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
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170

//! Apply a transformation to the response body.
//!
//! # Example
//!
//! ```
//! use bytes::Bytes;
//! use http::{Request, Response};
//! use hyper::Body;
//! use std::convert::Infallible;
//! use std::{pin::Pin, task::{Context, Poll}};
//! use tower_async::{ServiceBuilder, service_fn, ServiceExt, Service};
//! use tower_async_http::map_response_body::MapResponseBodyLayer;
//! use futures::ready;
//!
//! // A wrapper for a `hyper::Body` that prints the size of data chunks
//! struct PrintChunkSizesBody {
//!     inner: Body,
//! }
//!
//! impl PrintChunkSizesBody {
//!     fn new(inner: Body) -> Self {
//!         Self { inner }
//!     }
//! }
//!
//! impl http_body::Body for PrintChunkSizesBody {
//!     type Data = Bytes;
//!     type Error = hyper::Error;
//!
//!     fn poll_data(
//!         mut self: Pin<&mut Self>,
//!         cx: &mut Context<'_>,
//!     ) -> Poll<Option<Result<Self::Data, Self::Error>>> {
//!         if let Some(chunk) = ready!(Pin::new(&mut self.inner).poll_data(cx)?) {
//!             println!("chunk size = {}", chunk.len());
//!             Poll::Ready(Some(Ok(chunk)))
//!         } else {
//!             Poll::Ready(None)
//!         }
//!     }
//!
//!     fn poll_trailers(
//!         mut self: Pin<&mut Self>,
//!         cx: &mut Context<'_>,
//!     ) -> Poll<Result<Option<hyper::HeaderMap>, Self::Error>> {
//!         Pin::new(&mut self.inner).poll_trailers(cx)
//!     }
//!
//!     fn is_end_stream(&self) -> bool {
//!         self.inner.is_end_stream()
//!     }
//!
//!     fn size_hint(&self) -> http_body::SizeHint {
//!         self.inner.size_hint()
//!     }
//! }
//!
//! async fn handle<B>(_: Request<B>) -> Result<Response<Body>, Infallible> {
//!     // ...
//!     # Ok(Response::new(Body::empty()))
//! }
//!
//! # #[tokio::main]
//! # async fn main() -> Result<(), Box<dyn std::error::Error>> {
//! let mut svc = ServiceBuilder::new()
//!     // Wrap response bodies in `PrintChunkSizesBody`
//!     .layer(MapResponseBodyLayer::new(PrintChunkSizesBody::new))
//!     .service_fn(handle);
//!
//! // Call the service
//! let request = Request::new(Body::from("foobar"));
//!
//! svc.call(request).await?;
//! # Ok(())
//! # }
//! ```

use http::{Request, Response};
use std::fmt;
use tower_async_layer::Layer;
use tower_async_service::Service;

/// Apply a transformation to the response body.
///
/// See the [module docs](crate::map_response_body) for an example.
#[derive(Clone)]
pub struct MapResponseBodyLayer<F> {
    f: F,
}

impl<F> MapResponseBodyLayer<F> {
    /// Create a new [`MapResponseBodyLayer`].
    ///
    /// `F` is expected to be a function that takes a body and returns another body.
    pub fn new(f: F) -> Self {
        Self { f }
    }
}

impl<S, F> Layer<S> for MapResponseBodyLayer<F>
where
    F: Clone,
{
    type Service = MapResponseBody<S, F>;

    fn layer(&self, inner: S) -> Self::Service {
        MapResponseBody::new(inner, self.f.clone())
    }
}

impl<F> fmt::Debug for MapResponseBodyLayer<F> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("MapResponseBodyLayer")
            .field("f", &std::any::type_name::<F>())
            .finish()
    }
}

/// Apply a transformation to the response body.
///
/// See the [module docs](crate::map_response_body) for an example.
#[derive(Clone)]
pub struct MapResponseBody<S, F> {
    inner: S,
    f: F,
}

impl<S, F> MapResponseBody<S, F> {
    /// Create a new [`MapResponseBody`].
    ///
    /// `F` is expected to be a function that takes a body and returns another body.
    pub fn new(service: S, f: F) -> Self {
        Self { inner: service, f }
    }

    /// Returns a new [`Layer`] that wraps services with a `MapResponseBodyLayer` middleware.
    ///
    /// [`Layer`]: tower_async_layer::Layer
    pub fn layer(f: F) -> MapResponseBodyLayer<F> {
        MapResponseBodyLayer::new(f)
    }

    define_inner_service_accessors!();
}

impl<F, S, ReqBody, ResBody, NewResBody> Service<Request<ReqBody>> for MapResponseBody<S, F>
where
    S: Service<Request<ReqBody>, Response = Response<ResBody>>,
    F: FnMut(ResBody) -> NewResBody + Clone,
{
    type Response = Response<NewResBody>;
    type Error = S::Error;

    async fn call(&mut self, req: Request<ReqBody>) -> Result<Self::Response, Self::Error> {
        let res = self.inner.call(req).await?;
        Ok(res.map(self.f.clone()))
    }
}

impl<S, F> fmt::Debug for MapResponseBody<S, F>
where
    S: fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("MapResponseBody")
            .field("inner", &self.inner)
            .field("f", &std::any::type_name::<F>())
            .finish()
    }
}