factor our state diff fetcher for more general use (e.g. by the super node)

libraries/shared/fetcher/state_diff_fetcher.go

@@ -0,0 +1,72 @@
+// VulcanizeDB
+// Copyright © 2019 Vulcanize
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package fetcher
+
+import (
+	"github.com/ethereum/go-ethereum/statediff"
+
+	"github.com/vulcanize/vulcanizedb/pkg/geth/client"
+)
+
+// IStateDiffFetcher is the state diff fetching interface
+type IStateDiffFetcher interface {
+	FetchStateDiffsAt(blockHeights []uint64) ([]*statediff.Payload, error)
+}
+
+// BatchClient is an interface to a batch-fetching geth rpc client; created to allow mock insertion
+type BatchClient interface {
+	BatchCall(batch []client.BatchElem) error
+}
+
+// StateDiffFetcher is the state diff fetching struct
+type StateDiffFetcher struct {
+	client BatchClient
+}
+
+const method = "statediff_stateDiffAt"
+
+// NewStateDiffFetcher returns a IStateDiffFetcher
+func NewStateDiffFetcher(bc BatchClient) IStateDiffFetcher {
+	return &StateDiffFetcher{
+		client: bc,
+	}
+}
+
+// FetchStateDiffsAt fetches the statediff payloads at the given block heights
+// Calls StateDiffAt(ctx context.Context, blockNumber uint64) (*Payload, error)
+func (sdf *StateDiffFetcher) FetchStateDiffsAt(blockHeights []uint64) ([]*statediff.Payload, error) {
+	batch := make([]client.BatchElem, 0)
+	for _, height := range blockHeights {
+		batch = append(batch, client.BatchElem{
+			Method: method,
+			Args:   []interface{}{height},
+			Result: new(statediff.Payload),
+		})
+	}
+	batchErr := sdf.client.BatchCall(batch)
+	if batchErr != nil {
+		return nil, batchErr
+	}
+	results := make([]*statediff.Payload, 0, len(blockHeights))
+	for _, batchElem := range batch {
+		if batchElem.Error != nil {
+			return nil, batchElem.Error
+		}
+		results = append(results, batchElem.Result.(*statediff.Payload))
+	}
+	return results, nil
+}