Optimizations + some improvements (#105)

* Optimizations + some improvements

- optimized pkg/core/storage.HeaderHashes
- optimized pkg/rpc.performRequest (used json.Encoder)
- fixes for pkg/util.ReadVarUint and pkg/util.WriteVarUint
- optimized and fix fixed8 (Fixed8DecodeString / MarshalJSON) + tests
- optimized and fix uint160 (Bytes / Uint160DecodeString / Equal / MarshalJSON) + tests
- optimized and fix uint256 (Bytes / Equal / MarshalJSON) + tests
- preallocate for pkg/vm.buildStackOutput
- add go.mod / go.sum

* update version

VERSION

@@ -1 +1 @@
-0.44.10
+0.44.11

go.mod

@@ -0,0 +1,22 @@
+module github.com/CityOfZion/neo-go
+
+require (
+	github.com/anthdm/rfc6979 v0.0.0-20141003034818-6a90f24967eb
+	github.com/codahale/rfc6979 v0.0.0-20141003034818-6a90f24967eb // indirect
+	github.com/davecgh/go-spew v1.1.0 // indirect
+	github.com/go-redis/redis v6.10.2+incompatible
+	github.com/go-yaml/yaml v2.1.0+incompatible
+	github.com/golang/snappy v0.0.0-20170215233205-553a64147049 // indirect
+	github.com/onsi/gomega v1.4.2 // indirect
+	github.com/pkg/errors v0.8.0
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/sirupsen/logrus v1.0.5
+	github.com/stretchr/testify v1.2.1
+	github.com/syndtr/goleveldb v0.0.0-20180307113352-169b1b37be73
+	github.com/urfave/cli v1.20.0
+	golang.org/x/crypto v0.0.0-20180316180149-374053ea96cb
+	golang.org/x/text v0.3.0
+	golang.org/x/tools v0.0.0-20180318012157-96caea41033d
+	gopkg.in/airbrake/gobrake.v2 v2.0.9 // indirect
+	gopkg.in/gemnasium/logrus-airbrake-hook.v2 v2.1.2 // indirect
+)

