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
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
use std::{
    collections::VecDeque,
    fmt,
    future::Future,
    io, mem, net,
    pin::Pin,
    rc::Rc,
    task::{Context, Poll},
};

use actix_codec::{Framed, FramedParts};
use actix_rt::time::sleep_until;
use actix_service::Service;
use bitflags::bitflags;
use bytes::{Buf, BytesMut};
use futures_core::ready;
use pin_project_lite::pin_project;
use tokio::io::{AsyncRead, AsyncWrite};
use tokio_util::codec::{Decoder as _, Encoder as _};
use tracing::{error, trace};

use crate::{
    body::{BodySize, BoxBody, MessageBody},
    config::ServiceConfig,
    error::{DispatchError, ParseError, PayloadError},
    service::HttpFlow,
    Error, Extensions, OnConnectData, Request, Response, StatusCode,
};

use super::{
    codec::Codec,
    decoder::MAX_BUFFER_SIZE,
    payload::{Payload, PayloadSender, PayloadStatus},
    timer::TimerState,
    Message, MessageType,
};

const LW_BUFFER_SIZE: usize = 1024;
const HW_BUFFER_SIZE: usize = 1024 * 8;
const MAX_PIPELINED_MESSAGES: usize = 16;

bitflags! {
    pub struct Flags: u8 {
        /// Set when stream is read for first time.
        const STARTED          = 0b0000_0001;

        /// Set when full request-response cycle has occurred.
        const FINISHED         = 0b0000_0010;

        /// Set if connection is in keep-alive (inactive) state.
        const KEEP_ALIVE       = 0b0000_0100;

        /// Set if in shutdown procedure.
        const SHUTDOWN         = 0b0000_1000;

        /// Set if read-half is disconnected.
        const READ_DISCONNECT  = 0b0001_0000;

        /// Set if write-half is disconnected.
        const WRITE_DISCONNECT = 0b0010_0000;
    }
}

// there's 2 versions of Dispatcher state because of:
// https://github.com/taiki-e/pin-project-lite/issues/3
//
// tl;dr: pin-project-lite doesn't play well with other attribute macros

#[cfg(not(test))]
pin_project! {
    /// Dispatcher for HTTP/1.1 protocol
    pub struct Dispatcher<T, S, B, X, U>
    where
        S: Service<Request>,
        S::Error: Into<Response<BoxBody>>,

        B: MessageBody,

        X: Service<Request, Response = Request>,
        X::Error: Into<Response<BoxBody>>,

        U: Service<(Request, Framed<T, Codec>), Response = ()>,
        U::Error: fmt::Display,
    {
        #[pin]
        inner: DispatcherState<T, S, B, X, U>,
    }
}

#[cfg(test)]
pin_project! {
    /// Dispatcher for HTTP/1.1 protocol
    pub struct Dispatcher<T, S, B, X, U>
    where
        S: Service<Request>,
        S::Error: Into<Response<BoxBody>>,

        B: MessageBody,

        X: Service<Request, Response = Request>,
        X::Error: Into<Response<BoxBody>>,

        U: Service<(Request, Framed<T, Codec>), Response = ()>,
        U::Error: fmt::Display,
    {
        #[pin]
        pub(super) inner: DispatcherState<T, S, B, X, U>,

        // used in tests
        pub(super) poll_count: u64,
    }
}

pin_project! {
    #[project = DispatcherStateProj]
    pub(super) enum DispatcherState<T, S, B, X, U>
    where
        S: Service<Request>,
        S::Error: Into<Response<BoxBody>>,

        B: MessageBody,

        X: Service<Request, Response = Request>,
        X::Error: Into<Response<BoxBody>>,

        U: Service<(Request, Framed<T, Codec>), Response = ()>,
        U::Error: fmt::Display,
    {
        Normal { #[pin] inner: InnerDispatcher<T, S, B, X, U> },
        Upgrade { #[pin] fut: U::Future },
    }
}

pin_project! {
    #[project = InnerDispatcherProj]
    pub(super) struct InnerDispatcher<T, S, B, X, U>
    where
        S: Service<Request>,
        S::Error: Into<Response<BoxBody>>,

        B: MessageBody,

        X: Service<Request, Response = Request>,
        X::Error: Into<Response<BoxBody>>,

        U: Service<(Request, Framed<T, Codec>), Response = ()>,
        U::Error: fmt::Display,
    {
        flow: Rc<HttpFlow<S, X, U>>,
        pub(super) flags: Flags,
        peer_addr: Option<net::SocketAddr>,
        conn_data: Option<Rc<Extensions>>,
        config: ServiceConfig,
        error: Option<DispatchError>,

