Added health-check method

upstream/helpers.go

@@ -0,0 +1,23 @@
+package upstream
+
+import "github.com/miekg/dns"
+
+// Performs a simple health-check of the specified upstream
+func IsAlive(u Upstream) (bool, error) {
+
+	// Using ipv4only.arpa. domain as it is a part of DNS64 RFC and it should exist everywhere
+	ping := new(dns.Msg)
+	ping.SetQuestion("ipv4only.arpa.", dns.TypeA)
+
+	resp, err := u.Exchange(nil, ping)
+
+	// If we got a header, we're alright, basically only care about I/O errors 'n stuff.
+	if err != nil && resp != nil {
+		// Silly check, something sane came back.
+		if resp.Response || resp.Opcode == dns.OpcodeQuery {
+			err = nil
+		}
+	}
+
+	return err == nil, err
+}

upstream/https_upstream.go

@@ -10,16 +10,17 @@ import (
 	"golang.org/x/net/http2"
 	"io/ioutil"
 	"log"
+	"net"
 	"net/http"
 	"net/url"
+	"time"
 )
 
 const (
 	dnsMessageContentType = "application/dns-message"
+	defaultKeepAlive      = 30 * time.Second
 )
 
-// TODO: Add bootstrap DNS resolver field
-
 // HttpsUpstream is the upstream implementation for DNS-over-HTTPS
 type HttpsUpstream struct {
 	client   *http.Client
@@ -27,18 +28,39 @@ type HttpsUpstream struct {
 }
 
 // NewHttpsUpstream creates a new DNS-over-HTTPS upstream from hostname
-func NewHttpsUpstream(endpoint string) (Upstream, error) {
+func NewHttpsUpstream(endpoint string, bootstrap string) (Upstream, error) {
 	u, err := url.Parse(endpoint)
 	if err != nil {
 		return nil, err
 	}
 
+	// Initialize bootstrap resolver
+	bootstrapResolver := net.DefaultResolver
+	if bootstrap != "" {
+		bootstrapResolver = &net.Resolver{
+			PreferGo: true,
+			Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
+				var d net.Dialer
+				conn, err := d.DialContext(ctx, network, bootstrap)
+				return conn, err
+			},
+		}
+	}
+
+	dialer := &net.Dialer{
+		Timeout:   defaultTimeout,
+		KeepAlive: defaultKeepAlive,
+		DualStack: true,
+		Resolver:  bootstrapResolver,
+	}
+
 	// Update TLS and HTTP client configuration
 	tlsConfig := &tls.Config{ServerName: u.Hostname()}
 	transport := &http.Transport{
 		TLSClientConfig:    tlsConfig,
 		DisableCompression: true,
 		MaxIdleConns:       1,
+		DialContext:        dialer.DialContext,
 	}
 	http2.ConfigureTransport(transport)
 

upstream/upstream.go

@@ -42,8 +42,8 @@ func (p *UpstreamPlugin) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *
 	var reply *dns.Msg
 	var backendErr error
 
-	// TODO: Change the way we call upstreams
+	for i := range p.Upstreams {
-	for _, upstream := range p.Upstreams {
+		upstream := p.Upstreams[i]
 		reply, backendErr = upstream.Exchange(ctx, r)
 		if backendErr == nil {
 			w.WriteMsg(reply)

upstream/upstream_test.go

@@ -6,27 +6,107 @@ import (
 	"testing"
 )
 
+func TestDnsUpstreamIsAlive(t *testing.T) {
+
+	var tests = []struct {
+		endpoint string
+		proto    string
+	}{
+		{"8.8.8.8:53", "udp"},
+		{"8.8.8.8:53", "tcp"},
+		{"1.1.1.1:53", "udp"},
+	}
+
+	for _, test := range tests {
+		u, err := NewDnsUpstream(test.endpoint, test.proto, "")
+
+		if err != nil {
+			t.Errorf("cannot create a DNS upstream")
+		}
+
+		testUpstreamIsAlive(t, u)
+	}
+}
+
+func TestHttpsUpstreamIsAlive(t *testing.T) {
+
+	var tests = []struct {
+		url       string
+		bootstrap string
+	}{
+		{"https://cloudflare-dns.com/dns-query", "8.8.8.8:53"},
+		{"https://dns.google.com/experimental", "8.8.8.8:53"},
+		{"https://doh.cleanbrowsing.org/doh/security-filter/", ""}, // TODO: status 201??
+	}
+
+	for _, test := range tests {
+		u, err := NewHttpsUpstream(test.url, test.bootstrap)
+
+		if err != nil {
+			t.Errorf("cannot create a DNS-over-HTTPS upstream")
+		}
+
+		testUpstreamIsAlive(t, u)
+	}
+}
+
+func TestDnsOverTlsIsAlive(t *testing.T) {
+
+	var tests = []struct {
+		endpoint      string
+		tlsServerName string
+	}{
+		{"1.1.1.1:853", ""},
+		{"9.9.9.9:853", ""},
+		{"185.228.168.10:853", "security-filter-dns.cleanbrowsing.org"},
+	}
+
+	for _, test := range tests {
+		u, err := NewDnsUpstream(test.endpoint, "tcp-tls", test.tlsServerName)
+
+		if err != nil {
+			t.Errorf("cannot create a DNS-over-TLS upstream")
+		}
+
+		testUpstreamIsAlive(t, u)
+	}
+}
+
 func TestDnsUpstream(t *testing.T) {
 
-	u, err := NewDnsUpstream("8.8.8.8:53", "udp", "")
+	var tests = []struct {
+		endpoint string
+		proto    string
+	}{
+		{"8.8.8.8:53", "udp"},
+		{"8.8.8.8:53", "tcp"},
+		{"1.1.1.1:53", "udp"},
+	}
+
+	for _, test := range tests {
+		u, err := NewDnsUpstream(test.endpoint, test.proto, "")
 
 		if err != nil {
 			t.Errorf("cannot create a DNS upstream")
 		}
 
 		testUpstream(t, u)
+	}
 }
 
 func TestHttpsUpstream(t *testing.T) {
 
-	testCases := []string{
+	var tests = []struct {
-		"https://cloudflare-dns.com/dns-query",
+		url       string
-		"https://dns.google.com/experimental",
+		bootstrap string
-		"https://doh.cleanbrowsing.org/doh/security-filter/",
+	}{
+		{"https://cloudflare-dns.com/dns-query", "8.8.8.8:53"},
+		{"https://dns.google.com/experimental", "8.8.8.8:53"},
+		{"https://doh.cleanbrowsing.org/doh/security-filter/", ""},
 	}
 
-	for _, url := range testCases {
+	for _, test := range tests {
-		u, err := NewHttpsUpstream(url)
+		u, err := NewHttpsUpstream(test.url, test.bootstrap)
 
 		if err != nil {
 			t.Errorf("cannot create a DNS-over-HTTPS upstream")
@@ -58,6 +138,15 @@ func TestDnsOverTlsUpstream(t *testing.T) {
 	}
 }
 
+func testUpstreamIsAlive(t *testing.T, u Upstream) {
+	alive, err := IsAlive(u)
+	if !alive || err != nil {
+		t.Errorf("Upstream is not alive")
+	}
+
+	u.Close()
+}
+
 func testUpstream(t *testing.T, u Upstream) {
 
 	var tests = []struct {