io: implement generic array (de-)serialization

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

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) })
+}