        #[pin]
        pub(super) state: State<S, B, X>,
        // when Some(_) dispatcher is in state of receiving request payload
        payload: Option<PayloadSender>,
        messages: VecDeque<DispatcherMessage>,

        head_timer: TimerState,
        ka_timer: TimerState,
        shutdown_timer: TimerState,

        pub(super) io: Option<T>,
        read_buf: BytesMut,
        write_buf: BytesMut,
        codec: Codec,
    }
}

enum DispatcherMessage {
    Item(Request),
    Upgrade(Request),
    Error(Response<()>),
}

pin_project! {
    #[project = StateProj]
    pub(super) enum State<S, B, X>
    where
        S: Service<Request>,
        X: Service<Request, Response = Request>,
        B: MessageBody,
    {
        None,
        ExpectCall { #[pin] fut: X::Future },
        ServiceCall { #[pin] fut: S::Future },
        SendPayload { #[pin] body: B },
        SendErrorPayload { #[pin] body: BoxBody },
    }
}

impl<S, B, X> State<S, B, X>
where
    S: Service<Request>,
    X: Service<Request, Response = Request>,
    B: MessageBody,
{
    pub(super) fn is_none(&self) -> bool {
        matches!(self, State::None)
    }
}

impl<S, B, X> fmt::Debug for State<S, B, X>
where
    S: Service<Request>,
    X: Service<Request, Response = Request>,
    B: MessageBody,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::None => write!(f, "State::None"),
            Self::ExpectCall { .. } => {
                f.debug_struct("State::ExpectCall").finish_non_exhaustive()
            }
            Self::ServiceCall { .. } => {
                f.debug_struct("State::ServiceCall").finish_non_exhaustive()
            }
            Self::SendPayload { .. } => {
                f.debug_struct("State::SendPayload").finish_non_exhaustive()
            }
            Self::SendErrorPayload { .. } => f
                .debug_struct("State::SendErrorPayload")
                .finish_non_exhaustive(),
        }
    }
}

#[derive(Debug)]
enum PollResponse {
    Upgrade(Request),
    DoNothing,
    DrainWriteBuf,
}

impl<T, S, B, X, U> Dispatcher<T, S, B, X, U>
where
    T: AsyncRead + AsyncWrite + Unpin,

    S: Service<Request>,
    S::Error: Into<Response<BoxBody>>,
    S::Response: Into<Response<B>>,

    B: MessageBody,

    X: Service<Request, Response = Request>,
    X::Error: Into<Response<BoxBody>>,

    U: Service<(Request, Framed<T, Codec>), Response = ()>,
    U::Error: fmt::Display,
{
    /// Create HTTP/1 dispatcher.
    pub(crate) fn new(
        io: T,
        flow: Rc<HttpFlow<S, X, U>>,
        config: ServiceConfig,
        peer_addr: Option<net::SocketAddr>,
        conn_data: OnConnectData,
    ) -> Self {
        Dispatcher {
            inner: DispatcherState::Normal {
                inner: InnerDispatcher {
                    flow,
                    flags: Flags::empty(),
                    peer_addr,
                    conn_data: conn_data.0.map(Rc::new),
                    config: config.clone(),
                    error: None,

                    state: State::None,
                    payload: None,
                    messages: VecDeque::new(),

                    head_timer: TimerState::new(config.client_request_deadline().is_some()),
                    ka_timer: TimerState::new(config.keep_alive().enabled()),
                    shutdown_timer: TimerState::new(
                        config.client_disconnect_deadline().is_some(),
                    ),

                    io: Some(io),
                    read_buf: BytesMut::with_capacity(HW_BUFFER_SIZE),
                    write_buf: BytesMut::with_capacity(HW_BUFFER_SIZE),
                    codec: Codec::new(config),
                },
            },

            #[cfg(test)]
            poll_count: 0,
        }
    }
}

impl<T, S, B, X, U> InnerDispatcher<T, S, B, X, U>
where
    T: AsyncRead + AsyncWrite + Unpin,

    S: Service<Request>,
    S::Error: Into<Response<BoxBody>>,
    S::Response: Into<Response<B>>,

    B: MessageBody,

    X: Service<Request, Response = Request>,
    X::Error: Into<Response<BoxBody>>,

    U: Service<(Request, Framed<T, Codec>), Response = ()>,
    U::Error: fmt::Display,
{
    fn can_read(&self, cx: &mut Context<'_>) -> bool {
        if self.flags.contains(Flags::READ_DISCONNECT) {
            false
        } else if let Some(ref info) = self.payload {
            info.need_read(cx) == PayloadStatus::Read
        } else {
            true
        }
    }

    fn client_disconnected(self: Pin<&mut Self>) {
        let this = self.project();

        this.flags
            .insert(Flags::READ_DISCONNECT | Flags::WRITE_DISCONNECT);

        if let Some(mut payload) = this.payload.take() {
            payload.set_error(PayloadError::Incomplete(None));
        }
    }

