relay: Refactor choosing extend IPs (bcec1ec0) · Commits · The Tor Project / Core / Tor

src/feature/relay/circuitbuild_relay.c

+25 −20

Original line number	Diff line number	Diff line
		@@ -250,8 +250,27 @@ STATIC const tor_addr_port_t *
		circuit_choose_ip_ap_for_extend(const tor_addr_port_t *ipv4_ap,
		const tor_addr_port_t *ipv6_ap)
		{
		/* If we could make an IPv4 or an IPv6 connection, make an IPv6 connection
		* at random, with probability 1 in N.
		const bool ipv6_supported = router_has_advertised_ipv6_orport(get_options());

		/* If IPv6 is not supported, we can't use the IPv6 address. */
		if (!ipv6_supported) {
		ipv6_ap = NULL;
		}

		/* If there is no IPv6 address, IPv4 is always supported.
		* Until clients include IPv6 ORPorts, and most relays support IPv6,
		* this is the most common case. */
		if (!ipv6_ap) {
		return ipv4_ap;
		}

		/* If there is no IPv4 address, return the (possibly NULL) IPv6 address. */
		if (!ipv4_ap) {
		return ipv6_ap;
		}

		/* Now we have an IPv4 and an IPv6 address, and IPv6 is supported.
		* So make an IPv6 connection at random, with probability 1 in N.
		* 1 means "always IPv6 (and no IPv4)"
		* 2 means "equal probability of IPv4 or IPv6"
		* ... (and so on) ...
		@@ -260,11 +279,6 @@ circuit_choose_ip_ap_for_extend(const tor_addr_port_t *ipv4_ap,
		*/
		#define IPV6_CONNECTION_ONE_IN_N 2

		/* IPv4 is always supported */
		const bool ipv6_supported = router_has_advertised_ipv6_orport(get_options());

		if (ipv4_ap && ipv6_ap && ipv6_supported) {
		/* Choose between IPv4 and IPv6 at random */
		bool choose_ipv6 = crypto_fast_rng_one_in_n(get_thread_fast_rng(),
		IPV6_CONNECTION_ONE_IN_N);
		if (choose_ipv6) {
		@@ -272,15 +286,6 @@ circuit_choose_ip_ap_for_extend(const tor_addr_port_t *ipv4_ap,
		} else {
		return ipv4_ap;
		}
		} else if (ipv6_ap && ipv6_supported) {
		/* There's only one valid address: try to use it */
		return ipv6_ap;
		} else if (ipv4_ap) {
		return ipv4_ap;
		} else {
		/* IPv6-only extend, but IPv6 is not supported. */
		return NULL;
		}
		}

		/* When there is no open channel for an extend cell <b>ec</b>, set up the