Implement `start_batch` message batching #3793

jkczyz · 2025-05-22T17:11:21Z

Instead of batching commitment_signed messages using a batch TLV, the splicing spec has been updated to introduce a start_batch messages. It used to indicate that the next batch_size messages for the channel_id should be treated as one logical message. Update commitment_signed message to contain the funding_txid instead of both that and a batch_size. Also, update PeerManager to batch accordingly instead of the previous custom approach.

ldk-reviews-bot · 2025-05-22T17:11:25Z

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lightning/src/ln/peer_handler.rs

ldk-reviews-bot · 2025-05-22T18:09:46Z

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lightning/src/ln/peer_handler.rs

jkczyz · 2025-05-23T21:40:42Z

Fixed some places where we disconnected but didn't send a warning (or disconnected when we should ignore and send a warning) according too the spec. Feels a little verbose, so let me know if there is some utility for this that I'm missing.

ldk-reviews-bot · 2025-05-26T00:01:05Z

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ldk-reviews-bot · 2025-05-28T00:01:41Z

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wpaulino

Feel free to squash, CI is failing though. LGTM so far, we just have to wait for the message_type TLV to be amended to the spec.

jkczyz · 2025-05-29T18:18:53Z

Feel free to squash, CI is failing though. LGTM so far, we just have to wait for the message_type TLV to be amended to the spec.

Squashed. Fixed CI by running rustfmt on one file.

wpaulino · 2025-05-29T19:26:12Z

Up to you, but we can probably drop b1abb5d once the optional message_type TLV is added.

jkczyz · 2025-05-30T19:45:24Z

Up to you, but we can probably drop b1abb5d once the optional message_type TLV is added.

Added a fixup that uses the message_type TLV and drops MessageBatchImpl::Unknown -- along with the unreachables -- but otherwise kept the commit intact.

wpaulino · 2025-06-02T17:31:53Z

Good to squash

jkczyz · 2025-06-02T20:01:01Z

Squashed and fixed linter failures.

ldk-reviews-bot · 2025-06-02T20:48:16Z

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ldk-reviews-bot · 2025-06-04T21:00:28Z

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TheBlueMatt · 2025-06-04T21:20:45Z

lightning/src/ln/msgs.rs

 	htlc_signatures
 }, {
-	(0, batch, option),
+	(1, funding_txid, option),


Do we want to go ahead and set these to 1001 just in case things change again?

Is the concern we'll have this merged and released before the spec is finalized?

Pretty much, we can flip it back to 1 once we're ready to include splicing in a release.

Done. Also needed to update the expected encoding in a test, which unfortunately I didn't realize was broken after I rebased for the last push.

FYI: git range-diff ebf0d4e...43db395 should show the relevant changes.

Instead of batching commitment_signed messages using a batch TLV, the splicing spec has been updated to introduce a start_batch messages. It used to indicate that the next batch_size messages for the channel_id should be treated as one logical message. This commit simply adds the message while the following commits will implement the handling logic.

Update commitment_signed message to contain the funding_txid instead of both that and a batch_size. The spec was updated to batch messages using start_batch, which contains the batch_size. This commit also updates PeerManager to batch commitment_signed messages in this manner instead of the previous custom approach.

While the spec only includes commitment_signed messages in batches, there may be other types of batches in the future. Generalize the message batching code to allow for other types in the future.

If a message in a commitment_signed batch does not contain a funding_txid or has duplicates, the channel should be failed. Move this check from PeerManager to FundedChannel such that this can be done.

codecov · 2025-06-05T21:14:37Z

Codecov Report

Attention: Patch coverage is 11.42857% with 124 lines in your changes missing coverage. Please review.

