contracts/deposit: cache parsed ABI and avoid per-call parsing

changelog/GarmashAlex_chore-cache-deposit-abi-logs.md

@@ -0,0 +1,3 @@
+### Changed
+
+- cache parsed ABI and avoid per-call parsing in UnpackDepositLogData [#16061](https://github.com/OffchainLabs/prysm/pull/16061)

contracts/deposit/logs.go

@@ -1,24 +1,29 @@
 package deposit
 
 import (
-	"bytes"
+	"strings"
 
 	"github.com/ethereum/go-ethereum/accounts/abi"
 	"github.com/pkg/errors"
 )
 
-// UnpackDepositLogData unpacks the data from a deposit log using the ABI decoder.
-func UnpackDepositLogData(data []byte) (pubkey, withdrawalCredentials, amount, signature, index []byte, err error) {
-	reader := bytes.NewReader([]byte(DepositContractABI))
-	contractAbi, err := abi.JSON(reader)
+// parsed ABI cached at package level to avoid reparsing on every log unpack
+var depositABI abi.ABI
+
+func init() {
+	var err error
+	depositABI, err = abi.JSON(strings.NewReader(DepositContractABI))
 	if err != nil {
-		return nil, nil, nil, nil, nil, errors.Wrap(err, "unable to generate contract abi")
+		// DepositContractABI is a constant generated from the contract; failure here is unrecoverable
+		panic(err)
 	}
+}
 
-	unpackedLogs, err := contractAbi.Unpack("DepositEvent", data)
-	if err != nil {
+// UnpackDepositLogData unpacks the data from a deposit log using the ABI decoder.
+func UnpackDepositLogData(data []byte) (pubkey, withdrawalCredentials, amount, signature, index []byte, err error) {
+	evt := new(DepositContractDepositEvent)
+	if err := depositABI.UnpackIntoInterface(evt, "DepositEvent", data); err != nil {
 		return nil, nil, nil, nil, nil, errors.Wrap(err, "unable to unpack logs")
 	}
-
-	return unpackedLogs[0].([]byte), unpackedLogs[1].([]byte), unpackedLogs[2].([]byte), unpackedLogs[3].([]byte), unpackedLogs[4].([]byte), nil
+	return evt.Pubkey, evt.WithdrawalCredentials, evt.Amount, evt.Signature, evt.Index, nil
 }