    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
        let InnerDispatcherProj { io, write_buf, .. } = self.project();
        let mut io = Pin::new(io.as_mut().unwrap());

        let len = write_buf.len();
        let mut written = 0;

        while written < len {
            match io.as_mut().poll_write(cx, &write_buf[written..])? {
                Poll::Ready(0) => {
                    error!("write zero; closing");
                    return Poll::Ready(Err(io::Error::new(io::ErrorKind::WriteZero, "")));
                }

                Poll::Ready(n) => written += n,

                Poll::Pending => {
                    write_buf.advance(written);
                    return Poll::Pending;
                }
            }
        }

        // everything has written to I/O; clear buffer
        write_buf.clear();

        // flush the I/O and check if get blocked
        io.poll_flush(cx)
    }

    fn send_response_inner(
        self: Pin<&mut Self>,
        res: Response<()>,
        body: &impl MessageBody,
    ) -> Result<BodySize, DispatchError> {
        let this = self.project();

        let size = body.size();

        this.codec
            .encode(Message::Item((res, size)), this.write_buf)
            .map_err(|err| {
                if let Some(mut payload) = this.payload.take() {
                    payload.set_error(PayloadError::Incomplete(None));
                }

                DispatchError::Io(err)
            })?;

        Ok(size)
    }

    fn send_response(
        mut self: Pin<&mut Self>,
        res: Response<()>,
        body: B,
    ) -> Result<(), DispatchError> {
        let size = self.as_mut().send_response_inner(res, &body)?;
        let mut this = self.project();
        this.state.set(match size {
            BodySize::None | BodySize::Sized(0) => {
                this.flags.insert(Flags::FINISHED);
                State::None
            }
            _ => State::SendPayload { body },
        });

        Ok(())
    }

    fn send_error_response(
        mut self: Pin<&mut Self>,
        res: Response<()>,
        body: BoxBody,
    ) -> Result<(), DispatchError> {
        let size = self.as_mut().send_response_inner(res, &body)?;
        let mut this = self.project();
        this.state.set(match size {
            BodySize::None | BodySize::Sized(0) => {
                this.flags.insert(Flags::FINISHED);
                State::None
            }
            _ => State::SendErrorPayload { body },
        });

        Ok(())
    }

    fn send_continue(self: Pin<&mut Self>) {
        self.project()
            .write_buf
            .extend_from_slice(b"HTTP/1.1 100 Continue\r\n\r\n");
    }

    fn poll_response(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Result<PollResponse, DispatchError> {
        'res: loop {
            let mut this = self.as_mut().project();
            match this.state.as_mut().project() {
                // no future is in InnerDispatcher state; pop next message
                StateProj::None => match this.messages.pop_front() {
                    // handle request message
                    Some(DispatcherMessage::Item(req)) => {
                        // Handle `EXPECT: 100-Continue` header
                        if req.head().expect() {
                            // set InnerDispatcher state and continue loop to poll it
                            let fut = this.flow.expect.call(req);
                            this.state.set(State::ExpectCall { fut });
                        } else {
                            // set InnerDispatcher state and continue loop to poll it
                            let fut = this.flow.service.call(req);
                            this.state.set(State::ServiceCall { fut });
                        };
                    }

                    // handle error message
                    Some(DispatcherMessage::Error(res)) => {
                        // send_response would update InnerDispatcher state to SendPayload or None
                        // (If response body is empty)
                        // continue loop to poll it
                        self.as_mut().send_error_response(res, BoxBody::new(()))?;
                    }

                    // return with upgrade request and poll it exclusively
                    Some(DispatcherMessage::Upgrade(req)) => {
                        return Ok(PollResponse::Upgrade(req))
                    }

                    // all messages are dealt with
                    None => {
                        // start keep-alive if last request allowed it
                        this.flags.set(Flags::KEEP_ALIVE, this.codec.keep_alive());

                        return Ok(PollResponse::DoNothing);
                    }
                },

                StateProj::ServiceCall { fut } => {
                    match fut.poll(cx) {
                        // service call resolved. send response.
                        Poll::Ready(Ok(res)) => {
                            let (res, body) = res.into().replace_body(());
                            self.as_mut().send_response(res, body)?;
                        }

                        // send service call error as response
                        Poll::Ready(Err(err)) => {
                            let res: Response<BoxBody> = err.into();
                            let (res, body) = res.replace_body(());
                            self.as_mut().send_error_response(res, body)?;
                        }

                        // service call pending and could be waiting for more chunk messages
                        // (pipeline message limit and/or payload can_read limit)
                        Poll::Pending => {
                            // no new message is decoded and no new payload is fed
                            // nothing to do except waiting for new incoming data from client
                            if !self.as_mut().poll_request(cx)? {
                                return Ok(PollResponse::DoNothing);
                            }
                            // else loop
                        }
                    }
                }

