check if deliverTxResCh is still open, return an err otherwise (#2947)

deliverTxResCh, like any other eventBus (pubsub) channel, is closed when
eventBus is stopped. We must check if the channel is still open. The
alternative approach is to not close any channels, which seems a bit
odd.

Fixes #2408

CHANGELOG_PENDING.md

@@ -21,3 +21,4 @@ Special thanks to external contributors on this release:
 ### IMPROVEMENTS:
 
 ### BUG FIXES:
+- [rpc] \#2408 `/broadcast_tx_commit`: Fix "interface conversion: interface {} in nil, not EventDataTx" panic (could happen if somebody sent a tx using /broadcast_tx_commit while Tendermint was being stopped)

rpc/core/mempool.go

@@ -198,7 +198,10 @@ func BroadcastTxCommit(tx types.Tx) (*ctypes.ResultBroadcastTxCommit, error) {
 	// TODO: configurable?
 	var deliverTxTimeout = rpcserver.WriteTimeout / 2
 	select {
-	case deliverTxResMsg := <-deliverTxResCh: // The tx was included in a block.
+	case deliverTxResMsg, ok := <-deliverTxResCh: // The tx was included in a block.
+		if !ok {
+			return nil, errors.New("Error on broadcastTxCommit: expected DeliverTxResult, got nil. Did the Tendermint stop?")
+		}
 		deliverTxRes := deliverTxResMsg.(types.EventDataTx)
 		return &ctypes.ResultBroadcastTxCommit{
 			CheckTx:   *checkTxRes,