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
// Copyright 2018-2020 Parity Technologies (UK) Ltd.
// This file is part of Substrate.

// Substrate 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.

// Substrate 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 Substrate. If not, see <http://www.gnu.org/licenses/>.

//! Environment definition of the wasm smart-contract runtime.

use crate::{
	HostFnWeights, Schedule, Trait, CodeHash, BalanceOf, Error,
	exec::{Ext, StorageKey, TopicOf},
	gas::{Gas, GasMeter, Token, GasMeterResult},
	wasm::env_def::ConvertibleToWasm,
};
use sp_sandbox;
use parity_wasm::elements::ValueType;
use frame_system;
use frame_support::dispatch::DispatchError;
use sp_std::prelude::*;
use codec::{Decode, Encode};
use sp_runtime::traits::SaturatedConversion;
use sp_core::crypto::UncheckedFrom;
use sp_io::hashing::{
	keccak_256,
	blake2_256,
	blake2_128,
	sha2_256,
};
use pallet_contracts_primitives::{ExecResult, ExecReturnValue, ReturnFlags, ExecError};

/// Every error that can be returned to a contract when it calls any of the host functions.
#[repr(u32)]
pub enum ReturnCode {
	/// API call successful.
	Success = 0,
	/// The called function trapped and has its state changes reverted.
	/// In this case no output buffer is returned.
	CalleeTrapped = 1,
	/// The called function ran to completion but decided to revert its state.
	/// An output buffer is returned when one was supplied.
	CalleeReverted = 2,
	/// The passed key does not exist in storage.
	KeyNotFound = 3,
	/// Transfer failed because it would have brought the sender's total balance below the
	/// subsistence threshold.
	BelowSubsistenceThreshold = 4,
	/// Transfer failed for other reasons. Most probably reserved or locked balance of the
	/// sender prevents the transfer.
	TransferFailed = 5,
	/// The newly created contract is below the subsistence threshold after executing
	/// its constructor.
	NewContractNotFunded = 6,
	/// No code could be found at the supplied code hash.
	CodeNotFound = 7,
	/// The contract that was called is either no contract at all (a plain account)
	/// or is a tombstone.
	NotCallable = 8,
}

impl ConvertibleToWasm for ReturnCode {
	type NativeType = Self;
	const VALUE_TYPE: ValueType = ValueType::I32;
	fn to_typed_value(self) -> sp_sandbox::Value {
		sp_sandbox::Value::I32(self as i32)
	}
	fn from_typed_value(_: sp_sandbox::Value) -> Option<Self> {
		debug_assert!(false, "We will never receive a ReturnCode but only send it to wasm.");
		None
	}
}

impl From<ExecReturnValue> for ReturnCode {
	fn from(from: ExecReturnValue) -> Self {
		if from.flags.contains(ReturnFlags::REVERT) {
			Self::CalleeReverted
		} else {
			Self::Success
		}
	}
}

/// The data passed through when a contract uses `seal_return`.
struct ReturnData {
	/// The flags as passed through by the contract. They are still unchecked and
	/// will later be parsed into a `ReturnFlags` bitflags struct.
	flags: u32,
	/// The output buffer passed by the contract as return data.
	data: Vec<u8>,
}

/// Enumerates all possible reasons why a trap was generated.
///
/// This is either used to supply the caller with more information about why an error
/// occurred (the SupervisorError variant).
/// The other case is where the trap does not constitute an error but rather was invoked
/// as a quick way to terminate the application (all other variants).
enum TrapReason {
	/// The supervisor trapped the contract because of an error condition occurred during
	/// execution in privileged code.
	SupervisorError(DispatchError),
	/// Signals that trap was generated in response to call `seal_return` host function.
	Return(ReturnData),
	/// Signals that a trap was generated in response to a successful call to the
	/// `seal_terminate` host function.
	Termination,
	/// Signals that a trap was generated because of a successful restoration.
	Restoration,
}

#[cfg_attr(test, derive(Debug, PartialEq, Eq))]
#[derive(Copy, Clone)]
pub enum RuntimeToken {
	/// Charge the gas meter with the cost of a metering block. The charged costs are
	/// the supplied cost of the block plus the overhead of the metering itself.
	MeteringBlock(u32),
	/// Weight of calling `seal_caller`.
	Caller,
	/// Weight of calling `seal_address`.
	Address,
	/// Weight of calling `seal_gas_left`.
	GasLeft,
	/// Weight of calling `seal_balance`.
	Balance,
	/// Weight of calling `seal_value_transferred`.
	ValueTransferred,
	/// Weight of calling `seal_minimum_balance`.
	MinimumBalance,
	/// Weight of calling `seal_tombstone_deposit`.
	TombstoneDeposit,
	/// Weight of calling `seal_rent_allowance`.
	RentAllowance,
	/// Weight of calling `seal_block_number`.
	BlockNumber,
	/// Weight of calling `seal_now`.
	Now,
	/// Weight of calling `seal_weight_to_fee`.
	WeightToFee,
	/// Weight of calling `seal_input` without the weight of copying the input.
	InputBase,
	/// Weight of copying the input data for the given size.
	InputCopyOut(u32),
	/// Weight of calling `seal_return` for the given output size.
	Return(u32),
	/// Weight of calling `seal_terminate`.
	Terminate,
	/// Weight of calling `seal_restore_to` per number of supplied delta entries.
	RestoreTo(u32),
	/// Weight of calling `seal_random`. It includes the weight for copying the subject.
	Random,
	/// Weight of calling `seal_reposit_event` with the given number of topics and event size.
	DepositEvent{num_topic: u32, len: u32},
	/// Weight of calling `seal_set_rent_allowance`.
	SetRentAllowance,
	/// Weight of calling `seal_set_storage` for the given storage item size.
	SetStorage(u32),
	/// Weight of calling `seal_clear_storage`.
	ClearStorage,
	/// Weight of calling `seal_get_storage` without output weight.
	GetStorageBase,
	/// Weight of an item received via `seal_get_storage` for the given size.
	GetStorageCopyOut(u32),
	/// Weight of calling `seal_transfer`.
	Transfer,
	/// Weight of calling `seal_call` for the given input size.
	CallBase(u32),
	/// Weight of the transfer performed during a call.
	CallSurchargeTransfer,
	/// Weight of output received through `seal_call` for the given size.
	CallCopyOut(u32),
	/// Weight of calling `seal_instantiate` for the given input and salt without output weight.
	/// This includes the transfer as an instantiate without a value will always be below
	/// the existential deposit and is disregarded as corner case.
	InstantiateBase{input_data_len: u32, salt_len: u32},
	/// Weight of output received through `seal_instantiate` for the given size.
	InstantiateCopyOut(u32),
	/// Weight of calling `seal_hash_sha_256` for the given input size.
	HashSha256(u32),
	/// Weight of calling `seal_hash_keccak_256` for the given input size.
	HashKeccak256(u32),
	/// Weight of calling `seal_hash_blake2_256` for the given input size.
	HashBlake256(u32),
	/// Weight of calling `seal_hash_blake2_128` for the given input size.
	HashBlake128(u32),
}

