Change header callback to bytes, but default Milter to convert

to str with surrogateescape.

Milter/__init__.py

@@ -701,6 +701,13 @@ def connect_callback(ctx,hostname,family,hostaddr,nr_mask=P_NR_CONN):
     m._setctx(ctx)
   return m.connect(hostname,family,hostaddr)
 
+## @private
+# @brief check str/bytes decorator and invoke header method.
+def header_callback(ctx,fld,val):
+  m = ctx.getpriv()
+  s = val.decode(encoding='ascii',errors='surrogateescape')
+  return m.header(fld,s)
+
 ## @private
 # @brief Disconnect milterContext and call close method.
 def close_callback(ctx):