miscelaneous fixes on syncing, rpc and responding to peer's sync related requests (#3827)

- there was a bug in responding range blob requests where we would incorrectly label the first slot of an epoch as a non-skipped slot if it were skipped. this bug did not exist in the code for responding to block range request because the logic error was mitigated by defensive coding elsewhere
- there was a bug where a block received during range sync without a corresponding blob (and vice versa) was incorrectly interpreted as a stream termination
- RPC size limit fixes.
- Our blob cache was dead locking so I removed use of it for now.
- Because of our change in finalized sync batch size from 2 to 1 and our transition to using exact epoch boundaries for batches (rather than one slot past the epoch boundary), we need to sync finalized sync to 2 epochs + 1 slot past our peer's finalized slot in order to finalize the chain locally.
- use fork context bytes in rpc methods on both the server and client side

beacon_node/network/src/beacon_processor/worker/rpc_methods.rs

@@ -433,7 +433,17 @@ impl<T: BeaconChainTypes> Worker<T> {
         };
 
         // Pick out the required blocks, ignoring skip-slots.
-        let mut last_block_root = None;
+        let mut last_block_root = req
+            .start_slot
+            .checked_sub(1)
+            .map(|prev_slot| {
+                self.chain
+                    .block_root_at_slot(Slot::new(prev_slot), WhenSlotSkipped::Prev)
+            })
+            .transpose()
+            .ok()
+            .flatten()
+            .flatten();
         let maybe_block_roots = process_results(forwards_block_root_iter, |iter| {
             iter.take_while(|(_, slot)| slot.as_u64() < req.start_slot.saturating_add(req.count))
                 // map skip slots to None
@@ -602,7 +612,17 @@ impl<T: BeaconChainTypes> Worker<T> {
         };
 
         // Pick out the required blocks, ignoring skip-slots.
-        let mut last_block_root = None;
+        let mut last_block_root = req
+            .start_slot
+            .checked_sub(1)
+            .map(|prev_slot| {
+                self.chain
+                    .block_root_at_slot(Slot::new(prev_slot), WhenSlotSkipped::Prev)
+            })
+            .transpose()
+            .ok()
+            .flatten()
+            .flatten();
         let maybe_block_roots = process_results(forwards_block_root_iter, |iter| {
             iter.take_while(|(_, slot)| slot.as_u64() < req.start_slot.saturating_add(req.count))
                 // map skip slots to None
@@ -669,7 +689,7 @@ impl<T: BeaconChainTypes> Worker<T> {
                 self.log,
                 "BlobsByRange Response processed";
                 "peer" => %peer_id,
-                "msg" => "Failed to return all requested blocks",
+                "msg" => "Failed to return all requested blobs",
                 "start_slot" => req.start_slot,
                 "current_slot" => current_slot,
                 "requested" => req.count,

beacon_node/network/src/sync/network_context.rs

@@ -314,14 +314,24 @@ impl<T: BeaconChainTypes> SyncNetworkContext<T> {
                         let (chain_id, batch_id, info) = entry.get_mut();
                         let chain_id = chain_id.clone();
                         let batch_id = batch_id.clone();
+                        let stream_terminator = maybe_block.is_none();
                         info.add_block_response(maybe_block);
-                        let maybe_block = info.pop_response().map(|block_sidecar_pair| {
+                        let maybe_block_wrapped = info.pop_response().map(|block_sidecar_pair| {
                             BlockWrapper::BlockAndBlob { block_sidecar_pair }
                         });
+
+                        if stream_terminator && !info.is_finished() {
+                            return None;
+                        }
+                        if !stream_terminator && maybe_block_wrapped.is_none() {
+                            return None;
+                        }
+
                         if info.is_finished() {
                             entry.remove();
                         }
-                        Some((chain_id, batch_id, maybe_block))
+
+                        Some((chain_id, batch_id, maybe_block_wrapped))
                     }
                     Entry::Vacant(_) => None,
                 }
@@ -356,13 +366,24 @@ impl<T: BeaconChainTypes> SyncNetworkContext<T> {
                 let (chain_id, batch_id, info) = entry.get_mut();
                 let chain_id = chain_id.clone();
                 let batch_id = batch_id.clone();
+                let stream_terminator = maybe_sidecar.is_none();
                 info.add_sidecar_response(maybe_sidecar);
                 let maybe_block = info
                     .pop_response()
                     .map(|block_sidecar_pair| BlockWrapper::BlockAndBlob { block_sidecar_pair });
+
+                if stream_terminator && !info.is_finished() {
+                    return None;
+                }
+
+                if !stream_terminator && maybe_block.is_none() {
+                    return None;
+                }
+
                 if info.is_finished() {
                     entry.remove();
                 }
+
                 Some((chain_id, batch_id, maybe_block))
             }
             Entry::Vacant(_) => None,

beacon_node/network/src/sync/range_sync/chain.rs

@@ -137,10 +137,16 @@ impl<T: BeaconChainTypes> SyncingChain<T> {
 
         let id = SyncingChain::<T>::id(&target_head_root, &target_head_slot);
 
+        let target_slot = if is_finalized_segment {
+            target_head_slot + (2 * T::EthSpec::slots_per_epoch()) + 1
+        } else {
+            target_head_slot
+        };
+
         SyncingChain {
             id,
             start_epoch,
-            target_head_slot,
+            target_head_slot: target_slot,
             target_head_root,
             batches: BTreeMap::new(),
             peers,