Setting a new proxy is only effective after the first request (tested with WebEngine)

Setting a new proxy after the event loop is running is only effective after the first request is made:

1. start_app
2. set_proxy(proxy_1)
3. request() -> OK, uses proxy_1
4. set_proxy(proxy_2)
5. request() -> FAIL, uses proxy_1
6. request() -> OK, uses proxy_2

The same error happens with both

• QNetworkProxyFactory and
• QNetworkProxy::setApplicationProxy().

This error happens with:

• Debian Linux 5.10.0-13-amd64 #1 SMP Debian 5.10.106-1 x86_64 GNU/Linux
  QMake version 3.1
  Using Qt version 5.15.2 in /usr/lib/x86_64-linux-gnu

Works correctly with:

• Ubuntu Linux 5.13.0-39-generic #44~20.04.1-Ubuntu SMP x86_64 x86_64 x86_64 GNU/Linux
  QMake version 3.1
  Using Qt version 5.12.8 in /usr/lib/x86_64-linux-gnu

There is an attached test file. Usage instructions are in the test file.

From tests I have made with QNetworkProxyFactory, it seems that new proxy settings are evaluated after a request is made. But that is just an intuition.

I have tried the following (unsuccessfully) to work around the issue:

• set the same new proxy multiple time
• send a dummy request (non-existent URL) after setting a new proxy
• make sure to run the event loop / process pending events between setting a new proxy and sending a request