f docs on encrypt_message_with_header_0s

Author: TheBlueMatt

lightning/src/ln/peer_channel_encryptor.rs

@@ -427,6 +427,12 @@ impl PeerChannelEncryptor {
 		Ok(self.their_node_id.unwrap().clone())
 	}
 
+	/// 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), and have an extra 16 bytes of capacity remaining 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 {