Synchronize among devices

In some cases, we need to synchornize the messages among differrent devices. Each device could not get access to the file system of the other devices. The synchronization needs to be implemented by the web service. We design the LineHostBuffer based on flask and the LineHostMirror based on urllib3.

In the following example, we provide two scripts (client.py and host.py). The host should be launched before the client starts. Then the messages from the client would be catched by the host.

Client

client.py

import requests
import syncstream

address = 'http://localhost:5000/sync-stream'
buffer = syncstream.LineHostMirror(address=address)

with buffer:
    for i in range(3):
        print('Message', f'"{i:02d}".')
    print('Line break\nin middle.', end='')
    print('No line break.', end='')

# The following part could be split to another device.
data = requests.get(address).json()['data']
for mitem in data:
    print(mitem)

Host

host.py

import flask
import syncstream

app = flask.Flask('test')

syncstream.LineHostBuffer(api_route='/sync-stream', maxlen=10).serve(app)

if __name__ == '__main__':
    app.run('localhost', port=5000)

The buffer is defined on the host side. However, users do not need to do anything special with the host. The LineHostBuffer is only used for providng the API to an existing Flask app. In our example, writing and reading the messages are performed in client.py. In the first part, the stdout and stderr of the client is redirected to the remote host. Each time print is called, the message would be sent to the remote side. After all messages sent, we start another request for getting the results from the host. Actually, the reading and the writing operations could be split in two different scripts, even split on two different devices.

caution

Some packages (like pytest) may redirect the stdout and stderr. When working with such packages, LineHostMirror may fail to redirect the messages to the remote side.