Add Support for P2TR Fallback Addresses in BOLT-11 #9975

MPins · 2025-06-20T18:40:02Z

Change Description

Fixes #9591
Add Support for P2TR Fallback Addresses in BOLT-11 invoices

Steps to Test

lncli addinvoice --fallback_addr=bcrt1ps89hq0hxen5y6yxqqk88ssdyhe7hdr92fzudtcskk37p460ldazsl0sfsw

coderabbitai · 2025-06-20T18:40:08Z

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MPins · 2025-07-07T14:51:08Z

/gemini review

gemini-code-assist

Code Review

This pull request adds support for Pay-to-Taproot (P2TR) fallback addresses in BOLT-11 invoices. The changes include updating the invoice decoding and encoding logic to handle P2TR addresses, along with corresponding unit tests. I recommend adding a full integration test case to TestDecodeEncode to ensure the end-to-end encoding and decoding of invoices with P2TR fallback addresses works as expected. This will improve test coverage and help prevent future regressions.

zpay32/invoice_test.go

zpay32/decode.go

GustavoStingelin

💯

MPins · 2025-07-31T14:38:38Z

@saubyk this PR could be included in the lnd v0.20.0 milestone.

ziggie1984 · 2025-08-01T16:23:41Z

#9591 also mentions a spec update for all implementation to behave the same is this also planed ? This should then include test vectors and those test vectors should be tested here.

MPins · 2025-08-01T18:30:36Z

#9591 also mentions a spec update for all implementation to behave the same is this also planed ? This should then include test vectors and those test vectors should be tested here.

Hello @ziggie1984, I just reached out to @erickcestari (who opened the issue). Our understanding is that the spec already states that a P2TR address must be accepted:

f (9): data_length variable, depending on version. Fallback on-chain address: for Bitcoin, this starts with a 5-bit version and contains a witness program or P2PKH or P2SH address.

Handling cases where more than one fallback address is provided may be left to each implementation. I’ll open a PR in BOLT to add the test vector I created for this PR.

MPins · 2025-08-07T17:41:08Z

Hello @ziggie1984 the PR#1276 adding the test vector for a p2tr fallback address in BOLT 11 has been submitted.

Just to clarify — the test vector in this PR doesn’t include the s (payment secret) and 9 (features) tagged fields, following the same pattern as the other test vectors already presented here.

MPins · 2025-08-14T21:38:19Z

Hello @ziggie1984 the PR#1276 adding the test vector for a p2tr fallback address in BOLT 11 has been submitted.

Just to clarify — the test vector in this PR doesn’t include the s (payment secret) and 9 (features) tagged fields, following the same pattern as the other test vectors already presented here.

Hello @ziggie1984, the BOLT PR just received its first approval.
As noted, the fallback address might be deprecated in the future, so I think we can move forward with this PR and have LND accept the P2TR fallback address in the same way it handles the other address types.

ziggie1984

Had some minor comments, other than that it is good to go

channeldb/migration_01_to_11/zpay32/decode.go

zpay32/invoice_test.go

lightninglabs-deploy · 2025-09-03T16:38:28Z

@MPins, remember to re-request review from reviewers when ready

MPins · 2025-09-11T19:57:11Z

@ziggie1984 now it is using the P2TR test vector. Ready for your review.

ziggie1984

LGTM, I wonder how you created the invoice for the spec in the first place, was thinking you were using LND but doesn't look like it ?

starius · 2025-09-12T15:02:25Z

Manual testing of 0f84100 in signet:

$ lncli newaddress p2tr
{
    "address": "tb1prf2aym930gl4rx7tnvayexw3tcsg8n8nvy55a0rurqyqx6833a3q73rlx3"
}

$ lncli addinvoice --fallback_addr tb1prf2aym930gl4rx7tnvayexw3tcsg8n8nvy55a0rurqyqx6833a3q73rlx3
{
    "r_hash": "792e562ebe1fe61495d6852b5129338a04a3262069543f1fb01d6c531a9a5f4d",
    "payment_request": "lntbs1p5vgt47pp50yh9vt47rlnpf9wks544z2fn3gz2xf3qd92r78asr4k9xx56taxsdqqcqzzsxqyz5vqfp4prf2aym930gl4rx7tnvayexw3tcsg8n8nvy55a0rurqyqx6833a3qsp5dyg5ls0mxwq4hyw05q0qfydv8ccu6xfd7jvqu78d8nzrjktpw2uq9qxpqysgqn4ht9fxmt0srche7yv3zgseemapt85wjkej5ssskaqh6wc6clcx4n4rv624u4g8u4p57cupx3zdcjyw0057k78mjkunr62pwvswqe7cqqde48j",
    "add_index": "1",
    "payment_addr": "69114fc1fb33815b91cfa01e0491ac3e31cd192df4980e78ed3cc439596172b8"
}

