feat(blob): implement length method (celestiaorg#3606)

blob/blob.go

@@ -9,6 +9,7 @@ import (
 	tmproto "github.com/tendermint/tendermint/proto/tendermint/types"
 
 	"github.com/celestiaorg/celestia-app/pkg/appconsts"
+	"github.com/celestiaorg/celestia-app/pkg/shares"
 	"github.com/celestiaorg/celestia-app/x/blob/types"
 	"github.com/celestiaorg/nmt"
 
@@ -108,6 +109,30 @@ func (b *Blob) Index() int {
 	return b.index
 }
 
+// Length returns the number of shares in the blob.
+func (b *Blob) Length() (int, error) {
+	s, err := BlobsToShares(b)
+	if err != nil {
+		return 0, err
+	}
+
+	if len(s) == 0 {
+		return 0, errors.New("blob with zero shares received")
+	}
+
+	appShare, err := shares.NewShare(s[0])
+	if err != nil {
+		return 0, err
+	}
+
+	seqLength, err := appShare.SequenceLen()
+	if err != nil {
+		return 0, err
+	}
+
+	return shares.SparseSharesNeeded(seqLength), nil
+}
+
 func (b *Blob) compareCommitments(com Commitment) bool {
 	return bytes.Equal(b.Commitment, com)
 }

blob/blob_test.go

@@ -14,7 +14,8 @@ import (
 )
 
 func TestBlob(t *testing.T) {
-	appBlobs, err := blobtest.GenerateV0Blobs([]int{16}, false)
+	length := 16
+	appBlobs, err := blobtest.GenerateV0Blobs([]int{length}, false)
 	require.NoError(t, err)
 	blob, err := convertBlobs(appBlobs...)
 	require.NoError(t, err)
@@ -48,6 +49,14 @@ func TestBlob(t *testing.T) {
 				require.NoError(t, apptypes.ValidateBlobNamespace(ns))
 			},
 		},
+		{
+			name: "verify length",
+			expectedRes: func(t *testing.T) {
+				blobLength, err := blob[0].Length()
+				require.NoError(t, err)
+				assert.Equal(t, length, blobLength)
+			},
+		},
 		{
 			name: "shares to blobs",
 			expectedRes: func(t *testing.T) {

nodebuilder/blobstream/data_root_tuple_root.go

@@ -6,11 +6,10 @@ import (
 	"fmt"
 	"strconv"
 
-	nodeheader "github.com/celestiaorg/celestia-node/header"
-
 	"github.com/tendermint/tendermint/crypto/merkle"
 	"github.com/tendermint/tendermint/libs/bytes"
 
+	nodeheader "github.com/celestiaorg/celestia-node/header"
 	"github.com/celestiaorg/celestia-node/nodebuilder/header"
 )