rustot 0.4.1

AWS IoT
Documentation 
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use serde::de::DeserializeOwned;

use super::{Error, ShadowState, MAX_PAYLOAD_SIZE};

pub trait ShadowDAO<S: ShadowState + DeserializeOwned> {
    fn read(&mut self) -> Result<S, Error>;
    fn write(&mut self, state: &S) -> Result<(), Error>;
}

impl<S: ShadowState + DeserializeOwned> ShadowDAO<S> for () {
    fn read(&mut self) -> Result<S, Error> {
        Err(Error::NoPersistance)
    }

    fn write(&mut self, _state: &S) -> Result<(), Error> {
        Err(Error::NoPersistance)
    }
}

pub struct EmbeddedStorageDAO<T: embedded_storage::Storage, const OFFSET: u32>(T);

impl<T, const OFFSET: u32> From<T> for EmbeddedStorageDAO<T, OFFSET>
where
    T: embedded_storage::Storage,
{
    fn from(v: T) -> Self {
        Self::new(v)
    }
}

impl<T, const OFFSET: u32> EmbeddedStorageDAO<T, OFFSET>
where
    T: embedded_storage::Storage,
{
    pub fn new(storage: T) -> Self {
        Self(storage)
    }
}

const U32_SIZE: usize = core::mem::size_of::<u32>();

impl<S, T, const OFFSET: u32> ShadowDAO<S> for EmbeddedStorageDAO<T, OFFSET>
where
    S: ShadowState + DeserializeOwned,
    T: embedded_storage::Storage,
{
    fn read(&mut self) -> Result<S, Error> {
        let buf = &mut [0u8; MAX_PAYLOAD_SIZE];

        self.0.read(OFFSET, buf).map_err(|_| Error::DaoRead)?;

        match buf[..U32_SIZE].try_into() {
            Ok(len_bytes) => {
                let len = u32::from_le_bytes(len_bytes);
                if len == 0xFFFFFFFF || len as usize + U32_SIZE > buf.len() {
                    return Err(Error::InvalidPayload);
                }

                // FIXME: Choose this size as narrow as possible?
                let scratch = &mut [0u8; 256];

                Ok(serde_cbor::de::from_slice_with_scratch::<S>(
                    &buf[U32_SIZE..len as usize + U32_SIZE],
                    scratch,
                )
                .map_err(|_| Error::InvalidPayload)?)
            }
            _ => Err(Error::InvalidPayload),
        }
    }

    fn write(&mut self, state: &S) -> Result<(), Error> {
        assert!(MAX_PAYLOAD_SIZE <= self.0.capacity() - OFFSET as usize);

        let buf = &mut [0u8; MAX_PAYLOAD_SIZE];

        let mut serializer = serde_cbor::ser::Serializer::new(serde_cbor::ser::SliceWrite::new(
            &mut buf[U32_SIZE..],
        ))
        .packed_format();
        state
            .serialize(&mut serializer)
            .map_err(|_| Error::InvalidPayload)?;
        let len = serializer.into_inner().bytes_written();

        if len > MAX_PAYLOAD_SIZE {
            return Err(Error::Overflow);
        }

        buf[..U32_SIZE].copy_from_slice(&(len as u32).to_le_bytes());

        self.0
            .write(OFFSET, &buf[..len + U32_SIZE])
            .map_err(|_| Error::DaoWrite)?;

        Ok(())
    }
}

#[cfg(any(feature = "std", test))]
pub struct StdIODAO<T: std::io::Write + std::io::Read>(pub(crate) T);

#[cfg(any(feature = "std", test))]
impl<T> From<T> for StdIODAO<T>
where
    T: std::io::Write + std::io::Read,
{
    fn from(v: T) -> Self {
        Self::new(v)
    }
}

#[cfg(any(feature = "std", test))]
impl<T> StdIODAO<T>
where
    T: std::io::Write + std::io::Read,
{
    pub fn new(storage: T) -> Self {
        Self(storage)
    }
}

#[cfg(any(feature = "std", test))]
impl<S, T> ShadowDAO<S> for StdIODAO<T>
where
    S: ShadowState + DeserializeOwned,
    T: std::io::Write + std::io::Read,
{
    fn read(&mut self) -> Result<S, Error> {
        let bytes = &mut [0u8; MAX_PAYLOAD_SIZE];

        self.0.read(bytes).map_err(|_| Error::DaoRead)?;
        let (shadow, _) = serde_json_core::from_slice(bytes).map_err(|_| Error::InvalidPayload)?;
        Ok(shadow)
    }

    fn write(&mut self, state: &S) -> Result<(), Error> {
        let bytes =
            serde_json_core::to_vec::<_, MAX_PAYLOAD_SIZE>(state).map_err(|_| Error::Overflow)?;

        self.0.write(&bytes).map_err(|_| Error::DaoWrite)?;
        Ok(())
    }
}