From: Guus Sliepen <guus@sliepen.org>
Date: Mon, 4 May 2020 06:36:44 +0000 (+0200)
Subject: Ensure we retransmit the SYNACK packet if we didn't get an ACK back for it.
X-Git-Url: https://git.meshlink.io/?a=commitdiff_plain;h=4f6345726724732b564dd55b20ecb3e20a127bd0;p=utcp

Ensure we retransmit the SYNACK packet if we didn't get an ACK back for it.

We didn't start the retransmission timer when we got an incoming connection,
and we didn't send an ACK back when we received a retransmitted SYNACK
without any data.
---

diff --git a/utcp.c b/utcp.c
index 5eca4d3..47acf22 100644
--- a/utcp.c
+++ b/utcp.c
@@ -890,7 +890,7 @@ static void retransmit(struct utcp_connection *c) {
 
 	struct utcp *utcp = c->utcp;
 
-	if (utcp->retransmit) {
+	if(utcp->retransmit) {
 		utcp->retransmit(c);
 	}
 
@@ -1352,6 +1352,8 @@ synack:
 				print_packet(c, "send", &pkt, sizeof(hdr));
 				utcp->send(utcp, &pkt, sizeof(hdr));
 			}
+
+			start_retransmit_timer(c);
 		} else {
 			// No, we don't want your packets, send a RST back
 			len = 1;
@@ -1713,7 +1715,7 @@ skip_ack:
 			}
 
 			c->rcv.irs = hdr.seq;
-			c->rcv.nxt = hdr.seq;
+			c->rcv.nxt = hdr.seq + 1;
 
 			if(c->shut_wr) {
 				c->snd.last++;
@@ -1722,7 +1724,6 @@ skip_ack:
 				set_state(c, ESTABLISHED);
 			}
 
-			// TODO: notify application of this somehow.
 			break;
 
 		case SYN_RECEIVED:
@@ -1736,8 +1737,8 @@ skip_ack:
 		case CLOSING:
 		case LAST_ACK:
 		case TIME_WAIT:
-			// Ehm, no. We should never receive a second SYN.
-			return 0;
+			// This could be a retransmission. Ignore the SYN flag, but send an ACK back.
+			break;
 
 		default:
 #ifdef UTCP_DEBUG
@@ -1745,9 +1746,6 @@ skip_ack:
 #endif
 			return 0;
 		}
-
-		// SYN counts as one sequence number
-		c->rcv.nxt++;
 	}
 
 	// 6. Process new data