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229 lines
5 KiB
Markdown
229 lines
5 KiB
Markdown
# NEO-GO smart contract compiler
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The neo-go compiler compiles Go programs to bytecode that the NEO virtual machine can understand.
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## Currently supported
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### Go internals
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- type checking
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- multiple assignments
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- global variables
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- types int, string, byte and booleans
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- struct types + method receives
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- functions
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- composite literals `[]int, []string, []byte`
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- basic if statements
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- binary expressions
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- return statements
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- for loops
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- imports
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### Go builtins
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- len
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- append
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### VM API (interop layer)
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Compiler translates interop function calls into NEO VM syscalls or (for custom
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functions) into NEO VM instructions. [Refer to GoDoc](https://godoc.org/github.com/nspcc-dev/neo-go/pkg/interop) for full API documentation.
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#### Standard NEO Smart Contract API
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- account
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- asset
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- attribute
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- block
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- blockchain
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- contract
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- engine
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- header
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- input
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- iterator
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- output
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- runtime
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- storage
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- transaction
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#### Custom VM utility helper functions
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- crypto:
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- `SHA1`
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- `SHA256`
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- `Hash256`
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- `Hash160`
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- enumerator
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- util:
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- `Equals` (to emit `EQUALS` opcode, not needed usually)
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- `FromAddress(address string) []byte`
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## Not supported
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Due to the limitations of the NEO virtual machine, features listed below will not be supported.
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- channels
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- goroutines
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- returning multiple values from functions
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## Quick start
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### Compile a smart contract
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```
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./bin/neo-go contract compile -i mycontract.go
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```
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By default the filename will be the name of your .go file with the .avm extension, the file will be located in the same directory where your Go contract is. If you want another location for your compiled contract:
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```
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./bin/neo-go contract compile -i mycontract.go --out /Users/foo/bar/contract.avm
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```
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### Debugging your smart contract
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You can dump the opcodes generated by the compiler with the following command:
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```
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./bin/neo-go contract inspect -i mycontract.go
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```
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This will result in something like this:
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```
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INDEX OPCODE DESC
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0 0x54 PUSH4
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1 0xc5 NEWARRAY
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2 0x6b TOALTSTACK
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3 0x1 PUSHBYTES1
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3 0x2a *
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5 0x6a DUPFROMALTSTACK
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6 0x0 PUSH0
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7 0x52 PUSH2
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8 0x7a ROLL
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9 0xc4 SETITEM
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10 0x6a DUPFROMALTSTACK
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11 0x0 PUSH0
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12 0xc3 PICKITEM
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13 0x5a PUSH10
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14 0xa2 GTE
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15 0x64 JMPIFNOT
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16 0x7 7
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16 0x0 0
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18 0x51 PUSH1
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19 0x6c FROMALTSTACK
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20 0x75 DROP
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21 0x66 RET
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22 0x0 PUSH0
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23 0x6c FROMALTSTACK
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24 0x75 DROP
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25 0x66 RET
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```
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### Test invoke a compiled contract
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You can simulate a test invocation of your compiled contract by the VM, to know the total gas cost for example, with the following command:
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```
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./bin/neo-go contract testinvoke -i mycompiledcontract.avm
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```
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Will output something like:
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```
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{
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"state": "HALT, BREAK",
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"gas_consumed": "0.006",
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"Stack": [
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{
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"type": "Integer",
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"value": "9"
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}
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]
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}
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```
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At the moment this is implemented via RPC call to the remote server.
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## Smart contract examples
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Some examples are provided in the [examples directory](https://github.com/nspcc-dev/neo-go/tree/master/examples).
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### Check if the invoker of the contract is the owning address
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```Golang
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package mycontract
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import (
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"github.com/nspcc-dev/neo-go/pkg/interop/runtime"
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"github.com/nspcc-dev/neo-go/pkg/interop/util"
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)
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var owner = util.FromAddress("AJX1jGfj3qPBbpAKjY527nPbnrnvSx9nCg")
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func Main() bool {
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isOwner := runtime.CheckWitness(owner)
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if isOwner {
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runtime.Log("invoker is the owner")
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return true
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}
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return false
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}
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```
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### Simple token
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```Golang
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package mytoken
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import (
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"github.com/nspcc-dev/neo-go/pkg/interop/runtime"
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"github.com/nspcc-dev/neo-go/pkg/interop/storage"
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)
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var owner = util.FromAddress("AJX1jGfj3qPBbpAKjY527nPbnrnvSx9nCg")
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type Token struct {
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Name string
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Symbol string
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TotalSupply int
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Owner []byte
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}
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func (t Token) AddToCirculation(amount int) bool {
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ctx := storage.Context()
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inCirc := storage.Get(ctx, "in_circ").(int)
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inCirc += amount
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storage.Put(ctx, "in_circ", inCirc)
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return true
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}
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func newToken() Token {
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return Token{
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Name: "your awesome NEO token",
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Symbol: "YANT",
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TotalSupply: 1000,
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Owner: owner,
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}
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}
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func Main(operation string, args []interface{}) bool {
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token := newToken()
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trigger := runtime.GetTrigger()
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if trigger == runtime.Verification() {
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isOwner := runtime.CheckWitness(token.Owner)
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if isOwner {
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return true
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}
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return false
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}
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if trigger == runtime.Application() {
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if operation == "mintTokens" {
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token.AddToCirculation(100)
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}
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}
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return true
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}
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```
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## How to report compiler bugs
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1. Make a proper testcase (example testcases can be found in the tests folder)
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2. Create an issue on Github
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3. Make a PR with a reference to the created issue, containing the testcase that proves the bug
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4. Either you fix the bug yourself or wait for patch that solves the problem
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