diff --git a/bug.py b/bug.py
new file mode 100644
index 0000000..c8a1b96
--- /dev/null
+++ b/bug.py
@@ -0,0 +1,15 @@
+class A:
+    def __init__(self, arg=None):
+        if arg is None:
+            self.arg = {}
+
+    def set(self):
+        self.arg['something'] = 'something'
+
+
+a1 = A()
+a1.set()
+a2 = A()
+
+print(a2.arg)
+# output is {'something': 'something'}
diff --git a/mswp.py b/mswp.py
index 4396a6a..ef85a9b 100644
--- a/mswp.py
+++ b/mswp.py
@@ -1,11 +1,12 @@
 class Datapack:
     def __init__(self, method='post', app='all', version='msw/1.0', head=None, body=b'', check_head=True):
         if head is None:
-            self.head = {}
+            head = {}
+            self.head = head
         self.method = method
         self.app = app
         self.version = version
-        if not head and check_head:
+        if not self.head and check_head:
             self.head = {'nohead': "true"}
         else:
             self.head = head
@@ -21,7 +22,6 @@ class Datapack:
         self.encode_data = first_line + b'\n' + heads + b'\n' + self.body
 
     def decode(self, only_head=False):
-        self.head = {}
         index = self.encode_data.index(b'\n\n')
         upper = self.encode_data[:index]
         if not only_head:
@@ -37,3 +37,6 @@ class Datapack:
             self.head[i] = ii
         if only_head:
             return self.encode_data[index+2:]
+
+
+dp = Datapack()
diff --git a/plugins/net.py b/plugins/net.py
index 6bb5161..b1e1fcc 100644
--- a/plugins/net.py
+++ b/plugins/net.py
@@ -92,7 +92,7 @@ class Netrecv:
                         print('Null data')
                         break
                 except Exception as e:
-                    print('Decode error')
+                    print('Decode error %s: %s' % (type(e), str(e)))
                     break
                 # try unpack #
 
@@ -138,6 +138,13 @@ class Netrecv:
                                 aleady_write_down += still_need
                                 data = new_data[still_need:]
 
+                    else:
+                        file = open(dp.head['filename'], 'wb')
+                        file.write(data[:length])
+                        data = data[length:]
+
+                    file.close()
+
                 else:  # dp.method is not 'file'
                     length = int(dp.head['length'])
                     data_length = len(data)
diff --git a/test_file.py b/test_file.py
index b21b4a6..844380c 100644
--- a/test_file.py
+++ b/test_file.py
@@ -1,7 +1,7 @@
 import socket
 import time
 
-data = '''post log msw/1.0
+data = '''file log msw/1.0
 from: network
 flag: abcdefgh
 filename: download.txt