Added more necessary parts to compression.

writer_fragment.go

@@ -0,0 +1,21 @@
+package squashfs
+
+type fragment struct {
+	w     *Writer
+	files []*fileHolder
+	sizes []uint32
+}
+
+func (f *fragment) SizeLeft() uint32 {
+	totalSize := uint32(0)
+	for _, siz := range f.sizes {
+		totalSize += siz
+	}
+	return f.w.BlockSize - uint32(totalSize)
+}
+
+func (f *fragment) AddFragment(fil *fileHolder) {
+	//SizeLeft should already be checked
+	f.files = append(f.files, fil)
+	f.sizes = append(f.sizes, fil.blockSizes[len(fil.blockSizes)-1])
+}