io: implement generic array (de-)serialization

It is done through reflection and panics
in every unexpected situation.

pkg/core/account_state.go

@@ -94,12 +94,7 @@ func (s *AccountState) DecodeBinary(br *io.BinReader) {
 	br.ReadLE(&s.Version)
 	br.ReadLE(&s.ScriptHash)
 	br.ReadLE(&s.IsFrozen)
-	lenVotes := br.ReadVarUint()
-	s.Votes = make([]*keys.PublicKey, lenVotes)
-	for i := 0; i < int(lenVotes); i++ {
-		s.Votes[i] = &keys.PublicKey{}
-		s.Votes[i].DecodeBinary(br)
-	}
+	s.Votes = br.ReadArray(keys.PublicKey{}).([]*keys.PublicKey)
 
 	s.Balances = make(map[util.Uint256]util.Fixed8)
 	lenBalances := br.ReadVarUint()
@@ -117,10 +112,7 @@ func (s *AccountState) EncodeBinary(bw *io.BinWriter) {
 	bw.WriteLE(s.Version)
 	bw.WriteLE(s.ScriptHash)
 	bw.WriteLE(s.IsFrozen)
-	bw.WriteVarUint(uint64(len(s.Votes)))
-	for _, point := range s.Votes {
-		point.EncodeBinary(bw)
-	}
+	bw.WriteArray(s.Votes)
 
 	balances := s.nonZeroBalances()
 	bw.WriteVarUint(uint64(len(balances)))

pkg/core/block.go

@@ -128,13 +128,7 @@ func (b *Block) Trim() ([]byte, error) {
 // Serializable interface.
 func (b *Block) DecodeBinary(br *io.BinReader) {
 	b.BlockBase.DecodeBinary(br)
-
-	lentx := br.ReadVarUint()
-	b.Transactions = make([]*transaction.Transaction, lentx)
-	for i := 0; i < int(lentx); i++ {
-		b.Transactions[i] = &transaction.Transaction{}
-		b.Transactions[i].DecodeBinary(br)
-	}
+	b.Transactions = br.ReadArray(transaction.Transaction{}).([]*transaction.Transaction)
 }
 
 // EncodeBinary encodes the block to the given BinWriter, implementing

pkg/core/transaction/claim.go

@@ -11,18 +11,10 @@ type ClaimTX struct {
 
 // DecodeBinary implements Serializable interface.
 func (tx *ClaimTX) DecodeBinary(br *io.BinReader) {
-	lenClaims := br.ReadVarUint()
-	tx.Claims = make([]*Input, lenClaims)
-	for i := 0; i < int(lenClaims); i++ {
-		tx.Claims[i] = &Input{}
-		tx.Claims[i].DecodeBinary(br)
-	}
+	tx.Claims = br.ReadArray(Input{}).([]*Input)
 }
 
 // EncodeBinary implements Serializable interface.
 func (tx *ClaimTX) EncodeBinary(bw *io.BinWriter) {
-	bw.WriteVarUint(uint64(len(tx.Claims)))
-	for _, claim := range tx.Claims {
-		claim.EncodeBinary(bw)
-	}
+	bw.WriteArray(tx.Claims)
 }

pkg/core/transaction/state.go

@@ -11,18 +11,10 @@ type StateTX struct {
 
 // DecodeBinary implements Serializable interface.
 func (tx *StateTX) DecodeBinary(r *io.BinReader) {
-	lenDesc := r.ReadVarUint()
-	tx.Descriptors = make([]*StateDescriptor, lenDesc)
-	for i := 0; i < int(lenDesc); i++ {
-		tx.Descriptors[i] = &StateDescriptor{}
-		tx.Descriptors[i].DecodeBinary(r)
-	}
+	tx.Descriptors = r.ReadArray(StateDescriptor{}).([]*StateDescriptor)
 }
 
