add plain dns support

per multiformats/multiaddr#22 (comment)

dns.go

@@ -9,11 +9,19 @@ import (
 
 // Extracted from source of truth for multicodec codes: https://github.com/multiformats/multicodec
 const (
+	P_DNS     = 0x0035
 	P_DNS4    = 0x0036
 	P_DNS6    = 0x0037
 	P_DNSADDR = 0x0038
 )
 
+var DnsProtocol = ma.Protocol{
+	Code:       P_DNS,
+	Size:       ma.LengthPrefixedVarSize,
+	Name:       "dns",
+	VCode:      ma.CodeToVarint(P_DNS),
+	Transcoder: DnsTranscoder,
+}
 var Dns4Protocol = ma.Protocol{
 	Code:       P_DNS4,
 	Size:       ma.LengthPrefixedVarSize,
@@ -37,6 +45,10 @@ var DnsaddrProtocol = ma.Protocol{
 }
 
 func init() {
+	err := ma.AddProtocol(DnsProtocol)
+	if err != nil {
+		panic(fmt.Errorf("error registering dns protocol: %s", err))
+	}
 	err := ma.AddProtocol(Dns4Protocol)
 	if err != nil {
 		panic(fmt.Errorf("error registering dns4 protocol: %s", err))

resolve.go

@@ -8,7 +8,7 @@ import (
 	ma "github.com/multiformats/go-multiaddr"
 )
 
-var ResolvableProtocols = []ma.Protocol{DnsaddrProtocol, Dns4Protocol, Dns6Protocol}
+var ResolvableProtocols = []ma.Protocol{DnsaddrProtocol, Dns4Protocol, Dns6Protocol, DnsProtocol}
 var DefaultResolver = &Resolver{Backend: net.DefaultResolver}
 
 const dnsaddrTXTPrefix = "dnsaddr="
@@ -97,8 +97,9 @@ func (r *Resolver) Resolve(ctx context.Context, maddr ma.Multiaddr) ([]ma.Multia
 
 		var resolved []ma.Multiaddr
 		switch proto.Code {
-		case Dns4Protocol.Code, Dns6Protocol.Code:
-			v4 := proto.Code == Dns4Protocol.Code
+		case Dns4Protocol.Code, Dns6Protocol.Code, DnsProtocol.Code:
+			v4only := proto.Code == Dns4Protocol.Code
+			v6only := proto.Code == Dns6Protocol.Code
 
 			// XXX: Unfortunately, go does a pretty terrible job of
 			// differentiating between IPv6 and IPv4. A v4-in-v6
@@ -115,16 +116,16 @@ func (r *Resolver) Resolve(ctx context.Context, maddr ma.Multiaddr) ([]ma.Multia
 					err    error
 				)
 				ip4 := r.IP.To4()
-				if v4 {
-					if ip4 == nil {
+				if ip4 == nil {
+					if v4only {
 						continue
 					}
-					rmaddr, err = ma.NewMultiaddr("/ip4/" + ip4.String())
+					rmaddr, err = ma.NewMultiaddr("/ip6/" + r.IP.String())
 				} else {
-					if ip4 != nil {
+					if v6only {
 						continue
 					}
-					rmaddr, err = ma.NewMultiaddr("/ip6/" + r.IP.String())
+					rmaddr, err = ma.NewMultiaddr("/ip4/" + ip4.String())
 				}
 				if err != nil {
 					return nil, err