go.sum

@@ -0,0 +1,58 @@
+github.com/anthdm/rfc6979 v0.0.0-20141003034818-6a90f24967eb h1:UTxADjhpvBfb7LpAB+uu4uzlTJ3ZJyWA5En+KsYHed8=
+github.com/anthdm/rfc6979 v0.0.0-20141003034818-6a90f24967eb/go.mod h1:EjSkpESoXW3cDxVZzHil2eVMoGkYxb8Q7qgfV5JOTPs=
+github.com/codahale/rfc6979 v0.0.0-20141003034818-6a90f24967eb h1:EDmT6Q9Zs+SbUoc7Ik9EfrFqcylYqgPZ9ANSbTAntnE=
+github.com/codahale/rfc6979 v0.0.0-20141003034818-6a90f24967eb/go.mod h1:ZjrT6AXHbDs86ZSdt/osfBi5qfexBrKUdONk989Wnk4=
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/fsnotify/fsnotify v1.4.7 h1:IXs+QLmnXW2CcXuY+8Mzv/fWEsPGWxqefPtCP5CnV9I=
+github.com/fsnotify/fsnotify v1.4.7/go.mod h1:jwhsz4b93w/PPRr/qN1Yymfu8t87LnFCMoQvtojpjFo=
+github.com/go-redis/redis v6.10.2+incompatible h1:SLbqrO/Ik1nhXA5/cbEs1P5MUBo1Qq4ihlNfGnnipPw=
+github.com/go-redis/redis v6.10.2+incompatible/go.mod h1:NAIEuMOZ/fxfXJIrKDQDz8wamY7mA7PouImQ2Jvg6kA=
+github.com/go-yaml/yaml v2.1.0+incompatible h1:RYi2hDdss1u4YE7GwixGzWwVo47T8UQwnTLB6vQiq+o=
+github.com/go-yaml/yaml v2.1.0+incompatible/go.mod h1:w2MrLa16VYP0jy6N7M5kHaCkaLENm+P+Tv+MfurjSw0=
+github.com/golang/protobuf v1.2.0 h1:P3YflyNX/ehuJFLhxviNdFxQPkGK5cDcApsge1SqnvM=
+github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
+github.com/golang/snappy v0.0.0-20170215233205-553a64147049 h1:K9KHZbXKpGydfDN0aZrsoHpLJlZsBrGMFWbgLDGnPZk=
+github.com/golang/snappy v0.0.0-20170215233205-553a64147049/go.mod h1:/XxbfmMg8lxefKM7IXC3fBNl/7bRcc72aCRzEWrmP2Q=
+github.com/hpcloud/tail v1.0.0 h1:nfCOvKYfkgYP8hkirhJocXT2+zOD8yUNjXaWfTlyFKI=
+github.com/hpcloud/tail v1.0.0/go.mod h1:ab1qPbhIpdTxEkNHXyeSf5vhxWSCs/tWer42PpOxQnU=
+github.com/onsi/ginkgo v1.6.0 h1:Ix8l273rp3QzYgXSR+c8d1fTG7UPgYkOSELPhiY/YGw=
+github.com/onsi/ginkgo v1.6.0/go.mod h1:lLunBs/Ym6LB5Z9jYTR76FiuTmxDTDusOGeTQH+WWjE=
+github.com/onsi/gomega v1.4.2 h1:3mYCb7aPxS/RU7TI1y4rkEn1oKmPRjNJLNEXgw7MH2I=
+github.com/onsi/gomega v1.4.2/go.mod h1:ex+gbHU/CVuBBDIJjb2X0qEXbFg53c61hWP/1CpauHY=
+github.com/pkg/errors v0.8.0 h1:WdK/asTD0HN+q6hsWO3/vpuAkAr+tw6aNJNDFFf0+qw=
+github.com/pkg/errors v0.8.0/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/sirupsen/logrus v1.0.5 h1:8c8b5uO0zS4X6RPl/sd1ENwSkIc0/H2PaHxE3udaE8I=
+github.com/sirupsen/logrus v1.0.5/go.mod h1:pMByvHTf9Beacp5x1UXfOR9xyW/9antXMhjMPG0dEzc=
+github.com/stretchr/testify v1.2.1 h1:52QO5WkIUcHGIR7EnGagH88x1bUzqGXTC5/1bDTUQ7U=
+github.com/stretchr/testify v1.2.1/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+github.com/syndtr/goleveldb v0.0.0-20180307113352-169b1b37be73 h1:I2drr5K0tykBofr74ZEGliE/Hf6fNkEbcPyFvsy7wZk=
+github.com/syndtr/goleveldb v0.0.0-20180307113352-169b1b37be73/go.mod h1:Z4AUp2Km+PwemOoO/VB5AOx9XSsIItzFjoJlOSiYmn0=
+github.com/urfave/cli v1.20.0 h1:fDqGv3UG/4jbVl/QkFwEdddtEDjh/5Ov6X+0B/3bPaw=
+github.com/urfave/cli v1.20.0/go.mod h1:70zkFmudgCuE/ngEzBv17Jvp/497gISqfk5gWijbERA=
+golang.org/x/crypto v0.0.0-20180316180149-374053ea96cb h1:O6ztCaemiMr99EgJdgXrr0J7N0EQN1oky/0GxML9Avk=
+golang.org/x/crypto v0.0.0-20180316180149-374053ea96cb/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
+golang.org/x/net v0.0.0-20180906233101-161cd47e91fd h1:nTDtHvHSdCn1m6ITfMRqtOd/9+7a3s8RBNOZ3eYZzJA=
+golang.org/x/net v0.0.0-20180906233101-161cd47e91fd/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
+golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f h1:wMNYb4v58l5UBM7MYRLPG6ZhfOqbKu7X5eyFl8ZhKvA=
+golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sys v0.0.0-20180909124046-d0be0721c37e h1:o3PsSEY8E4eXWkXrIP9YJALUkVZqzHJT5DOasTyn8Vs=
+golang.org/x/sys v0.0.0-20180909124046-d0be0721c37e/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/tools v0.0.0-20180318012157-96caea41033d h1:Xmo0nLTRYewf0eXDvo12nMSuOgNQ4283hdbOHIUf7h8=
+golang.org/x/tools v0.0.0-20180318012157-96caea41033d/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
+gopkg.in/airbrake/gobrake.v2 v2.0.9 h1:7z2uVWwn7oVeeugY1DtlPAy5H+KYgB1KeKTnqjNatLo=
+gopkg.in/airbrake/gobrake.v2 v2.0.9/go.mod h1:/h5ZAUhDkGaJfjzjKLSjv6zCL6O0LLBxU4K+aSYdM/U=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/fsnotify.v1 v1.4.7 h1:xOHLXZwVvI9hhs+cLKq5+I5onOuwQLhQwiu63xxlHs4=
+gopkg.in/fsnotify.v1 v1.4.7/go.mod h1:Tz8NjZHkW78fSQdbUxIjBTcgA1z1m8ZHf0WmKUhAMys=
+gopkg.in/gemnasium/logrus-airbrake-hook.v2 v2.1.2 h1:OAj3g0cR6Dx/R07QgQe8wkA9RNjB2u4i700xBkIT4e0=
+gopkg.in/gemnasium/logrus-airbrake-hook.v2 v2.1.2/go.mod h1:Xk6kEKp8OKb+X14hQBKWaSkCsqBpgog8nAV2xsGOxlo=
+gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7 h1:uRGJdciOHaEIrze2W8Q3AKkepLTh2hOroT7a+7czfdQ=
+gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7/go.mod h1:dt/ZhP58zS4L8KSrWDmTeBkI65Dw0HsyUHuEVlX15mw=
+gopkg.in/yaml.v2 v2.2.1 h1:mUhvW9EsL+naU5Q3cakzfE91YhliOondGd6ZrsDBHQE=
+gopkg.in/yaml.v2 v2.2.1/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=

