From 34a2478113cca9763e6fcaa057acd759be78d3a2 Mon Sep 17 00:00:00 2001
From: Agnish Ghosh <iamagnix@gmail.com>
Date: Wed, 26 Jun 2024 16:05:58 +0530
Subject: [PATCH] add: blob recovery logic

---
 beacon_chain/spec/eip7594_helpers.nim | 53 +++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/beacon_chain/spec/eip7594_helpers.nim b/beacon_chain/spec/eip7594_helpers.nim
index cd3cd14d5..353238c34 100644
--- a/beacon_chain/spec/eip7594_helpers.nim
+++ b/beacon_chain/spec/eip7594_helpers.nim
@@ -140,6 +140,59 @@ proc recover_matrix*(partial_matrix: seq[MatrixEntry], blobCount: int): Result[s
         cells.add(e.cell)
         proofs.add(e.kzg_proof)
 
+proc recover_blobs*(
+    data_columns: seq[DataColumnSidecar],
+    columnCount: int,
+    blck: deneb.SignedBeaconBlock | 
+    electra.SignedBeaconBlock |
+    ForkySignedBeaconBlock):
+    Result[seq[KzgBlob], cstring] =
+
+  # This helper recovers blobs from the data column sidecars
+  if not (data_columns.len != 0):
+    return err("DataColumnSidecar: Length should not be 0")
+
+  var blobCount = data_columns[0].len
+  for data_column in data_columns:
+    if not (blobCount == data_column.column.len):
+      return err ("DataColumns do not have the same length")
+
+  var recovered_blobs = newSeqOfCap[KzgBlob](blobCount)
+
+  for blobIdx in 0 ..< blobCount:
+    var
+      cell_ids = newSeqOfCap[CellID](columnCount)
+      ckzgCells = newSeqOfCap[KzgCell](columnCount)
+
+    for data_column in data_columns:
+      cell_ids.add(data_column.index)
+
+      let 
+        column = data_column.column
+        cell = column[blobIdx]
+
+      # Transform the cell as a ckzg cell
+      var ckzgCell: Cell
+      for i in 0 ..< int(FIELD_ELEMENTS_PER_CELL):
+        ckzgCell[i] = cell[32*i ..< 32*(i+1)].toArray()
+
+      ckzgCells.add(ckzgCell)
+
+    # Recovering the blob
+    let recovered_cells = recoverAllCells(cell_ids, ckzgCells)
+    if not recovered_cells.isOk:
+      return err (fmt"Recovering all cells for blob - {blobIdx} failed: {recovered_cells.error}")
+
+    let recovered_blob_res = cellsToBlob(recovered_cells.get)
+    if not recovered_blob_res.isOk:
+      return err (fmt"Cells to blob for blob - {blobIdx} failed: {recovered_blob_res.error}")
+
+    recovered_blobs.add(recovered_blob_res.get)
+
+  ok(recovered_blobs)
+
+
+
 # https://github.com/ethereum/consensus-specs/blob/5f48840f4d768bf0e0a8156a3ed06ec333589007/specs/_features/eip7594/das-core.md#get_data_column_sidecars
 proc get_data_column_sidecars*(signed_block: deneb.SignedBeaconBlock | electra.SignedBeaconBlock | ForkySignedBeaconBlock, blobs: seq[KzgBlob]): Result[seq[DataColumnSidecar], cstring] =
   var