update transfer error messages (#7968)

* update transfer err messages

* apply @AdityaSripal review suggestion

x/ibc/applications/transfer/keeper/relay.go

@@ -1,6 +1,7 @@
 package keeper
 
 import (
+	"fmt"
 	"strings"
 
 	"github.com/armon/go-metrics"
@@ -137,7 +138,7 @@ func (k Keeper) SendTransfer(
 			// NOTE: should not happen as the module account was
 			// retrieved on the step above and it has enough balace
 			// to burn.
-			return err
+			panic(fmt.Sprintf("cannot burn coins after a successful send to a module account: %v", err))
 		}
 	}
 
@@ -222,7 +223,11 @@ func (k Keeper) OnRecvPacket(ctx sdk.Context, packet channeltypes.Packet, data t
 		// unescrow tokens
 		escrowAddress := types.GetEscrowAddress(packet.GetDestPort(), packet.GetDestChannel())
 		if err := k.bankKeeper.SendCoins(ctx, escrowAddress, receiver, sdk.NewCoins(token)); err != nil {
-			return err
+			// NOTE: this error is only expected to occur given an unexpected bug or a malicious
+			// counterparty module. The bug may occur in bank or any part of the code that allows
+			// the escrow address to be drained. A malicious counterparty module could drain the
+			// escrow address by allowing more tokens to be sent back then were escrowed.
+			return sdkerrors.Wrap(err, "unable to unescrow tokens, this may be caused by a malicious counterparty module or a bug: please open an issue on counterparty module")
 		}
 
 		defer func() {
@@ -281,7 +286,7 @@ func (k Keeper) OnRecvPacket(ctx sdk.Context, packet channeltypes.Packet, data t
 	if err := k.bankKeeper.SendCoinsFromModuleToAccount(
 		ctx, types.ModuleName, receiver, sdk.NewCoins(voucher),
 	); err != nil {
-		return err
+		panic(fmt.Sprintf("unable to send coins from module to account despite previously minting coins to module account: %v", err))
 	}
 
 	defer func() {
@@ -345,7 +350,15 @@ func (k Keeper) refundPacketToken(ctx sdk.Context, packet channeltypes.Packet, d
 	if types.SenderChainIsSource(packet.GetSourcePort(), packet.GetSourceChannel(), data.Denom) {
 		// unescrow tokens back to sender
 		escrowAddress := types.GetEscrowAddress(packet.GetSourcePort(), packet.GetSourceChannel())
-		return k.bankKeeper.SendCoins(ctx, escrowAddress, sender, sdk.NewCoins(token))
+		if err := k.bankKeeper.SendCoins(ctx, escrowAddress, sender, sdk.NewCoins(token)); err != nil {
+			// NOTE: this error is only expected to occur given an unexpected bug or a malicious
+			// counterparty module. The bug may occur in bank or any part of the code that allows
+			// the escrow address to be drained. A malicious counterparty module could drain the
+			// escrow address by allowing more tokens to be sent back then were escrowed.
+			return sdkerrors.Wrap(err, "unable to unescrow tokens, this may be caused by a malicious counterparty module or a bug: please open an issue on counterparty module")
+		}
+
+		return nil
 	}
 
 	// mint vouchers back to sender
@@ -355,7 +368,11 @@ func (k Keeper) refundPacketToken(ctx sdk.Context, packet channeltypes.Packet, d
 		return err
 	}
 
-	return k.bankKeeper.SendCoinsFromModuleToAccount(ctx, types.ModuleName, sender, sdk.NewCoins(token))
+	if err := k.bankKeeper.SendCoinsFromModuleToAccount(ctx, types.ModuleName, sender, sdk.NewCoins(token)); err != nil {
+		panic(fmt.Sprintf("unable to send coins from module to account despite previously minting coins to module account: %v", err))
+	}
+
+	return nil
 }
 
 // DenomPathFromHash returns the full denomination path prefix from an ibc denom with a hash