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
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
//! Client implementation of the HTTP/2.0 protocol.
//!
//! # Getting started
//!
//! Running an HTTP/2.0 client requires the caller to establish the underlying
//! connection as well as get the connection to a state that is ready to begin
//! the HTTP/2.0 handshake. See [here](../index.html#handshake) for more
//! details.
//!
//! This could be as basic as using Tokio's [`TcpStream`] to connect to a remote
//! host, but usually it means using either ALPN or HTTP/1.1 protocol upgrades.
//!
//! Once a connection is obtained, it is passed to [`handshake`], which will
//! begin the [HTTP/2.0 handshake]. This returns a future that completes once
//! the handshake process is performed and HTTP/2.0 streams may be initialized.
//!
//! [`handshake`] uses default configuration values. There are a number of
//! settings that can be changed by using [`Builder`] instead.
//!
//! Once the handshake future completes, the caller is provided with a
//! [`Connection`] instance and a [`SendRequest`] instance. The [`Connection`]
//! instance is used to drive the connection (see [Managing the connection]).
//! The [`SendRequest`] instance is used to initialize new streams (see [Making
//! requests]).
//!
//! # Making requests
//!
//! Requests are made using the [`SendRequest`] handle provided by the handshake
//! future. Once a request is submitted, an HTTP/2.0 stream is initialized and
//! the request is sent to the server.
//!
//! A request body and request trailers are sent using [`SendRequest`] and the
//! server's response is returned once the [`ResponseFuture`] future completes.
//! Both the [`SendStream`] and [`ResponseFuture`] instances are returned by
//! [`SendRequest::send_request`] and are tied to the HTTP/2.0 stream
//! initialized by the sent request.
//!
//! The [`SendRequest::poll_ready`] function returns `Ready` when a new HTTP/2.0
//! stream can be created, i.e. as long as the current number of active streams
//! is below [`MAX_CONCURRENT_STREAMS`]. If a new stream cannot be created, the
//! caller will be notified once an existing stream closes, freeing capacity for
//! the caller.  The caller should use [`SendRequest::poll_ready`] to check for
//! capacity before sending a request to the server.
//!
//! [`SendRequest`] enforces the [`MAX_CONCURRENT_STREAMS`] setting. The user
//! must not send a request if `poll_ready` does not return `Ready`. Attempting
//! to do so will result in an [`Error`] being returned.
//!
//! # Managing the connection
//!
//! The [`Connection`] instance is used to manage connection state. The caller
//! is required to call [`Connection::poll`] in order to advance state.
//! [`SendRequest::send_request`] and other functions have no effect unless
//! [`Connection::poll`] is called.
//!
//! The [`Connection`] instance should only be dropped once [`Connection::poll`]
//! returns `Ready`. At this point, the underlying socket has been closed and no
//! further work needs to be done.
//!
//! The easiest way to ensure that the [`Connection`] instance gets polled is to
//! submit the [`Connection`] instance to an [executor]. The executor will then
//! manage polling the connection until the connection is complete.
//! Alternatively, the caller can call `poll` manually.
//!
//! # Example
//!
//! ```rust, no_run
//!
//! use h2::client;
//!
//! use http::{Request, Method};
//! use std::error::Error;
//! use tokio::net::TcpStream;
//!
//! #[tokio::main]
//! pub async fn main() -> Result<(), Box<dyn Error>> {
//!     // Establish TCP connection to the server.
//!     let tcp = TcpStream::connect("127.0.0.1:5928").await?;
//!     let (h2, connection) = client::handshake(tcp).await?;
//!     tokio::spawn(async move {
//!         connection.await.unwrap();
//!     });
//!
//!     let mut h2 = h2.ready().await?;
//!     // Prepare the HTTP request to send to the server.
//!     let request = Request::builder()
//!                     .method(Method::GET)
//!                     .uri("https://www.example.com/")
//!                     .body(())
//!                     .unwrap();
//!
//!     // Send the request. The second tuple item allows the caller
//!     // to stream a request body.
//!     let (response, _) = h2.send_request(request, true).unwrap();
//!
//!     let (head, mut body) = response.await?.into_parts();
//!
//!     println!("Received response: {:?}", head);
//!
//!     // The `flow_control` handle allows the caller to manage
//!     // flow control.
//!     //
//!     // Whenever data is received, the caller is responsible for
//!     // releasing capacity back to the server once it has freed
//!     // the data from memory.
//!     let mut flow_control = body.flow_control().clone();
//!
//!     while let Some(chunk) = body.data().await {
//!         let chunk = chunk?;
//!         println!("RX: {:?}", chunk);
//!
//!         // Let the server send more data.
//!         let _ = flow_control.release_capacity(chunk.len());
//!     }
//!
//!     Ok(())
//! }
//! ```
//!
//! [`TcpStream`]: https://docs.rs/tokio-core/0.1/tokio_core/net/struct.TcpStream.html
//! [`handshake`]: fn.handshake.html
//! [executor]: https://docs.rs/futures/0.1/futures/future/trait.Executor.html
//! [`SendRequest`]: struct.SendRequest.html
//! [`SendStream`]: ../struct.SendStream.html
//! [Making requests]: #making-requests
//! [Managing the connection]: #managing-the-connection
//! [`Connection`]: struct.Connection.html
//! [`Connection::poll`]: struct.Connection.html#method.poll
//! [`SendRequest::send_request`]: struct.SendRequest.html#method.send_request
//! [`MAX_CONCURRENT_STREAMS`]: http://httpwg.org/specs/rfc7540.html#SettingValues
//! [`SendRequest`]: struct.SendRequest.html
//! [`ResponseFuture`]: struct.ResponseFuture.html
//! [`SendRequest::poll_ready`]: struct.SendRequest.html#method.poll_ready
//! [HTTP/2.0 handshake]: http://httpwg.org/specs/rfc7540.html#ConnectionHeader
//! [`Builder`]: struct.Builder.html
//! [`Error`]: ../struct.Error.html

use crate::codec::{Codec, SendError, UserError};
use crate::frame::{Headers, Pseudo, Reason, Settings, StreamId};
use crate::proto::{self, Error};
use crate::{FlowControl, PingPong, RecvStream, SendStream};

use bytes::{Buf, Bytes};
use http::{uri, HeaderMap, Method, Request, Response, Version};
use std::fmt;
use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};
use std::time::Duration;
use std::usize;
use tokio::io::{AsyncRead, AsyncWrite, AsyncWriteExt};
use tracing::Instrument;

