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
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
use crate::response::{IntoResponse, Response};
use axum_core::extract::FromRequestParts;
use futures_util::future::BoxFuture;
use http::Request;
use std::{
    any::type_name,
    convert::Infallible,
    fmt,
    future::Future,
    marker::PhantomData,
    pin::Pin,
    task::{Context, Poll},
};
use tower_layer::Layer;
use tower_service::Service;

/// Create a middleware from an async function that transforms a response.
///
/// This differs from [`tower::util::MapResponse`] in that it allows you to easily run axum-specific
/// extractors.
///
/// # Example
///
/// ```
/// use axum::{
///     Router,
///     routing::get,
///     middleware::map_response,
///     response::Response,
/// };
///
/// async fn set_header<B>(mut response: Response<B>) -> Response<B> {
///     response.headers_mut().insert("x-foo", "foo".parse().unwrap());
///     response
/// }
///
/// let app = Router::new()
///     .route("/", get(|| async { /* ... */ }))
///     .layer(map_response(set_header));
/// # let _: Router = app;
/// ```
///
/// # Running extractors
///
/// It is also possible to run extractors that implement [`FromRequestParts`]. These will be run
/// before calling the handler.
///
/// ```
/// use axum::{
///     Router,
///     routing::get,
///     middleware::map_response,
///     extract::Path,
///     response::Response,
/// };
/// use std::collections::HashMap;
///
/// async fn log_path_params<B>(
///     Path(path_params): Path<HashMap<String, String>>,
///     response: Response<B>,
/// ) -> Response<B> {
///     tracing::debug!(?path_params);
///     response
/// }
///
/// let app = Router::new()
///     .route("/", get(|| async { /* ... */ }))
///     .layer(map_response(log_path_params));
/// # let _: Router = app;
/// ```
///
/// Note that to access state you must use either [`map_response_with_state`].
///
/// # Returning any `impl IntoResponse`
///
/// It is also possible to return anything that implements [`IntoResponse`]
///
/// ```
/// use axum::{
///     Router,
///     routing::get,
///     middleware::map_response,
///     response::{Response, IntoResponse},
/// };
/// use std::collections::HashMap;
///
/// async fn set_header(response: Response) -> impl IntoResponse {
///     (
///         [("x-foo", "foo")],
///         response,
///     )
/// }
///
/// let app = Router::new()
///     .route("/", get(|| async { /* ... */ }))
///     .layer(map_response(set_header));
/// # let _: Router = app;
/// ```
pub fn map_response<F, T>(f: F) -> MapResponseLayer<F, (), T> {
    map_response_with_state((), f)
}

/// Create a middleware from an async function that transforms a response, with the given state.
///
/// See [`State`](crate::extract::State) for more details about accessing state.
///
/// # Example
///
/// ```rust
/// use axum::{
///     Router,
///     http::StatusCode,
///     routing::get,
///     response::Response,
///     middleware::map_response_with_state,
///     extract::State,
/// };
///
/// #[derive(Clone)]
/// struct AppState { /* ... */ }
///
/// async fn my_middleware<B>(
///     State(state): State<AppState>,
///     // you can add more extractors here but they must
///     // all implement `FromRequestParts`
///     // `FromRequest` is not allowed
///     response: Response<B>,
/// ) -> Response<B> {
///     // do something with `state` and `response`...
///     response
/// }
///
/// let state = AppState { /* ... */ };
///
/// let app = Router::new()
///     .route("/", get(|| async { /* ... */ }))
///     .route_layer(map_response_with_state(state.clone(), my_middleware))
///     .with_state(state);
/// # let _: axum::Router = app;
/// ```
pub fn map_response_with_state<F, S, T>(state: S, f: F) -> MapResponseLayer<F, S, T> {
    MapResponseLayer {
        f,
        state,
        _extractor: PhantomData,
    }
}

/// A [`tower::Layer`] from an async function that transforms a response.
///
/// Created with [`map_response`]. See that function for more details.
#[must_use]
pub struct MapResponseLayer<F, S, T> {
    f: F,
    state: S,
    _extractor: PhantomData<fn() -> T>,
}

impl<F, S, T> Clone for MapResponseLayer<F, S, T>
where
    F: Clone,
    S: Clone,
{
    fn clone(&self) -> Self {
        Self {
            f: self.f.clone(),
            state: self.state.clone(),
            _extractor: self._extractor,
        }
    }
}

impl<S, I, F, T> Layer<I> for MapResponseLayer<F, S, T>
where
    F: Clone,
    S: Clone,
{
    type Service = MapResponse<F, S, I, T>;

    fn layer(&self, inner: I) -> Self::Service {
        MapResponse {
            f: self.f.clone(),
            state: self.state.clone(),
            inner,
            _extractor: PhantomData,
        }
    }
}

impl<F, S, T> fmt::Debug for MapResponseLayer<F, S, T>
where
    S: fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("MapResponseLayer")
            // Write out the type name, without quoting it as `&type_name::<F>()` would
            .field("f", &format_args!("{}", type_name::<F>()))
            .field("state", &self.state)
            .finish()
    }
}

