[Lightning-dev] Receiving via unpublished channels

ZmnSCPxj ZmnSCPxj at protonmail.com
Thu Apr 26 23:35:16 UTC 2018

Good morning list,

While implementing support for `r` field in invoices, I stumbled upon some issues regarding *creating* invoices with `r` fields.

In order to receive via an unpublished channel, we need to know what onLightning fees the other side of that channel wants to charge.  We cannot use our own onLightning fees because our fees apply if we were forwarding to the other side.

However, in case of an unpublished channel, we do not send channel_announcement, and in that case we do not send channel_update.  So the other side of the channel never informs us of the onLightning fees they want to charge if we would receive funds by this channel.

An idea we want to consider is to simply send `channel_update` as soon as we lock in the channel: https://github.com/ElementsProject/lightning/pull/1330#issuecomment-383931817

I want to ask the other LN implementations (lnd, eclair, ucoin, lit) if we should consider standardizing this behavior (i.e. send `channel_update` after lockin  regardless of published/unpublished state).  It seems back-compatible: software which does not expect this behavior will simply drop the `channel_update` (as they do not follow a `channel_announcement`).

In any case, what was the intended way to get the onLightning fee rates to put into invoice `r` fields for private routes?

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