Standard Input Hanger for Brython Runner

An implementation of hanger server for Brython Runner.

To receive standard input from the Python code running in a web worker environment with Brython, Brython Runner uses a synchronous XHR to simulate the blocking input() function.

This is how input() works in Brython Runner:

1. When input() is called, Brython Runner instance in the web worker requests to open a data slot in the hanger server. Server reserves a space to store the data and returns a token for that space.
2. The instance in the web worker hands over the token to the browser's main thread.
3. The instance in the web worker then makes a synchronous XHR to read the data from hanger server with the token. Since the data is not available yet, the hanger server holds the connection until it receives the requested data.
4. Meanwhile, Brython Runner instance in the main thread receives the token from the web worker instance. The main thread instance then calls the callback function (options.stdin.readline()) to collect the data from the user.
5. When the main thread instance collected the standard input data from the user, it requests to write the data in the hanger server with the token.
6. Aha! Now the hanger server got the data, so it returns that data for the read request from the Brython Runner instance in the web worker that has been on hold for so long.
7. input() function can now return the data received from the server.

Installation

Set up a virtual environment and install dependencies:

$ python -m venv ./env
$ source ./env/bin/activate
(env) $ pip install -r requirements.txt

Usage

Run server:

(env) $ python app.py

Run server with host and port options:

(env) $ python app.py 0.0.0.0:9095

API

This server application serves a few simple functions.

POST /hanger/open/

The server opens a data slot. Returns a token (a string value with length=16) as a plain text.

POST /hanger/{token}/write/

The server writes data to the requested slot according to the token. Returns the token as a plain text.

POST /hanger/{token}/read/

The server reads data from the requested slot according to the token. Returns the data as a plain text.

When the requested data slot does not exist, the server responds with 404.

When the requested data slot exists but there is no data written in the slot, the server holds the connection and waits until it receives the data for that slot.