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refactor: simplify rebuildShares #197

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merged 3 commits into from
Jun 28, 2023
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@rootulp rootulp commented Jun 26, 2023

Closes #196

Since Decode returns original + parity shares, there is no need to separately rebuild the parity shares. This PR removes an unnecessary conditional inside rebuildShares which let us also remove a param to that function. After the refactor, a few helper methods were no longer used so they were also removed.

@rootulp rootulp self-assigned this Jun 26, 2023
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codecov bot commented Jun 26, 2023

Codecov Report

Merging #197 (fd86dfb) into master (9df814c) will decrease coverage by 0.57%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #197      +/-   ##
==========================================
- Coverage   81.36%   80.80%   -0.57%     
==========================================
  Files           7        7              
  Lines         526      500      -26     
==========================================
- Hits          428      404      -24     
+ Misses         58       57       -1     
+ Partials       40       39       -1     
Impacted Files Coverage Δ
extendeddatacrossword.go 70.94% <100.00%> (-2.71%) ⬇️

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@evan-forbes evan-forbes left a comment

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ahh okay so the encode and decode abstractions were (are?) leaky

@@ -249,7 +247,6 @@ func (eds *ExtendedDataSquare) solveCrosswordCol(
// 2. Whether the original shares could be decoded from the shares parameter.
// 3. [Optional] an error.
func (eds *ExtendedDataSquare) rebuildShares(
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do we need this function at all if its just decoding?

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@rootulp rootulp Jun 28, 2023

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good question, I can explore deleting it entirely in a FLUP issue

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TBH I'm only creating a new issue rather than tackling in this PR b/c I don't want to dismiss existing approvals 😞 #199

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LGTM! left two questions, but they are non-blocking as long as we are certain about them.

@@ -259,25 +256,6 @@ func (eds *ExtendedDataSquare) rebuildShares(
return nil, false, nil
}

if isExtendedPartIncomplete {
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[Question] I suppose there have not been any tests associated with this part of the code, as no test file has been updated in this PR, right?

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@@ -259,25 +256,6 @@ func (eds *ExtendedDataSquare) rebuildShares(
return nil, false, nil
}

if isExtendedPartIncomplete {
// If needed, rebuild the parity shares too.
rebuiltExtendedShares, err := eds.codec.Encode(rebuiltShares[0:eds.originalDataWidth])
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[Question] The only potential issue could arise if the parity portion is incomplete and the rebuilt extended shares obtained from rebuiltShares, err := eds.codec.Decode(shares) (the second half of rebuiltShares) and rebuiltExtendedShares, err := eds.codec.Encode(rebuiltShares[0:eds.originalDataWidth]) turn out to be different. Have we conducted any tests to verify this?

In the original code, we initially decode the entire row, and if the extended part (before decoding) is incomplete, we discard that part from the decoded version and replace it with the encoding result. However, in the new version, we retain whatever the decode function provides us with. If we are confident that these two have the same result, then everything looks good to me! (I think they should be the same)

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The only potential issue could arise if the parity portion is incomplete

I don't expect this to happen because Decode calls Reconstruct here and the godoc for Reconstruct claims:

// If there are too few shards to reconstruct the missing
// ones, ErrTooFewShards will be returned.

Ref: https://github.com/klauspost/reedsolomon/blob/523164698be98f1603cf1235f5a1de17728b2091/reedsolomon.go#L56-L57

@rootulp rootulp merged commit 2557620 into celestiaorg:master Jun 28, 2023
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Why rebuild extended shares?
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