                StateProj::SendPayload { mut body } => {
                    // keep populate writer buffer until buffer size limit hit,
                    // get blocked or finished.
                    while this.write_buf.len() < super::payload::MAX_BUFFER_SIZE {
                        match body.as_mut().poll_next(cx) {
                            Poll::Ready(Some(Ok(item))) => {
                                this.codec
                                    .encode(Message::Chunk(Some(item)), this.write_buf)?;
                            }

                            Poll::Ready(None) => {
                                this.codec.encode(Message::Chunk(None), this.write_buf)?;

                                // payload stream finished.
                                // set state to None and handle next message
                                this.state.set(State::None);
                                this.flags.insert(Flags::FINISHED);

                                continue 'res;
                            }

                            Poll::Ready(Some(Err(err))) => {
                                this.flags.insert(Flags::FINISHED);
                                return Err(DispatchError::Body(err.into()));
                            }

                            Poll::Pending => return Ok(PollResponse::DoNothing),
                        }
                    }

                    // buffer is beyond max size
                    // return and try to write the whole buffer to I/O stream.
                    return Ok(PollResponse::DrainWriteBuf);
                }

                StateProj::SendErrorPayload { mut body } => {
                    // TODO: de-dupe impl with SendPayload

                    // keep populate writer buffer until buffer size limit hit,
                    // get blocked or finished.
                    while this.write_buf.len() < super::payload::MAX_BUFFER_SIZE {
                        match body.as_mut().poll_next(cx) {
                            Poll::Ready(Some(Ok(item))) => {
                                this.codec
                                    .encode(Message::Chunk(Some(item)), this.write_buf)?;
                            }

                            Poll::Ready(None) => {
                                this.codec.encode(Message::Chunk(None), this.write_buf)?;

                                // payload stream finished
                                // set state to None and handle next message
                                this.state.set(State::None);
                                this.flags.insert(Flags::FINISHED);

                                continue 'res;
                            }

                            Poll::Ready(Some(Err(err))) => {
                                this.flags.insert(Flags::FINISHED);
                                return Err(DispatchError::Body(
                                    Error::new_body().with_cause(err).into(),
                                ));
                            }

                            Poll::Pending => return Ok(PollResponse::DoNothing),
                        }
                    }

                    // buffer is beyond max size
                    // return and try to write the whole buffer to stream
                    return Ok(PollResponse::DrainWriteBuf);
                }

                StateProj::ExpectCall { fut } => {
                    trace!("  calling expect service");

                    match fut.poll(cx) {
                        // expect resolved. write continue to buffer and set InnerDispatcher state
                        // to service call.
                        Poll::Ready(Ok(req)) => {
                            this.write_buf
                                .extend_from_slice(b"HTTP/1.1 100 Continue\r\n\r\n");
                            let fut = this.flow.service.call(req);
                            this.state.set(State::ServiceCall { fut });
                        }

                        // send expect error as response
                        Poll::Ready(Err(err)) => {
                            let res: Response<BoxBody> = err.into();
                            let (res, body) = res.replace_body(());
                            self.as_mut().send_error_response(res, body)?;
                        }

                        // expect must be solved before progress can be made.
                        Poll::Pending => return Ok(PollResponse::DoNothing),
                    }
                }
            }
        }
    }

    fn handle_request(
        mut self: Pin<&mut Self>,
        req: Request,
        cx: &mut Context<'_>,
    ) -> Result<(), DispatchError> {
        // initialize dispatcher state
        {
            let mut this = self.as_mut().project();

            // Handle `EXPECT: 100-Continue` header
            if req.head().expect() {
                // set dispatcher state to call expect handler
                let fut = this.flow.expect.call(req);
                this.state.set(State::ExpectCall { fut });
            } else {
                // set dispatcher state to call service handler
                let fut = this.flow.service.call(req);
                this.state.set(State::ServiceCall { fut });
            };
        };

        // eagerly poll the future once (or twice if expect is resolved immediately).
        loop {
            match self.as_mut().project().state.project() {
                StateProj::ExpectCall { fut } => {
                    match fut.poll(cx) {
                        // expect is resolved; continue loop and poll the service call branch.
                        Poll::Ready(Ok(req)) => {
                            self.as_mut().send_continue();

                            let mut this = self.as_mut().project();
                            let fut = this.flow.service.call(req);
                            this.state.set(State::ServiceCall { fut });

                            continue;
                        }

                        // future is error; send response and return a result
                        // on success to notify the dispatcher a new state is set and the outer loop
                        // should be continued
                        Poll::Ready(Err(err)) => {
                            let res: Response<BoxBody> = err.into();
                            let (res, body) = res.replace_body(());
                            return self.send_error_response(res, body);
                        }

