create custom resolvers from config

core/node/dns.go

@@ -1,11 +1,27 @@
 package node
 
 import (
+	"fmt"
+	"strings"
+
 	config "github.com/ipfs/go-ipfs-config"
+	doh "github.com/libp2p/go-doh-resolver"
 	madns "github.com/multiformats/go-multiaddr-dns"
 )
 
 func DNSResolver(cfg *config.Config) (*madns.Resolver, error) {
-	// TODO custom resolvers from config
-	return madns.DefaultResolver, nil
+	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)
+		}
+		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)
+		}
+		opts = append(opts, madns.WithDomainResolver(domain, doh.NewResolver(url)))
+	}
+	return madns.NewResolver(opts...)
 }