examples: add NFT example, fix #1845

examples/README.md

@@ -25,6 +25,7 @@ See the table below for the detailed examples description.
 | [engine](engine) | This contract demonstrates how to use `runtime` interop package which implements an API for `System.Runtime.*` NEO system calls. Please, refer to the `runtime` [package documentation](../pkg/interop/doc.go) for details. |
 | [events](events) | The contract shows how execution notifications with the different arguments types can be sent with the help of `runtime.Notify` function of the `runtime` interop package. Please, refer to the `runtime.Notify` [function documentation](../pkg/interop/runtime/runtime.go) for details. |
 | [iterator](iterator) | This example describes a way to work with NEO iterators. Please, refer to the `iterator` [package documentation](../pkg/interop/iterator/iterator.go) for details. |
+| [nft-nd](nft-nd) | NEP-11 non-divisible NFT. See NEP-11 token standard [specification](https://github.com/neo-project/proposals/pull/130) for details. |
 | [oracle](oracle) | Oracle demo contract exposing two methods that you can use to process URLs. It uses oracle native contract, see [interop package documentation](../pkg/interop/native/oracle/oracle.go) also. |
 | [runtime](runtime) | This contract demonstrates how to use special `_initialize` and `_deploy` methods. See the [compiler documentation](../docs/compiler.md#vm-api-interop-layer ) for methods details. It also shows the pattern for checking owner witness inside the contract with the help of `runtime.CheckWitness` interop [function](../pkg/interop/runtime/runtime.go). |
 | [storage](storage) | The contract implements API for basic operations with a contract storage. It shows hos to use `storage` interop package. See the `storage` [package documentation](../pkg/interop/storage/storage.go). |

