fix: worst case share indexes (#49)

square/builder.go

@@ -88,7 +88,7 @@ func (b *Builder) AppendBlobTx(blobTx *blob.BlobTx) bool {
 	iw := &blob.IndexWrapper{
 		Tx:           blobTx.Tx,
 		TypeId:       blob.ProtoIndexWrapperTypeID,
-		ShareIndexes: worstCaseShareIndexes(len(blobTx.Blobs), b.maxSquareSize),
+		ShareIndexes: worstCaseShareIndexes(len(blobTx.Blobs)),
 	}
 	size := proto.Size(iw)
 	pfbShareDiff := b.PfbCounter.Add(size)
@@ -407,14 +407,21 @@ func (e Element) maxShareOffset() int {
 	return e.NumShares + e.MaxPadding
 }
 
-// worstCaseShareIndexes returns the largest possible share indexes for a set
-// of blobs at a given appversion. Largest possible is "worst" in that protobuf
-// uses varints to encode integers, so larger integers can require more bytes to
-// encode.
-func worstCaseShareIndexes(blobs, maxSquareSize int) []uint32 {
+// worstCaseShareIndexes returns the largest possible share indexes for a set of
+// blobs. Largest possible is "worst" in that protobuf uses varints to encode
+// integers, so larger integers can require more bytes to encode.
+//
+// Note: the implementation of this function assumes that the worst case share
+// index is always 128 * 128 to preserve backwards compatibility with
+// celestia-app v1.x.
+func worstCaseShareIndexes(blobs int) []uint32 {
+	// TODO: de-duplicate this constant with celestia-app SquareSizeUpperBound constant.
+	// https://github.com/celestiaorg/celestia-app/blob/a93bb625c6dc0ae6c7c357e9991815a68ab33c79/pkg/appconsts/v1/app_consts.go#L5
+	squareSizeUpperBound := 128
+	worstCaseShareIndex := squareSizeUpperBound * squareSizeUpperBound
 	shareIndexes := make([]uint32, blobs)
 	for i := range shareIndexes {
-		shareIndexes[i] = uint32(maxSquareSize * maxSquareSize)
+		shareIndexes[i] = uint32(worstCaseShareIndex)
 	}
 	return shareIndexes
 }

square/builder_test.go

@@ -2,6 +2,8 @@ package square_test
 
 import (
 	"bytes"
+	_ "embed"
+	"encoding/json"
 	"fmt"
 	"math/rand"
 	"testing"
@@ -341,3 +343,33 @@ func generateBlobTxsWithNamespaces(namespaces []namespace.Namespace, blobSizes [
 	}
 	return txs
 }
+
+type block struct {
+	Txs [][]byte `protobuf:"bytes,1,rep,name=txs,proto3" json:"txs,omitempty"`
+}
+
+// TestBigBlock indirectly verifies that the worst case share padding
+// calculation is computed using the rules on celestia-app v1.x. This test does
+// so by using a big_block.json file generated via celestia-app v1.x and then
+// verifies the share index of a particular blob. Note: if worst case share
+// padding is modified then we expect this test to fail and need a new valid
+// testdata/big_block.json.
+//
+// https://github.com/celestiaorg/go-square/issues/47
+func TestBigBlock(t *testing.T) {
+	bigBlock := block{}
+	err := json.Unmarshal([]byte(bigBlockJSON), &bigBlock)
+	require.NoError(t, err)
+
+	builder, err := square.NewBuilder(defaultMaxSquareSize, defaultSubtreeRootThreshold, bigBlock.Txs...)
+	require.NoError(t, err)
+	assert.Len(t, builder.Blobs, 84)
+	assert.Len(t, builder.Pfbs, 25)
+
+	index, err := builder.FindBlobStartingIndex(0, 0)
+	require.NoError(t, err)
+	assert.Equal(t, 2234, index)
+}
+
+//go:embed "testdata/big_block.json"
+var bigBlockJSON string