Tailing websocket server for Python using websockets module

tailserver.py

# OSI License ID: Apache-2.0
#
#   Copyright 2020 Marek Baczyński
#
#   Licensed under the Apache License, Version 2.0 (the "License");
#   you may not use this file except in compliance with the License.
#   You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
#   Unless required by applicable law or agreed to in writing, software
#   distributed under the License is distributed on an "AS IS" BASIS,
#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#   See the License for the specific language governing permissions and
#   limitations under the License.

import asyncio
import json
import logging
import os
import time

from collections import deque

import websockets

log = logging.getLogger(__name__)


async def tailserver(websocket, path):
    this_module_dir = os.path.dirname(os.path.abspath(os.getcwd()))
    async for message in websocket:
        t0 = time.perf_counter()
        try:
            path = "." + path
            path_dir = os.path.abspath(os.path.dirname(path))
            if not path_dir.startswith(this_module_dir):
                await websocket.send(f'ERROR: not a file: {path}')
                continue
            if not os.path.isfile(path):
                await websocket.send(f'ERROR: not a file: {path}')
                continue
            try:
                lines_to_get = int(message)
            except ValueError:
                await websocket.send('ERROR: not an int')
                continue
            with open(path) as f:
                buf = deque(f, maxlen=lines_to_get)
            resp = ''.join(buf)
            await websocket.send(resp)
            t1 = time.perf_counter()
            client_addr, client_port = websocket.remote_address[:2]
            log.info('%s:"%s" %.5fs %s %s:%s', lines_to_get, path, t1 - t0, len(resp), client_addr, client_port)
        except Exception as e:
            log.exception('Exception when serving request for %s %s', lines_to_get, path)
            await websocket.send(f'ERROR: internal error: {e}')


def main():
    logging.basicConfig(level=logging.INFO)
    logger = logging.getLogger('websockets.server')
    logger.setLevel(logging.INFO)
    logger.addHandler(logging.StreamHandler())
    asyncio.get_event_loop().run_until_complete(
        websockets.serve(tailserver, 'localhost', 8765))
    asyncio.get_event_loop().run_forever()


if __name__ == '__main__':
    main()