pkg/core/storage/helpers.go

@@ -42,6 +42,13 @@ func CurrentHeaderHeight(s Store) (i uint32, h util.Uint256, err error) {
 	return
 }
 
+// uint32Slice attaches the methods of Interface to []int, sorting in increasing order.
+type uint32Slice []uint32
+
+func (p uint32Slice) Len() int           { return len(p) }
+func (p uint32Slice) Less(i, j int) bool { return p[i] < p[j] }
+func (p uint32Slice) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
+
 // HeaderHashes returns a sorted list of header hashes retrieved from
 // the given underlying Store.
 func HeaderHashes(s Store) ([]util.Uint256, error) {
@@ -56,19 +63,17 @@ func HeaderHashes(s Store) ([]util.Uint256, error) {
 	})
 
 	var (
-		i          = 0
+		hashes     []util.Uint256
-		sortedKeys = make([]int, len(hashMap))
+		sortedKeys = make([]uint32, 0, len(hashMap))
 	)
 
-	for k, _ := range hashMap {
+	for k := range hashMap {
-		sortedKeys[i] = int(k)
+		sortedKeys = append(sortedKeys, k)
-		i++
 	}
-	sort.Ints(sortedKeys)
+	sort.Sort(uint32Slice(sortedKeys))
 
-	hashes := []util.Uint256{}
 	for _, key := range sortedKeys {
-		values := hashMap[uint32(key)]
+		values := hashMap[key]
 		for _, hash := range values {
 			hashes = append(hashes, hash)
 		}

pkg/core/transaction/witness.go

@@ -43,7 +43,7 @@ func (w *Witness) EncodeBinary(writer io.Writer) error {
 
 // MarshalJSON implements the json marshaller interface.
 func (w *Witness) MarshalJSON() ([]byte, error) {
-	data := map[string]interface{}{
+	data := map[string]string{
 		"invocation":   hex.EncodeToString(w.InvocationScript),
 		"verification": hex.EncodeToString(w.VerificationScript),
 	}

pkg/rpc/client.go

@@ -83,18 +83,21 @@ func NewClient(ctx context.Context, endpoint string, opts ClientOptions) (*Clien
 }
 
 func (c *Client) performRequest(method string, p params, v interface{}) error {
-	r := request{
+	var (
-		JSONRPC: c.version,
+		r = request{
-		Method:  method,
+			JSONRPC: c.version,
-		Params:  p.values,
+			Method:  method,
-		ID:      1,
+			Params:  p.values,
-	}
+			ID:      1,
+		}
+		buf = new(bytes.Buffer)
+	)
 
