Small optimization: Invoke hash_from_parts() in only one place

lightning-invoice/src/de.rs

@@ -374,16 +374,15 @@ impl FromStr for SignedRawBolt11Invoice {
 
 		let raw_hrp: RawHrp = hrp.to_string().to_lowercase().parse()?;
 		let data_part = RawDataPart::from_base32(&data[..data.len() - SIGNATURE_LEN5])?;
+		let raw_invoice = RawBolt11Invoice {
+			hrp: raw_hrp,
+			data: data_part,
+		};
+		let hash = raw_invoice.signable_hash();
 
 		Ok(SignedRawBolt11Invoice {
-			raw_invoice: RawBolt11Invoice {
-				hrp: raw_hrp,
-				data: data_part,
-			},
-			hash: RawBolt11Invoice::hash_from_parts(
-				hrp.to_string().as_bytes(),
-				&data[..data.len() - SIGNATURE_LEN5],
-			),
+			raw_invoice,
+			hash,
 			signature: Bolt11InvoiceSignature::from_base32(&data[data.len() - SIGNATURE_LEN5..])?,
 		})
 	}

lightning-invoice/src/lib.rs

@@ -1001,18 +1001,12 @@ macro_rules! find_all_extract {
 #[allow(missing_docs)]
 impl RawBolt11Invoice {
 	/// Hash the HRP (as bytes) and signatureless data part (as Fe32 iterator)
-	fn hash_from_parts_iter<'s>(hrp_bytes: &[u8], data_without_signature_iter: Box<dyn Iterator<Item = Fe32> + 's>) -> [u8; 32] {
-		let data_part_signature = data_without_signature_iter.collect::<Vec<Fe32>>();
-		Self::hash_from_parts(hrp_bytes, &data_part_signature[..])
-	}
-
-	/// Hash the HRP as bytes and signatureless data part.
-	fn hash_from_parts(hrp_bytes: &[u8], data_without_signature: &[Fe32]) -> [u8; 32] {
+	fn hash_from_parts<'s>(hrp_bytes: &[u8], data_without_signature: Box<dyn Iterator<Item = Fe32> + 's>) -> [u8; 32] {
 		use crate::de::FromBase32;
 
-		let mut preimage = Vec::<u8>::from(hrp_bytes);
+		let mut data_part = data_without_signature.collect::<Vec<Fe32>>();
 
-		let mut data_part = Vec::from(data_without_signature);
+		// Need to pad before from_base32 conversion
 		let overhang = (data_part.len() * 5) % 8;
 		if overhang > 0 {
 			// add padding if data does not end at a byte boundary
@@ -1024,6 +1018,7 @@ impl RawBolt11Invoice {
 			}
 		}
 
+		let mut preimage = Vec::<u8>::from(hrp_bytes);
 		preimage.extend_from_slice(&Vec::<u8>::from_base32(&data_part)
 			.expect("No padding error may occur due to appended zero above."));
 
@@ -1036,7 +1031,7 @@ impl RawBolt11Invoice {
 	pub fn signable_hash(&self) -> [u8; 32] {
 		use crate::ser::Base32Iterable;
 
-		RawBolt11Invoice::hash_from_parts_iter(
+		Self::hash_from_parts(
 			self.hrp.to_string().as_bytes(),
 			self.data.fe_iter(),
 		)