accounts/abi: bugfix for unpacking nested arrays

The code previously assumed the arrays/slices were always 1 level
deep. While the packing supports nested arrays (!!!).

The current code for unpacking doesn't return the "consumed" length, so
this fix had to work around that by calculating it (i.e. packing and
 getting resulting length) after the unpacking of the array element.
It's far from ideal, but unpacking behaviour is fixed now.

accounts/abi/unpack.go

@@ -104,7 +104,6 @@ func forEachUnpack(t Type, output []byte, start, size int) (interface{}, error)
 
 	// this value will become our slice or our array, depending on the type
 	var refSlice reflect.Value
-	slice := output[start : start+size*32]
 
 	if t.T == SliceTy {
 		// declare our slice
@@ -116,17 +115,25 @@ func forEachUnpack(t Type, output []byte, start, size int) (interface{}, error)
 		return nil, fmt.Errorf("abi: invalid type in array/slice unpacking stage")
 	}
 
-	for i, j := start, 0; j*32 < len(slice); i, j = i+32, j+1 {
+	for i, j := start, 0; j < size; j++ {
-		// this corrects the arrangement so that we get all the underlying array values
-		if t.Elem.T == ArrayTy && j != 0 {
-			i = start + t.Elem.Size*32*j
-		}
 		inter, err := toGoType(i, *t.Elem, output)
 		if err != nil {
 			return nil, err
 		}
+
+		reflectedInter := reflect.ValueOf(inter)
+
+		//Although we just did the reverse, pack it, to get the length of the actual element.
+		//Getting the length directly from the "toGoType" would be way better,
+		// but it requires some refactoring to get it return the *consumed* length.
+		interPacked, err  := t.Elem.pack(reflectedInter)
+		if err != nil {
+			return nil, err
+		}
+		i += len(interPacked)
+
 		// append the item to our reflect slice
-		refSlice.Index(j).Set(reflect.ValueOf(inter))
+		refSlice.Index(j).Set(reflectedInter)
 	}
 
 	// return the interface