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Cannot read properties of null (reading 'on')

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
38/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
express, javascript, nodejs
Domain
backend

Research direction

Reproduce the failure by sending a second POST to /print in server.js, then inspect escpos-network/index.js at Network.open line 30 and the call from server.js line 37. Trace the network socket lifecycle through device.open and the printer close call; done means successive print requests no longer throw the null .on error.

Written by the indexing model from the issue text.

Description

Hi, I have a problem, when I start the server with this code

`'use strict';
const path = require('path')
const escpos = require('escpos')
escpos.Network = require('escpos-network');

const device = new escpos.Network('192.168.1.200', 9100);
const options = { encoding: "GB18030" }
const printer = new escpos.Printer(device)






var bodyParser = require('body-parser')
var app = require('express')()
var http = require('http').Server(app)
var cors = require('cors')
app.use(cors())
app.use(bodyParser.json())

const port = 4000;

app.post('/print', (req, res) => {
  res.json(
    { status: 'success' }
  )
  console.log(req.body)
  print(req.body.text)
});

http.listen(port, () => {
  console.log(`Printer: http://localhost:${port}`);
});

const print = (text) => {
  device.open(function () {
    printer
      .font('a')
      .align('ct')
      .style('bu')
      .size(3, 3)
      .text(text)
      .cut()
      .close();
  });
}
`

I can only do one print after which if I try to do another print I have this problem

TypeError: Cannot read properties of null (reading 'on') at Network.open (C:\Users\matti\Downloads\node-escpos-3\examples\web\node_modules\escpos-network\index.js:30:15) at print (C:\Users\matti\Downloads\node-escpos-3\examples\web\server.js:37:10) at C:\Users\matti\Downloads\node-escpos-3\examples\web\server.js:29:3 at Layer.handle [as handle_request] (C:\Users\matti\Downloads\node-escpos-3\examples\web\node_modules\express\lib\router\layer.js:95:5) at next (C:\Users\matti\Downloads\node-escpos-3\examples\web\node_modules\express\lib\router\route.js:144:13) at Route.dispatch (C:\Users\matti\Downloads\node-escpos-3\examples\web\node_modules\express\lib\router\route.js:114:3) at Layer.handle [as handle_request] (C:\Users\matti\Downloads\node-escpos-3\examples\web\node_modules\express\lib\router\layer.js:95:5) at C:\Users\matti\Downloads\node-escpos-3\examples\web\node_modules\express\lib\router\index.js:286:22 at Function.process_params (C:\Users\matti\Downloads\node-escpos-3\examples\web\node_modules\express\lib\router\index.js:348:12) at next (C:\Users\matti\Downloads\node-escpos-3\examples\web\node_modules\express\lib\router\index.js:280:10)

Please could you help me solve this problem, I can't seem to figure it out!

Dominant language
TypeScript
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