                        // future is pending; return Ok(()) to notify that a new state is
                        // set and the outer loop should be continue.
                        Poll::Pending => return Ok(()),
                    }
                }

                StateProj::ServiceCall { fut } => {
                    // return no matter the service call future's result.
                    return match fut.poll(cx) {
                        // Future is resolved. Send response and return a result. On success
                        // to notify the dispatcher a new state is set and the outer loop
                        // should be continue.
                        Poll::Ready(Ok(res)) => {
                            let (res, body) = res.into().replace_body(());
                            self.as_mut().send_response(res, body)
                        }

                        // see the comment on ExpectCall state branch's Pending
                        Poll::Pending => Ok(()),

                        // see the comment on ExpectCall state branch's Ready(Err(_))
                        Poll::Ready(Err(err)) => {
                            let res: Response<BoxBody> = err.into();
                            let (res, body) = res.replace_body(());
                            self.as_mut().send_error_response(res, body)
                        }
                    };
                }

                _ => {
                    unreachable!(
                        "State must be set to ServiceCall or ExceptCall in handle_request"
                    )
                }
            }
        }
    }

    /// Process one incoming request.
    ///
    /// Returns true if any meaningful work was done.
    fn poll_request(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Result<bool, DispatchError> {
        let pipeline_queue_full = self.messages.len() >= MAX_PIPELINED_MESSAGES;
        let can_not_read = !self.can_read(cx);

        // limit amount of non-processed requests
        if pipeline_queue_full || can_not_read {
            return Ok(false);
        }

        let mut this = self.as_mut().project();

        let mut updated = false;

        // decode from read buf as many full requests as possible
        loop {
            match this.codec.decode(this.read_buf) {
                Ok(Some(msg)) => {
                    updated = true;

                    match msg {
                        Message::Item(mut req) => {
                            // head timer only applies to first request on connection
                            this.head_timer.clear(line!());

                            req.head_mut().peer_addr = *this.peer_addr;

                            req.conn_data = this.conn_data.as_ref().map(Rc::clone);

                            match this.codec.message_type() {
                                // request has no payload
                                MessageType::None => {}

                                // Request is upgradable. Add upgrade message and break.
                                // Everything remaining in read buffer will be handed to
                                // upgraded Request.
                                MessageType::Stream if this.flow.upgrade.is_some() => {
                                    this.messages.push_back(DispatcherMessage::Upgrade(req));
                                    break;
                                }

                                // request is not upgradable
                                MessageType::Payload | MessageType::Stream => {
                                    // PayloadSender and Payload are smart pointers share the
                                    // same state. PayloadSender is attached to dispatcher and used
                                    // to sink new chunked request data to state. Payload is
                                    // attached to Request and passed to Service::call where the
                                    // state can be collected and consumed.
                                    let (sender, payload) = Payload::create(false);
                                    *req.payload() = crate::Payload::H1 { payload };
                                    *this.payload = Some(sender);
                                }
                            }

                            // handle request early when no future in InnerDispatcher state.
                            if this.state.is_none() {
                                self.as_mut().handle_request(req, cx)?;
                                this = self.as_mut().project();
                            } else {
                                this.messages.push_back(DispatcherMessage::Item(req));
                            }
                        }

                        Message::Chunk(Some(chunk)) => {
                            if let Some(ref mut payload) = this.payload {
                                payload.feed_data(chunk);
                            } else {
                                error!("Internal server error: unexpected payload chunk");
                                this.flags.insert(Flags::READ_DISCONNECT);
                                this.messages.push_back(DispatcherMessage::Error(
                                    Response::internal_server_error().drop_body(),
                                ));
                                *this.error = Some(DispatchError::InternalError);
                                break;
                            }
                        }

                        Message::Chunk(None) => {
                            if let Some(mut payload) = this.payload.take() {
                                payload.feed_eof();
                            } else {
                                error!("Internal server error: unexpected eof");
                                this.flags.insert(Flags::READ_DISCONNECT);
                                this.messages.push_back(DispatcherMessage::Error(
                                    Response::internal_server_error().drop_body(),
                                ));
                                *this.error = Some(DispatchError::InternalError);
                                break;
                            }
                        }
                    }
                }

                // decode is partial and buffer is not full yet
                // break and wait for more read
                Ok(None) => break,

                Err(ParseError::Io(err)) => {
                    trace!("I/O error: {}", &err);
                    self.as_mut().client_disconnected();
                    this = self.as_mut().project();
                    *this.error = Some(DispatchError::Io(err));
                    break;
                }

                Err(ParseError::TooLarge) => {
                    trace!("request head was too big; returning 431 response");

                    if let Some(mut payload) = this.payload.take() {
                        payload.set_error(PayloadError::Overflow);
                    }

