From 13c9491e49481f9800b297c4077653f1d42efd84 Mon Sep 17 00:00:00 2001
From: "Dr. Maxim Orlovsky" <orlovsky@pandoraprime.ch>
Date: Mon, 21 Nov 2022 15:29:34 +0100
Subject: [PATCH] Implement framer and multiplexer

---
 radicle-node/src/wire.rs            |   4 +-
 radicle-node/src/wire/transcoder.rs | 132 ++++++++++++++++++++++++++--
 2 files changed, 127 insertions(+), 9 deletions(-)

diff --git a/radicle-node/src/wire.rs b/radicle-node/src/wire.rs
index 2d65aa29..1204caa1 100644
--- a/radicle-node/src/wire.rs
+++ b/radicle-node/src/wire.rs
@@ -542,7 +542,7 @@ where
             deserializer,
         }) = self.inboxes.get_mut(addr)
         {
-            let bytes = transcoder.decrypt(raw_bytes);
+            let bytes = transcoder.decode(raw_bytes);
             deserializer.input(&bytes);
 
             loop {
@@ -584,7 +584,7 @@ impl<R, S, W, G, H: Handshake> Iterator for Wire<R, S, W, G, H> {
                 let Inbox { transcoder, .. } = self.inboxes.get_mut(&addr).expect(
                     "broken handshake implementation: data sent before handshake was complete",
                 );
-                let data = transcoder.encrypt(buf);
+                let data = transcoder.encode(buf);
                 Some(nakamoto::Io::Write(addr, data))
             }
             Some(Io::Event(e)) => Some(nakamoto::Io::Event(e)),
diff --git a/radicle-node/src/wire/transcoder.rs b/radicle-node/src/wire/transcoder.rs
index db2ff46b..2f25920a 100644
--- a/radicle-node/src/wire/transcoder.rs
+++ b/radicle-node/src/wire/transcoder.rs
@@ -1,5 +1,9 @@
-use nakamoto_net::Link;
+use std::collections::VecDeque;
 use std::convert::Infallible;
+use std::io;
+use std::io::Read;
+
+use nakamoto_net::Link;
 
 // TODO: Implement Try trait once stabilized
 /// Result of a state-machine transition.
@@ -50,15 +54,14 @@ impl Handshake for NoHandshake {
     }
 }
 
-/// Trait allowing transcoding a stream using some form of stream encryption
-/// and/or encoding.
+/// Trait allowing transcoding a stream using some form of stream encryption and/or encoding.
 pub trait Transcode {
     /// Decodes data received from the remote peer and update the internal state
     /// of the transcoder, if necessary.
-    fn decrypt(&mut self, data: &[u8]) -> Vec<u8>;
+    fn decode(&mut self, data: &[u8]) -> Vec<u8>;
 
     /// Encodes data before sending it to the remote peer.
-    fn encrypt(&mut self, data: Vec<u8>) -> Vec<u8>;
+    fn encode(&mut self, data: Vec<u8>) -> Vec<u8>;
 }
 
 /// Transcoder which does nothing.
@@ -66,11 +69,126 @@ pub trait Transcode {
 pub struct PlainTranscoder;
 
 impl Transcode for PlainTranscoder {
-    fn decrypt(&mut self, data: &[u8]) -> Vec<u8> {
+    fn decode(&mut self, data: &[u8]) -> Vec<u8> {
         data.to_vec()
     }
 
-    fn encrypt(&mut self, data: Vec<u8>) -> Vec<u8> {
+    fn encode(&mut self, data: Vec<u8>) -> Vec<u8> {
         data
     }
 }
+
+pub type Frame = Vec<u8>;
+
+#[derive(Copy, Clone, Debug)]
+pub struct OversizedData(usize);
+
+#[derive(Debug, Default)]
+pub struct Framer<T: Transcode> {
+    input: VecDeque<u8>,
+    inner: T,
+}
+
+impl<T: Transcode> Framer<T> {
+    pub fn new(inner: T) -> Self {
+        Framer {
+            input: Default::default(),
+            inner,
+        }
+    }
+
+    pub fn input(&mut self, encoded: &[u8]) {
+        self.input.extend(self.inner.decode(encoded));
+    }
+
+    pub fn frame(&mut self, decoded: Vec<u8>) -> Result<Frame, OversizedData> {
+        let mut data = self.inner.encode(decoded);
+        let len = data.len();
+        let len = u8::try_from(len).map_err(|_| OversizedData(len))?;
+        let len = len.to_be_bytes();
+        let mut buf = Vec::with_capacity(data.len() + 2);
+        buf.extend(len);
+        buf.append(&mut data);
+        Ok(buf)
+    }
+}
+
+impl<T: Transcode> Iterator for Framer<T> {
+    type Item = Frame;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.input.len() < 2 {
+            return None;
+        }
+        let mut len = [0u8; 2];
+        self.input
+            .read_exact(&mut len)
+            .expect("the length is checked");
+        let len = u16::from_be_bytes(len) as usize;
+        if self.input.len() < 2 + len {
+            return None;
+        }
+        self.input.pop_front();
+        self.input.pop_front();
+        let reminder = self.input.split_off(len);
+        let mut data = vec![0u8; len];
+        self.input.read_exact(&mut data).expect("checked length");
+        self.input = reminder;
+        Some(data)
+    }
+}
+
+#[derive(Copy, Clone, Debug)]
+pub struct ChannelError;
+
+#[derive(Clone, Ord, PartialOrd, Eq, PartialEq, Hash, Debug)]
+pub struct MuxMsg {
+    pub channel: u16,
+    pub data: Vec<u8>,
+}
+
+impl TryFrom<Frame> for MuxMsg {
+    type Error = ChannelError;
+
+    fn try_from(frame: Frame) -> Result<Self, Self::Error> {
+        if frame.len() < 2 {
+            return Err(ChannelError);
+        }
+        let mut channel = [0u8; 2];
+        let mut cursor = io::Cursor::new(frame);
+        cursor
+            .read_exact(&mut channel)
+            .expect("the length is checked");
+        let channel = u16::from_be_bytes(channel);
+        Ok(MuxMsg {
+            channel,
+            data: cursor.into_inner(),
+        })
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn transcode() {
+        let mut pipeline = Framer::new(PlainTranscoder);
+
+        let data = [
+            0x00, 0x04, 0x00, 0x00, b'a', b'b', 0x00, 0x07, 0x00, 0x01, b'M', b'a', b'x', b'i',
+            b'm',
+        ];
+        let mut expected_payloads = [(0u16, b"ab".to_vec()), (1, b"Maxim".to_vec())].into_iter();
+
+        for byte in data {
+            // Writing data byte by byte, ensuring that the reading is not broken
+            pipeline.input(&[byte]);
+            for frame in &mut pipeline {
+                let msg = MuxMsg::try_from(frame).unwrap();
+                let (channel, data) = expected_payloads.next().unwrap();
+                assert_eq!(msg, MuxMsg { channel, data });
+            }
+        }
+    }
+}