Merge pull request #1272 from lightning-signer/2022-01-sign-invoice-api

[rust-lightning] / lightning / src / util / invoice.rs

diff --git a/lightning/src/util/invoice.rs b/lightning/src/util/invoice.rs
new file mode 100644 (file)
index 0000000..0612ff7
--- /dev/null
+++ b/lightning/src/util/invoice.rs
@@ -0,0 +1,26 @@
+//! Low level invoice utilities.
+
+use bitcoin::bech32::{u5, FromBase32};
+use prelude::*;
+
+/// Construct the invoice's HRP and signatureless data into a preimage to be hashed.
+pub fn construct_invoice_preimage(hrp_bytes: &[u8], data_without_signature: &[u5]) -> Vec<u8> {
+       let mut preimage = Vec::<u8>::from(hrp_bytes);
+
+       let mut data_part = Vec::from(data_without_signature);
+       let overhang = (data_part.len() * 5) % 8;
+       if overhang > 0 {
+               // add padding if data does not end at a byte boundary
+               data_part.push(u5::try_from_u8(0).unwrap());
+
+               // if overhang is in (1..3) we need to add u5(0) padding two times
+               if overhang < 3 {
+                       data_part.push(u5::try_from_u8(0).unwrap());
+               }
+       }
+
+       preimage.extend_from_slice(&Vec::<u8>::from_base32(&data_part)
+               .expect("No padding error may occur due to appended zero above."));
+       preimage
+}
+