core: sort hashes and witnesses in VerifyWitnesses()

Fixes failure to verify some multi-witnesses transactions in Testnet chain. C#
code contains similar logic.

pkg/core/blockchain.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"fmt"
 	"math"
+	"sort"
 	"sync/atomic"
 	"time"
 
@@ -965,7 +966,9 @@ func (bc *Blockchain) GetScriptHashesForVerifying(t *transaction.Transaction) ([
 
 }
 
-// VerifyWitnesses verify the scripts (witnesses) that come with a transactions.
+// VerifyWitnesses verify the scripts (witnesses) that come with a given
+// transaction. It can reorder them by ScriptHash, because that's required to
+// match a slice of script hashes from the Blockchain.
 // Golang implementation of VerifyWitnesses method in C# (https://github.com/neo-project/neo/blob/master/neo/SmartContract/Helper.cs#L87).
 // Unfortunately the IVerifiable interface could not be implemented because we can't move the References method in blockchain.go to the transaction.go file
 func (bc *Blockchain) VerifyWitnesses(t *transaction.Transaction) error {
@@ -978,6 +981,8 @@ func (bc *Blockchain) VerifyWitnesses(t *transaction.Transaction) error {
 	if len(hashes) != len(witnesses) {
 		return errors.Errorf("expected len(hashes) == len(witnesses). got: %d != %d", len(hashes), len(witnesses))
 	}
+	sort.Slice(hashes, func(i, j int) bool { return hashes[i].Less(hashes[j]) })
+	sort.Slice(witnesses, func(i, j int) bool { return witnesses[i].ScriptHash().Less(witnesses[j].ScriptHash()) })
 	for i := 0; i < len(hashes); i++ {
 		verification := witnesses[i].VerificationScript
 

pkg/util/uint160.go

@@ -59,6 +59,18 @@ func (u Uint160) Equals(other Uint160) bool {
 	return u == other
 }
 
+// Less returns true if this value is less than given Uint160 value. It's
+// primarily intended to be used for sorting purposes.
+func (u Uint160) Less(other Uint160) bool {
+	for k := range u {
+		if u[k] == other[k] {
+			continue
+		}
+		return u[k] < other[k]
+	}
+	return false
+}
+
 // UnmarshalJSON implements the json unmarshaller interface.
 func (u *Uint160) UnmarshalJSON(data []byte) (err error) {
 	var js string

pkg/util/uint160_test.go

@@ -76,6 +76,21 @@ func TestUInt160Equals(t *testing.T) {
 	}
 }
 
+func TestUInt160Less(t *testing.T) {
+	a := "2d3b96ae1bcc5a585e075e3b81920210dec16302"
+	b := "2d3b96ae1bcc5a585e075e3b81920210dec16303"
+
+	ua, err := Uint160DecodeString(a)
+	assert.Nil(t, err)
+	ua2, err := Uint160DecodeString(a)
+	assert.Nil(t, err)
+	ub, err := Uint160DecodeString(b)
+	assert.Nil(t, err)
+	assert.Equal(t, true, ua.Less(ub))
+	assert.Equal(t, false, ua.Less(ua2))
+	assert.Equal(t, false, ub.Less(ua))
+}
+
 func TestUInt160String(t *testing.T) {
 	hexStr := "b28427088a3729b2536d10122960394e8be6721f"
 	hexRevStr := "1f72e68b4e39602912106d53b229378a082784b2"