chore: error handling in params construction (#934)

waku/v2/dnsdisc/enr.go

@@ -2,6 +2,7 @@ package dnsdisc
 
 import (
 	"context"
+	"errors"
 
 	"github.com/ethereum/go-ethereum/p2p/dnsdisc"
 	"github.com/ethereum/go-ethereum/p2p/enode"
@@ -18,18 +19,28 @@ type dnsDiscoveryParameters struct {
 	resolver   dnsdisc.Resolver
 }
 
-type DNSDiscoveryOption func(*dnsDiscoveryParameters)
+type DNSDiscoveryOption func(*dnsDiscoveryParameters) error
+
+var ErrExclusiveOpts = errors.New("cannot set both nameserver and resolver")
 
 // WithNameserver is a DnsDiscoveryOption that configures the nameserver to use
 func WithNameserver(nameserver string) DNSDiscoveryOption {
-	return func(params *dnsDiscoveryParameters) {
+	return func(params *dnsDiscoveryParameters) error {
+		if params.resolver != nil {
+			return ErrExclusiveOpts
+		}
 		params.nameserver = nameserver
+		return nil
 	}
 }
 
 func WithResolver(resolver dnsdisc.Resolver) DNSDiscoveryOption {
-	return func(params *dnsDiscoveryParameters) {
+	return func(params *dnsDiscoveryParameters) error {
+		if params.nameserver != "" {
+			return ErrExclusiveOpts
+		}
 		params.resolver = resolver
+		return nil
 	}
 }
 
@@ -56,7 +67,10 @@ func RetrieveNodes(ctx context.Context, url string, opts ...DNSDiscoveryOption)
 
 	params := new(dnsDiscoveryParameters)
 	for _, opt := range opts {
-		opt(params)
+		err := opt(params)
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	if params.resolver == nil {

waku/v2/dnsdisc/enr_test.go

@@ -63,3 +63,18 @@ func TestRetrieveNodes(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, len(discoveredNodes), 2)
 }
+
+func TestExclusiveOpts(t *testing.T) {
+	var opts []DNSDiscoveryOption
+
+	tree, url := makeTestTree("n", nil, nil)
+	resolver := mapResolver(tree.ToTXT("n"))
+
+	opts = append(opts, WithNameserver("1.1.1.1"), WithResolver(resolver))
+	_, err := RetrieveNodes(context.Background(), url, opts...)
+	require.Equal(t, err, ErrExclusiveOpts)
+
+	opts = append(opts, WithResolver(resolver), WithNameserver("1.1.1.1"))
+	_, err = RetrieveNodes(context.Background(), url, opts...)
+	require.Equal(t, err, ErrExclusiveOpts)
+}