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x/evm/spec/06_hooks.md
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@ -4,7 +4,9 @@ order: 6
# Hooks
The evm module implements an `EvmHooks` interface that extend the `Tx` processing logic externally. This supports EVM contracts to call native cosmos modules by
The `x/evm` module implements an `EvmHooks` interface that extend and customize the `Tx` processing logic externally.
This supports EVM contracts to call native cosmos modules by
1. defining a log signature and emitting the specific log from the smart contract,
2. recognizing those logs in the native tx processing code, and
@ -14,7 +16,8 @@ To do this, the interface includes a `PostTxProcessing` hook that registers cus
```go
type EvmHooks interface {
PostTxProcessing(ctx sdk.Context, txHash common.Hash, logs []*ethtypes.Log) error
// Must be called after tx is processed successfully, if return an error, the whole transaction is reverted.
PostTxProcessing(ctx sdk.Context, msg core.Message, receipt *ethtypes.Receipt) error
}
```
@ -23,11 +26,11 @@ type EvmHooks interface {
`PostTxProcessing` is only called after a EVM transaction finished successfully and delegates the call to underlying hooks. If no hook has been registered, this function returns with a `nil` error.
```go
func (k *Keeper) PostTxProcessing(txHash common.Hash, logs []*ethtypes.Log) error {
if k.hooks == nil {
return nil
}
return k.hooks.PostTxProcessing(k.Ctx(), txHash, logs)
func (k *Keeper) PostTxProcessing(ctx sdk.Context, msg core.Message, receipt *ethtypes.Receipt) error {
if k.hooks == nil {
return nil
}
return k.hooks.PostTxProcessing(k.Ctx(), msg, receipt)
}
```
@ -35,9 +38,9 @@ It's executed in the same cache context as the EVM transaction, if it returns an
The error returned by the hooks is translated to a VM error `failed to process native logs`, the detailed error message is stored in the return value. The message is sent to native modules asynchronously, there's no way for the caller to catch and recover the error.
## Use Case: Call Native erc20 Module on Evmos
## Use Case: Call Native ERC20 Module on Evmos
Here is an example taken from the [Evmos erc20 module](https://evmos.dev/modules/erc20/) that shows how the `EVMHooks` supports a contract calling a native module to convert ERC-20 Tokens intor Cosmos native Coins. Following the steps from above.
Here is an example taken from the Evmos [erc20 module](https://evmos.dev/modules/erc20/) that shows how the `EVMHooks` supports a contract calling a native module to convert ERC-20 Tokens into Cosmos native Coins. Following the steps from above.
You can define and emit a `Transfer` log signature in the smart contract like this:
@ -45,14 +48,14 @@ You can define and emit a `Transfer` log signature in the smart contract like th
event Transfer(address indexed from, address indexed to, uint256 value);
function _transfer(address sender, address recipient, uint256 amount) internal virtual {
require(sender != address(0), "ERC20: transfer from the zero address");
require(recipient != address(0), "ERC20: transfer to the zero address");
require(sender != address(0), "ERC20: transfer from the zero address");
require(recipient != address(0), "ERC20: transfer to the zero address");
_beforeTokenTransfer(sender, recipient, amount);
_beforeTokenTransfer(sender, recipient, amount);
_balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
_balances[recipient] = _balances[recipient].add(amount);
emit Transfer(sender, recipient, amount);
_balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
_balances[recipient] = _balances[recipient].add(amount);
emit Transfer(sender, recipient, amount);
}
```
@ -63,115 +66,125 @@ The application will register a `BankSendHook` to the `EvmKeeper`. It recognizes
const ERC20EventTransfer = "Transfer"
// PostTxProcessing implements EvmHooks.PostTxProcessing
func (k Keeper) PostTxProcessing(ctx sdk.Context, txHash common.Hash, logs []*ethtypes.Log) error {
params := k.GetParams(ctx)
if !params.EnableEVMHook {
return sdkerrors.Wrap(types.ErrInternalTokenPair, "EVM Hook is currently disabled")
}
func (k Keeper) PostTxProcessing(
ctx sdk.Context,
msg core.Message,
receipt *ethtypes.Receipt,
) error {
params := h.k.GetParams(ctx)
if !params.EnableErc20 || !params.EnableEVMHook {
// no error is returned to allow for other post processing txs
// to pass
return nil
}
erc20 := contracts.ERC20BurnableContract.ABI
erc20 := contracts.ERC20BurnableContract.ABI
for i, log := range logs {
if len(log.Topics) < 3 {
continue
}
for i, log := range receipt.Logs {
if len(log.Topics) < 3 {
continue
}
eventID := log.Topics[0] // event ID
eventID := log.Topics[0] // event ID
event, err := erc20.EventByID(eventID)
if err != nil {
// invalid event for ERC20
continue
}
event, err := erc20.EventByID(eventID)
if err != nil {
// invalid event for ERC20
continue
}
if event.Name != types.ERC20EventTransfer {
k.Logger(ctx).Info("emitted event", "name", event.Name, "signature", event.Sig)
