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Example Python + Websockets to emulate tail -f
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| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <meta charset="utf-8"> | |
| <meta http-equiv="X-UA-Compatible" content="IE=edge"> | |
| <title>Tail </title> | |
| <style> | |
| body {font-family: monospace;} | |
| p{ margin: 0;} | |
| ul{padding: 0;} | |
| li{list-style:none; padding: 0; margin: 0;} | |
| </style> | |
| </head> | |
| <body> | |
| <ul id="logger"> | |
| </ul> | |
| <script> | |
| const socket = new WebSocket('ws://localhost:9000'); | |
| var log = document.getElementById('logger') | |
| // Listen for messages | |
| socket.addEventListener('message', function (event) { | |
| var text = document.createTextNode(event.data) | |
| var li = document.createElement("li") | |
| li.appendChild(text) | |
| log.prepend(li) | |
| }); | |
| </script> | |
| </body> | |
| </html> |
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| """ | |
| We need websockets | |
| pip install websockets | |
| Run both servers: | |
| python tail.py webserver /var/log/syslog | |
| python tail.py tailserver /var/log/syslog | |
| Go to http://127.0.0.1:8000 | |
| Test in linux by: | |
| logger "this is a message" | |
| """ | |
| import sys | |
| import asyncio | |
| import websockets | |
| from wsgiref.simple_server import make_server | |
| loop = asyncio.get_event_loop() | |
| options = {} | |
| def line_offsets(file): | |
| """Seeks line offsets from file""" | |
| start_loc = file.tell() | |
| try: | |
| file.seek(0) | |
| # Read in the file once and build a list of line offsets | |
| line_offset = [] | |
| offset = 0 | |
| for line in file: | |
| line_offset.append(offset) | |
| offset += len(line) | |
| return line_offset | |
| finally: | |
| file.seek(start_loc) # Come back to the same spot | |
| async def tail(websocket, path): | |
| with open(options['path'], 'rt') as file: | |
| seek = line_offsets(file)[-20] | |
| sleep = None | |
| while True: | |
| file.seek(seek) | |
| line = file.readline() | |
| where = file.tell() | |
| if line: | |
| if seek != where: | |
| sleep = None | |
| await websocket.send(line.strip()) | |
| else: | |
| sleep = 0.04 | |
| seek = where | |
| if sleep: | |
| await asyncio.sleep(sleep) | |
| def wsgiapplication(environ, start_response): | |
| start_response('200 OK', [('Content-Type', 'text/html')]) | |
| return open('index.html', 'rb') | |
| def main(action): | |
| if action == 'webserver': | |
| with make_server('', 8000, wsgiapplication) as httpd: | |
| print("Serving on port 8000...") | |
| try: | |
| httpd.serve_forever() | |
| except KeyboardInterrupt: | |
| httpd.shutdown() | |
| elif action == 'tailserver': | |
| tail_server = websockets.serve(tail, '', 9000) | |
| loop.run_until_complete(tail_server) | |
| loop.run_forever() | |
| if __name__ == '__main__': | |
| assert len(sys.argv) == 3, "Required at least two arguments, action and log path." | |
| _, action, path = sys.argv | |
| options['path'] = path | |
| main(action) | |
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