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Smart Contracts

Smart Contracts

Changes in NEO3

All transactions in NEO3 are the invocation of the smart contract. In addition to some interop services and OpCode adjustments, NEO3 also features the following changes.

ADD
- Manifest: used to describe the features of the contract and deployed with NEF files
- native contracts: running in the native code rather than in the virtual machine, including NeoToken, GasToken and PolicyToken
- Accessing to network resources: to be added
- System Trigger: triggered when the node receives a new block and currently only triggers the execution of the native contract
- Interop Service: System.Binary.Serialize, System.Binary.Deserialize, System.Contract.Create, System.Contract.Update, System.Contract.Call, System.Contract.CallEx, System.Contract.IsStandard, System.Enumerator.Create, System.Enumerator.Next, System.Enumerator.Value, System.Enumerator.Concat, System.Iterator.Create, System.Iterator.Key, System.Iterator.Keys, System.Iterator.Values, System.Iterator.Concat, System.Json.Serialize, System.Json.Deserialize, System.Runtime.GetScriptContainer, System.Runtime.GetScriptContainer,System.Runtime.GetExecutingScriptHash, System.Runtime.GetCallingScriptHash, System.Runtime.GetEntryScriptHash, System.Runtime.GetInvocationCounter, System.Runtime.GetNotifications, System.Runtime.GasLeft, System.Storage.Find, Neo.Native.Deploy, Neo.Native.Tokens.NEO, Neo.Native.Tokens.GAS, Neo.Native.Policy, Neo.Crypto.ECDsaVerify, Neo.Crypto.ECDsaCheckMultiSig.
UPDATE
- Reduce the system fee for OpCode and interop services
DELETE
- Interop Service:System.ExecutionEngine.GetScriptContainer, System.ExecutionEngine.GetExecutingScriptHash, System.ExecutionEngine.GetCallingScriptHash, System.ExecutionEngine.GetEntryScriptHash, System.Runtime.Serialize, System.Runtime.Deserialize, System.Header.GetIndex, System.Header.GetHash, System.Header.GetPrevHash, System.Header.GetTimestamp, System.Block.GetTransactionCount, System.Block.GetTransactions, System.Block.GetTransaction, System.Transaction.GetHash, System.Contract.GetStorageContext, Neo.Runtime.GetTrigger, Neo.Runtime.CheckWitness, Neo.Runtime.Notify, Neo.Runtime.Log, Neo.Runtime.GetTime, Neo.Runtime.Serialize, Neo.Runtime.Deserialize, Neo.Blockchain.GetHeight, Neo.Blockchain.GetHeader, Neo.Blockchain.GetBlock, Neo.Blockchain.GetTransaction, Neo.Blockchain.GetTransactionHeight, Neo.Blockchain.GetAccount, Neo.Blockchain.GetValidators, Neo.Blockchain.GetAsset, Neo.Blockchain.GetContract, Neo.Header.GetHash, Neo.Header.GetVersion, Neo.Header.GetPrevHash, Neo.Header.GetMerkleRoot, Neo.Header.GetTimestamp, Neo.Header.GetIndex, Neo.Header.GetConsensusData, Neo.Header.GetNextConsensus, Neo.Block.GetTransactionCount , Neo.Block.GetTransactions, Neo.Block.GetTransaction, Neo.Transaction.GetHash, Neo.Transaction.GetType, Neo.Transaction.GetAttributes, Neo.Transaction.GetInputs, Neo.Transaction.GetOutputs, Neo.Transaction.GetReferences, Neo.Transaction.GetUnspentCoins, Neo.Transaction.GetWitnesses, Neo.InvocationTransaction.GetScript, Neo.Witness.GetVerificationScript, Neo.Attribute.GetUsage, Neo.Attribute.GetData, Neo.Input.GetHash, Neo.Input.GetIndex, Neo.Output.GetAssetId, Neo.Output.GetValue, Neo.Output.GetScriptHash, Neo.Account.GetScriptHash , Neo.Account.GetVotes, Neo.Account.GetBalance, Neo.Account.IsStandard, Neo.Asset.Create, Neo.Asset.Renew, Neo.Asset.GetAssetId , Neo.Asset.GetAssetType, Neo.Asset.GetAmount, Neo.Asset.GetAvailable, Neo.Asset.GetPrecision, Neo.Asset.GetOwner, Neo.Asset.GetAdmin, Neo.Asset.GetIssuer, Neo.Contract.Create, Neo.Contract.Migrate, Neo.Contract.Destroy, Neo.Contract.GetScript, Neo.Contract.IsPayable, Neo.Contract.GetStorageContext, Neo.Storage.GetContext , Neo.Storage.GetReadOnlyContext, Neo.Storage.Get, Neo.Storage.Put, Neo.Storage.Delete, Neo.Storage.Find, Neo.StorageContext.AsReadOnly, Neo.Enumerator.Create, Neo.Enumerator.Next, Neo.Enumerator.Value, Neo.Enumerator.Concat, Neo.Iterator.Create, Neo.Iterator.Key, Neo.Iterator.Keys, Neo.Iterator.Values, Neo.Iterator.Concat.