                    // request heads that overflow buffer size return a 431 error
                    this.messages
                        .push_back(DispatcherMessage::Error(Response::with_body(
                            StatusCode::REQUEST_HEADER_FIELDS_TOO_LARGE,
                            (),
                        )));

                    this.flags.insert(Flags::READ_DISCONNECT);
                    *this.error = Some(ParseError::TooLarge.into());

                    break;
                }

                Err(err) => {
                    trace!("parse error {}", &err);

                    if let Some(mut payload) = this.payload.take() {
                        payload.set_error(PayloadError::EncodingCorrupted);
                    }

                    // malformed requests should be responded with 400
                    this.messages.push_back(DispatcherMessage::Error(
                        Response::bad_request().drop_body(),
                    ));

                    this.flags.insert(Flags::READ_DISCONNECT);
                    *this.error = Some(err.into());
                    break;
                }
            }
        }

        Ok(updated)
    }

    fn poll_head_timer(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Result<(), DispatchError> {
        let this = self.as_mut().project();

        if let TimerState::Active { timer } = this.head_timer {
            if timer.as_mut().poll(cx).is_ready() {
                // timeout on first request (slow request) return 408

                trace!("timed out on slow request; replying with 408 and closing connection");

                let _ = self.as_mut().send_error_response(
                    Response::with_body(StatusCode::REQUEST_TIMEOUT, ()),
                    BoxBody::new(()),
                );

                self.project().flags.insert(Flags::SHUTDOWN);
            }
        };

        Ok(())
    }

    fn poll_ka_timer(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Result<(), DispatchError> {
        let this = self.as_mut().project();
        if let TimerState::Active { timer } = this.ka_timer {
            debug_assert!(
                this.flags.contains(Flags::KEEP_ALIVE),
                "keep-alive flag should be set when timer is active",
            );
            debug_assert!(
                this.state.is_none(),
                "dispatcher should not be in keep-alive phase if state is not none: {:?}",
                this.state,
            );

            // Assert removed by @robjtede on account of issue #2655. There are cases where an I/O
            // flush can be pending after entering the keep-alive state causing the subsequent flush
            // wake up to panic here. This appears to be a Linux-only problem. Leaving original code
            // below for posterity because a simple and reliable test could not be found to trigger
            // the behavior.
            // debug_assert!(
            //     this.write_buf.is_empty(),
            //     "dispatcher should not be in keep-alive phase if write_buf is not empty",
            // );

            // keep-alive timer has timed out
            if timer.as_mut().poll(cx).is_ready() {
                // no tasks at hand
                trace!("timer timed out; closing connection");
                this.flags.insert(Flags::SHUTDOWN);

                if let Some(deadline) = this.config.client_disconnect_deadline() {
                    // start shutdown timeout if enabled
                    this.shutdown_timer
                        .set_and_init(cx, sleep_until(deadline.into()), line!());
                } else {
                    // no shutdown timeout, drop socket
                    this.flags.insert(Flags::WRITE_DISCONNECT);
                }
            }
        }

        Ok(())
    }

    fn poll_shutdown_timer(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Result<(), DispatchError> {
        let this = self.as_mut().project();
        if let TimerState::Active { timer } = this.shutdown_timer {
            debug_assert!(
                this.flags.contains(Flags::SHUTDOWN),
                "shutdown flag should be set when timer is active",
            );

            // timed-out during shutdown; drop connection
            if timer.as_mut().poll(cx).is_ready() {
                trace!("timed-out during shutdown");
                return Err(DispatchError::DisconnectTimeout);
            }
        }

        Ok(())
    }

    /// Poll head, keep-alive, and disconnect timer.
    fn poll_timers(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Result<(), DispatchError> {
        self.as_mut().poll_head_timer(cx)?;
        self.as_mut().poll_ka_timer(cx)?;
        self.as_mut().poll_shutdown_timer(cx)?;

        Ok(())
    }

    /// Returns true when I/O stream can be disconnected after write to it.
    ///
    /// It covers these conditions:
    /// - `std::io::ErrorKind::ConnectionReset` after partial read;
    /// - all data read done.
    #[inline(always)] // TODO: bench this inline
    fn read_available(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Result<bool, DispatchError> {
        let this = self.project();

        if this.flags.contains(Flags::READ_DISCONNECT) {
            return Ok(false);
        };

        let mut io = Pin::new(this.io.as_mut().unwrap());

        let mut read_some = false;

        loop {
            // Return early when read buf exceed decoder's max buffer size.
            if this.read_buf.len() >= MAX_BUFFER_SIZE {
                // At this point it's not known IO stream is still scheduled to be waked up so
                // force wake up dispatcher just in case.
                //
                // Reason:
                // AsyncRead mostly would only have guarantee wake up when the poll_read
                // return Poll::Pending.
                //
                // Case:
                // When read_buf is beyond max buffer size the early return could be successfully
                // be parsed as a new Request. This case would not generate ParseError::TooLarge and
                // at this point IO stream is not fully read to Pending and would result in
                // dispatcher stuck until timeout (keep-alive).
                //
                // Note:
                // This is a perf choice to reduce branch on <Request as MessageType>::decode.
                //
                // A Request head too large to parse is only checked on `httparse::Status::Partial`.

