cobs/

dec.rs

/// The [`DecoderState`] is used to track the current state of a
/// streaming decoder. This struct does not contain the output buffer
/// (or a reference to one), and can be used when streaming the decoded
/// output to a custom data type.
#[derive(Debug, Default)]
pub enum DecoderState {
    /// State machine has not received any non-zero bytes
    #[default]
    Idle,

    /// 1-254 bytes, can be header or 00
    Grab(u8),

    /// 255 bytes, will be a header next
    GrabChain(u8),
}

fn add(to: &mut [u8], idx: usize, data: u8) -> Result<(), DecodeError> {
    *to.get_mut(idx).ok_or(DecodeError::TargetBufTooSmall)? = data;
    Ok(())
}

/// [`DecodeResult`] represents the possible non-error outcomes of
/// pushing an encoded data byte into the [`DecoderState`] state machine
#[derive(Debug)]
pub enum DecodeResult {
    /// The given input byte did not prompt an output byte, either because the
    /// state machine is still idle, or we have just processed a header byte.
    /// More data is needed to complete the message.
    NoData,

    /// Received start of a new frame.
    DataStart,

    /// We have received a complete and well-encoded COBS message. The
    /// contents of the associated output buffer may now be used
    DataComplete,

    /// The following byte should be appended to the current end of the decoded
    /// output buffer.
    /// More data is needed to complete the message.
    DataContinue(u8),
}

#[derive(Debug, PartialEq, Eq, thiserror::Error)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub enum DecodeError {
    #[error("empty input frame")]
    EmptyFrame,
    #[error("frame with invalid format, written {decoded_bytes:?} to decoded buffer")]
    InvalidFrame {
        /// Number of bytes written to the decoded buffer.
        decoded_bytes: usize,
    },
    #[error("target buffer too small")]
    TargetBufTooSmall,
}

impl DecoderState {
    /// Feed a single encoded byte into the state machine. If the input was
    /// unexpected, such as an early end of a framed message segment, an Error will
    /// be returned, and the current associated output buffer contents should be discarded.
    ///
    /// If a complete message is indicated, the decoding state machine will automatically
    /// reset itself to the Idle state, and may be used to begin decoding another message.
    ///
    /// NOTE: Sentinel value must be included in the input to this function for the
    /// decoding to complete
    pub fn feed(&mut self, data: u8) -> Result<DecodeResult, DecodeError> {
        use DecodeResult::*;
        use DecoderState::*;

        let (ret, state) = match (&self, data) {
            (Grab(i), n) => {
                if *i > 0 && n > 0 {
                    // We have not yet reached the end of a data run, decrement the run
                    // counter, and place the byte into the decoded output
                    (Ok(DataContinue(n)), Grab(*i - 1))
                } else if *i == 0 {
                    match n {
                        // We have reached the end of a data run indicated by an overhead
                        // byte, AND we have received the message terminator. This was a
                        // well framed message!
                        0x00 => (Ok(DataComplete), Idle),

                        // We have reached the end of a data run indicated by an overhead
                        // byte, and the next segment of 254 bytes will have no modified
                        // sentinel bytes
                        0xFF => (Ok(DataContinue(0)), GrabChain(0xFE)),

                        // We have reached the end of a data run indicated by an overhead
                        // byte, and we will treat this byte as a modified sentinel byte.
                        // place the sentinel byte in the output, and begin processing the
                        // next non-sentinel sequence
                        n => (Ok(DataContinue(0)), Grab(n - 1)),
                    }
                } else {
                    // We were not expecting the sequence to terminate, but here we are.
                    // Report an error due to early terminated message
                    (Err(DecodeError::InvalidFrame { decoded_bytes: 0 }), Idle)
                }
            }

            (GrabChain(i), n) => {
                if *i > 0 && n > 0 {
                    // We have not yet reached the end of a data run, decrement the run
                    // counter, and place the byte into the decoded output
                    (Ok(DataContinue(n)), GrabChain(*i - 1))
                } else if *i == 0 {
                    match n {
                        // We have reached the end of a data run indicated by an overhead
                        // byte, AND we have received the message terminator. This was a
                        // well framed message!
                        0x00 => (Ok(DataComplete), Idle),

                        // We have reached the end of a data run, and we will begin another
                        // data run with an overhead byte expected at the end
                        0xFF => (Ok(NoData), GrabChain(0xFE)),

