Avoid re-allocating to encrypt gossip messages when forwarding

[rust-lightning] / lightning / src / ln / peer_channel_encryptor.rs

diff --git a/lightning/src/ln/peer_channel_encryptor.rs b/lightning/src/ln/peer_channel_encryptor.rs
index 8b276990cb689846680fa7de24070a4a433325de..8569fa60ffef46268fd020578dc22cb1e455649d 100644 (file)
--- a/lightning/src/ln/peer_channel_encryptor.rs
+++ b/lightning/src/ln/peer_channel_encryptor.rs
@@ -427,16 +427,20 @@ impl PeerChannelEncryptor {
                Ok(self.their_node_id.unwrap().clone())
        }
 
-       /// Encrypts the given pre-serialized message, returning the encrypted version.
-       /// panics if msg.len() > 65535 or Noise handshake has not finished.
-       pub fn encrypt_buffer(&mut self, msg: &[u8]) -> Vec<u8> {
-               if msg.len() > LN_MAX_MSG_LEN {
+       /// Builds sendable bytes for a message.
+       ///
+       /// `msgbuf` must begin with 16 + 2 dummy/0 bytes, which will be filled with the encrypted
+       /// message length and its MAC. It should then be followed by the message bytes themselves
+       /// (including the two byte message type).
+       ///
+       /// For effeciency, the [`Vec::capacity`] should be at least 16 bytes larger than the
+       /// [`Vec::len`], to avoid reallocating for the message MAC, which will be appended to the vec.
+       fn encrypt_message_with_header_0s(&mut self, msgbuf: &mut Vec<u8>) {
+               let msg_len = msgbuf.len() - 16 - 2;
+               if msg_len > LN_MAX_MSG_LEN {
                        panic!("Attempted to encrypt message longer than 65535 bytes!");
                }
 
-               let mut res = Vec::with_capacity(msg.len() + 16*2 + 2);
-               res.resize(msg.len() + 16*2 + 2, 0);
-
                match self.noise_state {
                        NoiseState::Finished { ref mut sk, ref mut sn, ref mut sck, rk: _, rn: _, rck: _ } => {
                                if *sn >= 1000 {
@@ -446,16 +450,21 @@ impl PeerChannelEncryptor {
                                        *sn = 0;
                                }
 
-                               Self::encrypt_with_ad(&mut res[0..16+2], *sn, sk, &[0; 0], &(msg.len() as u16).to_be_bytes());
+                               Self::encrypt_with_ad(&mut msgbuf[0..16+2], *sn, sk, &[0; 0], &(msg_len as u16).to_be_bytes());
                                *sn += 1;
 
-                               Self::encrypt_with_ad(&mut res[16+2..], *sn, sk, &[0; 0], msg);
+                               Self::encrypt_in_place_with_ad(msgbuf, 16+2, *sn, sk, &[0; 0]);
                                *sn += 1;
                        },
                        _ => panic!("Tried to encrypt a message prior to noise handshake completion"),
                }
+       }
 
-               res
+       /// Encrypts the given pre-serialized message, returning the encrypted version.
+       /// panics if msg.len() > 65535 or Noise handshake has not finished.
+       pub fn encrypt_buffer(&mut self, mut msg: MessageBuf) -> Vec<u8> {
+               self.encrypt_message_with_header_0s(&mut msg.0);
+               msg.0
        }
 
        /// Encrypts the given message, returning the encrypted version.
@@ -468,29 +477,7 @@ impl PeerChannelEncryptor {
                res.0.resize(16 + 2, 0);
                wire::write(message, &mut res).expect("In-memory messages must never fail to serialize");
 
-               let msg_len = res.0.len() - 16 - 2;
-               if msg_len > LN_MAX_MSG_LEN {
-                       panic!("Attempted to encrypt message longer than 65535 bytes!");
-               }
-
-               match self.noise_state {
-                       NoiseState::Finished { ref mut sk, ref mut sn, ref mut sck, rk: _, rn: _, rck: _ } => {
-                               if *sn >= 1000 {
-                                       let (new_sck, new_sk) = hkdf_extract_expand_twice(sck, sk);
-                                       *sck = new_sck;
-                                       *sk = new_sk;
-                                       *sn = 0;
-                               }
-
-                               Self::encrypt_with_ad(&mut res.0[0..16+2], *sn, sk, &[0; 0], &(msg_len as u16).to_be_bytes());
-                               *sn += 1;
-
-                               Self::encrypt_in_place_with_ad(&mut res.0, 16+2, *sn, sk, &[0; 0]);
-                               *sn += 1;
-                       },
-                       _ => panic!("Tried to encrypt a message prior to noise handshake completion"),
-               }
-
+               self.encrypt_message_with_header_0s(&mut res.0);
                res.0
        }
 
@@ -557,9 +544,30 @@ impl PeerChannelEncryptor {
        }
 }
 
+/// A buffer which stores an encoded message (including the two message-type bytes) with some
+/// padding to allow for future encryption/MACing.
+pub struct MessageBuf(Vec<u8>);
+impl MessageBuf {
+       /// Creates a new buffer from an encoded message (i.e. the two message-type bytes followed by
+       /// the message contents).
+       ///
+       /// Panics if the message is longer than 2^16.
+       pub fn from_encoded(encoded_msg: &[u8]) -> Self {
+               if encoded_msg.len() > LN_MAX_MSG_LEN {
+                       panic!("Attempted to encrypt message longer than 65535 bytes!");
+               }
+               // In addition to the message (continaing the two message type bytes), we also have to add
+               // the message length header (and its MAC) and the message MAC.
+               let mut res = Vec::with_capacity(encoded_msg.len() + 16*2 + 2);
+               res.resize(encoded_msg.len() + 16 + 2, 0);
+               res[16 + 2..].copy_from_slice(&encoded_msg);
+               Self(res)
+       }
+}
+
 #[cfg(test)]
 mod tests {
-       use super::LN_MAX_MSG_LEN;
+       use super::{MessageBuf, LN_MAX_MSG_LEN};
 
        use bitcoin::secp256k1::{PublicKey, SecretKey};
        use bitcoin::secp256k1::Secp256k1;
@@ -775,7 +783,7 @@ mod tests {
 
                for i in 0..1005 {
                        let msg = [0x68, 0x65, 0x6c, 0x6c, 0x6f];
-                       let mut res = outbound_peer.encrypt_buffer(&msg);
+                       let mut res = outbound_peer.encrypt_buffer(MessageBuf::from_encoded(&msg));
                        assert_eq!(res.len(), 5 + 2*16 + 2);
 
                        let len_header = res[0..2+16].to_vec();
@@ -811,7 +819,7 @@ mod tests {
        fn max_message_len_encryption() {
                let mut outbound_peer = get_outbound_peer_for_initiator_test_vectors();
                let msg = [4u8; LN_MAX_MSG_LEN + 1];
-               outbound_peer.encrypt_buffer(&msg);
+               outbound_peer.encrypt_buffer(MessageBuf::from_encoded(&msg));
        }
 
        #[test]