1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120

// Copyright 2022 The Matrix.org Foundation C.I.C.
//
// Licensed 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 std::{marker::PhantomData, task::Poll};

use bytes::Buf;
use futures_util::FutureExt;
use http::{header::ACCEPT, HeaderValue, Request, Response};
use serde::de::DeserializeOwned;
use thiserror::Error;
use tower::{Layer, Service};

#[derive(Debug, Error)]
pub enum Error<Service> {
    /// An error from the inner service.
    #[error(transparent)]
    Service { inner: Service },

    #[error("could not parse JSON payload")]
    Deserialize {
        #[source]
        inner: serde_json::Error,
    },
}

impl<S> Error<S> {
    fn service(source: S) -> Self {
        Self::Service { inner: source }
    }

    fn deserialize(source: serde_json::Error) -> Self {
        Self::Deserialize { inner: source }
    }
}

#[derive(Clone)]
pub struct JsonResponse<S, T> {
    inner: S,
    _t: PhantomData<T>,
}

impl<S, T> JsonResponse<S, T> {
    pub const fn new(inner: S) -> Self {
        Self {
            inner,
            _t: PhantomData,
        }
    }
}

impl<S, T, B, C> Service<Request<B>> for JsonResponse<S, T>
where
    S: Service<Request<B>, Response = Response<C>>,
    S::Future: Send + 'static,
    C: Buf,
    T: DeserializeOwned,
{
    type Error = Error<S::Error>;
    type Response = Response<T>;
    type Future = futures_util::future::Map<
        S::Future,
        fn(Result<Response<C>, S::Error>) -> Result<Self::Response, Self::Error>,
    >;

    fn poll_ready(&mut self, cx: &mut std::task::Context<'_>) -> Poll<Result<(), Self::Error>> {
        self.inner.poll_ready(cx).map_err(Error::service)
    }

    fn call(&mut self, mut request: Request<B>) -> Self::Future {
        fn mapper<C, T, E>(res: Result<Response<C>, E>) -> Result<Response<T>, Error<E>>
        where
            C: Buf,
            T: DeserializeOwned,
        {
            let response = res.map_err(Error::service)?;
            let (parts, body) = response.into_parts();

            let body = serde_json::from_reader(body.reader()).map_err(Error::deserialize)?;

            let res = Response::from_parts(parts, body);
            Ok(res)
        }

        request
            .headers_mut()
            .insert(ACCEPT, HeaderValue::from_static("application/json"));

        self.inner.call(request).map(mapper::<C, T, S::Error>)
    }
}

#[derive(Clone, Copy)]
pub struct JsonResponseLayer<T> {
    _t: PhantomData<T>,
}

impl<T> Default for JsonResponseLayer<T> {
    fn default() -> Self {
        Self { _t: PhantomData }
    }
}

impl<S, T> Layer<S> for JsonResponseLayer<T> {
    type Service = JsonResponse<S, T>;

    fn layer(&self, inner: S) -> Self::Service {
        JsonResponse::new(inner)
    }
}