Manifest

Now each contract is required to provide a manifest file to describe its properties, including Groups, Features, ABI, Permissions, Trusts, SafeMethods, as shown below:

{
    "groups": [
        {
            "pubKey": "",
            "signature": ""
        }
    ],
    "features": {
        "storage": false,
        "payable": false
    },
    "abi": {
      "hash": "0x562851057d8afbc08fabc8c438d7cc771aef2195",
      "entrypoint": {
        "name": "main",
        "parameters": [
          {
            "name": "operation",
            "type": "String"
          },
          {
            "name": "args",
            "type": "Array"
          }
        ],
        "returntype": "Any"
      },
      "methods": [
        {
          "name": "name",
          "parameters": [],
          "returntype": "string"
        }
      ],
      "events": [
        {
          "name": "transfered",
          "parameters": [
            {"name": "from","type": "Hash160"},
            {"name": "to","type": "Hash160"},
            {"name": "value","type": "Integer"}
          ]
        }
      ]
    },
    "permissions": [
        {
            "contract": "*",
            "methods": "*"
        }
    ],
    "trusts": "*",
    "safemethods": "*"
}

Groups：Declare the groups to which the contract belongs. Each group is identified by a public key and a signature.
Features：Declare the features of the smart contract. Where the attribute value storage indicates that the contract can access the storage area, and the payable indicates the contract can accept the transfer of assets.
ABI：Declare the interface information about the smart contract, you can refer to NEP-3 for the details. The basic properties of the interface include:
- Hash: the script hash of the contract. It is encoded as a hexadecimal string in big-endian;
- EntryPoint: a Method object which describes the details of the entry point of the contract, including name, parameters, and the value returned;
- Methods: an array of Method objects which describe the details of each method in the contract;
- Events: an array of Event objects which describe the details of each event in the contract.
Based on the ABI information, mutual invocation between contracts can be realized.
Permissions：Declare which contracts may be invoked and which methods are called. If a contract invokes a contract or method that is not declared in the manifest at runtime, the invocation will fail.
Trusts：Declare which contracts or groups can call the contract safely.
SafeMethods：Declare an array containing a set of method names. SafeMethods usually won't modify the storage area, only involved in reading the blockchain data. If a method is marked as safe, the user interface will not give any warnings when it is called by any other contract.

Trigger

Triggers allow contracts to execute different logic depending on the usage scenario.

System Trigger

This type of trigger is newly added in NEO3, which is only used for native contract, such as NEO and GAS. It is triggered when the node receives a new block and currently only triggers the execution of the native contract. After receiving a new block, the node will be triggered by the System Trigger to invoke the onPersist method in all native contracts before the persistence.

This system trigger will not bring any affect to the normal smart contract.
Application Trigger

An application trigger is used to invoke a contract as an application function, which can accept multiple parameters, change blockchain status, and return values of any type. Here is a simple c# smart contract：
```
  public static Object Main(string operation, params object[] args)
  {
    if (Runtime.Trigger == TriggerType.Application)
    {
        if (operation == "FunctionA") return FunctionA(args);
    }  
  }
  public static bool FunctionA(params object[] args)
  {
    //some code  
  }
```
All transactions in NEO3 are the invocation of the smart contract. When a transaction is broadcast and confirmed, the smart contract is executed by the consensus node, and the normal node does not execute the smart contract when forwarding the transaction. Successful execution of a smart contract does not represent the success of the transaction, and the success of the transaction does not determine the success of the smart contract execution.
Verification Trigger

The purpose of the validation trigger is to call the contract as a verification function that accepts multiple arguments and should return a Boolean value indicating the validity of the transaction or block.

When you transfer tokens from account A to account B, the verification contract will be triggered. All the nodes that receive the transaction (including the normal node and the consensus node) will verify the contract of the account A. If the return value is true, the transfer is successful, and fails otherwise.

If the authentication contract fails to execute, the transaction will not be included in the blockchain.

The following code is a simple example of a verification contract. It returns true if condition A is satisfied, indicating the success of the transfer. Otherwise, it returns false and the transfer fails.
```
  using Neo.SmartContract.Framework;
  using Neo.SmartContract.Framework.Neo;

  public static bool Main(byte[] signature)
  {
      if (/*条件A*/)
          return true;
      else
          return false;
  }
```
The following code works the same as above, but with an additional check for the trigger in the runtime. The code of the verification part is executed only when the trigger is a verification trigger, which is of great use in complex smart contracts. If a smart contract implements multiple triggers, the type of triggers should be judged in the Main method.
```
using Neo.SmartContract.Framework;
using Neo.SmartContract.Framework.Neo;

public static bool Main(byte[] signature)
{
    if (Runtime.Trigger == TriggerType.Verification)
    {
        if (/* condition A*/)
                return true;
            else
                return false;
    }  
}
```

Native Contract

Introduction

Native contracts are executed directly in native code, rather than in a virtual machine. The native contract exposes its service name to other contracts for invocation. Currently, available NativeContract includes NeoToken, GasToken, and PolicyToken.