Project coverage is 89.84%. Comparing base (97f0e4b) to head (43db395).
Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/peer_handler.rs	2.77%	102 Missing and 3 partials ⚠️
lightning/src/ln/channel.rs	16.66%	10 Missing ⚠️
lightning/src/ln/channelmanager.rs	0.00%	3 Missing ⚠️
lightning/src/ln/wire.rs	0.00%	3 Missing ⚠️
lightning-net-tokio/src/lib.rs	0.00%	1 Missing ⚠️
lightning/src/ln/msgs.rs	87.50%	1 Missing ⚠️
lightning/src/util/test_utils.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3793      +/-   ##
==========================================
- Coverage   89.91%   89.84%   -0.07%     
==========================================
  Files         160      160              
  Lines      129307   129375      +68     
  Branches   129307   129375      +68     
==========================================
- Hits       116270   116241      -29     
- Misses      10349    10438      +89     
- Partials     2688     2696       +8

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TheBlueMatt · 2025-06-08T16:50:20Z

lightning/src/ln/msgs.rs

+	/// The number of messages to follow.
+	pub batch_size: u16,
+	/// The type of all messages expected in the batch.
+	pub message_type: Option<u16>,


Why is this an Option if we require it?

The spec doesn't spell out the requirements yet, but I assumed we'd need to send a warning before disconnecting. Also allows for additional logging.

jkczyz requested a review from TheBlueMatt May 22, 2025 17:11

wpaulino requested review from wpaulino and removed request for TheBlueMatt May 22, 2025 17:40

wpaulino reviewed May 22, 2025

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jkczyz force-pushed the 2025-05-start-batch branch from 97118cf to b2d073f Compare May 23, 2025 16:57

jkczyz mentioned this pull request May 23, 2025

Channel Splicing (feature 62/63) lightning/bolts#1160

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jkczyz commented May 23, 2025

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jkczyz force-pushed the 2025-05-start-batch branch from b2d073f to 5110534 Compare May 23, 2025 21:39

jkczyz requested a review from wpaulino May 23, 2025 21:41

wpaulino reviewed May 29, 2025

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jkczyz force-pushed the 2025-05-start-batch branch from 5110534 to c6d62c9 Compare May 29, 2025 18:17

jkczyz force-pushed the 2025-05-start-batch branch from c6d62c9 to f373238 Compare May 30, 2025 19:40

jkczyz force-pushed the 2025-05-start-batch branch from f373238 to ebf0d4e Compare June 2, 2025 20:00

jkczyz requested a review from wpaulino June 2, 2025 20:47

wpaulino requested review from TheBlueMatt and removed request for wpaulino June 2, 2025 20:59

jkczyz mentioned this pull request Jun 3, 2025

Introduce RenegotiatedFunding monitor update variant #3822

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TheBlueMatt previously approved these changes Jun 4, 2025

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jkczyz dismissed TheBlueMatt’s stale review via b4f9039 June 5, 2025 20:43

jkczyz force-pushed the 2025-05-start-batch branch from ebf0d4e to b4f9039 Compare June 5, 2025 20:43

jkczyz added 4 commits June 5, 2025 15:43

Add support for batches of other types

d4bbd42

While the spec only includes commitment_signed messages in batches, there may be other types of batches in the future. Generalize the message batching code to allow for other types in the future.

Fail channel for batched commitment_signed appropriately

43db395

If a message in a commitment_signed batch does not contain a funding_txid or has duplicates, the channel should be failed. Move this check from PeerManager to FundedChannel such that this can be done.

jkczyz force-pushed the 2025-05-start-batch branch from b4f9039 to 43db395 Compare June 5, 2025 21:05

jkczyz requested review from TheBlueMatt and wpaulino June 6, 2025 15:25

wpaulino approved these changes Jun 6, 2025

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TheBlueMatt approved these changes Jun 8, 2025

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TheBlueMatt merged commit ca2de2b into lightningdevkit:main Jun 8, 2025
27 of 28 checks passed

jkczyz mentioned this pull request Jun 12, 2025

Check if a batch is expected for commitment_signed #3852

Merged

jkczyz mentioned this pull request Jun 21, 2025

Dual-funded channels and Splicing Project Tracking #1621

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Implement start_batch message batching #3793

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Implement `start_batch` message batching #3793

Implement `start_batch` message batching #3793

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