feat: add client to allow passing custom resolver

dnsclient.go

@@ -11,16 +11,27 @@ import (
 
 const hexDigit = "0123456789abcdef"
 
+var DefaultClient *Client = &Client{resolver: net.DefaultResolver}
+
+type Client struct {
+	resolver *net.Resolver
+}
+
+func NewClient(resolver *net.Resolver) *Client {
+	return &Client{
+		resolver: resolver,
+	}
+}
+
 // LookupIP looks up a single IP with the API.
 // The service recommends that bulk lookups use the BulkClient out of respect
 // for their server load.
-func LookupIP(ctx context.Context, ip net.IP) (*Response, error) {
-	var r net.Resolver
+func (c *Client) LookupIP(ctx context.Context, ip net.IP) (*Response, error) {
 	lookupName, err := formatDNSLookupName(ip)
 	if err != nil {
 		return nil, err
 	}
-	txts, err := r.LookupTXT(ctx, lookupName)
+	txts, err := c.resolver.LookupTXT(ctx, lookupName)
 	if err != nil {
 		return nil, err
 	}
@@ -71,9 +82,8 @@ func LookupIP(ctx context.Context, ip net.IP) (*Response, error) {
 	return nil, fmt.Errorf("no records found")
 }
 
-func LookupASN(ctx context.Context, asn ASN) (*Response, error) {
-	var r net.Resolver
-	txts, err := r.LookupTXT(ctx, asn.String()+".asn.cymru.com")
+func (c *Client) LookupASN(ctx context.Context, asn ASN) (*Response, error) {
+	txts, err := c.resolver.LookupTXT(ctx, asn.String()+".asn.cymru.com")
 	if err != nil {
 		return nil, err
 	}
@@ -108,6 +118,17 @@ func LookupASN(ctx context.Context, asn ASN) (*Response, error) {
 	return nil, fmt.Errorf("no records found")
 }
 
+// LookupIP looks up a single IP with the API.
+// The service recommends that bulk lookups use the BulkClient out of respect
+// for their server load.
+func LookupIP(ctx context.Context, ip net.IP) (*Response, error) {
+	return DefaultClient.LookupIP(ctx, ip)
+}
+
+func LookupASN(ctx context.Context, asn ASN) (*Response, error) {
+	return DefaultClient.LookupASN(ctx, asn)
+}
+
 func formatDNSLookupName(ip net.IP) (string, error) {
 	switch {
 	case len(ip) == net.IPv4len || ip.To4() != nil: