From a0eb396289624ce4a048bc83549387b7aac7a2b4 Mon Sep 17 00:00:00 2001
From: Gus Gutoski <ggutoski@users.noreply.github.com>
Date: Wed, 26 Jun 2024 10:25:54 -0400
Subject: [PATCH] empty namespace table implies empty block payload, with tests

---
 sequencer/src/block/full_payload/ns_table.rs  | 12 ++++++----
 .../src/block/full_payload/ns_table/test.rs   | 22 +++++++++++++++++++
 2 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/sequencer/src/block/full_payload/ns_table.rs b/sequencer/src/block/full_payload/ns_table.rs
index 779d12c09..50ce3489e 100644
--- a/sequencer/src/block/full_payload/ns_table.rs
+++ b/sequencer/src/block/full_payload/ns_table.rs
@@ -221,10 +221,11 @@ impl NsTable {
     /// 1. Byte length must hold a whole number of entries.
     /// 2. All namespace IDs and offsets must increase monotonically. Offsets
     ///    must be nonzero.
-    /// 3. Header consistent with byte length (obsolete after
-    ///    <https://github.com/EspressoSystems/espresso-sequencer/issues/1604>)
-    /// 4. Final offset must equal `payload_byte_len` (obsolete after
-    ///    <https://github.com/EspressoSystems/espresso-sequencer/issues/1604>)
+    /// 3. Header consistent with byte length. (Obsolete after
+    ///    <https://github.com/EspressoSystems/espresso-sequencer/issues/1604>.)
+    /// 4. Final offset must equal `payload_byte_len`. (Obsolete after
+    ///    <https://github.com/EspressoSystems/espresso-sequencer/issues/1604>.)
+    ///    If the namespace table is empty then `payload_byte_len` must be 0.
     pub fn validate(
         &self,
         payload_byte_len: &PayloadByteLen,
@@ -242,6 +243,8 @@ impl NsTable {
             if final_offset != payload_byte_len.as_usize() {
                 return Err(InvalidFinalOffset);
             }
+        } else if payload_byte_len.as_usize() != 0 {
+            return Err(ExpectNonemptyNsTable);
         }
 
         Ok(())
@@ -372,6 +375,7 @@ pub enum NsTableValidationError {
     NonIncreasingEntries,
     InvalidHeader, // TODO this variant obsolete after https://github.com/EspressoSystems/espresso-sequencer/issues/1604
     InvalidFinalOffset, // TODO this variant obsolete after https://github.com/EspressoSystems/espresso-sequencer/issues/1604
+    ExpectNonemptyNsTable,
 }
 
 pub struct NsTableBuilder {
diff --git a/sequencer/src/block/full_payload/ns_table/test.rs b/sequencer/src/block/full_payload/ns_table/test.rs
index 47a22b53c..df92d25e1 100644
--- a/sequencer/src/block/full_payload/ns_table/test.rs
+++ b/sequencer/src/block/full_payload/ns_table/test.rs
@@ -101,6 +101,28 @@ async fn payload_byte_len() {
 
     // final offset less than payload byte len
     modify_final_offset(-1);
+
+    // zero-length payload
+    let empty_block = Payload::from_transactions([], &Default::default(), &Default::default())
+        .await
+        .unwrap()
+        .0;
+    assert_eq!(empty_block.ns_table().len().0, 0);
+    assert_eq!(
+        empty_block.ns_table().bytes,
+        usize_to_bytes::<NUM_NSS_BYTE_LEN>(0)
+    );
+    empty_block
+        .ns_table()
+        .validate(&empty_block.byte_len())
+        .unwrap();
+
+    // empty namespace table with nonempty payload
+    *block.ns_table_mut() = empty_block.ns_table().clone();
+    assert_eq!(
+        block.ns_table().validate(&payload_byte_len).unwrap_err(),
+        ExpectNonemptyNsTable
+    );
 }
 
 #[test]