                        // We have reached the end of a data run, and we will expect `n` data
                        // bytes unmodified, followed by a sentinel byte that must be modified
                        n => (Ok(NoData), Grab(n - 1)),
                    }
                } else {
                    // We were not expecting the sequence to terminate, but here we are.
                    // Report an error due to early terminated message
                    (Err(DecodeError::InvalidFrame { decoded_bytes: 0 }), Idle)
                }
            }

            // Currently Idle, received a terminator, ignore, stay idle
            (Idle, 0x00) => (Ok(NoData), Idle),

            // Currently Idle, received a byte indicating the
            // next 255 bytes have no zeroes, so we will have 254 unmodified
            // data bytes, then an overhead byte
            (Idle, 0xFF) => (Ok(DataStart), GrabChain(0xFE)),

            // Currently Idle, received a byte indicating there will be a
            // zero that must be modified in the next 1..=254 bytes
            (Idle, n) => (Ok(DataStart), Grab(n - 1)),
        };

        *self = state;
        ret
    }
}

#[derive(Debug, Default)]
struct CobsDecoderInner {
    /// Index of next byte to write in `dest`
    dest_idx: usize,

    /// Decoder state as an enum
    state: DecoderState,
}

impl CobsDecoderInner {
    const fn new() -> Self {
        Self {
            dest_idx: 0,
            state: DecoderState::Idle,
        }
    }

    /// Feed a single byte into the streaming CobsDecoder. Return values mean:
    ///
    /// * Ok(None) - State machine okay, more data needed
    /// * Ok(Some(N)) - A message of N bytes was successfully decoded
    /// * Err([DecodeError]) - Message decoding failed
    ///
    /// NOTE: Sentinel value must be included in the input to this function for the
    /// decoding to complete
    fn feed(&mut self, dest: &mut [u8], data: u8) -> Result<Option<usize>, DecodeError> {
        match self.state.feed(data) {
            Err(_) => Err(DecodeError::InvalidFrame {
                decoded_bytes: self.dest_idx,
            }),
            Ok(DecodeResult::NoData) => Ok(None),
            Ok(DecodeResult::DataStart) => {
                self.dest_idx = 0;
                Ok(None)
            }
            Ok(DecodeResult::DataContinue(n)) => {
                add(dest, self.dest_idx, n)?;
                self.dest_idx += 1;
                Ok(None)
            }
            Ok(DecodeResult::DataComplete) => Ok(Some(self.dest_idx)),
        }
    }

    /// Push a slice of bytes into the streaming CobsDecoder. Return values mean:
    ///
    /// * Ok(None) - State machine okay, more data needed
    /// * Ok(Some([DecodeReport]))) - A message was successfully decoded. The parse size of the
    ///   report specifies the consumed bytes of the passed data chunk.
    /// * Err([DecodeError]) - Message decoding failed
    ///
    /// If the decoder is used for continuous decoding, the user must take care of feeding any
    /// undecoded bytes of the input data back into the decoder. This can be done by
    /// [Self::push]ing the undecoded bytes (the last X bytes of the input with X being the length
    /// of the input minus the parsed length) into the decoder after a frame was decoded.
    ///
    /// NOTE: Sentinel value must be included in the input to this function for the
    /// decoding to complete
    pub fn push(
        &mut self,
        dest: &mut [u8],
        data: &[u8],
    ) -> Result<Option<DecodeReport>, DecodeError> {
        for (consumed_idx, byte) in data.iter().enumerate() {
            let opt_decoded_bytes = self.feed(dest, *byte)?;
            if let Some(decoded_bytes_ct) = opt_decoded_bytes {
                // convert from index to number of bytes consumed
                return Ok(Some(DecodeReport {
                    frame_size: decoded_bytes_ct,
                    parsed_size: consumed_idx + 1,
                }));
            }
        }

        Ok(None)
    }
}

/// The [`CobsDecoder`] type is used to decode a stream of bytes to a
/// given mutable output slice. This is often useful when heap data
/// structures are not available, or when not all message bytes are
/// received at a single point in time.
#[derive(Debug)]
pub struct CobsDecoder<'a> {
    /// Destination slice for decoded message
    dest: &'a mut [u8],
    inner: CobsDecoderInner,
}

impl<'a> CobsDecoder<'a> {
    /// Create a new streaming Cobs Decoder. Provide the output buffer
    /// for the decoded message to be placed in
    pub const fn new(dest: &'a mut [u8]) -> CobsDecoder<'a> {
        CobsDecoder {
            dest,
            inner: CobsDecoderInner::new(),
        }
    }

