chore: add a grc20 example smart contract

Signed-off-by: Manfred Touron <[email protected]>

examples/gno.land/p/grc/grc20/grc20.gno

@@ -0,0 +1,64 @@
+package grc20
+
+import "std"
+
+type GRC20 interface {
+	// Returns the amount of tokens in existence.
+	TotalSupply() uint64
+
+	// Returns the amount of tokens owned by `account`.
+	BalanceOf(address std.Address) uint64
+
+	// Moves `amount` tokens from the caller's account to `to`.
+	//
+	// Returns a boolean value indicating whether the operation succeeded.
+	//
+	// Emits a {EventTransfer} event.
+	Transfer(to std.Address, amount uint64) bool
+
+	// Returns the remaining number of tokens that `spender` will be
+	// allowed to spend on behalf of `owner` through {transferFrom}. This is
+	// zero by default.
+	//
+	// This value changes when {approve} or {transferFrom} are called.
+	Allowance(owner, spender std.Address) uint64
+
+	// Sets `amount` as the allowance of `spender` over the caller's tokens.
+	// Returns a boolean value indicating whether the operation succeeded.
+	//
+	// IMPORTANT: Beware that changing an allowance with this method brings the risk
+	// that someone may use both the old and the new allowance by unfortunate
+	// transaction ordering. One possible solution to mitigate this race
+	// condition is to first reduce the spender's allowance to 0 and set the
+	// desired value afterwards:
+	// https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
+	//
+	// Emits an {EventApproval} event.
+	Approve(spender std.Address, amount uint64) bool
+
+	// Moves `amount` tokens from `from` to `to` using the
+	// allowance mechanism. `amount` is then deducted from the caller's
+	// allowance.
+	//
+	// Returns a boolean value indicating whether the operation succeeded.
+	//
+	// Emits a {EventTransfer} event.
+	TransferFrom(from, to std.Address, amount uint64) bool
+}
+
+// Emitted when `value` tokens are moved from one account (`from`) to another (`to`).
+//
+// Note that `value` may be zero.
+type TransferEvent struct {
+	From  std.Address
+	To    std.Address
+	Value uint64
+}
+
+// Emitted when the allowance of a `spender` for an `owner` is set by
+// a call to {approve}. `value` is the new allowance.
+type ApprovalEvent struct {
+	Owner   std.Address
+	Spender std.Address
+	Value   uint64
+}

examples/gno.land/p/ufmt/ufmt.gno

@@ -0,0 +1,45 @@
+package ufmt
+
+import "strconv"
+
+func Sprintf(format string, values ...interface{}) string {
+	offset := 0
+	fmtlen := len(format)
+	r := ""
+
+	for i := 0; i < fmtlen; i++ {
+		k := format[i]
+		isLast := i == fmtlen-1
+		switch {
+		case k == '%' && !isLast:
+			value := values[offset]
+			switch format[i+1] {
+			case 's':
+				r += value.(string)
+			case 'd':
+				switch v := value.(type) {
+				case int:
+					r += strconv.Itoa(v)
+				case int64:
+					r += strconv.Itoa(int(v))
+				case uint:
+					r += strconv.FormatUint(uint64(v), 10)
+				case uint64:
+					r += strconv.FormatUint(v, 10)
+				default:
+					r += "(unhandled)"
+				}
+			case '%':
+				r += "%"
+			default:
+				r += "(unhandled)"
+			}
+
+			i++
+			offset++
+		default:
+			r += string(k)
+		}
+	}
+	return r
+}

