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Merged
cpq merged 1 commit into from
Jun 3, 2026
+100 −3
Merged

Honor peer TCP window #3572

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19 changes: 18 additions & 1 deletion mongoose.c
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Original file line number Diff line number Diff line change
Expand Up @@ -6787,6 +6787,8 @@ struct connstate {
uint64_t timer; // TCP timer (see 'ttype' below)
uint32_t acked; // Last ACK-ed number
size_t unacked; // Not acked bytes
uint32_t maxseq; // Max send seq (ack + window)
uint16_t win; // destination current window size
uint16_t dmss; // destination MSS (from TCP opts)
uint8_t mac[sizeof(struct mg_l2addr)]; // Peer hw address
uint8_t ttype; // Timer type:
Expand Down Expand Up @@ -8032,6 +8034,7 @@ static struct mg_connection *accept_conn(struct mg_connection *lsn,
s = (struct connstate *) (c + 1);
s->dmss = mss; // from options in client SYN
s->seq = mg_ntohl(pkt->tcp->ack), s->ack = mg_ntohl(pkt->tcp->seq);
s->win = mg_ntohs(pkt->tcp->win), s->maxseq = (uint32_t)(s->seq + s->win);
#if MG_ENABLE_IPV6
if (lsn->loc.is_ip6) {
c->rem.addr.ip6[0] = pkt->ip6->src[0],
Expand Down Expand Up @@ -8124,10 +8127,13 @@ long mg_io_send(struct mg_connection *c, const void *buf, size_t len) {
len = trim_len(c, len);
if (c->is_udp) {
if (!udp_send(c, buf, len)) return MG_IO_WAIT;
} else { // TCP, cap to peer's MSS
} else { // TCP, cap to peer's MSS and check window
struct mg_tcpip_if *ifp = c->mgr->ifp;
size_t sent;
uint32_t room = s->maxseq - s->seq;
if (room == 0) return MG_IO_WAIT;
if (len > s->dmss) len = s->dmss; // RFC-6691: reduce if sending opts
if ((uint32_t) len > room) len = room;
sent = tx_tcp(ifp, s->mac, &c->loc, &c->rem, TH_PUSH | TH_ACK,
mg_htonl(s->seq), mg_htonl(s->ack), buf, len);
if (sent == 0) {
Expand Down Expand Up @@ -8162,6 +8168,12 @@ static void handle_tls_recv(struct mg_connection *c) {
}
}

static void handle_ack(struct connstate *s, uint32_t ackno, uint16_t win) {
if (ackno < (s->seq - s->win) || ackno > s->seq) return;
s->maxseq = (uint32_t)(ackno + win);
s->win = win;
}

static void read_conn(struct mg_connection *c, struct pkt *pkt) {
struct connstate *s = (struct connstate *) (c + 1);
struct mg_iobuf *io = c->is_tls ? &c->rtls : &c->recv;
Expand Down Expand Up @@ -8201,6 +8213,8 @@ static void read_conn(struct mg_connection *c, struct pkt *pkt) {
mg_htonl(s->ack), NULL, 0);
return; // no data to process
} else if (pkt->pay.len == 0) { // this is an ACK
if (pkt->tcp->flags & TH_ACK)
handle_ack(s, mg_ntohl(pkt->tcp->ack), mg_ntohs(pkt->tcp->win));
if (s->fin_rcvd && s->ttype == MIP_TTYPE_FIN) s->twclosure = true;
return; // no data to process
} else if (seq != s->ack) {
Expand All @@ -8218,6 +8232,8 @@ static void read_conn(struct mg_connection *c, struct pkt *pkt) {
mg_error(c, "oom");
return; // drop it
}
if (pkt->tcp->flags & TH_ACK)
handle_ack(s, mg_ntohl(pkt->tcp->ack), mg_ntohs(pkt->tcp->win));
// Copy TCP payload into the IO buffer. If the connection is plain text,
// we copy to c->recv. If the connection is TLS, this data is encrypted,
// therefore we copy that encrypted data to the c->rtls iobuffer instead,
Expand Down Expand Up @@ -8336,6 +8352,7 @@ static void rx_tcp(struct mg_tcpip_if *ifp, struct pkt *pkt) {
if (!handle_opt(s, pkt->tcp, pkt->ip6 != NULL))
return; // process options (MSS)
s->seq = mg_ntohl(pkt->tcp->ack), s->ack = mg_ntohl(pkt->tcp->seq) + 1;
s->win = mg_ntohs(pkt->tcp->win), s->maxseq = (uint32_t)(s->seq + s->win);
tx_tcp_ctrlresp(ifp, pkt, TH_ACK, pkt->tcp->ack);
c->is_connecting = 0; // Client connected
settmout(c, MIP_TTYPE_KEEPALIVE);
Expand Down
19 changes: 18 additions & 1 deletion src/net_builtin.c
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,8 @@ struct connstate {
uint64_t timer; // TCP timer (see 'ttype' below)
uint32_t acked; // Last ACK-ed number
size_t unacked; // Not acked bytes
uint32_t maxseq; // Max send seq (ack + window)
uint16_t win; // destination current window size
uint16_t dmss; // destination MSS (from TCP opts)
uint8_t mac[sizeof(struct mg_l2addr)]; // Peer hw address
uint8_t ttype; // Timer type:
Expand Down Expand Up @@ -1268,6 +1270,7 @@ static struct mg_connection *accept_conn(struct mg_connection *lsn,
s = (struct connstate *) (c + 1);
s->dmss = mss; // from options in client SYN
s->seq = mg_ntohl(pkt->tcp->ack), s->ack = mg_ntohl(pkt->tcp->seq);
s->win = mg_ntohs(pkt->tcp->win), s->maxseq = (uint32_t)(s->seq + s->win);
#if MG_ENABLE_IPV6
if (lsn->loc.is_ip6) {
c->rem.addr.ip6[0] = pkt->ip6->src[0],
Expand Down Expand Up @@ -1360,10 +1363,13 @@ long mg_io_send(struct mg_connection *c, const void *buf, size_t len) {
len = trim_len(c, len);
if (c->is_udp) {
if (!udp_send(c, buf, len)) return MG_IO_WAIT;
} else { // TCP, cap to peer's MSS
} else { // TCP, cap to peer's MSS and check window
struct mg_tcpip_if *ifp = c->mgr->ifp;
size_t sent;
uint32_t room = s->maxseq - s->seq;
if (room == 0) return MG_IO_WAIT;
if (len > s->dmss) len = s->dmss; // RFC-6691: reduce if sending opts
if ((uint32_t) len > room) len = room;
sent = tx_tcp(ifp, s->mac, &c->loc, &c->rem, TH_PUSH | TH_ACK,
mg_htonl(s->seq), mg_htonl(s->ack), buf, len);
if (sent == 0) {
Expand Down Expand Up @@ -1398,6 +1404,12 @@ static void handle_tls_recv(struct mg_connection *c) {
}
}

