config: Allow interface names for listener addresses

[jrick]

This allows --listen and --rpclisten config options to specify
interface names, instead of only exact IP addresses. If an interface
is named, all IP addresses associated with the interface during config
parsing will be added to the normalized listeners.

Closes #2622.

[jrick]

This isn't working for IPv6 link-local addresses.

2021-03-15 11:35:43.705 [WRN] SRVR: Can't listen on [fe80::1]:19108: listen tcp6 [fe80::1]:19108: bind: can't assign requested address

The listen address must include the zone. For example, this listener works:

$ dcrd --testnet --listen=fe80::1%lo0
...
2021-03-15 11:38:29.808 [INF] CMGR: Server listening on [fe80::1%lo0]:19108

There also should be a way to change the port that will be listened on, instead of only supporting the default port. I'm not sure what syntax should be used for this.

[dnldd]

I got this in testing:

❯ dcrd --rpcuser=user --rpcpass=pass --profile=127.0.0.1:2555 --appdata=/home/dnldd/mh/node --datadi
r=/home/dnldd/mh/node/data --debuglevel=info --listen=wlp2s0 --listen=lo --listen=127.0.0.1:9108 --t
xindex --addrindex                                                                                  
listeners are: ([]string) (len=4 cap=5) {                                                           
 (string) (len=18) "192.168.100.6:9108",                                                            
 (string) (len=32) "[fe80::ddaa:db81:2421:a1b1]:9108",                                              
 (string) (len=14) "127.0.0.1:9108",                                                                
 (string) (len=10) "[::1]:9108"                                                                     
}            

...


2021-03-15 15:58:27.843 [WRN] SRVR: Can't listen on [fe80::ddaa:db81:2421:a1b1]:9108: listen tcp6 [f
e80::ddaa:db81:2421:a1b1]:9108: bind: invalid argument   

Seems fine for ipv4, regarding the warning I do not have an ipv6 address so can't confirm there is an issue with that.

[jrick]

Yeah, see my comment above. fe80::/10 is a link local network, so that will need the zone appended.

Even if you don't have IPv6 connectivity to the internet, your interface is still configured with that link-local address, and dcrd should still listen on it.

[dnldd]

Can confirm I'm no longer getting the ipv6 related warning with the updated PR.

[jrick]

This is also affecting options like --connect which also use the address normalization, and I'm not sure if we really want that behavior. At the very least, with --connect, if an interface is going to be allowed, it should maybe only use the first address, and not all of them. I'm wondering what others think should be done for these options.

[dnldd]

Yeah for --connect it'd b better to only normalize just the addresses specified only. We probably need a parameter for normalizeAddresses to toggle when to get interface addresses or not.

[davecgh]

We've tested the listen and connect functionality works as intended on OpenBSD, Mac, Linux, and Windows.

I also sanity checked the RPC node connect works as intended on Windows and Linux.