/// Initializes new HTTP/2.0 streams on a connection by sending a request.
///
/// This type does no work itself. Instead, it is a handle to the inner
/// connection state held by [`Connection`]. If the associated connection
/// instance is dropped, all `SendRequest` functions will return [`Error`].
///
/// [`SendRequest`] instances are able to move to and operate on separate tasks
/// / threads than their associated [`Connection`] instance. Internally, there
/// is a buffer used to stage requests before they get written to the
/// connection. There is no guarantee that requests get written to the
/// connection in FIFO order as HTTP/2.0 prioritization logic can play a role.
///
/// [`SendRequest`] implements [`Clone`], enabling the creation of many
/// instances that are backed by a single connection.
///
/// See [module] level documentation for more details.
///
/// [module]: index.html
/// [`Connection`]: struct.Connection.html
/// [`Clone`]: https://doc.rust-lang.org/std/clone/trait.Clone.html
/// [`Error`]: ../struct.Error.html
pub struct SendRequest<B: Buf> {
    inner: proto::Streams<B, Peer>,
    pending: Option<proto::OpaqueStreamRef>,
}

/// Returns a `SendRequest` instance once it is ready to send at least one
/// request.
#[derive(Debug)]
pub struct ReadySendRequest<B: Buf> {
    inner: Option<SendRequest<B>>,
}

/// Manages all state associated with an HTTP/2.0 client connection.
///
/// A `Connection` is backed by an I/O resource (usually a TCP socket) and
/// implements the HTTP/2.0 client logic for that connection. It is responsible
/// for driving the internal state forward, performing the work requested of the
/// associated handles ([`SendRequest`], [`ResponseFuture`], [`SendStream`],
/// [`RecvStream`]).
///
/// `Connection` values are created by calling [`handshake`]. Once a
/// `Connection` value is obtained, the caller must repeatedly call [`poll`]
/// until `Ready` is returned. The easiest way to do this is to submit the
/// `Connection` instance to an [executor].
///
/// [module]: index.html
/// [`handshake`]: fn.handshake.html
/// [`SendRequest`]: struct.SendRequest.html
/// [`ResponseFuture`]: struct.ResponseFuture.html
/// [`SendStream`]: ../struct.SendStream.html
/// [`RecvStream`]: ../struct.RecvStream.html
/// [`poll`]: #method.poll
/// [executor]: https://docs.rs/futures/0.1/futures/future/trait.Executor.html
///
/// # Examples
///
/// ```
/// # use tokio::io::{AsyncRead, AsyncWrite};
/// # use h2::client;
/// # use h2::client::*;
/// #
/// # async fn doc<T>(my_io: T) -> Result<(), h2::Error>
/// # where T: AsyncRead + AsyncWrite + Send + Unpin + 'static,
/// # {
///     let (send_request, connection) = client::handshake(my_io).await?;
///     // Submit the connection handle to an executor.
///     tokio::spawn(async { connection.await.expect("connection failed"); });
///
///     // Now, use `send_request` to initialize HTTP/2.0 streams.
///     // ...
/// # Ok(())
/// # }
/// #
/// # pub fn main() {}
/// ```
#[must_use = "futures do nothing unless polled"]
pub struct Connection<T, B: Buf = Bytes> {
    inner: proto::Connection<T, Peer, B>,
}

/// A future of an HTTP response.
#[derive(Debug)]
#[must_use = "futures do nothing unless polled"]
pub struct ResponseFuture {
    inner: proto::OpaqueStreamRef,
    push_promise_consumed: bool,
}

/// A future of a pushed HTTP response.
///
/// We have to differentiate between pushed and non pushed because of the spec
/// <https://httpwg.org/specs/rfc7540.html#PUSH_PROMISE>
/// > PUSH_PROMISE frames MUST only be sent on a peer-initiated stream
/// > that is in either the "open" or "half-closed (remote)" state.
#[derive(Debug)]
#[must_use = "futures do nothing unless polled"]
pub struct PushedResponseFuture {
    inner: ResponseFuture,
}

/// A pushed response and corresponding request headers
#[derive(Debug)]
pub struct PushPromise {
    /// The request headers
    request: Request<()>,

    /// The pushed response
    response: PushedResponseFuture,
}

/// A stream of pushed responses and corresponding promised requests
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct PushPromises {
    inner: proto::OpaqueStreamRef,
}

/// Builds client connections with custom configuration values.
///
/// Methods can be chained in order to set the configuration values.
///
/// The client is constructed by calling [`handshake`] and passing the I/O
/// handle that will back the HTTP/2.0 server.
///
/// New instances of `Builder` are obtained via [`Builder::new`].
///
/// See function level documentation for details on the various client
/// configuration settings.
///
/// [`Builder::new`]: struct.Builder.html#method.new
/// [`handshake`]: struct.Builder.html#method.handshake
///
/// # Examples
///
/// ```
/// # use tokio::io::{AsyncRead, AsyncWrite};
/// # use h2::client::*;
/// # use bytes::Bytes;
/// #
/// # async fn doc<T: AsyncRead + AsyncWrite + Unpin>(my_io: T)
///     -> Result<((SendRequest<Bytes>, Connection<T, Bytes>)), h2::Error>
/// # {
/// // `client_fut` is a future representing the completion of the HTTP/2.0
/// // handshake.
/// let client_fut = Builder::new()
///     .initial_window_size(1_000_000)
///     .max_concurrent_streams(1000)
///     .handshake(my_io);
/// # client_fut.await
/// # }
/// #
/// # pub fn main() {}
/// ```
#[derive(Clone, Debug)]
pub struct Builder {
    /// Time to keep locally reset streams around before reaping.
    reset_stream_duration: Duration,

    /// Initial maximum number of locally initiated (send) streams.
    /// After receiving a Settings frame from the remote peer,
    /// the connection will overwrite this value with the
    /// MAX_CONCURRENT_STREAMS specified in the frame.
    initial_max_send_streams: usize,

    /// Initial target window size for new connections.
    initial_target_connection_window_size: Option<u32>,

    /// Maximum number of locally reset streams to keep at a time.
    reset_stream_max: usize,

    /// Initial `Settings` frame to send as part of the handshake.
    settings: Settings,

    /// The stream ID of the first (lowest) stream. Subsequent streams will use
    /// monotonically increasing stream IDs.
    stream_id: StreamId,
}