    /// Feed a single byte into the streaming decoder. Return values mean:
    ///
    /// * Ok(None) - State machine okay, more data needed
    /// * Ok(Some(N)) - A message of N bytes was successfully decoded
    /// * Err([DecodeError]) - Message decoding failed
    ///
    /// NOTE: Sentinel value must be included in the input to this function for the
    /// decoding to complete
    pub fn feed(&mut self, data: u8) -> Result<Option<usize>, DecodeError> {
        self.inner.feed(self.dest, data)
    }

    /// Push a slice of bytes into the streaming CobsDecoder. Return values mean:
    ///
    /// * Ok(None) - State machine okay, more data needed
    /// * Ok(Some([DecodeReport]))) - A message was successfully decoded. The parse size of the
    ///   report specifies the consumed bytes of the passed data chunk.
    /// * Err([DecodeError]) - Message decoding failed
    ///
    /// If the decoder is used for continuous decoding, the user must take care of feeding any
    /// undecoded bytes of the input data back into the decoder. This can be done by
    /// [Self::push]ing the undecoded bytes (the last X bytes of the input with X being the length
    /// of the input minus the parsed length) into the decoder after a frame was decoded.
    ///
    /// NOTE: Sentinel value must be included in the input to this function for the
    /// decoding to complete
    pub fn push(&mut self, data: &[u8]) -> Result<Option<DecodeReport>, DecodeError> {
        self.inner.push(self.dest, data)
    }

    /// Destination buffer which contains decoded frames.
    #[inline]
    pub fn dest(&self) -> &[u8] {
        self.dest
    }

    /// Destination buffer which contains decoded frames.
    ///
    /// This allows using the buffer for other purposes than decoding after a frame was found.
    /// Changing the buffer in any other state might corrupt a frame which might currently be
    /// decoded.
    #[inline]
    pub fn dest_mut(&mut self) -> &mut [u8] {
        self.dest
    }
}

/// The [`CobsDecoderHeapless`] type is used to decode a stream of bytes to a given mutable output
/// slice. It owns the heapless decoding buffer.
///
/// This structure uses a heapless vector as the decoding buffer to avoid lifetimes.
#[derive(Default, Debug)]
pub struct CobsDecoderHeapless<const N: usize> {
    /// Destination slice for decoded message
    dest: heapless::Vec<u8, N>,
    inner: CobsDecoderInner,
}

impl<const N: usize> CobsDecoderHeapless<N> {
    /// This constructor internally creates the heapless vector.
    pub fn new() -> Self {
        let vec = heapless::Vec::new();
        Self::new_with_vec(vec)
    }

    /// This constructor allows passing the heapless vector to use.
    ///
    /// This can be useful to place the heapless vector into the static BSS section instead of the
    /// stack.
    pub fn new_with_vec(mut vec: heapless::Vec<u8, N>) -> Self {
        vec.resize(vec.capacity(), 0).unwrap();
        Self {
            dest: vec,
            inner: CobsDecoderInner::new(),
        }
    }

    /// Feed a single byte into the streaming decoder. Return values mean:
    ///
    /// * Ok(None) - State machine okay, more data needed
    /// * Ok(Some(N)) - A message of N bytes was successfully decoded
    /// * Err([DecodeError]) - Message decoding failed
    ///
    /// NOTE: Sentinel value must be included in the input to this function for the
    /// decoding to complete
    pub fn feed(&mut self, data: u8) -> Result<Option<usize>, DecodeError> {
        self.inner.feed(&mut self.dest, data)
    }

    /// Push a slice of bytes into the streaming CobsDecoder. Return values mean:
    ///
    /// * Ok(None) - State machine okay, more data needed
    /// * Ok(Some([DecodeReport]))) - A message was successfully decoded. The parse size of the
    ///   report specifies the consumed bytes of the passed data chunk.
    /// * Err([DecodeError]) - Message decoding failed
    ///
    /// If the decoder is used for continuous decoding, the user must take care of feeding any
    /// undecoded bytes of the input data back into the decoder. This can be done by
    /// [Self::push]ing the undecoded bytes (the last X bytes of the input with X being the length
    /// of the input minus the parsed length) into the decoder after a frame was decoded.
    ///
    /// NOTE: Sentinel value must be included in the input to this function for the
    /// decoding to complete
    pub fn push(&mut self, data: &[u8]) -> Result<Option<DecodeReport>, DecodeError> {
        self.inner.push(&mut self.dest, data)
    }

