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
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
use std::borrow::Cow;
#[cfg(feature = "stream")]
use std::error::Error as StdError;
use std::fmt;

use bytes::Bytes;
use futures_channel::mpsc;
use futures_channel::oneshot;
use futures_core::Stream; // for mpsc::Receiver
#[cfg(feature = "stream")]
use futures_util::TryStreamExt;
use http::HeaderMap;
use http_body::{Body as HttpBody, SizeHint};

use super::DecodedLength;
#[cfg(feature = "stream")]
use crate::common::sync_wrapper::SyncWrapper;
use crate::common::Future;
#[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
use crate::common::Never;
use crate::common::{task, watch, Pin, Poll};
#[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
use crate::proto::h2::ping;

type BodySender = mpsc::Sender<Result<Bytes, crate::Error>>;
type TrailersSender = oneshot::Sender<HeaderMap>;

/// A stream of `Bytes`, used when receiving bodies.
///
/// A good default [`HttpBody`](crate::body::HttpBody) to use in many
/// applications.
#[must_use = "streams do nothing unless polled"]
pub struct Body {
    kind: Kind,
    /// Keep the extra bits in an `Option<Box<Extra>>`, so that
    /// Body stays small in the common case (no extras needed).
    extra: Option<Box<Extra>>,
}

enum Kind {
    Once(Option<Bytes>),
    Chan {
        content_length: DecodedLength,
        want_tx: watch::Sender,
        data_rx: mpsc::Receiver<Result<Bytes, crate::Error>>,
        trailers_rx: oneshot::Receiver<HeaderMap>,
    },
    #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
    H2 {
        ping: ping::Recorder,
        content_length: DecodedLength,
        recv: h2::RecvStream,
    },
    #[cfg(feature = "ffi")]
    Ffi(crate::ffi::UserBody),
    #[cfg(feature = "stream")]
    Wrapped(
        SyncWrapper<
            Pin<Box<dyn Stream<Item = Result<Bytes, Box<dyn StdError + Send + Sync>>> + Send>>,
        >,
    ),
}

struct Extra {
    /// Allow the client to pass a future to delay the `Body` from returning
    /// EOF. This allows the `Client` to try to put the idle connection
    /// back into the pool before the body is "finished".
    ///
    /// The reason for this is so that creating a new request after finishing
    /// streaming the body of a response could sometimes result in creating
    /// a brand new connection, since the pool didn't know about the idle
    /// connection yet.
    delayed_eof: Option<DelayEof>,
}

#[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
type DelayEofUntil = oneshot::Receiver<Never>;

enum DelayEof {
    /// Initial state, stream hasn't seen EOF yet.
    #[cfg(any(feature = "http1", feature = "http2"))]
    #[cfg(feature = "client")]
    NotEof(DelayEofUntil),
    /// Transitions to this state once we've seen `poll` try to
    /// return EOF (`None`). This future is then polled, and
    /// when it completes, the Body finally returns EOF (`None`).
    #[cfg(any(feature = "http1", feature = "http2"))]
    #[cfg(feature = "client")]
    Eof(DelayEofUntil),
}

/// A sender half created through [`Body::channel()`].
///
/// Useful when wanting to stream chunks from another thread.
///
/// ## Body Closing
///
/// Note that the request body will always be closed normally when the sender is dropped (meaning
/// that the empty terminating chunk will be sent to the remote). If you desire to close the
/// connection with an incomplete response (e.g. in the case of an error during asynchronous
/// processing), call the [`Sender::abort()`] method to abort the body in an abnormal fashion.
///
/// [`Body::channel()`]: struct.Body.html#method.channel
/// [`Sender::abort()`]: struct.Sender.html#method.abort
#[must_use = "Sender does nothing unless sent on"]
pub struct Sender {
    want_rx: watch::Receiver,
    data_tx: BodySender,
    trailers_tx: Option<TrailersSender>,
}

const WANT_PENDING: usize = 1;
const WANT_READY: usize = 2;

impl Body {
    /// Create an empty `Body` stream.
    ///
    /// # Example
    ///
    /// ```
    /// use hyper::{Body, Request};
    ///
    /// // create a `GET /` request
    /// let get = Request::new(Body::empty());
    /// ```
    #[inline]
    pub fn empty() -> Body {
        Body::new(Kind::Once(None))
    }