impl<T: Trait> Token<T> for RuntimeToken
where
	T::AccountId: UncheckedFrom<T::Hash>, T::AccountId: AsRef<[u8]>
{
	type Metadata = HostFnWeights<T>;

	fn calculate_amount(&self, s: &Self::Metadata) -> Gas {
		use self::RuntimeToken::*;
		match *self {
			MeteringBlock(amount) => s.gas.saturating_add(amount.into()),
			Caller => s.caller,
			Address => s.address,
			GasLeft => s.gas_left,
			Balance => s.balance,
			ValueTransferred => s.value_transferred,
			MinimumBalance => s.minimum_balance,
			TombstoneDeposit => s.tombstone_deposit,
			RentAllowance => s.rent_allowance,
			BlockNumber => s.block_number,
			Now => s.now,
			WeightToFee => s.weight_to_fee,
			InputBase => s.input,
			InputCopyOut(len) => s.input_per_byte.saturating_mul(len.into()),
			Return(len) => s.r#return
				.saturating_add(s.return_per_byte.saturating_mul(len.into())),
			Terminate => s.terminate,
			RestoreTo(delta) => s.restore_to
				.saturating_add(s.restore_to_per_delta.saturating_mul(delta.into())),
			Random => s.random,
			DepositEvent{num_topic, len} => s.deposit_event
				.saturating_add(s.deposit_event_per_topic.saturating_mul(num_topic.into()))
				.saturating_add(s.deposit_event_per_byte.saturating_mul(len.into())),
			SetRentAllowance => s.set_rent_allowance,
			SetStorage(len) => s.set_storage
				.saturating_add(s.set_storage_per_byte.saturating_mul(len.into())),
			ClearStorage => s.clear_storage,
			GetStorageBase => s.get_storage,
			GetStorageCopyOut(len) => s.get_storage_per_byte.saturating_mul(len.into()),
			Transfer => s.transfer,
			CallBase(len) => s.call
				.saturating_add(s.call_per_input_byte.saturating_mul(len.into())),
			CallSurchargeTransfer => s.call_transfer_surcharge,
			CallCopyOut(len) => s.call_per_output_byte.saturating_mul(len.into()),
			InstantiateBase{input_data_len, salt_len} => s.instantiate
				.saturating_add(s.instantiate_per_input_byte.saturating_mul(input_data_len.into()))
				.saturating_add(s.instantiate_per_salt_byte.saturating_mul(salt_len.into())),
			InstantiateCopyOut(len) => s.instantiate_per_output_byte
				.saturating_mul(len.into()),
			HashSha256(len) => s.hash_sha2_256
				.saturating_add(s.hash_sha2_256_per_byte.saturating_mul(len.into())),
			HashKeccak256(len) => s.hash_keccak_256
				.saturating_add(s.hash_keccak_256_per_byte.saturating_mul(len.into())),
			HashBlake256(len) => s.hash_blake2_256
				.saturating_add(s.hash_blake2_256_per_byte.saturating_mul(len.into())),
			HashBlake128(len) => s.hash_blake2_128
				.saturating_add(s.hash_blake2_128_per_byte.saturating_mul(len.into())),
		}
	}
}

/// This is only appropriate when writing out data of constant size that does not depend on user
/// input. In this case the costs for this copy was already charged as part of the token at
/// the beginning of the API entry point.
fn already_charged(_: u32) -> Option<RuntimeToken> {
	None
}

/// Finds duplicates in a given vector.
///
/// This function has complexity of O(n log n) and no additional memory is required, although
/// the order of items is not preserved.
fn has_duplicates<T: PartialEq + AsRef<[u8]>>(items: &mut Vec<T>) -> bool {
	// Sort the vector
	items.sort_by(|a, b| {
		Ord::cmp(a.as_ref(), b.as_ref())
	});
	// And then find any two consecutive equal elements.
	items.windows(2).any(|w| {
		match w {
			&[ref a, ref b] => a == b,
			_ => false,
		}
	})
}

/// Can only be used for one call.
pub struct Runtime<'a, E: Ext + 'a> {
	ext: &'a mut E,
	input_data: Option<Vec<u8>>,
	schedule: &'a Schedule<E::T>,
	memory: sp_sandbox::Memory,
	gas_meter: &'a mut GasMeter<E::T>,
	trap_reason: Option<TrapReason>,
}

impl<'a, E> Runtime<'a, E>
where
	E: Ext + 'a,
	<E::T as frame_system::Trait>::AccountId:
		UncheckedFrom<<E::T as frame_system::Trait>::Hash> + AsRef<[u8]>
{
	pub fn new(
		ext: &'a mut E,
		input_data: Vec<u8>,
		schedule: &'a Schedule<E::T>,
		memory: sp_sandbox::Memory,
		gas_meter: &'a mut GasMeter<E::T>,
	) -> Self {
		Runtime {
			ext,
			input_data: Some(input_data),
			schedule,
			memory,
			gas_meter,
			trap_reason: None,
		}
	}

	/// Converts the sandbox result and the runtime state into the execution outcome.
	///
	/// It evaluates information stored in the `trap_reason` variable of the runtime and
	/// bases the outcome on the value if this variable. Only if `trap_reason` is `None`
	/// the result of the sandbox is evaluated.
	pub fn to_execution_result(
		self,
		sandbox_result: Result<sp_sandbox::ReturnValue, sp_sandbox::Error>,
	) -> ExecResult {
		// If a trap reason is set we base our decision solely on that.
		if let Some(trap_reason) = self.trap_reason {
			return match trap_reason {
				// The trap was the result of the execution `return` host function.
				TrapReason::Return(ReturnData{ flags, data }) => {
					let flags = ReturnFlags::from_bits(flags).ok_or_else(||
						"used reserved bit in return flags"
					)?;
					Ok(ExecReturnValue {
						flags,
						data,
					})
				},
				TrapReason::Termination => {
					Ok(ExecReturnValue {
						flags: ReturnFlags::empty(),
						data: Vec::new(),
					})
				},
				TrapReason::Restoration => {
					Ok(ExecReturnValue {
						flags: ReturnFlags::empty(),
						data: Vec::new(),
					})
				},
				TrapReason::SupervisorError(error) => Err(error)?,
			}
		}

		// Check the exact type of the error.
		match sandbox_result {
			// No traps were generated. Proceed normally.
			Ok(_) => {
				Ok(ExecReturnValue { flags: ReturnFlags::empty(), data: Vec::new() })
			}
			// `Error::Module` is returned only if instantiation or linking failed (i.e.
			// wasm binary tried to import a function that is not provided by the host).
			// This shouldn't happen because validation process ought to reject such binaries.
			//
			// Because panics are really undesirable in the runtime code, we treat this as
			// a trap for now. Eventually, we might want to revisit this.
			Err(sp_sandbox::Error::Module) =>
				Err("validation error")?,
			// Any other kind of a trap should result in a failure.
			Err(sp_sandbox::Error::Execution) | Err(sp_sandbox::Error::OutOfBounds) =>
				Err(Error::<E::T>::ContractTrapped)?
		}
	}

