diff --git a/shadowsocks/obfsplugin/http_simple.py b/shadowsocks/obfsplugin/http_simple.py
index 4dc8d49..926ba85 100644
--- a/shadowsocks/obfsplugin/http_simple.py
+++ b/shadowsocks/obfsplugin/http_simple.py
@@ -90,8 +90,9 @@ class http_simple(plain.plain):
     def client_encode(self, buf):
         if self.has_sent_header:
             return buf
-        if len(buf) > 64:
-            headlen = random.randint(1, 64)
+        head_size = self.get_head_size(buf, 30)
+        if len(buf) - head_size > 64:
+            headlen = head_size + random.randint(1, 64)
         else:
             headlen = len(buf)
         headdata = buf[:headlen]
diff --git a/shadowsocks/obfsplugin/plain.py b/shadowsocks/obfsplugin/plain.py
index 5450e7a..a99fb0b 100644
--- a/shadowsocks/obfsplugin/plain.py
+++ b/shadowsocks/obfsplugin/plain.py
@@ -22,6 +22,8 @@ import sys
 import hashlib
 import logging
 
+from shadowsocks.common import ord
+
 def create_obfs(method):
     return plain(method)
 
@@ -70,3 +72,15 @@ class plain(object):
     def dispose(self):
         pass
 
+    def get_head_size(self, buf, def_value):
+        if len(buf) < 2:
+            return def_value
+        head_type = ord(buf[0]) & 0xF
+        if head_type == 1:
+            return 7
+        if head_type == 4:
+            return 19
+        if head_type == 3:
+            return 4 + ord(buf[1])
+        return def_value
+
diff --git a/shadowsocks/obfsplugin/verify_simple.py b/shadowsocks/obfsplugin/verify_simple.py
index 03c73b2..16c8342 100644
--- a/shadowsocks/obfsplugin/verify_simple.py
+++ b/shadowsocks/obfsplugin/verify_simple.py
@@ -82,17 +82,6 @@ class verify_base(plain.plain):
     def server_decode(self, buf):
         return (buf, True, False)
 
-    def get_head_size(self, buf, def_value):
-        if len(buf) < 2:
-            return def_value
-        if ord(buf[0]) == 1:
-            return 7
-        if ord(buf[0]) == 4:
-            return 19
-        if ord(buf[0]) == 3:
-            return 4 + ord(buf[1])
-        return def_value
-
 class verify_simple(verify_base):
     def __init__(self, method):
         super(verify_simple, self).__init__(method)