-	b, err := json.Marshal(r)
+	if err := json.NewEncoder(buf).Encode(r); err != nil {
-	if err != nil {
 		return err
 	}
-	req, err := http.NewRequest("POST", c.endpoint.String(), bytes.NewReader(b))
+
+	req, err := http.NewRequest("POST", c.endpoint.String(), buf)
 	if err != nil {
 		return err
 	}

pkg/util/fixed8.go

@@ -1,7 +1,6 @@
 package util
 
 import (
-	"bytes"
 	"encoding/json"
 	"errors"
 	"strconv"
@@ -20,7 +19,7 @@ type Fixed8 int64
 
 // String implements the Stringer interface.
 func (f Fixed8) String() string {
-	buf := new(bytes.Buffer)
+	buf := new(strings.Builder)
 	val := int64(f)
 	if val < 0 {
 		buf.WriteRune('-')
@@ -54,20 +53,23 @@ func NewFixed8(val int) Fixed8 {
 // with precision up to 10^-8
 func Fixed8DecodeString(s string) (Fixed8, error) {
 	parts := strings.SplitN(s, ".", 2)
-	ip, err := strconv.Atoi(parts[0])
+	ip, err := strconv.ParseInt(parts[0], 10, 64)
 	if err != nil {
 		return 0, errInvalidString
 	} else if len(parts) == 1 {
-		return NewFixed8(ip), nil
+		return Fixed8(ip * decimals), nil
 	}
 
-	fp, err := strconv.Atoi(parts[1])
+	fp, err := strconv.ParseInt(parts[1], 10, 64)
 	if err != nil || fp >= decimals {
 		return 0, errInvalidString
 	}
 	for i := len(parts[1]); i < precision; i++ {
 		fp *= 10
 	}
+	if ip < 0 {
+		return Fixed8(ip*decimals - fp), nil
+	}
 	return Fixed8(ip*decimals + fp), nil
 }
 
@@ -91,3 +93,8 @@ func (f *Fixed8) UnmarshalJSON(data []byte) error {
 	*f = Fixed8(decimals * fl)
 	return nil
 }
+
+// MarshalJSON implements the json marshaller interface.
+func (f Fixed8) MarshalJSON() ([]byte, error) {
+	return []byte(`"` + f.String() + `"`), nil
+}

pkg/util/fixed8_test.go

@@ -2,6 +2,7 @@ package util
 
 import (
 	"encoding/json"
+	"strconv"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -39,19 +40,25 @@ func TestFixed8DecodeString(t *testing.T) {
 }
 
 func TestFixed8UnmarshalJSON(t *testing.T) {
-	fl := float64(123.45)
+	var testCases = []float64{
-	str := "123.45"
+		123.45,
-	expected, _ := Fixed8DecodeString(str)
+		-123.45,
+	}
 
-	// UnmarshalJSON should decode floats
+	for _, fl := range testCases {
-	var u1 Fixed8
+		str := strconv.FormatFloat(fl, 'g', -1, 64)
-	s, _ := json.Marshal(fl)
+		expected, _ := Fixed8DecodeString(str)
-	assert.Nil(t, json.Unmarshal(s, &u1))
-	assert.Equal(t, expected, u1)
 
-	// UnmarshalJSON should decode strings
+		// UnmarshalJSON should decode floats
-	var u2 Fixed8
+		var u1 Fixed8
-	s, _ = json.Marshal(str)
+		s, _ := json.Marshal(fl)
-	assert.Nil(t, json.Unmarshal(s, &u2))
+		assert.Nil(t, json.Unmarshal(s, &u1))
-	assert.Equal(t, expected, u2)
+		assert.Equal(t, expected, u1)
+
+		// UnmarshalJSON should decode strings
+		var u2 Fixed8
+		s, _ = json.Marshal(str)
+		assert.Nil(t, json.Unmarshal(s, &u2))
+		assert.Equal(t, expected, u2)
+	}
 }

pkg/util/io.go

@@ -19,24 +19,22 @@ import (
 func ReadVarUint(r io.Reader) uint64 {
 	var b uint8
 	binary.Read(r, binary.LittleEndian, &b)
-
+	switch b {
-	if b == 0xfd {
+	case 0xfd:
 		var v uint16
 		binary.Read(r, binary.LittleEndian, &v)
 		return uint64(v)
-	}
+	case 0xfe:
-	if b == 0xfe {
 		var v uint32
 		binary.Read(r, binary.LittleEndian, &v)
 		return uint64(v)
-	}
+	case 0xff:
-	if b == 0xff {
 		var v uint64
 		binary.Read(r, binary.LittleEndian, &v)
 		return v
+	default:
+		return uint64(b)
 	}
-
-	return uint64(b)
 }
 
