refactor: project structure

internal/filter/filter.go

@@ -0,0 +1,25 @@
+package filter
+
+import (
+	"fmt"
+	"net"
+)
+
+// IP filters a list of resolved IPs and returns the first match
+// for the requested address family (IPv4 or IPv6).
+func IP(ips []net.IP, ipv6 bool) (string, error) {
+	if ipv6 {
+		for _, ip := range ips {
+			if ip.To16() != nil && ip.To4() == nil {
+				return ip.String(), nil
+			}
+		}
+	} else {
+		for _, ip := range ips {
+			if ip.To4() != nil && ip.To16() != nil {
+				return ip.String(), nil
+			}
+		}
+	}
+	return "", fmt.Errorf("no suitable IP address found")
+}