NeoToken

Referred to as NEO, it acts as the governance token which is used to enforce the management of the Neo network and conforms to the NEP-5 standard. It has a hard cap total of 100 million tokens, with the smallest unit of 1, and is not divisible. NEO was pre-mined during the genesis block creation. The specific interface details are as follows：

Method marked * is NEP-5 standard interface.

name： Name of the token

Parameters	none
Return	Type	Description
Return	String	Name of the token
Fee(GAS)	0.00

Example in C# contract

using Neo.SmartContract.Framework;
using Neo.SmartContract.Framework.System;

public static object Main(string method, object[] args)
{
  private static string neoScriptHash = "0x43cf98eddbe047e198a3e5d57006311442a0ca15";
    if (Runtime.Trigger == TriggerType.Application)
    {
        if (method == "neoName") {
          string name = Contract.Call(neoScriptHash.HexToBytes(), "name", new object[]{});
          return name;
        }
    }  
}

Build Script

Using System.Contract.Call to invoke contract:

PUSH0
NEWARRAY
PUSHBYTES4  6e616d65
PUSHBYTES20 0x43cf98eddbe047e198a3e5d57006311442a0ca15
SYSCALL     0x627d5b52

C# code to build the script：

ScriptBuilder sb = new ScriptBuilder()
UInt160 scriptHash = UInt160.Parse("0x43cf98eddbe047e198a3e5d57006311442a0ca15");
sb.EmitPush(0);
sb.Emit(OpCode.NEWARRAY);
sb.EmitPush("name");
sb.EmitPush(scriptHash.ToArray());
sb.EmitSysCall(InteropService.System_Contract_Call);
byte[] script = sb.ToArray();

symbol：Symbol of the token

Parameters none

Return Type Description

String Symbol of the token

Fee(GAS) 0.00
decimals: Decimals of the token

Parameters none

Return Type Description

uint Decimal

Fee(GAS) 0.00
totalSupply*: Total supply

Parameters none

Return Type Description

BigInteger Total supply

Fee(GAS) 0.01
balanceOf: Balance of an account

Parameters Parameter Type Description

account Hash160 ScriptHash of the account
Return Type Description

Integer Balance

Fee(GAS) 0.01

Parameters	none
Return	Type	Description
String	Symbol of the token
Fee(GAS)	0.00

Parameters	none
Return	Type	Description
uint	Decimal
Fee(GAS)	0.00

Parameters	none
Return	Type	Description
BigInteger	Total supply
Fee(GAS)	0.01

Parameters	Parameter	Type	Description
account	Hash160	ScriptHash of the account
Return	Type	Description
Integer	Balance
Fee(GAS)	0.01

transfer: Transfer token from one to another

Parameters	Parameter	Type	Description
	from	Hash160	ScriptHash who want to transfer
	to	Hash160	ScriptHash of the receiver
	amount	Integer	Amount of the token
Return	Type	Description
Return	Boolean	Result, true: success，false: failure
Fee(GAS)	0.08

Example in C# contract

using Neo.SmartContract.Framework;
using Neo.SmartContract.Framework.System;

public static object Main(string method, object[] args)
{
  private static string neoScriptHash = "0x43cf98eddbe047e198a3e5d57006311442a0ca15";
    if (Runtime.Trigger == TriggerType.Application)
    {
        if (method == "transferNeo") {
          byte[] from  = "AesUJTLg93cWMTSzp2snxpBJSCets89ebM".ToScriptHash();
          byte[] to    = "AMhbbwR8r6LuTx5okkZudvvp3LW6Fh1Y7o".ToScriptHash();
          BigInterger value = new BigInteger(100000000);
          bool result = Contract.Call(neoScriptHash.HexToBytes(), "transfer", new Object[]{from, to, value.AsByteArray()});
          return result;
        }
    }  
}

Build Script

Using System.Contract.Call to invoke contract:

PUSHBYTE4   00e1f505
PUSHBYTE20  4101b2a928fd88e1d976fd23c2db25a822338a08
PUSHBYTE20  fd59e6a0e3eee5cd9cea7233f01e1cc9c8b23502
PUSH3
PACK
PUSHBYTES4  7472616e73666572
PUSHBYTES20 0x43cf98eddbe047e198a3e5d57006311442a0ca15
SYSCALL     0x627d5b52

C# code to build the script：

ScriptBuilder sb = new ScriptBuilder()
UInt160 scriptHash = UInt160.Parse("0x43cf98eddbe047e198a3e5d57006311442a0ca15");
UInt160 from = UInt160.Parse("0xfd59e6a0e3eee5cd9cea7233f01e1cc9c8b23502");
UInt160 to = UInt160.Parse("0x4101b2a928fd88e1d976fd23c2db25a822338a08");
long value = 1000000000;
sb.EmitPush(value);
sb.EmitPush(to);
sb.EmitPush(from);
sb.Emit(OpCode.PUSH3);
sb.Emit(OpCode.PACK);
sb.EmitPush("transfer");
sb.EmitPush(scriptHash.ToArray());
sb.EmitSysCall(InteropService.System_Contract_Call);
byte[] script = sb.ToArray();

unClaimGas：Get the amount of GAS unclaimed at the specified height

Parameters	Parameter	Type	Description
	account	Hash160	ScriptHash of the account
	end	Integer	The height to be queried
Return	Type	Description
Return	Integer	GAS unclaimed
Fee(GAS)	0.03

