inline-docs: Describe RPC fetcher

pkg/fetch/rpc.go

@@ -12,26 +12,28 @@ import (
 	"github.com/grassrootseconomics/w3-celo-patch/w3types"
 )
 
+// RPCOpts reprsents the required paramters for an RPC fetcher.
 type RPCOpts struct {
 	RPCProvider *celo.Provider
 }
 
+// RPC is a RPC based block and transaction fetcher.
 type RPC struct {
 	provider *celo.Provider
 }
 
+// NewRPCFetcher returns a new RPC fetcher which implemnts Fetch.
+// Note: No rate limiting feeature.
 func NewRPCFetcher(o RPCOpts) Fetch {
 	return &RPC{
 		provider: o.RPCProvider,
 	}
 }
 
-// This method makes 2 calls. 1 for the block and 1 batched call for txs + receipts.
-// Should work on free tier RPC services.
+// Block fetches via RPC and transforms the response to adapt to the GraphQL JSON response struct.
 func (f *RPC) Block(ctx context.Context, blockNumber uint64) (FetchResponse, error) {
 	var (
-		block types.Block
-
+		block         types.Block
 		fetchResponse FetchResponse
 	)
 
@@ -39,7 +41,7 @@ func (f *RPC) Block(ctx context.Context, blockNumber uint64) (FetchResponse, err
 		ctx,
 		eth.BlockByNumber(big.NewInt(int64(blockNumber))).Returns(&block),
 	); err != nil {
-		return FetchResponse{}, err
+		return fetchResponse, err
 	}
 
 	txCount := len(block.Transactions())
@@ -48,6 +50,7 @@ func (f *RPC) Block(ctx context.Context, blockNumber uint64) (FetchResponse, err
 	txs := make([]types.Transaction, txCount)
 	txsReceipt := make([]types.Receipt, txCount)
 
+	// Prepare batch calls.
 	for i, tx := range block.Transactions() {
 		batchCalls[i] = eth.Tx(tx.Hash()).Returns(&txs[i])
 		batchCalls[txCount+i] = eth.TxReceipt(tx.Hash()).Returns(&txsReceipt[i])
@@ -57,32 +60,36 @@ func (f *RPC) Block(ctx context.Context, blockNumber uint64) (FetchResponse, err
 		ctx,
 		batchCalls...,
 	); err != nil {
-		return FetchResponse{}, nil
+		return fetchResponse, err
 	}
 
+	// Transform response and adapt to FetchResponse.
 	for i := 0; i < txCount; i++ {
-		tx := Transaction{}
+		var txObject Transaction
 
-		tx.Block.Number = block.NumberU64()
-		tx.Block.Timestamp = hexutil.EncodeUint64(block.Time())
-		tx.Hash = txsReceipt[i].TxHash.Hex()
-		tx.Index = txsReceipt[i].TransactionIndex
+		txObject.Block.Number = block.NumberU64()
+		txObject.Block.Timestamp = hexutil.EncodeUint64(block.Time())
 
 		from, err := types.Sender(types.LatestSignerForChainID(txs[i].ChainId()), &txs[i])
 		if err != nil {
-			return FetchResponse{}, err
+			return fetchResponse, err
 		}
+		txObject.From.Address = strings.ToLower(from.Hex())
+		// This check ignores contract deployment transactions.
+		if txs[i].To() != nil {
+			txObject.To.Address = strings.ToLower(txs[i].To().Hex())
+		}
+		txObject.Value = hexutil.EncodeBig(txs[i].Value())
+		txObject.InputData = hexutil.Encode(txs[i].Data())
 
-		tx.From.Address = strings.ToLower(from.Hex())
-		tx.To.Address = strings.ToLower(txs[i].To().Hex())
-		tx.Value = hexutil.EncodeBig(txs[i].Value())
-		tx.InputData = hexutil.Encode(txs[i].Data())
-		tx.Status = txsReceipt[i].Status
-		tx.GasUsed = txsReceipt[i].GasUsed
+		txObject.Hash = txsReceipt[i].TxHash.Hex()
+		txObject.Index = txsReceipt[i].TransactionIndex
+		txObject.Status = txsReceipt[i].Status
+		txObject.GasUsed = txsReceipt[i].GasUsed
 
 		fetchResponse.Data.Block.Transactions = append(
 			fetchResponse.Data.Block.Transactions,
-			tx,
+			txObject,
 		)
 	}