static void handle_ack(struct connstate *s, uint32_t ackno, uint16_t win) {
if (ackno < (s->seq - s->win) || ackno > s->seq) return;
s->maxseq = (uint32_t)(ackno + win);
s->win = win;
}

static void read_conn(struct mg_connection *c, struct pkt *pkt) {
struct connstate *s = (struct connstate *) (c + 1);
struct mg_iobuf *io = c->is_tls ? &c->rtls : &c->recv;
Expand Down Expand Up @@ -1437,6 +1449,8 @@ static void read_conn(struct mg_connection *c, struct pkt *pkt) {
mg_htonl(s->ack), NULL, 0);
return; // no data to process
} else if (pkt->pay.len == 0) { // this is an ACK
if (pkt->tcp->flags & TH_ACK)
handle_ack(s, mg_ntohl(pkt->tcp->ack), mg_ntohs(pkt->tcp->win));
if (s->fin_rcvd && s->ttype == MIP_TTYPE_FIN) s->twclosure = true;
return; // no data to process
} else if (seq != s->ack) {
Expand All @@ -1454,6 +1468,8 @@ static void read_conn(struct mg_connection *c, struct pkt *pkt) {
mg_error(c, "oom");
return; // drop it
}
if (pkt->tcp->flags & TH_ACK)
handle_ack(s, mg_ntohl(pkt->tcp->ack), mg_ntohs(pkt->tcp->win));
// Copy TCP payload into the IO buffer. If the connection is plain text,
// we copy to c->recv. If the connection is TLS, this data is encrypted,
// therefore we copy that encrypted data to the c->rtls iobuffer instead,
Expand Down Expand Up @@ -1572,6 +1588,7 @@ static void rx_tcp(struct mg_tcpip_if *ifp, struct pkt *pkt) {
if (!handle_opt(s, pkt->tcp, pkt->ip6 != NULL))
return; // process options (MSS)
s->seq = mg_ntohl(pkt->tcp->ack), s->ack = mg_ntohl(pkt->tcp->seq) + 1;
s->win = mg_ntohs(pkt->tcp->win), s->maxseq = (uint32_t)(s->seq + s->win);
tx_tcp_ctrlresp(ifp, pkt, TH_ACK, pkt->tcp->ack);
c->is_connecting = 0; // Client connected
settmout(c, MIP_TTYPE_KEEPALIVE);
Expand Down
65 changes: 64 additions & 1 deletion test/mip_test.c
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,8 @@

#include "driver_mock.c"

