From 5d6e5c3df35d148819a9ff9a94184f5222b19e7e Mon Sep 17 00:00:00 2001
From: "Tobin C. Harding" <me@tobin.cc>
Date: Tue, 19 Sep 2023 09:53:57 +1000
Subject: [PATCH] decode: Add empty data check

Currently we index into the data field without first checking it is not
empty. For context, the indexing is done _before_ we do segwit validity
checks which check for correct data lengths.

This is a real noob bug , bad Tobin - no biscuit.

Add a check for the empty array before indexing into it.
---
 src/primitives/decode.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/primitives/decode.rs b/src/primitives/decode.rs
index 67103b553..f6f2b0759 100644
--- a/src/primitives/decode.rs
+++ b/src/primitives/decode.rs
@@ -368,6 +368,10 @@ impl<'s> SegwitHrpstring<'s> {
     pub fn new(s: &'s str) -> Result<Self, SegwitHrpstringError> {
         let unchecked = UncheckedHrpstring::new(s)?;
 
+        if unchecked.data.is_empty() {
+            return Err(SegwitHrpstringError::MissingWitnessVersion);
+        }
+
         // Unwrap ok since check_characters (in `Self::new`) checked the bech32-ness of this char.
         let witness_version = Fe32::from_char(unchecked.data[0].into()).unwrap();
         if witness_version.to_u8() > 16 {