#[derive(Debug)]
pub(crate) struct Peer;

// ===== impl SendRequest =====

impl<B> SendRequest<B>
where
    B: Buf + 'static,
{
    /// Returns `Ready` when the connection can initialize a new HTTP/2.0
    /// stream.
    ///
    /// This function must return `Ready` before `send_request` is called. When
    /// `Poll::Pending` is returned, the task will be notified once the readiness
    /// state changes.
    ///
    /// See [module] level docs for more details.
    ///
    /// [module]: index.html
    pub fn poll_ready(&mut self, cx: &mut Context) -> Poll<Result<(), crate::Error>> {
        ready!(self.inner.poll_pending_open(cx, self.pending.as_ref()))?;
        self.pending = None;
        Poll::Ready(Ok(()))
    }

    /// Consumes `self`, returning a future that returns `self` back once it is
    /// ready to send a request.
    ///
    /// This function should be called before calling `send_request`.
    ///
    /// This is a functional combinator for [`poll_ready`]. The returned future
    /// will call `SendStream::poll_ready` until `Ready`, then returns `self` to
    /// the caller.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use h2::client::*;
    /// # use http::*;
    /// # async fn doc(send_request: SendRequest<&'static [u8]>)
    /// # {
    /// // First, wait until the `send_request` handle is ready to send a new
    /// // request
    /// let mut send_request = send_request.ready().await.unwrap();
    /// // Use `send_request` here.
    /// # }
    /// # pub fn main() {}
    /// ```
    ///
    /// See [module] level docs for more details.
    ///
    /// [`poll_ready`]: #method.poll_ready
    /// [module]: index.html
    pub fn ready(self) -> ReadySendRequest<B> {
        ReadySendRequest { inner: Some(self) }
    }

    /// Sends a HTTP/2.0 request to the server.
    ///
    /// `send_request` initializes a new HTTP/2.0 stream on the associated
    /// connection, then sends the given request using this new stream. Only the
    /// request head is sent.
    ///
    /// On success, a [`ResponseFuture`] instance and [`SendStream`] instance
    /// are returned. The [`ResponseFuture`] instance is used to get the
    /// server's response and the [`SendStream`] instance is used to send a
    /// request body or trailers to the server over the same HTTP/2.0 stream.
    ///
    /// To send a request body or trailers, set `end_of_stream` to `false`.
    /// Then, use the returned [`SendStream`] instance to stream request body
    /// chunks or send trailers. If `end_of_stream` is **not** set to `false`
    /// then attempting to call [`SendStream::send_data`] or
    /// [`SendStream::send_trailers`] will result in an error.
    ///
    /// If no request body or trailers are to be sent, set `end_of_stream` to
    /// `true` and drop the returned [`SendStream`] instance.
    ///
    /// # A note on HTTP versions
    ///
    /// The provided `Request` will be encoded differently depending on the
    /// value of its version field. If the version is set to 2.0, then the
    /// request is encoded as per the specification recommends.
    ///
    /// If the version is set to a lower value, then the request is encoded to
    /// preserve the characteristics of HTTP 1.1 and lower. Specifically, host
    /// headers are permitted and the `:authority` pseudo header is not
    /// included.
    ///
    /// The caller should always set the request's version field to 2.0 unless
    /// specifically transmitting an HTTP 1.1 request over 2.0.
    ///
    /// # Examples
    ///
    /// Sending a request with no body
    ///
    /// ```rust
    /// # use h2::client::*;
    /// # use http::*;
    /// # async fn doc(send_request: SendRequest<&'static [u8]>)
    /// # {
    /// // First, wait until the `send_request` handle is ready to send a new
    /// // request
    /// let mut send_request = send_request.ready().await.unwrap();
    /// // Prepare the HTTP request to send to the server.
    /// let request = Request::get("https://www.example.com/")
    ///     .body(())
    ///     .unwrap();
    ///
    /// // Send the request to the server. Since we are not sending a
    /// // body or trailers, we can drop the `SendStream` instance.
    /// let (response, _) = send_request.send_request(request, true).unwrap();
    /// let response = response.await.unwrap();
    /// // Process the response
    /// # }
    /// # pub fn main() {}
    /// ```
    ///
    /// Sending a request with a body and trailers
    ///
    /// ```rust
    /// # use h2::client::*;
    /// # use http::*;
    /// # async fn doc(send_request: SendRequest<&'static [u8]>)
    /// # {
    /// // First, wait until the `send_request` handle is ready to send a new
    /// // request
    /// let mut send_request = send_request.ready().await.unwrap();
    ///
    /// // Prepare the HTTP request to send to the server.
    /// let request = Request::get("https://www.example.com/")
    ///     .body(())
    ///     .unwrap();
    ///
    /// // Send the request to the server. If we are not sending a
    /// // body or trailers, we can drop the `SendStream` instance.
    /// let (response, mut send_stream) = send_request
    ///     .send_request(request, false).unwrap();
    ///
    /// // At this point, one option would be to wait for send capacity.
    /// // Doing so would allow us to not hold data in memory that
    /// // cannot be sent. However, this is not a requirement, so this
    /// // example will skip that step. See `SendStream` documentation
    /// // for more details.
    /// send_stream.send_data(b"hello", false).unwrap();
    /// send_stream.send_data(b"world", false).unwrap();
    ///
    /// // Send the trailers.
    /// let mut trailers = HeaderMap::new();
    /// trailers.insert(
    ///     header::HeaderName::from_bytes(b"my-trailer").unwrap(),
    ///     header::HeaderValue::from_bytes(b"hello").unwrap());
    ///
    /// send_stream.send_trailers(trailers).unwrap();
    ///
    /// let response = response.await.unwrap();
    /// // Process the response
    /// # }
    /// # pub fn main() {}
    /// ```
    ///
    /// [`ResponseFuture`]: struct.ResponseFuture.html
    /// [`SendStream`]: ../struct.SendStream.html
    /// [`SendStream::send_data`]: ../struct.SendStream.html#method.send_data
    /// [`SendStream::send_trailers`]: ../struct.SendStream.html#method.send_trailers
    pub fn send_request(
        &mut self,
        request: Request<()>,
        end_of_stream: bool,
    ) -> Result<(ResponseFuture, SendStream<B>), crate::Error> {
        self.inner
            .send_request(request, end_of_stream, self.pending.as_ref())
            .map_err(Into::into)
            .map(|stream| {
                if stream.is_pending_open() {
                    self.pending = Some(stream.clone_to_opaque());
                }

                let response = ResponseFuture {
                    inner: stream.clone_to_opaque(),
                    push_promise_consumed: false,
                };

                let stream = SendStream::new(stream);

