This is an annoying issue if the user has his hostname set wrong. It is NOT catastrophic if that is the case. But we currently treat it that way. Instead, it should be logged as a WARNING.
Specifically, whether or not the hostname is setup correctly has nothing to do with whether or not a given port is free.
This has a big impact on customers. The error says that, say, port 4848 is in use. The user checks and finds that nothing is using port 4848. Confusion sets in at that point.
It is unlikely that the customer will bump into this issue. He would have to have a bad hostname. I.e. a hostname that can't be resolved by DNS. With the fix we emit a warning with the exact problem so that he can now fix it permanently.
The cost to fix it is minimal, in fact it is already fixed and waiting to go in. If it doesn't go into 4.0 it'll go into 4.0.1
The fix is not too complicated. The main complication is setting it up to emit only one warning message, then fine messages after that.
The actual fix itself is simply catching the right exception at the exact right place and swallowing it rather than turning it into a fatal error.
There is little risk. Automated tests, including QuickLook test this area all the time.
No doc impact.
QA need only run their usual standard tests