app/config/config.go: adding decodeShorhandShipConfig() for mapstructure decoding.

app/config/config.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"reflect"
 	"time"
 
 	"github.com/eosswedenorg/thalos/app/log"
@@ -51,15 +52,34 @@ func New() Config {
 			MaxFileSize: 10 * 1000 * 1000, // 10 mb
 			MaxTime:     time.Hour * 24,
 		},
-		Ship: ShipConfig{
+		Ship: defaultShipConfig(""),
-			StartBlockNum:       shipclient.NULL_BLOCK_NUMBER,
-			EndBlockNum:         shipclient.NULL_BLOCK_NUMBER,
-			MaxMessagesInFlight: 10,
-			IrreversibleOnly:    false,
-		},
 		Redis: RedisConfig{
 			Addr:   "localhost:6379",
 			Prefix: "ship",
 		},
 	}
 }
+
+func defaultShipConfig(url string) ShipConfig {
+	return ShipConfig{
+		Url:                 url,
+		StartBlockNum:       shipclient.NULL_BLOCK_NUMBER,
+		EndBlockNum:         shipclient.NULL_BLOCK_NUMBER,
+		MaxMessagesInFlight: 10,
+		IrreversibleOnly:    false,
+	}
+}
+
+// mapstructure DecodeHook that can parse a shorthand ship config (only string instead of struct.)
+func decodeShorthandShipConfig(from reflect.Value, to reflect.Value) (interface{}, error) {
+	shipType := reflect.TypeOf(ShipConfig{})
+
+	// If to is a struct and is assignable to a ShipConfig and from is a string.
+	// Then we treat the from value as ShipConfig.Url
+	if to.Kind() == reflect.Struct && to.Type().AssignableTo(shipType) && from.Kind() == reflect.String {
+		return defaultShipConfig(from.String()), nil
+	}
+
+	// If not, decode as normal.
+	return from.Interface(), nil
+}