hare

commit c3610791a32991d46814afa36c19a9c2521424ec
parent f882bb8727c7b012e6aa030eb6165553dae29331
Author: Drew DeVault <sir@cmpwn.com>
Date:   Wed, 23 Jun 2021 16:17:43 -0400

net::dns: send requests to all nameservers at once

Signed-off-by: Drew DeVault <sir@cmpwn.com>

Diffstat:
M
net/dns/query.ha
 | 
36
++++++++++++++++++++++++++----------

1 file changed, 26 insertions(+), 10 deletions(-)
diff --git a/net/dns/query.ha b/net/dns/query.ha
@@ -6,9 +6,13 @@ use unix::resolvconf;
 // free the return value with [[message_free]].
 //
 // If no DNS servers are provided, the system default servers (if any) are used.
-export fn query(query: *message, addr: ip::addr...) (*message | error) = {
-	if (len(addr) == 0) {
-		addr = resolvconf::load();
+export fn query(query: *message, servers: ip::addr...) (*message | error) = {
+	if (len(servers) == 0) {
+		servers = resolvconf::load();
+	};
+	if (len(servers) == 0) {
+		// Fall back to localhost
+		servers = [[127, 0, 0, 1]: ip::addr4];
 	};
 
 	let socket = udp::listen(ip::ANY_V4, 0)?;
@@ -17,8 +21,12 @@ export fn query(query: *message, addr: ip::addr...) (*message | error) = {
 	// TODO: Use TCP for messages >512 bytes
 	let sendbuf: [512]u8 = [0...];
 	let z = encode(sendbuf, query)?;
-	// TODO: Query multiple servers
-	udp::sendto(socket, sendbuf[..z], addr[0], 53)?;
+
+	// We send requests in parallel to all configured servers and take the
+	// first one which sends us a reasonable answer.
+	for (let i = 0z; i < len(servers); i += 1) {
+		udp::sendto(socket, sendbuf[..z], servers[i], 53)?;
+	};
 
 	let header = header { ... };
 	let recvbuf: [512]u8 = [0...];
@@ -26,19 +34,27 @@ export fn query(query: *message, addr: ip::addr...) (*message | error) = {
 		// TODO: Add timeout
 		let src: ip::addr = ip::ANY_V4;
 		z = udp::recvfrom(socket, recvbuf, &src, null)?;
-		if (!ip::equal(src, addr[0])) {
+
+		let expected = false;
+		for (let i = 0z; i < len(servers); i += 1) {
+			if (ip::equal(src, servers[i])) {
+				expected = true;
+				break;
+			};
+		};
+		if (!expected) {
 			continue;
 		};
 
 		let dec = decoder_init(recvbuf[..z]);
 		decode_header(&dec, &header)?;
-		if (header.id != query.header.id || header.op.qr != qr::RESPONSE) {
-			continue;
+		if (header.id == query.header.id && header.op.qr == qr::RESPONSE) {
+			break;
 		};
-
-		break;
 	};
 
+	assert(!header.op.tc, "TODO: Retry with TCP for truncated DNS response");
+
 	check_rcode(header.op.rcode)?;
 	return decode(recvbuf[..z])?;
 };