Backport adjusting the BABE epoch index (#991)

* Backport adjusting the BABE epoch index * PR link
smol-dot · Aug 8, 2023 · abc961e · abc961e
1 parent c9a1693
commit abc961e
Show file tree

Hide file tree

Showing 2 changed files with 17 additions and 4 deletions.
diff --git a/lib/src/verify/babe.rs b/lib/src/verify/babe.rs
@@ -322,7 +322,16 @@ pub fn verify_header(config: VerifyConfig) -> Result<VerifySuccess, VerifyError>
         }
     };
 
-    // TODO: check that we didn't entirely skip an epoch?
+    // Calculate the epoch index of the epoch of the block.
+    // This is the vast majority of the time equal to `block_epoch_info.epoch_index`. However,
+    // if no block has been produced for an entire epoch, the value needs to be increased by the
+    // number of skipped epochs.
+    let block_epoch_index = block_epoch_info.epoch_index
+        + block_epoch_info
+            .start_slot_number
+            .map_or(0, |start_slot_number| {
+                (slot_number - start_slot_number) / config.slots_per_epoch
+            });
 
     // TODO: in case of epoch change, should also check the randomness value; while the runtime
     //       checks that the randomness value is correct, light clients in particular do not
@@ -354,7 +363,7 @@ pub fn verify_header(config: VerifyConfig) -> Result<VerifySuccess, VerifyError>
     let epoch_transition_target = match config.header.digest.babe_epoch_information() {
         None => None,
         Some((info, None)) => Some(chain_information::BabeEpochInformation {
-            epoch_index: block_epoch_info.epoch_index.checked_add(1).unwrap(),
+            epoch_index: block_epoch_index.checked_add(1).unwrap(),
             start_slot_number: Some(
                 block_epoch_info
                     .start_slot_number
@@ -368,7 +377,7 @@ pub fn verify_header(config: VerifyConfig) -> Result<VerifySuccess, VerifyError>
             allowed_slots: block_epoch_info.allowed_slots,
         }),
         Some((info, Some(epoch_cfg))) => Some(chain_information::BabeEpochInformation {
-            epoch_index: block_epoch_info.epoch_index.checked_add(1).unwrap(),
+            epoch_index: block_epoch_index.checked_add(1).unwrap(),
             start_slot_number: Some(
                 block_epoch_info
                     .start_slot_number
@@ -426,7 +435,7 @@ pub fn verify_header(config: VerifyConfig) -> Result<VerifySuccess, VerifyError>
         let transcript = {
             let mut transcript = merlin::Transcript::new(&b"BABE"[..]);
             transcript.append_u64(b"slot number", slot_number);
-            transcript.append_u64(b"current epoch", block_epoch_info.epoch_index);
+            transcript.append_u64(b"current epoch", block_epoch_index);
             transcript.append_message(b"chain randomness", &block_epoch_info.randomness[..]);
             transcript
         };

diff --git a/wasm-node/CHANGELOG.md b/wasm-node/CHANGELOG.md
@@ -7,6 +7,10 @@
 - The `operation-body-done`, `operation-call-done`, `operation-storage-done`, `operation-storage-items`, `operation-waiting-for-continue`, `operation-inaccessible`, and `operation-error` events, and the `closest-descendant-merkle-value`, `descendants-values`, and `descendants-hashes` item types of the new JSON-RPC API have been renamed and are now camelCased (`operationBodyDone`, `operationStorageItems`, `descendantsValues`, etc.), in accordance with the latest changes in the JSON-RPC API specification. ([#973](https://github.com/smol-dot/smoldot/pull/973))
 - The `chainSpec_unstable` JSON-RPC functions have been renamed to `chainSpec_v1`, in accordance with the latest changes in the JSON-RPC API specification. ([#989](https://github.com/smol-dot/smoldot/pull/989))
 
+### Fixed
+
+- A change in the logic of BABE has been backported. Smoldot no longer considers blocks as invalid after no block has been authored for an entire epoch. ([#991](https://github.com/smol-dot/smoldot/pull/991))
+
 ## 1.0.14 - 2023-07-26
 
 ### Changed