                (response, stream)
            })
    }
}

impl<B> fmt::Debug for SendRequest<B>
where
    B: Buf,
{
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt.debug_struct("SendRequest").finish()
    }
}

impl<B> Clone for SendRequest<B>
where
    B: Buf,
{
    fn clone(&self) -> Self {
        SendRequest {
            inner: self.inner.clone(),
            pending: None,
        }
    }
}

#[cfg(feature = "unstable")]
impl<B> SendRequest<B>
where
    B: Buf,
{
    /// Returns the number of active streams.
    ///
    /// An active stream is a stream that has not yet transitioned to a closed
    /// state.
    pub fn num_active_streams(&self) -> usize {
        self.inner.num_active_streams()
    }

    /// Returns the number of streams that are held in memory.
    ///
    /// A wired stream is a stream that is either active or is closed but must
    /// stay in memory for some reason. For example, there are still outstanding
    /// userspace handles pointing to the slot.
    pub fn num_wired_streams(&self) -> usize {
        self.inner.num_wired_streams()
    }
}

// ===== impl ReadySendRequest =====

impl<B> Future for ReadySendRequest<B>
where
    B: Buf + 'static,
{
    type Output = Result<SendRequest<B>, crate::Error>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        match &mut self.inner {
            Some(send_request) => {
                ready!(send_request.poll_ready(cx))?;
            }
            None => panic!("called `poll` after future completed"),
        }

        Poll::Ready(Ok(self.inner.take().unwrap()))
    }
}

// ===== impl Builder =====

impl Builder {
    /// Returns a new client builder instance initialized with default
    /// configuration values.
    ///
    /// Configuration methods can be chained on the return value.
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio::io::{AsyncRead, AsyncWrite};
    /// # use h2::client::*;
    /// # use bytes::Bytes;
    /// #
    /// # async fn doc<T: AsyncRead + AsyncWrite + Unpin>(my_io: T)
    /// # -> Result<((SendRequest<Bytes>, Connection<T, Bytes>)), h2::Error>
    /// # {
    /// // `client_fut` is a future representing the completion of the HTTP/2.0
    /// // handshake.
    /// let client_fut = Builder::new()
    ///     .initial_window_size(1_000_000)
    ///     .max_concurrent_streams(1000)
    ///     .handshake(my_io);
    /// # client_fut.await
    /// # }
    /// #
    /// # pub fn main() {}
    /// ```
    pub fn new() -> Builder {
        Builder {
            reset_stream_duration: Duration::from_secs(proto::DEFAULT_RESET_STREAM_SECS),
            reset_stream_max: proto::DEFAULT_RESET_STREAM_MAX,
            initial_target_connection_window_size: None,
            initial_max_send_streams: usize::MAX,
            settings: Default::default(),
            stream_id: 1.into(),
        }
    }

    /// Indicates the initial window size (in octets) for stream-level
    /// flow control for received data.
    ///
    /// The initial window of a stream is used as part of flow control. For more
    /// details, see [`FlowControl`].
    ///
    /// The default value is 65,535.
    ///
    /// [`FlowControl`]: ../struct.FlowControl.html
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio::io::{AsyncRead, AsyncWrite};
    /// # use h2::client::*;
    /// # use bytes::Bytes;
    /// #
    /// # async fn doc<T: AsyncRead + AsyncWrite + Unpin>(my_io: T)
    /// # -> Result<((SendRequest<Bytes>, Connection<T, Bytes>)), h2::Error>
    /// # {
    /// // `client_fut` is a future representing the completion of the HTTP/2.0
    /// // handshake.
    /// let client_fut = Builder::new()
    ///     .initial_window_size(1_000_000)
    ///     .handshake(my_io);
    /// # client_fut.await
    /// # }
    /// #
    /// # pub fn main() {}
    /// ```
    pub fn initial_window_size(&mut self, size: u32) -> &mut Self {
        self.settings.set_initial_window_size(Some(size));
        self
    }

    /// Indicates the initial window size (in octets) for connection-level flow control
    /// for received data.
    ///
    /// The initial window of a connection is used as part of flow control. For more details,
    /// see [`FlowControl`].
    ///
    /// The default value is 65,535.
    ///
    /// [`FlowControl`]: ../struct.FlowControl.html
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio::io::{AsyncRead, AsyncWrite};
    /// # use h2::client::*;
    /// # use bytes::Bytes;
    /// #
    /// # async fn doc<T: AsyncRead + AsyncWrite + Unpin>(my_io: T)
    /// # -> Result<((SendRequest<Bytes>, Connection<T, Bytes>)), h2::Error>
    /// # {
    /// // `client_fut` is a future representing the completion of the HTTP/2.0
    /// // handshake.
    /// let client_fut = Builder::new()
    ///     .initial_connection_window_size(1_000_000)
    ///     .handshake(my_io);
    /// # client_fut.await
    /// # }
    /// #
    /// # pub fn main() {}
    /// ```
    pub fn initial_connection_window_size(&mut self, size: u32) -> &mut Self {
        self.initial_target_connection_window_size = Some(size);
        self
    }

    /// Indicates the size (in octets) of the largest HTTP/2.0 frame payload that the
    /// configured client is able to accept.
    ///
    /// The sender may send data frames that are **smaller** than this value,
    /// but any data larger than `max` will be broken up into multiple `DATA`
    /// frames.
    ///
    /// The value **must** be between 16,384 and 16,777,215. The default value is 16,384.
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio::io::{AsyncRead, AsyncWrite};
    /// # use h2::client::*;
    /// # use bytes::Bytes;
    /// #
    /// # async fn doc<T: AsyncRead + AsyncWrite + Unpin>(my_io: T)
    /// # -> Result<((SendRequest<Bytes>, Connection<T, Bytes>)), h2::Error>
    /// # {
    /// // `client_fut` is a future representing the completion of the HTTP/2.0
    /// // handshake.
    /// let client_fut = Builder::new()
    ///     .max_frame_size(1_000_000)
    ///     .handshake(my_io);
    /// # client_fut.await
    /// # }
    /// #
    /// # pub fn main() {}
    /// ```
    ///
    /// # Panics
    ///
    /// This function panics if `max` is not within the legal range specified
    /// above.
    pub fn max_frame_size(&mut self, max: u32) -> &mut Self {
        self.settings.set_max_frame_size(Some(max));
        self
    }

