Improve error message names

encode.go

@@ -244,7 +244,7 @@ func DecodeDynamicLength(buf []byte, maxSize int) (int, error) {
 	offset := binary.LittleEndian.Uint32(buf[:4])
 	length, ok := DivideInt(int(offset), bytesPerLengthOffset)
 	if !ok {
-		return 0, fmt.Errorf("bad")
+		return 0, fmt.Errorf("incorrect length division")
 	}
 	if length > maxSize {
 		return 0, fmt.Errorf("too big for the list")
@@ -255,12 +255,15 @@ func DecodeDynamicLength(buf []byte, maxSize int) (int, error) {
 // UnmarshalDynamic unmarshals the dynamic items from the input
 func UnmarshalDynamic(src []byte, length int, f func(indx int, b []byte) error) error {
 	var err error
+	size := uint64(len(src))
+
 	if length == 0 {
+		if size != 0 && size != 4 {
+			return ErrSize
+		}
 		return nil
 	}
 
-	size := uint64(len(src))
-
 	indx := 0
 	dst := src
 
@@ -277,10 +280,10 @@ func UnmarshalDynamic(src []byte, length int, f func(indx int, b []byte) error)
 			endOffset = uint64(len(src))
 		}
 		if offset > endOffset {
-			return fmt.Errorf("four")
+			return fmt.Errorf("incorrect end of offset: %d %d", offset, endOffset)
 		}
 		if endOffset > size {
-			return fmt.Errorf("five")
+			return fmt.Errorf("incorrect end of offset size: %d %d", endOffset, size)
 		}
 
 		err := f(indx, src[offset:endOffset])
@@ -302,10 +305,10 @@ func UnmarshalDynamic(src []byte, length int, f func(indx int, b []byte) error)
 func DivideInt2(a, b, max int) (int, error) {
 	num, ok := DivideInt(a, b)
 	if !ok {
-		return 0, fmt.Errorf("xx")
+		return 0, fmt.Errorf("failed to divide int %d by %d", a, b)
 	}
 	if num > max {
-		return 0, fmt.Errorf("yy")
+		return 0, fmt.Errorf("num %d is greater than max %d", num, max)
 	}
 	return num, nil
 }

encode_test.go

@@ -1,12 +1,16 @@
 package ssz
 
 import (
+	"bytes"
+	"fmt"
 	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strconv"
 	"strings"
 	"testing"
+
+	"github.com/stretchr/testify/require"
 )
 
 func TestBitlist(t *testing.T) {
@@ -106,3 +110,36 @@ func TestEncode_ExtendUint(t *testing.T) {
 		t.Fatal("uint8 cannot be nil")
 	}
 }
+
+func TestUnmarshalDynamic(t *testing.T) {
+	{
+		buf := []byte{}
+		buf = WriteOffset(buf, 4*1)
+		buf = append(buf, 0x1)
+
+		num, err := DecodeDynamicLength(buf, 10)
+		require.NoError(t, err)
+
+		err = UnmarshalDynamic(buf, num, func(i int, b []byte) error {
+			if !bytes.Equal(b, []byte{0x1}) {
+				return fmt.Errorf("bad")
+			}
+			return nil
+		})
+		require.NoError(t, err)
+	}
+
+	{
+		buf := []byte{}
+		buf = WriteOffset(buf, 0)
+		buf = append(buf, 0x1)
+
+		num, err := DecodeDynamicLength(buf, 10)
+		require.NoError(t, err)
+
+		err = UnmarshalDynamic(buf, num, func(i int, b []byte) error {
+			return nil
+		})
+		require.Equal(t, ErrSize, err)
+	}
+}

sszgen/generator/unmarshal.go

@@ -274,7 +274,7 @@ func (v *Value) umarshalContainer(start bool, dst string) (str string) {
 				return ssz.ErrOffset
 			}
 			{{ if .firstOffsetCheck }}
-			if {{.offset}} < {{.firstOffsetCheck}} {
+			if {{.offset}} != {{.firstOffsetCheck}} {
 				return ssz.ErrInvalidVariableOffset
 			}
 			{{ end }}