From 3d4469cedec7e4bcb256440eac5c490f3853639e Mon Sep 17 00:00:00 2001
From: KtorZ <matthias.benkort@gmail.com>
Date: Thu, 27 Aug 2020 19:22:00 +0200
Subject: [PATCH] pass down withdrawal value to 'handleCannotCoverFee' to
 prevent underflow in fee calculation.

---
 lib/core/src/Cardano/Wallet.hs | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/lib/core/src/Cardano/Wallet.hs b/lib/core/src/Cardano/Wallet.hs
index eaff67baf02..5d64ead107f 100644
--- a/lib/core/src/Cardano/Wallet.hs
+++ b/lib/core/src/Cardano/Wallet.hs
@@ -1459,7 +1459,7 @@ estimateFeeForPayment ctx wid recipients withdrawal = do
         guardCoinSelection minUtxo cs
 
     estimateFeeForCoinSelection $ (Fee . feeBalance <$> selectCoins)
-        `catchE` handleCannotCover utxo recipients
+        `catchE` handleCannotCover utxo withdrawal recipients
 
 -- | When estimating fee, it is rather cumbersome to return "cannot cover fee"
 -- whereas clients are just asking for an estimation. Therefore, we convert
@@ -1468,13 +1468,19 @@ estimateFeeForPayment ctx wid recipients withdrawal = do
 handleCannotCover
     :: Monad m
     => UTxO
+    -> Quantity "lovelace" Word64
     -> NonEmpty TxOut
     -> ErrSelectForPayment e
     -> ExceptT (ErrSelectForPayment e) m Fee
-handleCannotCover utxo outs = \case
+handleCannotCover utxo (Quantity withdrawal) outs = \case
     ErrSelectForPaymentFee (ErrCannotCoverFee missing) -> do
-        let available = fromIntegral (W.balance utxo) - sum (getCoin . coin <$> outs)
-        pure $ Fee $ available + missing
+        let available
+                = fromIntegral (W.balance utxo)
+                + fromIntegral withdrawal
+        let payment
+                = sum (getCoin . coin <$> outs)
+        pure $ Fee $
+            available + missing - payment
     e ->
         throwE e