rpc: optimize tx index lookup (#810)

Closes: #760

Solution:
- emit tx index to cosmos events
- rpc side try to use the events, but fallback to heavier approach when fails.

Update rpc/ethereum/namespaces/eth/api.go

changelog

fix lint

fix TxIndexFromEvents

fix

Update rpc/ethereum/backend/backend.go

Co-authored-by: Federico Kunze Küllmer <31522760+fedekunze@users.noreply.github.com>

x/evm/keeper/msg_server.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"strconv"
 
 	tmbytes "github.com/tendermint/tendermint/libs/bytes"
 	tmtypes "github.com/tendermint/tendermint/types"
@@ -26,6 +27,7 @@ func (k *Keeper) EthereumTx(goCtx context.Context, msg *types.MsgEthereumTx) (*t
 
 	sender := msg.From
 	tx := msg.AsTransaction()
+	txIndex := k.GetTxIndexTransient()
 
 	response, err := k.ApplyTransaction(tx)
 	if err != nil {
@@ -36,6 +38,8 @@ func (k *Keeper) EthereumTx(goCtx context.Context, msg *types.MsgEthereumTx) (*t
 		sdk.NewAttribute(sdk.AttributeKeyAmount, tx.Value().String()),
 		// add event for ethereum transaction hash format
 		sdk.NewAttribute(types.AttributeKeyEthereumTxHash, response.Hash),
+		// add event for index of valid ethereum tx
+		sdk.NewAttribute(types.AttributeKeyTxIndex, strconv.FormatInt(int64(txIndex), 10)),
 	}
 
 	if len(ctx.TxBytes()) > 0 {

x/evm/spec/07_events.md

@@ -15,6 +15,7 @@ The `x/evm` module emits the Cosmos SDK events after a state execution. The EVM
 | ethereum_tx | `"contract"`       | `{hex_address}`         |
 | ethereum_tx | `"txHash"`         | `{tendermint_hex_hash}` |
 | ethereum_tx | `"ethereumTxHash"` | `{hex_hash}`            |
+| ethereum_tx | `"txIndex"`        | `{tx_index}`            |
 | tx_log      | `"txLog"`          | `{tx_log}`              |
 | message     | `"sender"`         | `{eth_address}`         |
 | message     | `"action"`         | `"ethereum"`            |

x/evm/types/events.go

@@ -10,6 +10,7 @@ const (
 	AttributeKeyRecipient       = "recipient"
 	AttributeKeyTxHash          = "txHash"
 	AttributeKeyEthereumTxHash  = "ethereumTxHash"
+	AttributeKeyTxIndex         = "txIndex"
 	AttributeKeyTxType          = "txType"
 	AttributeKeyTxLog           = "txLog"
 	// tx failed in eth vm execution