Example in C# contract

using Neo.SmartContract.Framework;
using Neo.SmartContract.Framework.System;

public static object Main(string method, object[] args)
{
private static string neoScriptHash = "0x43cf98eddbe047e198a3e5d57006311442a0ca15";
  if (Runtime.Trigger == TriggerType.Application)
  {
      if (method == "accountUnClaimGas") {
        byte[] account = "AXx1A21wcoXuVxxxggkQChxQP5EGYe6zsN".ToScriptHash();
        int height = 1000000;
        int gas = Contract.Call(neoScriptHash.HexToBytes(), "unClaimGas", new Object[]{account, height});
        return gas;
      }
  }  
}

Build Script

Using System.Contract.Call to invoke contract:

PUSHBYTE3   40420f
PUSHBYTE20  b16c70b94928ddb62f5793fbc98d6245ee308ecd
PUSH2
PACK
PUSHBYTES4  756e436c61696d476173
PUSHBYTES20 0x43cf98eddbe047e198a3e5d57006311442a0ca15
SYSCALL     0x627d5b52

C# code to build the script：

ScriptBuilder sb = new ScriptBuilder()
UInt160 scriptHash = UInt160.Parse("0x43cf98eddbe047e198a3e5d57006311442a0ca15");
UInt160 account = UInt160.Parse("0xb16c70b94928ddb62f5793fbc98d6245ee308ecd");
int height = 1000000
sb.EmitPush(height);
sb.EmitPush(account);
sb.Emit(OpCode.PUSH2);
sb.Emit(OpCode.PACK);
sb.EmitPush("unClaimGas");
sb.EmitPush(scriptHash.ToArray());
sb.EmitSysCall(InteropService.System_Contract_Call);
byte[] script = sb.ToArray();

RegisterValidator：Register to become a candidate for the validator

Parameters Parameter Type Description

pubKey PublicKey Public key of the account

Return Type Description

Boolean Result. true: sucess, false: failure

Fee(GAS) 0.05
getRegisteredValidators：Gets the information of currently registered validators and backup nodes

Parameters none

Return Type Description

Array Public keys of all validators and backup nodes

Fee(GAS) 1.00
getValidators: Get all current validators

Parameters none

Return Type Description

Array Public keys of all current validators

Fee(GAS) 1.00
getNextBlockValidators: Get validators of the next block

Parameters none

Return Type Description

Array Public keys of validators in the next round of consensus

Fee(GAS) 1.00

Parameters	Parameter	Type	Description
pubKey	PublicKey	Public key of the account
Return	Type	Description
Boolean	Result. true: sucess, false: failure
Fee(GAS)	0.05

Parameters	none
Return	Type	Description
Array	Public keys of all validators and backup nodes
Fee(GAS)	1.00

Parameters	none
Return	Type	Description
Array	Public keys of all current validators
Fee(GAS)	1.00

Parameters	none
Return	Type	Description
Array	Public keys of validators in the next round of consensus
Fee(GAS)	1.00

vote：Vote for to validators

Parameters	Parameter	Type	Description
	account	Hash160	Voter's ScriptHash
	pubkeys	Array	The public keys of validators one vote to
Return	Type	Description
Return	Boolean	Result. true: success, false: failure
Fee(GAS)	5.00

GasToken

Referred to as GAS, Neo's fuel token, used to pay the handling fee, in line with NEP-5 standards. Transaction costs and consensus node incentives on the Neo network are paid in GAS. The total amount of GAS is 100 million, and the minimum unit is 0.00000001. GAS is registered in the founding block but not distributed. GAS distribution mechanism: When a new block is generated, a new GAS is generated, and the generated GAS and system fees are distributed to NEO holders. The calculation and distribution of GAS are automatically performed when the NEO balance in the user's address changes. The calculation method is as follows:

Where m is the height of the block where the user last extracted the GAS, n is the current block height, and NEO is the number of NEOs held by the user during m to n. BlockBonus represents the amount of GAS that each block can extract. SystemFee represents the sum of the system fees for all transactions in this block.

GasToken methods details following：

Method marked * is NEP-5 standard interface

name: Name of the token

Parameters none

Return Type Description

String Name of the token

Fee(GAS) 0.00
symbol: Symbol of the token

Parameters none

Return Type Description

String Symbol of the token

Fee(GAS) 0.00
decimals: Decimals of the token

Parameters none

Return Type Description

uint Decimal

Fee(GAS) 0.00
totalSupply: Total supply

Parameters none

Return Type Description

BigInteger Total supply

Fee(GAS) 0.01
balanceOf: Balance of a specific account

Parameters Parameter Type Description

account Hash160 ScriptHash of the account to be queried

Return Type Description

Integer Balance

Fee(GAS) 0.01

Parameters	none
Return	Type	Description
String	Name of the token
Fee(GAS)	0.00

Parameters	none
Return	Type	Description
String	Symbol of the token
Fee(GAS)	0.00

Parameters	none
Return	Type	Description
uint	Decimal
Fee(GAS)	0.00

Parameters	none
Return	Type	Description
BigInteger	Total supply
Fee(GAS)	0.01

Parameters	Parameter	Type	Description
account	Hash160	ScriptHash of the account to be queried
Return	Type	Description
Integer	Balance
Fee(GAS)	0.01

transfer: Transfer token from one account to another

Parameters	Parameter	Type	Description
	from	Hash160	ScriptHash of the sender's account
	to	Hash160	ScriptHash of the receiver's account
	amount	Integer	Transferred amount
Return	Type	Description
Return	Boolean	Result, true: success，false: failure
Fee(GAS)	0.08

getSysFeeAmount: Total system fee till a specific height

Parameters Parameter Type Description

index Integer The height one want to query

Return Type Description

Integer Total system fee

Fee(GAS) 0.01

Parameters	Parameter	Type	Description
index	Integer	The height one want to query
Return	Type	Description
Integer	Total system fee
Fee(GAS)	0.01

PolicyContract

It is the contract for configuring the consensus strategy and saves relevant parameters in the consensus process, including maximum transactions per block, maximum low-priority transactions per block, maximum low-priority-transaction size, the fee per byte, etc. The interface is described in detail below：

getMaxTransactionPerBlock: Get maximum transactions per block.

Parameters none

Return Type Description

Integer Maximum transaction count per block

Fee(GAS) 0.01
GetFeePerByte： Get system fee per byte

Parameters none

Return Type Description

Integer Fee per byte

Fee(GAS) 0.01
getBlockedAccounts: Get the addresses in the blacklist

Parameters none

Return Type Description

Array Address blacklist

Fee(GAS) 0.01
setMaxTransactionsPerBlock: Set maximum transactions count per block

Parameters Parameter Type Description

value Integer Maximum transactions count to be set

Return Type Description

Boolean Result. true: success, false: failure

Fee(GAS) 0.03
setFeePerByte：Set system fee per byte.

Parameters Parameter Type Description

value Integer System fee per byte

Return Type Description

Boolean Result. true: success, false: failure

Fee(GAS) 0.03
blockAccount：Add an account into the blacklist.

Parameters Parameter Type Description

account Hash160 ScriptHash of the account to be added

Return Type Description

Boolean Result. true: success, false: failure

Fee(GAS) 0.03
unblockAccount：Remove an account from the blacklist.

Parameters Parameter Type Description

account Hash160 ScriptHash of the account to be removed

Return Type Description

Boolean Result. true: success, false: failure

Fee(GAS) 0.03

Parameters	none
Return	Type	Description
Integer	Maximum transaction count per block
Fee(GAS)	0.01

Parameters	none
Return	Type	Description
Integer	Fee per byte
Fee(GAS)	0.01

Parameters	none
Return	Type	Description
Array	Address blacklist
Fee(GAS)	0.01

Parameters	Parameter	Type	Description
value	Integer	Maximum transactions count to be set
Return	Type	Description
Boolean	Result. true: success, false: failure
Fee(GAS)	0.03

Parameters	Parameter	Type	Description
value	Integer	System fee per byte
Return	Type	Description
Boolean	Result. true: success, false: failure
Fee(GAS)	0.03

Parameters	Parameter	Type	Description
account	Hash160	ScriptHash of the account to be added
Return	Type	Description
Boolean	Result. true: success, false: failure
Fee(GAS)	0.03

Parameters	Parameter	Type	Description
account	Hash160	ScriptHash of the account to be removed
Return	Type	Description
Boolean	Result. true: success, false: failure
Fee(GAS)	0.03

For more NativeContract, Please stay stunned

NativeContract Deployment

NativeContract is deployed in the Genesis Block by calling the interop interface of Neo.Native.Deploy, and can only be executed in the Genesis Block.

Interop Service

The interop service layer provides APIs for smart contracts to access the blockchain data, including the block information, transaction information, contract information, asset information, etc. Besides, the interop service layer provides the persistence capability for each contract. Each Neo smart contract is allowed to optionally enable a private storage area with the form of key-value pair. The context of persisting the storage for Neo smart contracts is determined by the callee of the contract, not the caller. The caller needs to pass its storage context to the callee (that is, authorization) before the callee can perform the read-write operation. There are two types of interop service, namely System and Neo.

Principle of Interop Service

When the Neo program starts, it registers a series of interop interfaces to the virtual machine for smart contract invocation.

Service Name Each interoperation has a service name, such as System.Contract.Call。
Mapping Method Each interop service corresponds to a native method. Also taking the System.Contract.Call as an example, private static bool Contract_Call(ApplicationEngine engine) is the method invoked in the client.
System Fee Each interop interface has its method for system fee calculation or fixed system fee.
Triggering Each interop interface has a supported trigger mode. For instance, TriggerType.All supports all triggers.

When registering, the Neo client encapsulates the service name of the interop interface, the mapping method, the method of calculating system fee, and the supported trigger mode as an InteropDescriptor and stores it in the Dictionary with the index of the hash value of the interop interface name, which is calculated as follows: BitConverter.ToUInt32(Encoding.ASCII.GetBytes(ServiceName).Sha256(), 0)

For example the hash of System.Contract.Call is 0x627d5b52

Usage of Interop Service

Smart Contract The interop interface used in the smart contract is provided by the corresponding smart contract development framework, which can be invoked directly. When compiled, the interop interface is compiled by the compiler into the operating instructions that can be executed in NeoVM.
Script of the Transaction The execution script can be constructed with the hash value of the interop service name and the SYSCALL operator.

