Add MTU_INFO protocol message.

[tinc] / src / protocol_misc.c

diff --git a/src/protocol_misc.c b/src/protocol_misc.c
index b2bc40e..5fde833 100644 (file)
--- a/src/protocol_misc.c
+++ b/src/protocol_misc.c
@@ -237,3 +237,92 @@ bool udp_info_h(connection_t *c, const char* request) {
 
        return send_udp_info(from, to);
 }
+
+/* Transmitting MTU information */
+
+bool send_mtu_info(node_t *from, node_t *to, int mtu) {
+       /* Skip cases where sending MTU info messages doesn't make sense.
+          This is done here in order to avoid repeating the same logic in multiple callsites. */
+
+       if(to == myself)
+               return true;
+
+       if(!to->status.reachable)
+               return true;
+
+       if(from == myself && to->connection)
+               return true;
+
+       if((to->nexthop->options >> 24) < 6)
+               return true;
+
+       /* We will send the passed-in MTU value, unless we believe ours is better. */
+
+       node_t *via = (from->via == myself) ? from->nexthop : from->via;
+       if(from->minmtu == from->maxmtu && from->via == myself) {
+               /* We have a direct measurement. Override the value entirely.
+                  Note that we only do that if we are sitting as a static relay in the path;
+                  otherwise, we can't guarantee packets will flow through us, and increasing
+                  MTU could therefore end up being too optimistic. */
+               mtu = from->minmtu;
+       } else if(via->minmtu == via->maxmtu) {
+               /* Static relay. Ensure packets will make it through the entire relay path. */
+               mtu = MIN(mtu, via->minmtu);
+       } else if(via->nexthop->minmtu == via->nexthop->maxmtu) {
+               /* Dynamic relay. Ensure packets will make it through the entire relay path. */
+               mtu = MIN(mtu, via->nexthop->minmtu);
+       }
+
+       /* If none of the conditions above match in the steady state, it means we're using TCP,
+          so the MTU is irrelevant. That said, it is still important to honor the MTU that was passed in,
+          because other parts of the relay path might be able to use UDP, which means they care about the MTU. */
+
+       return send_request(to->nexthop->connection, "%d %s %s %d", MTU_INFO, from->name, to->name, mtu);
+}
+
+bool mtu_info_h(connection_t *c, const char* request) {
+       char from_name[MAX_STRING_SIZE];
+       char to_name[MAX_STRING_SIZE];
+       int mtu;
+
+       if(sscanf(request, "%*d "MAX_STRING" "MAX_STRING" %d", from_name, to_name, &mtu) != 3) {
+               logger(DEBUG_ALWAYS, LOG_ERR, "Got bad %s from %s (%s)", "MTU_INFO", c->name, c->hostname);
+               return false;
+       }
+
+       if(mtu < 512) {
+               logger(DEBUG_ALWAYS, LOG_ERR, "Got bad %s from %s (%s): %s", "MTU_INFO", c->name, c->hostname, "invalid MTU");
+               return false;
+       }
+
+       mtu = MIN(mtu, MTU);
+
+       if(!check_id(from_name) || !check_id(to_name)) {
+               logger(DEBUG_ALWAYS, LOG_ERR, "Got bad %s from %s (%s): %s", "MTU_INFO", c->name, c->hostname, "invalid name");
+               return false;
+       }
+
+       node_t *from = lookup_node(from_name);
+       if(!from) {
+               logger(DEBUG_ALWAYS, LOG_ERR, "Got %s from %s (%s) origin %s which does not exist in our connection list", "MTU_INFO", c->name, c->hostname, from_name);
+               return true;
+       }
+
+       /* If we don't know the current MTU for that node, use the one we received.
+          Even if we're about to make our own measurements, the value we got from downstream nodes should be pretty close
+          so it's a good idea to use it in the mean time. */
+       if(from->mtu != mtu && from->minmtu != from->maxmtu) {
+               logger(DEBUG_TRAFFIC, LOG_INFO, "Using provisional MTU %d for node %s (%s)", mtu, from->name, from->hostname);
+               from->mtu = mtu;
+       }
+
+       node_t *to = lookup_node(to_name);
+       if(!to) {
+               logger(DEBUG_ALWAYS, LOG_ERR, "Got %s from %s (%s) destination %s which does not exist in our connection list", "MTU_INFO", c->name, c->hostname, to_name);
+               return true;
+       }
+
+       /* Continue passing the MTU value (or a better one if we have it) up the chain. */
+
+       return send_mtu_info(from, to, mtu);
+}