[FIXED] Python Flask : Route vs add_url_rule, SSE

Issue

Using add_url_rule fails but @app.route('') works fine.

Hello, I am trying to add SSE (Server Sent Events) to a Python Flask app. Unfortunately the app uses SOMEOBJECT.app.add_url_rule to manage routes, so using the decorators doesn't work for me in this case.

from flask import Flask, Response
import random
import time

app = Flask(__name__)
def eventStream():
    # will send simple SSE style responses
    while True:
        waittt = random.random()
        time.sleep(waittt)
        yield "data: {}\n\n".format(str(waittt))
# This route works fine :)
@app.route("/streamroute")
def stream():
    return Response(eventStream(), mimetype="text/event-stream")

# This route doesn't work :(
app.add_url_rule("/stream", stream)
app.run(debug=True)

OK curl http://localhost:5000/streamroute

KO curl http://localhost:5000/stream

Solution

from flask import Flask, Response                                              
import random                                                                  
import time                                                                    
                                                                               
app = Flask(__name__)                                                          
def eventStream():                                                             
    # will send simple SSE style responses                                     
    while True:                                                                
        waittt = random.random()                                               
        time.sleep(waittt)                                                     
        yield "data: {}\n\n".format(str(waittt))                               
# This route works fine :)                                                     
@app.route('/streamroute')                                                     
def stream():                                                                  
    return Response(eventStream(), mimetype="text/event-stream")               
                                                                               
# This route doesn't work :(                                                   
app.add_url_rule('/stream', 'stream', stream)                                   
app.run(debug=True)    

See the docs below, the correct syntax is:

app.add_url_rule('/stream', 'stream', stream)        

For more: https://flask.palletsprojects.com/en/2.0.x/api/#flask.Flask.add_url_rule

Answered By - wgwz