cord-message 0.3.0

use crate::{errors::*, message::Message};
use bytes::{buf::BufMut, BytesMut};
use error_chain::bail;
use tokio_util::codec::{Decoder, Encoder};

use std::{convert::TryInto, mem, result::Result as StdResult, u16, u32, u8};

macro_rules! read_int_frame {
    ($src:expr, $assign_to:expr, $type:ty) => {
        if $assign_to.is_none() {
            let len = mem::size_of::<$type>();

            // Check we have adequate data in the buffer before proceeding
            if $src.len() < len {
                return Ok(None);
            }

            // Using `unwrap()` here should be safe as the buffer is first resized to the
            // length of the array.
            $assign_to = Some(<$type>::from_be_bytes(
                (*$src.split_to(len)).try_into().unwrap(),
            ));
        }
    };
}

macro_rules! read_str_frame {
    ($src:expr, $assign_to:expr, $len:expr) => {
        if $assign_to.is_none() {
            // Check we have adequate data in the buffer before proceeding
            if $src.len() < $len {
                return Ok(None);
            }

            // If the namespace contains non-UTF8 bytes, replace them with
            // U+FFFD REPLACEMENT CHARACTER. This allows the decoding to continue despite
            // the bad data. In future it may be better to reject non-UTF8 encoded
            // messages entirely, but will require returning Option<Message> or similar
            // to avoid terminating the stream altogether by returning an error.
            $assign_to = Some(String::from_utf8_lossy(&$src.split_to($len)).into_owned());
        }
    };
}

#[derive(Debug, Default)]
pub struct Codec {
    discriminant: Option<u8>,
    ns_length: Option<u16>,
    namespace: Option<String>,
    data_length: Option<u32>,
    data: Option<String>,
}

// Message framing on the wire looks like:
//      [u8             ][u16      ][bytestr  ][u32        ][bytestr]
//      [ns_discriminant][ns_length][namespace][data_length][data   ]
impl Encoder<Message> for Codec {
    type Error = Error;

    fn encode(&mut self, message: Message, dst: &mut BytesMut) -> StdResult<(), Self::Error> {
        // Ensure the namespace will fit into a u16 buffer
        if message.namespace().len() > u16::MAX as usize {
            bail!(ErrorKind::OversizedNamespace);
        }

        // Reserve enough buffer to write the namespace
        // 3 = u8 (1 byte) + u16 (2 bytes)
        dst.reserve(3 + message.namespace().len());

        // Write the message type to buffer
        dst.put_u8(message.poor_mans_discriminant());

        // Write namespace bytes to buffer
        dst.put_u16(message.namespace().len() as u16);
        dst.extend_from_slice(message.namespace().as_bytes());

        if let Message::Event(_, data) = message {
            // Ensure the message data will fit into a u32 buffer
            if data.len() > u32::MAX as usize {
                bail!(ErrorKind::OversizedData);
            }

            // Reserve enough buffer to write the data
            // 4 = u32 (4 bytes)
            dst.reserve(4 + data.len());

            // Write data bytes to buffer
            dst.put_u32(data.len() as u32);
            dst.extend_from_slice(data.as_bytes());
        }

        Ok(())
    }
}

impl Decoder for Codec {
    type Item = Message;
    type Error = Error;

    fn decode(&mut self, src: &mut BytesMut) -> StdResult<Option<Self::Item>, Self::Error> {
        // Read the discriminant (the type of message we're receiving)
        read_int_frame!(src, self.discriminant, u8);

        // Check that the discriminant is valid
        self.discriminant = self
            .discriminant
            .filter(Message::test_poor_mans_discriminant);

        if self.discriminant.is_none() {
            bail!("Unknown Message discriminant");
        }

        // Read the namespace's length
        read_int_frame!(src, self.ns_length, u16);

        // Read the namespace
        read_str_frame!(
            src,
            self.namespace,
            *self.ns_length.as_ref().unwrap() as usize
        );

        // The magic number "4" represents the discriminant value for Message::Event. If
        // we are receiving a Message::Event, there is an extra data component to read.
        if *self.discriminant.as_ref().unwrap() == 4 {
            // Read the data's length
            read_int_frame!(src, self.data_length, u32);

            // Read the data
            read_str_frame!(src, self.data, *self.data_length.as_ref().unwrap() as usize);
        }

        // Reset these values in preparation for the next message
        self.ns_length = None;
        self.data_length = None;

        Ok(Some(Message::from_poor_mans_discriminant(
            self.discriminant.take().unwrap(),
            self.namespace.take().unwrap().into(),
            self.data.take(),
        )))
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use bytes::Bytes;

    #[test]
    fn test_encode_nodata_ok() {
        let msg = Message::Provide("/my/namespace".into());
        let mut bytes = BytesMut::new();
        let mut encoder = Codec::default();
        encoder
            .encode(msg, &mut bytes)
            .expect("Failed to encode message");
        assert_eq!(bytes, Bytes::from("\0\0\r/my/namespace"));
    }

