added check for overflow/underflow

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

@@ -1,6 +1,7 @@
 package grc20
 
 import (
+ "errors"
  "std"
  "strconv"
 
@@ -24,6 +25,8 @@ type Banker struct {
  token *token // to share the same pointer
 }
 
+const uint64_max = 1<<64 - 1
+
 func NewBanker(name, symbol string, decimals uint) *Banker {
  if name == "" {
  panic("name should not be empty")
@@ -55,7 +58,11 @@ func (b *Banker) Mint(address std.Address, amount uint64) error {
  return ErrInvalidAddress
  }
 
- // TODO: check for overflow
+ // check for overflow
+ if uint64_max - b.totalSupply < amount {
+ err := ufmt.Sprintf("you can't mint more than %d tokens", uint64_max - b.totalSupply)
+ return errors.New(err)
+ }
 
  b.totalSupply += amount
  currentBalance := b.BalanceOf(address)

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

@@ -12,6 +12,7 @@ var (
  ErrInsufficientAllowance = errors.New("insufficient allowance")
  ErrInvalidAddress = errors.New("invalid address")
  ErrCannotTransferToSelf = errors.New("cannot send transfer to self")
+ ErrUnderflow = errors.New("the a;ount is higher than the total supply")
 )
 
 type Token interface {

examples/gno.land/p/demo/grc/grc20/z_0_filetest.gno

@@ -0,0 +1,22 @@
+package main
+
+import (
+ "std"
+ "gno.land/p/demo/testutils"
+
+ banker "gno.land/p/demo/grc/grc20"
+)
+const uint64_max = 1<<64 - 1
+
+func main() {
+ b := banker.NewBanker("Dummy", "DUMMY", 6)
+ var owner = testutils.TestAddress("owner")
+ // Mint uint64_max - 1000 tokens for owner
+ b.Mint(owner, uint64_max - 1000)
+ // Try to mint 1001 tokens for owner, should fail because it exceeds the limit
+ println(b.Mint(owner, 1001).Error())
+
+}
+
+// Output:
+// you can't mint more than 1000 tokens