                match this.payload {
                    // When dispatcher has a payload the responsibility of wake ups is shifted to
                    // `h1::payload::Payload` unless the payload is needing a read, in which case it
                    // might not have access to the waker and could result in the dispatcher
                    // getting stuck until timeout.
                    //
                    // Reason:
                    // Self wake up when there is payload would waste poll and/or result in
                    // over read.
                    //
                    // Case:
                    // When payload is (partial) dropped by user there is no need to do
                    // read anymore. At this case read_buf could always remain beyond
                    // MAX_BUFFER_SIZE and self wake up would be busy poll dispatcher and
                    // waste resources.
                    Some(ref p) if p.need_read(cx) != PayloadStatus::Read => {}
                    _ => cx.waker().wake_by_ref(),
                }

                return Ok(false);
            }

            // grow buffer if necessary.
            let remaining = this.read_buf.capacity() - this.read_buf.len();
            if remaining < LW_BUFFER_SIZE {
                this.read_buf.reserve(HW_BUFFER_SIZE - remaining);
            }

            match tokio_util::io::poll_read_buf(io.as_mut(), cx, this.read_buf) {
                Poll::Ready(Ok(n)) => {
                    this.flags.remove(Flags::FINISHED);

                    if n == 0 {
                        return Ok(true);
                    }

                    read_some = true;
                }

                Poll::Pending => {
                    return Ok(false);
                }

                Poll::Ready(Err(err)) => {
                    return match err.kind() {
                        // convert WouldBlock error to the same as Pending return
                        io::ErrorKind::WouldBlock => Ok(false),

                        // connection reset after partial read
                        io::ErrorKind::ConnectionReset if read_some => Ok(true),

                        _ => Err(DispatchError::Io(err)),
                    };
                }
            }
        }
    }

    /// call upgrade service with request.
    fn upgrade(self: Pin<&mut Self>, req: Request) -> U::Future {
        let this = self.project();
        let mut parts = FramedParts::with_read_buf(
            this.io.take().unwrap(),
            mem::take(this.codec),
            mem::take(this.read_buf),
        );
        parts.write_buf = mem::take(this.write_buf);
        let framed = Framed::from_parts(parts);
        this.flow.upgrade.as_ref().unwrap().call((req, framed))
    }
}

impl<T, S, B, X, U> Future for Dispatcher<T, S, B, X, U>
where
    T: AsyncRead + AsyncWrite + Unpin,

    S: Service<Request>,
    S::Error: Into<Response<BoxBody>>,
    S::Response: Into<Response<B>>,

    B: MessageBody,

    X: Service<Request, Response = Request>,
    X::Error: Into<Response<BoxBody>>,

    U: Service<(Request, Framed<T, Codec>), Response = ()>,
    U::Error: fmt::Display,
{
    type Output = Result<(), DispatchError>;

    #[inline]
    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        let this = self.as_mut().project();

        #[cfg(test)]
        {
            *this.poll_count += 1;
        }

        match this.inner.project() {
            DispatcherStateProj::Upgrade { fut: upgrade } => upgrade.poll(cx).map_err(|err| {
                error!("Upgrade handler error: {}", err);
                DispatchError::Upgrade
            }),

            DispatcherStateProj::Normal { mut inner } => {
                trace!("start flags: {:?}", &inner.flags);

                trace_timer_states(
                    "start",
                    &inner.head_timer,
                    &inner.ka_timer,
                    &inner.shutdown_timer,
                );

                inner.as_mut().poll_timers(cx)?;

                let poll = if inner.flags.contains(Flags::SHUTDOWN) {
                    if inner.flags.contains(Flags::WRITE_DISCONNECT) {
                        Poll::Ready(Ok(()))
                    } else {
                        // flush buffer and wait on blocked
                        ready!(inner.as_mut().poll_flush(cx))?;
                        Pin::new(inner.as_mut().project().io.as_mut().unwrap())
                            .poll_shutdown(cx)
                            .map_err(DispatchError::from)
                    }
                } else {
                    // read from I/O stream and fill read buffer
                    let should_disconnect = inner.as_mut().read_available(cx)?;

