Find unused port for codechecker server

[tal66]

Hi, this closes #3657.
if default port is not available, and the user didn't ask for a specific one - let the os find a port.

[bruntib]

Thanks for the improvement, it's a very nice job!
I think, however, that finding a free port shouldn't be an automatic thing even in case of using the default port. If the default port (8001) is not free then it still should be an error. We should only get a free port from os only if the user explicitly provides port 0.

[tal66]

so the user can just use -p 0 in that case. btw, i think you should change the -v option, it is expected to mean verbose in my opinion

[bruntib]

Oh, sorry, the specification in the original ticket is not accurate. You implemented it according to the specification, but I think we shouldn't consider port 8001 as a special case. We should choose one of these alternatives:

• If the user provides a port number then we use that. If it's not free then an error message should be printed. If the user doesn't provide any port number then we use 8001 which also can be occupied in which case an error message is printed. If user provides 0 as port number explicitly then then os should find a free one.
• If the user doesn't provide a port number then CodeChecker should work as if 0 was given. With other words: 0 could be the default port number.

In my previous comment I suggested the first option, because many other CodeChecker commands are assuming this port number. For example CodeChecker store stores to port 8001 by default, so that's why I's vote on the first alternative.

[tal66]

without my commit these are the scenarios:
-p 0 - os finds a port
-p <num> - use num or error
(no port request) - use 8001 or error
which match your first alternative.

[tal66]

could change the error message to say "Server can't be started ... use -p 0 to find a free port automatically", without any code changes.

[bruntib]

Yes, that message would be a good solution. I've checked the original version of this ticket in an internal ticket system and this task belonged to an old CodeChecker version. Port 0 really works as expected by now, sorry, I haven't checked it before creating this ticket. My bad :(

[tal66]

no problem. I canceled the changes, and just changed the message

[bruntib]

Thank you!