From 0936723c815fc6fc72aaa2f5c97e1c6f9a8d89e4 Mon Sep 17 00:00:00 2001
From: Yiannis Marangos <yiannis@eiger.co>
Date: Mon, 11 Mar 2024 07:53:12 +0200
Subject: [PATCH] feat(types): Add constructor for creating EDS of an empty
 block (#241)

---
 types/src/rsmt2d.rs     | 26 +++++++++++++++++++++++++-
 types/src/test_utils.rs | 16 +++-------------
 2 files changed, 28 insertions(+), 14 deletions(-)

diff --git a/types/src/rsmt2d.rs b/types/src/rsmt2d.rs
index c3bd8294..ea2eb7bf 100644
--- a/types/src/rsmt2d.rs
+++ b/types/src/rsmt2d.rs
@@ -9,7 +9,7 @@ use crate::consts::data_availability_header::{
 };
 use crate::namespaced_data::{NamespacedData, NamespacedDataId};
 use crate::nmt::{Namespace, NamespacedSha2Hasher, Nmt, NmtExt, NS_SIZE};
-use crate::{bail_validation, DataAvailabilityHeader, Error, Result};
+use crate::{bail_validation, DataAvailabilityHeader, Error, InfoByte, Result};
 
 /// Represents either column or row of the [`ExtendedDataSquare`].
 ///
@@ -237,6 +237,19 @@ impl ExtendedDataSquare {
         Ok(eds)
     }
 
+    /// Crate a new EDS that represents an empty block
+    pub fn empty() -> ExtendedDataSquare {
+        // ODS in this case it is just one tail padded share.
+        let ods = vec![[
+            Namespace::TAIL_PADDING.as_bytes(),
+            &[InfoByte::new(0, true).unwrap().as_u8()],
+            &[0; SHARE_SIZE - NS_SIZE - 1],
+        ]
+        .concat()];
+
+        ExtendedDataSquare::from_ods(ods).expect("invalid EDS")
+    }
+
     /// Create a new EDS out of the provided original data square shares.
     ///
     /// This method is similar to the [`ExtendedDataSquare::new`] but parity data
@@ -466,6 +479,7 @@ pub(crate) fn is_ods_square(row: u16, column: u16, square_width: u16) -> bool {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::ExtendedHeader;
 
     #[test]
     fn axis_type_serialization() {
@@ -716,4 +730,14 @@ mod tests {
         ExtendedDataSquare::new(vec![share(1); square_width.pow(2)], "fake".to_string())
             .unwrap_err();
     }
+
+    #[test]
+    fn empty_block_eds() {
+        let s = include_str!("../test_data/chain1/extended_header_block_1.json");
+        let genesis: ExtendedHeader = serde_json::from_str(s).unwrap();
+
+        let eds = ExtendedDataSquare::empty();
+        let dah = DataAvailabilityHeader::from_eds(&eds);
+        assert_eq!(dah, genesis.dah);
+    }
 }
diff --git a/types/src/test_utils.rs b/types/src/test_utils.rs
index 34d40c5b..d65199e7 100644
--- a/types/src/test_utils.rs
+++ b/types/src/test_utils.rs
@@ -12,7 +12,7 @@ pub use crate::byzantine::test_utils::corrupt_eds;
 use crate::consts::appconsts::{SHARE_INFO_BYTES, SHARE_SIZE};
 use crate::consts::version;
 use crate::hash::{Hash, HashExt};
-use crate::nmt::{Namespace, NamespacedHash, NamespacedHashExt, NS_SIZE};
+use crate::nmt::{Namespace, NS_SIZE};
 use crate::{DataAvailabilityHeader, ExtendedDataSquare, ExtendedHeader, ValidatorSet};
 
 /// [`ExtendedHeader`] generator for testing purposes.
@@ -411,12 +411,7 @@ fn generate_new(
                 proposer_priority: 0_i64.into(),
             }),
         ),
-        dah: dah.unwrap_or_else(|| {
-            DataAvailabilityHeader::new_unchecked(
-                vec![NamespacedHash::empty_root(), NamespacedHash::empty_root()],
-                vec![NamespacedHash::empty_root(), NamespacedHash::empty_root()],
-            )
-        }),
+        dah: dah.unwrap_or_else(|| DataAvailabilityHeader::from_eds(&ExtendedDataSquare::empty())),
     };
 
     hash_and_sign(&mut header, signing_key);
@@ -485,12 +480,7 @@ fn generate_next(
             }],
         },
         validator_set: current.validator_set.clone(),
-        dah: dah.unwrap_or_else(|| {
-            DataAvailabilityHeader::new_unchecked(
-                vec![NamespacedHash::empty_root(), NamespacedHash::empty_root()],
-                vec![NamespacedHash::empty_root(), NamespacedHash::empty_root()],
-            )
-        }),
+        dah: dah.unwrap_or_else(|| DataAvailabilityHeader::from_eds(&ExtendedDataSquare::empty())),
     };
 
     hash_and_sign(&mut header, signing_key);