	/// Charge the gas meter with the specified token.
	///
	/// Returns `Err(HostError)` if there is not enough gas.
	fn charge_gas<Tok>(&mut self, token: Tok) -> Result<(), sp_sandbox::HostError>
	where
		Tok: Token<E::T, Metadata=HostFnWeights<E::T>>,
	{
		match self.gas_meter.charge(&self.schedule.host_fn_weights, token) {
			GasMeterResult::Proceed => Ok(()),
			GasMeterResult::OutOfGas =>  {
				self.trap_reason = Some(
					TrapReason::SupervisorError(Error::<E::T>::OutOfGas.into())
				);
				Err(sp_sandbox::HostError)
			},
		}
	}

	/// Read designated chunk from the sandbox memory.
	///
	/// Returns `Err` if one of the following conditions occurs:
	///
	/// - requested buffer is not within the bounds of the sandbox memory.
	fn read_sandbox_memory(&mut self, ptr: u32, len: u32)
	-> Result<Vec<u8>, sp_sandbox::HostError>
	{
		let mut buf = vec![0u8; len as usize];
		self.memory.get(ptr, buf.as_mut_slice())
			.map_err(|_| self.store_err(Error::<E::T>::OutOfBounds))?;
		Ok(buf)
	}

	/// Read designated chunk from the sandbox memory into the supplied buffer.
	///
	/// Returns `Err` if one of the following conditions occurs:
	///
	/// - requested buffer is not within the bounds of the sandbox memory.
	fn read_sandbox_memory_into_buf(&mut self, ptr: u32, buf: &mut [u8])
	-> Result<(), sp_sandbox::HostError>
	{
		self.memory.get(ptr, buf).map_err(|_| self.store_err(Error::<E::T>::OutOfBounds))
	}

	/// Read designated chunk from the sandbox memory and attempt to decode into the specified type.
	///
	/// Returns `Err` if one of the following conditions occurs:
	///
	/// - requested buffer is not within the bounds of the sandbox memory.
	/// - the buffer contents cannot be decoded as the required type.
	fn read_sandbox_memory_as<D: Decode>(&mut self, ptr: u32, len: u32)
	-> Result<D, sp_sandbox::HostError>
	{
		let buf = self.read_sandbox_memory(ptr, len)?;
		D::decode(&mut &buf[..]).map_err(|_| self.store_err(Error::<E::T>::DecodingFailed))
	}

	/// Write the given buffer to the designated location in the sandbox memory.
	///
	/// Returns `Err` if one of the following conditions occurs:
	///
	/// - designated area is not within the bounds of the sandbox memory.
	fn write_sandbox_memory(&mut self, ptr: u32, buf: &[u8]) -> Result<(), sp_sandbox::HostError> {
		self.memory.set(ptr, buf).map_err(|_| self.store_err(Error::<E::T>::OutOfBounds))
	}

	/// Write the given buffer and its length to the designated locations in sandbox memory and
	/// charge gas according to the token returned by `create_token`.
	//
	/// `out_ptr` is the location in sandbox memory where `buf` should be written to.
	/// `out_len_ptr` is an in-out location in sandbox memory. It is read to determine the
	/// length of the buffer located at `out_ptr`. If that buffer is large enough the actual
	/// `buf.len()` is written to this location.
	///
	/// If `out_ptr` is set to the sentinel value of `u32::max_value()` and `allow_skip` is true the
	/// operation is skipped and `Ok` is returned. This is supposed to help callers to make copying
	/// output optional. For example to skip copying back the output buffer of an `seal_call`
	/// when the caller is not interested in the result.
	///
	/// `create_token` can optionally instruct this function to charge the gas meter with the token
	/// it returns. `create_token` receives the variable amount of bytes that are about to be copied by
	/// this function.
	///
	/// In addition to the error conditions of `write_sandbox_memory` this functions returns
	/// `Err` if the size of the buffer located at `out_ptr` is too small to fit `buf`.
	fn write_sandbox_output(
		&mut self,
		out_ptr: u32,
		out_len_ptr: u32,
		buf: &[u8],
		allow_skip: bool,
		create_token: impl FnOnce(u32) -> Option<RuntimeToken>,
	) -> Result<(), sp_sandbox::HostError>
	{
		if allow_skip && out_ptr == u32::max_value() {
			return Ok(());
		}

		let buf_len = buf.len() as u32;
		let len: u32 = self.read_sandbox_memory_as(out_len_ptr, 4)?;

		if len < buf_len {
			Err(self.store_err(Error::<E::T>::OutputBufferTooSmall))?
		}

		if let Some(token) = create_token(buf_len) {
			self.charge_gas(token)?;
		}

		self.memory.set(out_ptr, buf).and_then(|_| {
			self.memory.set(out_len_ptr, &buf_len.encode())
		})
		.map_err(|_| self.store_err(Error::<E::T>::OutOfBounds))?;

		Ok(())
	}

	/// Computes the given hash function on the supplied input.
	///
	/// Reads from the sandboxed input buffer into an intermediate buffer.
	/// Returns the result directly to the output buffer of the sandboxed memory.
	///
	/// It is the callers responsibility to provide an output buffer that
	/// is large enough to hold the expected amount of bytes returned by the
	/// chosen hash function.
	///
	/// # Note
	///
	/// The `input` and `output` buffers may overlap.
	fn compute_hash_on_intermediate_buffer<F, R>(
		&mut self,
		hash_fn: F,
		input_ptr: u32,
		input_len: u32,
		output_ptr: u32,
	) -> Result<(), sp_sandbox::HostError>
	where
		F: FnOnce(&[u8]) -> R,
		R: AsRef<[u8]>,
	{
		// Copy input into supervisor memory.
		let input = self.read_sandbox_memory(input_ptr, input_len)?;
		// Compute the hash on the input buffer using the given hash function.
		let hash = hash_fn(&input);
		// Write the resulting hash back into the sandboxed output buffer.
		self.write_sandbox_memory(output_ptr, hash.as_ref())?;
		Ok(())
	}

	/// Stores a DispatchError returned from an Ext function into the trap_reason.
	///
	/// This allows through supervisor generated errors to the caller.
	fn store_err<Error>(&mut self, err: Error) -> sp_sandbox::HostError
	where
		Error: Into<DispatchError>,
	{
		self.trap_reason = Some(TrapReason::SupervisorError(err.into()));
		sp_sandbox::HostError
	}

	/// Used by Runtime API that calls into other contracts.
	///
	/// Those need to transform the the `ExecResult` returned from the execution into
	/// a `ReturnCode`. If this conversion fails because the `ExecResult` constitutes a
	/// a fatal error then this error is stored in the `ExecutionContext` so it can be
	/// extracted for display in the UI.
	fn map_exec_result(&mut self, result: ExecResult) -> Result<ReturnCode, sp_sandbox::HostError> {
		match Self::exec_into_return_code(result) {
			Ok(code) => Ok(code),
			Err(err) => Err(self.store_err(err)),
		}
	}