Here is an example for calling the name method of the contract 0x43cf98eddbe047e198a3e5d57006311442a0ca15 via System.Contract.Call：

PUSH0
NEWARRAY
PUSHBYTES4  6e616d65
PUSHBYTES20 0x43cf98eddbe047e198a3e5d57006311442a0ca15
SYSCALL     0x627d5b52

C# code：

ScriptBuilder sb = new ScriptBuilder()
sb.EmitPush(0);
sb.Emit(OpCode.NEWARRAY);
sb.EmitPush(operation);
sb.EmitPush(scriptHash);
sb.EmitSysCall(InteropService.System_Contract_Call); //Call interop service
byte[] script = sb.ToArray();

In C#, it can be called as follows：

using Neo.SmartContract.Framework;
using Neo.SmartContract.Framework.Neo;

namespace MyContract
{
public class MyContract: SmartContract
{
  public static readonly byte[] GAS = HexToBytes("0xa1760976db5fcdfab2a9930e8f6ce875b2d18225");
  public static object main(string method, object[] args)
  {
    if (method == "transferGAS") {
      if (args.Length < 3) return false;
      return Contract.Call(GAS, "Transfer", args);
    }
  }
}
}

Interop services are divided into System part and Neo part. The specific interfaces are as follows:

System Part

System.Binary.Serialize

Description	Convert StackItem to byte array
Fee (GAS)	0.001

System.Binary.Deserialize

Description	Convert byte array to StackItem
Fee (GAS)	0.005

System.Blockchain.GetHeight

Description	Get the height of the current block
Fee (GAS)	0.000004

System.Blockchain.GetBlock

Description	Get a block with the hash or block height
Fee (GAS)	0.025

System.Blockchain.GetTransaction

Description	Get a transaction with the txid
Fee (GAS)	0.01

System.Blockchain.GetTransactionHeight

Description	Get the height of the block where the transaction included with the txid
Fee (GAS)	0.01

System.Blockchain.GetTransactionFromBlock

Description	Get a transaction with the txid in the block
Fee (GAS)	0.01

System.Blockchain.GetContract

Description	Get a contract with the hash
Fee (GAS)	0.01

System.Contract.Create

Description	Deploy a contract
Explanation	The size of the script contract cannot exceed 1MB and the size of the manifest cannot exceed 2KB
Fee (GAS)	(Script.Size + Manifest.Size) * GasPerByte

System.Contract.Update

Description	Upgrade a contract
Explanation	The size of the script contract cannot exceed 1MB and it cannot be deployed before. The size of the manifest cannot exceed 2KB. The old contract will be destroyed after the upgrade.
Fee (GAS)	(Script.Size + Manifest.Size) * GasPerByte

System.Contract.Destroy

Description	Destroy a contract
Fee (GAS)	0.01

System.Contract.Call

Description	Invoke a contract
Fee (GAS)	0.01

System.Contract.CallEx

Description	Invoke a contract with the Flag
Fee (GAS)	0.01

System.Contract.IsStandard

Description	Check whether the contract is a standard contract
Fee (GAS)	0.0003

System.Enumerator.Create

Description	Create a enumerator
Fee (GAS)	0.000004

System.Enumerator.Next

Description	Check if the enumerator has more element
Fee (GAS)	0.01

System.Enumerator.Value

Description	Get the current value of the enumerator
Fee (GAS)	0.000004

System.Enumerator.Concat

Description	Concat two enumerators
Fee (GAS)	0.000004

System.Iterator.Create

Description	Create an iterator
Fee (GAS)	0.000004

System.Iterator.Key

Description	Get the current key of the iterator
Fee (GAS)	0.000004

System.Iterator.Keys

Description	Get all keys of the iterator
Fee (GAS)	0.000004

System.Iterator.Values

Description	Get all values of the iterator
Fee (GAS)	0.000004

System.Iterator.Concat

Description	Concat two iterators
Fee (GAS)	0.000004

System.Json.Serialize

Description	Serialize a stack item to byte array
Fee (GAS)	0.001

System.Json.Deserialize

Description	Convert json object to stack item
Fee (GAS)	0.005

System.Runtime.Platform

Description	Get the platform information of the contract being executed
Fee (GAS)	0.0000025

System.Runtime.GetTrigger

Description	Get the triggering condition of the contract
Fee (GAS)	0.0000025

System.Runtime.GetTime

Description	Get the timestamp of the current block
Fee (GAS)	0.0000025

System.Runtime.GetScriptContainer

Description	Get the script container of the contract
Fee (GAS)	0.0000025

System.Runtime.GetExecutingScriptHash

Description	Get the script hash of the executing contract
Fee (GAS)	0.000004

System.Runtime.GetCallingScriptHash

Description	Get the script hash of the calling contract
Fee (GAS)	0.000004

System.Runtime.GetEntryScriptHash

Description	Get the script hash of the entry contract
Fee (GAS)	0.000004

System.Runtime.CheckWitness

Description	Verify whether the container calling the contract is signed by the script hash of the specific account
Fee (GAS)	0.0003