examples/gno.land/r/foo20/foo.gno

@@ -0,0 +1,286 @@
+package foo20
+
+import (
+	"std"
+	"strings"
+
+	"gno.land/p/avl"
+	"gno.land/p/grc/grc20"
+	"gno.land/p/ufmt"
+)
+
+type Token struct {
+	// TODO: use big.Int or a custom uint256 instead of uint64?
+
+	grc20.GRC20 // implements the GRC20 interface
+
+	name        string
+	symbol      string
+	decimals    uint
+	totalSupply uint64
+
+	balances   *avl.MutTree // std.Address(owner) -> uint64
+	allowances *avl.MutTree // string(owner+":"+spender) -> uint64
+}
+
+func newToken(name, symbol string, decimals uint) *Token {
+	// FIXME: check for limits
+
+	return &Token{
+		name:     name,
+		symbol:   symbol,
+		decimals: decimals,
+
+		balances:   avl.NewMutTree(),
+		allowances: avl.NewMutTree(),
+	}
+}
+
+var foo *Token
+var admin std.Address = "g1us8428u2a5satrlxzagqqa5m6vmuze025anjlj" // TODO: helper to change admin
+
+const zeroAddress = std.Address("")
+
+func init() {
+	foo = newToken("Foo", "FOO", 4)
+	foo.mint("g1us8428u2a5satrlxzagqqa5m6vmuze025anjlj", 1000000*10000) // @administrator (1M)
+	foo.mint("g1u7y667z64x2h7vc6fmpcprgey4ck233jaww9zq", 10000*10000)   // @manfred (10k)
+}
+
+// GRC20 implementation.
+//
+
+// TODO: create a reusable interface with optional hooks.
+// TODO: simplify the API and try to use events when available.
+// TODO: useful Render() method.
+// TODO: add a lot of unit tests, really a lot.
+
+func (t *Token) TotalSupply() uint64 {
+	return t.totalSupply
+}
+
+func (t *Token) BalanceOf(address std.Address) uint64 {
+	return t.balanceOf(address)
+}
+
+func (t *Token) Transfer(to std.Address, amount uint64) {
+	caller := std.GetCallerAt(3)
+	t.transfer(caller, to, amount)
+}
+
+func (t *Token) Allowance(owner, spender std.Address) uint64 {
+	return t.allowance(owner, spender)
+}
+
+func (t *Token) Approve(spender std.Address, amount uint64) {
+	owner := std.GetCallerAt(3)
+	t.approve(owner, spender, amount)
+}
+
+func (t *Token) TransferFrom(from, to std.Address, amount uint64) {
+	spender := std.GetCallerAt(3)
+	t.spendAllowance(from, spender, amount)
+	t.transfer(from, to, amount)
+}
+
+// Administration helpers implementation.
+//
+
+func (t *Token) Mint(address std.Address, amount uint64) {
+	caller := std.GetCallerAt(3)
+	assertIsAdmin(caller)
+	t.mint(address, amount)
+}
+
+func (t *Token) Burn(address std.Address, amount uint64) {
+	caller := std.GetCallerAt(3)
+	assertIsAdmin(caller)
+	t.burn(address, amount)
+}
+
+// private helpers
+//
+
+func (t *Token) mint(address std.Address, amount uint64) {
+	checkIsValidAddress(address)
+	// TODO: check for overflow
+
+	t.totalSupply += amount
+	currentBalance := t.balanceOf(address)
+	newBalance := currentBalance + amount
+
+	t.balances.Set(string(address), newBalance)
+
+	event := grc20.TransferEvent{zeroAddress, address, amount}
+	emit(&event)
+}
+
+func (t *Token) burn(address std.Address, amount uint64) {
+	checkIsValidAddress(address)
+	// TODO: check for overflow
+
+	currentBalance := t.balanceOf(address)
+	if currentBalance < amount {
+		panic("insufficient balance")
+	}
+
+	t.totalSupply -= amount
+	newBalance := currentBalance - amount
+
+	t.balances.Set(string(address), newBalance)
+
+	event := grc20.TransferEvent{address, zeroAddress, amount}
+	emit(&event)
+}
+
+func (t *Token) balanceOf(address std.Address) uint64 {
+	checkIsValidAddress(address)
+
+	balance, found := t.balances.Get(address.String())
+	if !found {