    /// Sets the max size of received header frames.
    ///
    /// This advisory setting informs a peer of the maximum size of header list
    /// that the sender is prepared to accept, in octets. The value is based on
    /// the uncompressed size of header fields, including the length of the name
    /// and value in octets plus an overhead of 32 octets for each header field.
    ///
    /// This setting is also used to limit the maximum amount of data that is
    /// buffered to decode HEADERS frames.
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio::io::{AsyncRead, AsyncWrite};
    /// # use h2::client::*;
    /// # use bytes::Bytes;
    /// #
    /// # async fn doc<T: AsyncRead + AsyncWrite + Unpin>(my_io: T)
    /// # -> Result<((SendRequest<Bytes>, Connection<T, Bytes>)), h2::Error>
    /// # {
    /// // `client_fut` is a future representing the completion of the HTTP/2.0
    /// // handshake.
    /// let client_fut = Builder::new()
    ///     .max_header_list_size(16 * 1024)
    ///     .handshake(my_io);
    /// # client_fut.await
    /// # }
    /// #
    /// # pub fn main() {}
    /// ```
    pub fn max_header_list_size(&mut self, max: u32) -> &mut Self {
        self.settings.set_max_header_list_size(Some(max));
        self
    }

    /// Sets the maximum number of concurrent streams.
    ///
    /// The maximum concurrent streams setting only controls the maximum number
    /// of streams that can be initiated by the remote peer. In other words,
    /// when this setting is set to 100, this does not limit the number of
    /// concurrent streams that can be created by the caller.
    ///
    /// It is recommended that this value be no smaller than 100, so as to not
    /// unnecessarily limit parallelism. However, any value is legal, including
    /// 0. If `max` is set to 0, then the remote will not be permitted to
    /// initiate streams.
    ///
    /// Note that streams in the reserved state, i.e., push promises that have
    /// been reserved but the stream has not started, do not count against this
    /// setting.
    ///
    /// Also note that if the remote *does* exceed the value set here, it is not
    /// a protocol level error. Instead, the `h2` library will immediately reset
    /// the stream.
    ///
    /// See [Section 5.1.2] in the HTTP/2.0 spec for more details.
    ///
    /// [Section 5.1.2]: https://http2.github.io/http2-spec/#rfc.section.5.1.2
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio::io::{AsyncRead, AsyncWrite};
    /// # use h2::client::*;
    /// # use bytes::Bytes;
    /// #
    /// # async fn doc<T: AsyncRead + AsyncWrite + Unpin>(my_io: T)
    /// # -> Result<((SendRequest<Bytes>, Connection<T, Bytes>)), h2::Error>
    /// # {
    /// // `client_fut` is a future representing the completion of the HTTP/2.0
    /// // handshake.
    /// let client_fut = Builder::new()
    ///     .max_concurrent_streams(1000)
    ///     .handshake(my_io);
    /// # client_fut.await
    /// # }
    /// #
    /// # pub fn main() {}
    /// ```
    pub fn max_concurrent_streams(&mut self, max: u32) -> &mut Self {
        self.settings.set_max_concurrent_streams(Some(max));
        self
    }

    /// Sets the initial maximum of locally initiated (send) streams.
    ///
    /// The initial settings will be overwritten by the remote peer when
    /// the Settings frame is received. The new value will be set to the
    /// `max_concurrent_streams()` from the frame.
    ///
    /// This setting prevents the caller from exceeding this number of
    /// streams that are counted towards the concurrency limit.
    ///
    /// Sending streams past the limit returned by the peer will be treated
    /// as a stream error of type PROTOCOL_ERROR or REFUSED_STREAM.
    ///
    /// See [Section 5.1.2] in the HTTP/2.0 spec for more details.
    ///
    /// [Section 5.1.2]: https://http2.github.io/http2-spec/#rfc.section.5.1.2
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio::io::{AsyncRead, AsyncWrite};
    /// # use h2::client::*;
    /// # use bytes::Bytes;
    /// #
    /// # async fn doc<T: AsyncRead + AsyncWrite + Unpin>(my_io: T)
    /// # -> Result<((SendRequest<Bytes>, Connection<T, Bytes>)), h2::Error>
    /// # {
    /// // `client_fut` is a future representing the completion of the HTTP/2.0
    /// // handshake.
    /// let client_fut = Builder::new()
    ///     .initial_max_send_streams(1000)
    ///     .handshake(my_io);
    /// # client_fut.await
    /// # }
    /// #
    /// # pub fn main() {}
    /// ```
    pub fn initial_max_send_streams(&mut self, initial: usize) -> &mut Self {
        self.initial_max_send_streams = initial;
        self
    }

    /// Sets the maximum number of concurrent locally reset streams.
    ///
    /// When a stream is explicitly reset, the HTTP/2.0 specification requires
    /// that any further frames received for that stream must be ignored for
    /// "some time".
    ///
    /// In order to satisfy the specification, internal state must be maintained
    /// to implement the behavior. This state grows linearly with the number of
    /// streams that are locally reset.
    ///
    /// The `max_concurrent_reset_streams` setting configures sets an upper
    /// bound on the amount of state that is maintained. When this max value is
    /// reached, the oldest reset stream is purged from memory.
    ///
    /// Once the stream has been fully purged from memory, any additional frames
    /// received for that stream will result in a connection level protocol
    /// error, forcing the connection to terminate.
    ///
    /// The default value is 10.
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio::io::{AsyncRead, AsyncWrite};
    /// # use h2::client::*;
    /// # use bytes::Bytes;
    /// #
    /// # async fn doc<T: AsyncRead + AsyncWrite + Unpin>(my_io: T)
    /// # -> Result<((SendRequest<Bytes>, Connection<T, Bytes>)), h2::Error>
    /// # {
    /// // `client_fut` is a future representing the completion of the HTTP/2.0
    /// // handshake.
    /// let client_fut = Builder::new()
    ///     .max_concurrent_reset_streams(1000)
    ///     .handshake(my_io);
    /// # client_fut.await
    /// # }
    /// #
    /// # pub fn main() {}
    /// ```
    pub fn max_concurrent_reset_streams(&mut self, max: usize) -> &mut Self {
        self.reset_stream_max = max;
        self
    }