    /// Create a `Body` stream with an associated sender half.
    ///
    /// Useful when wanting to stream chunks from another thread.
    #[inline]
    pub fn channel() -> (Sender, Body) {
        Self::new_channel(DecodedLength::CHUNKED, /*wanter =*/ false)
    }

    pub(crate) fn new_channel(content_length: DecodedLength, wanter: bool) -> (Sender, Body) {
        let (data_tx, data_rx) = mpsc::channel(0);
        let (trailers_tx, trailers_rx) = oneshot::channel();

        // If wanter is true, `Sender::poll_ready()` won't becoming ready
        // until the `Body` has been polled for data once.
        let want = if wanter { WANT_PENDING } else { WANT_READY };

        let (want_tx, want_rx) = watch::channel(want);

        let tx = Sender {
            want_rx,
            data_tx,
            trailers_tx: Some(trailers_tx),
        };
        let rx = Body::new(Kind::Chan {
            content_length,
            want_tx,
            data_rx,
            trailers_rx,
        });

        (tx, rx)
    }

    /// Wrap a futures `Stream` in a box inside `Body`.
    ///
    /// # Example
    ///
    /// ```
    /// # use hyper::Body;
    /// let chunks: Vec<Result<_, std::io::Error>> = vec![
    ///     Ok("hello"),
    ///     Ok(" "),
    ///     Ok("world"),
    /// ];
    ///
    /// let stream = futures_util::stream::iter(chunks);
    ///
    /// let body = Body::wrap_stream(stream);
    /// ```
    ///
    /// # Optional
    ///
    /// This function requires enabling the `stream` feature in your
    /// `Cargo.toml`.
    #[cfg(feature = "stream")]
    #[cfg_attr(docsrs, doc(cfg(feature = "stream")))]
    pub fn wrap_stream<S, O, E>(stream: S) -> Body
    where
        S: Stream<Item = Result<O, E>> + Send + 'static,
        O: Into<Bytes> + 'static,
        E: Into<Box<dyn StdError + Send + Sync>> + 'static,
    {
        let mapped = stream.map_ok(Into::into).map_err(Into::into);
        Body::new(Kind::Wrapped(SyncWrapper::new(Box::pin(mapped))))
    }

    fn new(kind: Kind) -> Body {
        Body { kind, extra: None }
    }

    #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
    pub(crate) fn h2(
        recv: h2::RecvStream,
        content_length: DecodedLength,
        ping: ping::Recorder,
    ) -> Self {
        let body = Body::new(Kind::H2 {
            ping,
            content_length,
            recv,
        });

        body
    }

    #[cfg(any(feature = "http1", feature = "http2"))]
    #[cfg(feature = "client")]
    pub(crate) fn delayed_eof(&mut self, fut: DelayEofUntil) {
        self.extra_mut().delayed_eof = Some(DelayEof::NotEof(fut));
    }

    fn take_delayed_eof(&mut self) -> Option<DelayEof> {
        self.extra
            .as_mut()
            .and_then(|extra| extra.delayed_eof.take())
    }

    #[cfg(any(feature = "http1", feature = "http2"))]
    fn extra_mut(&mut self) -> &mut Extra {
        self.extra
            .get_or_insert_with(|| Box::new(Extra { delayed_eof: None }))
    }