$ lncli decodepayreq lntbs1p5vgt47pp50yh9vt47rlnpf9wks544z2fn3gz2xf3qd92r78asr4k9xx56taxsdqqcqzzsxqyz5vqfp4prf2aym930gl4rx7tnvayexw3tcsg8n8nvy55a0rurqyqx6833a3qsp5dyg5ls0mxwq4hyw05q0qfydv8ccu6xfd7jvqu78d8nzrjktpw2uq9qxpqysgqn4ht9fxmt0srche7yv3zgseemapt85wjkej5ssskaqh6wc6clcx4n4rv624u4g8u4p57cupx3zdcjyw0057k78mjkunr62pwvswqe7cqqde48j | jq .fallback_addr
"tb1prf2aym930gl4rx7tnvayexw3tcsg8n8nvy55a0rurqyqx6833a3q73rlx3"

Works as expected!

starius

LGTM! 🏆
The code looks great, pending comments.
I tested it manually in signet - works perfectly!

zpay32/invoice_test.go

zpay32/decode.go

zpay32/invoice_internal_test.go

zpay32/invoice_test.go

MPins · 2025-09-12T15:19:26Z

LGTM, I wonder how you created the invoice for the spec in the first place, was thinking you were using LND but doesn't look like it ?

Thanks!

Since I also needed to create an invalid invoice, I used lightning-payencode and modified it to fit my needs. I also submitted some PRs to make it compatible with the recent specs, but it seems Rusty is no longer maintaining the project.

MPins · 2025-09-12T18:20:51Z

LGTM! 🏆 The code looks great, pending comments. I tested it manually in signet - works perfectly!

Thanks! I’ve addressed all the comments, except for the one about encoding back the invoice — I left a reply on that thread with my thoughts. 😉

MPins force-pushed the issue-9591 branch 5 times, most recently from 109c703 to 069f6d1 Compare June 22, 2025 00:51

gemini-code-assist bot reviewed Jul 7, 2025

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saubyk assigned MPins Jul 7, 2025

GustavoStingelin suggested changes Jul 10, 2025

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MPins force-pushed the issue-9591 branch from 069f6d1 to aa4b1be Compare July 18, 2025 15:35

MPins requested a review from GustavoStingelin July 18, 2025 15:47

MPins force-pushed the issue-9591 branch from aa4b1be to f585fca Compare July 26, 2025 01:07

GustavoStingelin approved these changes Jul 26, 2025

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MPins force-pushed the issue-9591 branch from f585fca to 2a07fb9 Compare August 14, 2025 22:26

ziggie1984 reviewed Aug 27, 2025

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MPins force-pushed the issue-9591 branch from 2a07fb9 to 3dd595f Compare September 8, 2025 23:33

MPins requested a review from ziggie1984 September 9, 2025 11:13

MPins force-pushed the issue-9591 branch 2 times, most recently from 4f34854 to 0f84100 Compare September 11, 2025 18:49

ziggie1984 approved these changes Sep 12, 2025

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zpay32: add support for P2TR fallback addresses

e746df3

MPins force-pushed the issue-9591 branch from 0f84100 to 2c73158 Compare September 12, 2025 17:46

MPins added 2 commits September 12, 2025 12:26

zpay32: add test case for P2TR fallback addresses

9d79250

doc: release-notes-0.20.0

97f2fbb

MPins force-pushed the issue-9591 branch from 2c73158 to 97f2fbb Compare September 12, 2025 19:26

starius approved these changes Sep 12, 2025

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ellemouton merged commit 6b279fb into lightningnetwork:master Sep 15, 2025
37 of 39 checks passed

Add Support for P2TR Fallback Addresses in BOLT-11 #9975

Add Support for P2TR Fallback Addresses in BOLT-11 #9975

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