option_channel_type was negotiated but channel_type is missing

[joostjager]

Background

Cannot open a channel to Eclair

Your environment

• lnd v0.14.1-beta
• eclair Add support for option_payment_metadata ACINQ/eclair#2063

Steps to reproduce

• Connect Eclair to LND
• LND initiates channel open via lncli openchannel

Expected behaviour

Channel opened.

Actual behaviour

Error: option_channel_type was negotiated but channel_type is missing

Investigation

It seems that lnd is silently not sending the channel type tlv when OpenChannelRequest.CommitmentType isn't set. The lncli default is to not set the channel type.

lnd/rpcserver.go

Line 1995 in c75c3bd

break

[Crypt-iQ]

The above error is an eclair error option_channel_type was negotiated but channel_type is missing right?

[joostjager]

Yes

[Roasbeef]

Seems they've changed behavior (in master?) since their last release.

It seems that lnd is silently not sending the channel type tlv when OpenChannelRequest.CommitmentType isn't set.

Thing is, we don't necessarily know if the other side actually supports the feature when a user goes to open a channel type. So we opt to not use explicit funding if the user doesn't select a type manually.

As the spec is written right now, it's technically ok for them to always require it (the "MAY" wording), but there're still some other ambiguous cases, like: we don't set it, but they do (in accept_channel) now we both go to implicit. So it's up to an implementation today if they always want it or not.

edit: ok so we were compatible with the pre feature bit version (their original deployment), but seems not their current master branch (post feature bit)?

[Roasbeef]

Ok, cleared things up here with some of the other BOLT-ers, we can both ensure that users don't get downgraded, but also maintain compat across all levels. We'll soon have some CI up to run cdecker's old cross-impl tests to make sure this gets caught during the rc process (ideally we only target the last major release, since the master branch can at times be a moving target).