add: recover matrix (#6553)

AllTests-mainnet.md

@@ -539,8 +539,9 @@ OK: 1/1 Fail: 0/1 Skip: 0/1
 ## EIP-7594 Unit Tests
 ```diff
 + EIP-7594: Compute Matrix                                                                   OK
++ EIP:7594: Recover Matrix                                                                   OK
 ```
-OK: 1/1 Fail: 0/1 Skip: 0/1
+OK: 2/2 Fail: 0/2 Skip: 0/2
 ## EL Configuration
 ```diff
 + Empty config file                                                                          OK
@@ -1124,4 +1125,4 @@ OK: 2/2 Fail: 0/2 Skip: 0/2
 OK: 9/9 Fail: 0/9 Skip: 0/9
 
 ---TOTAL---
-OK: 761/766 Fail: 0/766 Skip: 5/766
+OK: 762/767 Fail: 0/767 Skip: 5/767

beacon_chain/spec/eip7594_helpers.nim

@@ -120,6 +120,41 @@ proc compute_matrix*(blobs: seq[KzgBlob]): Result[seq[MatrixEntry], cstring] =
 
   ok(extended_matrix)
 
+# https://github.com/ethereum/consensus-specs/blob/v1.5.0-alpha.5/specs/_features/eip7594/das-core.md#recover_matrix
+proc recover_matrix*(partial_matrix: seq[MatrixEntry],
+                     blobCount: int): 
+                     Result[seq[MatrixEntry], cstring] =
+  ## This helper demonstrates how to apply recover_cells_and_kzg_proofs
+  ## The data structure for storing cells is implementation-dependent
+  var extended_matrix: seq[MatrixEntry]
+  for blob_index in 0..<blobCount:
+    var
+      cell_indices: seq[CellIndex]
+      cells: seq[Cell]
+
+    for e in partial_matrix:
+      if e.row_index == uint64(blob_index):
+        cell_indices.add(e.column_index)
+        cells.add(e.cell)
+
+    let recoveredCellsAndKzgProofs = 
+      recoverCellsAndKzgProofs(cell_indices, cells)
+    if not recoveredCellsAndKzgProofs.isOk:
+      return err("Issue in recovering cells and proofs")
+
+    for i in 0..<recoveredCellsAndKzgProofs.get.cells.len:
+      let 
+        cell = recoveredCellsAndKzgProofs.get.cells[i]
+        proof = recoveredCellsAndKzgProofs.get.proofs[i]
+      extended_matrix.add(MatrixEntry(
+        cell: cell,
+        kzg_proof: proof,
+        row_index: blob_index.uint64,
+        column_index: i.uint64
+      ))
+
+  ok(extended_matrix)
+
 # https://github.com/ethereum/consensus-specs/blob/v1.5.0-alpha.5/specs/_features/eip7594/peer-sampling.md#get_extended_sample_count
 func get_extended_sample_count*(samples_per_slot: int,
                                 allowed_failures: int):

tests/test_eip7594_helpers.nim

@@ -66,6 +66,34 @@ suite "EIP-7594 Unit Tests":
         doAssert len(row) == kzg_abi.CELLS_PER_EXT_BLOB
     testComputeExtendedMatrix()
 
+  test "EIP:7594: Recover Matrix":
+    proc testRecoverMatrix() =
+      var rng = initRand(126)
+
+      # Number of samples we shall be recovering
+      const N_SAMPLES = kzg_abi.CELLS_PER_EXT_BLOB div 2
+
+      # Compute an extended matrix with a random
+      # blob count for this test
+      let
+        blob_count = rng.rand(1..(NUMBER_OF_COLUMNS.int))
+        blobs = createSampleKzgBlobs(blob_count, rng.rand(int))
+        extended_matrix = compute_matrix(blobs)
+
+      # Construct a matrix with some entries missing
+      var partial_matrix: seq[MatrixEntry]
+      for blob_entries in chunks(extended_matrix.get, kzg_abi.CELLS_PER_EXT_BLOB):
+        var blb_entry = blob_entries
+        rng.shuffle(blb_entry)
+        partial_matrix.add(blb_entry[0..N_SAMPLES-1])
+
+      # Given the partial matrix, recover the missing entries
+      let recovered_matrix = recover_matrix(partial_matrix, blob_count)
+
+      # Ensure that the recovered matrix matches the original matrix
+      doAssert recovered_matrix.get == extended_matrix.get, "Both matrices don't match!"
+    testRecoverMatrix()
+
 suite "EIP-7594 Sampling Tests":
   test "EIP7594: Extended Sample Count":
     proc testExtendedSampleCount() =