examples/nft-nd/nft.go

@@ -0,0 +1,250 @@
+/*
+Package nft contains non-divisible non-fungible NEP11-compatible token
+implementation. This token can be minted with GAS transfer to contract address,
+it will hash some data (including data provided in transfer) and produce
+base58-encoded string that is your NFT. Since it's based on hashing and basically
+you own a hash it's HASHY.
+*/
+package nft
+
+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/iterator"
+	"github.com/nspcc-dev/neo-go/pkg/interop/native/crypto"
+	"github.com/nspcc-dev/neo-go/pkg/interop/native/gas"
+	"github.com/nspcc-dev/neo-go/pkg/interop/native/management"
+	"github.com/nspcc-dev/neo-go/pkg/interop/native/std"
+	"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"
+)
+
+// Prefixes used for contract data storage.
+const (
+	totalSupplyPrefix = "s"
+	accountPrefix     = "a"
+	tokenPrefix       = "t"
+)
+
+var (
+	// contractOwner is a special address that can perform some management
+	// functions on this contract like updating/destroying it and can also
+	// be used for contract address verification.
+	contractOwner = util.FromAddress("NX1yL5wDx3inK2qUVLRVaqCLUxYnAbv85S")
+)
+
+// Symbol returns token symbol, it's HASHY.
+func Symbol() string {
+	return "HASHY"
+}
+
+// Decimals returns token decimals, this NFT is non-divisible, so it's 0.
+func Decimals() int {
+	return 0
+}
+
+// TotalSupply is a contract method that returns the number of tokens minted.
+func TotalSupply() int {
+	return totalSupply(storage.GetReadOnlyContext())
+}
+
+// totalSupply is an internal implementation of TotalSupply operating with
+// given context. The number itself is stored raw in the DB with totalSupplyPrefix
+// key.
+func totalSupply(ctx storage.Context) int {
+	var res int
+
+	val := storage.Get(ctx, []byte(totalSupplyPrefix))
+	if val != nil {
+		res = val.(int)
+	}
+	return res
+}
+
+// mkAccountKey creates DB key for account specified by concatenating accountPrefix
+// and account address.
+func mkAccountKey(holder interop.Hash160) []byte {
+	res := []byte(accountPrefix)
+	return append(res, holder...)
+}
+
+// mkStringKey creates DB key for token specified by concatenating tokenPrefix
+// and token ID.
+func mkTokenKey(token []byte) []byte {
+	res := []byte(tokenPrefix)
+	return append(res, token...)
+}
+
+// BalanceOf returns the number of tokens owned by specified address.
+func BalanceOf(holder interop.Hash160) int {
+	if len(holder) != 20 {
+		panic("bad owner address")
+	}
+	ctx := storage.GetReadOnlyContext()
+	tokens := getTokensOf(ctx, holder)
+	return len(tokens)
+}
+
+// getTokensOf is an internal implementation of TokensOf, tokens are stored
+// as a serialized slice of strings in the DB, so it gets and unwraps them
+// (or returns an empty slice).
+func getTokensOf(ctx storage.Context, holder interop.Hash160) []string {
+	var res = []string{}
+
+	key := mkAccountKey(holder)
+	val := storage.Get(ctx, key)
+	if val != nil {
+		res = std.Deserialize(val.([]byte)).([]string)
+	}
+	return res
+}
+
+// setTokensOf saves current tokens owned by account if there are any,
+// otherwise it just drops the appropriate key from the DB.
+func setTokensOf(ctx storage.Context, holder interop.Hash160, tokens []string) {
+	key := mkAccountKey(holder)
+	if len(tokens) != 0 {
+		val := std.Serialize(tokens)
+		storage.Put(ctx, key, val)
+	} else {
+		storage.Delete(ctx, key)
+	}
+}
+
+// TokensOf returns an iterator with all tokens held by specified address.
+func TokensOf(holder interop.Hash160) iterator.Iterator {
+	if len(holder) != 20 {
+		panic("bad owner address")
+	}
+	ctx := storage.GetReadOnlyContext()
+	tokens := getTokensOf(ctx, holder)
+
+	return iterator.Create(tokens)
+}
+
+// getOwnerOf returns current owner of the specified token or panics if token
+// ID is invalid. Owner is stored as value of the token key (prefix + token ID).
+func getOwnerOf(ctx storage.Context, token []byte) interop.Hash160 {
+	key := mkTokenKey(token)
+	val := storage.Get(ctx, key)
+	if val == nil {
+		panic("no token found")
+	}
+	return val.(interop.Hash160)
+}
+
+// setOwnerOf writes current owner of the specified token into the DB.
+func setOwnerOf(ctx storage.Context, token []byte, holder interop.Hash160) {
+	key := mkTokenKey(token)
+	storage.Put(ctx, key, holder)
+}
+
+// OwnerOf returns owner of specified token.
+func OwnerOf(token []byte) interop.Hash160 {
+	ctx := storage.GetReadOnlyContext()
+	return getOwnerOf(ctx, token)
+}
+
+// Transfer token from its owner to another user, notice that it only has two
+// parameters because token owner can be deduced from token ID itself and RC1
+// implementation doesn't yet have 'data' parameter as in NEP-17 Transfer.
+func Transfer(to interop.Hash160, token []byte) bool {
+	if len(to) != 20 {
+		panic("invalid 'to' address")
+	}
+	ctx := storage.GetContext()
+	owner := getOwnerOf(ctx, token)
+
+	// Note that although calling script hash is not checked explicitly in
+	// this contract it is in fact checked for in `CheckWitness` itself.
+	if !runtime.CheckWitness(owner) {
+		return false
+	}
+
+	if string(owner) != string(to) {
+		toksOwner := getTokensOf(ctx, owner)
+		toksTo := getTokensOf(ctx, to)
+
+		var newToksOwner = []string{}
+		for _, tok := range toksOwner {
+			if tok != string(token) {
+				newToksOwner = append(newToksOwner, tok)
+			}
+		}
+		toksTo = append(toksTo, string(token))
+		setTokensOf(ctx, owner, newToksOwner)
+		setTokensOf(ctx, to, toksTo)
+		setOwnerOf(ctx, token, to)
+	}
+	postTransfer(owner, to, token)
+	return true
+}
+
+// postTransfer emits Transfer event and calls onNEP11Payment if needed.
+func postTransfer(from interop.Hash160, to interop.Hash160, token []byte) {
+	runtime.Notify("Transfer", from, to, 1, token)
+	if management.GetContract(to) != nil {
+		contract.Call(to, "onNEP11Payment", contract.All, from, 1, token)
+	}
+}
+
+// OnNEP17Payment mints tokens if at least 10 GAS is provided. You don't call
+// this method directly, instead it's called by GAS contract when you transfer
+// GAS from your address to the address of this NFT contract.
+func OnNEP17Payment(from interop.Hash160, amount int, data interface{}) {
+	if string(runtime.GetCallingScriptHash()) != gas.Hash {
+		panic("only GAS is accepted")
+	}
+	if amount < 10_00000000 {
+		panic("minting HASHY costs at least 10 GAS")
+	}
+	var tokIn = []byte{}
+	var ctx = storage.GetContext()
+
+	total := totalSupply(ctx)
+	tokIn = append(tokIn, []byte(std.Itoa(total, 10))...)
+	tokIn = append(tokIn, []byte(std.Itoa(amount, 10))...)
+	tokIn = append(tokIn, from...)
+	tx := runtime.GetScriptContainer()
+	tokIn = append(tokIn, tx.Hash...)
+	if data != nil {
+		tokIn = append(tokIn, std.Serialize(data)...)
+	}
+
+	tokenHash := crypto.Sha256(tokIn)
+	token := std.Base58Encode(tokenHash)
+
+	toksOf := getTokensOf(ctx, from)
+	toksOf = append(toksOf, token)
+	setTokensOf(ctx, from, toksOf)
+	setOwnerOf(ctx, []byte(token), from)
+
+	total++
+	storage.Put(ctx, []byte(totalSupplyPrefix), total)
+
+	postTransfer(nil, from, []byte(token))
+}
+
+// Verify allows owner to manage contract's address, including earned GAS
+// transfer from contract's address to somewhere else. It just checks for transaction
+// to also be signed by contract owner, so contract's witness should be empty.
+func Verify() bool {
+	return runtime.CheckWitness(contractOwner)
+}
+
+// Destroy destroys the contract, only owner can do that.
+func Destroy() {
+	if !Verify() {
+		panic("only owner can destroy")
+	}
+	management.Destroy()
+}
+
+// Update updates the contract, only owner can do that.
+func Update(nef, manifest []byte) {
+	if !Verify() {
+		panic("only owner can update")
+	}
+	management.Update(nef, manifest)
+}

examples/nft-nd/nft.yml

@@ -0,0 +1,14 @@
+name: "HASHY NFT"
+supportedstandards: ["NEP-11"]
+safemethods: ["balanceOf", "decimals", "symbol", "totalSupply", "tokensOf", "ownerOf"]
+events:
+  - name: Transfer
+    parameters:
+      - name: from
+        type: Hash160
+      - name: to
+        type: Hash160
+      - name: amount
+        type: Integer
+      - name: tokenId
+        type: ByteArray