	/// Try to convert an error into a `ReturnCode`.
	///
	/// Used to decide between fatal and non-fatal errors.
	fn map_dispatch_result<T>(&mut self, result: Result<T, DispatchError>)
	-> Result<ReturnCode, sp_sandbox::HostError>
	{
		let err = if let Err(err) = result {
			err
		} else {
			return Ok(ReturnCode::Success)
		};

		match Self::err_into_return_code(err) {
			Ok(code) => Ok(code),
			Err(err) => Err(self.store_err(err)),
		}
	}

	/// Fallible conversion of `DispatchError` to `ReturnCode`.
	fn err_into_return_code(from: DispatchError) -> Result<ReturnCode, DispatchError> {
		use ReturnCode::*;

		let below_sub = Error::<E::T>::BelowSubsistenceThreshold.into();
		let transfer_failed = Error::<E::T>::TransferFailed.into();
		let not_funded = Error::<E::T>::NewContractNotFunded.into();
		let no_code = Error::<E::T>::CodeNotFound.into();
		let invalid_contract = Error::<E::T>::NotCallable.into();

		match from {
			x if x == below_sub => Ok(BelowSubsistenceThreshold),
			x if x == transfer_failed => Ok(TransferFailed),
			x if x == not_funded => Ok(NewContractNotFunded),
			x if x == no_code => Ok(CodeNotFound),
			x if x == invalid_contract => Ok(NotCallable),
			err => Err(err)
		}
	}

	/// Fallible conversion of a `ExecResult` to `ReturnCode`.
	fn exec_into_return_code(from: ExecResult) -> Result<ReturnCode, DispatchError> {
		use pallet_contracts_primitives::ErrorOrigin::Callee;

		let ExecError { error, origin } = match from {
			Ok(retval) => return Ok(retval.into()),
			Err(err) => err,
		};

		match (error, origin) {
			(_, Callee) => Ok(ReturnCode::CalleeTrapped),
			(err, _) => Self::err_into_return_code(err)
		}
	}
}

// ***********************************************************
// * AFTER MAKING A CHANGE MAKE SURE TO UPDATE COMPLEXITY.MD *
// ***********************************************************

// Define a function `fn init_env<E: Ext>() -> HostFunctionSet<E>` that returns
// a function set which can be imported by an executed contract.
//
// # Note
//
// Any input that leads to a out of bound error (reading or writing) or failing to decode
// data passed to the supervisor will lead to a trap. This is not documented explicitly
// for every function.
define_env!(Env, <E: Ext>,

	// Account for used gas. Traps if gas used is greater than gas limit.
	//
	// NOTE: This is a implementation defined call and is NOT a part of the public API.
	// This call is supposed to be called only by instrumentation injected code.
	//
	// - amount: How much gas is used.
	gas(ctx, amount: u32) => {
		ctx.charge_gas(RuntimeToken::MeteringBlock(amount))?;
		Ok(())
	},

	// Set the value at the given key in the contract storage.
	//
	// The value length must not exceed the maximum defined by the contracts module parameters.
	// Storing an empty value is disallowed.
	//
	// # Parameters
	//
	// - `key_ptr`: pointer into the linear memory where the location to store the value is placed.
	// - `value_ptr`: pointer into the linear memory where the value to set is placed.
	// - `value_len`: the length of the value in bytes.
	//
	// # Traps
	//
	// - If value length exceeds the configured maximum value length of a storage entry.
	// - Upon trying to set an empty storage entry (value length is 0).
	seal_set_storage(ctx, key_ptr: u32, value_ptr: u32, value_len: u32) => {
		ctx.charge_gas(RuntimeToken::SetStorage(value_len))?;
		if value_len > ctx.ext.max_value_size() {
			Err(ctx.store_err(Error::<E::T>::ValueTooLarge))?;
		}
		let mut key: StorageKey = [0; 32];
		ctx.read_sandbox_memory_into_buf(key_ptr, &mut key)?;
		let value = Some(ctx.read_sandbox_memory(value_ptr, value_len)?);
		ctx.ext.set_storage(key, value);
		Ok(())
	},

	// Clear the value at the given key in the contract storage.
	//
	// # Parameters
	//
	// - `key_ptr`: pointer into the linear memory where the location to clear the value is placed.
	seal_clear_storage(ctx, key_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::ClearStorage)?;
		let mut key: StorageKey = [0; 32];
		ctx.read_sandbox_memory_into_buf(key_ptr, &mut key)?;
		ctx.ext.set_storage(key, None);
		Ok(())
	},

	// Retrieve the value under the given key from storage.
	//
	// # Parameters
	//
	// - `key_ptr`: pointer into the linear memory where the key of the requested value is placed.
	// - `out_ptr`: pointer to the linear memory where the value is written to.
	// - `out_len_ptr`: in-out pointer into linear memory where the buffer length
	//   is read from and the value length is written to.
	//
	// # Errors
	//
	// `ReturnCode::KeyNotFound`
	seal_get_storage(ctx, key_ptr: u32, out_ptr: u32, out_len_ptr: u32) -> ReturnCode => {
		ctx.charge_gas(RuntimeToken::GetStorageBase)?;
		let mut key: StorageKey = [0; 32];
		ctx.read_sandbox_memory_into_buf(key_ptr, &mut key)?;
		if let Some(value) = ctx.ext.get_storage(&key) {
			ctx.write_sandbox_output(out_ptr, out_len_ptr, &value, false, |len| {
				Some(RuntimeToken::GetStorageCopyOut(len))
			})?;
			Ok(ReturnCode::Success)
		} else {
			Ok(ReturnCode::KeyNotFound)
		}
	},

	// Transfer some value to another account.
	//
	// # Parameters
	//
	// - account_ptr: a pointer to the address of the beneficiary account
	//   Should be decodable as an `T::AccountId`. Traps otherwise.
	// - account_len: length of the address buffer.
	// - value_ptr: a pointer to the buffer with value, how much value to send.
	//   Should be decodable as a `T::Balance`. Traps otherwise.
	// - value_len: length of the value buffer.
	//
	// # Errors
	//
	// `ReturnCode::BelowSubsistenceThreshold`
	// `ReturnCode::TransferFailed`
	seal_transfer(
		ctx,
		account_ptr: u32,
		account_len: u32,
		value_ptr: u32,
		value_len: u32
	) -> ReturnCode => {
		ctx.charge_gas(RuntimeToken::Transfer)?;
		let callee: <<E as Ext>::T as frame_system::Trait>::AccountId =
			ctx.read_sandbox_memory_as(account_ptr, account_len)?;
		let value: BalanceOf<<E as Ext>::T> =
			ctx.read_sandbox_memory_as(value_ptr, value_len)?;

		let result = ctx.ext.transfer(&callee, value);
		ctx.map_dispatch_result(result)
	},

	// Make a call to another contract.
	//
	// The callees output buffer is copied to `output_ptr` and its length to `output_len_ptr`.
	// The copy of the output buffer can be skipped by supplying the sentinel value
	// of `u32::max_value()` to `output_ptr`.
	//
	// # Parameters
	//
	// - callee_ptr: a pointer to the address of the callee contract.
	//   Should be decodable as an `T::AccountId`. Traps otherwise.
	// - callee_len: length of the address buffer.
	// - gas: how much gas to devote to the execution.
	// - value_ptr: a pointer to the buffer with value, how much value to send.
	//   Should be decodable as a `T::Balance`. Traps otherwise.
	// - value_len: length of the value buffer.
	// - input_data_ptr: a pointer to a buffer to be used as input data to the callee.
	// - input_data_len: length of the input data buffer.
	// - output_ptr: a pointer where the output buffer is copied to.
	// - output_len_ptr: in-out pointer to where the length of the buffer is read from
	//   and the actual length is written to.
	//
	// # Errors
	//
	// An error means that the call wasn't successful output buffer is returned unless
	// stated otherwise.
	//
	// `ReturnCode::CalleeReverted`: Output buffer is returned.
	// `ReturnCode::CalleeTrapped`
	// `ReturnCode::BelowSubsistenceThreshold`
	// `ReturnCode::TransferFailed`
	// `ReturnCode::NotCallable`
	seal_call(
		ctx,
		callee_ptr: u32,
		callee_len: u32,
		gas: u64,
		value_ptr: u32,
		value_len: u32,
		input_data_ptr: u32,
		input_data_len: u32,
		output_ptr: u32,
		output_len_ptr: u32
	) -> ReturnCode => {
		ctx.charge_gas(RuntimeToken::CallBase(input_data_len))?;
		let callee: <<E as Ext>::T as frame_system::Trait>::AccountId =
			ctx.read_sandbox_memory_as(callee_ptr, callee_len)?;
		let value: BalanceOf<<E as Ext>::T> = ctx.read_sandbox_memory_as(value_ptr, value_len)?;
		let input_data = ctx.read_sandbox_memory(input_data_ptr, input_data_len)?;

		if value > 0u32.into() {
			ctx.charge_gas(RuntimeToken::CallSurchargeTransfer)?;
		}

		let nested_gas_limit = if gas == 0 {
			ctx.gas_meter.gas_left()
		} else {
			gas.saturated_into()
		};
		let ext = &mut ctx.ext;
		let call_outcome = ctx.gas_meter.with_nested(nested_gas_limit, |nested_meter| {
			match nested_meter {
				Some(nested_meter) => {
					ext.call(
						&callee,
						value,
						nested_meter,
						input_data,
					)
				}
				// there is not enough gas to allocate for the nested call.
				None => Err(Error::<<E as Ext>::T>::OutOfGas.into()),
			}
		});

		if let Ok(output) = &call_outcome {
			ctx.write_sandbox_output(output_ptr, output_len_ptr, &output.data, true, |len| {
				Some(RuntimeToken::CallCopyOut(len))
			})?;
		}
		ctx.map_exec_result(call_outcome)
	},

	// Instantiate a contract with the specified code hash.
	//
	// This function creates an account and executes the constructor defined in the code specified
	// by the code hash. The address of this new account is copied to `address_ptr` and its length
	// to `address_len_ptr`. The constructors output buffer is copied to `output_ptr` and its
	// length to `output_len_ptr`. The copy of the output buffer and address can be skipped by
	// supplying the sentinel value of `u32::max_value()` to `output_ptr` or `address_ptr`.
	//
	// After running the constructor it is verfied that the contract account holds at
	// least the subsistence threshold. If that is not the case the instantion fails and
	// the contract is not created.
	//
	// # Parameters
	//
	// - code_hash_ptr: a pointer to the buffer that contains the initializer code.
	// - code_hash_len: length of the initializer code buffer.
	// - gas: how much gas to devote to the execution of the initializer code.
	// - value_ptr: a pointer to the buffer with value, how much value to send.
	//   Should be decodable as a `T::Balance`. Traps otherwise.
	// - value_len: length of the value buffer.
	// - input_data_ptr: a pointer to a buffer to be used as input data to the initializer code.
	// - input_data_len: length of the input data buffer.
	// - address_ptr: a pointer where the new account's address is copied to.
	// - address_len_ptr: in-out pointer to where the length of the buffer is read from
	//		and the actual length is written to.
	// - output_ptr: a pointer where the output buffer is copied to.
	// - output_len_ptr: in-out pointer to where the length of the buffer is read from
	//   and the actual length is written to.
	// - salt_ptr: Pointer to raw bytes used for address deriviation. See `fn contract_address`.
	// - salt_len: length in bytes of the supplied salt.
	//
	// # Errors
	//
	// Please consult the `ReturnCode` enum declaration for more information on those
	// errors. Here we only note things specific to this function.
	//
	// An error means that the account wasn't created and no address or output buffer
	// is returned unless stated otherwise.
	//
	// `ReturnCode::CalleeReverted`: Output buffer is returned.
	// `ReturnCode::CalleeTrapped`
	// `ReturnCode::BelowSubsistenceThreshold`
	// `ReturnCode::TransferFailed`
	// `ReturnCode::NewContractNotFunded`
	// `ReturnCode::CodeNotFound`
	seal_instantiate(
		ctx,
		code_hash_ptr: u32,
		code_hash_len: u32,
		gas: u64,
		value_ptr: u32,
		value_len: u32,
		input_data_ptr: u32,
		input_data_len: u32,
		address_ptr: u32,
		address_len_ptr: u32,
		output_ptr: u32,
		output_len_ptr: u32,
		salt_ptr: u32,
		salt_len: u32
	) -> ReturnCode => {
		ctx.charge_gas(RuntimeToken::InstantiateBase {input_data_len, salt_len})?;
		let code_hash: CodeHash<<E as Ext>::T> =
			ctx.read_sandbox_memory_as(code_hash_ptr, code_hash_len)?;
		let value: BalanceOf<<E as Ext>::T> = ctx.read_sandbox_memory_as(value_ptr, value_len)?;
		let input_data = ctx.read_sandbox_memory(input_data_ptr, input_data_len)?;
		let salt = ctx.read_sandbox_memory(salt_ptr, salt_len)?;

		let nested_gas_limit = if gas == 0 {
			ctx.gas_meter.gas_left()
		} else {
			gas.saturated_into()
		};
		let ext = &mut ctx.ext;
		let instantiate_outcome = ctx.gas_meter.with_nested(nested_gas_limit, |nested_meter| {
			match nested_meter {
				Some(nested_meter) => {
					ext.instantiate(
						&code_hash,
						value,
						nested_meter,
						input_data,
						&salt,
					)
				}
				// there is not enough gas to allocate for the nested call.
				None => Err(Error::<<E as Ext>::T>::OutOfGas.into()),
			}
		});
		if let Ok((address, output)) = &instantiate_outcome {
			if !output.flags.contains(ReturnFlags::REVERT) {
				ctx.write_sandbox_output(
					address_ptr, address_len_ptr, &address.encode(), true, already_charged,
				)?;
			}
			ctx.write_sandbox_output(output_ptr, output_len_ptr, &output.data, true, |len| {
				Some(RuntimeToken::InstantiateCopyOut(len))
			})?;
		}
		ctx.map_exec_result(instantiate_outcome.map(|(_id, retval)| retval))
	},

	// Remove the calling account and transfer remaining balance.
	//
	// This function never returns. Either the termination was successful and the
	// execution of the destroyed contract is halted. Or it failed during the termination
	// which is considered fatal and results in a trap + rollback.
	//
	// - beneficiary_ptr: a pointer to the address of the beneficiary account where all
	//   where all remaining funds of the caller are transfered.
	//   Should be decodable as an `T::AccountId`. Traps otherwise.
	// - beneficiary_len: length of the address buffer.
	//
	// # Traps
	//
	// - The contract is live i.e is already on the call stack.
	seal_terminate(
		ctx,
		beneficiary_ptr: u32,
		beneficiary_len: u32
	) => {
		ctx.charge_gas(RuntimeToken::Terminate)?;
		let beneficiary: <<E as Ext>::T as frame_system::Trait>::AccountId =
			ctx.read_sandbox_memory_as(beneficiary_ptr, beneficiary_len)?;

		if let Ok(_) = ctx.ext.terminate(&beneficiary).map_err(|e| ctx.store_err(e)) {
			ctx.trap_reason = Some(TrapReason::Termination);
		}
		Err(sp_sandbox::HostError)
	},

	seal_input(ctx, buf_ptr: u32, buf_len_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::InputBase)?;
		if let Some(input) = ctx.input_data.take() {
			ctx.write_sandbox_output(buf_ptr, buf_len_ptr, &input, false, |len| {
				Some(RuntimeToken::InputCopyOut(len))
			})
		} else {
			Err(sp_sandbox::HostError)
		}
	},

	// Cease contract execution and save a data buffer as a result of the execution.
	//
	// This function never retuns as it stops execution of the caller.
	// This is the only way to return a data buffer to the caller. Returning from
	// execution without calling this function is equivalent to calling:
	// ```
	// seal_return(0, 0, 0);
	// ```
	//
	// The flags argument is a bitfield that can be used to signal special return
	// conditions to the supervisor:
	// --- lsb ---
	// bit 0      : REVERT - Revert all storage changes made by the caller.
	// bit [1, 31]: Reserved for future use.
	// --- msb ---
	//
	// Using a reserved bit triggers a trap.
	seal_return(ctx, flags: u32, data_ptr: u32, data_len: u32) => {
		ctx.charge_gas(RuntimeToken::Return(data_len))?;
		ctx.trap_reason = Some(TrapReason::Return(ReturnData {
			flags,
			data: ctx.read_sandbox_memory(data_ptr, data_len)?,
		}));

		// The trap mechanism is used to immediately terminate the execution.
		// This trap should be handled appropriately before returning the result
		// to the user of this crate.
		Err(sp_sandbox::HostError)
	},

	// Stores the address of the caller into the supplied buffer.
	//
	// The value is stored to linear memory at the address pointed to by `out_ptr`.
	// `out_len_ptr` must point to a u32 value that describes the available space at
	// `out_ptr`. This call overwrites it with the size of the value. If the available
	// space at `out_ptr` is less than the size of the value a trap is triggered.
	//
	// If this is a top-level call (i.e. initiated by an extrinsic) the origin address of the
	// extrinsic will be returned. Otherwise, if this call is initiated by another contract then the
	// address of the contract will be returned. The value is encoded as T::AccountId.
	seal_caller(ctx, out_ptr: u32, out_len_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::Caller)?;
		ctx.write_sandbox_output(
			out_ptr, out_len_ptr, &ctx.ext.caller().encode(), false, already_charged
		)
	},

	// Stores the address of the current contract into the supplied buffer.
	//
	// The value is stored to linear memory at the address pointed to by `out_ptr`.
	// `out_len_ptr` must point to a u32 value that describes the available space at
	// `out_ptr`. This call overwrites it with the size of the value. If the available
	// space at `out_ptr` is less than the size of the value a trap is triggered.
	seal_address(ctx, out_ptr: u32, out_len_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::Address)?;
		ctx.write_sandbox_output(
			out_ptr, out_len_ptr, &ctx.ext.address().encode(), false, already_charged
		)
	},

	// Stores the price for the specified amount of gas into the supplied buffer.
	//
	// The value is stored to linear memory at the address pointed to by `out_ptr`.
	// `out_len_ptr` must point to a u32 value that describes the available space at
	// `out_ptr`. This call overwrites it with the size of the value. If the available
	// space at `out_ptr` is less than the size of the value a trap is triggered.
	//
	// The data is encoded as T::Balance.
	//
	// # Note
	//
	// It is recommended to avoid specifying very small values for `gas` as the prices for a single
	// gas can be smaller than one.
	seal_weight_to_fee(ctx, gas: u64, out_ptr: u32, out_len_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::WeightToFee)?;
		ctx.write_sandbox_output(
			out_ptr, out_len_ptr, &ctx.ext.get_weight_price(gas).encode(), false, already_charged
		)
	},

	// Stores the amount of gas left into the supplied buffer.
	//
	// The value is stored to linear memory at the address pointed to by `out_ptr`.
	// `out_len_ptr` must point to a u32 value that describes the available space at
	// `out_ptr`. This call overwrites it with the size of the value. If the available
	// space at `out_ptr` is less than the size of the value a trap is triggered.
	//
	// The data is encoded as Gas.
	seal_gas_left(ctx, out_ptr: u32, out_len_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::GasLeft)?;
		ctx.write_sandbox_output(
			out_ptr, out_len_ptr, &ctx.gas_meter.gas_left().encode(), false, already_charged
		)
	},

	// Stores the balance of the current account into the supplied buffer.
	//
	// The value is stored to linear memory at the address pointed to by `out_ptr`.
	// `out_len_ptr` must point to a u32 value that describes the available space at
	// `out_ptr`. This call overwrites it with the size of the value. If the available
	// space at `out_ptr` is less than the size of the value a trap is triggered.
	//
	// The data is encoded as T::Balance.
	seal_balance(ctx, out_ptr: u32, out_len_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::Balance)?;
		ctx.write_sandbox_output(
			out_ptr, out_len_ptr, &ctx.ext.balance().encode(), false, already_charged
		)
	},

	// Stores the value transferred along with this call or as endowment into the supplied buffer.
	//
	// The value is stored to linear memory at the address pointed to by `out_ptr`.
	// `out_len_ptr` must point to a u32 value that describes the available space at
	// `out_ptr`. This call overwrites it with the size of the value. If the available
	// space at `out_ptr` is less than the size of the value a trap is triggered.
	//
	// The data is encoded as T::Balance.
	seal_value_transferred(ctx, out_ptr: u32, out_len_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::ValueTransferred)?;
		ctx.write_sandbox_output(
			out_ptr, out_len_ptr, &ctx.ext.value_transferred().encode(), false, already_charged
		)
	},

	// Stores a random number for the current block and the given subject into the supplied buffer.
	//
	// The value is stored to linear memory at the address pointed to by `out_ptr`.
	// `out_len_ptr` must point to a u32 value that describes the available space at
	// `out_ptr`. This call overwrites it with the size of the value. If the available
	// space at `out_ptr` is less than the size of the value a trap is triggered.
	//
	// The data is encoded as T::Hash.
	seal_random(ctx, subject_ptr: u32, subject_len: u32, out_ptr: u32, out_len_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::Random)?;
		if subject_len > ctx.schedule.limits.subject_len {
			return Err(sp_sandbox::HostError);
		}
		let subject_buf = ctx.read_sandbox_memory(subject_ptr, subject_len)?;
		ctx.write_sandbox_output(
			out_ptr, out_len_ptr, &ctx.ext.random(&subject_buf).encode(), false, already_charged
		)
	},

	// Load the latest block timestamp into the supplied buffer
	//
	// The value is stored to linear memory at the address pointed to by `out_ptr`.
	// `out_len_ptr` must point to a u32 value that describes the available space at
	// `out_ptr`. This call overwrites it with the size of the value. If the available
	// space at `out_ptr` is less than the size of the value a trap is triggered.
	seal_now(ctx, out_ptr: u32, out_len_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::Now)?;
		ctx.write_sandbox_output(
			out_ptr, out_len_ptr, &ctx.ext.now().encode(), false, already_charged
		)
	},

	// Stores the minimum balance (a.k.a. existential deposit) into the supplied buffer.
	//
	// The data is encoded as T::Balance.
	seal_minimum_balance(ctx, out_ptr: u32, out_len_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::MinimumBalance)?;
		ctx.write_sandbox_output(
			out_ptr, out_len_ptr, &ctx.ext.minimum_balance().encode(), false, already_charged
		)
	},

	// Stores the tombstone deposit into the supplied buffer.
	//
	// The value is stored to linear memory at the address pointed to by `out_ptr`.
	// `out_len_ptr` must point to a u32 value that describes the available space at
	// `out_ptr`. This call overwrites it with the size of the value. If the available
	// space at `out_ptr` is less than the size of the value a trap is triggered.
	//
	// The data is encoded as T::Balance.
	//
	// # Note
	//
	// The tombstone deposit is on top of the existential deposit. So in order for
	// a contract to leave a tombstone the balance of the contract must not go
	// below the sum of existential deposit and the tombstone deposit. The sum
	// is commonly referred as subsistence threshold in code.
	seal_tombstone_deposit(ctx, out_ptr: u32, out_len_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::TombstoneDeposit)?;
		ctx.write_sandbox_output(
			out_ptr, out_len_ptr, &ctx.ext.tombstone_deposit().encode(), false, already_charged
		)
	},

	// Try to restore the given destination contract sacrificing the caller.
	//
	// This function will compute a tombstone hash from the caller's storage and the given code hash
	// and if the hash matches the hash found in the tombstone at the specified address - kill
	// the caller contract and restore the destination contract and set the specified `rent_allowance`.
	// All caller's funds are transfered to the destination.
	//
	// If there is no tombstone at the destination address, the hashes don't match or this contract
	// instance is already present on the contract call stack, a trap is generated.
	//
	// Otherwise, the destination contract is restored. This function is diverging and stops execution
	// even on success.
	//
	// `dest_ptr`, `dest_len` - the pointer and the length of a buffer that encodes `T::AccountId`
	// with the address of the to be restored contract.
	// `code_hash_ptr`, `code_hash_len` - the pointer and the length of a buffer that encodes
	// a code hash of the to be restored contract.
	// `rent_allowance_ptr`, `rent_allowance_len` - the pointer and the length of a buffer that
	// encodes the rent allowance that must be set in the case of successful restoration.
	// `delta_ptr` is the pointer to the start of a buffer that has `delta_count` storage keys
	// laid out sequentially.
	//
	// # Traps
	//
	// - Tombstone hashes do not match
	// - Calling cantract is live i.e is already on the call stack.
	seal_restore_to(
		ctx,
		dest_ptr: u32,
		dest_len: u32,
		code_hash_ptr: u32,
		code_hash_len: u32,
		rent_allowance_ptr: u32,
		rent_allowance_len: u32,
		delta_ptr: u32,
		delta_count: u32
	) => {
		ctx.charge_gas(RuntimeToken::RestoreTo(delta_count))?;
		let dest: <<E as Ext>::T as frame_system::Trait>::AccountId =
			ctx.read_sandbox_memory_as(dest_ptr, dest_len)?;
		let code_hash: CodeHash<<E as Ext>::T> =
			ctx.read_sandbox_memory_as(code_hash_ptr, code_hash_len)?;
		let rent_allowance: BalanceOf<<E as Ext>::T> =
			ctx.read_sandbox_memory_as(rent_allowance_ptr, rent_allowance_len)?;
		let delta = {
			// We can eagerly allocate because we charged for the complete delta count already
			let mut delta = Vec::with_capacity(delta_count as usize);
			let mut key_ptr = delta_ptr;

			for _ in 0..delta_count {
				const KEY_SIZE: usize = 32;

				// Read the delta into the provided buffer and collect it into the buffer.
				let mut delta_key: StorageKey = [0; KEY_SIZE];
				ctx.read_sandbox_memory_into_buf(key_ptr, &mut delta_key)?;
				delta.push(delta_key);

				// Offset key_ptr to the next element.
				key_ptr = key_ptr.checked_add(KEY_SIZE as u32).ok_or_else(|| sp_sandbox::HostError)?;
			}

			delta
		};

		if let Ok(()) = ctx.ext.restore_to(
			dest,
			code_hash,
			rent_allowance,
			delta,
		).map_err(|e| ctx.store_err(e)) {
			ctx.trap_reason = Some(TrapReason::Restoration);
		}
		Err(sp_sandbox::HostError)
	},

	// Deposit a contract event with the data buffer and optional list of topics. There is a limit
	// on the maximum number of topics specified by `event_topics`.
	//
	// - topics_ptr - a pointer to the buffer of topics encoded as `Vec<T::Hash>`. The value of this
	//   is ignored if `topics_len` is set to 0. The topics list can't contain duplicates.
	// - topics_len - the length of the topics buffer. Pass 0 if you want to pass an empty vector.
	// - data_ptr - a pointer to a raw data buffer which will saved along the event.
	// - data_len - the length of the data buffer.
	seal_deposit_event(ctx, topics_ptr: u32, topics_len: u32, data_ptr: u32, data_len: u32) => {
		let num_topic = topics_len
			.checked_div(sp_std::mem::size_of::<TopicOf<E::T>>() as u32)
			.ok_or_else(|| ctx.store_err("Zero sized topics are not allowed"))?;
		ctx.charge_gas(RuntimeToken::DepositEvent {
			num_topic,
			len: data_len,
		})?;
		if data_len > ctx.ext.max_value_size() {
			Err(ctx.store_err(Error::<E::T>::ValueTooLarge))?;
		}

		let mut topics: Vec::<TopicOf<<E as Ext>::T>> = match topics_len {
			0 => Vec::new(),
			_ => ctx.read_sandbox_memory_as(topics_ptr, topics_len)?,
		};

		// If there are more than `event_topics`, then trap.
		if topics.len() > ctx.schedule.limits.event_topics as usize {
			return Err(sp_sandbox::HostError);
		}

		// Check for duplicate topics. If there are any, then trap.
		if has_duplicates(&mut topics) {
			return Err(sp_sandbox::HostError);
		}

		let event_data = ctx.read_sandbox_memory(data_ptr, data_len)?;

		ctx.ext.deposit_event(topics, event_data);

		Ok(())
	},

	// Set rent allowance of the contract
	//
	// - value_ptr: a pointer to the buffer with value, how much to allow for rent
	//   Should be decodable as a `T::Balance`. Traps otherwise.
	// - value_len: length of the value buffer.
	seal_set_rent_allowance(ctx, value_ptr: u32, value_len: u32) => {
		ctx.charge_gas(RuntimeToken::SetRentAllowance)?;
		let value: BalanceOf<<E as Ext>::T> =
			ctx.read_sandbox_memory_as(value_ptr, value_len)?;
		ctx.ext.set_rent_allowance(value);

		Ok(())
	},

	// Stores the rent allowance into the supplied buffer.
	//
	// The value is stored to linear memory at the address pointed to by `out_ptr`.
	// `out_len_ptr` must point to a u32 value that describes the available space at
	// `out_ptr`. This call overwrites it with the size of the value. If the available
	// space at `out_ptr` is less than the size of the value a trap is triggered.
	//
	// The data is encoded as T::Balance.
	seal_rent_allowance(ctx, out_ptr: u32, out_len_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::RentAllowance)?;
		ctx.write_sandbox_output(
			out_ptr, out_len_ptr, &ctx.ext.rent_allowance().encode(), false, already_charged
		)
	},

	// Prints utf8 encoded string from the data buffer.
	// Only available on `--dev` chains.
	// This function may be removed at any time, superseded by a more general contract debugging feature.
	seal_println(ctx, str_ptr: u32, str_len: u32) => {
		let data = ctx.read_sandbox_memory(str_ptr, str_len)?;
		if let Ok(utf8) = core::str::from_utf8(&data) {
			sp_runtime::print(utf8);
		}
		Ok(())
	},

	// Stores the current block number of the current contract into the supplied buffer.
	//
	// The value is stored to linear memory at the address pointed to by `out_ptr`.
	// `out_len_ptr` must point to a u32 value that describes the available space at
	// `out_ptr`. This call overwrites it with the size of the value. If the available
	// space at `out_ptr` is less than the size of the value a trap is triggered.
	seal_block_number(ctx, out_ptr: u32, out_len_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::BlockNumber)?;
		ctx.write_sandbox_output(
			out_ptr, out_len_ptr, &ctx.ext.block_number().encode(), false, already_charged
		)
	},

	// Computes the SHA2 256-bit hash on the given input buffer.
	//
	// Returns the result directly into the given output buffer.
	//
	// # Note
	//
	// - The `input` and `output` buffer may overlap.
	// - The output buffer is expected to hold at least 32 bytes (256 bits).
	// - It is the callers responsibility to provide an output buffer that
	//   is large enough to hold the expected amount of bytes returned by the
	//   chosen hash function.
	//
	// # Parameters
	//
	// - `input_ptr`: the pointer into the linear memory where the input
	//                data is placed.
	// - `input_len`: the length of the input data in bytes.
	// - `output_ptr`: the pointer into the linear memory where the output
	//                 data is placed. The function will write the result
	//                 directly into this buffer.
	seal_hash_sha2_256(ctx, input_ptr: u32, input_len: u32, output_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::HashSha256(input_len))?;
		ctx.compute_hash_on_intermediate_buffer(sha2_256, input_ptr, input_len, output_ptr)
	},

	// Computes the KECCAK 256-bit hash on the given input buffer.
	//
	// Returns the result directly into the given output buffer.
	//
	// # Note
	//
	// - The `input` and `output` buffer may overlap.
	// - The output buffer is expected to hold at least 32 bytes (256 bits).
	// - It is the callers responsibility to provide an output buffer that
	//   is large enough to hold the expected amount of bytes returned by the
	//   chosen hash function.
	//
	// # Parameters
	//
	// - `input_ptr`: the pointer into the linear memory where the input
	//                data is placed.
	// - `input_len`: the length of the input data in bytes.
	// - `output_ptr`: the pointer into the linear memory where the output
	//                 data is placed. The function will write the result
	//                 directly into this buffer.
	seal_hash_keccak_256(ctx, input_ptr: u32, input_len: u32, output_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::HashKeccak256(input_len))?;
		ctx.compute_hash_on_intermediate_buffer(keccak_256, input_ptr, input_len, output_ptr)
	},

	// Computes the BLAKE2 256-bit hash on the given input buffer.
	//
	// Returns the result directly into the given output buffer.
	//
	// # Note
	//
	// - The `input` and `output` buffer may overlap.
	// - The output buffer is expected to hold at least 32 bytes (256 bits).
	// - It is the callers responsibility to provide an output buffer that
	//   is large enough to hold the expected amount of bytes returned by the
	//   chosen hash function.
	//
	// # Parameters
	//
	// - `input_ptr`: the pointer into the linear memory where the input
	//                data is placed.
	// - `input_len`: the length of the input data in bytes.
	// - `output_ptr`: the pointer into the linear memory where the output
	//                 data is placed. The function will write the result
	//                 directly into this buffer.
	seal_hash_blake2_256(ctx, input_ptr: u32, input_len: u32, output_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::HashBlake256(input_len))?;
		ctx.compute_hash_on_intermediate_buffer(blake2_256, input_ptr, input_len, output_ptr)
	},

	// Computes the BLAKE2 128-bit hash on the given input buffer.
	//
	// Returns the result directly into the given output buffer.
	//
	// # Note
	//
	// - The `input` and `output` buffer may overlap.
	// - The output buffer is expected to hold at least 16 bytes (128 bits).
	// - It is the callers responsibility to provide an output buffer that
	//   is large enough to hold the expected amount of bytes returned by the
	//   chosen hash function.
	//
	// # Parameters
	//
	// - `input_ptr`: the pointer into the linear memory where the input
	//                data is placed.
	// - `input_len`: the length of the input data in bytes.
	// - `output_ptr`: the pointer into the linear memory where the output
	//                 data is placed. The function will write the result
	//                 directly into this buffer.
	seal_hash_blake2_128(ctx, input_ptr: u32, input_len: u32, output_ptr: u32) => {
		ctx.charge_gas(RuntimeToken::HashBlake128(input_len))?;
		ctx.compute_hash_on_intermediate_buffer(blake2_128, input_ptr, input_len, output_ptr)
	},
);