 // EncodeBinary implements Serializable interface.
 func (tx *StateTX) EncodeBinary(w *io.BinWriter) {
-	w.WriteVarUint(uint64(len(tx.Descriptors)))
-	for _, desc := range tx.Descriptors {
-		desc.EncodeBinary(w)
-	}
+	w.WriteArray(tx.Descriptors)
 }

pkg/core/transaction/transaction.go

@@ -95,33 +95,10 @@ func (t *Transaction) DecodeBinary(br *io.BinReader) {
 	br.ReadLE(&t.Version)
 	t.decodeData(br)
 
-	lenAttrs := br.ReadVarUint()
-	t.Attributes = make([]*Attribute, lenAttrs)
-	for i := 0; i < int(lenAttrs); i++ {
-		t.Attributes[i] = &Attribute{}
-		t.Attributes[i].DecodeBinary(br)
-	}
-
-	lenInputs := br.ReadVarUint()
-	t.Inputs = make([]*Input, lenInputs)
-	for i := 0; i < int(lenInputs); i++ {
-		t.Inputs[i] = &Input{}
-		t.Inputs[i].DecodeBinary(br)
-	}
-
-	lenOutputs := br.ReadVarUint()
-	t.Outputs = make([]*Output, lenOutputs)
-	for i := 0; i < int(lenOutputs); i++ {
-		t.Outputs[i] = &Output{}
-		t.Outputs[i].DecodeBinary(br)
-	}
-
-	lenScripts := br.ReadVarUint()
-	t.Scripts = make([]*Witness, lenScripts)
-	for i := 0; i < int(lenScripts); i++ {
-		t.Scripts[i] = &Witness{}
-		t.Scripts[i].DecodeBinary(br)
-	}
+	t.Attributes = br.ReadArray(Attribute{}).([]*Attribute)
+	t.Inputs = br.ReadArray(Input{}).([]*Input)
+	t.Outputs = br.ReadArray(Output{}).([]*Output)
+	t.Scripts = br.ReadArray(Witness{}).([]*Witness)
 
 	// Create the hash of the transaction at decode, so we dont need
 	// to do it anymore.
@@ -167,10 +144,7 @@ func (t *Transaction) decodeData(r *io.BinReader) {
 // EncodeBinary implements Serializable interface.
 func (t *Transaction) EncodeBinary(bw *io.BinWriter) {
 	t.encodeHashableFields(bw)
-	bw.WriteVarUint(uint64(len(t.Scripts)))
-	for _, s := range t.Scripts {
-		s.EncodeBinary(bw)
-	}
+	bw.WriteArray(t.Scripts)
 }
 
 // encodeHashableFields encodes the fields that are not used for
@@ -185,22 +159,13 @@ func (t *Transaction) encodeHashableFields(bw *io.BinWriter) {
 	}
 
 	// Attributes
-	bw.WriteVarUint(uint64(len(t.Attributes)))
-	for _, attr := range t.Attributes {
-		attr.EncodeBinary(bw)
-	}
+	bw.WriteArray(t.Attributes)
 
 	// Inputs
-	bw.WriteVarUint(uint64(len(t.Inputs)))
-	for _, in := range t.Inputs {
-		in.EncodeBinary(bw)
-	}
+	bw.WriteArray(t.Inputs)
 
 	// Outputs
-	bw.WriteVarUint(uint64(len(t.Outputs)))
-	for _, out := range t.Outputs {
-		out.EncodeBinary(bw)
-	}
+	bw.WriteArray(t.Outputs)
 }
 
 // createHash creates the hash of the transaction.

pkg/io/binaryReader.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/binary"
 	"io"
+	"reflect"
 )
 
 // BinReader is a convenient wrapper around a io.Reader and err object.
@@ -33,6 +34,38 @@ func (r *BinReader) ReadLE(v interface{}) {
 	r.Err = binary.Read(r.r, binary.LittleEndian, v)
 }
 