    /// Sets the duration to remember locally reset streams.
    ///
    /// When a stream is explicitly reset, the HTTP/2.0 specification requires
    /// that any further frames received for that stream must be ignored for
    /// "some time".
    ///
    /// In order to satisfy the specification, internal state must be maintained
    /// to implement the behavior. This state grows linearly with the number of
    /// streams that are locally reset.
    ///
    /// The `reset_stream_duration` setting configures the max amount of time
    /// this state will be maintained in memory. Once the duration elapses, the
    /// stream state is purged from memory.
    ///
    /// Once the stream has been fully purged from memory, any additional frames
    /// received for that stream will result in a connection level protocol
    /// error, forcing the connection to terminate.
    ///
    /// The default value is 30 seconds.
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio::io::{AsyncRead, AsyncWrite};
    /// # use h2::client::*;
    /// # use std::time::Duration;
    /// # use bytes::Bytes;
    /// #
    /// # async fn doc<T: AsyncRead + AsyncWrite + Unpin>(my_io: T)
    /// # -> Result<((SendRequest<Bytes>, Connection<T, Bytes>)), h2::Error>
    /// # {
    /// // `client_fut` is a future representing the completion of the HTTP/2.0
    /// // handshake.
    /// let client_fut = Builder::new()
    ///     .reset_stream_duration(Duration::from_secs(10))
    ///     .handshake(my_io);
    /// # client_fut.await
    /// # }
    /// #
    /// # pub fn main() {}
    /// ```
    pub fn reset_stream_duration(&mut self, dur: Duration) -> &mut Self {
        self.reset_stream_duration = dur;
        self
    }

    /// Enables or disables server push promises.
    ///
    /// This value is included in the initial SETTINGS handshake. When set, the
    /// server MUST NOT send a push promise. Setting this value to value to
    /// false in the initial SETTINGS handshake guarantees that the remote server
    /// will never send a push promise.
    ///
    /// This setting can be changed during the life of a single HTTP/2.0
    /// connection by sending another settings frame updating the value.
    ///
    /// Default value: `true`.
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio::io::{AsyncRead, AsyncWrite};
    /// # use h2::client::*;
    /// # use std::time::Duration;
    /// # use bytes::Bytes;
    /// #
    /// # async fn doc<T: AsyncRead + AsyncWrite + Unpin>(my_io: T)
    /// # -> Result<((SendRequest<Bytes>, Connection<T, Bytes>)), h2::Error>
    /// # {
    /// // `client_fut` is a future representing the completion of the HTTP/2.0
    /// // handshake.
    /// let client_fut = Builder::new()
    ///     .enable_push(false)
    ///     .handshake(my_io);
    /// # client_fut.await
    /// # }
    /// #
    /// # pub fn main() {}
    /// ```
    pub fn enable_push(&mut self, enabled: bool) -> &mut Self {
        self.settings.set_enable_push(enabled);
        self
    }

    /// Sets the first stream ID to something other than 1.
    #[cfg(feature = "unstable")]
    pub fn initial_stream_id(&mut self, stream_id: u32) -> &mut Self {
        self.stream_id = stream_id.into();
        assert!(
            self.stream_id.is_client_initiated(),
            "stream id must be odd"
        );
        self
    }

    /// Creates a new configured HTTP/2.0 client backed by `io`.
    ///
    /// It is expected that `io` already be in an appropriate state to commence
    /// the [HTTP/2.0 handshake]. The handshake is completed once both the connection
    /// preface and the initial settings frame is sent by the client.
    ///
    /// The handshake future does not wait for the initial settings frame from the
    /// server.
    ///
    /// Returns a future which resolves to the [`Connection`] / [`SendRequest`]
    /// tuple once the HTTP/2.0 handshake has been completed.
    ///
    /// This function also allows the caller to configure the send payload data
    /// type. See [Outbound data type] for more details.
    ///
    /// [HTTP/2.0 handshake]: http://httpwg.org/specs/rfc7540.html#ConnectionHeader
    /// [`Connection`]: struct.Connection.html
    /// [`SendRequest`]: struct.SendRequest.html
    /// [Outbound data type]: ../index.html#outbound-data-type.
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// # use tokio::io::{AsyncRead, AsyncWrite};
    /// # use h2::client::*;
    /// # use bytes::Bytes;
    /// #
    /// # async fn doc<T: AsyncRead + AsyncWrite + Unpin>(my_io: T)
    ///     -> Result<((SendRequest<Bytes>, Connection<T, Bytes>)), h2::Error>
    /// # {
    /// // `client_fut` is a future representing the completion of the HTTP/2.0
    /// // handshake.
    /// let client_fut = Builder::new()
    ///     .handshake(my_io);
    /// # client_fut.await
    /// # }
    /// #
    /// # pub fn main() {}
    /// ```
    ///
    /// Configures the send-payload data type. In this case, the outbound data
    /// type will be `&'static [u8]`.
    ///
    /// ```
    /// # use tokio::io::{AsyncRead, AsyncWrite};
    /// # use h2::client::*;
    /// #
    /// # async fn doc<T: AsyncRead + AsyncWrite + Unpin>(my_io: T)
    /// # -> Result<((SendRequest<&'static [u8]>, Connection<T, &'static [u8]>)), h2::Error>
    /// # {
    /// // `client_fut` is a future representing the completion of the HTTP/2.0
    /// // handshake.
    /// let client_fut = Builder::new()
    ///     .handshake::<_, &'static [u8]>(my_io);
    /// # client_fut.await
    /// # }
    /// #
    /// # pub fn main() {}
    /// ```
    pub fn handshake<T, B>(
        &self,
        io: T,
    ) -> impl Future<Output = Result<(SendRequest<B>, Connection<T, B>), crate::Error>>
    where
        T: AsyncRead + AsyncWrite + Unpin,
        B: Buf + 'static,
    {
        Connection::handshake2(io, self.clone())
    }
}

impl Default for Builder {
    fn default() -> Builder {
        Builder::new()
    }
}

