DevProxy interferes with other apps which urls aren't watched

[ThaDaVos]

Description

Currently when I enable DevProxy (as I need it for development) - some other apps, like the New Outlook and Whatsapp Desktop Client - stop functioning, like they don't seem to have internet access anymore until I stop the DevProxy and sometimes have to restart the app first, especially Whatsapp.

Expected behaviour

No interference with other apps which URLs aren't watched

Actual behaviour

Interference with other apps which URLs aren't watched

Steps to reproduce

Below happens instantly after starting the proxy, but sometimes after a little while - it's flakey buy always happens eventually

Outlook (using an Microsoft Exchange Online account, don't know if this is important)

1. Open Outlook
2. Start DevProxy
3. Send yourself an email from your phone - or even from Outlook (won't send)
4. It never shows up in Outlook as it lost internet access - same goes for trying to open an email which you haven't opened yet, or when trying to search

Whatsapp

1. Open Whatsapp
2. Start DevProxy
3. Try to send or download a file - messages seem to go through but not always

Dev Proxy Version

0.28.0

Operating system (environment)

Windows

Shell

PowerShell

Configuration file

{
	"$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v0.28.0/rc.schema.json",
	"plugins": [
		{
			"name": "DevToolsPlugin",
			"enabled": true,
			"pluginPath": "~appFolder/plugins/dev-proxy-plugins.dll"
		}
	],
	"urlsToWatch": [
		"https://b2bapi.snelstart.nl/*",
		"https://auth.snelstart.nl/*"
	],
	"logLevel": "information",
	"newVersionNotification": "stable",
	"showSkipMessages": true
}

Additional Info

No response

[waldekmastykarz]

Thanks for reporting the issue and sorry for the trouble @ThaDaVos. Have you by any chance seen a similar issue with other proxies such as Fiddler? I wonder if what you're seeing could be caused by certificate pinning or something similar. Even though Dev Proxy is not decrypting these URLs, it's still present in the request pipeline.

As a possible workaround you could consider:

1. If you know URLs used by other apps, exclude them from going through a proxy altogether. You can do this from Settings > Network & Internet > Proxy > Use the proxy server except for addresses that start with the following entries.
2. Don't register Dev Proxy as a system proxy (--as-system-proxy false in command line or "asSystemProxy": false in devproxyrc.json) and explicitly send your application traffic to Dev Proxy (eg. by setting the https_proxy env var for your application)

I hope this helps.

[ThaDaVos]

Just checked with Whatsapp - and using the watchProcessNames doesn't solve the issue sadly

[waldekmastykarz]

Watching specific processes is only a filter for processing: after a request reached Dev Proxy, we decide if Dev Proxy should pass it on to its plugins or not, but by then it's already too late for the app, so we would really need to look for another approach.

It's the first time I'm hearing about Clarion, but based on what I was able to find out, it seems like it doesn't automatically pick up system proxy settings and requires them to be configured in the application. Is that correct or are you seeing different and that portion works just fine, and you only struggle with Dev Proxy blocking other apps on your machine?

[ThaDaVos]

I am from Clarion calling into a DotNet library (so System.Net.Http) so that is probably why it works with the system proxy - still I rather prevent changing code to work around this - so your mentioned 1 is the only workaround to keep using it as system proxy?

[waldekmastykarz]

OK, so System.Net.Http should pick up environment variables for configuring HTTP proxy. Could you try specifying https_proxy: http://127.0.0.1:8000 in your app's configuration (I don't know how you're launching your app and which IDE you use so the exact steps might differ. Eg. in VSCode, you'd put it in .vscode/launch.json) while setting Dev Proxy as non-system-proxy and see if it works?

[zendu]

I use Dev Proxy as system proxy (default behavior) and added "!https://*" as last entry in urlsToWatch array. This allowed my other apps to resume functioning.

[zendu]

I take it back. I thought it solved the problem, but it actually did not. It defies the purpose of using dev proxy if rest of the system comes to halt. I use an app that may be calling more URLs than I want to watch and intercept. So setting the proxy using environment variables is not going to solve the problem.

[zendu]

Teams, Git with Azure DevOps Repos, M365 Copilot all refuse to work when dev proxy is running.

[waldekmastykarz]

I take it back. I thought it solved the problem, but it actually did not. It defies the purpose of using dev proxy if rest of the system comes to halt. I use an app that may be calling more URLs than I want to watch and intercept. So setting the proxy using environment variables is not going to solve the problem.

If you don't want Dev Proxy to affect other apps on your system, then the solution is to not register Dev Proxy as a system proxy and specifically route the traffic of your application through Dev Proxy. You can then use Dev Proxy's settings to choose which URLs you want to intercept and which you want to pass through.