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[KILO]: DynComms Prefactor: Refactor/evaluate htlc view #9097

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ProofOfKeags
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@ProofOfKeags ProofOfKeags commented Sep 12, 2024

Change Description

This is the next logical chunk extracted off the front of #8755. This is a pure refactor change. The core behavior of the code modified should be identical.

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make unit

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@ProofOfKeags ProofOfKeags added refactoring dynamic commitments size/kilo medium, proper context needed, less than 1000 lines labels Sep 12, 2024
@ProofOfKeags ProofOfKeags added this to the v0.19.0 milestone Sep 12, 2024
@ProofOfKeags ProofOfKeags self-assigned this Sep 12, 2024
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Nice refactor, simplifying power of Dual really shines 👌

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@yyforyongyu: review reminder
@ziggie1984: review reminder
@ProofOfKeags, remember to re-request review from reviewers when ready

@ProofOfKeags ProofOfKeags changed the title [KILO]: Refactor/evaluate htlc view [KILO]: DynComms Prefactor: Refactor/evaluate htlc view Oct 2, 2024
@ProofOfKeags ProofOfKeags force-pushed the refactor/evaluate-htlc-view branch 2 times, most recently from 238720a to d2e2ef6 Compare October 8, 2024 08:54
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Nothing major left from me, will take a final pass when CI is happy + second reviewer has taken a look 👍 Screenshot 2024-10-08 at 2 26 44 PM

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// corresponding to whoseCommitmentChain.
isUncommitted := func(update *paymentDescriptor) bool {
switch update.EntryType {
case Add:
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Just looking for a sanity check on my understanding here, nothing actionable:

  • Previously we would only mutate entries with zero add height that are not in skipUs/skipThem maps.
  • This change reduces the check to only look at add height.

This is okay because:

  • An Add entry is only in skipUs / skipThem if a settle/fail entry exits for them in the other party's log.
  • We can't have an Add with zero add height in the skip list, because the add MUST be irrevocably committed before we try to resolve it

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Yes that's right. However I'd also offer a different way of looking at it:

  • Adds only ever have the add height set.
  • Settles/Fails only have the remove height set.
  • FeeUpdates have both.
  • The definition of "uncommitted" is not having the correct entry from the above list set.
  • The point of returning the uncommitted updates is that we want to set the heights in the outer scope as opposed to threading the mutateState argument.
  • When the next height gets locked in, everything that is uncommitted gets its heights set (for the given whoseCommitChain)

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// TestProcessAddRemoveEntry tests the updating of our and their balances when
// we process adds, settles and fails. It also tests the mutating of add and
// remove heights.
func TestProcessAddRemoveEntry(t *testing.T) {
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CI failing rn, but I would like to sanity check coveralls to make sure we're not losing any coverage before merge.

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Splendid refactor 🤩,

Approving when the CI passes.

Also I agree with Carla to not lose coverage here while removing some code parts.

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Most of my questions have been addressed offline, and just need to get the CI to pass.

The purpose of this commit is to begin the process of packing
symmetric fields into the newly introduced Dual structure. The
reason for this is that the Dual structure has a handy indexing
method where we can supply a ChannelParty and get back a value.
This will cut down on the amount of branching code in the main
lines of the codebase logic, making it easier to follow what is
going on.
This commit begins the process of moving towards a more principled
means of state tracking. We eliminate the mutateState argument from
processAddEntry and processRemoveEntry and move the responsibility
of mutating said state to the call-sites.

The current call-sites of these functions still have their *own*
mutateState argument which will be eliminated during upcoming commits.
However, following the principle of micro-commits I opted to break
these changes up to make review simpler.
This commit redoes the API and semantics of processFeeUpdate to make
it consistent with the semantics of it's sister functions. This is
part of an ongoing series of commits to remove mutateState arguments
pervasively from the codebase.

As with the previous commit this makes state mutation the caller's
responsibility. This temporarily increases code duplication at the
call-sites, but this will unlock other refactor opportunities.
In this commit we observe that the previous commit reduced the role
of this function to a single assignment statement with numerous newly
irrelevant parameters. This commit makes the choice of inlining it at
the two call-sites within evaluateHTLCView and removing the funciton
definition entirely. This also allows us to drop a huge portion of
newly irrelevant test code.
@ProofOfKeags ProofOfKeags force-pushed the refactor/evaluate-htlc-view branch 4 times, most recently from 7126446 to 7e3cfe2 Compare October 11, 2024 10:58
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CI is "as green as it gets". Coveralls unit is flat. All comments addressed. One possible TODO outstanding launched by a comment from @carlaKC. Re-requesting for final confirmation.

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Just reviewed the push diff, LGTM!

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Had a final question regarding the removed tests.

Can you rerun the CI / check commits (pull_request) test

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}
}

// TestProcessAddRemoveEntry tests the updating of our and their balances when
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I understand that we do not need to check the mutate state anymore but where do we now test that the balances are updated correctly for the different payment descriptors ?

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Moreover the mutation is now pulled out into an upper level, are there unit-tests for it ? Cannot see a unit-test for computeView which now does the mutating now, maybe we could add one ?

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as in the lifetime payment flows? I can try to design a test around that but I don't think the lifetime payment flow stuff is mission critical. With regards to the state updates of the payment descriptor commit heights, that is already implicitly tested by the itests during any payment that gets made, I think.

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ok normally I tend to favour having a complete unit-test suite rather than relying on itests, but given the fact that computeview had no unit-test beforehand having an unit-test for computeView would be nice but it's a non-blocking comment.

In line with previous commits we are progressively removing the
mutateState argument from this call stack for a more principled
software design approach.

NOTE FOR REVIEWERS:
We take a naive approach to updating the tests here and simply
take the functionality we are removing from evaluateHTLCView and
run it directly after the function in the test suite.

It's possible that we should instead remove this from the test
suite altogether but I opted to take a more conservative approach
with respect to reducing the scope of tests. If you have opinions
here, please make them known.
This commit removes another raw boolean value and replaces it with
a more clear type/name. This will also assist us when we later try
and consolidate the logic of evaluateHTLCView into a single
coherent computation.
This commit moves the collection of updates behind a Dual structure.
This allows us in a later commit to index into it via a ChannelParty
parameter which will simplify the loops in evaluateHTLCView.
This commit simplifies how we compute the commitment fee rate based
off of the live updates. Prior to this commit we processed all of
the FeeUpdate paymentDescriptors of both ChannelParty's. Now we only
process the last FeeUpdate of the OpeningParty
We had four for-loops in evaluateHTLCView that were exact mirror
images of each other. By making use of the new ChannelParty and
Dual facilities introduced in prior commits, we consolidate these
into two for-loops.
This further reduces loop complexity in evaluateHTLCView by using
explicit filter steps rather than loop continue statements.
This commit observes that processAddEntry and processRemoveEntry
are only invoked at a single call-site. Here we inline them at their
call-sites, which will unlock further simplifications of the code
that will allow us to remove pointer mutations in favor of explicit
expression oriented programming.

We also delete the tests associated with these functions, the overall
functionality is implicitly tested by the TestEvaluateHTLCView tests.
Here we return the balance deltas from evaluateHTLCView rather than
passing in references to variables that will be modified. It is a
far cleaner and compositional approach which allows readers of this
code to more effectively reason about the code without having to
keep the whole codebase in their head.
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Can you rerun the CI / check commits (pull_request) test

It has been re-run and has passed.

@ProofOfKeags ProofOfKeags merged commit 7bf9b59 into lightningnetwork:master Oct 14, 2024
31 of 34 checks passed
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