npm run dev error System.Net.HttpListenerException

[DropperDEV]

Describe the bug

Steps to Reproduce

Open a Power Apps project using Vite and the Power Platform CLI

Run the following command:

npm run dev

Wait for Vite to start on http://localhost:3000

Observe that pac code run throws a System.Net.HttpListenerException

Power Apps fails to load the local app

Expected behavior

Power Apps should load the local app successfully — as it used to before this issue began.

Actual behavior

The app fails to load, and pac code run terminates with an unrecoverable error (System.Net.HttpListenerException).

Screenshots or Error Messages

> appname@0.0.0 dev
> concurrently "vite" "pac code run"

[0]   VITE v7.1.9  ready in 321 ms
[0]   ➜  Local:   http://localhost:3000/
[0]   ➜  Network: http://<local-ip>:3000/
[1] Connected as <user@domain.com>
[1] power.config.json available at http://localhost:8080/
[1] You can test the app locally using:
      https://apps.powerapps.com/play/e/<environment-id>/a/local?_localAppUrl=http://localhost:3000/&_localConnectionUrl=http://localhost:8080/
[1] The app encountered an unrecoverable error and needs to close.
    Exception Type: System.Net.HttpListenerException
    Session ID: d181f245-fe0d-407d-b733-eb6f9b6e4184
[1] Diagnostic logs can be found at:
    C:\Users\<username>\AppData\Local\Microsoft\PowerAppsCLI\Microsoft.PowerApps.CLI.1.49.4\tools\logs\pac-log.txt
[1] pac code run exited with code 0

Environment information

• Node.js: v22.14.0

• npm: 10.9.2

• Power Platform CLI: 1.49.4 Windows MSI

• Build tool: Vite

Additional context

• The issue started recently; the same setup used to work without issues.

• This is not app-specific — it happens with any Power Apps project I try to run locally using npm run dev.

• Verified that ports 3000 and 8080 are not in use by other processes.

• Tried the following commands with no success:

• pac install latest

• npm rebuild

• npm cache clean --force

• Restarted VS Code and the machine multiple times.

• The issue persists consistently on every run.

[saussam18]

I also have been experiencing this issue internally - ill try and get a script you can run temporarily to fix this, but still trying to figure out what the root cause may be in PAC-CLI

[DropperDEV]

I also have been experiencing this issue internally - ill try and get a script you can run temporarily to fix this, but still trying to figure out what the root cause may be in PAC-CLI

Thanks for the update!
I really appreciate you confirming that the issue is reproducible internally.

I’ve been using Power Apps Code extensively to build a fairly complex app — including custom pagination and several interconnected systems — so this issue has a significant impact on my current development workflow.

Please let me know once the temporary script is available; I’d be happy to test it right away and share detailed feedback or logs.

If it helps with your investigation, I can also provide my pac-log.txt file or any additional diagnostic details.

Thanks again for looking into this and for your support!

[saussam18]

Just as an update, it looks like there was a windows update that broke the package we are using in PAC-CLI: https://windowsforum.com/threads/windows-11-kb5066835-breaks-localhost-http-2-via-http-sys.385044/

I am trying to see if there is another update that fixes this, but will still try and get a simple node script out sometime today in the meantime to unblock

[saussam18]

This worked for us internally from that above article, just need to make sure windows defender had the latest update

Update Microsoft Defender Security Intelligence definitions and reboot.
Why: multiple users reported that installing the latest Defender definition update resolved the issue for them. It’s a low-cost first step and should be tried before more invasive actions. This is not guaranteed to fix every case but is worth attempting. (reddit.com)

[saussam18]

Here is also a quick node script you can run if the CLI is not working

const http = require('http');
const fs = require('fs');
const path = require('path');

const PORT = 8080;
const HOST = 'localhost';
const FILE_NAME = 'power.config.json';
const FILE_PATH = path.join(__dirname, FILE_NAME);

// Create HTTP server
const server = http.createServer((req, res) => {
  if (req.url === `/`) {
    fs.readFile(FILE_PATH, (err, data) => {
      if (err) {
        res.writeHead(404, { 'Content-Type': 'text/plain' });
        return res.end('File not found');
      }
      res.writeHead(200, { 'Content-Type': 'application/json' });
      res.end(data);
    });
  } else {
    res.writeHead(404, { 'Content-Type': 'text/plain' });
    res.end('Not found');
  }
});

server.listen(PORT, HOST, () => {
  console.log(`Server running at http://${HOST}:${PORT}`);
});

Can usually run by saving this code with the power.config.json, naming it server.cjs, and running like node server.cjs, which should spin up the port and allow you to run code apps locally.

[DropperDEV]

This worked for us internally from that above article, just need to make sure windows defender had the latest update

Update Microsoft Defender Security Intelligence definitions and reboot. Why: multiple users reported that installing the latest Defender definition update resolved the issue for them. It’s a low-cost first step and should be tried before more invasive actions. This is not guaranteed to fix every case but is worth attempting. (reddit.com)

This solution worked perfectly. Thank you for your help. I’ll close the issue now.