continue
}
if event.Name != types.ERC20EventTransfer {
h.k.Logger(ctx).Info("emitted event", "name", event.Name, "signature", event.Sig)
continue
}
transferEvent, err := erc20.Unpack(event.Name, log.Data)
if err != nil {
k.Logger(ctx).Error("failed to unpack transfer event", "error", err.Error())
continue
}
transferEvent, err := erc20.Unpack(event.Name, log.Data)
if err != nil {
h.k.Logger(ctx).Error("failed to unpack transfer event", "error", err.Error())
continue
}
if len(transferEvent) == 0 {
continue
}
if len(transferEvent) == 0 {
continue
}
tokens, ok := transferEvent[0].(*big.Int)
// safety check and ignore if amount not positive
if !ok || tokens == nil || tokens.Sign() != 1 {
continue
}
tokens, ok := transferEvent[0].(*big.Int)
// safety check and ignore if amount not positive
if !ok || tokens == nil || tokens.Sign() != 1 {
continue
}
// check that the contract is a registered token pair
contractAddr := log.Address
// check that the contract is a registered token pair
contractAddr := log.Address
id := k.GetERC20Map(ctx, contractAddr)
id := h.k.GetERC20Map(ctx, contractAddr)
if len(id) == 0 {
// no token is registered for the caller contract
continue
}
if len(id) == 0 {
// no token is registered for the caller contract
continue
}
pair, found := k.GetTokenPair(ctx, id)
if !found {
continue
}
pair, found := h.k.GetTokenPair(ctx, id)
if !found {
continue
}
// check that relaying for the pair is enabled
if !pair.Enabled {
return fmt.Errorf("internal relaying is disabled for pair %s, please create a governance proposal", contractAddr) // convert to SDK error
}
// check that conversion for the pair is enabled
if !pair.Enabled {
// continue to allow transfers for the ERC20 in case the token pair is disabled
h.k.Logger(ctx).Debug(
"ERC20 token -> Cosmos coin conversion is disabled for pair",
"coin", pair.Denom, "contract", pair.Erc20Address,
)
continue
}
// ignore as the burning always transfers to the zero address
to := common.BytesToAddress(log.Topics[2].Bytes())
if !bytes.Equal(to.Bytes(), types.ModuleAddress.Bytes()) {
continue
}
// ignore as the burning always transfers to the zero address
to := common.BytesToAddress(log.Topics[2].Bytes())
if !bytes.Equal(to.Bytes(), types.ModuleAddress.Bytes()) {
continue
}
// check that the event is Burn from the ERC20Burnable interface
// NOTE: assume that if they are burning the token that has been registered as a pair, they want to mint a Cosmos coin
// check that the event is Burn from the ERC20Burnable interface
// NOTE: assume that if they are burning the token that has been registered as a pair, they want to mint a Cosmos coin
// create the corresponding sdk.Coin that is paired with ERC20
coins := sdk.Coins{{Denom: pair.Denom, Amount: sdk.NewIntFromBigInt(tokens)}}
// create the corresponding sdk.Coin that is paired with ERC20
coins := sdk.Coins{{Denom: pair.Denom, Amount: sdk.NewIntFromBigInt(tokens)}}
// Mint the coin only if ERC20 is external
switch pair.ContractOwner {
case types.OWNER_MODULE:
_, err = k.CallEVM(ctx, erc20, types.ModuleAddress, contractAddr, "burn", tokens)
case types.OWNER_EXTERNAL:
err = k.bankKeeper.MintCoins(ctx, types.ModuleName, coins)
default:
err = types.ErrUndefinedOwner
}
// Mint the coin only if ERC20 is external
switch pair.ContractOwner {
case types.OWNER_MODULE:
_, err = h.k.CallEVM(ctx, erc20, types.ModuleAddress, contractAddr, true, "burn", tokens)
case types.OWNER_EXTERNAL:
err = h.k.bankKeeper.MintCoins(ctx, types.ModuleName, coins)
default:
err = types.ErrUndefinedOwner
}
if err != nil {
k.Logger(ctx).Debug(
"failed to process EVM hook for ER20 -> coin conversion",
"coin", pair.Denom, "contract", pair.Erc20Address, "error", err.Error(),
)
continue
}
if err != nil {
h.k.Logger(ctx).Debug(
"failed to process EVM hook for ER20 -> coin conversion",
"coin", pair.Denom, "contract", pair.Erc20Address, "error", err.Error(),
)
continue
}
// Only need last 20 bytes from log.topics
from := common.BytesToAddress(log.Topics[1].Bytes())
recipient := sdk.AccAddress(from.Bytes())
// Only need last 20 bytes from log.topics
from := common.BytesToAddress(log.Topics[1].Bytes())
recipient := sdk.AccAddress(from.Bytes())
// transfer the tokens from ModuleAccount to sender address
if err := k.bankKeeper.SendCoinsFromModuleToAccount(ctx, types.ModuleName, recipient, coins); err != nil {
k.Logger(ctx).Debug(
"failed to process EVM hook for ER20 -> coin conversion",
"tx-hash", txHash.Hex(), "log-idx", i,
"coin", pair.Denom, "contract", pair.Erc20Address, "error", err.Error(),
)
continue
}
}
// transfer the tokens from ModuleAccount to sender address
if err := h.k.bankKeeper.SendCoinsFromModuleToAccount(ctx, types.ModuleName, recipient, coins); err != nil {
h.k.Logger(ctx).Debug(
"failed to process EVM hook for ER20 -> coin conversion",
"tx-hash", receipt.TxHash.Hex(), "log-idx", i,
"coin", pair.Denom, "contract", pair.Erc20Address, "error", err.Error(),
)
continue
}
}
return nil
}
return nil
```
Lastly, register the hook in `app.go`: