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
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
// This file is part of Substrate.

// Copyright (C) 2017-2021 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.

//! Main entry point of the sc-network crate.
//!
//! There are two main structs in this module: [`NetworkWorker`] and [`NetworkService`].
//! The [`NetworkWorker`] *is* the network and implements the `Future` trait. It must be polled in
//! order for the network to advance.
//! The [`NetworkService`] is merely a shared version of the [`NetworkWorker`]. You can obtain an
//! `Arc<NetworkService>` by calling [`NetworkWorker::service`].
//!
//! The methods of the [`NetworkService`] are implemented by sending a message over a channel,
//! which is then processed by [`NetworkWorker::poll`].

use crate::{
	ExHashT, NetworkStateInfo, NetworkStatus,
	behaviour::{self, Behaviour, BehaviourOut},
	config::{parse_str_addr, Params, Role, TransportConfig},
	DhtEvent,
	discovery::DiscoveryConfig,
	error::Error,
	network_state::{
		NetworkState, NotConnectedPeer as NetworkStateNotConnectedPeer, Peer as NetworkStatePeer,
	},
	on_demand_layer::AlwaysBadChecker,
	light_client_handler,
	protocol::{
		self,
		NotifsHandlerError,
		NotificationsSink,
		PeerInfo,
		Protocol,
		Ready,
		event::Event,
		sync::SyncState,
	},
	transport, ReputationChange,
};
use futures::{channel::oneshot, prelude::*};
use libp2p::{PeerId, multiaddr, Multiaddr};
use libp2p::core::{
	ConnectedPoint,
	Executor,
	connection::{
		ConnectionLimits,
		ConnectionError,
		PendingConnectionError
	},
	either::EitherError,
	upgrade
};
use libp2p::kad::record;
use libp2p::ping::handler::PingFailure;
use libp2p::swarm::{
	AddressScore,
	NetworkBehaviour,
	SwarmBuilder,
	SwarmEvent,
	protocols_handler::NodeHandlerWrapperError
};
use log::{error, info, trace, warn};
use metrics::{Metrics, MetricSources, Histogram, HistogramVec};
use parking_lot::Mutex;
use sc_peerset::PeersetHandle;
use sp_consensus::import_queue::{BlockImportError, BlockImportResult, ImportQueue, Link};
use sp_runtime::traits::{Block as BlockT, NumberFor};
use sp_utils::mpsc::{tracing_unbounded, TracingUnboundedReceiver, TracingUnboundedSender};
use std::{
	borrow::Cow,
	collections::{HashMap, HashSet},
	convert::TryFrom as _,
	fs,
	iter,
	marker::PhantomData,
	num:: NonZeroUsize,
	pin::Pin,
	str,
	sync::{
		atomic::{AtomicBool, AtomicUsize, Ordering},
		Arc,
	},
	task::Poll,
};

pub use behaviour::{ResponseFailure, InboundFailure, RequestFailure, OutboundFailure};

mod metrics;
mod out_events;
#[cfg(test)]
mod tests;

/// Substrate network service. Handles network IO and manages connectivity.
pub struct NetworkService<B: BlockT + 'static, H: ExHashT> {
	/// Number of peers we're connected to.
	num_connected: Arc<AtomicUsize>,
	/// The local external addresses.
	external_addresses: Arc<Mutex<Vec<Multiaddr>>>,
	/// Are we actively catching up with the chain?
	is_major_syncing: Arc<AtomicBool>,
	/// Local copy of the `PeerId` of the local node.
	local_peer_id: PeerId,
	/// Bandwidth logging system. Can be queried to know the average bandwidth consumed.
	bandwidth: Arc<transport::BandwidthSinks>,
	/// Peerset manager (PSM); manages the reputation of nodes and indicates the network which
	/// nodes it should be connected to or not.
	peerset: PeersetHandle,
	/// Channel that sends messages to the actual worker.
	to_worker: TracingUnboundedSender<ServiceToWorkerMsg<B, H>>,
	/// For each peer and protocol combination, an object that allows sending notifications to
	/// that peer. Updated by the [`NetworkWorker`].
	peers_notifications_sinks: Arc<Mutex<HashMap<(PeerId, Cow<'static, str>), NotificationsSink>>>,
	/// Field extracted from the [`Metrics`] struct and necessary to report the
	/// notifications-related metrics.
	notifications_sizes_metric: Option<HistogramVec>,
	/// Marker to pin the `H` generic. Serves no purpose except to not break backwards
	/// compatibility.
	_marker: PhantomData<H>,
}

impl<B: BlockT + 'static, H: ExHashT> NetworkWorker<B, H> {
	/// Creates the network service.
	///
	/// Returns a `NetworkWorker` that implements `Future` and must be regularly polled in order
	/// for the network processing to advance. From it, you can extract a `NetworkService` using
	/// `worker.service()`. The `NetworkService` can be shared through the codebase.
	pub fn new(params: Params<B, H>) -> Result<NetworkWorker<B, H>, Error> {
		// Ensure the listen addresses are consistent with the transport.
		ensure_addresses_consistent_with_transport(
			params.network_config.listen_addresses.iter(),
			&params.network_config.transport,
		)?;
		ensure_addresses_consistent_with_transport(
			params.network_config.boot_nodes.iter().map(|x| &x.multiaddr),
			&params.network_config.transport,
		)?;
		ensure_addresses_consistent_with_transport(
			params.network_config.default_peers_set.reserved_nodes.iter().map(|x| &x.multiaddr),
			&params.network_config.transport,
		)?;
		for extra_set in &params.network_config.extra_sets {
			ensure_addresses_consistent_with_transport(
				extra_set.set_config.reserved_nodes.iter().map(|x| &x.multiaddr),
				&params.network_config.transport,
			)?;
		}
		ensure_addresses_consistent_with_transport(
			params.network_config.public_addresses.iter(),
			&params.network_config.transport,
		)?;

		let (to_worker, from_service) = tracing_unbounded("mpsc_network_worker");

		if let Some(path) = &params.network_config.net_config_path {
			fs::create_dir_all(path)?;
		}

		// Private and public keys configuration.
		let local_identity = params.network_config.node_key.clone().into_keypair()?;
		let local_public = local_identity.public();
		let local_peer_id = local_public.clone().into_peer_id();
		info!(
			target: "sub-libp2p",
			"🏷 Local node identity is: {}",
			local_peer_id.to_base58(),
		);

		let (protocol, peerset_handle, mut known_addresses) = Protocol::new(
			protocol::ProtocolConfig {
				roles: From::from(&params.role),
				max_parallel_downloads: params.network_config.max_parallel_downloads,
			},
			params.chain.clone(),
			params.transaction_pool,
			params.protocol_id.clone(),
			&params.role,
			&params.network_config,
			params.block_announce_validator,
			params.metrics_registry.as_ref(),
		)?;

		// List of multiaddresses that we know in the network.
		let mut bootnodes = Vec::new();
		let mut boot_node_ids = HashSet::new();

		// Process the bootnodes.
		for bootnode in params.network_config.boot_nodes.iter() {
			bootnodes.push(bootnode.peer_id.clone());
			boot_node_ids.insert(bootnode.peer_id.clone());
			known_addresses.push((bootnode.peer_id.clone(), bootnode.multiaddr.clone()));
		}

		let boot_node_ids = Arc::new(boot_node_ids);

		// Check for duplicate bootnodes.
		known_addresses.iter()
			.try_for_each(|(peer_id, addr)|
				if let Some(other) = known_addresses
					.iter()
					.find(|o| o.1 == *addr && o.0 != *peer_id)
				{
					Err(Error::DuplicateBootnode {
						address: addr.clone(),
						first_id: peer_id.clone(),
						second_id: other.0.clone(),
					})
				} else {
					Ok(())
				}
			)?;

		// Print a message about the deprecation of sentry nodes.
		let print_deprecated_message = match &params.role {
			Role::Sentry { .. } => true,
			Role::Authority { sentry_nodes } if !sentry_nodes.is_empty() => true,
			_ => false,
		};
		if print_deprecated_message {
			log::warn!(
				"🙇 Sentry nodes are deprecated, and the `--sentry` and  `--sentry-nodes` \
				CLI options will eventually be removed in a future version. The Substrate \
				and Polkadot networking protocol require validators to be \
				publicly-accessible. Please do not block access to your validator nodes. \
				For details, see https://github.com/paritytech/substrate/issues/6845."
			);
		}

		let checker = params.on_demand.as_ref()
			.map(|od| od.checker().clone())
			.unwrap_or_else(|| Arc::new(AlwaysBadChecker));

		let num_connected = Arc::new(AtomicUsize::new(0));
		let is_major_syncing = Arc::new(AtomicBool::new(false));

		// Build the swarm.
		let (mut swarm, bandwidth): (Swarm<B, H>, _) = {
			let user_agent = format!(
				"{} ({})",
				params.network_config.client_version,
				params.network_config.node_name
			);
			let light_client_handler = {
				let config = light_client_handler::Config::new(&params.protocol_id);
				light_client_handler::LightClientHandler::new(
					config,
					params.chain,
					checker,
					peerset_handle.clone(),
				)
			};

			let discovery_config = {
				let mut config = DiscoveryConfig::new(local_public.clone());
				config.with_user_defined(known_addresses);
				config.discovery_limit(u64::from(params.network_config.default_peers_set.out_peers) + 15);
				config.add_protocol(params.protocol_id.clone());
				config.allow_non_globals_in_dht(params.network_config.allow_non_globals_in_dht);
				config.use_kademlia_disjoint_query_paths(params.network_config.kademlia_disjoint_query_paths);

				match params.network_config.transport {
					TransportConfig::MemoryOnly => {
						config.with_mdns(false);
						config.allow_private_ipv4(false);
					}
					TransportConfig::Normal { enable_mdns, allow_private_ipv4, .. } => {
						config.with_mdns(enable_mdns);
						config.allow_private_ipv4(allow_private_ipv4);
					}
				}

				config
			};

			let (transport, bandwidth) = {
				let (config_mem, config_wasm) = match params.network_config.transport {
					TransportConfig::MemoryOnly => (true, None),
					TransportConfig::Normal { wasm_external_transport, .. } =>
						(false, wasm_external_transport)
				};

				// The yamux buffer size limit is configured to be equal to the maximum frame size
				// of all protocols. 10 bytes are added to each limit for the length prefix that
				// is not included in the upper layer protocols limit but is still present in the
				// yamux buffer. These 10 bytes correspond to the maximum size required to encode
				// a variable-length-encoding 64bits number. In other words, we make the
				// assumption that no notification larger than 2^64 will ever be sent.
				let yamux_maximum_buffer_size = {
					let requests_max = params.network_config
						.request_response_protocols.iter()
						.map(|cfg| usize::try_from(cfg.max_request_size).unwrap_or(usize::max_value()));
					let responses_max = params.network_config
						.request_response_protocols.iter()
						.map(|cfg| usize::try_from(cfg.max_response_size).unwrap_or(usize::max_value()));
					let notifs_max = params.network_config
						.extra_sets.iter()
						.map(|cfg| usize::try_from(cfg.max_notification_size).unwrap_or(usize::max_value()));

					// A "default" max is added to cover all the other protocols: ping, identify,
					// kademlia.
					let default_max = 1024 * 1024;
					iter::once(default_max)
						.chain(requests_max).chain(responses_max).chain(notifs_max)
						.max().expect("iterator known to always yield at least one element; qed")
						.saturating_add(10)
				};

				transport::build_transport(
					local_identity,
					config_mem,
					config_wasm,
					params.network_config.yamux_window_size,
					yamux_maximum_buffer_size
				)
			};

			let behaviour = {
				let result = Behaviour::new(
					protocol,
					params.role,
					user_agent,
					local_public,
					light_client_handler,
					discovery_config,
					params.block_request_protocol_config,
					params.network_config.request_response_protocols,
				);

				match result {
					Ok(b) => b,
					Err(crate::request_responses::RegisterError::DuplicateProtocol(proto)) => {
						return Err(Error::DuplicateRequestResponseProtocol {
							protocol: proto,
						})
					},
				}
			};

			let mut builder = SwarmBuilder::new(transport, behaviour, local_peer_id.clone())
				.connection_limits(ConnectionLimits::default()
					.with_max_established_per_peer(Some(crate::MAX_CONNECTIONS_PER_PEER as u32))
					.with_max_established_incoming(Some(crate::MAX_CONNECTIONS_ESTABLISHED_INCOMING))
				)
				.substream_upgrade_protocol_override(upgrade::Version::V1Lazy)
				.notify_handler_buffer_size(NonZeroUsize::new(32).expect("32 != 0; qed"))
				.connection_event_buffer_size(1024);
			if let Some(spawner) = params.executor {
				struct SpawnImpl<F>(F);
				impl<F: Fn(Pin<Box<dyn Future<Output = ()> + Send>>)> Executor for SpawnImpl<F> {
					fn exec(&self, f: Pin<Box<dyn Future<Output = ()> + Send>>) {
						(self.0)(f)
					}
				}
				builder = builder.executor(Box::new(SpawnImpl(spawner)));
			}
			(builder.build(), bandwidth)
		};

		// Initialize the metrics.
		let metrics = match &params.metrics_registry {
			Some(registry) => {
				Some(metrics::register(registry, MetricSources {
					bandwidth: bandwidth.clone(),
					major_syncing: is_major_syncing.clone(),
					connected_peers: num_connected.clone(),
				})?)
			}
			None => None
		};

		// Listen on multiaddresses.
		for addr in &params.network_config.listen_addresses {
			if let Err(err) = Swarm::<B, H>::listen_on(&mut swarm, addr.clone()) {
				warn!(target: "sub-libp2p", "Can't listen on {} because: {:?}", addr, err)
			}
		}

		// Add external addresses.
		for addr in &params.network_config.public_addresses {
			Swarm::<B, H>::add_external_address(&mut swarm, addr.clone(), AddressScore::Infinite);
		}

		let external_addresses = Arc::new(Mutex::new(Vec::new()));
		let peers_notifications_sinks = Arc::new(Mutex::new(HashMap::new()));

		let service = Arc::new(NetworkService {
			bandwidth,
			external_addresses: external_addresses.clone(),
			num_connected: num_connected.clone(),
			is_major_syncing: is_major_syncing.clone(),
			peerset: peerset_handle,
			local_peer_id,
			to_worker,
			peers_notifications_sinks: peers_notifications_sinks.clone(),
			notifications_sizes_metric:
				metrics.as_ref().map(|metrics| metrics.notifications_sizes.clone()),
			_marker: PhantomData,
		});

		Ok(NetworkWorker {
			external_addresses,
			num_connected,
			is_major_syncing,
			network_service: swarm,
			service,
			import_queue: params.import_queue,
			from_service,
			light_client_rqs: params.on_demand.and_then(|od| od.extract_receiver()),
			event_streams: out_events::OutChannels::new(params.metrics_registry.as_ref())?,
			peers_notifications_sinks,
			metrics,
			boot_node_ids,
		})
	}

	/// High-level network status information.
	pub fn status(&self) -> NetworkStatus<B> {
		NetworkStatus {
			sync_state: self.sync_state(),
			best_seen_block: self.best_seen_block(),
			num_sync_peers: self.num_sync_peers(),
			num_connected_peers: self.num_connected_peers(),
			num_active_peers: self.num_active_peers(),
			total_bytes_inbound: self.total_bytes_inbound(),
			total_bytes_outbound: self.total_bytes_outbound(),
		}
	}

	/// Returns the total number of bytes received so far.
	pub fn total_bytes_inbound(&self) -> u64 {
		self.service.bandwidth.total_inbound()
	}

	/// Returns the total number of bytes sent so far.
	pub fn total_bytes_outbound(&self) -> u64 {
		self.service.bandwidth.total_outbound()
	}

	/// Returns the number of peers we're connected to.
	pub fn num_connected_peers(&self) -> usize {
		self.network_service.user_protocol().num_connected_peers()
	}

	/// Returns the number of peers we're connected to and that are being queried.
	pub fn num_active_peers(&self) -> usize {
		self.network_service.user_protocol().num_active_peers()
	}

	/// Current global sync state.
	pub fn sync_state(&self) -> SyncState {
		self.network_service.user_protocol().sync_state()
	}

	/// Target sync block number.
	pub fn best_seen_block(&self) -> Option<NumberFor<B>> {
		self.network_service.user_protocol().best_seen_block()
	}

	/// Number of peers participating in syncing.
	pub fn num_sync_peers(&self) -> u32 {
		self.network_service.user_protocol().num_sync_peers()
	}

	/// Number of blocks in the import queue.
	pub fn num_queued_blocks(&self) -> u32 {
		self.network_service.user_protocol().num_queued_blocks()
	}

	/// Returns the number of downloaded blocks.
	pub fn num_downloaded_blocks(&self) -> usize {
		self.network_service.user_protocol().num_downloaded_blocks()
	}

	/// Number of active sync requests.
	pub fn num_sync_requests(&self) -> usize {
		self.network_service.user_protocol().num_sync_requests()
	}

	/// Adds an address for a node.
	pub fn add_known_address(&mut self, peer_id: PeerId, addr: Multiaddr) {
		self.network_service.add_known_address(peer_id, addr);
	}

	/// Return a `NetworkService` that can be shared through the code base and can be used to
	/// manipulate the worker.
	pub fn service(&self) -> &Arc<NetworkService<B, H>> {
		&self.service
	}

	/// You must call this when a new block is finalized by the client.
	pub fn on_block_finalized(&mut self, hash: B::Hash, header: B::Header) {
		self.network_service.user_protocol_mut().on_block_finalized(hash, &header);
	}

	/// Inform the network service about new best imported block.
	pub fn new_best_block_imported(&mut self, hash: B::Hash, number: NumberFor<B>) {
		self.network_service.user_protocol_mut().new_best_block_imported(hash, number);
	}

	/// Returns the local `PeerId`.
	pub fn local_peer_id(&self) -> &PeerId {
		Swarm::<B, H>::local_peer_id(&self.network_service)
	}

	/// Returns the list of addresses we are listening on.
	///
	/// Does **NOT** include a trailing `/p2p/` with our `PeerId`.
	pub fn listen_addresses(&self) -> impl Iterator<Item = &Multiaddr> {
		Swarm::<B, H>::listeners(&self.network_service)
	}

	/// Get network state.
	///
	/// **Note**: Use this only for debugging. This API is unstable. There are warnings literally
	/// everywhere about this. Please don't use this function to retrieve actual information.
	pub fn network_state(&mut self) -> NetworkState {
		let swarm = &mut self.network_service;
		let open = swarm.user_protocol().open_peers().cloned().collect::<Vec<_>>();

		let connected_peers = {
			let swarm = &mut *swarm;
			open.iter().filter_map(move |peer_id| {
				let known_addresses = NetworkBehaviour::addresses_of_peer(&mut **swarm, peer_id)
					.into_iter().collect();

				let endpoint = if let Some(e) = swarm.node(peer_id).map(|i| i.endpoint()) {
					e.clone().into()
				} else {
					error!(target: "sub-libp2p", "Found state inconsistency between custom protocol \
						and debug information about {:?}", peer_id);
					return None
				};

				Some((peer_id.to_base58(), NetworkStatePeer {
					endpoint,
					version_string: swarm.node(peer_id)
						.and_then(|i| i.client_version().map(|s| s.to_owned())),
					latest_ping_time: swarm.node(peer_id).and_then(|i| i.latest_ping()),
					known_addresses,
				}))
			}).collect()
		};

		let not_connected_peers = {
			let swarm = &mut *swarm;
			swarm.known_peers().into_iter()
				.filter(|p| open.iter().all(|n| n != p))
				.map(move |peer_id| {
					(peer_id.to_base58(), NetworkStateNotConnectedPeer {
						version_string: swarm.node(&peer_id)
							.and_then(|i| i.client_version().map(|s| s.to_owned())),
						latest_ping_time: swarm.node(&peer_id).and_then(|i| i.latest_ping()),
						known_addresses: NetworkBehaviour::addresses_of_peer(&mut **swarm, &peer_id)
							.into_iter().collect(),
					})
				})
				.collect()
		};

		let peer_id = Swarm::<B, H>::local_peer_id(&swarm).to_base58();
		let listened_addresses = Swarm::<B, H>::listeners(&swarm).cloned().collect();
		let external_addresses = Swarm::<B, H>::external_addresses(&swarm)
			.map(|r| &r.addr)
			.cloned()
			.collect();

		NetworkState {
			peer_id,
			listened_addresses,
			external_addresses,
			connected_peers,
			not_connected_peers,
			peerset: swarm.user_protocol_mut().peerset_debug_info(),
		}
	}

	/// Get currently connected peers.
	pub fn peers_debug_info(&mut self) -> Vec<(PeerId, PeerInfo<B>)> {
		self.network_service.user_protocol_mut()
			.peers_info()
			.map(|(id, info)| (id.clone(), info.clone()))
			.collect()
	}

	/// Removes a `PeerId` from the list of reserved peers.
	pub fn remove_reserved_peer(&self, peer: PeerId) {
		self.service.remove_reserved_peer(peer);
	}

	/// Adds a `PeerId` and its address as reserved. The string should encode the address
	/// and peer ID of the remote node.
	pub fn add_reserved_peer(&self, peer: String) -> Result<(), String> {
		self.service.add_reserved_peer(peer)
	}
}

impl<B: BlockT + 'static, H: ExHashT> NetworkService<B, H> {
	/// Returns the local `PeerId`.
	pub fn local_peer_id(&self) -> &PeerId {
		&self.local_peer_id
	}

	/// Set authorized peers.
	///
	/// Need a better solution to manage authorized peers, but now just use reserved peers for
	/// prototyping.
	pub fn set_authorized_peers(&self, peers: HashSet<PeerId>) {
		let _ = self
			.to_worker
			.unbounded_send(ServiceToWorkerMsg::SetReserved(peers));
	}

	/// Set authorized_only flag.
	///
	/// Need a better solution to decide authorized_only, but now just use reserved_only flag for
	/// prototyping.
	pub fn set_authorized_only(&self, reserved_only: bool) {
		let _ = self
			.to_worker
			.unbounded_send(ServiceToWorkerMsg::SetReservedOnly(reserved_only));
	}

	/// Appends a notification to the buffer of pending outgoing notifications with the given peer.
	/// Has no effect if the notifications channel with this protocol name is not open.
	///
	/// If the buffer of pending outgoing notifications with that peer is full, the notification
	/// is silently dropped and the connection to the remote will start being shut down. This
	/// happens if you call this method at a higher rate than the rate at which the peer processes
	/// these notifications, or if the available network bandwidth is too low.
	///
	/// For this reason, this method is considered soft-deprecated. You are encouraged to use
	/// [`NetworkService::notification_sender`] instead.
	///
	/// > **Note**: The reason why this is a no-op in the situation where we have no channel is
	/// >			that we don't guarantee message delivery anyway. Networking issues can cause
	/// >			connections to drop at any time, and higher-level logic shouldn't differentiate
	/// >			between the remote voluntarily closing a substream or a network error
	/// >			preventing the message from being delivered.
	///
	/// The protocol must have been registered with
	/// [`NetworkConfiguration::notifications_protocols`](crate::config::NetworkConfiguration::notifications_protocols).
	///
	pub fn write_notification(&self, target: PeerId, protocol: Cow<'static, str>, message: Vec<u8>) {
		// We clone the `NotificationsSink` in order to be able to unlock the network-wide
		// `peers_notifications_sinks` mutex as soon as possible.
		let sink = {
			let peers_notifications_sinks = self.peers_notifications_sinks.lock();
			if let Some(sink) = peers_notifications_sinks.get(&(target.clone(), protocol.clone())) {
				sink.clone()
			} else {
				// Notification silently discarded, as documented.
				log::debug!(
					target: "sub-libp2p",
					"Attempted to send notification on missing or closed substream: {:?}",
					protocol,
				);
				return;
			}
		};

		if let Some(notifications_sizes_metric) = self.notifications_sizes_metric.as_ref() {
			notifications_sizes_metric
				.with_label_values(&["out", &protocol])
				.observe(message.len() as f64);
		}

		// Sending is communicated to the `NotificationsSink`.
		trace!(
			target: "sub-libp2p",
			"External API => Notification({:?}, {:?}, {} bytes)",
			target,
			protocol,
			message.len()
		);
		trace!(target: "sub-libp2p", "Handler({:?}) <= Sync notification", target);
		sink.send_sync_notification(message);
	}

	/// Obtains a [`NotificationSender`] for a connected peer, if it exists.
	///
	/// A `NotificationSender` is scoped to a particular connection to the peer that holds
	/// a receiver. With a `NotificationSender` at hand, sending a notification is done in two steps:
	///
	/// 1.  [`NotificationSender::ready`] is used to wait for the sender to become ready
	/// for another notification, yielding a [`NotificationSenderReady`] token.
	/// 2.  [`NotificationSenderReady::send`] enqueues the notification for sending. This operation
	/// can only fail if the underlying notification substream or connection has suddenly closed.
	///
	/// An error is returned by [`NotificationSenderReady::send`] if there exists no open
	/// notifications substream with that combination of peer and protocol, or if the remote
	/// has asked to close the notifications substream. If that happens, it is guaranteed that an
	/// [`Event::NotificationStreamClosed`] has been generated on the stream returned by
	/// [`NetworkService::event_stream`].
	///
	/// If the remote requests to close the notifications substream, all notifications successfully
	/// enqueued using [`NotificationSenderReady::send`] will finish being sent out before the
	/// substream actually gets closed, but attempting to enqueue more notifications will now
	/// return an error. It is however possible for the entire connection to be abruptly closed,
	/// in which case enqueued notifications will be lost.
	///
	/// The protocol must have been registered with
	/// [`NetworkConfiguration::notifications_protocols`](crate::config::NetworkConfiguration::notifications_protocols).
	///
	/// # Usage
	///
	/// This method returns a struct that allows waiting until there is space available in the
	/// buffer of messages towards the given peer. If the peer processes notifications at a slower
	/// rate than we send them, this buffer will quickly fill up.
	///
	/// As such, you should never do something like this:
	///
	/// ```ignore
	/// // Do NOT do this
	/// for peer in peers {
	/// 	if let Ok(n) = network.notification_sender(peer, ...) {
	///			if let Ok(s) = n.ready().await {
	///				let _ = s.send(...);
	///			}
	/// 	}
	/// }
	/// ```
	///
	/// Doing so would slow down all peers to the rate of the slowest one. A malicious or
	/// malfunctioning peer could intentionally process notifications at a very slow rate.
	///
	/// Instead, you are encouraged to maintain your own buffer of notifications on top of the one
	/// maintained by `sc-network`, and use `notification_sender` to progressively send out
	/// elements from your buffer. If this additional buffer is full (which will happen at some
	/// point if the peer is too slow to process notifications), appropriate measures can be taken,
	/// such as removing non-critical notifications from the buffer or disconnecting the peer
	/// using [`NetworkService::disconnect_peer`].
	///
	///
	/// Notifications              Per-peer buffer
	///   broadcast    +------->   of notifications   +-->  `notification_sender`  +-->  Internet
	///                    ^       (not covered by
	///                    |         sc-network)
	///                    +
	///      Notifications should be dropped
	///             if buffer is full
	///
	///
	/// See also the [`gossip`](crate::gossip) module for a higher-level way to send
	/// notifications.
	///
	pub fn notification_sender(
		&self,
		target: PeerId,
		protocol: Cow<'static, str>,
	) -> Result<NotificationSender, NotificationSenderError> {
		// We clone the `NotificationsSink` in order to be able to unlock the network-wide
		// `peers_notifications_sinks` mutex as soon as possible.
		let sink = {
			let peers_notifications_sinks = self.peers_notifications_sinks.lock();
			if let Some(sink) = peers_notifications_sinks.get(&(target, protocol.clone())) {
				sink.clone()
			} else {
				return Err(NotificationSenderError::Closed);
			}
		};

		let notification_size_metric = self.notifications_sizes_metric.as_ref().map(|histogram| {
			histogram.with_label_values(&["out", &protocol])
		});

		Ok(NotificationSender {
			sink,
			protocol_name: protocol,
			notification_size_metric,
		})
	}

	/// Returns a stream containing the events that happen on the network.
	///
	/// If this method is called multiple times, the events are duplicated.
	///
	/// The stream never ends (unless the `NetworkWorker` gets shut down).
	///
	/// The name passed is used to identify the channel in the Prometheus metrics. Note that the
	/// parameter is a `&'static str`, and not a `String`, in order to avoid accidentally having
	/// an unbounded set of Prometheus metrics, which would be quite bad in terms of memory
	pub fn event_stream(&self, name: &'static str) -> impl Stream<Item = Event> {
		let (tx, rx) = out_events::channel(name);
		let _ = self.to_worker.unbounded_send(ServiceToWorkerMsg::EventStream(tx));
		rx
	}

	/// Sends a single targeted request to a specific peer. On success, returns the response of
	/// the peer.
	///
	/// Request-response protocols are a way to complement notifications protocols, but
	/// notifications should remain the default ways of communicating information. For example, a
	/// peer can announce something through a notification, after which the recipient can obtain
	/// more information by performing a request.
	/// As such, this function is meant to be called only with peers we are already connected to.
	/// Calling this method with a `target` we are not connected to will *not* attempt to connect
	/// to said peer.
	///
	/// No limit or throttling of concurrent outbound requests per peer and protocol are enforced.
	/// Such restrictions, if desired, need to be enforced at the call site(s).
	///
	/// The protocol must have been registered through
	/// [`NetworkConfiguration::request_response_protocols`](
	/// crate::config::NetworkConfiguration::request_response_protocols).
	pub async fn request(
		&self,
		target: PeerId,
		protocol: impl Into<Cow<'static, str>>,
		request: Vec<u8>
	) -> Result<Vec<u8>, RequestFailure> {
		let (tx, rx) = oneshot::channel();
		let _ = self.to_worker.unbounded_send(ServiceToWorkerMsg::Request {
			target,
			protocol: protocol.into(),
			request,
			pending_response: tx
		});

		match rx.await {
			Ok(v) => v,
			// The channel can only be closed if the network worker no longer exists. If the
			// network worker no longer exists, then all connections to `target` are necessarily
			// closed, and we legitimately report this situation as a "ConnectionClosed".
			Err(_) => Err(RequestFailure::Network(OutboundFailure::ConnectionClosed)),
		}
	}

	/// You may call this when new transactons are imported by the transaction pool.
	///
	/// All transactions will be fetched from the `TransactionPool` that was passed at
	/// initialization as part of the configuration and propagated to peers.
	pub fn trigger_repropagate(&self) {
		let _ = self.to_worker.unbounded_send(ServiceToWorkerMsg::PropagateTransactions);
	}

	/// You must call when new transaction is imported by the transaction pool.
	///
	/// This transaction will be fetched from the `TransactionPool` that was passed at
	/// initialization as part of the configuration and propagated to peers.
	pub fn propagate_transaction(&self, hash: H) {
		let _ = self.to_worker.unbounded_send(ServiceToWorkerMsg::PropagateTransaction(hash));
	}

	/// Make sure an important block is propagated to peers.
	///
	/// In chain-based consensus, we often need to make sure non-best forks are
	/// at least temporarily synced. This function forces such an announcement.
	pub fn announce_block(&self, hash: B::Hash, data: Option<Vec<u8>>) {
		let _ = self.to_worker.unbounded_send(ServiceToWorkerMsg::AnnounceBlock(hash, data));
	}

	/// Report a given peer as either beneficial (+) or costly (-) according to the
	/// given scalar.
	pub fn report_peer(&self, who: PeerId, cost_benefit: ReputationChange) {
		self.peerset.report_peer(who, cost_benefit);
	}

	/// Disconnect from a node as soon as possible.
	///
	/// This triggers the same effects as if the connection had closed itself spontaneously.
	///
	/// See also [`NetworkService::remove_from_peers_set`], which has the same effect but also
	/// prevents the local node from re-establishing an outgoing substream to this peer until it
	/// is added again.
	pub fn disconnect_peer(&self, who: PeerId, protocol: impl Into<Cow<'static, str>>) {
		let _ = self.to_worker.unbounded_send(ServiceToWorkerMsg::DisconnectPeer(who, protocol.into()));
	}

	/// Request a justification for the given block from the network.
	///
	/// On success, the justification will be passed to the import queue that was part at
	/// initialization as part of the configuration.
	pub fn request_justification(&self, hash: &B::Hash, number: NumberFor<B>) {
		let _ = self
			.to_worker
			.unbounded_send(ServiceToWorkerMsg::RequestJustification(*hash, number));
	}

	/// Are we in the process of downloading the chain?
	pub fn is_major_syncing(&self) -> bool {
		self.is_major_syncing.load(Ordering::Relaxed)
	}

	/// Start getting a value from the DHT.
	///
	/// This will generate either a `ValueFound` or a `ValueNotFound` event and pass it as an
	/// item on the [`NetworkWorker`] stream.
	pub fn get_value(&self, key: &record::Key) {
		let _ = self
			.to_worker
			.unbounded_send(ServiceToWorkerMsg::GetValue(key.clone()));
	}

	/// Start putting a value in the DHT.
	///
	/// This will generate either a `ValuePut` or a `ValuePutFailed` event and pass it as an
	/// item on the [`NetworkWorker`] stream.
	pub fn put_value(&self, key: record::Key, value: Vec<u8>) {
		let _ = self
			.to_worker
			.unbounded_send(ServiceToWorkerMsg::PutValue(key, value));
	}

	/// Connect to unreserved peers and allow unreserved peers to connect for syncing purposes.
	pub fn accept_unreserved_peers(&self) {
		let _ = self
			.to_worker
			.unbounded_send(ServiceToWorkerMsg::SetReservedOnly(false));
	}

	/// Disconnect from unreserved peers and deny new unreserved peers to connect for syncing
	/// purposes.
	pub fn deny_unreserved_peers(&self) {
		let _ = self
			.to_worker
			.unbounded_send(ServiceToWorkerMsg::SetReservedOnly(true));
	}

	/// Adds a `PeerId` and its address as reserved. The string should encode the address
	/// and peer ID of the remote node.
	///
	/// Returns an `Err` if the given string is not a valid multiaddress
	/// or contains an invalid peer ID (which includes the local peer ID).
	pub fn add_reserved_peer(&self, peer: String) -> Result<(), String> {
		let (peer_id, addr) = parse_str_addr(&peer).map_err(|e| format!("{:?}", e))?;
		// Make sure the local peer ID is never added to the PSM.
		if peer_id == self.local_peer_id {
			return Err("Local peer ID cannot be added as a reserved peer.".to_string())
		}

		let _ = self
			.to_worker
			.unbounded_send(ServiceToWorkerMsg::AddKnownAddress(peer_id.clone(), addr));
		let _ = self
			.to_worker
			.unbounded_send(ServiceToWorkerMsg::AddReserved(peer_id));
		Ok(())
	}

	/// Removes a `PeerId` from the list of reserved peers.
	pub fn remove_reserved_peer(&self, peer_id: PeerId) {
		let _ = self
			.to_worker
			.unbounded_send(ServiceToWorkerMsg::RemoveReserved(peer_id));
	}

	/// Add peers to a peer set.
	///
	/// Each `Multiaddr` must end with a `/p2p/` component containing the `PeerId`. It can also
	/// consist of only `/p2p/<peerid>`.
	///
	/// Returns an `Err` if one of the given addresses is invalid or contains an
	/// invalid peer ID (which includes the local peer ID).
	pub fn add_peers_to_reserved_set(&self, protocol: Cow<'static, str>, peers: HashSet<Multiaddr>) -> Result<(), String> {
		let peers = self.split_multiaddr_and_peer_id(peers)?;

		for (peer_id, addr) in peers.into_iter() {
			// Make sure the local peer ID is never added to the PSM.
			if peer_id == self.local_peer_id {
				return Err("Local peer ID cannot be added as a reserved peer.".to_string())
			}

			if !addr.is_empty() {
				let _ = self
					.to_worker
					.unbounded_send(ServiceToWorkerMsg::AddKnownAddress(peer_id.clone(), addr));
			}
			let _ = self
				.to_worker
				.unbounded_send(ServiceToWorkerMsg::AddSetReserved(protocol.clone(), peer_id));
		}

		Ok(())
	}

	/// Remove peers from a peer set.
	///
	/// Each `Multiaddr` must end with a `/p2p/` component containing the `PeerId`.
	///
	/// Returns an `Err` if one of the given addresses is invalid or contains an
	/// invalid peer ID (which includes the local peer ID).
	//
	// NOTE: technically, this function only needs `Vec<PeerId>`, but we use `Multiaddr` here for convenience.
	pub fn remove_peers_from_reserved_set(
		&self,
		protocol: Cow<'static, str>,
		peers: HashSet<Multiaddr>
	) -> Result<(), String> {
		let peers = self.split_multiaddr_and_peer_id(peers)?;
		for (peer_id, _) in peers.into_iter() {
			let _ = self
				.to_worker
				.unbounded_send(ServiceToWorkerMsg::RemoveSetReserved(protocol.clone(), peer_id));
		}
		Ok(())
	}

	/// Configure an explicit fork sync request.
	/// Note that this function should not be used for recent blocks.
	/// Sync should be able to download all the recent forks normally.
	/// `set_sync_fork_request` should only be used if external code detects that there's
	/// a stale fork missing.
	/// Passing empty `peers` set effectively removes the sync request.
	pub fn set_sync_fork_request(&self, peers: Vec<PeerId>, hash: B::Hash, number: NumberFor<B>) {
		let _ = self
			.to_worker
			.unbounded_send(ServiceToWorkerMsg::SyncFork(peers, hash, number));
	}

	/// Add a peer to a set of peers.
	///
	/// If the set has slots available, it will try to open a substream with this peer.
	///
	/// Each `Multiaddr` must end with a `/p2p/` component containing the `PeerId`. It can also
	/// consist of only `/p2p/<peerid>`.
	///
	/// Returns an `Err` if one of the given addresses is invalid or contains an
	/// invalid peer ID (which includes the local peer ID).
	pub fn add_to_peers_set(&self, protocol: Cow<'static, str>, peers: HashSet<Multiaddr>) -> Result<(), String> {
		let peers = self.split_multiaddr_and_peer_id(peers)?;

		for (peer_id, addr) in peers.into_iter() {
			// Make sure the local peer ID is never added to the PSM.
			if peer_id == self.local_peer_id {
				return Err("Local peer ID cannot be added as a reserved peer.".to_string())
			}

			if !addr.is_empty() {
				let _ = self
					.to_worker
					.unbounded_send(ServiceToWorkerMsg::AddKnownAddress(peer_id.clone(), addr));
			}
			let _ = self
				.to_worker
				.unbounded_send(ServiceToWorkerMsg::AddToPeersSet(protocol.clone(), peer_id));
		}

		Ok(())
	}

	/// Remove peers from a peer set.
	///
	/// If we currently have an open substream with this peer, it will soon be closed.
	///
	/// Each `Multiaddr` must end with a `/p2p/` component containing the `PeerId`.
	///
	/// Returns an `Err` if one of the given addresses is invalid or contains an
	/// invalid peer ID (which includes the local peer ID).
	//
	// NOTE: technically, this function only needs `Vec<PeerId>`, but we use `Multiaddr` here for convenience.
	pub fn remove_from_peers_set(&self, protocol: Cow<'static, str>, peers: HashSet<Multiaddr>) -> Result<(), String> {
		let peers = self.split_multiaddr_and_peer_id(peers)?;
		for (peer_id, _) in peers.into_iter() {
			let _ = self
				.to_worker
				.unbounded_send(ServiceToWorkerMsg::RemoveFromPeersSet(protocol.clone(), peer_id));
		}
		Ok(())
	}

	/// Returns the number of peers we're connected to.
	pub fn num_connected(&self) -> usize {
		self.num_connected.load(Ordering::Relaxed)
	}

	/// Inform the network service about new best imported block.
	pub fn new_best_block_imported(&self, hash: B::Hash, number: NumberFor<B>) {
		let _ = self
			.to_worker
			.unbounded_send(ServiceToWorkerMsg::NewBestBlockImported(hash, number));
	}

	/// Utility function to extract `PeerId` from each `Multiaddr` for peer set updates.
	///
	/// Returns an `Err` if one of the given addresses is invalid or contains an
	/// invalid peer ID (which includes the local peer ID).
	fn split_multiaddr_and_peer_id(&self, peers: HashSet<Multiaddr>) -> Result<Vec<(PeerId, Multiaddr)>, String> {
		peers.into_iter()
			.map(|mut addr| {
				let peer = match addr.pop() {
					Some(multiaddr::Protocol::P2p(key)) => PeerId::from_multihash(key)
						.map_err(|_| "Invalid PeerId format".to_string())?,
					_ => return Err("Missing PeerId from address".to_string()),
				};

				// Make sure the local peer ID is never added to the PSM
				// or added as a "known address", even if given.
				if peer == self.local_peer_id {
					Err("Local peer ID in peer set.".to_string())
				} else {
					Ok((peer, addr))
				}
			})
			.collect::<Result<Vec<(PeerId, Multiaddr)>, String>>()
	}
}

impl<B: BlockT + 'static, H: ExHashT> sp_consensus::SyncOracle
	for NetworkService<B, H>
{
	fn is_major_syncing(&mut self) -> bool {
		NetworkService::is_major_syncing(self)
	}

	fn is_offline(&mut self) -> bool {
		self.num_connected.load(Ordering::Relaxed) == 0
	}
}

impl<'a, B: BlockT + 'static, H: ExHashT> sp_consensus::SyncOracle
	for &'a NetworkService<B, H>
{
	fn is_major_syncing(&mut self) -> bool {
		NetworkService::is_major_syncing(self)
	}

	fn is_offline(&mut self) -> bool {
		self.num_connected.load(Ordering::Relaxed) == 0
	}
}

impl<B, H> NetworkStateInfo for NetworkService<B, H>
	where
		B: sp_runtime::traits::Block,
		H: ExHashT,
{
	/// Returns the local external addresses.
	fn external_addresses(&self) -> Vec<Multiaddr> {
		self.external_addresses.lock().clone()
	}

	/// Returns the local Peer ID.
	fn local_peer_id(&self) -> PeerId {
		self.local_peer_id.clone()
	}
}

/// A `NotificationSender` allows for sending notifications to a peer with a chosen protocol.
#[must_use]
pub struct NotificationSender {
	sink: NotificationsSink,

	/// Name of the protocol on the wire.
	protocol_name: Cow<'static, str>,

	/// Field extracted from the [`Metrics`] struct and necessary to report the
	/// notifications-related metrics.
	notification_size_metric: Option<Histogram>,
}

impl NotificationSender {
	/// Returns a future that resolves when the `NotificationSender` is ready to send a notification.
	pub async fn ready<'a>(&'a self) -> Result<NotificationSenderReady<'a>, NotificationSenderError> {
		Ok(NotificationSenderReady {
			ready: match self.sink.reserve_notification().await {
				Ok(r) => r,
				Err(()) => return Err(NotificationSenderError::Closed),
			},
			peer_id: self.sink.peer_id(),
			protocol_name: &self.protocol_name,
			notification_size_metric: self.notification_size_metric.clone(),
		})
	}
}

/// Reserved slot in the notifications buffer, ready to accept data.
#[must_use]
pub struct NotificationSenderReady<'a> {
	ready: Ready<'a>,

	/// Target of the notification.
	peer_id: &'a PeerId,

	/// Name of the protocol on the wire.
	protocol_name: &'a Cow<'static, str>,

	/// Field extracted from the [`Metrics`] struct and necessary to report the
	/// notifications-related metrics.
	notification_size_metric: Option<Histogram>,
}

impl<'a> NotificationSenderReady<'a> {
	/// Consumes this slots reservation and actually queues the notification.
	pub fn send(self, notification: impl Into<Vec<u8>>) -> Result<(), NotificationSenderError> {
		let notification = notification.into();

		if let Some(notification_size_metric) = &self.notification_size_metric {
			notification_size_metric.observe(notification.len() as f64);
		}

		trace!(
			target: "sub-libp2p",
			"External API => Notification({:?}, {}, {} bytes)",
			self.peer_id,
			self.protocol_name,
			notification.len()
		);
		trace!(target: "sub-libp2p", "Handler({:?}) <= Async notification", self.peer_id);

		self.ready
			.send(notification)
			.map_err(|()| NotificationSenderError::Closed)
	}
}

/// Error returned by [`NetworkService::send_notification`].
#[derive(Debug, derive_more::Display, derive_more::Error)]
pub enum NotificationSenderError {
	/// The notification receiver has been closed, usually because the underlying connection closed.
	///
	/// Some of the notifications most recently sent may not have been received. However,
	/// the peer may still be connected and a new `NotificationSender` for the same
	/// protocol obtained from [`NetworkService::notification_sender`].
	Closed,
	/// Protocol name hasn't been registered.
	BadProtocol,
}

/// Messages sent from the `NetworkService` to the `NetworkWorker`.
///
/// Each entry corresponds to a method of `NetworkService`.
enum ServiceToWorkerMsg<B: BlockT, H: ExHashT> {
	PropagateTransaction(H),
	PropagateTransactions,
	RequestJustification(B::Hash, NumberFor<B>),
	AnnounceBlock(B::Hash, Option<Vec<u8>>),
	GetValue(record::Key),
	PutValue(record::Key, Vec<u8>),
	AddKnownAddress(PeerId, Multiaddr),
	SetReservedOnly(bool),
	AddReserved(PeerId),
	RemoveReserved(PeerId),
	SetReserved(HashSet<PeerId>),
	AddSetReserved(Cow<'static, str>, PeerId),
	RemoveSetReserved(Cow<'static, str>, PeerId),
	AddToPeersSet(Cow<'static, str>, PeerId),
	RemoveFromPeersSet(Cow<'static, str>, PeerId),
	SyncFork(Vec<PeerId>, B::Hash, NumberFor<B>),
	EventStream(out_events::Sender),
	Request {
		target: PeerId,
		protocol: Cow<'static, str>,
		request: Vec<u8>,
		pending_response: oneshot::Sender<Result<Vec<u8>, RequestFailure>>,
	},
	DisconnectPeer(PeerId, Cow<'static, str>),
	NewBestBlockImported(B::Hash, NumberFor<B>),
}

/// Main network worker. Must be polled in order for the network to advance.
///
/// You are encouraged to poll this in a separate background thread or task.
#[must_use = "The NetworkWorker must be polled in order for the network to advance"]
pub struct NetworkWorker<B: BlockT + 'static, H: ExHashT> {
	/// Updated by the `NetworkWorker` and loaded by the `NetworkService`.
	external_addresses: Arc<Mutex<Vec<Multiaddr>>>,
	/// Updated by the `NetworkWorker` and loaded by the `NetworkService`.
	num_connected: Arc<AtomicUsize>,
	/// Updated by the `NetworkWorker` and loaded by the `NetworkService`.
	is_major_syncing: Arc<AtomicBool>,
	/// The network service that can be extracted and shared through the codebase.
	service: Arc<NetworkService<B, H>>,
	/// The *actual* network.
	network_service: Swarm<B, H>,
	/// The import queue that was passed at initialization.
	import_queue: Box<dyn ImportQueue<B>>,
	/// Messages from the [`NetworkService`] that must be processed.
	from_service: TracingUnboundedReceiver<ServiceToWorkerMsg<B, H>>,
	/// Receiver for queries from the light client that must be processed.
	light_client_rqs: Option<TracingUnboundedReceiver<light_client_handler::Request<B>>>,
	/// Senders for events that happen on the network.
	event_streams: out_events::OutChannels,
	/// Prometheus network metrics.
	metrics: Option<Metrics>,
	/// The `PeerId`'s of all boot nodes.
	boot_node_ids: Arc<HashSet<PeerId>>,
	/// For each peer and protocol combination, an object that allows sending notifications to
	/// that peer. Shared with the [`NetworkService`].
	peers_notifications_sinks: Arc<Mutex<HashMap<(PeerId, Cow<'static, str>), NotificationsSink>>>,
}

impl<B: BlockT + 'static, H: ExHashT> Future for NetworkWorker<B, H> {
	type Output = ();

	fn poll(mut self: Pin<&mut Self>, cx: &mut std::task::Context) -> Poll<Self::Output> {
		let this = &mut *self;

		// Poll the import queue for actions to perform.
		this.import_queue.poll_actions(cx, &mut NetworkLink {
			protocol: &mut this.network_service,
		});

		// Check for new incoming light client requests.
		if let Some(light_client_rqs) = this.light_client_rqs.as_mut() {
			while let Poll::Ready(Some(rq)) = light_client_rqs.poll_next_unpin(cx) {
				// This can error if there are too many queued requests already.
				if this.network_service.light_client_request(rq).is_err() {
					log::warn!("Couldn't start light client request: too many pending requests");
				}
				if let Some(metrics) = this.metrics.as_ref() {
					metrics.issued_light_requests.inc();
				}
			}
		}

		// At the time of writing of this comment, due to a high volume of messages, the network
		// worker sometimes takes a long time to process the loop below. When that happens, the
		// rest of the polling is frozen. In order to avoid negative side-effects caused by this
		// freeze, a limit to the number of iterations is enforced below. If the limit is reached,
		// the task is interrupted then scheduled again.
		//
		// This allows for a more even distribution in the time taken by each sub-part of the
		// polling.
		let mut num_iterations = 0;
		loop {
			num_iterations += 1;
			if num_iterations >= 100 {
				cx.waker().wake_by_ref();
				break;
			}

			// Process the next message coming from the `NetworkService`.
			let msg = match this.from_service.poll_next_unpin(cx) {
				Poll::Ready(Some(msg)) => msg,
				Poll::Ready(None) => return Poll::Ready(()),
				Poll::Pending => break,
			};

			match msg {
				ServiceToWorkerMsg::AnnounceBlock(hash, data) =>
					this.network_service.user_protocol_mut().announce_block(hash, data),
				ServiceToWorkerMsg::RequestJustification(hash, number) =>
					this.network_service.user_protocol_mut().request_justification(&hash, number),
				ServiceToWorkerMsg::PropagateTransaction(hash) =>
					this.network_service.user_protocol_mut().propagate_transaction(&hash),
				ServiceToWorkerMsg::PropagateTransactions =>
					this.network_service.user_protocol_mut().propagate_transactions(),
				ServiceToWorkerMsg::GetValue(key) =>
					this.network_service.get_value(&key),
				ServiceToWorkerMsg::PutValue(key, value) =>
					this.network_service.put_value(key, value),
				ServiceToWorkerMsg::SetReservedOnly(reserved_only) =>
					this.network_service.user_protocol_mut().set_reserved_only(reserved_only),
				ServiceToWorkerMsg::SetReserved(peers) =>
					this.network_service.user_protocol_mut().set_reserved_peers(peers),
				ServiceToWorkerMsg::AddReserved(peer_id) =>
					this.network_service.user_protocol_mut().add_reserved_peer(peer_id),
				ServiceToWorkerMsg::RemoveReserved(peer_id) =>
					this.network_service.user_protocol_mut().remove_reserved_peer(peer_id),
				ServiceToWorkerMsg::AddSetReserved(protocol, peer_id) =>
					this.network_service.user_protocol_mut().add_set_reserved_peer(protocol, peer_id),
				ServiceToWorkerMsg::RemoveSetReserved(protocol, peer_id) =>
					this.network_service.user_protocol_mut().remove_set_reserved_peer(protocol, peer_id),
				ServiceToWorkerMsg::AddKnownAddress(peer_id, addr) =>
					this.network_service.add_known_address(peer_id, addr),
				ServiceToWorkerMsg::AddToPeersSet(protocol, peer_id) =>
					this.network_service.user_protocol_mut().add_to_peers_set(protocol, peer_id),
				ServiceToWorkerMsg::RemoveFromPeersSet(protocol, peer_id) =>
					this.network_service.user_protocol_mut().remove_from_peers_set(protocol, peer_id),
				ServiceToWorkerMsg::SyncFork(peer_ids, hash, number) =>
					this.network_service.user_protocol_mut().set_sync_fork_request(peer_ids, &hash, number),
				ServiceToWorkerMsg::EventStream(sender) =>
					this.event_streams.push(sender),
				ServiceToWorkerMsg::Request { target, protocol, request, pending_response } => {
					this.network_service.send_request(&target, &protocol, request, pending_response);
				},
				ServiceToWorkerMsg::DisconnectPeer(who, protocol_name) =>
					this.network_service.user_protocol_mut().disconnect_peer(&who, &protocol_name),
				ServiceToWorkerMsg::NewBestBlockImported(hash, number) =>
					this.network_service.user_protocol_mut().new_best_block_imported(hash, number),
			}
		}

		// `num_iterations` serves the same purpose as in the previous loop.
		// See the previous loop for explanations.
		let mut num_iterations = 0;
		loop {
			num_iterations += 1;
			if num_iterations >= 1000 {
				cx.waker().wake_by_ref();
				break;
			}

			// Process the next action coming from the network.
			let next_event = this.network_service.next_event();
			futures::pin_mut!(next_event);
			let poll_value = next_event.poll_unpin(cx);

			match poll_value {
				Poll::Pending => break,
				Poll::Ready(SwarmEvent::Behaviour(BehaviourOut::BlockImport(origin, blocks))) => {
					if let Some(metrics) = this.metrics.as_ref() {
						metrics.import_queue_blocks_submitted.inc();
					}
					this.import_queue.import_blocks(origin, blocks);
				},
				Poll::Ready(SwarmEvent::Behaviour(BehaviourOut::JustificationImport(origin, hash, nb, justification))) => {
					if let Some(metrics) = this.metrics.as_ref() {
						metrics.import_queue_justifications_submitted.inc();
					}
					this.import_queue.import_justification(origin, hash, nb, justification);
				},
				Poll::Ready(SwarmEvent::Behaviour(BehaviourOut::InboundRequest { protocol, result, .. })) => {
					if let Some(metrics) = this.metrics.as_ref() {
						match result {
							Ok(serve_time) => {
								metrics.requests_in_success_total
									.with_label_values(&[&protocol])
									.observe(serve_time.as_secs_f64());
							}
							Err(err) => {
								let reason = match err {
									ResponseFailure::Network(InboundFailure::Timeout) => "timeout",
									ResponseFailure::Network(InboundFailure::UnsupportedProtocols) =>
										"unsupported",
									ResponseFailure::Network(InboundFailure::ResponseOmission) =>
										"busy-omitted",
									ResponseFailure::Network(InboundFailure::ConnectionClosed) =>
										"connection-closed",
								};

								metrics.requests_in_failure_total
									.with_label_values(&[&protocol, reason])
									.inc();
							}
						}
					}
				},
				Poll::Ready(SwarmEvent::Behaviour(BehaviourOut::RequestFinished {
					protocol, duration, result, ..
				})) => {
					if let Some(metrics) = this.metrics.as_ref() {
						match result {
							Ok(_) => {
								metrics.requests_out_success_total
									.with_label_values(&[&protocol])
									.observe(duration.as_secs_f64());
							}
							Err(err) => {
								let reason = match err {
									RequestFailure::NotConnected => "not-connected",
									RequestFailure::UnknownProtocol => "unknown-protocol",
									RequestFailure::Refused => "refused",
									RequestFailure::Obsolete => "obsolete",
									RequestFailure::Network(OutboundFailure::DialFailure) =>
										"dial-failure",
									RequestFailure::Network(OutboundFailure::Timeout) =>
										"timeout",
									RequestFailure::Network(OutboundFailure::ConnectionClosed) =>
										"connection-closed",
									RequestFailure::Network(OutboundFailure::UnsupportedProtocols) =>
										"unsupported",
								};

								metrics.requests_out_failure_total
									.with_label_values(&[&protocol, reason])
									.inc();
							}
						}
					}
				},
				Poll::Ready(SwarmEvent::Behaviour(BehaviourOut::RandomKademliaStarted(protocol))) => {
					if let Some(metrics) = this.metrics.as_ref() {
						metrics.kademlia_random_queries_total
							.with_label_values(&[&protocol.as_ref()])
							.inc();
					}
				},
				Poll::Ready(SwarmEvent::Behaviour(BehaviourOut::NotificationStreamOpened {
					remote, protocol, notifications_sink, role
				})) => {
					if let Some(metrics) = this.metrics.as_ref() {
						metrics.notifications_streams_opened_total
							.with_label_values(&[&protocol]).inc();
					}
					{
						let mut peers_notifications_sinks = this.peers_notifications_sinks.lock();
						peers_notifications_sinks.insert((remote.clone(), protocol.clone()), notifications_sink);
					}
					this.event_streams.send(Event::NotificationStreamOpened {
						remote,
						protocol,
						role,
					});
				},
				Poll::Ready(SwarmEvent::Behaviour(BehaviourOut::NotificationStreamReplaced {
					remote, protocol, notifications_sink
				})) => {
					let mut peers_notifications_sinks = this.peers_notifications_sinks.lock();
					if let Some(s) = peers_notifications_sinks.get_mut(&(remote, protocol)) {
						*s = notifications_sink;
					} else {
						log::error!(
							target: "sub-libp2p",
							"NotificationStreamReplaced for non-existing substream"
						);
					}

					// TODO: Notifications might have been lost as a result of the previous
					// connection being dropped, and as a result it would be preferable to notify
					// the users of this fact by simulating the substream being closed then
					// reopened.
					// The code below doesn't compile because `role` is unknown. Propagating the
					// handshake of the secondary connections is quite an invasive change and
					// would conflict with https://github.com/paritytech/substrate/issues/6403.
					// Considering that dropping notifications is generally regarded as
					// acceptable, this bug is at the moment intentionally left there and is
					// intended to be fixed at the same time as
					// https://github.com/paritytech/substrate/issues/6403.
					/*this.event_streams.send(Event::NotificationStreamClosed {
						remote,
						protocol,
					});
					this.event_streams.send(Event::NotificationStreamOpened {
						remote,
						protocol,
						role,
					});*/
				},
				Poll::Ready(SwarmEvent::Behaviour(BehaviourOut::NotificationStreamClosed { remote, protocol })) => {
					if let Some(metrics) = this.metrics.as_ref() {
						metrics.notifications_streams_closed_total
							.with_label_values(&[&protocol[..]]).inc();
					}
					this.event_streams.send(Event::NotificationStreamClosed {
						remote: remote.clone(),
						protocol: protocol.clone(),
					});
					{
						let mut peers_notifications_sinks = this.peers_notifications_sinks.lock();
						peers_notifications_sinks.remove(&(remote.clone(), protocol));
					}
				},
				Poll::Ready(SwarmEvent::Behaviour(BehaviourOut::NotificationsReceived { remote, messages })) => {
					if let Some(metrics) = this.metrics.as_ref() {
						for (protocol, message) in &messages {
							metrics.notifications_sizes
								.with_label_values(&["in", protocol])
								.observe(message.len() as f64);
						}
					}
					this.event_streams.send(Event::NotificationsReceived {
						remote,
						messages,
					});
				},
				Poll::Ready(SwarmEvent::Behaviour(BehaviourOut::SyncConnected(remote))) => {
					this.event_streams.send(Event::SyncConnected { remote });
				},
				Poll::Ready(SwarmEvent::Behaviour(BehaviourOut::SyncDisconnected(remote))) => {
					this.event_streams.send(Event::SyncDisconnected { remote });
				},
				Poll::Ready(SwarmEvent::Behaviour(BehaviourOut::Dht(event, duration))) => {
					if let Some(metrics) = this.metrics.as_ref() {
						let query_type = match event {
							DhtEvent::ValueFound(_) => "value-found",
							DhtEvent::ValueNotFound(_) => "value-not-found",
							DhtEvent::ValuePut(_) => "value-put",
							DhtEvent::ValuePutFailed(_) => "value-put-failed",
						};
						metrics.kademlia_query_duration.with_label_values(&[query_type])
							.observe(duration.as_secs_f64());
					}

					this.event_streams.send(Event::Dht(event));
				},
				Poll::Ready(SwarmEvent::ConnectionEstablished { peer_id, endpoint, num_established }) => {
					trace!(target: "sub-libp2p", "Libp2p => Connected({:?})", peer_id);

					if let Some(metrics) = this.metrics.as_ref() {
						let direction = match endpoint {
							ConnectedPoint::Dialer { .. } => "out",
							ConnectedPoint::Listener { .. } => "in",
						};
						metrics.connections_opened_total.with_label_values(&[direction]).inc();

						if num_established.get() == 1 {
							metrics.distinct_peers_connections_opened_total.inc();
						}
					}
				},
				Poll::Ready(SwarmEvent::ConnectionClosed { peer_id, cause, endpoint, num_established }) => {
					trace!(target: "sub-libp2p", "Libp2p => Disconnected({:?}, {:?})", peer_id, cause);
					if let Some(metrics) = this.metrics.as_ref() {
						let direction = match endpoint {
							ConnectedPoint::Dialer { .. } => "out",
							ConnectedPoint::Listener { .. } => "in",
						};
						let reason = match cause {
							Some(ConnectionError::IO(_)) => "transport-error",
							Some(ConnectionError::Handler(NodeHandlerWrapperError::Handler(EitherError::A(EitherError::A(
								EitherError::A(EitherError::B(EitherError::A(
								PingFailure::Timeout)))))))) => "ping-timeout",
							Some(ConnectionError::Handler(NodeHandlerWrapperError::Handler(EitherError::A(EitherError::A(
								EitherError::A(EitherError::A(
								NotifsHandlerError::SyncNotificationsClogged))))))) => "sync-notifications-clogged",
							Some(ConnectionError::Handler(NodeHandlerWrapperError::Handler(_))) => "protocol-error",
							Some(ConnectionError::Handler(NodeHandlerWrapperError::KeepAliveTimeout)) => "keep-alive-timeout",
							None => "actively-closed",
						};
						metrics.connections_closed_total.with_label_values(&[direction, reason]).inc();

