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Expose channel_reserve_satoshis via ChannelParameters #4319

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Expose channel_reserve_satoshis via ChannelParameters #4319

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@yashbhutwala yashbhutwala commented Jan 16, 2026

Summary

  • Add channel_reserve_satoshis: Option<u64> field to ChannelParameters struct
  • For V1 channels: Returns Some(value) with the explicit reserve from open_channel message
  • For V2 channels: Returns None since reserve is calculated from total channel value (initiator + acceptor funding), which isn't known at OpenChannelRequest time
  • Move channel_parameters() from CommonOpenChannelFields to individual OpenChannel and OpenChannelV2 impls to handle V1/V2 difference correctly
  • Add test test_open_channel_request_channel_reserve_satoshis to verify the implementation

Fixes #3909

Revives the closed PR #3910 with the approach suggested by reviewers:

  • Uses Option<u64> instead of trying to read from wire for V2 (which doesn't have this field)
  • Follows @wpaulino's suggestion to move channel_parameters() to OpenChannel/OpenChannelV2
  • Properly documents the V1 vs V2 behavior

Test plan

  • cargo check -p lightning passes
  • All 1191 lightning tests pass (cargo test -p lightning --lib)
  • New test test_open_channel_request_channel_reserve_satoshis validates V1 channels correctly populate the field
  • All 41 channel_open_tests pass

🤖 Generated with Claude Code

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ldk-reviews-bot commented Jan 16, 2026 •
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👋 Thanks for assigning @tankyleo as a reviewer!
I'll wait for their review and will help manage the review process.
Once they submit their review, I'll check if a second reviewer would be helpful.

@yashbhutwala
Expose channel_reserve_satoshis via ChannelParameters
2f585af 
Add `channel_reserve_satoshis: Option<u64>` to `ChannelParameters` so
users can access the counterparty's channel reserve when handling the
`OpenChannelRequest` event.

For V1 channels (`open_channel`), this returns `Some(value)` with the
explicit reserve from the message.

For V2 channels (`open_channel2`), this returns `None` because the
reserve is calculated as `max(1% of total_channel_value, dust_limit)`
per spec, where total_channel_value includes both parties' funding.
Since the acceptor's contribution is unknown at `OpenChannelRequest`
time, the final reserve cannot be determined.

Move `channel_parameters()` from `CommonOpenChannelFields` to separate
implementations on `OpenChannel` and `OpenChannelV2` to handle the
V1/V2 difference correctly.

Fixes lightningdevkit#3909
@yashbhutwala yashbhutwala force-pushed the expose-channel-reserve-satoshis branch from cd475ee to 2f585af Compare January 16, 2026 16:28
@yashbhutwala yashbhutwala mentioned this pull request Jan 16, 2026
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codecov bot commented Jan 16, 2026 •
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Codecov Report

❌ Patch coverage is 51.72414% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.60%. Comparing base (4281e49) to head (2f585af).
⚠️ Report is 3 commits behind head on main.

Files with missing lines Patch % Lines
lightning/src/ln/msgs.rs 50.00% 13 Missing ⚠️
lightning/src/ln/channelmanager.rs 66.66% 1 Missing ⚠️
Additional details and impacted files 
@@            Coverage Diff             @@
##             main    #4319      +/-   ##
==========================================
- Coverage   86.61%   86.60%   -0.01%     
==========================================
  Files         158      158              
  Lines      102730   102748      +18     
  Branches   102730   102748      +18     
==========================================
+ Hits        88977    88989      +12     
- Misses      11335    11342       +7     
+ Partials     2418     2417       -1
Flag Coverage Δ
fuzzing 36.08% <51.72%> (-1.01%) ⬇️
tests 85.90% <51.72%> (-0.01%) ⬇️

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@tankyleo tankyleo self-requested a review January 16, 2026 18:14
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ldk-reviews-bot commented Jan 19, 2026

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Hey @valentinewallace @tankyleo! This PR has been waiting for your review.
Please take a look when you have a chance. If you're unable to review, please let us know so we can find another reviewer.

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ldk-reviews-bot commented Jan 19, 2026

🔔 1st Reminder

Hey @valentinewallace @tankyleo! This PR has been waiting for your review.
Please take a look when you have a chance. If you're unable to review, please let us know so we can find another reviewer.

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ldk-reviews-bot commented Jan 21, 2026

🔔 2nd Reminder

Hey @valentinewallace @tankyleo! This PR has been waiting for your review.
Please take a look when you have a chance. If you're unable to review, please let us know so we can find another reviewer.

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Please take a look when you have a chance. If you're unable to review, please let us know so we can find another reviewer.

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@valentinewallace valentinewallace Awaiting requested review from valentinewallace

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Expose channel_reserve_satoshis via ChannelParameters in OpenChannelRequest

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