+// ReadArray reads a slice or an array of pointer to t from r and returns.
+func (r *BinReader) ReadArray(t interface{}) interface{} {
+	elemType := reflect.ValueOf(t).Type()
+	method, ok := reflect.PtrTo(elemType).MethodByName("DecodeBinary")
+	if !ok || !isDecodeBinaryMethod(method) {
+		panic(elemType.String() + " does not have DecodeBinary(*io.BinReader)")
+	}
+
+	sliceType := reflect.SliceOf(reflect.PtrTo(elemType))
+	if r.Err != nil {
+		return reflect.Zero(sliceType).Interface()
+	}
+
+	l := int(r.ReadVarUint())
+	arr := reflect.MakeSlice(sliceType, l, l)
+	for i := 0; i < l; i++ {
+		elem := arr.Index(i)
+		method := elem.MethodByName("DecodeBinary")
+		elem.Set(reflect.New(elemType))
+		method.Call([]reflect.Value{reflect.ValueOf(r)})
+	}
+
+	return arr.Interface()
+}
+
+func isDecodeBinaryMethod(method reflect.Method) bool {
+	t := method.Type
+	return t != nil &&
+		t.NumIn() == 2 && t.In(1) == reflect.TypeOf((*BinReader)(nil)) &&
+		t.NumOut() == 0
+}
+
 // ReadBE reads from the underlying io.Reader
 // into the interface v in big-endian format.
 func (r *BinReader) ReadBE(v interface{}) {

pkg/io/binaryWriter.go

@@ -3,6 +3,7 @@ package io
 import (
 	"encoding/binary"
 	"io"
+	"reflect"
 )
 
 // BinWriter is a convenient wrapper around a io.Writer and err object.
@@ -34,6 +35,37 @@ func (w *BinWriter) WriteBE(v interface{}) {
 	w.Err = binary.Write(w.w, binary.BigEndian, v)
 }
 
+// WriteArray writes a slice or an array arr into w.
+func (w *BinWriter) WriteArray(arr interface{}) {
+	switch val := reflect.ValueOf(arr); val.Kind() {
+	case reflect.Slice, reflect.Array:
+		typ := val.Type().Elem()
+		method, ok := typ.MethodByName("EncodeBinary")
+		if !ok || !isEncodeBinaryMethod(method) {
+			panic(typ.String() + " does not have EncodeBinary(*BinWriter)")
+		}
+
+		if w.Err != nil {
+			return
+		}
+
+		w.WriteVarUint(uint64(val.Len()))
+		for i := 0; i < val.Len(); i++ {
+			method := val.Index(i).MethodByName("EncodeBinary")
+			method.Call([]reflect.Value{reflect.ValueOf(w)})
+		}
+	default:
+		panic("not an array")
+	}
+}
+
+func isEncodeBinaryMethod(method reflect.Method) bool {
+	t := method.Type
+	return t != nil &&
+		t.NumIn() == 2 && t.In(1) == reflect.TypeOf((*BinWriter)(nil)) &&
+		t.NumOut() == 0
+}
+
 // WriteVarUint writes a uint64 into the underlying writer using variable-length encoding.
 func (w *BinWriter) WriteVarUint(val uint64) {
 	if w.Err != nil {