/// Creates a new configured HTTP/2.0 client with default configuration
/// values backed by `io`.
///
/// It is expected that `io` already be in an appropriate state to commence
/// the [HTTP/2.0 handshake]. See [Handshake] for more details.
///
/// Returns a future which resolves to the [`Connection`] / [`SendRequest`]
/// tuple once the HTTP/2.0 handshake has been completed. The returned
/// [`Connection`] instance will be using default configuration values. Use
/// [`Builder`] to customize the configuration values used by a [`Connection`]
/// instance.
///
/// [HTTP/2.0 handshake]: http://httpwg.org/specs/rfc7540.html#ConnectionHeader
/// [Handshake]: ../index.html#handshake
/// [`Connection`]: struct.Connection.html
/// [`SendRequest`]: struct.SendRequest.html
///
/// # Examples
///
/// ```
/// # use tokio::io::{AsyncRead, AsyncWrite};
/// # use h2::client;
/// # use h2::client::*;
/// #
/// # async fn doc<T: AsyncRead + AsyncWrite + Unpin>(my_io: T) -> Result<(), h2::Error>
/// # {
/// let (send_request, connection) = client::handshake(my_io).await?;
/// // The HTTP/2.0 handshake has completed, now start polling
/// // `connection` and use `send_request` to send requests to the
/// // server.
/// # Ok(())
/// # }
/// #
/// # pub fn main() {}
/// ```
pub async fn handshake<T>(io: T) -> Result<(SendRequest<Bytes>, Connection<T, Bytes>), crate::Error>
where
    T: AsyncRead + AsyncWrite + Unpin,
{
    let builder = Builder::new();
    builder
        .handshake(io)
        .instrument(tracing::trace_span!("client_handshake", io = %std::any::type_name::<T>()))
        .await
}

// ===== impl Connection =====

async fn bind_connection<T>(io: &mut T) -> Result<(), crate::Error>
where
    T: AsyncRead + AsyncWrite + Unpin,
{
    tracing::debug!("binding client connection");

    let msg: &'static [u8] = b"PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n";
    io.write_all(msg).await.map_err(crate::Error::from_io)?;

    tracing::debug!("client connection bound");

    Ok(())
}

impl<T, B> Connection<T, B>
where
    T: AsyncRead + AsyncWrite + Unpin,
    B: Buf + 'static,
{
    async fn handshake2(
        mut io: T,
        builder: Builder,
    ) -> Result<(SendRequest<B>, Connection<T, B>), crate::Error> {
        bind_connection(&mut io).await?;

        // Create the codec
        let mut codec = Codec::new(io);

        if let Some(max) = builder.settings.max_frame_size() {
            codec.set_max_recv_frame_size(max as usize);
        }

        if let Some(max) = builder.settings.max_header_list_size() {
            codec.set_max_recv_header_list_size(max as usize);
        }

        // Send initial settings frame
        codec
            .buffer(builder.settings.clone().into())
            .expect("invalid SETTINGS frame");

        let inner = proto::Connection::new(
            codec,
            proto::Config {
                next_stream_id: builder.stream_id,
                initial_max_send_streams: builder.initial_max_send_streams,
                reset_stream_duration: builder.reset_stream_duration,
                reset_stream_max: builder.reset_stream_max,
                settings: builder.settings.clone(),
            },
        );
        let send_request = SendRequest {
            inner: inner.streams().clone(),
            pending: None,
        };

        let mut connection = Connection { inner };
        if let Some(sz) = builder.initial_target_connection_window_size {
            connection.set_target_window_size(sz);
        }

        Ok((send_request, connection))
    }

    /// Sets the target window size for the whole connection.
    ///
    /// If `size` is greater than the current value, then a `WINDOW_UPDATE`
    /// frame will be immediately sent to the remote, increasing the connection
    /// level window by `size - current_value`.
    ///
    /// If `size` is less than the current value, nothing will happen
    /// immediately. However, as window capacity is released by
    /// [`FlowControl`] instances, no `WINDOW_UPDATE` frames will be sent
    /// out until the number of "in flight" bytes drops below `size`.
    ///
    /// The default value is 65,535.
    ///
    /// See [`FlowControl`] documentation for more details.
    ///
    /// [`FlowControl`]: ../struct.FlowControl.html
    /// [library level]: ../index.html#flow-control
    pub fn set_target_window_size(&mut self, size: u32) {
        assert!(size <= proto::MAX_WINDOW_SIZE);
        self.inner.set_target_window_size(size);
    }

    /// Set a new `INITIAL_WINDOW_SIZE` setting (in octets) for stream-level
    /// flow control for received data.
    ///
    /// The `SETTINGS` will be sent to the remote, and only applied once the
    /// remote acknowledges the change.
    ///
    /// This can be used to increase or decrease the window size for existing
    /// streams.
    ///
    /// # Errors
    ///
    /// Returns an error if a previous call is still pending acknowledgement
    /// from the remote endpoint.
    pub fn set_initial_window_size(&mut self, size: u32) -> Result<(), crate::Error> {
        assert!(size <= proto::MAX_WINDOW_SIZE);
        self.inner.set_initial_window_size(size)?;
        Ok(())
    }

    /// Takes a `PingPong` instance from the connection.
    ///
    /// # Note
    ///
    /// This may only be called once. Calling multiple times will return `None`.
    pub fn ping_pong(&mut self) -> Option<PingPong> {
        self.inner.take_user_pings().map(PingPong::new)
    }

    /// Returns the maximum number of concurrent streams that may be initiated
    /// by this client.
    ///
    /// This limit is configured by the server peer by sending the
    /// [`SETTINGS_MAX_CONCURRENT_STREAMS` parameter][1] in a `SETTINGS` frame.
    /// This method returns the currently acknowledged value recieved from the
    /// remote.
    ///
    /// [settings]: https://tools.ietf.org/html/rfc7540#section-5.1.2
    pub fn max_concurrent_send_streams(&self) -> usize {
        self.inner.max_send_streams()
    }

    /// Returns the maximum number of concurrent streams that may be initiated
    /// by the server on this connection.
    ///
    /// This returns the value of the [`SETTINGS_MAX_CONCURRENT_STREAMS`
    /// parameter][1] sent in a `SETTINGS` frame that has been
    /// acknowledged by the remote peer. The value to be sent is configured by
    /// the [`Builder::max_concurrent_streams`][2] method before handshaking
    /// with the remote peer.
    ///
    /// [1]: https://tools.ietf.org/html/rfc7540#section-5.1.2
    /// [2]: ../struct.Builder.html#method.max_concurrent_streams
    pub fn max_concurrent_recv_streams(&self) -> usize {
        self.inner.max_recv_streams()
    }
}

impl<T, B> Future for Connection<T, B>
where
    T: AsyncRead + AsyncWrite + Unpin,
    B: Buf + 'static,
{
    type Output = Result<(), crate::Error>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        self.inner.maybe_close_connection_if_no_streams();
        self.inner.poll(cx).map_err(Into::into)
    }
}

impl<T, B> fmt::Debug for Connection<T, B>
where
    T: AsyncRead + AsyncWrite,
    T: fmt::Debug,
    B: fmt::Debug + Buf,
{
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt::Debug::fmt(&self.inner, fmt)
    }
}

