add binary UUID support to postgres

Check if the value is a byte array of 16 bytes and its type is named "uuid" or "guid", and if so, use postgres `uuid` type.

postgres.go

@@ -5,6 +5,7 @@ import (
 	"database/sql/driver"
 	"fmt"
 	"reflect"
+	"strings"
 	"time"
 
 	"github.com/lib/pq/hstore"
@@ -52,13 +53,31 @@ func (postgres) SqlTag(value reflect.Value, size int, autoIncrease bool) string
 			return "hstore"
 		}
 	default:
-		if _, ok := value.Interface().([]byte); ok {
+		if isByteArray(value) {
+			if isUUID(value) {
+				return "uuid"
+			}
 			return "bytea"
 		}
 	}
 	panic(fmt.Sprintf("invalid sql type %s (%s) for postgres", value.Type().Name(), value.Kind().String()))
 }
 
+var byteType = reflect.TypeOf(uint8(0))
+
+func isByteArray(value reflect.Value) bool {
+	return value.Kind() == reflect.Array && value.Type().Elem() == byteType
+}
+
+func isUUID(value reflect.Value) bool {
+	if value.Type().Len() != 16 {
+		return false
+	}
+	typename := value.Type().Name()
+	lower := strings.ToLower(typename)
+	return "uuid" == lower || "guid" == lower
+}
+
 func (s postgres) ReturningStr(tableName, key string) string {
 	return fmt.Sprintf("RETURNING %v.%v", tableName, key)
 }