[RFC] event: expose BOLT12 invoice in PaymentSuccessful for proof of payment by vincenzopalazzo · Pull Request #733 · lightningdevkit/ldk-node

vincenzopalazzo · 2025-12-29T13:51:52Z

This patch adds the bolt12_invoice field to the PaymentSuccessful event, enabling users to obtain proof of payment for BOLT12 transactions.

Problem:
Previously, after a successful BOLT12 payment, users had no way to access the paid invoice data. This made it impossible to provide proof of payment to third parties, who need both the payment preimage and the original invoice to verify that sha256(preimage) matches the invoice's payment_hash.

Solution:
Add a bolt12_invoice: Option<Vec<u8>> field to PaymentSuccessful that contains the serialized BOLT12 invoice bytes. The invoice is serialized using LDK's standard encoding, which can be parsed back using Bolt12Invoice::try_from(bytes) in native Rust, or by hex-encoding the bytes and using Bolt12Invoice.from_str() in FFI bindings.

Design decisions:

Store as Vec<u8> rather than the complex PaidBolt12Invoice type to avoid UniFFI limitations with objects in enum variants
Return None for StaticInvoice (async payments) since proof of payment is not possible for those payment types anyway
Use TLV tag 7 for serialization, maintaining backward compatibility with existing persisted events

This implementation follows the maintainer guidance from PR #563 to expose the invoice via the event rather than storing it in the payment store.

ldk-reviews-bot · 2025-12-29T13:51:54Z

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vincenzopalazzo · 2025-12-29T13:53:30Z

@tnull IDK if this is a good design to have with the ffi, but I had to work around some unify ffi limitation with the enum type that is used inside the PaymentSend in rust-lightning

ldk-reviews-bot · 2025-12-31T14:03:37Z

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ldk-reviews-bot · 2026-01-03T00:00:36Z

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ldk-reviews-bot · 2026-01-05T00:01:25Z

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tnull

Exposing the BOLT12 invoice makes sense to me, though we should do it properly instead of just exposing the bytes.

src/event.rs

tnull

The changes are getting closer, but please make sure to avoid unnecessary boilerplate and stick to the approach we took for the other types (like Offer, Refund, etc).

This also needs a rebase by now, sorry!

Btw, please re-request review when you made updates, otherwise I might not always see it immediately.

bindings/ldk_node.udl

src/types.rs

ldk-reviews-bot · 2026-01-12T12:09:56Z

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ldk-reviews-bot · 2026-01-14T12:10:38Z

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ldk-reviews-bot · 2026-01-19T00:00:18Z

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bindings/ldk_node.udl

src/payment/mod.rs

src/event.rs

tnull · 2026-03-02T08:35:16Z

@vincenzopalazzo We now landed the uniffi v0.29 upgrade, so this should be unblocked. Note that as part of that upgrade we switched to use proc macros where possible, in particular Event is no longer exposed via the UDL file. So this should be unblocked, please rebase and let me know how it goes!

vincenzopalazzo · 2026-03-02T17:33:54Z

Thanks @tnull I used the help of claude to navigate a little bit the changes and now I pushed it (I have to change some name inside the enum for the kotlin naming convention hope this is not a big deal.

Please let me know if this is good enough or if there is a better way to implement the functionality in the codebase, thanks

tnull

Cool, mostly looks good, just some comments regarding cleanups we should now be able to do?

src/payment/mod.rs

src/types.rs

tests/integration_tests_rust.rs

src/ffi/types.rs

tnull · 2026-03-04T11:27:16Z

src/ffi/types.rs

+impl Writeable for PaidBolt12Invoice {
+	fn write<W: Writer>(&self, w: &mut W) -> Result<(), lightning::io::Error> {
+		// We clone `self` to convert it into the LDK native type for serialization.
+		// This only runs during event persistence, so the overhead is acceptable.


Ugh, this is still pretty bad. We should really avoid this, though I played with the different options here and I'm still not sure what else I find preferable. Seems every approach that avoids cloning the data (in particular struct wrapping for uniffi) will revert back to a lot of complications.

Let's make this comment a TODO: Find way to avoid cloning invoice data so I don't totally forget to revisit this, and then we should be able to move forward here to unblock you.

Yeah, I was not able to avoid it because the into() will close the type anyway, and I do not think it is a good idea to duplicate the code here, but probably I am underestimating how many times this method is called?

BTW, I updated the comment! Thanks for the feedback

src/payment/mod.rs

…ment Add the `bolt12_invoice: Option<PaidBolt12Invoice>` field to the `PaymentSuccessful` event, enabling users to obtain proof of payment for BOLT12 transactions. For non-uniffi builds, import `PaidBolt12Invoice` directly from `lightning::events` rather than re-exporting through `types.rs`. For uniffi builds, use the custom `ffi::PaidBolt12Invoice` wrapper that handles Arc-wrapping for enum variants. The proof-of-payment assertion is integrated into the existing `simple_bolt12_send_receive` test rather than a separate test. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tnull

Landing this. I think after #811 we could explore whether it makes sense to move the invoice to be stored in PaymentMetadataStore. Now tracked at #816

vincenzopalazzo marked this pull request as ready for review December 29, 2025 13:53

ldk-reviews-bot requested a review from tnull December 29, 2025 14:02

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storage: store the bolt12invoice invoice #563

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thesimplekid mentioned this pull request Jan 15, 2026

feat: uniffi bindings for golang cashubtc/cdk#1118

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vincenzopalazzo mentioned this pull request Jan 15, 2026

Expose PaidBolt12Invoice in bindings after UniFFI 0.29+ upgrade #757

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Explore whether PaidBolt12Invoice should be moved to PaymentMetadataStore #816

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tnull merged commit fae2746 into lightningdevkit:main Mar 4, 2026
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