Get route hints to own node via RPC

[hsjoberg]

When using keysend for sending to a node only private channels, one would need to provide route hints.
To be able to get route hints for a node, AFAICT the only way to do that is to call AddInvoice with private: true.
It's not an optimal solution as that would also trigger SubscribeInvoices stream.

It would be good to have a QueryRouteHints API function that gets all route hints to a node.

I could work on this depending on the difficulty of the task, but I'm opening an issue about it to keep track of this functionality and for discussion.

[joostjager]

Another workaround is to query the private channels using ListChannels and then fetch the remote routing policy using GetChanInfo for each channel.

QueryRouteHints is another option, but that may eventually be superseded by an rpc call that generates a complete keysend bolt11 invoice.

[hsjoberg]

Another workaround is to query the private channels using ListChannels and then fetch the remote routing policy using GetChanInfo for each channel.

You're right, that's definitely a good workaround.
QueryRouteHints is more of a convenience thing.

QueryRouteHints is another option, but that may eventually be superseded by an rpc call that generates a complete keysend bolt11 invoice.

Good point, it makes sense to standardize keysending through bolt11 and/or a new schema.
I'm not sure about the strategy of the RPC interface, but as there are other low-level functions I guess it makes sense to complement it.

[djkazic]

@joostjager that is a generic approach that works for normal SCIDs. However, it breaks with SCID aliases.

Example:

Invoice routing hint embedded chanID (compact form):
17592186044416000748

chaninfo and listchannels displayed routing hint (normal form): 
17592186044416000000

SCID aliases are larger than uint64, so while AddInvoice is capable of calling ToUint64() before adding a route hint, the rpcserver returns the unmodified SCID alias which will not work when added as a routing hint.

As a result, there is no easy way for Blixt to do a rpc call like listchannels and grab a SCID alias to use as a routing hint.

Edit: I got an explanation for this discrepancy. It's not because the SCID size or ToUint64, it's actually because the SCID alias on our side is displayed by listchannels, while what we want is the peer SCID alias.