fix: signal incompatibility in fec::decode

Needs review: stupid copy of fec::recode_random code.

src/fec.rs

@@ -445,6 +445,28 @@ pub fn decode<F: PrimeField>(shards: Vec<Shard<F>>) -> Result<Vec<u8>, KomodoErr
         return Err(KomodoError::TooFewShards(np, k as usize));
     }
 
+    // TODO: review code below, borrowed from recode_random()
+    for (i, (s1, s2)) in shards.iter().zip(shards.iter().skip(1)).enumerate() {
+        if s1.k != s2.k {
+            return Err(KomodoError::IncompatibleShards(format!(
+                "k is not the same at {}: {} vs {}",
+                i, s1.k, s2.k
+            )));
+        }
+        if s1.hash != s2.hash {
+            return Err(KomodoError::IncompatibleShards(format!(
+                "hash is not the same at {}: {:?} vs {:?}",
+                i, s1.hash, s2.hash
+            )));
+        }
+        if s1.size != s2.size {
+            return Err(KomodoError::IncompatibleShards(format!(
+                "size is not the same at {}: {} vs {}",
+                i, s1.size, s2.size
+            )));
+        }
+    }
+
     let encoding_mat = Matrix::from_vec_vec(
         shards
             .iter()

[STEVAN Antoine]

looks to me like this is now used in multiple places, maybe it will be time to refactor after this