cmd: Modified listchaintxns command.

- Added reverse flag to listchaintxns command.
- Listchaintxns command returns error when start_height is
less than end_height if end_height is not -1.

cmd/commands/commands.go

@@ -2248,7 +2248,7 @@ var listChainTxnsCommand = cli.Command{
 	to an address our wallet controls, or spent utxos that we held. The
 	start_height and end_height flags can be used to specify an inclusive
 	block range over which to query for transactions. If the end_height is
-	less than the start_height, transactions will be queried in reverse.
+	less than the start_height, an error will be returned.
 	To get all transactions until the chain tip, including unconfirmed
 	transactions (identifiable with BlockHeight=0), set end_height to -1.
 	By default, this call will get all transactions our wallet was involved
@@ -2267,10 +2267,24 @@ func listChainTxns(ctx *cli.Context) error {
 		MaxTransactions: uint32(ctx.Uint64("max_transactions")),
 	}
 
-	if ctx.IsSet("start_height") {
+	switch {
+	case ctx.IsSet("start_height") && ctx.IsSet("end_height"):
+		startHeight := ctx.Int64("start_height")
+		endHeight := ctx.Int64("end_height")
+
+		if endHeight != -1 && startHeight > endHeight {
+			return errors.New("start_height should " +
+				"be less than end_height if end_height " +
+				"is not equal to -1")
+		}
+
+		req.StartHeight = int32(startHeight)
+		req.EndHeight = int32(endHeight)
+
+	case ctx.IsSet("start_height"):
 		req.StartHeight = int32(ctx.Int64("start_height"))
-	}
-	if ctx.IsSet("end_height") {
+
+	case ctx.IsSet("end_height"):
 		req.EndHeight = int32(ctx.Int64("end_height"))
 	}