr);
1107 c->utcp->send(c->utcp, &hdr, sizeof hdr);
1112 * One call to this function will loop through all connections,
1113 * checking if something needs to be resent or not.
1114 * The return value is the time to the next timeout in milliseconds,
1115 * or maybe a negative value if the timeout is infinite.
1117 struct timeval utcp_timeout(struct utcp *utcp) {
1119 gettimeofday(&now, NULL);
1120 struct timeval next = {now.tv_sec + 3600, now.tv_usec};
1122 for(int i = 0; i < utcp->nconnections; i++) {
1123 struct utcp_connection *c = utcp->connections[i];
1127 if(c->state == CLOSED) {
1129 debug("Reaping %p\n", c);
1136 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &now, <)) {
1140 c->recv(c, NULL, 0);
1144 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &now, <)) {
1148 if(c->poll && buffer_free(&c->sndbuf) && (c->state == ESTABLISHED || c->state == CLOSE_WAIT))
1149 c->poll(c, buffer_free(&c->sndbuf));
1151 if(timerisset(&c->conn_timeout) && timercmp(&c->conn_timeout, &next, <))
1152 next = c->conn_timeout;
1154 if(c->snd.nxt != c->snd.una) {
1155 c->rtrx_timeout = now;
1156 c->rtrx_timeout.tv_sec++;
1158 timerclear(&c->rtrx_timeout);
1161 if(timerisset(&c->rtrx_timeout) && timercmp(&c->rtrx_timeout, &next, <))
1162 next = c->rtrx_timeout;
1165 struct timeval diff;
1166 timersub(&next, &now, &diff);
1170 bool utcp_is_active(struct utcp *utcp) {
1174 for(int i = 0; i < utcp->nconnections; i++)
1175 if(utcp->connections[i]->state != CLOSED && utcp->connections[i]->state != TIME_WAIT)
1181 struct utcp *utcp_init(utcp_accept_t accept, utcp_pre_accept_t pre_accept, utcp_send_t send, void *priv) {
1182 struct utcp *utcp = calloc(1, sizeof *utcp);
1191 utcp->accept = accept;
1192 utcp->pre_accept = pre_accept;
1201 void utcp_exit(struct utcp *utcp) {
1204 for(int i = 0; i < utcp->nconnections; i++) {
1205 if(!utcp->connections[i]->reapable)
1206 debug("Warning, freeing unclosed connection %p\n", utcp->connections[i]);
1207 buffer_exit(&utcp->connections[i]->sndbuf);
1208 free(utcp->connections[i]);
1210 free(utcp->connections);
1214 uint16_t utcp_get_mtu(struct utcp *utcp) {
1215 return utcp ? utcp->mtu : 0;
1218 void utcp_set_mtu(struct utcp *utcp, uint16_t mtu) {
1219 // TODO: handle overhead of the header
1224 int utcp_get_user_timeout(struct utcp *u) {
1225 return u ? u->timeout : 0;
1228 void utcp_set_user_timeout(struct utcp *u, int timeout) {
1230 u->timeout = timeout;
1233 size_t utcp_get_sndbuf(struct utcp_connection *c) {
1234 return c ? c->sndbuf.maxsize : 0;
1237 size_t utcp_get_sndbuf_free(struct utcp_connection *c) {
1238 if(c && (c->state == ESTABLISHED || c->state == CLOSE_WAIT))
1239 return buffer_free(&c->sndbuf);
1244 void utcp_set_sndbuf(struct utcp_connection *c, size_t size) {
1247 c->sndbuf.maxsize = size;
1248 if(c->sndbuf.maxsize != size)
1249 c->sndbuf.maxsize = -1;
1252 bool utcp_get_nodelay(struct utcp_connection *c) {
1253 return c ? c->nodelay : false;
1256 void utcp_set_nodelay(struct utcp_connection *c, bool nodelay) {
1258 c->nodelay = nodelay;
1261 bool utcp_get_keepalive(struct utcp_connection *c) {
1262 return c ? c->keepalive : false;
1265 void utcp_set_keepalive(struct utcp_connection *c, bool keepalive) {
1267 c->keepalive = keepalive;
1270 size_t utcp_get_outq(struct utcp_connection *c) {
1271 return c ? seqdiff(c->snd.nxt, c->snd.una) : 0;
1274 void utcp_set_recv_cb(struct utcp_connection *c, utcp_recv_t recv) {
1279 void utcp_set_poll_cb(struct utcp_connection *c, utcp_poll_t poll) {
1284 void utcp_set_accept_cb(struct utcp *utcp, utcp_accept_t accept, utcp_pre_accept_t pre_accept) {
1286 utcp->accept = accept;
1287 utcp->pre_accept = pre_accept;