f - make metadata slicing explicit

Author: jkczyz

lightning/src/offers/signer.rs

@@ -235,14 +235,17 @@ pub(super) fn verify_payer_metadata<'a, T: secp256k1::Signing>(
 	let mut encrypted_payment_id = [0u8; PaymentId::LENGTH];
 	encrypted_payment_id.copy_from_slice(&metadata[..PaymentId::LENGTH]);
 
-	let metadata = &metadata[PaymentId::LENGTH..];
-	let mut hmac = hmac_for_message(metadata, expanded_key, iv_bytes, tlv_stream)?;
+	let mut hmac = hmac_for_message(
+		&metadata[PaymentId::LENGTH..], expanded_key, iv_bytes, tlv_stream
+	)?;
 	hmac.input(WITH_ENCRYPTED_PAYMENT_ID_HMAC_INPUT);
 	hmac.input(&encrypted_payment_id);
 
-	verify_metadata(metadata, Hmac::from_engine(hmac), signing_pubkey, secp_ctx)?;
+	verify_metadata(
+		&metadata[PaymentId::LENGTH..], Hmac::from_engine(hmac), signing_pubkey, secp_ctx
+	)?;
 
-	let nonce = Nonce::try_from(&metadata[..Nonce::LENGTH]).unwrap();
+	let nonce = Nonce::try_from(&metadata[PaymentId::LENGTH..][..Nonce::LENGTH]).unwrap();
 	let payment_id = expanded_key.crypt_for_offer(encrypted_payment_id, &nonce.0);
 
 	Ok(PaymentId(payment_id))