onion_utils: extract decrypting faiure packet into method

Will be used in the next commit to parse onion errors from blinded paths in
tests only.

diff --git a/lightning/src/ln/onion_utils.rs b/lightning/src/ln/onion_utils.rs
index 31f2f7827bcb57c42d7b2a625a842abdaa00ab17..08fe7a73ae6f225df9ca9f873e8da1407689c3d1 100644 (file)
--- a/lightning/src/ln/onion_utils.rs
+++ b/lightning/src/ln/onion_utils.rs
@@ -433,11 +433,22 @@ pub(crate) struct DecodedOnionFailure {
        pub(crate) onion_error_data: Option<Vec<u8>>,
 }
 
+/// Note that we always decrypt `packet` in-place here even if the deserialization into
+/// [`msgs::DecodedOnionErrorPacket`] ultimately fails.
+fn decrypt_onion_error_packet(
+       packet: &mut Vec<u8>, shared_secret: SharedSecret
+) -> Result<msgs::DecodedOnionErrorPacket, msgs::DecodeError> {
+       let ammag = gen_ammag_from_shared_secret(shared_secret.as_ref());
+       let mut chacha = ChaCha20::new(&ammag, &[0u8; 8]);
+       chacha.process_in_place(packet);
+       msgs::DecodedOnionErrorPacket::read(&mut Cursor::new(packet))
+}
+
 /// Process failure we got back from upstream on a payment we sent (implying htlc_source is an
 /// OutboundRoute).
 #[inline]
 pub(super) fn process_onion_failure<T: secp256k1::Signing, L: Deref>(
-       secp_ctx: &Secp256k1<T>, logger: &L, htlc_source: &HTLCSource, mut packet_decrypted: Vec<u8>
+       secp_ctx: &Secp256k1<T>, logger: &L, htlc_source: &HTLCSource, mut encrypted_packet: Vec<u8>
 ) -> DecodedOnionFailure where L::Target: Logger {
        let (path, session_priv, first_hop_htlc_msat) = if let &HTLCSource::OutboundRoute {
                ref path, ref session_priv, ref first_hop_htlc_msat, ..
@@ -504,15 +515,7 @@ pub(super) fn process_onion_failure<T: secp256k1::Signing, L: Deref>(
                let amt_to_forward = htlc_msat - route_hop.fee_msat;
                htlc_msat = amt_to_forward;
 
-               let ammag = gen_ammag_from_shared_secret(shared_secret.as_ref());
-
-               let mut decryption_tmp = Vec::with_capacity(packet_decrypted.len());
-               decryption_tmp.resize(packet_decrypted.len(), 0);
-               let mut chacha = ChaCha20::new(&ammag, &[0u8; 8]);
-               chacha.process(&packet_decrypted, &mut decryption_tmp[..]);
-               packet_decrypted = decryption_tmp;
-
-               let err_packet = match msgs::DecodedOnionErrorPacket::read(&mut Cursor::new(&packet_decrypted)) {
+               let err_packet = match decrypt_onion_error_packet(&mut encrypted_packet, shared_secret) {
                        Ok(p) => p,
                        Err(_) => return
                };