feat: init base logic for rpc fetcher

pkg/fetch/rpc.go

@@ -0,0 +1,64 @@
+package fetch
+
+import (
+	"context"
+	"math/big"
+
+	"github.com/celo-org/celo-blockchain/core/types"
+	celo "github.com/grassrootseconomics/cic-celo-sdk"
+	"github.com/grassrootseconomics/w3-celo-patch/module/eth"
+	"github.com/grassrootseconomics/w3-celo-patch/w3types"
+)
+
+type RPCOpts struct {
+	RPCProvider *celo.Provider
+}
+
+type RPC struct {
+	provider *celo.Provider
+}
+
+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.
+func (f *RPC) Block(ctx context.Context, blockNumber uint64) (FetchResponse, error) {
+	var (
+		block types.Block
+
+		fetchResponse FetchResponse
+	)
+
+	if err := f.provider.Client.CallCtx(
+		ctx,
+		eth.BlockByNumber(big.NewInt(int64(blockNumber))).Returns(&block),
+	); err != nil {
+		return FetchResponse{}, nil
+	}
+
+	txCount := len(block.Transactions())
+	batchCalls := make([]w3types.Caller, txCount*2)
+
+	txs := make([]types.Transaction, txCount)
+	txsReceipt := make([]types.Receipt, txCount)
+
+	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])
+	}
+
+	if err := f.provider.Client.CallCtx(
+		ctx,
+		batchCalls...,
+	); err != nil {
+		return FetchResponse{}, nil
+	}
+
+	// TODO: Create FetchResponse
+
+	return fetchResponse, nil
+}