Test index-out-of-bounds in Features::to_context

When there are fewer known `from` feature bytes than known `to` feature
bytes, an index-out-of-bounds error can occur if the `from` features
have unknown features set in a byte past the greatest known `from`
feature byte.

diff --git a/lightning/src/ln/features.rs b/lightning/src/ln/features.rs
index a9f5a10ee2dad14395e18eda253cbaba2943106c..5d908ee01a4957bd7c85d305043af8e5204523a2 100644 (file)
--- a/lightning/src/ln/features.rs
+++ b/lightning/src/ln/features.rs
@@ -301,7 +301,7 @@ mod sealed {
                set_shutdown_any_segwit_required);
 
        #[cfg(test)]
-       define_feature!(123456789, UnknownFeature, [NodeContext, ChannelContext],
+       define_feature!(123456789, UnknownFeature, [NodeContext, ChannelContext, InvoiceContext],
                "Feature flags for an unknown feature used in testing.", set_unknown_feature_optional,
                set_unknown_feature_required);
 }
@@ -774,6 +774,16 @@ mod tests {
                assert!(!init_features.supports_gossip_queries());
        }
 
+       #[test]
+       fn convert_to_context_with_unknown_flags() {
+               // Ensure the `from` context has fewer known feature bytes than the `to` context.
+               assert!(InvoiceFeatures::known().byte_count() < NodeFeatures::known().byte_count());
+               let invoice_features = InvoiceFeatures::known().set_unknown_feature_optional();
+               assert!(invoice_features.supports_unknown_bits());
+               let node_features: NodeFeatures = invoice_features.to_context();
+               assert!(!node_features.supports_unknown_bits());
+       }
+
        #[test]
        fn set_feature_bits() {
                let features = InvoiceFeatures::empty()