Locked funds due to funding a channel with a transaction with the wrong txid from a P2SH wallet

[openoms]

I have attempted to fund a channel from an external P2SH wallet
When converting the PSBT to a rawtxn the txid has changed.
The transaction broadcasted sent the the right amount to the right address, but the txid was not which was passed to fundchannel_complete.
Unfortunately the transaction has confirmed quickly so now I need to find a way to recover it.
The channel peer is Fulmo - running c-lightning also.

To help to reproduce:
Funding start:

$  lightning-cli fundchannel_start 024a8228d764091fce2ed67e1a7404f83e38ea3c7cb42030a2789e73cf3b341365 1980400 11000 false
{
   "funding_address": "bc1qa8guuljuzsc9auqcz7vrr8lw33yy6kmyglw0f9lg33cevqmaffdq73fr5g",
   "scriptpubkey": "0020e9d1ce7e5c14305ef0181798319fee8c484d5b6447dcf497e88c7196037d4a5a"
}

The created PSBT contained the scriptpubkey:

 $ bitcoin-cli decodepsbt 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 | grep 0020e9d1ce7e5c14305ef0181798319fee8c484d5b6447dcf497e88c7196037d4a5a
          "hex": "0020e9d1ce7e5c14305ef0181798319fee8c484d5b6447dcf497e88c7196037d4a5a",

And the txid ( Specter Desktop showed also: 408abf9ae8e2228266ea30985fa3bb47ee5e9fb964263bf2bb4166226bb33ea3):

$ bitcoin-cli decodepsbt 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 | grep txid
    "txid": "408abf9ae8e2228266ea30985fa3bb47ee5e9fb964263bf2bb4166226bb33ea3",
        "txid": "9157a524c7a8a75002a08f7d571562654c5dde57fd0fab802495302df73d353c",

TXID Confirmed in Specter Desktop

Passed the txid to fundchannel_complete:

$ lightning-cli fundchannel_complete 024a8228d764091fce2ed67e1a7404f83e38ea3c7cb42030a2789e73cf3b341365 408abf9ae8e2228266ea30985fa3bb47ee5e9fb964263bf2bb4166226bb33ea3 0
{
   "channel_id": "a33eb36b226641bbf23b2664b99f5eee47bba35f9830ea668222e2e89abf8a40",
   "commitments_secured": true
}

Now the issue was that imported the PSBT to Electrum to broadcast and did not realize that it shows a changed TXID (but the funding address and amount remained the same):

The raw transaction broadcasted:

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

The actual confirmed transaction: https://blockstream.info/search?q=f74459ad229f47edb0835925c4211f51bac2a879bd466173f02b43a9fdce38ae

As discussed with on the developer meeting with @rustyrussell :

• When the accident already happened a (dev) tool to extract the funding pubkeys and sign the manually constructed transaction could help to recover the funds although the cooperation of the channel peer is needed.
• There were problems identified before when funding from P2SH wallets - could there be checks in place to avoid a similar thing happen in the future? Possibly even an externally built transaction could be broadcasted by c-lightning so it it could make the last checks.

Thank you for your time spent on looking into this.

[rustyrussell]

OK, the txid of the global tx is NOT the txid of the PSBT! I spoke with @achow101 and I think we both winced that bitcoin-core and spectre display the txid, as it's dangerous.

Now, for non-P2SH-wrapped segwit inputs, the txid of the PSBT will be the global tx TXID. But they're the exception! We have a function of our own which calculates it properly (https://github.com/ElementsProject/lightning/blob/master/bitcoin/psbt.c#L787).

Perhaps we should allow fundchannel_complete to take a PSBT? Then it would Do The Right Thing? @niftynei ?

[niftynei]

Perhaps we should allow fundchannel_complete to take a PSBT? Then it would Do The Right Thing? @niftynei ?

Agreed. A PSBT and/or a raw transaction in lieu of the txid & outpoint would be a huge improvement here.

We can identify the appropriate out-index by finding the expected funding script, etc.

[openoms]

Next related question here is if there is anything left that can be done now or possibly in the future if the 2016 blocks have passed since the attempted funding?

Or is there any data which can be extracted now and possibly used later and will be deleted at the pending channel expiry?

[openoms]

Ok learned on the developer meeting and IRC that this proposal can help the case:
lightning/bolts#854 even retrospectively if the peer happens to remember enough to recover. Will continue with testing and exploring the details.