From ee549a2af9202e2e6206ad6a824701367e203858 Mon Sep 17 00:00:00 2001
From: niftynei <niftynei@gmail.com>
Date: Tue, 16 Jun 2020 17:07:28 -0500
Subject: [PATCH] tx: fix case where input amounts are less than total outputs

when attempting to calculate the fees for a tx where we don't own all of
the outputs, we can overshoot the feerate
---
 bitcoin/tx.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/bitcoin/tx.c b/bitcoin/tx.c
index 57cc593fd..2056bc195 100644
--- a/bitcoin/tx.c
+++ b/bitcoin/tx.c
@@ -121,7 +121,9 @@ struct amount_sat bitcoin_tx_compute_fee_w_inputs(const struct bitcoin_tx *tx,
 
 		ok = amount_sat_sub(&input_val, input_val,
 				    amount_asset_to_sat(&asset));
-		assert(ok);
+		if (!ok)
+			return AMOUNT_SAT(0);
+
 	}
 	return input_val;
 }