From 41c78b8d980438bba76f3c3d9eabe8705af0d87e Mon Sep 17 00:00:00 2001
From: Csaba Kiraly <csaba.kiraly@gmail.com>
Date: Wed, 22 Nov 2023 14:27:48 +0100
Subject: [PATCH] decode: fix CID assigned to padding block

Signed-off-by: Csaba Kiraly <csaba.kiraly@gmail.com>
---
 codex/erasure/erasure.nim | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/codex/erasure/erasure.nim b/codex/erasure/erasure.nim
index 3b82f9df..d22aee51 100644
--- a/codex/erasure/erasure.nim
+++ b/codex/erasure/erasure.nim
@@ -463,7 +463,8 @@ proc decode*(
 
         for i in 0..<encoded.ecK:
           let idx = newIndex(encoded, step, column, i)
-          if data[i].len <= 0 and not cids[idx].isEmpty:
+          if data[i].len <= 0 and not (cids[idx].isEmpty or encoded.isPadding(idx)):
+            # if block was missing, and it wasn't padding, restore the block
             without blk =? bt.Block.new(recovered[i]), error:
               trace "Unable to create block!", exc = error.msg
               return failure(error)
@@ -475,6 +476,10 @@ proc decode*(
 
             cids[idx] = blk.cid
             recoveredIndices.add(idx)
+          elif data[i].len <= 0 and encoded.isPadding(idx):
+            without emptyBlockCid =? emptyCid(encoded.version, encoded.hcodec, encoded.codec), err:
+              return failure(err)
+            cids[idx] = emptyBlockCid
   except CancelledError as exc:
     trace "Erasure coding decoding cancelled"
     raise exc # cancellation needs to be propagated