    #[test]
    fn test_encode_event_ok() {
        let msg = Message::Event("/my/namespace".into(), "abc, easy as 123".into());
        let mut bytes = BytesMut::new();
        let mut encoder = Codec::default();
        encoder
            .encode(msg, &mut bytes)
            .expect("Failed to encode message");
        assert_eq!(
            bytes,
            Bytes::from("\x04\0\r/my/namespace\0\0\0\x10abc, easy as 123")
        );
    }

    #[test]
    fn test_encode_oversized_namespace() {
        #[allow(clippy::cast_lossless)]
        let long_str = String::from_utf8(vec![0; (u16::MAX as u32 + 1) as usize]).unwrap();
        let msg = Message::Unsubscribe(long_str.into());
        let mut bytes = BytesMut::new();
        let mut encoder = Codec::default();
        match encoder
            .encode(msg, &mut bytes)
            .err()
            .expect("Test passed unexpectedly")
            .kind()
        {
            ErrorKind::OversizedNamespace => (),
            _ => panic!("Test passed unexpectedly"),
        }
    }

    #[test]
    #[ignore]
    fn test_encode_oversized_data() {
        // XXX Creating a String this large is very very very slow! In future this should
        // be mocked somehow.
        #[allow(clippy::cast_lossless)]
        let long_str = String::from_utf8(vec![0; (u32::MAX as u64 + 1) as usize]).unwrap();
        let msg = Message::Event("/".into(), long_str);
        let mut bytes = BytesMut::new();
        let mut encoder = Codec::default();
        match encoder
            .encode(msg, &mut bytes)
            .err()
            .expect("Test passed unexpectedly")
            .kind()
        {
            ErrorKind::OversizedData => (),
            _ => panic!("Test passed unexpectedly"),
        }
    }

    #[test]
    fn test_decode_ok() {
        let mut bytes = BytesMut::from("\x01\0\r/my/namespace");
        let mut decoder = Codec::default();
        let msg = decoder
            .decode(&mut bytes)
            .expect("Failed to decode message");
        assert_eq!(msg, Some(Message::Revoke("/my/namespace".into())));
    }

    #[test]
    fn test_decode_invalid_discriminant() {
        let mut bytes = BytesMut::from("\x09");
        let mut decoder = Codec::default();
        match decoder.decode(&mut bytes) {
            Ok(_) => panic!("Failed to detect invalid Message discriminant"),
            Err(e) => assert_eq!(e.description(), "Unknown Message discriminant"),
        }
    }

    #[test]
    fn test_decode_partial() {
        let mut bytes = BytesMut::new();
        let mut decoder = Codec::default();

        // Test decoding nothing
        let response = decoder
            .decode(&mut bytes)
            .expect("Failed to decode message");
        assert!(response.is_none());

        // Test decoding the discriminant
        bytes.put_u8(Message::Event("/".into(), String::new()).poor_mans_discriminant());
        let response = decoder
            .decode(&mut bytes)
            .expect("Failed to decode message");
        assert!(response.is_none());

        // Test decoding partial namespace
        bytes.put_u16(13);
        bytes.extend_from_slice(b"/my/name");
        let response = decoder
            .decode(&mut bytes)
            .expect("Failed to decode message");
        assert!(response.is_none());

        // Test decoding the rest of the namespace
        bytes.extend_from_slice(b"space");
        let response = decoder
            .decode(&mut bytes)
            .expect("Failed to decode message");
        assert!(response.is_none());

        // Test decoding partial data
        bytes.put_u32(5);
        bytes.extend_from_slice(b"a");
        let response = decoder
            .decode(&mut bytes)
            .expect("Failed to decode message");
        assert!(response.is_none());

        // Test decoding the rest of the data
        bytes.extend_from_slice(b"bcde");
        let msg = decoder
            .decode(&mut bytes)
            .expect("Failed to decode message");
        assert_eq!(
            msg,
            Some(Message::Event("/my/namespace".into(), "abcde".into()))
        );
    }

    #[test]
    fn test_decode_multiple() {
        let mut decoder = Codec::default();

        let mut bytes = BytesMut::from("\x01\0\r/my/namespace");
        let msg = decoder
            .decode(&mut bytes)
            .expect("Failed to decode message");
        assert_eq!(msg, Some(Message::Revoke("/my/namespace".into())));

        bytes.put_u8(4);
        bytes.put_u16(4);
        bytes.extend_from_slice(b"/moo");
        bytes.put_u32(3);
        bytes.extend_from_slice(b"cow");
        let msg = decoder
            .decode(&mut bytes)
            .expect("Failed to decode message");
        assert_eq!(msg, Some(Message::Event("/moo".into(), "cow".into())));
    }
}