 // WriteVarUint writes a variable unsigned integer.
@@ -45,24 +43,26 @@ func WriteVarUint(w io.Writer, val uint64) error {
 		return errors.New("value out of range")
 	}
 	if val < 0xfd {
-		binary.Write(w, binary.LittleEndian, uint8(val))
+		return binary.Write(w, binary.LittleEndian, uint8(val))
-		return nil
 	}
 	if val < 0xFFFF {
-		binary.Write(w, binary.LittleEndian, byte(0xfd))
+		if err := binary.Write(w, binary.LittleEndian, byte(0xfd)); err != nil {
-		binary.Write(w, binary.LittleEndian, uint16(val))
+			return err
-		return nil
+		}
+		return binary.Write(w, binary.LittleEndian, uint16(val))
 	}
 	if val < 0xFFFFFFFF {
-		binary.Write(w, binary.LittleEndian, byte(0xfe))
+		if err := binary.Write(w, binary.LittleEndian, byte(0xfe)); err != nil {
-		binary.Write(w, binary.LittleEndian, uint32(val))
+			return err
-		return nil
+		}
+		return binary.Write(w, binary.LittleEndian, uint32(val))
 	}
 
-	binary.Write(w, binary.LittleEndian, byte(0xff))
+	if err := binary.Write(w, binary.LittleEndian, byte(0xff)); err != nil {
-	binary.Write(w, binary.LittleEndian, val)
+		return err
+	}
 
-	return nil
+	return binary.Write(w, binary.LittleEndian, val)
 }
 
 // ReadVarBytes reads a variable length byte array.

pkg/util/uint160.go

@@ -16,7 +16,8 @@ const uint160Size = 20
 type Uint160 [uint160Size]uint8
 
 // Uint160DecodeString attempts to decode the given string into an Uint160.
-func Uint160DecodeString(s string) (u Uint160, err error) {
+func Uint160DecodeString(s string) (Uint160, error) {
+	var u Uint160
 	if len(s) != uint160Size*2 {
 		return u, fmt.Errorf("expected string size of %d got %d", uint160Size*2, len(s))
 	}
@@ -51,11 +52,7 @@ func Uint160FromScript(script []byte) (u Uint160, err error) {
 
 // Bytes returns the byte slice representation of u.
 func (u Uint160) Bytes() []byte {
-	b := make([]byte, uint160Size)
+	return u[:]
-	for i := 0; i < uint160Size; i++ {
-		b[i] = byte(u[i])
-	}
-	return b
 }
 
 // BytesReverse return a reversed byte representation of u.
@@ -70,12 +67,7 @@ func (u Uint160) String() string {
 
 // Equals returns true if both Uint256 values are the same.
 func (u Uint160) Equals(other Uint160) bool {
-	for i := 0; i < uint160Size; i++ {
+	return u == other
-		if u[i] != other[i] {
-			return false
-		}
-	}
-	return true
 }
 
 // UnmarshalJSON implements the json unmarshaller interface.
@@ -93,7 +85,5 @@ func (u *Uint160) UnmarshalJSON(data []byte) (err error) {
 
 // MarshalJSON implements the json marshaller interface.
 func (u Uint160) MarshalJSON() ([]byte, error) {
-	return json.Marshal(
+	return []byte(`"0x` + u.String() + `"`), nil
-		fmt.Sprintf("0x%s", hex.EncodeToString(ArrayReverse(u.Bytes()))),
-	)
 }

pkg/util/uint160_test.go

@@ -2,7 +2,6 @@ package util
 
 import (
 	"encoding/hex"
-	"encoding/json"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -10,19 +9,29 @@ import (
 
 func TestUint160UnmarshalJSON(t *testing.T) {
 	str := "2d3b96ae1bcc5a585e075e3b81920210dec16302"
-	expected, _ := Uint160DecodeString(str)
+	expected, err := Uint160DecodeString(str)
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	// UnmarshalJSON should decode hex-strings
-	var u1 Uint160
+	var u1, u2 Uint160
-	s, _ := json.Marshal(str)
+
-	assert.Nil(t, json.Unmarshal(s, &u1))
+	if err = u1.UnmarshalJSON([]byte(`"` + str + `"`)); err != nil {
+		t.Fatal(err)
+	}
 	assert.True(t, expected.Equals(u1))
 
