Add context middleware (with example of usage)

examples/example_context_middleware.py

@@ -0,0 +1,47 @@
+from aiogram import Bot, types
+from aiogram.contrib.middlewares.context import ContextMiddleware
+from aiogram.dispatcher import Dispatcher
+from aiogram.types import ParseMode
+from aiogram.utils import markdown as md
+from aiogram.utils.executor import start_polling
+
+API_TOKEN = 'BOT TOKEN HERE'
+
+bot = Bot(token=API_TOKEN)
+dp = Dispatcher(bot)
+
+# Setup Context middleware
+data: ContextMiddleware = dp.middleware.setup(ContextMiddleware())
+
+
+# Write custom filter
+async def demo_filter(message: types.Message):
+    # Store some data in context
+    command = data['command'] = message.get_command() or ''
+    args = data['args'] = message.get_args() or ''
+    data['has_args'] = bool(args)
+    data['some_random_data'] = 42
+    return command != '/bad_command'
+
+
+@dp.message_handler(demo_filter)
+async def send_welcome(message: types.Message):
+    # Get data from context
+    # All of that available only in current context and from current update object
+    # `data`- pseudo-alias for `ctx.get_update().conf['_context_data']`
+    command = data['command']
+    args = data['args']
+    rand = data['some_random_data']
+    has_args = data['has_args']
+
+    # Send as pre-formatted code block.
+    await message.reply(md.hpre(f"""command: {command}
+args: {['Not available', 'available'][has_args]}: {args}
+some random data: {rand}
+message ID: {message.message_id}
+message: {message.html_text}
+    """), parse_mode=ParseMode.HTML)
+
+
+if __name__ == '__main__':
+    start_polling(dp)