Kestrel port binding default to 80 or 443 / No error/warn/info/debug when "{abc}" provided

Hello 👋

Describe the bug

Invalid Http/Https binding can be defaulted without any log and go on

After few long minutes (hours?) of debugging we found out that invalid port configuration will not say anything and silent. Why did it takes so long ? Because we were looking for the https binding that was https://*:8443 on our POD, and it seems that another appsettings...json file still had an http://*:{place.holder} that was not replaced So it seems that it defaulted to port 80 without saying anything at all.

The behavior was AccessDeniedException on a Socket binding attempt (because Pods should not run as root so any binding bellow 1024 is forbidden)

Questions

so I wonder about 3 things now :

• should the SocketException / AccessDenied be explicit on the full binding url that was denied ? => http://[::]:80 or http://*:80`
• should there be at least a WARNING on the fact that a string with letter and placerhoder is probably not a valid URI / Port ?
• is there any form of URI that would makes this valid: http://*:{foo.bar.kix} with the port 80 ?

To Reproduce

dotnet new webapi
dotnet publish
cd ./bin/Debug/net5.0/publish/
$env:ASPNETCORE_URLS="https://*:{abc}"
./foo.exe

Further technical details

• ASP.NET Core version : both 3.1.x and 5.0-preview6
• Include the output of dotnet --info