+	s, err := expected.MarshalJSON()
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	// UnmarshalJSON should decode hex-strings prefixed by 0x
-	var u2 Uint160
+	if err = u2.UnmarshalJSON(s); err != nil {
-	s, _ = json.Marshal("0x" + str)
+		t.Fatal(err)
-	assert.Nil(t, json.Unmarshal(s, &u2))
+	}
-	assert.True(t, expected.Equals(u2))
+	assert.True(t, expected.Equals(u1))
 }
 
 func TestUInt160DecodeString(t *testing.T) {

pkg/util/uint256.go

@@ -38,11 +38,7 @@ func Uint256DecodeBytes(b []byte) (u Uint256, err error) {
 
 // Bytes returns a byte slice representation of u.
 func (u Uint256) Bytes() []byte {
-	b := make([]byte, uint256Size)
+	return u[:]
-	for i := 0; i < uint256Size; i++ {
-		b[i] = byte(u[i])
-	}
-	return b
 }
 
 // BytesReverse return a reversed byte representation of u.
@@ -52,7 +48,7 @@ func (u Uint256) BytesReverse() []byte {
 
 // Equals returns true if both Uint256 values are the same.
 func (u Uint256) Equals(other Uint256) bool {
-	return u.String() == other.String()
+	return u == other
 }
 
 // String implements the stringer interface.
@@ -75,5 +71,5 @@ func (u *Uint256) UnmarshalJSON(data []byte) (err error) {
 
 // MarshalJSON implements the json marshaller interface.
 func (u Uint256) MarshalJSON() ([]byte, error) {
-	return json.Marshal(fmt.Sprintf("0x%s", u.String()))
+	return []byte(`"0x` + u.String() + `"`), nil
 }

pkg/util/uint256_test.go

@@ -2,7 +2,6 @@ package util
 
 import (
 	"encoding/hex"
-	"encoding/json"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -10,19 +9,29 @@ import (
 
 func TestUint256UnmarshalJSON(t *testing.T) {
 	str := "f037308fa0ab18155bccfc08485468c112409ea5064595699e98c545f245f32d"
-	expected, _ := Uint256DecodeString(str)
+	expected, err := Uint256DecodeString(str)
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	// UnmarshalJSON should decode hex-strings
-	var u1 Uint256
+	var u1, u2 Uint256
-	s, _ := json.Marshal(str)
+
-	assert.Nil(t, json.Unmarshal(s, &u1))
+	if err = u1.UnmarshalJSON([]byte(`"` + str + `"`)); err != nil {
+		t.Fatal(err)
+	}
 	assert.True(t, expected.Equals(u1))
 
+	s, err := expected.MarshalJSON()
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	// UnmarshalJSON should decode hex-strings prefixed by 0x
-	var u2 Uint256
+	if err = u2.UnmarshalJSON(s); err != nil {
-	s, _ = json.Marshal("0x" + str)
+		t.Fatal(err)
-	assert.Nil(t, json.Unmarshal(s, &u2))
+	}
-	assert.True(t, expected.Equals(u2))
+	assert.True(t, expected.Equals(u1))
 }
 
 func TestUint256DecodeString(t *testing.T) {

pkg/vm/output.go

@@ -10,14 +10,12 @@ type stackItem struct {
 }
 
 func buildStackOutput(s *Stack) string {
-	items := make([]stackItem, s.Len())
+	items := make([]stackItem, 0, s.Len())
-	i := 0
 	s.Iter(func(e *Element) {
-		items[i] = stackItem{
+		items = append(items, stackItem{
 			Value: e.value,
 			Type:  e.value.String(),
-		}
+		})
-		i++
 	})
 
 	b, _ := json.MarshalIndent(items, "", "    ")