First stab at multiplexer

stack/multiplexer.go

@@ -0,0 +1,51 @@
+package stack
+
+import (
+	"github.com/tendermint/basecoin"
+	"github.com/tendermint/basecoin/txs"
+	"github.com/tendermint/basecoin/types"
+)
+
+const (
+	NameMultiplexer = "mplx"
+)
+
+type Multiplexer struct{}
+
+func (_ Multiplexer) Name() string {
+	return NameMultiplexer
+}
+
+var _ Middleware = Multiplexer{}
+
+func (_ Multiplexer) CheckTx(ctx basecoin.Context, store types.KVStore, tx basecoin.Tx, next basecoin.Checker) (res basecoin.Result, err error) {
+	if mtx, ok := tx.Unwrap().(*txs.MultiTx); ok {
+		return runAll(ctx, store, mtx.Txs, next.CheckTx)
+	}
+	return next.CheckTx(ctx, store, tx)
+}
+
+func (_ Multiplexer) DeliverTx(ctx basecoin.Context, store types.KVStore, tx basecoin.Tx, next basecoin.Deliver) (res basecoin.Result, err error) {
+	if mtx, ok := tx.Unwrap().(*txs.MultiTx); ok {
+		return runAll(ctx, store, mtx.Txs, next.DeliverTx)
+	}
+	return next.DeliverTx(ctx, store, tx)
+}
+
+func runAll(ctx basecoin.Context, store types.KVStore, txs []basecoin.Tx, next basecoin.CheckerFunc) (res basecoin.Result, err error) {
+	// store all results, unless anything errors
+	rs := make([]basecoin.Result, len(txs))
+	for i, stx := range txs {
+		rs[i], err = next(ctx, store, stx)
+		if err != nil {
+			return
+		}
+	}
+	// now combine the results into one...
+	return combine(rs), nil
+}
+
+func combine(res []basecoin.Result) basecoin.Result {
+	// TODO: how to combine???
+	return res[0]
+}