Parse config file at startup and produce errors if some important sections are missing

[lelutin]

• onionrouter version: 0.6.2
• Python version: 3.9.2
• Operating System: debian bullseye

Description

Once a configuration file exists and the daemon is able to start, it might end up responding to requests with errors about some configuration sections or options missing when postfix sends a request to it.

For example:

$ nc localhost 23000
[email protected]
500 No section: 'IGNORED'

or with only the IGNORED section delimiter present without anything in it:

$ nc localhost 23000
[email protected]
500 No option 'domains' in section: 'IGNORED'

Since the daemon will effectively be useless (and will indefinitely stall queries by postfix) it would make more sense for the daemon to find those configuration problems and noisily exit upon starting up. This would make it easier to debug the problem and make the service functional.