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## Description
ref: #9585
This PR if the 1st step (out of 2) in the #9585 refactor. It transforms baseapp's ABCI {Check,Deliver}Tx into middleware stacks. A middleware is defined by the following interfaces:
```go
// types/tx package
type Handler interface {
CheckTx(ctx context.Context, tx sdk.Tx, req abci.RequestCheckTx) (abci.ResponseCheckTx, error)
DeliverTx(ctx context.Context, tx sdk.Tx, req abci.RequestDeliverTx) (abci.ResponseDeliverTx, error)
SimulateTx(ctx context.Context, tx sdk.Tx, req RequestSimulateTx) (ResponseSimulateTx, error)
}
type Middleware func(Handler) Handler
```
This Pr doesn't migrate antehandlers, but only baseapp's runTx and runMsgs as middlewares. It bundles antehandlers into one single middleware (for now).
More specifically, it introduces the 5 following middlewares:
| Middleware | Description |
| ----------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| RunMsgsTxMiddleware | This middleware replaces the old baseapp's `runMsgs`. |
| LegacyAnteMiddleware | This middleware is temporary, it bundles all antehandlers into one middleware. It's only created for the purpose of breaking the refactor into 2 pieces. **It will be removed in Part 2**, and each antehandler will be replaced by its own middleware. |
| IndexEventsTxMiddleware | This is a simple middleware that chooses which events to index in Tendermint. Replaces `baseapp.indexEvents` (which unfortunately still exists in baseapp too, because it's used to index Begin/EndBlock events) |
| RecoveryTxMiddleware | This index recovers from panics. It replaces baseapp.runTx's panic recovery. |
| GasTxMiddleware | This replaces the [`Setup`](https://github.com/cosmos/cosmos-sdk/blob/master/x/auth/ante/setup.go) Antehandler. It sets a GasMeter on sdk.Context. Note that before, GasMeter was set on sdk.Context inside the antehandlers, and there was some mess around the fact that antehandlers had their own panic recovery system so that the GasMeter could be read by baseapp's recovery system. Now, this mess is all removed: one middleware sets GasMeter, another one handles recovery. |
---
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