                    // after reading something from stream, clear keep-alive timer
                    if !inner.read_buf.is_empty() && inner.flags.contains(Flags::KEEP_ALIVE) {
                        let inner = inner.as_mut().project();
                        inner.flags.remove(Flags::KEEP_ALIVE);
                        inner.ka_timer.clear(line!());
                    }

                    if !inner.flags.contains(Flags::STARTED) {
                        inner.as_mut().project().flags.insert(Flags::STARTED);

                        if let Some(deadline) = inner.config.client_request_deadline() {
                            inner.as_mut().project().head_timer.set_and_init(
                                cx,
                                sleep_until(deadline.into()),
                                line!(),
                            );
                        }
                    }

                    inner.as_mut().poll_request(cx)?;

                    if should_disconnect {
                        // I/O stream should to be closed
                        let inner = inner.as_mut().project();
                        inner.flags.insert(Flags::READ_DISCONNECT);
                        if let Some(mut payload) = inner.payload.take() {
                            payload.feed_eof();
                        }
                    };

                    loop {
                        // poll response to populate write buffer
                        // drain indicates whether write buffer should be emptied before next run
                        let drain = match inner.as_mut().poll_response(cx)? {
                            PollResponse::DrainWriteBuf => true,

                            PollResponse::DoNothing => {
                                // KEEP_ALIVE is set in send_response_inner if client allows it
                                // FINISHED is set after writing last chunk of response
                                if inner.flags.contains(Flags::KEEP_ALIVE | Flags::FINISHED) {
                                    if let Some(timer) = inner.config.keep_alive_deadline() {
                                        inner.as_mut().project().ka_timer.set_and_init(
                                            cx,
                                            sleep_until(timer.into()),
                                            line!(),
                                        );
                                    }
                                }

                                false
                            }

                            // upgrade request and goes Upgrade variant of DispatcherState.
                            PollResponse::Upgrade(req) => {
                                let upgrade = inner.upgrade(req);
                                self.as_mut()
                                    .project()
                                    .inner
                                    .set(DispatcherState::Upgrade { fut: upgrade });
                                return self.poll(cx);
                            }
                        };

                        // we didn't get WouldBlock from write operation, so data get written to
                        // kernel completely (macOS) and we have to write again otherwise response
                        // can get stuck
                        //
                        // TODO: want to find a reference for this behavior
                        // see introduced commit: 3872d3ba
                        let flush_was_ready = inner.as_mut().poll_flush(cx)?.is_ready();

                        // this assert seems to always be true but not willing to commit to it until
                        // we understand what Nikolay meant when writing the above comment
                        // debug_assert!(flush_was_ready);

                        if !flush_was_ready || !drain {
                            break;
                        }
                    }

                    // client is gone
                    if inner.flags.contains(Flags::WRITE_DISCONNECT) {
                        trace!("client is gone; disconnecting");
                        return Poll::Ready(Ok(()));
                    }

                    let inner_p = inner.as_mut().project();
                    let state_is_none = inner_p.state.is_none();

                    // read half is closed; we do not process any responses
                    if inner_p.flags.contains(Flags::READ_DISCONNECT) && state_is_none {
                        trace!("read half closed; start shutdown");
                        inner_p.flags.insert(Flags::SHUTDOWN);
                    }

                    // keep-alive and stream errors
                    if state_is_none && inner_p.write_buf.is_empty() {
                        if let Some(err) = inner_p.error.take() {
                            error!("stream error: {}", &err);
                            return Poll::Ready(Err(err));
                        }

                        // disconnect if keep-alive is not enabled
                        if inner_p.flags.contains(Flags::FINISHED)
                            && !inner_p.flags.contains(Flags::KEEP_ALIVE)
                        {
                            inner_p.flags.remove(Flags::FINISHED);
                            inner_p.flags.insert(Flags::SHUTDOWN);
                            return self.poll(cx);
                        }

                        // disconnect if shutdown
                        if inner_p.flags.contains(Flags::SHUTDOWN) {
                            return self.poll(cx);
                        }
                    }

                    trace_timer_states(
                        "end",
                        inner_p.head_timer,
                        inner_p.ka_timer,
                        inner_p.shutdown_timer,
                    );

                    Poll::Pending
                };

                trace!("end flags: {:?}", &inner.flags);

                poll
            }
        }
    }
}

#[allow(dead_code)]
fn trace_timer_states(
    label: &str,
    head_timer: &TimerState,
    ka_timer: &TimerState,
    shutdown_timer: &TimerState,
) {
    trace!("{} timers:", label);

    if head_timer.is_enabled() {
        trace!("  head {}", &head_timer);
    }

    if ka_timer.is_enabled() {
        trace!("  keep-alive {}", &ka_timer);
    }

    if shutdown_timer.is_enabled() {
        trace!("  shutdown {}", &shutdown_timer);
    }
}