Recover from RBF on Channel Open, Confirmed On-Chain, Stuck Pending Old TXN

[atomantic]

Edit: This problem is from me doing something stupid, so hopefully this thread will aid anyone else who does the same. Somehow I landed on a thread somewhere that suggested simply broadcasting an RBF transaction would be good enough--and I missed the bit in the LND docs that say you can't do that for channel opens.

The situation:

• I had a pending channel open with a fee that was too low for the demand period (it wasn't really very low)
• I decided I should RBF to increase the fee and get it through so I manually broadcasted this onchain without using the lncli bumpfee tools
• Now I have a successful transaction, confirmed dozens on times onchain, but a pending open that is still looking at the txn id of the pre-RBF txn.

[atomantic]

ok, after reading more of the LND guide, I see that RBF is not a valid way to increase fees on a channel open.
Chantools guide says I should NOT abandonchannel since this txn is confirmed onchain.
What's the best way to close this out and recover?

[guggero]

Correct, using RBF is the worst thing you can do with a channel funding transaction! Only CPFP is allowed (that's what lncli wallet bumpfee does).
The reason is this: When you open a channel, you send funds to a 2-of-2 multisig address to which your node only has one key. Since that's dangerous, as you need cooperation of your peer to get the funds out, your wallet will only sign that transaction once it has a counter-signed commitment transaction that spends those funds again and reflects the current initial channel balance.
But that commitment transaction references the TXID of a specific funding transaction. If you publish another funding transaction with a different TXID, you basically invalidate the commitment transaction.

So fixing this isn't just a case of updating an entry in the database. You need a new signature from your peer. You can use the chantools rescuefunding (and your peer chantools signrescuefunding).

[atomantic]

Thanks @guggero -- I'm getting an error when running chantools rescuefunding:

error fetching UTXO info for outpoint MY_CHANNEL_POINT: transaction not found

Looks like the default API of blockstream doesn't persist the info for the RBF source. I tried setting --apiurl "https://mempool.space/api" -- I see the txn on mempool. But I'm not finding it there either...

Do you know another API source that might work?

[atomantic]

Ah, nevermind. I missed supplying the --confirmedchannelpoint

Great tool! I'll post a full recovery summary for posterity once complete :)

[atomantic]

Alright. For anyone else who somehow manages to do what I did, here's how to resolve it when running on an Umbrel node:

1. Edit ~/umbrel/app-data/data/lnd/umbrel-lnd.conf to add reset-wallet-transactions=true
2. Restart umbrel (this will rescan the wallet to fix UTXO sync issue and may take a while after restart) — you can watch along via ssh into umbrel and sudo docker logs —follow ${the docker id of the lnd container}
3. Install chantools -- note: I installed this on my host machine rather than installing it on the umbrel
4. Backup lightning db from umbrel to local host so we don’t have to stop the lnd service to use the db: scp umbrel@umbrel.local:~/umbrel/app-data/lightning/data/lnd/data/graph/mainnet/channel.db channel.db
5. get a new bitcoin onchain deposit address from your node (DEPOSIT_ADDR)
6. Use chantools rescuefunding:

chantools rescuefunding --channeldb ./channel.db --dbchannelpoint OLD_TXN_ID:0 --confirmedchannelpoint NEW_RBF_TXN_ID:0 --sweepaddr DEPOSIT_ADDR

7. Contact the peer and have them use chantools signrescuefunding, providing them with the output from above:

chantools signrescuefunding --psbt YOUR_PSBT

11. Broadcast signed transaction
12. Kill the pending channel:

sudo ~/umbrel/scripts/app compose lightning exec lnd lncli abandonchannel --chan_point OLD_TXN_ID:0 --i_know_what_i_am_doing

13. open a new channel to the peer

Final question for you @guggero: Does the peer also have to run abandonchannel to clear their db of the bad open from my node or will my abandonment convey across the network? I ask because they have their maxpendingchannels set to 1 and it appears my attempts to make a new connection are blocked because of that.

[guggero]

Yes, the peer can run the abandonchannel command. Or they can wait for 2 weeks, the responder side to a channel open is supposed to discard a channel if the funding transaction doesn't confirm within 2 weeks.