System.Runtime.GetInvocationCounter

Description	Get invocation count of the current contract
Fee (GAS)	0.000004

System.Runtime.Log

Description	Record the log
Fee (GAS)	0.005

System.Runtime.Notify

Description	Notify the client executing the contract
Fee (GAS)	0.01

System.Runtime.GetNotifications

Description	Get notifications of a contract
Fee (GAS)	0.0001

System.Runtime.GasLeft

Description	Get the unconsumed GAS
Fee (GAS)	0.00000400

System.Storage.GetContext

Description	Get storage context of the current contract
Explanation	the IsReadOnly flag of StorageContext is false
Fee (GAS)	0.000004

System.Storage.GetReadOnlyContext

Description	Get storage context of the current contract in read-only mode
Explanation	the IsReadOnly flag of StorageContext is true
Fee (GAS)	0.000004

System.Storage.Get

Description	Get value from the storage by key
Fee (GAS)	0.01

System.Storage.Find

Description	Find the data in the storage area of the current storage context with the specified prefix
Fee (GAS)	0.01

System.Storage.Put

Description	Put key-value into storage based on the storage context
Fee (GAS)	(Key.Size + Value.Size) * GasPerByte

System.Storage.PutEx

Description	Put Key-Value into the storage based on the storage context and the flag
Explanation	The parameter StorageFlags defines the attribute of the written data. The default value is None, indicating that data can be read and written. If it is Constant, the data cannot be modified or deleted once it is written to the storage area.
Fee (GAS)	(Key.Size + Value.Size) * GasPerByte

System.Storage.Delete

Description	Delete the stored Key-Value data from the storage area by the Key
Explanation	Data cannot be deleted if its StorageFlags is Constant
Fee (GAS)	0.01

System.StorageContext.AsReadOnly

Description	Set the current context to read-only mode
Explanation	Set the IsReadOnly flag of the StorageContext to true
Fee (GAS)	0.000004

Neo Part

Neo.Native.Deploy

Description	Deploy and initialize all native contracts
Explanation	It can only be invoked in the genesis block
Fee (GAS)	0

Neo.Native.Tokens.NEO

Method Name	Description	Fee (GAS)
name	Get token name, ie: NEO	0
symbol	Get token symbol, ie: neo	0
decimals	Get decimals	0
totalSupply	Get the total supply	0.01
balanceOf	Get balance of the token	0.01
transfer	Transfer the token	0.08
registerValidator	Register to be a validator	0.05
vote	Vote	5
getRegisteredValidators	Get registered validators	1
getValidators	Get validators	1
unclaimedGas	Get unclaimed Gas	0.03

Neo.Native.Tokens.GAS

Method Name	Description	Fee (GAS)
name	Get token name, ie: GAS	0
symbol	Get token symbol, ie: gas	0
decimals	Get decimals	0
totalSupply	Get the total supply	0.01
balanceOf	Get balance of the token	0.01
transfer	Transfer the token	0.08
getSysFeeAmount	Get the amount of the system fee	0.01

Neo.Native.Policy

Method Name	Description	Fee (GAS)
getMaxTransactionsPerBlock	Get max transaction number per block	0.01
getMaxBlockSize	Get max block size	0.01
getFeePerByte	Get fee per byte	0.01
setMaxBlockSize	Set the max block size	0.03
getBlockedAccounts	Get blocked accounts	0.01
setMaxTransactionsPerBlock	Set max transaction per block	0.03
setFeePerByte	Set fee per byte	0.03
blockAccount	Set blocked accounts	0.03
unblockAccount	Unblock accounts	0.03

Neo.Crypto.ECDsaVerify

Description	Verify signature of the current script container by public key
Fee (GAS)	0.01

Neo.Crypto.ECDsaCheckMultiSig

Description	Verify the multiple signature of the current script container by public key
Fee (GAS)	0.01 * n

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Contract Invocation

Invoke another contract in contract

When writing a contract, you can invoke other contracts through the interop service provided by the development frameworkSystem.Contract.Call. Here is an example in C#:

using Neo.SmartContract.Framework;
using Neo.SmartContract.Framework.Neo;

namespace MyContract
{
public class MyContract: SmartContract
{
  public static readonly byte[] GAS = HexToBytes("0xa1760976db5fcdfab2a9930e8f6ce875b2d18225");
  public static object main(string method, object[] args)
  {
    if (method == "transferGAS") {
      if (args.Length < 3) return false;
      return Contract.Call(GAS, "transfer", args);
    }
  }
}
}

Invoke contract in script

In the case of the execution script constructed manually, the contract should be invoked with the interop service System.Contract.Call and the ScriptHash of the contract. Please refer to How to use interop services

Here is an example for invoking method transfer of the contract 0x43cf98eddbe047e198a3e5d57006311442a0ca15 via System.Contract.Call：

