Issues with displaying website through the proxy

I created a simple passthrough proxy and try to use it with FF.

The problem is, that for some reason the https://twitter.com website doesn’t load at all or loads partially when the proxy is used. I cannot identify the reason, this is what I see in the logs:

Proxying HTTP/1 CONNECT to twitter.com:443
Generating certificate for twitter.com
Handling request for https://twitter.com/
Request matched rule: Match requests for anything, and then pass the request through to the target host.

and then after a long delay:

Failed to handle request: Error: connect ETIMEDOUT 104.244.42.65:443
    at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1157:16) {
  errno: -110,
  code: 'ETIMEDOUT',
  syscall: 'connect',
  address: '104.244.42.65',
  port: 443,
  statusCode: 502,
  statusMessage: 'Error communicating with upstream server'
}
Failed to handle request: Error: connect ETIMEDOUT 104.244.42.65:443
    at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1157:16) {
  errno: -110,
  code: 'ETIMEDOUT',
  syscall: 'connect',
  address: '104.244.42.65',
  port: 443,
  statusCode: 502,
  statusMessage: 'Error communicating with upstream server'
}
Failed to handle request: Error: connect ETIMEDOUT 104.244.42.65:443
    at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1157:16) {
  errno: -110,
  code: 'ETIMEDOUT',
  syscall: 'connect',
  address: '104.244.42.65',
  port: 443,
  statusCode: 502,
  statusMessage: 'Error communicating with upstream server'
}
Failed to handle request: Error: connect ETIMEDOUT 104.244.42.65:443
    at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1157:16) {
  errno: -110,
  code: 'ETIMEDOUT',
  syscall: 'connect',
  address: '104.244.42.65',
  port: 443,
  statusCode: 502,
  statusMessage: 'Error communicating with upstream server'
}

FF outout:

Now, if I enable the system level VPN, it does start working! So basically twitter.com without proxy works, and also it works with proxy with VPN

It seems like FF can do something that http://twitter.com requires, but what my proxy (or the underlying mockttp) can’t do. What it could be? Does anyone have any idea?

This is my source code: https://github.com/OnkelTem/passthrough-web-proxy

[pimterry]

Huh, interesting! Interfering government proxies sound very annoying, sorry about that, but yes it looks like HTTP Toolkit is doing the right thing in that case. Connecting upstream directly genuinely times out, and it correctly shows that as the error. I’ll close this.

Very interesting that it’s intermittent though, I’d be curious to know how they’re implementing the block internally to cause that. Maybe it’s by IP, and round-robin DNS is sending you to different Twitter IPs each time, and not all of them are blocked?

Anyway, if using a VPN works, that’s probably the best option. Alternatively you might find that the proxyConfig option gives you a more direct workaround without needing to remember to use the VPN, if you can find an accessible proxy hosted outside Russia to route around the issue.

[OnkelTem]

So this one can be closed I suppose, as it doesn’t seem to be relevant. I apologize for spending your time. Thank you for the quick response and helpful ideas!