eth/filters: change filter block to be by-ref (#26054)

This PR changes the block field in the filter to be a pointer, to disambiguate between empty hash and no hash

eth/filters/filter.go

@@ -34,7 +34,7 @@ type Filter struct {
 	addresses []common.Address
 	topics    [][]common.Hash
 
-	block      common.Hash // Block hash if filtering a single block
+	block      *common.Hash // Block hash if filtering a single block
 	begin, end int64        // Range interval if filtering multiple blocks
 
 	matcher *bloombits.Matcher
@@ -78,7 +78,7 @@ func (sys *FilterSystem) NewRangeFilter(begin, end int64, addresses []common.Add
 func (sys *FilterSystem) NewBlockFilter(block common.Hash, addresses []common.Address, topics [][]common.Hash) *Filter {
 	// Create a generic filter and convert it into a block filter
 	filter := newFilter(sys, addresses, topics)
-	filter.block = block
+	filter.block = &block
 	return filter
 }
 
@@ -96,8 +96,8 @@ func newFilter(sys *FilterSystem, addresses []common.Address, topics [][]common.
 // first block that contains matches, updating the start of the filter accordingly.
 func (f *Filter) Logs(ctx context.Context) ([]*types.Log, error) {
 	// If we're doing singleton block filtering, execute and return
-	if f.block != (common.Hash{}) {
-		header, err := f.sys.backend.HeaderByHash(ctx, f.block)
+	if f.block != nil {
+		header, err := f.sys.backend.HeaderByHash(ctx, *f.block)
 		if err != nil {
 			return nil, err
 		}