    fn poll_eof(&mut self, cx: &mut task::Context<'_>) -> Poll<Option<crate::Result<Bytes>>> {
        match self.take_delayed_eof() {
            #[cfg(any(feature = "http1", feature = "http2"))]
            #[cfg(feature = "client")]
            Some(DelayEof::NotEof(mut delay)) => match self.poll_inner(cx) {
                ok @ Poll::Ready(Some(Ok(..))) | ok @ Poll::Pending => {
                    self.extra_mut().delayed_eof = Some(DelayEof::NotEof(delay));
                    ok
                }
                Poll::Ready(None) => match Pin::new(&mut delay).poll(cx) {
                    Poll::Ready(Ok(never)) => match never {},
                    Poll::Pending => {
                        self.extra_mut().delayed_eof = Some(DelayEof::Eof(delay));
                        Poll::Pending
                    }
                    Poll::Ready(Err(_done)) => Poll::Ready(None),
                },
                Poll::Ready(Some(Err(e))) => Poll::Ready(Some(Err(e))),
            },
            #[cfg(any(feature = "http1", feature = "http2"))]
            #[cfg(feature = "client")]
            Some(DelayEof::Eof(mut delay)) => match Pin::new(&mut delay).poll(cx) {
                Poll::Ready(Ok(never)) => match never {},
                Poll::Pending => {
                    self.extra_mut().delayed_eof = Some(DelayEof::Eof(delay));
                    Poll::Pending
                }
                Poll::Ready(Err(_done)) => Poll::Ready(None),
            },
            #[cfg(any(
                not(any(feature = "http1", feature = "http2")),
                not(feature = "client")
            ))]
            Some(delay_eof) => match delay_eof {},
            None => self.poll_inner(cx),
        }
    }

    #[cfg(feature = "ffi")]
    pub(crate) fn as_ffi_mut(&mut self) -> &mut crate::ffi::UserBody {
        match self.kind {
            Kind::Ffi(ref mut body) => return body,
            _ => {
                self.kind = Kind::Ffi(crate::ffi::UserBody::new());
            }
        }

        match self.kind {
            Kind::Ffi(ref mut body) => body,
            _ => unreachable!(),
        }
    }

    fn poll_inner(&mut self, cx: &mut task::Context<'_>) -> Poll<Option<crate::Result<Bytes>>> {
        match self.kind {
            Kind::Once(ref mut val) => Poll::Ready(val.take().map(Ok)),
            Kind::Chan {
                content_length: ref mut len,
                ref mut data_rx,
                ref mut want_tx,
                ..
            } => {
                want_tx.send(WANT_READY);

                match ready!(Pin::new(data_rx).poll_next(cx)?) {
                    Some(chunk) => {
                        len.sub_if(chunk.len() as u64);
                        Poll::Ready(Some(Ok(chunk)))
                    }
                    None => Poll::Ready(None),
                }
            }
            #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
            Kind::H2 {
                ref ping,
                recv: ref mut h2,
                content_length: ref mut len,
            } => match ready!(h2.poll_data(cx)) {
                Some(Ok(bytes)) => {
                    let _ = h2.flow_control().release_capacity(bytes.len());
                    len.sub_if(bytes.len() as u64);
                    ping.record_data(bytes.len());
                    Poll::Ready(Some(Ok(bytes)))
                }
                Some(Err(e)) => Poll::Ready(Some(Err(crate::Error::new_body(e)))),
                None => Poll::Ready(None),
            },

            #[cfg(feature = "ffi")]
            Kind::Ffi(ref mut body) => body.poll_data(cx),

            #[cfg(feature = "stream")]
            Kind::Wrapped(ref mut s) => match ready!(s.get_mut().as_mut().poll_next(cx)) {
                Some(res) => Poll::Ready(Some(res.map_err(crate::Error::new_body))),
                None => Poll::Ready(None),
            },
        }
    }

    #[cfg(feature = "http1")]
    pub(super) fn take_full_data(&mut self) -> Option<Bytes> {
        if let Kind::Once(ref mut chunk) = self.kind {
            chunk.take()
        } else {
            None
        }
    }
}

impl Default for Body {
    /// Returns `Body::empty()`.
    #[inline]
    fn default() -> Body {
        Body::empty()
    }
}

impl HttpBody for Body {
    type Data = Bytes;
    type Error = crate::Error;

    fn poll_data(
        mut self: Pin<&mut Self>,
        cx: &mut task::Context<'_>,
    ) -> Poll<Option<Result<Self::Data, Self::Error>>> {
        self.poll_eof(cx)
    }

