sharding: merklize body into chunkroot and save in db

Former-commit-id: 30327145ac18f8822bdfc661c50591aa33917547 [formerly bc513e68023723a4d848d2e773e77efeb7ddc9df]
Former-commit-id: 3da18bf84b164cab555f5bde8f3cf5ae19b18b26

sharding/collation.go

@@ -190,3 +190,20 @@ func Deserialize(serialisedBlob []byte) (*[]*types.Transaction, error) {
 
 	return &txs, nil
 }
+
+
+// Chunks is a wrapper around a chunk array to implement DerivableList,
+// which allows us to Merklize the chunks into the chunkRoot
+type Chunks []byte
+
+// Len returns the number of chunks in this list.
+func (ch Chunks) Len() int { return len(ch) }
+
+// GetRlp returns the RLP encoding of one chunk from the list.
+func (ch Chunks) GetRlp(i int) []byte {
+	bytes, err := rlp.EncodeToBytes(ch[i])
+	if err != nil {
+		panic(err)
+	}
+	return bytes
+}

sharding/shard.go

@@ -6,6 +6,7 @@ import (
 	"math/big"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/rlp"
 )
 
@@ -179,11 +180,13 @@ func (s *Shard) SaveHeader(header *CollationHeader) error {
 
 // SaveBody adds the collation body to the shardDB and sets availability.
 func (s *Shard) SaveBody(body []byte) error {
-	// TODO: check if body is empty and throw error.
-	// TODO: dependent on blob serialization.
-	// chunkRoot := getChunkRoot(body) using the blob algorithm utils.
-	// right now we will just take the raw keccak256 of the body until #92 is merged.
-	chunkRoot := common.BytesToHash(body)
+	// check if body is empty and throw error.
+	if body == nil {
+		return fmt.Errorf("body is empty")
+	}
+
+	chunks := Chunks(body)
+	chunkRoot := types.DeriveSha(chunks) // merklize the serialized blobs
 	s.SetAvailability(&chunkRoot, true)
 	return s.shardDB.Put(chunkRoot, body)
 }