// ===== impl ResponseFuture =====

impl Future for ResponseFuture {
    type Output = Result<Response<RecvStream>, crate::Error>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        let (parts, _) = ready!(self.inner.poll_response(cx))?.into_parts();
        let body = RecvStream::new(FlowControl::new(self.inner.clone()));

        Poll::Ready(Ok(Response::from_parts(parts, body)))
    }
}

impl ResponseFuture {
    /// Returns the stream ID of the response stream.
    ///
    /// # Panics
    ///
    /// If the lock on the stream store has been poisoned.
    pub fn stream_id(&self) -> crate::StreamId {
        crate::StreamId::from_internal(self.inner.stream_id())
    }
    /// Returns a stream of PushPromises
    ///
    /// # Panics
    ///
    /// If this method has been called before
    /// or the stream was itself was pushed
    pub fn push_promises(&mut self) -> PushPromises {
        if self.push_promise_consumed {
            panic!("Reference to push promises stream taken!");
        }
        self.push_promise_consumed = true;
        PushPromises {
            inner: self.inner.clone(),
        }
    }
}

// ===== impl PushPromises =====

impl PushPromises {
    /// Get the next `PushPromise`.
    pub async fn push_promise(&mut self) -> Option<Result<PushPromise, crate::Error>> {
        futures_util::future::poll_fn(move |cx| self.poll_push_promise(cx)).await
    }

    #[doc(hidden)]
    pub fn poll_push_promise(
        &mut self,
        cx: &mut Context<'_>,
    ) -> Poll<Option<Result<PushPromise, crate::Error>>> {
        match self.inner.poll_pushed(cx) {
            Poll::Ready(Some(Ok((request, response)))) => {
                let response = PushedResponseFuture {
                    inner: ResponseFuture {
                        inner: response,
                        push_promise_consumed: false,
                    },
                };
                Poll::Ready(Some(Ok(PushPromise { request, response })))
            }
            Poll::Ready(Some(Err(e))) => Poll::Ready(Some(Err(e.into()))),
            Poll::Ready(None) => Poll::Ready(None),
            Poll::Pending => Poll::Pending,
        }
    }
}

#[cfg(feature = "stream")]
impl futures_core::Stream for PushPromises {
    type Item = Result<PushPromise, crate::Error>;

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

// ===== impl PushPromise =====

impl PushPromise {
    /// Returns a reference to the push promise's request headers.
    pub fn request(&self) -> &Request<()> {
        &self.request
    }

    /// Returns a mutable reference to the push promise's request headers.
    pub fn request_mut(&mut self) -> &mut Request<()> {
        &mut self.request
    }

    /// Consumes `self`, returning the push promise's request headers and
    /// response future.
    pub fn into_parts(self) -> (Request<()>, PushedResponseFuture) {
        (self.request, self.response)
    }
}

// ===== impl PushedResponseFuture =====

impl Future for PushedResponseFuture {
    type Output = Result<Response<RecvStream>, crate::Error>;

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

impl PushedResponseFuture {
    /// Returns the stream ID of the response stream.
    ///
    /// # Panics
    ///
    /// If the lock on the stream store has been poisoned.
    pub fn stream_id(&self) -> crate::StreamId {
        self.inner.stream_id()
    }
}

// ===== impl Peer =====

impl Peer {
    pub fn convert_send_message(
        id: StreamId,
        request: Request<()>,
        end_of_stream: bool,
    ) -> Result<Headers, SendError> {
        use http::request::Parts;

        let (
            Parts {
                method,
                uri,
                headers,
                version,
                ..
            },
            _,
        ) = request.into_parts();

        let is_connect = method == Method::CONNECT;

        // Build the set pseudo header set. All requests will include `method`
        // and `path`.
        let mut pseudo = Pseudo::request(method, uri);

        if pseudo.scheme.is_none() {
            // If the scheme is not set, then there are a two options.
            //
            // 1) Authority is not set. In this case, a request was issued with
            //    a relative URI. This is permitted **only** when forwarding
            //    HTTP 1.x requests. If the HTTP version is set to 2.0, then
            //    this is an error.
            //
            // 2) Authority is set, then the HTTP method *must* be CONNECT.
            //
            // It is not possible to have a scheme but not an authority set (the
            // `http` crate does not allow it).
            //
            if pseudo.authority.is_none() {
                if version == Version::HTTP_2 {
                    return Err(UserError::MissingUriSchemeAndAuthority.into());
                } else {
                    // This is acceptable as per the above comment. However,
                    // HTTP/2.0 requires that a scheme is set. Since we are
                    // forwarding an HTTP 1.1 request, the scheme is set to
                    // "http".
                    pseudo.set_scheme(uri::Scheme::HTTP);
                }
            } else if !is_connect {
                // TODO: Error
            }
        }

        // Create the HEADERS frame
        let mut frame = Headers::new(id, pseudo, headers);

        if end_of_stream {
            frame.set_end_stream()
        }

        Ok(frame)
    }
}

impl proto::Peer for Peer {
    type Poll = Response<()>;

    const NAME: &'static str = "Client";

    fn r#dyn() -> proto::DynPeer {
        proto::DynPeer::Client
    }

    fn is_server() -> bool {
        false
    }

    fn convert_poll_message(
        pseudo: Pseudo,
        fields: HeaderMap,
        stream_id: StreamId,
    ) -> Result<Self::Poll, Error> {
        let mut b = Response::builder();

        b = b.version(Version::HTTP_2);

        if let Some(status) = pseudo.status {
            b = b.status(status);
        }

        let mut response = match b.body(()) {
            Ok(response) => response,
            Err(_) => {
                // TODO: Should there be more specialized handling for different
                // kinds of errors
                return Err(Error::library_reset(stream_id, Reason::PROTOCOL_ERROR));
            }
        };

        *response.headers_mut() = fields;

        Ok(response)
    }
}