Introduction

this compiler is forked from CityOfZion/neo-go, compile go smart contract code to avm file.

How to use

Use built binary file "neo-go-compile"

./neo-go-compiler

use --help to get detail information

Compile smart contract

./neo-go-compiler contract compile -i <path/contract.go> [-abi] [-o <out put path/file.avm>]

-o is optional to indicate the output avm file path

-abi is generage abi file or not, if yes, you will find the .json under the same directory

Dump opcode

./neo-go-compiler contract opdump -i <path/contract.go> 

output :

INDEX    OPCODE    DESC             
0        0x56      Opush6           
1        0xc5      Onewarray        
2        0x6b      Otoaltstack      
3        0x6c      Ofromaltstack    
4        0x76      Odup             
5        0x6b      Otoaltstack      
6        0x 0      Opush0           
...

Neo and Ontology

Smart contract for Neo and Ontology has some difference on their APIs

No	Ontology	Neo	comments
1	GetStorageContext	GetContext	get storage context
2	PutStorage	Put	save to storage
3	GetStorage	Get	query from storage
4	DeleteSorage	Delete	delete from storage
5	RuntimeGetTrigger	GetTrigger	get trigger
6	RuntimeCheckWitness	CheckWitness	check witness
7	-	GetCurrentBlock	get current block
8	RuntimeGetTime	GetTime	get time stamp
9	RuntimeNotify	Notify	add a notify
10	RuntimeLog	Log	add a log
11	Invoke	-	invoke native contract
12	GetAttrUsage	-	get attribute usage
13	GetAttrData	-	get attribute data
14	GetHeaderVersion	-	get header version
15	GetHeaderNextConsensus	-	get header next consensus
16	GetHeaderConsensusData	-	get header consensus data
17	GetHeaderMerkleRoot	-	get header merkle root
18	GetTransactionType	-	get transaction type
19	GetTransactionAttributes	-	get transaction attributes
20	MigrateContract	-	migrate contract
21	GetContractScript	-	get contract script

Other APIs

the following apis supports both Ontology and Neo

No	Name	comments
1	GetScriptContainer	get script container
2	GetExecutingScriptHash	get current contract hash
3	GetCallingScriptHash	get calling contract hash
4	GetEntryScriptHash	get entry script hash
5	GetBlockTransactionCount	get transactions count of block
6	GetBlockTransactions	get transactions of block
7	GetBlockTransaction	get a specified transaction
8	GetBlockchainHeight	get current block height
9	GetBlockchainHeader	get block header
10	GetBlockchainBlock	get block
11	GetContract	get contract
12	GetTransactionHeight	get transaction height
13	GetHeaderIndex	get header height
14	GetHeaderHash	get header hash
15	GetHeaderPrevHash	get header previous hash
16	GetHeaderTimestamp	get header timestamp
17	GetTransHash	get transaction hash
18	GetContractStorageContext	get contract storage context
19	GetReadOnlyStorageContext	get readonly storage context
20	StorageCtxAsReadOnly	make storage readonly
21	RuntimeSerialize	serialize collection to bytearray
22	RuntimeDeserialize	deserialize bytearray

How to write smart contract in golang

You can write your smart contract code in any editors which provides the golang grammar check.

The entry function in golang contract must be like following:

func Main(operation string, args []interface{}) interface{} {
	if operation == "someoperation1"{ 
        do something 
    }
    if operation == "someoperation2"{
        do something
    }
    ...
}

"operation" represents the actual method name to invoke

"args" represents the parameters to be passed in .

Supported Types

Golang neovm contract is a subset of golang, only support the following types:

string , int , int64, []byte, byte, bool

Not supported

1. Multiple return values
2. Error
3. for ... range (Ontology need to support "KEYS" opcode)
4. go routine
5. get or set elements from a byte array

Address

Generally, all addresses in smart contract should be []byte

1. As parameter: like C# and python ,you need to pass the Hex format address parameters .

   addr := args[0].([]byte)
   

   ​

2. As constant variables

   contractAddr:=[]byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01}
   
   

3. Use tools.ToScriptHash()

   owner = tools.ToScriptHash("Ad4pjz2bqep4RhQrUAzMuZJkBC3qJ1tZuT")
   

   *Note: the parameter of ToScriptHash must be a constant string

   ​

Storage

first , you need to declare a storage context :

Ontology

ctx = storage.GetStorageContext()

NEO

ctx = storage.GetContext()

then calling Put, Get or Delete method to access the storage

Ontology

storage.PutStorage(ctx, key, val)
result := storage.GetStorage(ctx,key)
storage.DeleteStorage(ctx,key)

NEO

storage.Put(ctx, key, val)
result := storage.Get(ctx,key)
storage.Delete(ctx,key)

Transfer ONT/ONG

In smart contract , you need to invoke native contract to transfer ONT and ONG

func transONT(from []byte, to []byte, amount int64) bool {
	if runtime.RuntimeCheckWitness(from) == false{return false}
	contractAddr:=[]byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01}
	param := appcall.State{from,to,amount}
	ver := 1
	bs :=native.Invoke(ver,contractAddr,"transfer",[]interface{}{param})
	if bs != nil && tools.BytesEquals(bs,[]byte("1")){
		return true
	}else{
		return false
	}
}

You can also define a struct to carry transfer parameters :

type transferParam struct{
	From []byte
	To []byte
	Amount int64
}
...
param := transferParam(from,to,amount)

AppCall

In order to call an other smart contract, you need to use appcall.AppCall:

 appcall.AppCall("APPWgNbWvUdQjQxeN7RduYweH3caaM1LM1","transfer",args)
 appcall.AppCall("83e69795f9c314a8c4f483e221927f41285a8653","transfer",args)

the first parameter must be constant string, either hex or base58 format address is acceptable.

*Note: Do not define the address string like this:

addr := "APPWgNbWvUdQjQxeN7RduYweH3caaM1LM1"
appcall.AppCall(addr,"transfer",args)

the second parameter is method name to call.

the last parameter is the arguments .

Tools

Here are some utility functions :

BytesEquals: to compare to byte arrays equality. (you can't loop the byte array to compare every single byte in neovm)

	if bs != nil && tools.BytesEquals(bs,[]byte("1")){
		return true
	}else{
		return false
	}

ToScriptHash: refer to the Address section

Cat: concat two byte arrays :

newbytes:=tools.Cat(transfer_prefix, owner)

Other restrictions

expressions with in if statement must compare explicitly

if runtime.RuntimeCheckWitness(from) == false {
		return false
}

Examples:

please check the examples under "contracts" directory