Api exposure callbacks

[BSd3v]

This PR strives to allow callbacks to be exposed by the underlying server as an API by simply passing the callback a api_endpoint. The api will accept a body with the functional arguments provided as kwargs.

[BSd3v]

Here is an example of how to spin up the app and how to perform the api calls:

app.py

import time
import dash
from dash import html, dcc, Input, Output, ctx, callback
from flask import jsonify
import asyncio
import json

app = dash.Dash(__name__, use_async=True)
app.layout = html.Div([
    html.Button("Slow Callback", id="slow-btn"),
    html.Div(id="slow-output"),
    html.Button("Fast Callback", id="fast-btn"),
    html.Div(id="fast-output"),
])

async def get_async_data(n_clicks):
    # Simulate an async data fetch
    await asyncio.sleep(1)
    return f"Data fetched - {n_clicks}"

def get_data(n_clicks):
    # Simulate an async data fetch
    time.sleep(1)
    return f"Data fetched - {n_clicks}"

@app.callback(
    Output("slow-output", "children"),
    Input("slow-btn", "n_clicks"),
    prevent_initial_call=True,
    api_endpoint='/api/slow_callback',  # Example API path for the slow callback
)
def slow_callback(n_clicks):
    start = time.time()
    data = {}
    for i in range(5):
        data[f'step_{i}'] = get_data(n_clicks)
    ret = f"{json.dumps(data)} Time taken: {time.time() - start:.2f} seconds"
    if ctx:
        return ret
    return jsonify(ret)

@app.callback(
    Output("fast-output", "children"),
    Input("fast-btn", "n_clicks"),
    prevent_initial_call=True,
    api_endpoint='/api/fast_callback',  # Example API path for the fast callback
)
async def fast_callback(n_clicks):
    start = time.time()
    coros = [get_async_data(n_clicks) for _ in range(5)]
    results = await asyncio.gather(*coros)
    data = {f'step_{i}_async': result for i, result in enumerate(results)}
    ret = f"{json.dumps(data)} Time taken: {time.time() - start:.2f} seconds"
    if ctx:
        return ret
    return jsonify(ret)

app.setup_apis()

if __name__ == "__main__":
    app.run(debug=True)

api calls

import requests

resp = requests.post('http://127.0.0.1:8050/api/slow_callback',
                     json={"n_clicks": 1},
                    headers={"Content-Type": "application/json"})

print(resp.json())

resp = requests.post('http://127.0.0.1:8050/api/fast_callback',
                     json={"n_clicks": 1},
                    headers={"Content-Type": "application/json"})

print(resp.json())

[T4rk1n]

This look like a nice feature, just need to add a docstring to the new argument and a test.

[BSd3v]

@T4rk1n

Is there another way to setup the apis rather than calling app.setup_apis()

[T4rk1n]

Let's only keep the GLOBAL_API_PATHS and use that for the registering.

[T4rk1n]

Let's only have the global one, having two variables for the same functionality creates issue like #3419 and add complexity.

[T4rk1n]

I think it's missing a call to setup_apis or is it meant to be called by the user?

[BSd3v]

Routes must be registered by the dev before the server is started, therefore it cant go here to automatically setup.