Support FILETRANSFER command

Author: chrisdambrosio

lib/jeff/command/file_transfer.ex

@@ -13,17 +13,17 @@ defmodule Jeff.Command.FileTransfer do
 
   @type t :: %__MODULE__{
           type: 1..255,
-          total_size: pos_integer(),
-          offset: pos_integer(),
+          total_size: non_neg_integer(),
+          offset: non_neg_integer(),
           data: binary(),
-          fragment_size: pos_integer()
+          fragment_size: non_neg_integer()
         }
 
   @type param() ::
           {:type, 1..255}
-          | {:total_size, pos_integer()}
-          | {:offset, pos_integer()}
-          | {:fragment_size, pos_integer()}
+          | {:total_size, non_neg_integer()}
+          | {:offset, non_neg_integer()}
+          | {:fragment_size, non_neg_integer()}
           | {:data, binary()}
   @type params() :: t() | [param()]
 
@@ -32,7 +32,7 @@ defmodule Jeff.Command.FileTransfer do
     struct(__MODULE__, params)
   end
 
-  @spec encode(params()) :: <<_::64>>
+  @spec encode(params()) :: binary()
   def encode(params) do
     settings = new(params)