    fn poll_trailers(
        #[cfg_attr(not(feature = "http2"), allow(unused_mut))] mut self: Pin<&mut Self>,
        #[cfg_attr(not(feature = "http2"), allow(unused))] cx: &mut task::Context<'_>,
    ) -> Poll<Result<Option<HeaderMap>, Self::Error>> {
        match self.kind {
            #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
            Kind::H2 {
                recv: ref mut h2,
                ref ping,
                ..
            } => match ready!(h2.poll_trailers(cx)) {
                Ok(t) => {
                    ping.record_non_data();
                    Poll::Ready(Ok(t))
                }
                Err(e) => Poll::Ready(Err(crate::Error::new_h2(e))),
            },
            Kind::Chan {
                ref mut trailers_rx,
                ..
            } => match ready!(Pin::new(trailers_rx).poll(cx)) {
                Ok(t) => Poll::Ready(Ok(Some(t))),
                Err(_) => Poll::Ready(Ok(None)),
            },
            #[cfg(feature = "ffi")]
            Kind::Ffi(ref mut body) => body.poll_trailers(cx),
            _ => Poll::Ready(Ok(None)),
        }
    }

    fn is_end_stream(&self) -> bool {
        match self.kind {
            Kind::Once(ref val) => val.is_none(),
            Kind::Chan { content_length, .. } => content_length == DecodedLength::ZERO,
            #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
            Kind::H2 { recv: ref h2, .. } => h2.is_end_stream(),
            #[cfg(feature = "ffi")]
            Kind::Ffi(..) => false,
            #[cfg(feature = "stream")]
            Kind::Wrapped(..) => false,
        }
    }

    fn size_hint(&self) -> SizeHint {
        macro_rules! opt_len {
            ($content_length:expr) => {{
                let mut hint = SizeHint::default();

                if let Some(content_length) = $content_length.into_opt() {
                    hint.set_exact(content_length);
                }

                hint
            }};
        }

        match self.kind {
            Kind::Once(Some(ref val)) => SizeHint::with_exact(val.len() as u64),
            Kind::Once(None) => SizeHint::with_exact(0),
            #[cfg(feature = "stream")]
            Kind::Wrapped(..) => SizeHint::default(),
            Kind::Chan { content_length, .. } => opt_len!(content_length),
            #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
            Kind::H2 { content_length, .. } => opt_len!(content_length),
            #[cfg(feature = "ffi")]
            Kind::Ffi(..) => SizeHint::default(),
        }
    }
}

impl fmt::Debug for Body {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        #[derive(Debug)]
        struct Streaming;
        #[derive(Debug)]
        struct Empty;
        #[derive(Debug)]
        struct Full<'a>(&'a Bytes);

        let mut builder = f.debug_tuple("Body");
        match self.kind {
            Kind::Once(None) => builder.field(&Empty),
            Kind::Once(Some(ref chunk)) => builder.field(&Full(chunk)),
            _ => builder.field(&Streaming),
        };

        builder.finish()
    }
}

/// # Optional
///
/// This function requires enabling the `stream` feature in your
/// `Cargo.toml`.
#[cfg(feature = "stream")]
impl Stream for Body {
    type Item = crate::Result<Bytes>;

    fn poll_next(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Option<Self::Item>> {
        HttpBody::poll_data(self, cx)
    }
}

/// # Optional
///
/// This function requires enabling the `stream` feature in your
/// `Cargo.toml`.
#[cfg(feature = "stream")]
impl From<Box<dyn Stream<Item = Result<Bytes, Box<dyn StdError + Send + Sync>>> + Send>> for Body {
    #[inline]
    fn from(
        stream: Box<dyn Stream<Item = Result<Bytes, Box<dyn StdError + Send + Sync>>> + Send>,
    ) -> Body {
        Body::new(Kind::Wrapped(SyncWrapper::new(stream.into())))
    }
}

impl From<Bytes> for Body {
    #[inline]
    fn from(chunk: Bytes) -> Body {
        if chunk.is_empty() {
            Body::empty()
        } else {
            Body::new(Kind::Once(Some(chunk)))
        }
    }
}

impl From<Vec<u8>> for Body {
    #[inline]
    fn from(vec: Vec<u8>) -> Body {
        Body::from(Bytes::from(vec))
    }
}

impl From<&'static [u8]> for Body {
    #[inline]
    fn from(slice: &'static [u8]) -> Body {
        Body::from(Bytes::from(slice))
    }
}