+		return 0
+	}
+	return balance.(uint64)
+}
+
+func (t *Token) spendAllowance(owner, spender std.Address, amount uint64) {
+	checkIsValidAddress(owner)
+	checkIsValidAddress(spender)
+
+	currentAllowance := t.allowance(owner, spender)
+	if currentAllowance < amount {
+		panic("insufficient allowance")
+	}
+}
+
+func (t *Token) transfer(from, to std.Address, amount uint64) {
+	checkIsValidAddress(from)
+	checkIsValidAddress(to)
+
+	if from == to {
+		panic("cannot send transfer to self")
+	}
+
+	toBalance := t.balanceOf(to)
+	fromBalance := t.balanceOf(from)
+
+	if fromBalance < amount {
+		panic("insufficient balance")
+	}
+
+	newToBalance := toBalance + amount
+	newFromBalance := fromBalance - amount
+
+	t.balances.Set(string(to), newToBalance)
+	t.balances.Set(string(from), newFromBalance)
+
+	event := grc20.TransferEvent{from, to, amount}
+	emit(&event)
+}
+
+func (t *Token) allowance(owner, spender std.Address) uint64 {
+	checkIsValidAddress(owner)
+	checkIsValidAddress(spender)
+
+	key := owner.String() + ":" + spender.String()
+
+	allowance, found := t.allowances.Get(key)
+	if !found {
+		return 0
+	}
+
+	return allowance.(uint64)
+}
+
+func (t *Token) approve(owner, spender std.Address, amount uint64) {
+	checkIsValidAddress(owner)
+	checkIsValidAddress(spender)
+
+	key := owner.String() + ":" + spender.String()
+	t.allowances.Set(key, amount)
+
+	event := grc20.ApprovalEvent{owner, spender, amount}
+	emit(&event)
+}
+
+func checkIsValidAddress(addr std.Address) {
+	if addr.String() == "" {
+		panic("invalid address")
+	}
+}
+
+func assertIsAdmin(address std.Address) {
+	if address != admin {
+		panic("restricted access")
+	}
+}
+
+// method proxies as public functions.
+//
+
+// getters.
+
+func TotalSupply() uint64                         { return foo.TotalSupply() }
+func BalanceOf(address std.Address) uint64        { return foo.BalanceOf(address) }
+func Allowance(owner, spender std.Address) uint64 { return foo.Allowance(owner, spender) }
+
+// setters.
+
+func Transfer(to std.Address, amount uint64) {
+	//std.AssertOriginCall() // FIXME: inconsistent
+	foo.Transfer(to, amount)
+}
+
+func Approve(spender std.Address, amount uint64) {
+	//std.AssertOriginCall() // FIXME: inconsistent
+	foo.Approve(spender, amount)
+}
+
+func TransferFrom(from, to std.Address, amount uint64) {
+	//std.AssertOriginCall() // FIXME: inconsistent
+	foo.TransferFrom(from, to, amount)
+}
+
+// administration.
+
+func Mint(address std.Address, amount uint64) {
+	//std.AssertOriginCall() // FIXME: inconsistent
+	foo.Mint(address, amount)
+}
+
+func Burn(address std.Address, amount uint64) {
+	//std.AssertOriginCall() // FIXME: inconsistent
+	foo.Burn(address, amount)
+}
+
+// placeholders.
+//
+
+func emit(event interface{}) {
+	// TODO: should we do something there?
+	// noop
+}
+
+// render.
+//
+
+func Render(path string) string {
+	parts := strings.Split(path, "/")
+	c := len(parts)
+
+	switch {
+	case path == "":
+		str := ""
+		str += ufmt.Sprintf("# %s ($%s)\n\n", foo.name, foo.symbol)
+		str += ufmt.Sprintf("* **Decimals**: %d\n", foo.decimals)
+		str += ufmt.Sprintf("* **Total supply**: %d\n", foo.totalSupply)
+		str += ufmt.Sprintf("* **Known accounts**: %d\n", foo.balances.Size())
+		return str
+	case c == 2 && parts[0] == "balance":
+		addr := std.Address(parts[1])
+		balance := foo.BalanceOf(addr)
+		return ufmt.Sprintf("%d\n", balance)
+	default:
+		return "404\n"
+	}
+}