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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

use super::{Codec, DecodeBuf, Decoder, EncodeBuf, Encoder};
use prost::Message;
use std::marker::PhantomData;

/// A [`Codec`] that implements `application/grpc+proto` via the prost library..
#[derive(Debug, Clone)]
pub struct ProstCodec<T, U> {
    _pd: PhantomData<(T, U)>,
}

impl<T, U> Default for ProstCodec<T, U> {
    fn default() -> Self {
        Self { _pd: PhantomData }
    }
}

impl<T, U> Codec for ProstCodec<T, U>
where
    T: Message + Send + 'static,
    U: Message + Default + Send + 'static,
{
    type Encode = T;
    type Decode = U;

    type Encoder = ProstEncoder<T>;
    type Decoder = ProstDecoder<U>;

    fn encoder(&mut self) -> Self::Encoder {
        ProstEncoder(PhantomData)
    }

    fn decoder(&mut self) -> Self::Decoder {
        ProstDecoder(PhantomData)
    }
}

/// A [`Encoder`] that knows how to encode `T`.
#[derive(Debug, Clone, Default)]
pub struct ProstEncoder<T>(PhantomData<T>);

impl<T: Message> Encoder for ProstEncoder<T> {
    type Item = T;
    type Error = crate::status::Status;

    fn encode(&mut self, item: Self::Item, buf: &mut EncodeBuf<'_>) -> Result<(), Self::Error> {
        item.encode(buf)
            .expect("Message only errors if not enough space");

        Ok(())
    }
}

/// A [`Decoder`] that knows how to decode `U`.
#[derive(Debug, Clone, Default)]
pub struct ProstDecoder<U>(PhantomData<U>);

impl<U: Message + Default> Decoder for ProstDecoder<U> {
    type Item = U;
    type Error = crate::status::Status;

    fn decode(&mut self, buf: &mut DecodeBuf<'_>) -> Result<Option<Self::Item>, Self::Error> {
        let item = Message::decode(buf)
            .map(Option::Some)
            .map_err(from_decode_error)?;

        Ok(item)
    }
}

fn from_decode_error(error: prost::DecodeError) -> crate::status::Status {
    // Map Protobuf parse errors to an INTERNAL status code, as per
    // https://github.com/grpc/grpc/blob/master/doc/statuscodes.md
    crate::status::Status::new(crate::status::Code::Internal, error.to_string())
}