impl From<Cow<'static, [u8]>> for Body {
    #[inline]
    fn from(cow: Cow<'static, [u8]>) -> Body {
        match cow {
            Cow::Borrowed(b) => Body::from(b),
            Cow::Owned(o) => Body::from(o),
        }
    }
}

impl From<String> for Body {
    #[inline]
    fn from(s: String) -> Body {
        Body::from(Bytes::from(s.into_bytes()))
    }
}

impl From<&'static str> for Body {
    #[inline]
    fn from(slice: &'static str) -> Body {
        Body::from(Bytes::from(slice.as_bytes()))
    }
}

impl From<Cow<'static, str>> for Body {
    #[inline]
    fn from(cow: Cow<'static, str>) -> Body {
        match cow {
            Cow::Borrowed(b) => Body::from(b),
            Cow::Owned(o) => Body::from(o),
        }
    }
}

impl Sender {
    /// Check to see if this `Sender` can send more data.
    pub fn poll_ready(&mut self, cx: &mut task::Context<'_>) -> Poll<crate::Result<()>> {
        // Check if the receiver end has tried polling for the body yet
        ready!(self.poll_want(cx)?);
        self.data_tx
            .poll_ready(cx)
            .map_err(|_| crate::Error::new_closed())
    }

    fn poll_want(&mut self, cx: &mut task::Context<'_>) -> Poll<crate::Result<()>> {
        match self.want_rx.load(cx) {
            WANT_READY => Poll::Ready(Ok(())),
            WANT_PENDING => Poll::Pending,
            watch::CLOSED => Poll::Ready(Err(crate::Error::new_closed())),
            unexpected => unreachable!("want_rx value: {}", unexpected),
        }
    }

    async fn ready(&mut self) -> crate::Result<()> {
        futures_util::future::poll_fn(|cx| self.poll_ready(cx)).await
    }

    /// Send data on data channel when it is ready.
    pub async fn send_data(&mut self, chunk: Bytes) -> crate::Result<()> {
        self.ready().await?;
        self.data_tx
            .try_send(Ok(chunk))
            .map_err(|_| crate::Error::new_closed())
    }

    /// Send trailers on trailers channel.
    pub async fn send_trailers(&mut self, trailers: HeaderMap) -> crate::Result<()> {
        let tx = match self.trailers_tx.take() {
            Some(tx) => tx,
            None => return Err(crate::Error::new_closed()),
        };
        tx.send(trailers).map_err(|_| crate::Error::new_closed())
    }

    /// Try to send data on this channel.
    ///
    /// # Errors
    ///
    /// Returns `Err(Bytes)` if the channel could not (currently) accept
    /// another `Bytes`.
    ///
    /// # Note
    ///
    /// This is mostly useful for when trying to send from some other thread
    /// that doesn't have an async context. If in an async context, prefer
    /// `send_data()` instead.
    pub fn try_send_data(&mut self, chunk: Bytes) -> Result<(), Bytes> {
        self.data_tx
            .try_send(Ok(chunk))
            .map_err(|err| err.into_inner().expect("just sent Ok"))
    }

    /// Aborts the body in an abnormal fashion.
    pub fn abort(self) {
        let _ = self
            .data_tx
            // clone so the send works even if buffer is full
            .clone()
            .try_send(Err(crate::Error::new_body_write_aborted()));
    }

    #[cfg(feature = "http1")]
    pub(crate) fn send_error(&mut self, err: crate::Error) {
        let _ = self.data_tx.try_send(Err(err));
    }
}

impl fmt::Debug for Sender {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        #[derive(Debug)]
        struct Open;
        #[derive(Debug)]
        struct Closed;

        let mut builder = f.debug_tuple("Sender");
        match self.want_rx.peek() {
            watch::CLOSED => builder.field(&Closed),
            _ => builder.field(&Open),
        };

        builder.finish()
    }
}

#[cfg(test)]
mod tests {
    use std::mem;
    use std::task::Poll;

    use super::{Body, DecodedLength, HttpBody, Sender, SizeHint};

    #[test]
    fn test_size_of() {
        // These are mostly to help catch *accidentally* increasing
        // the size by too much.