						// `num_established` represents the number of *remaining* connections.
						if num_established == 0 {
							metrics.distinct_peers_connections_closed_total.inc();
						}
					}
				},
				Poll::Ready(SwarmEvent::NewListenAddr(addr)) => {
					trace!(target: "sub-libp2p", "Libp2p => NewListenAddr({})", addr);
					if let Some(metrics) = this.metrics.as_ref() {
						metrics.listeners_local_addresses.inc();
					}
				},
				Poll::Ready(SwarmEvent::ExpiredListenAddr(addr)) => {
					info!(target: "sub-libp2p", "📪 No longer listening on {}", addr);
					if let Some(metrics) = this.metrics.as_ref() {
						metrics.listeners_local_addresses.dec();
					}
				},
				Poll::Ready(SwarmEvent::UnreachableAddr { peer_id, address, error, .. }) => {
					trace!(
						target: "sub-libp2p", "Libp2p => Failed to reach {:?} through {:?}: {}",
						peer_id,
						address,
						error,
					);

					if this.boot_node_ids.contains(&peer_id) {
						if let PendingConnectionError::InvalidPeerId = error {
							error!(
								"💔 The bootnode you want to connect to at `{}` provided a different peer ID than the one you expect: `{}`.",
								address,
								peer_id,
							);
						}
					}

					if let Some(metrics) = this.metrics.as_ref() {
						match error {
							PendingConnectionError::ConnectionLimit(_) =>
								metrics.pending_connections_errors_total.with_label_values(&["limit-reached"]).inc(),
							PendingConnectionError::InvalidPeerId =>
								metrics.pending_connections_errors_total.with_label_values(&["invalid-peer-id"]).inc(),
							PendingConnectionError::Transport(_) | PendingConnectionError::IO(_) =>
								metrics.pending_connections_errors_total.with_label_values(&["transport-error"]).inc(),
						}
					}
				}
				Poll::Ready(SwarmEvent::Dialing(peer_id)) =>
					trace!(target: "sub-libp2p", "Libp2p => Dialing({:?})", peer_id),
				Poll::Ready(SwarmEvent::IncomingConnection { local_addr, send_back_addr }) => {
					trace!(target: "sub-libp2p", "Libp2p => IncomingConnection({},{}))",
						local_addr, send_back_addr);
					if let Some(metrics) = this.metrics.as_ref() {
						metrics.incoming_connections_total.inc();
					}
				},
				Poll::Ready(SwarmEvent::IncomingConnectionError { local_addr, send_back_addr, error }) => {
					trace!(target: "sub-libp2p", "Libp2p => IncomingConnectionError({},{}): {}",
						local_addr, send_back_addr, error);
					if let Some(metrics) = this.metrics.as_ref() {
						let reason = match error {
							PendingConnectionError::ConnectionLimit(_) => "limit-reached",
							PendingConnectionError::InvalidPeerId => "invalid-peer-id",
							PendingConnectionError::Transport(_) |
							PendingConnectionError::IO(_) => "transport-error",
						};

						metrics.incoming_connections_errors_total.with_label_values(&[reason]).inc();
					}
				},
				Poll::Ready(SwarmEvent::BannedPeer { peer_id, endpoint }) => {
					trace!(target: "sub-libp2p", "Libp2p => BannedPeer({}). Connected via {:?}.",
						peer_id, endpoint);
					if let Some(metrics) = this.metrics.as_ref() {
						metrics.incoming_connections_errors_total.with_label_values(&["banned"]).inc();
					}
				},
				Poll::Ready(SwarmEvent::UnknownPeerUnreachableAddr { address, error }) =>
					trace!(target: "sub-libp2p", "Libp2p => UnknownPeerUnreachableAddr({}): {}",
						address, error),
				Poll::Ready(SwarmEvent::ListenerClosed { reason, addresses }) => {
					if let Some(metrics) = this.metrics.as_ref() {
						metrics.listeners_local_addresses.sub(addresses.len() as u64);
					}
					let addrs = addresses.into_iter().map(|a| a.to_string())
						.collect::<Vec<_>>().join(", ");
					match reason {
						Ok(()) => error!(
							target: "sub-libp2p",
							"📪 Libp2p listener ({}) closed gracefully",
							addrs
						),
						Err(e) => error!(
							target: "sub-libp2p",
							"📪 Libp2p listener ({}) closed: {}",
							addrs, e
						),
					}
				},
				Poll::Ready(SwarmEvent::ListenerError { error }) => {
					trace!(target: "sub-libp2p", "Libp2p => ListenerError: {}", error);
					if let Some(metrics) = this.metrics.as_ref() {
						metrics.listeners_errors_total.inc();
					}
				},
			};
		}

		let num_connected_peers = this.network_service.user_protocol_mut().num_connected_peers();

		// Update the variables shared with the `NetworkService`.
		this.num_connected.store(num_connected_peers, Ordering::Relaxed);
		{
			let external_addresses = Swarm::<B, H>::external_addresses(&this.network_service)
				.map(|r| &r.addr)
				.cloned()
				.collect();
			*this.external_addresses.lock() = external_addresses;
		}

		let is_major_syncing = match this.network_service.user_protocol_mut().sync_state() {
			SyncState::Idle => false,
			SyncState::Downloading => true,
		};

		this.is_major_syncing.store(is_major_syncing, Ordering::Relaxed);

		if let Some(metrics) = this.metrics.as_ref() {
			for (proto, buckets) in this.network_service.num_entries_per_kbucket() {
				for (lower_ilog2_bucket_bound, num_entries) in buckets {
					metrics.kbuckets_num_nodes
						.with_label_values(&[&proto.as_ref(), &lower_ilog2_bucket_bound.to_string()])
						.set(num_entries as u64);
				}
			}
			for (proto, num_entries) in this.network_service.num_kademlia_records() {
				metrics.kademlia_records_count.with_label_values(&[&proto.as_ref()]).set(num_entries as u64);
			}
			for (proto, num_entries) in this.network_service.kademlia_records_total_size() {
				metrics.kademlia_records_sizes_total.with_label_values(&[&proto.as_ref()]).set(num_entries as u64);
			}
			metrics.peerset_num_discovered.set(this.network_service.user_protocol().num_discovered_peers() as u64);
			metrics.peerset_num_requested.set(this.network_service.user_protocol().requested_peers().count() as u64);
			metrics.pending_connections.set(
				Swarm::network_info(&this.network_service).connection_counters().num_pending() as u64
			);
		}

		Poll::Pending
	}
}

impl<B: BlockT + 'static, H: ExHashT> Unpin for NetworkWorker<B, H> {
}

/// The libp2p swarm, customized for our needs.
type Swarm<B, H> = libp2p::swarm::Swarm<Behaviour<B, H>>;

// Implementation of `import_queue::Link` trait using the available local variables.
struct NetworkLink<'a, B: BlockT, H: ExHashT> {
	protocol: &'a mut Swarm<B, H>,
}

impl<'a, B: BlockT, H: ExHashT> Link<B> for NetworkLink<'a, B, H> {
	fn blocks_processed(
		&mut self,
		imported: usize,
		count: usize,
		results: Vec<(Result<BlockImportResult<NumberFor<B>>, BlockImportError>, B::Hash)>
	) {
		self.protocol.user_protocol_mut().on_blocks_processed(imported, count, results)
	}
	fn justification_imported(&mut self, who: PeerId, hash: &B::Hash, number: NumberFor<B>, success: bool) {
		self.protocol.user_protocol_mut().justification_import_result(who, hash.clone(), number, success);
	}
	fn request_justification(&mut self, hash: &B::Hash, number: NumberFor<B>) {
		self.protocol.user_protocol_mut().request_justification(hash, number)
	}
}

fn ensure_addresses_consistent_with_transport<'a>(
	addresses: impl Iterator<Item = &'a Multiaddr>,
	transport: &TransportConfig,
) -> Result<(), Error> {
	if matches!(transport, TransportConfig::MemoryOnly) {
		let addresses: Vec<_> = addresses
			.filter(|x| x.iter()
				.any(|y| !matches!(y, libp2p::core::multiaddr::Protocol::Memory(_)))
			)
			.cloned()
			.collect();

		if !addresses.is_empty() {
			return Err(Error::AddressesForAnotherTransport {
				transport: transport.clone(),
				addresses,
			});
		}
	} else {
		let addresses: Vec<_> = addresses
			.filter(|x| x.iter()
				.any(|y| matches!(y, libp2p::core::multiaddr::Protocol::Memory(_)))
			)
			.cloned()
			.collect();

		if !addresses.is_empty() {
			return Err(Error::AddressesForAnotherTransport {
				transport: transport.clone(),
				addresses,
			});
		}
	}

	Ok(())
}