PUSHBYTES4  0x00e1f505
PUSHBYTES20 0xfb5fd311a3ae2b2c8ab6b63c10502f9cf58ebeed
PUSHBYTES20 0xa6b9b510a67009e61f4f95115c188437f76dd2d0
PUSH3
PACK                                                      //The third parameter, parameter list
PUSHBYTES4  0x6e616d65                                    //The second parameter, method name
PUSHBYTES20 0x43cf98eddbe047e198a3e5d57006311442a0ca15    //The first parameter, contract's ScriptHash
SYSCALL     0x627d5b52                                    //Calling interop service by hash

C# code：

ScriptBuilder sb        = new ScriptBuilder();
UInt160 scriptHash      = UInt160.Parse("0x43cf98eddbe047e198a3e5d57006311442a0ca15");
string operation        = "transfer";
ContractParameter from  = new ContractParameter(ContractParameterType.Hash160);
ContractParameter to    = new ContractParameter(ContractParameterType.Hash160);
ContractParameter value = new ContractParameter(ContractParameterType.Integer);

from.SetValue("0xa6b9b510a67009e61f4f95115c188437f76dd2d0");
to.SetValue("0xfb5fd311a3ae2b2c8ab6b63c10502f9cf58ebeed");
value.SetValue("100000000");

sb.EmitAppCall(scriptHash, operation, new ContractParameter[]{from, to, value});
byte[] script = sb.ToArray();

public static ScriptBuilder EmitAppCall(this ScriptBuilder sb, UInt160 scriptHash, string operation, params ContractParameter[] args)
{
  for (int i = args.Length - 1; i >= 0; i--)
      sb.EmitPush(args[i]);
  sb.EmitPush(args.Length);
  sb.Emit(OpCode.PACK);
  sb.EmitPush(operation);
  sb.EmitPush(scriptHash.ToArray());
  sb.EmitSysCall(InteropService.System_Contract_Call);
  return sb;
}

Contract Upgrade

You can upgrade the contract to modify the logic of the contract and keep the data in the storage area after the contract is deployed, but you need to implement the upgrade interface in the old contract through invoking the Neo.Contract.Update method.

When the upgrade interface is called in the old contract, the method will build a new smart contract based on the parameters passed in. If the old contract has a storage area, the storage area will be transferred to the new contract. After the upgrade, the old contract will be deleted, as well as its storage area (if any). The old contract will then be unavailable and instead, the hash of the new contract should be used.

C# code:

using Neo.SmartContract.Framework;
using Neo.SmartContract.Framework.Neo;
using Neo.SmartContract.Framework.System;

public static bool Main(string method, params object[] args){
  if (method == "update") {
    if (args.Length < 2) return false;
    if (!Runtime.CheckWitness()) return false;
    byte[] newScript = args[0];
    string manifest = (string)args[1];
    update(newScript, manifest);
    return true;
  }
  return true;
}
void update(byte[] newScript, string manifest)
{
  Contract.Update(newScript, manifest);
}

Contract Destroying

The smart contract supports the destruction operation after the release, but the interface for destroying the contract needs to be reserved in the old contract, mainly involved in the invocation of System.Contract.Destroy method.

C# code：

using Neo.SmartContract.Framework;
using Neo.SmartContract.Framework.System;

public static bool Main(string method, params object[] args){
  if (method == "destroy") {
    destroy();
}
  return true;
}

void destroy(){
Contract.Destroy();
}

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Files

SmartContract

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SmartContract

Folders and files

parent directory

README.md

Smart Contracts

Changes in NEO3

Manifest

Trigger

Native Contract

Introduction

NeoToken

GasToken

PolicyContract

NativeContract Deployment

Interop Service

Principle of Interop Service

Usage of Interop Service

System Part

System.Binary.Serialize

System.Binary.Deserialize

System.Blockchain.GetHeight

System.Blockchain.GetBlock

System.Blockchain.GetTransaction

System.Blockchain.GetTransactionHeight

System.Blockchain.GetTransactionFromBlock

System.Blockchain.GetContract

System.Contract.Create

System.Contract.Update

System.Contract.Destroy

System.Contract.Call

System.Contract.CallEx

System.Contract.IsStandard

System.Enumerator.Create

System.Enumerator.Next

System.Enumerator.Value

System.Enumerator.Concat

System.Iterator.Create

System.Iterator.Key

System.Iterator.Keys

System.Iterator.Values

System.Iterator.Concat

System.Json.Serialize

System.Json.Deserialize

System.Runtime.Platform

System.Runtime.GetTrigger

System.Runtime.GetTime

System.Runtime.GetScriptContainer

System.Runtime.GetExecutingScriptHash

System.Runtime.GetCallingScriptHash

System.Runtime.GetEntryScriptHash

System.Runtime.CheckWitness

System.Runtime.GetInvocationCounter

System.Runtime.Log

System.Runtime.Notify

System.Runtime.GetNotifications

System.Runtime.GasLeft

System.Storage.GetContext

System.Storage.GetReadOnlyContext

System.Storage.Get

System.Storage.Find

System.Storage.Put

System.Storage.PutEx

System.Storage.Delete

System.StorageContext.AsReadOnly

Neo Part

Neo.Native.Deploy

Neo.Native.Tokens.NEO

Neo.Native.Tokens.GAS

Neo.Native.Policy

Neo.Crypto.ECDsaVerify

Neo.Crypto.ECDsaCheckMultiSig

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