    /// Destination buffer which contains decoded frames.
    #[inline]
    pub fn dest(&self) -> &[u8] {
        &self.dest
    }

    /// Destination buffer which contains decoded frames.
    ///
    /// This allows using the buffer for other purposes than decoding after a frame was found.
    /// Changing the buffer in any other state might corrupt a frame which might currently be
    /// decoded.
    #[inline]
    pub fn dest_mut(&mut self) -> &mut [u8] {
        &mut self.dest
    }

    /// Reset the decoding state machine.
    #[inline]
    pub fn reset(&mut self) {
        self.inner = Default::default();
    }
}

/// The [`CobsDecoderOwned`] type is used to decode a stream of bytes to a given mutable output
/// slice. It owns the decoding buffer.
///
/// This structure allocates the buffer once at construction but does not perform
/// runtime allocations. This simplifies keeping a streaming decoder structure as a field
/// of a structure because it does not require a lifetime.
#[cfg(feature = "alloc")]
#[derive(Debug)]
pub struct CobsDecoderOwned {
    /// Destination slice for decoded message
    dest: alloc::vec::Vec<u8>,
    inner: CobsDecoderInner,
}

#[cfg(feature = "alloc")]
impl CobsDecoderOwned {
    /// Create a new streaming Cobs Decoder. Provide the output buffer
    /// for the decoded message to be placed in
    pub fn new(dest_buf_size: usize) -> Self {
        Self {
            dest: alloc::vec![0; dest_buf_size],
            inner: CobsDecoderInner::new(),
        }
    }

    /// Feed a single byte into the streaming decoder. Return values mean:
    ///
    /// * Ok(None) - State machine okay, more data needed
    /// * Ok(Some(N)) - A message of N bytes was successfully decoded
    /// * Err([DecodeError]) - Message decoding failed
    ///
    /// NOTE: Sentinel value must be included in the input to this function for the
    /// decoding to complete
    pub fn feed(&mut self, data: u8) -> Result<Option<usize>, DecodeError> {
        self.inner.feed(&mut self.dest, data)
    }

    /// Push a slice of bytes into the streaming CobsDecoder. Return values mean:
    ///
    /// * Ok(None) - State machine okay, more data needed
    /// * Ok(Some([DecodeReport]))) - A message was successfully decoded. The parse size of the
    ///   report specifies the consumed bytes of the passed data chunk.
    /// * Err([DecodeError]) - Message decoding failed
    ///
    /// If the decoder is used for continuous decoding, the user must take care of feeding any
    /// undecoded bytes of the input data back into the decoder. This can be done by
    /// [Self::push]ing the undecoded bytes (the last X bytes of the input with X being the length
    /// of the input minus the parsed length) into the decoder after a frame was decoded.
    ///
    /// NOTE: Sentinel value must be included in the input to this function for the
    /// decoding to complete
    pub fn push(&mut self, data: &[u8]) -> Result<Option<DecodeReport>, DecodeError> {
        self.inner.push(&mut self.dest, data)
    }

    /// Destination buffer which contains decoded frames.
    #[inline]
    pub fn dest(&self) -> &[u8] {
        &self.dest
    }

    /// Destination buffer which contains decoded frames.
    ///
    /// This allows using the buffer for other purposes than decoding after a frame was found.
    /// Changing the buffer in any other state might corrupt a frame which might currently be
    /// decoded.
    #[inline]
    pub fn dest_mut(&mut self) -> &mut [u8] {
        &mut self.dest
    }

    /// Reset the decoding state machine.
    #[inline]
    pub fn reset(&mut self) {
        self.inner = Default::default();
    }
}

/// Decodes the `source` buffer into the `dest` buffer.
///
/// This function uses the typical sentinel value of 0.
pub fn decode(source: &[u8], dest: &mut [u8]) -> Result<DecodeReport, DecodeError> {
    if source.is_empty() {
        return Err(DecodeError::EmptyFrame);
    }

    let mut dec = CobsDecoder::new(dest);

    // Did we decode a message, using some or all of the buffer?
    if let Some(result) = dec.push(source)? {
        return Ok(result);
    }

