Stop setting SERVER_PORT env key if nil

[franciscojmc]

The SERVER_PORT is optional but must not be set if it is not present.

Fixes socketry/falcon#118.

Types of Changes

• Bug fix.

Contribution

• I added tests for my changes.
• I tested my changes locally.
• I agree to the Developer's Certificate of Origin 1.1.

[franciscojmc]

I opted to go with the delete approach to avoid repeating the same logic in each rack version adapter.

[ioquatix]

This low level adapter is fairly performance critical. In this case, we have 3 hash operations, (1) an assignment of SERVER_PORT to nil, then an unconditional lookup of SERVER_PORT, and a delete operation. I think it's okay to duplicate the code for each adapter to ensure that on the fast path, no hash operations are involved, so I'd prefer if we have something like:

if server_port
  env[CGI::SERVER_PORT] = server_port
end

Duplicating the code between the adaptors is okay in this case, since in my mind they are independent specifications (even if they are the same in this regard). Does that seem reasonable?

[franciscojmc]

Absolutely. Considering the performance-critical nature of this code path, I agree with all your points. Will update the implementation accordingly.

[ioquatix]

Thanks for your contribution.