Open and accept zero reserve channels

[tankyleo]

Fixes #1801

[ldk-reviews-bot]

👋 Thanks for assigning @TheBlueMatt 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.

[codecov]

Codecov Report

❌ Patch coverage is 78.74818% with 146 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.91%. Comparing base (14e522f) to head (5fa3a7c).
⚠️ Report is 25 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/channel.rs	70.64%	121 Missing and 2 partials ⚠️
lightning/src/ln/channelmanager.rs	81.70%	15 Missing ⚠️
lightning/src/ln/functional_test_utils.rs	94.33%	6 Missing ⚠️
lightning/src/sign/tx_builder.rs	97.46%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4428      +/-   ##
==========================================
- Coverage   85.94%   85.91%   -0.03%     
==========================================
  Files         159      159              
  Lines      104644   105103     +459     
  Branches   104644   105103     +459     
==========================================
+ Hits        89934    90298     +364     
- Misses      12204    12300      +96     
+ Partials     2506     2505       -1     

Flag	Coverage Δ
tests	85.91% <78.74%> (-0.03%)	⬇️

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[TheBlueMatt]

chanmon_consistency needs to be updated to have a 0-reserve channel or two (I believe we now have three channels between each pair of peers, so we can just do it on a subset of them, in fact we could have three separate channel types for better coverage).

[TheBlueMatt]

nit: If that's the only difference let's say create_channel_to_trusted_peer_0_reserve? Nice to be explicit, imo.

[TheBlueMatt]

Two questions. Shouldn't we check that if a channel has the 0-reserve feature bit and if it is fail if the user isn't accepting 0-reserve? Also why shouldn't we just set it now? I'm not sure we need to bother with a staging bit, really, honestly...

[TheBlueMatt]

Needs rebase now :/

[tankyleo]

Needs rebase now :/

Let me know if you prefer I rebase first

[TheBlueMatt]

Feel free to go ahead and rebase and squash, yea.

[tankyleo]

Squash diff (do not click compare just above, I pushed the wrong branch, and later corrected it):

https://github.com/lightningdevkit/rust-lightning/compare/253db4d9a05cda43f74c2835448126d3205b27b8..43be438f70ba28ad7918e407026a78763ac2b368

[tankyleo]

git range-diff main 43be438 7fde002

1:  bfba6e993 ! 1:  b916c3596 Add inbound and outbound checks for zero reserve channels
    @@ lightning/src/ln/channel.rs: impl FundingScope {

                // New reserve values are based on the new channel value and are v2-specific
     -          let counterparty_selected_channel_reserve_satoshis =
    --                  Some(get_v2_channel_reserve_satoshis(post_channel_value, MIN_CHAN_DUST_LIMIT_SATOSHIS));
    +-                  get_v2_channel_reserve_satoshis(post_channel_value, MIN_CHAN_DUST_LIMIT_SATOSHIS);
     -          let holder_selected_channel_reserve_satoshis = get_v2_channel_reserve_satoshis(
     -                  post_channel_value,
     -                  context.counterparty_dust_limit_satoshis,
    @@ lightning/src/ln/channel.rs: impl FundingScope {
     +                  == 0
     +          {
     +                  // If we previously had a 0-value reserve, continue with the same reserve
    -+                  Some(0)
    ++                  0
     +          } else {
    -+                  Some(get_v2_channel_reserve_satoshis(post_channel_value, MIN_CHAN_DUST_LIMIT_SATOSHIS))
    ++                  get_v2_channel_reserve_satoshis(post_channel_value, MIN_CHAN_DUST_LIMIT_SATOSHIS)
     +          };
     +          let holder_selected_channel_reserve_satoshis =
     +                  if prev_funding.holder_selected_channel_reserve_satoshis == 0 {
    @@ lightning/src/sign/tx_builder.rs: fn get_next_commitment_stats(
        );

     @@ lightning/src/sign/tx_builder.rs: fn get_available_balances(
    -   let fee_spike_buffer_htlc =
                if channel_type.supports_anchor_zero_fee_commitments() { 0 } else { 1 };

    +   // Note that the feerate is 0 in zero-fee commitment channels, so this statement is a noop
     -  let local_feerate = feerate_per_kw
     +  let spiked_feerate = feerate_per_kw
                * if is_outbound_from_holder && !channel_type.supports_anchors_zero_fee_htlc_tx() {
2:  1f8ca6c66 = 2:  53fc9a354 Add 0-reserve to `accept_inbound_channel_from_trusted_peer`
3:  1b94f7cc3 = 3:  da0520818 Add `ChannelManager::create_channel_to_trusted_peer_0reserve`
4:  19b8d7943 = 4:  1905f94e7 Shakedown zero reserve channels
5:  de2366da4 = 5:  4e6a7527a Format `ChannelManager::create_channel_internal` and...
6:  43be438f7 = 6:  7fde002e7 Update `chanmon_consistency` to include 0FC and 0-reserve channels

[ldk-reviews-bot]

✅ Added second reviewer: @joostjager

[ldk-reviews-bot]

🔔 1st Reminder

Hey @TheBlueMatt @joostjager! 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.