pkg/io/binaryrw_test.go

@@ -5,6 +5,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 // mocks io.Reader and io.Writer, always fails to Write() or Read().
@@ -191,3 +192,83 @@ func TestWriteVarUint100000000000(t *testing.T) {
 	assert.Nil(t, br.Err)
 	assert.Equal(t, val, res)
 }
+
+type testSerializable uint16
+
+// EncodeBinary implements io.Serializable interface.
+func (t testSerializable) EncodeBinary(w *BinWriter) {
+	w.WriteLE(t)
+}
+
+// DecodeBinary implements io.Serializable interface.
+func (t *testSerializable) DecodeBinary(r *BinReader) {
+	r.ReadLE(t)
+}
+
+func TestBinWriter_WriteArray(t *testing.T) {
+	var arr [3]testSerializable
+	for i := range arr {
+		arr[i] = testSerializable(i)
+	}
+
+	expected := []byte{3, 0, 0, 1, 0, 2, 0}
+
+	w := NewBufBinWriter()
+	w.WriteArray(arr)
+	require.NoError(t, w.Err)
+	require.Equal(t, expected, w.Bytes())
+
+	w.Reset()
+	w.WriteArray(arr[:])
+	require.NoError(t, w.Err)
+	require.Equal(t, expected, w.Bytes())
+
+	arrS := make([]Serializable, len(arr))
+	for i := range arrS {
+		arrS[i] = &arr[i]
+	}
+
+	w.Reset()
+	w.WriteArray(arr)
+	require.NoError(t, w.Err)
+	require.Equal(t, expected, w.Bytes())
+
+	w.Reset()
+	require.Panics(t, func() { w.WriteArray(1) })
+
+	w.Reset()
+	w.Err = errors.New("error")
+	w.WriteArray(arr[:])
+	require.Error(t, w.Err)
+	require.Equal(t, w.Bytes(), []byte(nil))
+
+	w.Reset()
+	w.Err = errors.New("error")
+	require.Panics(t, func() { w.WriteArray([]int{}) })
+
+	w.Reset()
+	w.Err = errors.New("error")
+	require.Panics(t, func() { w.WriteArray(make(chan testSerializable)) })
+}
+
+func TestBinReader_ReadArray(t *testing.T) {
+	data := []byte{3, 0, 0, 1, 0, 2, 0}
+	r := NewBinReaderFromBuf(data)
+	result := r.ReadArray(testSerializable(0))
+	elems := []testSerializable{0, 1, 2}
+	require.Equal(t, []*testSerializable{&elems[0], &elems[1], &elems[2]}, result)
+
+	r = NewBinReaderFromBuf(data)
+	r.Err = errors.New("error")
+	result = r.ReadArray(testSerializable(0))
+	require.Error(t, r.Err)
+	require.Equal(t, ([]*testSerializable)(nil), result)
+
+	r = NewBinReaderFromBuf([]byte{0})
+	result = r.ReadArray(testSerializable(0))
+	require.NoError(t, r.Err)
+	require.Equal(t, []*testSerializable{}, result)
+
+	r = NewBinReaderFromBuf([]byte{0})
+	require.Panics(t, func() { r.ReadArray(0) })
+}

pkg/network/payload/address.go

@@ -67,19 +67,10 @@ func NewAddressList(n int) *AddressList {
 
 // DecodeBinary implements Serializable interface.
 func (p *AddressList) DecodeBinary(br *io.BinReader) {
-	listLen := br.ReadVarUint()
-
-	p.Addrs = make([]*AddressAndTime, listLen)
-	for i := 0; i < int(listLen); i++ {
-		p.Addrs[i] = &AddressAndTime{}
-		p.Addrs[i].DecodeBinary(br)
-	}
+	p.Addrs = br.ReadArray(AddressAndTime{}).([]*AddressAndTime)
 }
 
 // EncodeBinary implements Serializable interface.
 func (p *AddressList) EncodeBinary(bw *io.BinWriter) {
-	bw.WriteVarUint(uint64(len(p.Addrs)))
-	for _, addr := range p.Addrs {
-		addr.EncodeBinary(bw)
-	}
+	bw.WriteArray(p.Addrs)
 }

pkg/network/payload/headers.go

@@ -37,9 +37,5 @@ func (p *Headers) DecodeBinary(br *io.BinReader) {
 
 // EncodeBinary implements Serializable interface.
 func (p *Headers) EncodeBinary(bw *io.BinWriter) {
-	bw.WriteVarUint(uint64(len(p.Hdrs)))
-
-	for _, header := range p.Hdrs {
-		header.EncodeBinary(bw)
-	}
+	bw.WriteArray(p.Hdrs)
 }