Funding transaction withholding support #8546
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Looks good to me so far. I'll build the "Client-Trusts-LSP" mode for the LSP on top of this PR to see if it contains everything we need once #8569 got merged. |
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It fails on duplicates. It would ideally succeed, but bug reported: ElementsProject/libwally-core#509 Signed-off-by: Rusty Russell <[email protected]> Changelog-Fixed: JSON-RPC: `signpsbt` no longer crashes if asked to sign an already-signed PSBT with taproot paths.
This can definitely happen with zeroconf and the about-to-be-implemented withheld=True: ``` lightningd-1 2025-09-12T13:17:50.848Z **BROKEN** 022d223620a359a47ff7f7ac447c85c46c923da53389221a0054c11c1e3ca31d59-chan#1: Illegal gossip state transition: CGOSSIP_WAITING_FOR_SCID->CGOSSIP_CHANNEL_UNANNOUNCED_DYING ``` Signed-off-by: Rusty Russell <[email protected]>
Signed-off-by: Rusty Russell <[email protected]>
Interestingly, @niftynei added a funding_psbt column to the db in 2020, but we don't use it (it was removed early 2021 with the "inflight" architecture). So we don't need to add a new column, just plumb it back in. Signed-off-by: Rusty Russell <[email protected]>
Signed-off-by: Rusty Russell <[email protected]>
Signed-off-by: Rusty Russell <[email protected]> Changelog-Fixed: Protocol: we now re-transmit unseen funding transactions on startup, for more robustness.
…e sendpsbt. Signed-off-by: Rusty Russell <[email protected]>
Changelog-Added: JSON-RPC: `psbt` field in `funding` in listpeerchannels, and `funding_psbt` in listclosedchannels. Signed-off-by: Rusty Russell <[email protected]>
…re-send. This covers the other corner case, where we crash before actually signing and sending the PSBT. We can spot this because the channel is in AWAITING_LOCKIN and we have a PSBT, but it's not signed yet. Signed-off-by: Rusty Russell <[email protected]>
Normally we don't care, but if we're withholding it, keep it around so we can sign & broadcast later. Signed-off-by: Rusty Russell <[email protected]>
…els. Signed-off-by: Rusty Russell <[email protected]> Changelog-Added: JSON-RPC: `listpeerchannels` `funding` object `withheld` flag, and `listclosedchannels` `funding_withheld` flags, indicating fundchannel_complete was called with the `withheld` parameter true.
…ithheld channel. There's no funding tx to spend. Signed-off-by: Rusty Russell <[email protected]>
…art. Signed-off-by: Rusty Russell <[email protected]>
This is just a polite way of telling us that if we close, don't bother broadcasting since we didn't broadcast the funding tx. Changelog-Added: JSON-RPC: `fundchannel_complete` new parameter `withhold` (default false). Signed-off-by: Rusty Russell <[email protected]>
Signed-off-by: Rusty Russell <[email protected]>
Signed-off-by: Rusty Russell <[email protected]>
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This is useful for implementing an LSP, where you want to open a zero conf channel, and only broadcast the actual funding tx once they've sent enough to make it worthwhile.
The first few patches actually fix an unrelated bug I realized when looking at this: if we crash, nothing broadcasts the funding transactions again. If bitcoind doesn't keep it, or if it didn't make it to bitcoind, the transaction will never reach the blockchain.
The flow is: