core: add transaction.HasSigner method

pkg/core/transaction/transaction.go

@@ -407,3 +407,13 @@ func (t *Transaction) isValid() error {
 	}
 	return nil
 }
+
+// HasSigner returns true in case if hash is present in the list of signers.
+func (t *Transaction) HasSigner(hash util.Uint160) bool {
+	for _, h := range t.Signers {
+		if h.Account.Equals(hash) {
+			return true
+		}
+	}
+	return false
+}

pkg/core/transaction/transaction_test.go

@@ -12,6 +12,7 @@ import (
 
 	"github.com/nspcc-dev/neo-go/pkg/config/netmode"
 	"github.com/nspcc-dev/neo-go/pkg/encoding/address"
+	"github.com/nspcc-dev/neo-go/pkg/internal/random"
 	"github.com/nspcc-dev/neo-go/pkg/internal/testserdes"
 	"github.com/nspcc-dev/neo-go/pkg/util"
 )
@@ -248,3 +249,14 @@ func TestTransaction_GetAttributes(t *testing.T) {
 		require.Equal(t, conflictsAttrs, tx.GetAttributes(typ))
 	})
 }
+
+func TestTransaction_HasSigner(t *testing.T) {
+	u1, u2 := random.Uint160(), random.Uint160()
+	tx := Transaction{
+		Signers: []Signer{
+			{Account: u1}, {Account: u2},
+		},
+	}
+	require.True(t, tx.HasSigner(u1))
+	require.False(t, tx.HasSigner(util.Uint160{}))
+}