Can't mutual close with pending HTLC

[thomash-acinq]

Background

When trying to close a channel with a lnd node, the node returned the error cannot co-op close channel w/ active htlcs

Steps to reproduce

Open a channel to a lnd node, add a HTLC , send a shutdown message.

Expected behaviour

The node should wait for the HTLC to be resolved, not add any new HTLC, and then reply with a shutdown message.
BOLT 2: Channel Close

Actual behaviour

The lnd node returns an error: cannot co-op close channel w/ active htlcs

[Crypt-iQ]

We're aware and plan to fix this in the future

[Roasbeef]

Related issue: #4819

[Roasbeef]

On the API level we return this error so the user gets quick feedback that a co-op close isn't possible at that time. On the p2p level, we currently use the same codepath, but should instead defer and wait till things clear up (or the channel force closes?).

[Crypt-iQ]

This is one area of the spec I had trouble with. I think the spec could use better wording here also.