do proper testing

setup.go

@@ -6,12 +6,16 @@ import (
 	"github.com/coredns/coredns/core/dnsserver"
 	"github.com/coredns/coredns/plugin"
 	"net"
+	"strconv"
+	"strings"
 )
 
 // syntheticConfig holds the configuration options for the synthetic plugin.
 type syntheticConfig struct {
 	net     []*net.IPNet
 	forward string
+	ttl     uint32
+	prefix  string
 }
 
 // init registers this plugin.
@@ -45,12 +49,40 @@ func setup(c *caddy.Controller) error {
 					config.forward = arg
 				}
 
+			// Configuration for the TTL value
+			case "ttl":
+				args := c.RemainingArgs()
+				for _, arg := range args {
+					ttl64, err := strconv.ParseUint(arg, 10, 32)
+					if err != nil {
+						return fmt.Errorf("synthetic: invalid ttl value: %v", arg)
+					}
+					config.ttl = uint32(ttl64)
+				}
+
+				// configuration for the prefix value (defaults to `ip`)
+			case "prefix":
+				args := c.RemainingArgs()
+				for _, arg := range args {
+					config.prefix = arg
+				}
+
 			default:
 				return c.Errf("unknown property '%s'", v)
 			}
 		}
 	}
 
+	if config.forward == "" {
+		return c.Err("synthetic: forward zone must be specified")
+	}
+	if config.prefix == "" {
+		config.prefix = "ip"
+	}
+	if !strings.HasSuffix(config.prefix, "-") {
+		config.prefix = config.prefix + "-"
+	}
+
 	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
 		return synthetic{Next: next, Config: config}
 	})