fix(dns): sigsegv on unreachable

dns.go

@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"crypto/tls"
+	"errors"
 	"net"
 	"sync"
 	"time"
@@ -10,6 +11,10 @@ import (
 	"github.com/fumiama/terasu"
 )
 
+var (
+	ErrNoDNSAvailable = errors.New("no dns available")
+)
+
 var dnsdialer = net.Dialer{
 	Timeout: time.Second * 8,
 }
@@ -51,6 +56,8 @@ func (ds *dnsservers) add(m map[string][]string) {
 }
 
 func (ds *dnsservers) dial(ctx context.Context) (tlsConn *tls.Conn, err error) {
+	err = ErrNoDNSAvailable
+
 	ds.RLock()
 	defer ds.RUnlock()
 

dns_test.go

@@ -6,17 +6,21 @@ import (
 	"fmt"
 	"net"
 	"testing"
+	"time"
 
 	"github.com/fumiama/terasu"
 )
 
 func TestResolver(t *testing.T) {
 	t.Log("canUseIPv6:", canUseIPv6.Get())
-	addrs, err := resolver.LookupHost(context.TODO(), "dns.google")
+	addrs, err := resolver.LookupHost(context.TODO(), "api.mangacopy.com")
 	if err != nil {
 		t.Fatal(err)
 	}
 	t.Log(addrs)
+	if len(addrs) == 0 {
+		t.Fail()
+	}
 }
 
 func TestDNS(t *testing.T) {
@@ -24,6 +28,39 @@ func TestDNS(t *testing.T) {
 		dotv6servers.test()
 	}
 	dotv4servers.test()
+	for i := 0; i < 100; i++ {
+		addrs, err := resolver.LookupHost(context.TODO(), "api.mangacopy.com")
+		if err != nil {
+			t.Fatal(err)
+		}
+		t.Log(addrs)
+		if len(addrs) == 0 {
+			t.Fail()
+		}
+		time.Sleep(time.Millisecond * 50)
+	}
+}
+
+func TestBadDNS(t *testing.T) {
+	if canUseIPv6.Get() {
+		dotv6servers = dnsservers{
+			m: map[string][]*dnsstat{},
+		}
+		dotv6servers.add(map[string][]string{"test.bad.host": {"169.254.122.111"}})
+	} else {
+		dotv4servers = dnsservers{
+			m: map[string][]*dnsstat{},
+		}
+		dotv4servers.add(map[string][]string{"test.bad.host": {"169.254.122.111:853"}})
+	}
+	for i := 0; i < 10; i++ {
+		addrs, err := resolver.LookupHost(context.TODO(), "api.mangacopy.com")
+		t.Log(err)
+		if err == nil && len(addrs) > 0 {
+			t.Fatal("unexpected")
+		}
+		time.Sleep(time.Millisecond * 50)
+	}
 }
 
 func (ds *dnsservers) test() {

http.go

@@ -20,6 +20,10 @@ import (
 	"golang.org/x/net/http2"
 )
 
+var (
+	ErrEmptyHostAddress = errors.New("empty host addr")
+)
+
 var httpdialer = net.Dialer{
 	Timeout: time.Minute,
 }
@@ -56,7 +60,7 @@ var cli = comandyClient(http.Client{
 				lookupTable.Set(host, addrs)
 			}
 			if len(addr) == 0 {
-				return nil, errors.New("empty host addr")
+				return nil, ErrEmptyHostAddress
 			}
 			var tlsConn *tls.Conn
 			for _, a := range addrs {