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
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
use super::{IntoResponseParts, Response, ResponseParts};
use crate::{body::Body, BoxError};
use bytes::{buf::Chain, Buf, Bytes, BytesMut};
use http::{
    header::{self, HeaderMap, HeaderName, HeaderValue},
    Extensions, StatusCode,
};
use http_body::{Frame, SizeHint};
use std::{
    borrow::Cow,
    convert::Infallible,
    fmt,
    pin::Pin,
    task::{Context, Poll},
};

/// Trait for generating responses.
///
/// Types that implement `IntoResponse` can be returned from handlers.
///
/// # Implementing `IntoResponse`
///
/// You generally shouldn't have to implement `IntoResponse` manually, as axum
/// provides implementations for many common types.
///
/// However it might be necessary if you have a custom error type that you want
/// to return from handlers:
///
/// ```rust
/// use axum::{
///     Router,
///     body::{self, Bytes},
///     routing::get,
///     http::StatusCode,
///     response::{IntoResponse, Response},
/// };
///
/// enum MyError {
///     SomethingWentWrong,
///     SomethingElseWentWrong,
/// }
///
/// impl IntoResponse for MyError {
///     fn into_response(self) -> Response {
///         let body = match self {
///             MyError::SomethingWentWrong => "something went wrong",
///             MyError::SomethingElseWentWrong => "something else went wrong",
///         };
///
///         // its often easiest to implement `IntoResponse` by calling other implementations
///         (StatusCode::INTERNAL_SERVER_ERROR, body).into_response()
///     }
/// }
///
/// // `Result<impl IntoResponse, MyError>` can now be returned from handlers
/// let app = Router::new().route("/", get(handler));
///
/// async fn handler() -> Result<(), MyError> {
///     Err(MyError::SomethingWentWrong)
/// }
/// # let _: Router = app;
/// ```
///
/// Or if you have a custom body type you'll also need to implement
/// `IntoResponse` for it:
///
/// ```rust
/// use axum::{
///     body,
///     routing::get,
///     response::{IntoResponse, Response},
///     body::Body,
///     Router,
/// };
/// use http::HeaderMap;
/// use bytes::Bytes;
/// use http_body::Frame;
/// use std::{
///     convert::Infallible,
///     task::{Poll, Context},
///     pin::Pin,
/// };
///
/// struct MyBody;
///
/// // First implement `Body` for `MyBody`. This could for example use
/// // some custom streaming protocol.
/// impl http_body::Body for MyBody {
///     type Data = Bytes;
///     type Error = Infallible;
///
///     fn poll_frame(
///         self: Pin<&mut Self>,
///         cx: &mut Context<'_>,
///     ) -> Poll<Option<Result<Frame<Self::Data>, Self::Error>>> {
///         # unimplemented!()
///         // ...
///     }
/// }
///
/// // Now we can implement `IntoResponse` directly for `MyBody`
/// impl IntoResponse for MyBody {
///     fn into_response(self) -> Response {
///         Response::new(Body::new(self))
///     }
/// }
///
/// // `MyBody` can now be returned from handlers.
/// let app = Router::new().route("/", get(|| async { MyBody }));
/// # let _: Router = app;
/// ```
pub trait IntoResponse {
    /// Create a response.
    fn into_response(self) -> Response;
}

impl IntoResponse for StatusCode {
    fn into_response(self) -> Response {
        let mut res = ().into_response();
        *res.status_mut() = self;
        res
    }
}

impl IntoResponse for () {
    fn into_response(self) -> Response {
        Body::empty().into_response()
    }
}

impl IntoResponse for Infallible {
    fn into_response(self) -> Response {
        match self {}
    }
}

impl<T, E> IntoResponse for Result<T, E>
where
    T: IntoResponse,
    E: IntoResponse,
{
    fn into_response(self) -> Response {
        match self {
            Ok(value) => value.into_response(),
            Err(err) => err.into_response(),
        }
    }
}

impl<B> IntoResponse for Response<B>
where
    B: http_body::Body<Data = Bytes> + Send + 'static,
    B::Error: Into<BoxError>,
{
    fn into_response(self) -> Response {
        self.map(Body::new)
    }
}