    // If we consumed the entire buffer, but did NOT get a message,
    // AND the message did not end with a zero, try providing one to
    // complete the decoding.
    if source.last() != Some(&0) {
        // Explicitly push sentinel of zero
        if let Some(result) = dec.push(&[0])? {
            return Ok(DecodeReport {
                frame_size: result.frame_size(),
                parsed_size: source.len(),
            });
        }
    }

    // Nope, no early message, no missing terminator, just failed to decode
    Err(DecodeError::InvalidFrame {
        decoded_bytes: dec.inner.dest_idx,
    })
}

/// A report of the source and destination bytes used during in-place decoding
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub struct DecodeReport {
    parsed_size: usize,
    frame_size: usize,
}

impl DecodeReport {
    /// The number of source bytes parsed.
    #[inline]
    pub fn parsed_size(&self) -> usize {
        self.parsed_size
    }

    /// The decoded frame size.
    #[inline]
    pub fn frame_size(&self) -> usize {
        self.frame_size
    }
}

/// Decodes a message in-place.
///
/// This is the same function as [decode_in_place], but provides a report
/// of both the number of source bytes consumed as well as the size of the
/// destination used.
pub fn decode_in_place_report(buf: &mut [u8]) -> Result<DecodeReport, DecodeError> {
    let mut source_index = 0;
    let mut dest_index = 0;

    if buf.is_empty() {
        return Err(DecodeError::EmptyFrame);
    }

    // Stop at the first terminator, if any
    let src_end = if let Some(end) = buf.iter().position(|b| *b == 0) {
        end
    } else {
        buf.len()
    };

    while source_index < src_end {
        let code = buf[source_index];

        if source_index + code as usize > src_end && code != 1 {
            return Err(DecodeError::InvalidFrame {
                decoded_bytes: dest_index,
            });
        }

        source_index += 1;

        for _ in 1..code {
            *buf.get_mut(dest_index)
                .ok_or(DecodeError::TargetBufTooSmall)? = buf[source_index];
            source_index += 1;
            dest_index += 1;
        }

        if 0xFF != code && source_index < src_end {
            *buf.get_mut(dest_index)
                .ok_or(DecodeError::TargetBufTooSmall)? = 0;
            dest_index += 1;
        }
    }

    Ok(DecodeReport {
        frame_size: dest_index,
        parsed_size: source_index,
    })
}

/// Decodes a message in-place.
///
/// This is the same function as [decode], but replaces the encoded message
/// with the decoded message instead of writing to another buffer.
///
/// The returned `usize` is the number of bytes used for the DECODED value,
/// NOT the number of source bytes consumed during decoding.
pub fn decode_in_place(buff: &mut [u8]) -> Result<usize, DecodeError> {
    decode_in_place_report(buff).map(|res| res.frame_size())
}

/// Decodes the `source` buffer into the `dest` buffer using an arbitrary sentinel value.
///
/// This is done by XOR-ing each byte of the source message with the chosen sentinel value,
/// which transforms the message into the same message encoded with a sentinel value of 0.
/// Then the regular decoding transformation is performed.
///
/// The returned `usize` is the number of bytes used for the DECODED value,
/// NOT the number of source bytes consumed during decoding.
pub fn decode_with_sentinel(
    source: &[u8],
    dest: &mut [u8],
    sentinel: u8,
) -> Result<usize, DecodeError> {
    for (x, y) in source.iter().zip(dest.iter_mut()) {
        *y = *x ^ sentinel;
    }
    decode_in_place(dest)
}

/// Decodes a message in-place using an arbitrary sentinel value.
///
/// The returned `usize` is the number of bytes used for the DECODED value,
/// NOT the number of source bytes consumed during decoding.
pub fn decode_in_place_with_sentinel(buff: &mut [u8], sentinel: u8) -> Result<usize, DecodeError> {
    for x in buff.iter_mut() {
        *x ^= sentinel;
    }
    decode_in_place(buff)
}

#[cfg(feature = "alloc")]
/// Decodes the `source` buffer into a vector.
pub fn decode_vec(source: &[u8]) -> Result<alloc::vec::Vec<u8>, DecodeError> {
    let mut decoded = alloc::vec![0; source.len()];
    let result = decode(source, &mut decoded[..])?;
    decoded.truncate(result.frame_size());
    Ok(decoded)
}

