neo-go/examples/token/nep17/nep17.go

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package nep17
import (
"github.com/nspcc-dev/neo-go/pkg/interop"
"github.com/nspcc-dev/neo-go/pkg/interop/contract"
"github.com/nspcc-dev/neo-go/pkg/interop/native/management"
"github.com/nspcc-dev/neo-go/pkg/interop/runtime"
"github.com/nspcc-dev/neo-go/pkg/interop/storage"
"github.com/nspcc-dev/neo-go/pkg/interop/util"
)
// Token holds all token info
type Token struct {
// Token name
Name string
// Ticker symbol
Symbol string
// Amount of decimals
Decimals int
// Token owner address
Owner []byte
// Total tokens * multiplier
TotalSupply int
// Storage key for circulation value
CirculationKey string
}
// getIntFromDB is a helper that checks for nil result of storage.Get and returns
// zero as the default value.
func getIntFromDB(ctx storage.Context, key []byte) int {
var res int
val := storage.Get(ctx, key)
if val != nil {
res = val.(int)
}
return res
}
// GetSupply gets the token totalSupply value from VM storage
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func (t Token) GetSupply(ctx storage.Context) int {
return getIntFromDB(ctx, []byte(t.CirculationKey))
}
// BalanceOf gets the token balance of a specific address
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func (t Token) BalanceOf(ctx storage.Context, holder []byte) int {
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return getIntFromDB(ctx, holder)
}
// Transfer token from one user to another
func (t Token) Transfer(ctx storage.Context, from, to interop.Hash160, amount int, data interface{}) bool {
amountFrom := t.CanTransfer(ctx, from, to, amount)
if amountFrom == -1 {
return false
}
if amountFrom == 0 {
storage.Delete(ctx, from)
}
if amountFrom > 0 {
diff := amountFrom - amount
storage.Put(ctx, from, diff)
}
amountTo := getIntFromDB(ctx, to)
totalAmountTo := amountTo + amount
if totalAmountTo != 0 {
storage.Put(ctx, to, totalAmountTo)
}
runtime.Notify("Transfer", from, to, amount)
if to != nil && management.GetContract(to) != nil {
contract.Call(to, "onNEP17Payment", contract.All, from, amount, data)
}
return true
}
// CanTransfer returns the amount it can transfer
func (t Token) CanTransfer(ctx storage.Context, from []byte, to []byte, amount int) int {
if len(to) != 20 || !IsUsableAddress(from) {
return -1
}
amountFrom := getIntFromDB(ctx, from)
if amountFrom < amount {
return -1
}
// Tell Transfer the result is equal - special case since it uses Delete
if amountFrom == amount {
return 0
}
// return amountFrom value back to Transfer, reduces extra Get
return amountFrom
}
// IsUsableAddress checks if the sender is either the correct NEO address or SC address
func IsUsableAddress(addr []byte) bool {
if len(addr) == 20 {
if runtime.CheckWitness(addr) {
return true
}
// Check if a smart contract is calling scripthash
callingScriptHash := runtime.GetCallingScriptHash()
if util.Equals(callingScriptHash, addr) {
return true
}
}
return false
}
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// Mint initial supply of tokens
func (t Token) Mint(ctx storage.Context, to interop.Hash160) bool {
if !IsUsableAddress(t.Owner) {
return false
}
minted := storage.Get(ctx, []byte("minted"))
if minted != nil && minted.(bool) == true {
return false
}
storage.Put(ctx, to, t.TotalSupply)
storage.Put(ctx, []byte("minted"), true)
storage.Put(ctx, []byte(t.CirculationKey), t.TotalSupply)
var from interop.Hash160
runtime.Notify("Transfer", from, to, t.TotalSupply)
return true
}