impl IntoResponse for http::response::Parts {
    fn into_response(self) -> Response {
        Response::from_parts(self, Body::empty())
    }
}

impl IntoResponse for Body {
    fn into_response(self) -> Response {
        Response::new(self)
    }
}

impl IntoResponse for &'static str {
    fn into_response(self) -> Response {
        Cow::Borrowed(self).into_response()
    }
}

impl IntoResponse for String {
    fn into_response(self) -> Response {
        Cow::<'static, str>::Owned(self).into_response()
    }
}

impl IntoResponse for Box<str> {
    fn into_response(self) -> Response {
        String::from(self).into_response()
    }
}

impl IntoResponse for Cow<'static, str> {
    fn into_response(self) -> Response {
        let mut res = Body::from(self).into_response();
        res.headers_mut().insert(
            header::CONTENT_TYPE,
            HeaderValue::from_static(mime::TEXT_PLAIN_UTF_8.as_ref()),
        );
        res
    }
}

impl IntoResponse for Bytes {
    fn into_response(self) -> Response {
        let mut res = Body::from(self).into_response();
        res.headers_mut().insert(
            header::CONTENT_TYPE,
            HeaderValue::from_static(mime::APPLICATION_OCTET_STREAM.as_ref()),
        );
        res
    }
}

impl IntoResponse for BytesMut {
    fn into_response(self) -> Response {
        self.freeze().into_response()
    }
}

impl<T, U> IntoResponse for Chain<T, U>
where
    T: Buf + Unpin + Send + 'static,
    U: Buf + Unpin + Send + 'static,
{
    fn into_response(self) -> Response {
        let (first, second) = self.into_inner();
        let mut res = Response::new(Body::new(BytesChainBody {
            first: Some(first),
            second: Some(second),
        }));
        res.headers_mut().insert(
            header::CONTENT_TYPE,
            HeaderValue::from_static(mime::APPLICATION_OCTET_STREAM.as_ref()),
        );
        res
    }
}

struct BytesChainBody<T, U> {
    first: Option<T>,
    second: Option<U>,
}

impl<T, U> http_body::Body for BytesChainBody<T, U>
where
    T: Buf + Unpin,
    U: Buf + Unpin,
{
    type Data = Bytes;
    type Error = Infallible;

    fn poll_frame(
        mut self: Pin<&mut Self>,
        _cx: &mut Context<'_>,
    ) -> Poll<Option<Result<Frame<Self::Data>, Self::Error>>> {
        if let Some(mut buf) = self.first.take() {
            let bytes = buf.copy_to_bytes(buf.remaining());
            return Poll::Ready(Some(Ok(Frame::data(bytes))));
        }

        if let Some(mut buf) = self.second.take() {
            let bytes = buf.copy_to_bytes(buf.remaining());
            return Poll::Ready(Some(Ok(Frame::data(bytes))));
        }

        Poll::Ready(None)
    }

    fn is_end_stream(&self) -> bool {
        self.first.is_none() && self.second.is_none()
    }

    fn size_hint(&self) -> SizeHint {
        match (self.first.as_ref(), self.second.as_ref()) {
            (Some(first), Some(second)) => {
                let total_size = first.remaining() + second.remaining();
                SizeHint::with_exact(total_size as u64)
            }
            (Some(buf), None) => SizeHint::with_exact(buf.remaining() as u64),
            (None, Some(buf)) => SizeHint::with_exact(buf.remaining() as u64),
            (None, None) => SizeHint::with_exact(0),
        }
    }
}

impl IntoResponse for &'static [u8] {
    fn into_response(self) -> Response {
        Cow::Borrowed(self).into_response()
    }
}

impl<const N: usize> IntoResponse for &'static [u8; N] {
    fn into_response(self) -> Response {
        self.as_slice().into_response()
    }
}

impl<const N: usize> IntoResponse for [u8; N] {
    fn into_response(self) -> Response {
        self.to_vec().into_response()
    }
}

impl IntoResponse for Vec<u8> {
    fn into_response(self) -> Response {
        Cow::<'static, [u8]>::Owned(self).into_response()
    }
}

impl IntoResponse for Box<[u8]> {
    fn into_response(self) -> Response {
        Vec::from(self).into_response()
    }
}

