update resolver config parsing, add eth. resolver by default

core/node/dns.go

@@ -7,21 +7,48 @@ import (
 	config "github.com/ipfs/go-ipfs-config"
 	doh "github.com/libp2p/go-doh-resolver"
 	madns "github.com/multiformats/go-multiaddr-dns"
+
+	"github.com/miekg/dns"
 )
 
+const ethResolverURL = "https://eth.link/dns-query"
+
+func newResolver(url string) (madns.BasicResolver, error) {
+	if !strings.HasPrefix(url, "https://") {
+		return nil, fmt.Errorf("invalid resolver url: %s", url)
+	}
+
+	return doh.NewResolver(url), nil
+}
+
 func DNSResolver(cfg *config.Config) (*madns.Resolver, error) {
 	var opts []madns.Option
-	if url := cfg.DNS.DefaultResolver; url != "" {
-		if !strings.HasPrefix(url, "https://") {
-			return nil, fmt.Errorf("invalid default resolver url: %s", url)
+
+	hasEth := false
+	for domain, url := range cfg.DNS.Resolvers {
+		if !dns.IsFqdn(domain) {
+			return nil, fmt.Errorf("invalid domain %s; must be FQDN", domain)
 		}
-		opts = append(opts, madns.WithDefaultResolver(doh.NewResolver(url)))
-	}
-	for domain, url := range cfg.DNS.CustomResolvers {
-		if !strings.HasPrefix(url, "https://") {
-			return nil, fmt.Errorf("invalid domain resolver url for %s: %s", domain, url)
+
+		rslv, err := newResolver(url)
+		if err != nil {
+			return nil, fmt.Errorf("bad resolver for %s: %w", domain, err)
+		}
+
+		if domain != "." {
+			opts = append(opts, madns.WithDomainResolver(domain, rslv))
+		} else {
+			opts = append(opts, madns.WithDefaultResolver(rslv))
+		}
+
+		if domain == "eth." {
+			hasEth = true
 		}
-		opts = append(opts, madns.WithDomainResolver(domain, doh.NewResolver(url)))
 	}
+
+	if !hasEth {
+		opts = append(opts, madns.WithDomainResolver("eth.", doh.NewResolver(ethResolverURL)))
+	}
+
 	return madns.NewResolver(opts...)
 }