        let body_size = mem::size_of::<Body>();
        let body_expected_size = mem::size_of::<u64>() * 6;
        assert!(
            body_size <= body_expected_size,
            "Body size = {} <= {}",
            body_size,
            body_expected_size,
        );

        assert_eq!(body_size, mem::size_of::<Option<Body>>(), "Option<Body>");

        assert_eq!(
            mem::size_of::<Sender>(),
            mem::size_of::<usize>() * 5,
            "Sender"
        );

        assert_eq!(
            mem::size_of::<Sender>(),
            mem::size_of::<Option<Sender>>(),
            "Option<Sender>"
        );
    }

    #[test]
    fn size_hint() {
        fn eq(body: Body, b: SizeHint, note: &str) {
            let a = body.size_hint();
            assert_eq!(a.lower(), b.lower(), "lower for {:?}", note);
            assert_eq!(a.upper(), b.upper(), "upper for {:?}", note);
        }

        eq(Body::from("Hello"), SizeHint::with_exact(5), "from str");

        eq(Body::empty(), SizeHint::with_exact(0), "empty");

        eq(Body::channel().1, SizeHint::new(), "channel");

        eq(
            Body::new_channel(DecodedLength::new(4), /*wanter =*/ false).1,
            SizeHint::with_exact(4),
            "channel with length",
        );
    }

    #[tokio::test]
    async fn channel_abort() {
        let (tx, mut rx) = Body::channel();

        tx.abort();

        let err = rx.data().await.unwrap().unwrap_err();
        assert!(err.is_body_write_aborted(), "{:?}", err);
    }

    #[tokio::test]
    async fn channel_abort_when_buffer_is_full() {
        let (mut tx, mut rx) = Body::channel();

        tx.try_send_data("chunk 1".into()).expect("send 1");
        // buffer is full, but can still send abort
        tx.abort();

        let chunk1 = rx.data().await.expect("item 1").expect("chunk 1");
        assert_eq!(chunk1, "chunk 1");

        let err = rx.data().await.unwrap().unwrap_err();
        assert!(err.is_body_write_aborted(), "{:?}", err);
    }

    #[test]
    fn channel_buffers_one() {
        let (mut tx, _rx) = Body::channel();

        tx.try_send_data("chunk 1".into()).expect("send 1");

        // buffer is now full
        let chunk2 = tx.try_send_data("chunk 2".into()).expect_err("send 2");
        assert_eq!(chunk2, "chunk 2");
    }

    #[tokio::test]
    async fn channel_empty() {
        let (_, mut rx) = Body::channel();

        assert!(rx.data().await.is_none());
    }

    #[test]
    fn channel_ready() {
        let (mut tx, _rx) = Body::new_channel(DecodedLength::CHUNKED, /*wanter = */ false);

        let mut tx_ready = tokio_test::task::spawn(tx.ready());

        assert!(tx_ready.poll().is_ready(), "tx is ready immediately");
    }

    #[test]
    fn channel_wanter() {
        let (mut tx, mut rx) = Body::new_channel(DecodedLength::CHUNKED, /*wanter = */ true);

        let mut tx_ready = tokio_test::task::spawn(tx.ready());
        let mut rx_data = tokio_test::task::spawn(rx.data());

        assert!(
            tx_ready.poll().is_pending(),
            "tx isn't ready before rx has been polled"
        );

        assert!(rx_data.poll().is_pending(), "poll rx.data");
        assert!(tx_ready.is_woken(), "rx poll wakes tx");

        assert!(
            tx_ready.poll().is_ready(),
            "tx is ready after rx has been polled"
        );
    }

    #[test]
    fn channel_notices_closure() {
        let (mut tx, rx) = Body::new_channel(DecodedLength::CHUNKED, /*wanter = */ true);

        let mut tx_ready = tokio_test::task::spawn(tx.ready());

        assert!(
            tx_ready.poll().is_pending(),
            "tx isn't ready before rx has been polled"
        );

        drop(rx);
        assert!(tx_ready.is_woken(), "dropping rx wakes tx");

        match tx_ready.poll() {
            Poll::Ready(Err(ref e)) if e.is_closed() => (),
            unexpected => panic!("tx poll ready unexpected: {:?}", unexpected),
        }
    }
}