#define TCP_TEST_WIN 3000 // arbitrary peer window size to test txwindow

static int s_num_tests = 0;
static bool s_error = false;
static int s_sent_fragment = 0;
Expand Down Expand Up @@ -116,6 +118,17 @@ static void tcpclosure_fn(struct mg_connection *c, int ev, void *ev_data) {
(void) c, (void) ev_data;
}

static void txwindow_fn(struct mg_connection *c, int ev, void *ev_data) {
if (ev == MG_EV_ACCEPT) {
char bigdata[2 * TCP_TEST_WIN + 256];
*(int *) c->fn_data = 0;
mg_send(c, bigdata, sizeof(bigdata));
} else if (ev == MG_EV_WRITE) {
++(*(int *) c->fn_data);
}
(void) c, (void) ev_data;
}

static void client_fn(struct mg_connection *c, int ev, void *ev_data) {
if (ev == MG_EV_ERROR || ev == MG_EV_CONNECT) (*(int *) c->fn_data) = ev;
(void) c, (void) ev_data;
Expand All @@ -139,7 +152,7 @@ static void frag_send_fn(struct mg_connection *c, int ev, void *ev_data) {
if (ev == MG_EV_POLL) {
if (!s_sent) {
struct connstate *s = (struct connstate *) (c + 1);
s->dmss = 1500; // mock set some destination MSS way larger
s->dmss = 1500, s->maxseq = 1500; // mock set dest MSS and win way larger
c->send.len = 1200; // setting TCP payload size
s_sent = true;
}
Expand Down Expand Up @@ -214,6 +227,7 @@ static void create_tcp_seg(struct eth *e, struct ipp *ipp, uint32_t seq,
t.ack = mg_htonl(ack);
t.sport = mg_htons(sport);
t.dport = mg_htons(dport);
t.win = mg_htons(TCP_TEST_WIN);
t.off = (uint8_t) ((sizeof(t) / 4) << 4) + (uint8_t) ((opts_len / 4) << 4);
memcpy(s_driver_data.buf, e, sizeof(*e));
#if MG_ENABLE_IPV6
Expand Down Expand Up @@ -898,6 +912,54 @@ static void test_tcp_retransmit(void) {
mg_mgr_free(&mgr);
}


static void test_tcp_txwindow(void) {
struct mg_mgr mgr;
struct eth e;
struct ip ip;
struct ipp ipp;
struct tcp *t = (struct tcp *) (s_driver_data.buf + sizeof(e) + sizeof(ip));
int count = 0, stallcount;
uint32_t seq;
//bool response_recv = true;
struct mg_tcpip_driver driver;
struct mg_tcpip_if mif;

ipp.ip4 = &ip;
ipp.ip6 = NULL;

init_tcp_tests(&mgr, &e, &ipp, &driver, &mif, txwindow_fn);
mgr.conns->fn_data = &count;
init_tcp_handshake(&e, &ipp, &mgr); // starts with seq_no=1000, ackno=2
ASSERT((t->seq == mg_htonl(2)));
do {
while (!received_response(&s_driver_data)) mg_mgr_poll(&mgr, 0);
seq = (uint32_t)(mg_htonl(t->seq) + s_driver_data.len - (size_t)((char *)((uint32_t *)t + (t->off >> 4)) - s_driver_data.buf));
} while (seq < (TCP_TEST_WIN + 2));
stallcount = count;
mg_mgr_poll(&mgr, 0), s_driver_data.len = 0;
mg_mgr_poll(&mgr, 0), s_driver_data.len = 0;
ASSERT((stallcount == count));
s_driver_data.tx_ready = false;
create_tcp_simpleseg(&e, &ipp, 1001, seq - TCP_TEST_WIN/2, TH_ACK, 0); // send ACK for half window
while (!received_response(&s_driver_data)) mg_mgr_poll(&mgr, 0);
ASSERT((stallcount < count));
do {
while (!received_response(&s_driver_data)) mg_mgr_poll(&mgr, 0);
seq = (uint32_t)(mg_htonl(t->seq) + s_driver_data.len - (size_t)((char *)((uint32_t *)t + (t->off >> 4)) - s_driver_data.buf));
} while (seq < (TCP_TEST_WIN + TCP_TEST_WIN/2 + 2));
stallcount = count;
mg_mgr_poll(&mgr, 0), s_driver_data.len = 0;
mg_mgr_poll(&mgr, 0), s_driver_data.len = 0;
ASSERT((stallcount == count));
s_driver_data.tx_ready = false;
create_tcp_simpleseg(&e, &ipp, 1001, seq, TH_ACK, 0); // send ACK
while (!received_response(&s_driver_data)) mg_mgr_poll(&mgr, 0);
ASSERT((stallcount < count));
s_driver_data.len = 0;
mg_mgr_free(&mgr);
}

static void test_frag_recv_path(void) {
struct mg_mgr mgr;
struct eth e;
Expand Down Expand Up @@ -1058,6 +1120,7 @@ static void test_tcp(bool ipv6) {
if (!ipv6) {
test_tcp_backlog();
test_tcp_retransmit();
test_tcp_txwindow();
}
}

Expand Down
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