#[cfg(feature = "alloc")]
/// Decodes the `source` buffer into a vector with an arbitrary sentinel value.
pub fn decode_vec_with_sentinel(
    source: &[u8],
    sentinel: u8,
) -> Result<alloc::vec::Vec<u8>, DecodeError> {
    let mut decoded = alloc::vec![0; source.len()];
    let n = decode_with_sentinel(source, &mut decoded[..], sentinel)?;
    decoded.truncate(n);
    Ok(decoded)
}

#[deprecated(since = "0.5.0", note = "use DecodeReport instead")]
pub type DecodingResult = DecodeReport;

#[cfg(test)]
mod tests {
    use crate::{encode, encode_vec_including_sentinels};

    use super::*;

    #[test]
    fn decode_malformed() {
        let malformed_buf: [u8; 32] = [
            68, 69, 65, 68, 66, 69, 69, 70, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
            0, 0, 0, 0, 0, 0,
        ];
        let mut dest_buf: [u8; 32] = [0; 32];
        if let Err(DecodeError::InvalidFrame { decoded_bytes }) =
            decode(&malformed_buf, &mut dest_buf)
        {
            assert_eq!(decoded_bytes, 7);
        } else {
            panic!("decoding worked when it should not have");
        }
    }

    #[test]
    fn decode_empty() {
        #[cfg(feature = "alloc")]
        matches!(decode_vec(&[]).unwrap_err(), DecodeError::EmptyFrame);
        matches!(
            decode_in_place(&mut []).unwrap_err(),
            DecodeError::EmptyFrame
        );
        matches!(
            decode(&[], &mut [0; 256]).unwrap_err(),
            DecodeError::EmptyFrame
        );
    }

    #[test]
    fn decode_target_buf_too_small() {
        let encoded = &[3, 10, 11, 2, 12];
        let expected_decoded_len = 4;
        for i in 0..expected_decoded_len - 1 {
            let mut dest = alloc::vec![0; i];
            let result = decode(encoded, &mut dest);
            assert_eq!(result, Err(DecodeError::TargetBufTooSmall));
        }
    }

    fn continuous_decoding(decoder: &mut CobsDecoder, expected_data: &[u8], encoded_frame: &[u8]) {
        for _ in 0..10 {
            for byte in encoded_frame.iter().take(encoded_frame.len() - 1) {
                decoder.feed(*byte).unwrap();
            }
            if let Ok(Some(sz_msg)) = decoder.feed(encoded_frame[encoded_frame.len() - 1]) {
                assert_eq!(sz_msg, expected_data.len());
                assert_eq!(expected_data, &decoder.dest()[0..sz_msg]);
            } else {
                panic!("decoding call did not yield expected frame");
            }
        }
    }

    fn continuous_decoding_heapless(
        decoder: &mut CobsDecoderHeapless<32>,
        expected_data: &[u8],
        encoded_frame: &[u8],
    ) {
        for _ in 0..10 {
            for byte in encoded_frame.iter().take(encoded_frame.len() - 1) {
                decoder.feed(*byte).unwrap();
            }
            if let Ok(Some(sz_msg)) = decoder.feed(encoded_frame[encoded_frame.len() - 1]) {
                assert_eq!(sz_msg, expected_data.len());
                assert_eq!(expected_data, &decoder.dest()[0..sz_msg]);
            } else {
                panic!("decoding call did not yield expected frame");
            }
        }
    }

    fn continuous_decoding_owned(
        decoder: &mut CobsDecoderOwned,
        expected_data: &[u8],
        encoded_frame: &[u8],
    ) {
        for _ in 0..10 {
            for byte in encoded_frame.iter().take(encoded_frame.len() - 1) {
                decoder.feed(*byte).unwrap();
            }
            if let Ok(Some(sz_msg)) = decoder.feed(encoded_frame[encoded_frame.len() - 1]) {
                assert_eq!(sz_msg, expected_data.len());
                assert_eq!(expected_data, &decoder.dest()[0..sz_msg]);
            } else {
                panic!("decoding call did not yield expected frame");
            }
        }
    }

    #[test]
    fn stream_continuously() {
        let mut dest: [u8; 16] = [0; 16];
        let data = b"hello world";
        let mut encoded_data: [u8; 16] = [0; 16];
        let mut encoded_len = encode(data, &mut encoded_data);
        // Sentinel byte at end.
        encoded_data[encoded_len] = 0x00;
        encoded_len += 1;
        // Stream continuously using only `push`. The decoding buffer should not overflow.
        let mut decoder = CobsDecoder::new(&mut dest);
        continuous_decoding(&mut decoder, data, &encoded_data[0..encoded_len]);
    }

