From 176859ed926febfa16055d9e8e8f57ddc72cb9ba Mon Sep 17 00:00:00 2001
From: jp1ac4 <121959000+jp1ac4@users.noreply.github.com>
Date: Fri, 20 Oct 2023 09:50:43 +0100
Subject: [PATCH] commands: add weights before converting to vbytes

Converting to vbytes first can lead to a larger result and
therefore a lower feerate, which could fall below 1 and fail the
sanity check.
---
 src/commands/mod.rs    | 9 ++++++++-
 src/descriptors/mod.rs | 2 +-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/commands/mod.rs b/src/commands/mod.rs
index 0bdf09e8..705ce698 100644
--- a/src/commands/mod.rs
+++ b/src/commands/mod.rs
@@ -202,7 +202,14 @@ fn sanity_check_psbt(
     }
 
     // Check the feerate isn't insane.
-    let tx_vb = (tx.vsize() + spent_desc.max_sat_vbytes() * tx.input.len()) as u64;
+    // Add weights together before converting to vbytes to avoid rounding up multiple times
+    // and increasing the result, which could lead to the feerate in sats/vb falling below 1.
+    let tx_wu = tx.weight().to_wu() + (spent_desc.max_sat_weight() * tx.input.len()) as u64;
+    let tx_vb = tx_wu
+        .checked_add(descriptors::WITNESS_FACTOR as u64 - 1)
+        .unwrap()
+        .checked_div(descriptors::WITNESS_FACTOR as u64)
+        .unwrap();
     let feerate_sats_vb = abs_fee
         .checked_div(tx_vb)
         .ok_or(CommandError::InsaneFees(InsaneFeeInfo::InvalidFeerate))?;
diff --git a/src/descriptors/mod.rs b/src/descriptors/mod.rs
index 72f1a919..f5b1564e 100644
--- a/src/descriptors/mod.rs
+++ b/src/descriptors/mod.rs
@@ -17,7 +17,7 @@ pub use keys::*;
 pub mod analysis;
 pub use analysis::*;
 
-const WITNESS_FACTOR: usize = 4;
+pub const WITNESS_FACTOR: usize = 4;
 
 #[derive(Debug)]
 pub enum LianaDescError {