PngImageView - Converting An Image To Base64 And Vice Versa For Display In An Image Using LGI (Lua + Gtk)

main_window.ui

<?xml version="1.0" encoding="UTF-8"?>
<!-- Generated with glade 3.22.1 -->
<interface>
  <requires lib="gtk+" version="3.20"/>
  <object class="GtkFileFilter" id="filter_png">
    <mime-types>
      <mime-type>image/png</mime-type>
    </mime-types>
  </object>
  <object class="GtkWindow" id="window">
    <property name="can_focus">False</property>
    <property name="resizable">False</property>
    <property name="window_position">center</property>
    <property name="default_width">400</property>
    <property name="default_height">600</property>
    <child type="titlebar">
      <object class="GtkHeaderBar">
        <property name="visible">True</property>
        <property name="can_focus">False</property>
        <property name="title" translatable="yes">TITULO</property>
        <property name="subtitle" translatable="yes">SUBTITULO</property>
      </object>
    </child>
    <child>
      <object class="GtkBox">
        <property name="visible">True</property>
        <property name="can_focus">False</property>
        <property name="orientation">vertical</property>
        <property name="spacing">2</property>
        <child>
          <object class="GtkFileChooserButton" id="input_file">
            <property name="visible">True</property>
            <property name="can_focus">False</property>
            <property name="margin_left">2</property>
            <property name="margin_right">2</property>
            <property name="margin_top">2</property>
            <property name="margin_bottom">2</property>
            <property name="title" translatable="yes"/>
          </object>
          <packing>
            <property name="expand">False</property>
            <property name="fill">True</property>
            <property name="position">0</property>
          </packing>
        </child>
        <child>
          <object class="GtkImage" id="img">
            <property name="visible">True</property>
            <property name="can_focus">False</property>
            <property name="margin_left">2</property>
            <property name="margin_right">2</property>
            <property name="margin_top">2</property>
            <property name="margin_bottom">2</property>
            <property name="stock">gtk-missing-image</property>
          </object>
          <packing>
            <property name="expand">True</property>
            <property name="fill">True</property>
            <property name="position">1</property>
          </packing>
        </child>
      </object>
    </child>
  </object>
</interface>

PngImageView.lua

#!/usr/bin/lua5.1
--[[--
 @package
 @filename  PngImageView.lua
 @version   1.0
 @author    Díaz Urbaneja Víctor Eduardo Diex <victor.vector008@gmail.com>
 @date      22.05.2020 17:20:01 -04
]]

local base64 = require('base64') -- github.com/iskolbin/lbase64
local lgi = require('lgi')
local Gtk = lgi.require('Gtk', '3.0')
local Gio = lgi.Gio
local GdkPixbuf = lgi.GdkPixbuf

local assert = lgi.assert
local builder = Gtk.Builder()

assert(builder:add_from_file('main_window.ui'), "Error loading the file")

local ui = builder.objects

ui.input_file:add_filter(ui.filter_png)
function ui.input_file:on_selection_changed()
	--------------------------------------------------------------------------------
	local dir_img = ui.input_file:get_filename()
	local file = io.open(dir_img, 'rb')
	local image_file = file:read('*a')
	local image_encode = base64.encode(image_file)

	local image_decode = base64.decode(image_encode)
	--------------------------------------------------------------------------------

	local stream = Gio.MemoryInputStream.new_from_data(image_decode)
	local image = GdkPixbuf.Pixbuf.new_from_stream(stream)
	image = image:scale_simple(320, 320, 'BILINEAR')
	ui.img:set_from_pixbuf(image)
end

function ui.window:on_destroy()
	Gtk.main_quit()
end

ui.window:show_all()
Gtk.main()