    #[test]
    fn stream_continuously_owned() {
        let data = b"hello world";
        let mut encoded_data: [u8; 16] = [0; 16];
        let mut encoded_len = encode(data, &mut encoded_data);
        // Sentinel byte at end.
        encoded_data[encoded_len] = 0x00;
        encoded_len += 1;
        // Stream continuously using only `push`. The decoding buffer should not overflow.
        let mut decoder = CobsDecoderOwned::new(32);
        continuous_decoding_owned(&mut decoder, data, &encoded_data[0..encoded_len]);
    }

    #[test]
    fn stream_continuously_heapless() {
        let data = b"hello world";
        let mut encoded_data: [u8; 16] = [0; 16];
        let mut encoded_len = encode(data, &mut encoded_data);
        // Sentinel byte at end.
        encoded_data[encoded_len] = 0x00;
        encoded_len += 1;
        // Stream continuously using only `push`. The decoding buffer should not overflow.
        let mut decoder = CobsDecoderHeapless::new();
        continuous_decoding_heapless(&mut decoder, data, &encoded_data[0..encoded_len]);
    }

    #[test]
    fn stream_continuously_2() {
        let mut dest: [u8; 16] = [0; 16];
        let data = b"hello world";
        let mut encoded_data: [u8; 16] = [0; 16];
        let mut encoded_len = encode(data, &mut encoded_data[1..]);
        // Sentinel byte at start and end.
        encoded_data[0] = 0x00;
        encoded_data[encoded_len + 1] = 0x00;
        encoded_len += 2;
        // Stream continuously using only `push`. The decoding buffer should not overflow.
        let mut decoder = CobsDecoder::new(&mut dest);
        continuous_decoding(&mut decoder, data, &encoded_data[0..encoded_len]);
    }

    #[test]
    fn stream_continuously_2_owned() {
        let data = b"hello world";
        let mut encoded_data: [u8; 16] = [0; 16];
        let mut encoded_len = encode(data, &mut encoded_data[1..]);
        // Sentinel byte at start and end.
        encoded_data[0] = 0x00;
        encoded_data[encoded_len + 1] = 0x00;
        encoded_len += 2;
        // Stream continuously using only `push`. The decoding buffer should not overflow.
        let mut decoder = CobsDecoderOwned::new(32);
        continuous_decoding_owned(&mut decoder, data, &encoded_data[0..encoded_len]);
    }

    #[test]
    fn test_owned_decoder_push_function() {
        let data = b"hello world";
        let encoded_data = encode_vec_including_sentinels(data);
        let mut decoder = CobsDecoderOwned::new(32);
        let report = decoder.push(&encoded_data).unwrap().unwrap();
        assert_eq!(report.parsed_size(), encoded_data.len());
        assert_eq!(report.frame_size(), data.len());
        assert_eq!(&decoder.dest()[0..report.frame_size()], data);
        assert_eq!(&decoder.dest_mut()[0..report.frame_size()], data);
    }

    #[test]
    fn test_decoder_push_function() {
        let mut dest_buf: [u8; 32] = [0; 32];
        let data = b"hello world";
        let encoded_data = encode_vec_including_sentinels(data);
        let mut decoder = CobsDecoder::new(&mut dest_buf);
        let report = decoder.push(&encoded_data).unwrap().unwrap();
        assert_eq!(report.parsed_size(), encoded_data.len());
        assert_eq!(report.frame_size(), data.len());
        assert_eq!(&decoder.dest()[0..report.frame_size()], data);
        assert_eq!(&decoder.dest_mut()[0..report.frame_size()], data);
    }

    #[test]
    fn test_decoder_heapless_push_function() {
        let data = b"hello world";
        let encoded_data = encode_vec_including_sentinels(data);
        let mut decoder = CobsDecoderHeapless::<32>::new();
        let report = decoder.push(&encoded_data).unwrap().unwrap();
        assert_eq!(report.parsed_size(), encoded_data.len());
        assert_eq!(report.frame_size(), data.len());
        assert_eq!(&decoder.dest()[0..report.frame_size()], data);
        assert_eq!(&decoder.dest_mut()[0..report.frame_size()], data);
    }
}