Config option for disabling NAT discovery

In some locations (e.g. datacenters) you don't need NAT discovery. Sometimes it'll take its full couple of seconds though! If we can disable that, restarts of the daemon will be faster.

[whyrusleeping]

This should be pretty easy to do, should probably go under the Swarm config group and be called NatPortMap, default value true (if not present in the config, set it to true).

It needs to pass an option to the host construction method so that it can pass or not pass an option to the basichost.New here: https://github.com/ipfs/go-ipfs/blob/master/core/core.go#L731

Instead of passing a bool for 'NatPortMap' to this method with already way too many parameters, lets add an options struct as a parameter that we can extend later with more of these tweaks.

[kevina]

@whyrusleeping

if not present in the config, set it to true

where would be a good place to do this? at the moment is is non obvious.

[whyrusleeping]

in repo/fsrepo/serialize/serialize.go, at the bottom in the Load function, we just create an empty config before passing it to ReadConfigFile. If you set values in that, they will remain set to that value if the field is missing from the json.

Youre right, this is non-obvious, we should document it a bit while we're at it

[kevina]

Okay will do, It looks like this will be the first time we used a default value other than the go default of False, 0, or the empty string.

[whyrusleeping]

Yeah, i don't think we knew how to do this before, otherwise the NoSync option would have been just Sync

[kevina]

Yeah, i don't think we knew how to do this before, otherwise the NoSync option would have been just Sync

So it turned out is was not sufficient to set the defaults in just the Load function, they also needed to be set in initConfig in fsrepo.go so I created a SetDefaults() method on the config structure. P.R. coming soon with some test to make sure the NoSync option really defaults to true.