chore: add a dns.OSConfigurator implementation that uses the CoderVPN protocol

ethanndickson · ethanndickson · commit 279a2dbdf727 · 2024-11-04T04:37:12.000Z
diff --git a/tailnet/conn.go b/tailnet/conn.go
@@ -22,6 +22,7 @@ import (
 	"tailscale.com/envknob"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/net/connstats"
+	"tailscale.com/net/dns"
 	"tailscale.com/net/netmon"
 	"tailscale.com/net/netns"
 	"tailscale.com/net/tsdial"
@@ -106,6 +107,9 @@ type Options struct {
 	ClientType proto.TelemetryEvent_ClientType
 	// TelemetrySink is optional.
 	TelemetrySink TelemetrySink
+	// DNSConfigurator is optional, and is passed to the underlying wireguard
+	// engine.
+	DNSConfigurator dns.OSConfigurator
 }
 
 // TelemetrySink allows tailnet.Conn to send network telemetry to the Coder
@@ -178,6 +182,7 @@ func NewConn(options *Options) (conn *Conn, err error) {
 		Dialer:       dialer,
 		ListenPort:   options.ListenPort,
 		SetSubsystem: sys.Set,
+		DNS:          options.DNSConfigurator,
 	})
 	if err != nil {
 		return nil, xerrors.Errorf("create wgengine: %w", err)
diff --git a/vpn/dns.go b/vpn/dns.go
@@ -0,0 +1,55 @@
+package vpn
+
+import "tailscale.com/net/dns"
+
+func NewVPNManager(t *Tunnel) dns.OSConfigurator {
+	return &vpnDNSManager{tunnel: t}
+}
+
+type vpnDNSManager struct {
+	tunnel *Tunnel
+}
+
+func (v *vpnDNSManager) SetDNS(cfg dns.OSConfig) error {
+	servers := make([]string, 0, len(cfg.Nameservers))
+	for _, ns := range cfg.Nameservers {
+		servers = append(servers, ns.String())
+	}
+	searchDomains := make([]string, 0, len(cfg.SearchDomains))
+	for _, domain := range cfg.SearchDomains {
+		searchDomains = append(searchDomains, domain.WithoutTrailingDot())
+	}
+	matchDomains := make([]string, 0, len(cfg.MatchDomains))
+	for _, domain := range cfg.MatchDomains {
+		matchDomains = append(matchDomains, domain.WithoutTrailingDot())
+	}
+	return v.tunnel.ApplyNetworkSettings(v.tunnel.ctx, &NetworkSettingsRequest{
+		DnsSettings: &NetworkSettingsRequest_DNSSettings{
+			Servers:              servers,
+			SearchDomains:        searchDomains,
+			DomainName:           "coder",
+			MatchDomains:         matchDomains,
+			MatchDomainsNoSearch: false,
+		},
+	})
+}
+
+func (vpnDNSManager) GetBaseConfig() (dns.OSConfig, error) {
+	// Tailscale calls this function to blend the OS's DNS configuration with
+	// it's own, so this is only called if `SupportsSplitDNS` returns false.
+	return dns.OSConfig{}, dns.ErrGetBaseConfigNotSupported
+}
+
+func (*vpnDNSManager) SupportsSplitDNS() bool {
+	// macOS & Windows 10+ support split DNS, so we'll assume all CoderVPN
+	// clients do too.
+	return true
+}
+
+// Close implements dns.OSConfigurator.
+func (*vpnDNSManager) Close() error {
+	// There's no cleanup that we need to initiate from within the dylib.
+	return nil
+}
+
+var _ dns.OSConfigurator = (*vpnDNSManager)(nil)