impl IntoResponse for Cow<'static, [u8]> {
    fn into_response(self) -> Response {
        let mut res = Body::from(self).into_response();
        res.headers_mut().insert(
            header::CONTENT_TYPE,
            HeaderValue::from_static(mime::APPLICATION_OCTET_STREAM.as_ref()),
        );
        res
    }
}

impl<R> IntoResponse for (StatusCode, R)
where
    R: IntoResponse,
{
    fn into_response(self) -> Response {
        let mut res = self.1.into_response();
        *res.status_mut() = self.0;
        res
    }
}

impl IntoResponse for HeaderMap {
    fn into_response(self) -> Response {
        let mut res = ().into_response();
        *res.headers_mut() = self;
        res
    }
}

impl IntoResponse for Extensions {
    fn into_response(self) -> Response {
        let mut res = ().into_response();
        *res.extensions_mut() = self;
        res
    }
}

impl<K, V, const N: usize> IntoResponse for [(K, V); N]
where
    K: TryInto<HeaderName>,
    K::Error: fmt::Display,
    V: TryInto<HeaderValue>,
    V::Error: fmt::Display,
{
    fn into_response(self) -> Response {
        (self, ()).into_response()
    }
}

impl<R> IntoResponse for (http::response::Parts, R)
where
    R: IntoResponse,
{
    fn into_response(self) -> Response {
        let (parts, res) = self;
        (parts.status, parts.headers, parts.extensions, res).into_response()
    }
}

impl<R> IntoResponse for (http::response::Response<()>, R)
where
    R: IntoResponse,
{
    fn into_response(self) -> Response {
        let (template, res) = self;
        let (parts, ()) = template.into_parts();
        (parts, res).into_response()
    }
}

impl<R> IntoResponse for (R,)
where
    R: IntoResponse,
{
    fn into_response(self) -> Response {
        let (res,) = self;
        res.into_response()
    }
}

macro_rules! impl_into_response {
    ( $($ty:ident),* $(,)? ) => {
        #[allow(non_snake_case)]
        impl<R, $($ty,)*> IntoResponse for ($($ty),*, R)
        where
            $( $ty: IntoResponseParts, )*
            R: IntoResponse,
        {
            fn into_response(self) -> Response {
                let ($($ty),*, res) = self;

                let res = res.into_response();
                let parts = ResponseParts { res };

                $(
                    let parts = match $ty.into_response_parts(parts) {
                        Ok(parts) => parts,
                        Err(err) => {
                            return err.into_response();
                        }
                    };
                )*

                parts.res
            }
        }

        #[allow(non_snake_case)]
        impl<R, $($ty,)*> IntoResponse for (StatusCode, $($ty),*, R)
        where
            $( $ty: IntoResponseParts, )*
            R: IntoResponse,
        {
            fn into_response(self) -> Response {
                let (status, $($ty),*, res) = self;

                let res = res.into_response();
                let parts = ResponseParts { res };

                $(
                    let parts = match $ty.into_response_parts(parts) {
                        Ok(parts) => parts,
                        Err(err) => {
                            return err.into_response();
                        }
                    };
                )*

                (status, parts.res).into_response()
            }
        }

        #[allow(non_snake_case)]
        impl<R, $($ty,)*> IntoResponse for (http::response::Parts, $($ty),*, R)
        where
            $( $ty: IntoResponseParts, )*
            R: IntoResponse,
        {
            fn into_response(self) -> Response {
                let (outer_parts, $($ty),*, res) = self;

                let res = res.into_response();
                let parts = ResponseParts { res };
                $(
                    let parts = match $ty.into_response_parts(parts) {
                        Ok(parts) => parts,
                        Err(err) => {
                            return err.into_response();
                        }
                    };
                )*

                (outer_parts, parts.res).into_response()
            }
        }

        #[allow(non_snake_case)]
        impl<R, $($ty,)*> IntoResponse for (http::response::Response<()>, $($ty),*, R)
        where
            $( $ty: IntoResponseParts, )*
            R: IntoResponse,
        {
            fn into_response(self) -> Response {
                let (template, $($ty),*, res) = self;
                let (parts, ()) = template.into_parts();
                (parts, $($ty),*, res).into_response()
            }
        }
    }
}

all_the_tuples_no_last_special_case!(impl_into_response);