pyserial reading serial port in flask (maybe using gevent)

Question

I\'m building a webserver that would need to read (and keep reading) the serial port of the machine it\'s running on.
The purpose is to be able to read a barcode scanner, an

Answer 1

Answering my own questions

1. It seems that indeed only Firefox supports CORS for SSE for now -> article
2. With help from Janus Troelsen I figured out how to keep the connection open and send several barcodes across the line (see code below)
3. Performance-wise it seems that I can only make one connection, but that might be because I have only one serial port, the subsequent connections can't open the serial port anymore. I think it will work from flask, but something with socketio and gevents will perfom better because it's more suited for the job. There's an interesting article here.

For the code:

import flask
import serial
from time import sleep

app = flask.Flask(__name__)
app.debug = True

def event_barcode():
    messageid = 0
    ser = serial.Serial()
    ser.port = 0
    ser.baudrate = 9600
    ser.bytesize = 8
    ser.parity = serial.PARITY_NONE
    ser.stopbits = serial.STOPBITS_ONE
    ser.timeout = 0
    try:
        ser.open()
    except serial.SerialException, e:
         yield 'event:error\n' + 'data:' + 'Serial port error({0}): {1}\n\n'.format(e.errno, e.strerror)
         messageid = messageid + 1
    str_list = []
    while True:
        sleep(0.01)
        nextchar = ser.read()
        if nextchar:
            str_list.append(nextchar)
        else:
            if len(str_list) > 0:
                yield 'id:' + str(messageid) + '\n' + 'data:' + ''.join(str_list) + '\n\n'
                messageid = messageid + 1
                str_list = []

@app.route('/barcode')
def barcode():
    newresponse = flask.Response(event_barcode(), mimetype="text/event-stream")
    newresponse.headers.add('Access-Control-Allow-Origin', '*')
    newresponse.headers.add('Cache-Control', 'no-cache')
    return newresponse

if __name__ == '__main__':
    app.run(port=8080, threaded=True)

Because I want to support multiple browsers, SSE is not the way to go for me right now. I will look into websockets and try and work from that.