fix types.ChainAnteDecorators() panic (#5742) (#6669)

ChainAnteDecorators() panics when no arguments are supplied.
This change its behaviour and the function now returns a nil
AnteHandler in case no AnteDecorator instances are supplied.

Closes: #5741

CHANGELOG.md

@@ -79,6 +79,7 @@ options `pruning-keep-recent`, `pruning-keep-every`, and `pruning-interval`. The
 dictate how many recent versions are kept on disk and the offset of what versions are kept after that
 respectively, and the latter defines the height interval in which versions are deleted in a batch.
 **Note, there are some client-facing API breaking changes with regard to IAVL, stores, and pruning settings.**
+* (types) [\#5741](https://github.com/cosmos/cosmos-sdk/issues/5741) Prevent `ChainAnteDecorators()` from panicking when empty `AnteDecorator` slice is supplied.
 
 ## [v0.38.4] - 2020-05-21
 

Makefile

@@ -35,6 +35,7 @@ update-swagger-docs: statik
 
 mocks: $(MOCKS_DIR)
 	mockgen -source=x/auth/types/account_retriever.go -package mocks -destination tests/mocks/account_retriever.go
+	mockgen -source=types/handler.go -package mocks -destination tests/mocks/types_handler.go
 .PHONY: mocks
 
 $(MOCKS_DIR):

types/handler.go

@@ -25,15 +25,15 @@ type AnteDecorator interface {
 // MUST set GasMeter with the FIRST AnteDecorator. Failing to do so will cause
 // transactions to be processed with an infinite gasmeter and open a DOS attack vector.
 // Use `ante.SetUpContextDecorator` or a custom Decorator with similar functionality.
+// Returns nil when no AnteDecorator are supplied.
 func ChainAnteDecorators(chain ...AnteDecorator) AnteHandler {
-	if (chain[len(chain)-1] != Terminator{}) {
-		chain = append(chain, Terminator{})
+	if len(chain) == 0 {
+		return nil
 	}
 
-	if len(chain) == 1 {
-		return func(ctx Context, tx Tx, simulate bool) (Context, error) {
-			return chain[0].AnteHandle(ctx, tx, simulate, nil)
-		}
+	// handle non-terminated decorators chain
+	if (chain[len(chain)-1] != Terminator{}) {
+		chain = append(chain, Terminator{})
 	}
 
 	return func(ctx Context, tx Tx, simulate bool) (Context, error) {

types/handler_test.go

@@ -0,0 +1,28 @@
+package types_test
+
+import (
+	"testing"
+
+	"github.com/golang/mock/gomock"
+	"github.com/stretchr/testify/require"
+
+	"github.com/cosmos/cosmos-sdk/tests/mocks"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+)
+
+func TestChainAnteDecorators(t *testing.T) {
+	t.Parallel()
+	// test panic
+	require.Nil(t, sdk.ChainAnteDecorators([]sdk.AnteDecorator{}...))
+
+	ctx, tx := sdk.Context{}, sdk.Tx(nil)
+	mockCtrl := gomock.NewController(t)
+	mockAnteDecorator1 := mocks.NewMockAnteDecorator(mockCtrl)
+	mockAnteDecorator1.EXPECT().AnteHandle(gomock.Eq(ctx), gomock.Eq(tx), true, gomock.Any()).Times(1)
+	sdk.ChainAnteDecorators(mockAnteDecorator1)(ctx, tx, true)
+
+	mockAnteDecorator2 := mocks.NewMockAnteDecorator(mockCtrl)
+	mockAnteDecorator1.EXPECT().AnteHandle(gomock.Eq(ctx), gomock.Eq(tx), true, mockAnteDecorator2).Times(1)
+	mockAnteDecorator2.EXPECT().AnteHandle(gomock.Eq(ctx), gomock.Eq(tx), true, nil).Times(1)
+	sdk.ChainAnteDecorators(mockAnteDecorator1, mockAnteDecorator2)
+}