Set congestion control algorithm before synack is sent on destination

[Midori Kato]

Hi,

I implement congestion control algorithm that needs negotiation using tcp option during three-way handshake. Because the current flowgrind doesn't set socket option before listen() on the destination, the destination socket doesn't add necessary tcp option in SYNACK. In the result, the negotiation is always failed. I avoid this issue using the following patch.

This flowgrind extension will be minor issue because most of congestion control needs no negotiation during three-way handshake except for multi-path tcp. If you think this extension is essential, please adopt to flowgrind.

diff --git a/src/destination.c b/src/destination.c
index b89ad79..b0507f2 100644
--- a/src/destination.c
+++ b/src/destination.c
@@ -114,6 +114,9 @@ static int create_listen_socket(struct _flow *flow, char *bind_addr,
        if (flow->settings.mtcp)
                set_tcp_mtcp(fd);

+ if (flow->settings.cc_alg)
+ set_congestion_control(fd, flow->settings.cc_alg);
+
        if (listen(fd, 0) < 0) {
                logging_log(LOG_ALERT, "listen failed: %s",
                            strerror(errno));

[Christian Samsel (oxygenx)]

Hi Midori,

Patch looks reasonable. If you going to supply more patches maybe you could create a github account and do pull requests? this way it is easier to add the patches and you will credibility for the patches.

regards, Christian

[Christian Samsel (oxygenx)]

committed