core, interop: add strLen method for native StdLib contract

Close #3195.

Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>

pkg/compiler/interop_test.go

@@ -277,6 +277,29 @@ func TestCurrentSigners(t *testing.T) {
 	})
 }
 
+func TestStdLib_StrLen(t *testing.T) {
+	bc, acc := chain.NewSingle(t)
+	e := neotest.NewExecutor(t, bc, acc, acc)
+	src := `package foo
+		import (
+			"github.com/nspcc-dev/neo-go/pkg/interop/native/std"
+		)
+		func Main(s string) int {
+			return std.StrLen(s)
+		}`
+	ctr := neotest.CompileSource(t, e.CommitteeHash, strings.NewReader(src), &compiler.Options{Name: "Helper"})
+	e.DeployContract(t, ctr, nil)
+	c := e.CommitteeInvoker(ctr.Hash)
+
+	expected := stackitem.Make(1)
+	c.Invoke(t, expected, "main", "🦆")
+	c.Invoke(t, expected, "main", "ã")
+	c.Invoke(t, expected, "main", "a")
+
+	expected = stackitem.Make(7)
+	c.Invoke(t, expected, "main", "abc 123")
+}
+
 func spawnVM(t *testing.T, ic *interop.Context, src string) *vm.VM {
 	b, di, err := compiler.CompileWithOptions("foo.go", strings.NewReader(src), nil)
 	require.NoError(t, err)

pkg/core/native/std.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"math/big"
 	"strings"
+	"unicode/utf8"
 
 	"github.com/mr-tron/base58"
 	"github.com/nspcc-dev/neo-go/pkg/config"
@@ -159,6 +160,11 @@ func newStd() *Std {
 	md = newMethodAndPrice(s.stringSplit3, 1<<8, callflag.NoneFlag)
 	s.AddMethod(md, desc)
 
+	desc = newDescriptor("strLen", smartcontract.IntegerType,
+		manifest.NewParameter("str", smartcontract.StringType))
+	md = newMethodAndPrice(s.strLen, 1<<8, callflag.NoneFlag)
+	s.AddMethod(md, desc)
+
 	return s
 }
 
@@ -421,6 +427,12 @@ func (s *Std) stringSplitAux(str, sep string, removeEmpty bool) []stackitem.Item
 	return result
 }
 
+func (s *Std) strLen(_ *interop.Context, args []stackitem.Item) stackitem.Item {
+	str := s.toLimitedString(args[0])
+
+	return stackitem.NewBigInteger(big.NewInt(int64(utf8.RuneCountInString(str))))
+}
+
 // Metadata implements the Contract interface.
 func (s *Std) Metadata() *interop.ContractMD {
 	return &s.ContractMD

pkg/core/native/std_test.go

@@ -558,3 +558,25 @@ func TestStringSplit(t *testing.T) {
 			func() { s.stringSplit2(ic, []stackitem.Item{s1, s2}) })
 	})
 }
+
+func TestStd_StrLen(t *testing.T) {
+	s := newStd()
+	ic := &interop.Context{VM: vm.New()}
+
+	check := func(t *testing.T, expected int64, str string) {
+		args := []stackitem.Item{stackitem.Make(str)}
+		actual := s.strLen(ic, args)
+		l, ok := actual.Value().(*big.Int)
+		require.True(t, ok)
+		require.Equal(t, expected, l.Int64())
+	}
+
+	// These tests are taken from https://github.com/neo-project/neo/pull/2854/files.
+	check(t, 1, "🦆")
+	check(t, 1, "ã")
+	check(t, 1, "a")
+
+	bad := string(rune(0xff))
+	check(t, 1, bad)
+	check(t, 3, bad+"ab")
+}

pkg/interop/native/std/std.go

@@ -173,3 +173,10 @@ func StringSplitNonEmpty(s, sep string) []string {
 	return neogointernal.CallWithToken(Hash, "stringSplit", int(contract.NoneFlag),
 		s, sep, true).([]string)
 }
+
+// StrLen returns length of the string in Utf- characters.
+// It uses `strLen` method of StdLib native contract.
+func StrLen(s string) int {
+	return neogointernal.CallWithToken(Hash, "strLen", int(contract.NoneFlag),
+		s).(int)
+}