Specify a default listening port

[NuSkooler]

When using Cabal behind a firewall/NAT environment, we need a way to specify explicit listening port or port ranges such that they can be allowed through. For example, my setup looks like this:

{ internet } <--> pfSense firewall <--> CentOS 7 firewalld <--> cabal

I must NAT through the firewall and open up a port(s) at firewalld as well.

As instructed in chat, a starting point is simply patching swarm.js:

`hyperswarm({ preferredPort: 49737 })`

This does the trick as a test. However, a configurable set of port/port ranges would be better to allow for conflicts/etc. I would submit a PR but I just started poking around with this yesterday and don't know the code base yet 😅

[cblgh]

thanks for making the issue @NuSkooler! i like the following way of solving this:

• choosing a default port and setting it in swarm.js
  • let's make sure to choose a port number that does not conflict with beaker or hyperdivision's projects & products (as there is a chance of overlap in users for cabal & beaker :)
• allow passing in a port option to cabal-core, which overrides the default port
• add a --port option to cabal-cli to make it easy for people to use in practice
• support port in config.yml (thanks kira!)

[hackergrrl]

This could also be a useful thing to support in cabal's config.yml