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add TCP backlog to handle client MSS

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Sergio R. Caprile committed 2025-08-22 11:42:41 -03:00
1 parent 3aaf7d0da7
commit 7ee1f14a6d
4 files changed
+413 -143
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src/net_builtin.c
+78 -11
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@@ -582,7 +582,7 @@ static size_t tx_tcp_pkt(struct mg_tcpip_if *ifp, struct pkt *pkt,
}
static struct mg_connection *accept_conn(struct mg_connection *lsn,
struct pkt *pkt) {
struct pkt *pkt, uint16_t mss) {
struct mg_connection *c = mg_alloc_conn(lsn->mgr);
struct connstate *s;
if (c == NULL) {
@@ -590,7 +590,7 @@ static struct mg_connection *accept_conn(struct mg_connection *lsn,
return NULL;
}
s = (struct connstate *) (c + 1);
s->dmss = 536; // assume default, RFC-9293 3.7.1
s->dmss = mss; // from options in client SYN
s->seq = mg_ntohl(pkt->tcp->ack), s->ack = mg_ntohl(pkt->tcp->seq);
memcpy(s->mac, pkt->eth->src, sizeof(s->mac));
settmout(c, MIP_TTYPE_KEEPALIVE);
@@ -694,7 +694,7 @@ static void read_conn(struct mg_connection *c, struct pkt *pkt) {
if (pkt->tcp->flags & TH_FIN) {
uint8_t flags = TH_ACK;
if (mg_ntohl(pkt->tcp->seq) != s->ack) {
MG_VERBOSE(("ignoring FIN, SEQ != ACK: %x %x", mg_ntohl(pkt->tcp->seq), s->ack));
MG_VERBOSE(("ignoring FIN, %x != %x", mg_ntohl(pkt->tcp->seq), s->ack));
tx_tcp(c->mgr->ifp, s->mac, rem_ip, TH_ACK, c->loc.port, c->rem.port,
mg_htonl(s->seq), mg_htonl(s->ack), "", 0);
return;
@@ -777,6 +777,57 @@ static void read_conn(struct mg_connection *c, struct pkt *pkt) {
}
}
// TCP backlog
struct mg_backlog {
uint16_t port, mss; // use port=0 for available entries
uint8_t age;
};
static int backlog_insert(struct mg_connection *c, uint16_t port,
uint16_t mss) {
struct mg_backlog *p = (struct mg_backlog *) c->data;
size_t i;
for (i = 0; i < sizeof(c->data) / sizeof(*p); i++) {
if (p[i].port != 0) continue;
p[i].age = 2; // remove after two calls, average 1.5 call rate
p[i].port = port, p[i].mss = mss;
return (int) i;
}
return -1;
}
static struct mg_backlog *backlog_retrieve(struct mg_connection *c,
uint16_t key, uint16_t port) {
struct mg_backlog *p = (struct mg_backlog *) c->data;
if (key >= sizeof(c->data) / sizeof(*p)) return NULL;
if (p[key].port != port) return NULL;
p += key;
return p;
}
static void backlog_remove(struct mg_connection *c, uint16_t key) {
struct mg_backlog *p = (struct mg_backlog *) c->data;
p[key].port = 0;
}
static void backlog_maintain(struct mg_connection *c) {
struct mg_backlog *p = (struct mg_backlog *) c->data;
size_t i; // dec age and remove those where it reaches 0
for (i = 0; i < sizeof(c->data) / sizeof(*p); i++) {
if (p[i].port == 0) continue;
if (p[i].age != 0) --p[i].age;
if (p[i].age == 0) p[i].port = 0;
}
}
static void backlog_poll(struct mg_mgr *mgr) {
struct mg_connection *c = NULL;
for (c = mgr->conns; c != NULL; c = c->next) {
if (!c->is_udp && c->is_listening) backlog_maintain(c);
}
}
// process options (MSS)
static void handle_opt(struct connstate *s, struct tcp *tcp) {
uint8_t *opts = (uint8_t *) (tcp + 1);
@@ -834,15 +885,30 @@ static void rx_tcp(struct mg_tcpip_if *ifp, struct pkt *pkt) {
if (c->is_accepted) mg_error(c, "peer RST"); // RFC-1122 4.2.2.13
// ignore RST if not connected
} else if (pkt->tcp->flags & TH_SYN) {
// TODO(): handle_opt(s, pkt->tcp); // process options (MSS)
// At this point, s = NULL, there is no connection.
// Use peer's source port as ISN, in order to recognise the handshake
uint32_t isn = mg_htonl((uint32_t) mg_ntohs(pkt->tcp->sport));
tx_tcp_pkt(ifp, pkt, TH_SYN | TH_ACK, isn, NULL, 0);
struct connstate cs; // At this point, s = NULL, there is no connection
int key;
uint32_t isn;
if (pkt->tcp->sport != 0) {
handle_opt(&cs, pkt->tcp); // process options (MSS)
key = backlog_insert(c, pkt->tcp->sport, cs.dmss); // backlog options (MSS)
if (key < 0) return; // no room in backlog, discard SYN, client retries
// Use peer's src port and bl key as ISN, to later identify the handshake
isn = (mg_htonl(((uint32_t)key << 16) | mg_ntohs(pkt->tcp->sport)));
tx_tcp_pkt(ifp, pkt, TH_SYN | TH_ACK, isn, NULL, 0);
} // what should we do when port=0 ? Linux takes port 0 as any other port
} else if (pkt->tcp->flags & TH_FIN) {
tx_tcp_pkt(ifp, pkt, TH_FIN | TH_ACK, pkt->tcp->ack, NULL, 0);
} else if (mg_htonl(pkt->tcp->ack) == mg_htons(pkt->tcp->sport) + 1U) {
accept_conn(c, pkt);
} else if ((uint16_t) (mg_htonl(pkt->tcp->ack) - 1) ==
mg_htons(pkt->tcp->sport)) {
uint16_t key = (uint16_t) ((mg_htonl(pkt->tcp->ack) - 1) >> 16);
struct mg_backlog *b = backlog_retrieve(c, key, pkt->tcp->sport);
if (b != NULL) {
accept_conn(c, pkt, b->mss); // pass options
backlog_remove(c, key);
} else if (!c->is_accepted) { // not an actual match, reset
tx_tcp_pkt(ifp, pkt, TH_RST | TH_ACK, pkt->tcp->ack, NULL, 0);
// TODO(scaprile): revisit this and below, weird scenarios
}
} else if (!c->is_accepted) { // no peer
tx_tcp_pkt(ifp, pkt, TH_RST | TH_ACK, pkt->tcp->ack, NULL, 0);
} else {
@@ -970,6 +1036,7 @@ static void mg_tcpip_poll(struct mg_tcpip_if *ifp, uint64_t now) {
names[ifp->state], mg_print_ip4, &ifp->ip, ifp->nrecv, ifp->nsent,
ifp->ndrop, ifp->nerr));
#endif
backlog_poll(ifp->mgr);
}
// Handle gw ARP request timeout, order is important
if (expired_1000ms && ifp->state == MG_TCPIP_STATE_IP) {
@@ -1303,7 +1370,7 @@ static void setdns4(struct mg_tcpip_if *ifp, uint32_t *ip) {
MG_DEBUG(("Set DNS URL to %s", dnsc->url));
if (ifp->mgr->use_dns6) return;
if (dnsc->c != NULL) mg_close_conn(dnsc->c);
if (!mg_dnsc_init(ifp->mgr, dnsc)) // create DNS connection
if (!mg_dnsc_init(ifp->mgr, dnsc)) // create DNS connection
MG_ERROR(("DNS connection creation failed"));
}