From 59a1b849f002544ce932894016d5b2e8cc2fe43a Mon Sep 17 00:00:00 2001
From: Aaron Bieber <aaron@bolddaemon.com>
Date: Fri, 14 Jan 2022 16:30:20 -0700
Subject: [PATCH] net/dns/resolvd: store nameservers

Currently only search domains are stored. This was an oversight
(under?) on my part.

As things are now, when MagicDNS is on and "Override local DNS" is
off, the dns forwarder has to timeout before names resolve. This
introduces a pretty annoying lang that makes everything feel
extremely slow. You will also see an error: "upstream nameservers
not set".

I tested with "Override local DNS" on and off. In both situations
things seem to function as expected (and quickly).

Signed-off-by: Aaron Bieber <aaron@bolddaemon.com>
(cherry picked from commit 411c6c316cf617046b4002a69dd404f4938d061d)
---
 net/dns/resolvd.go | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/net/dns/resolvd.go b/net/dns/resolvd.go
index 42b09ee5a..5ccde75ec 100644
--- a/net/dns/resolvd.go
+++ b/net/dns/resolvd.go
@@ -16,6 +16,7 @@ import (
 	"regexp"
 	"strings"
 
+	"inet.af/netaddr"
 	"tailscale.com/types/logger"
 	"tailscale.com/util/dnsname"
 )
@@ -130,6 +131,25 @@ func (m resolvdManager) readResolvConf() (config OSConfig, err error) {
 			config.SearchDomains = append(config.SearchDomains, fqdn)
 			continue
 		}
+
+		if strings.HasPrefix(line, "nameserver") {
+			s := strings.TrimPrefix(line, "nameserver")
+			parts := strings.Split(s, " # ")
+			if len(parts) == 0 {
+				return OSConfig{}, err
+			}
+			nameserver := strings.TrimSpace(parts[0])
+			ip, err := netaddr.ParseIP(nameserver)
+			if err != nil {
+				return OSConfig{}, err
+			}
+			config.Nameservers = append(config.Nameservers, ip)
+			continue
+		}
+	}
+
+	if err = scanner.Err(); err != nil {
+		return OSConfig{}, err
 	}
 
 	return config, nil