Hold a reference to byte arrays when serializing to bech32

When we serialize from a byte array to bech32 in
`lightning-invoice`, we can either copy the array itself into the
iterator or hold a reference to the array and iterate through that.

In aa2f6b47df312f026213d0ceaaff20ffe955c377 we opted to copy the
array into the iterator, which is fine for the current array sizes
we're working with, but does result in additional memory on the
stack if, in the future, we end up writing large arrays.

Instead, here, we switch to using the slice serialization code when
writing arrays, (very marginally) reducing code size and reducing
stack usage.

diff --git a/lightning-invoice/src/ser.rs b/lightning-invoice/src/ser.rs
index 3d79a25331499c5d69b48ad5da91a8d3060c0083..66571ee35f9219d8ce8a3b7cc5e831efb4fad7de 100644 (file)
--- a/lightning-invoice/src/ser.rs
+++ b/lightning-invoice/src/ser.rs
@@ -29,7 +29,7 @@ pub(crate) trait Base32Len: Base32Iterable {
 
 impl<const N: usize> Base32Iterable for [u8; N] {
        fn fe_iter<'s>(&'s self) -> Box<dyn Iterator<Item = Fe32> + 's> {
-               Box::new((*self).into_iter().bytes_to_fes())
+               self[..].fe_iter()
        }
 }