/// A middleware created from an async function that transforms a response.
///
/// Created with [`map_response`]. See that function for more details.
pub struct MapResponse<F, S, I, T> {
    f: F,
    inner: I,
    state: S,
    _extractor: PhantomData<fn() -> T>,
}

impl<F, S, I, T> Clone for MapResponse<F, S, I, T>
where
    F: Clone,
    I: Clone,
    S: Clone,
{
    fn clone(&self) -> Self {
        Self {
            f: self.f.clone(),
            inner: self.inner.clone(),
            state: self.state.clone(),
            _extractor: self._extractor,
        }
    }
}

macro_rules! impl_service {
    (
        $($ty:ident),*
    ) => {
        #[allow(non_snake_case, unused_mut)]
        impl<F, Fut, S, I, B, ResBody, $($ty,)*> Service<Request<B>> for MapResponse<F, S, I, ($($ty,)*)>
        where
            F: FnMut($($ty,)* Response<ResBody>) -> Fut + Clone + Send + 'static,
            $( $ty: FromRequestParts<S> + Send, )*
            Fut: Future + Send + 'static,
            Fut::Output: IntoResponse + Send + 'static,
            I: Service<Request<B>, Response = Response<ResBody>, Error = Infallible>
                + Clone
                + Send
                + 'static,
            I::Future: Send + 'static,
            B: Send + 'static,
            ResBody: Send + 'static,
            S: Clone + Send + Sync + 'static,
        {
            type Response = Response;
            type Error = Infallible;
            type Future = ResponseFuture;

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


            fn call(&mut self, req: Request<B>) -> Self::Future {
                let not_ready_inner = self.inner.clone();
                let mut ready_inner = std::mem::replace(&mut self.inner, not_ready_inner);

                let mut f = self.f.clone();
                let _state = self.state.clone();

                let future = Box::pin(async move {
                    let (mut parts, body) = req.into_parts();

                    $(
                        let $ty = match $ty::from_request_parts(&mut parts, &_state).await {
                            Ok(value) => value,
                            Err(rejection) => return rejection.into_response(),
                        };
                    )*

                    let req = Request::from_parts(parts, body);

                    match ready_inner.call(req).await {
                        Ok(res) => {
                            f($($ty,)* res).await.into_response()
                        }
                        Err(err) => match err {}
                    }
                });

                ResponseFuture {
                    inner: future
                }
            }
        }
    };
}

impl_service!();
impl_service!(T1);
impl_service!(T1, T2);
impl_service!(T1, T2, T3);
impl_service!(T1, T2, T3, T4);
impl_service!(T1, T2, T3, T4, T5);
impl_service!(T1, T2, T3, T4, T5, T6);
impl_service!(T1, T2, T3, T4, T5, T6, T7);
impl_service!(T1, T2, T3, T4, T5, T6, T7, T8);
impl_service!(T1, T2, T3, T4, T5, T6, T7, T8, T9);
impl_service!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10);
impl_service!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11);
impl_service!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12);
impl_service!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13);
impl_service!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14);
impl_service!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15);
impl_service!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16);

impl<F, S, I, T> fmt::Debug for MapResponse<F, S, I, T>
where
    S: fmt::Debug,
    I: fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("MapResponse")
            .field("f", &format_args!("{}", type_name::<F>()))
            .field("inner", &self.inner)
            .field("state", &self.state)
            .finish()
    }
}

/// Response future for [`MapResponse`].
pub struct ResponseFuture {
    inner: BoxFuture<'static, Response>,
}

impl Future for ResponseFuture {
    type Output = Result<Response, Infallible>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        self.inner.as_mut().poll(cx).map(Ok)
    }
}

impl fmt::Debug for ResponseFuture {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("ResponseFuture").finish()
    }
}

#[cfg(test)]
mod tests {
    #[allow(unused_imports)]
    use super::*;
    use crate::{test_helpers::TestClient, Router};

    #[crate::test]
    async fn works() {
        async fn add_header<B>(mut res: Response<B>) -> Response<B> {
            res.headers_mut().insert("x-foo", "foo".parse().unwrap());
            res
        }

        let app = Router::new().layer(map_response(add_header));
        let client = TestClient::new(app);

        let res = client.get("/").await;

        assert_eq!(res.headers()["x-foo"], "foo");
    }
}