对python 自定义协议的方法详解

import struct
import ctypes

class E(Exception):
 def __init__(self, what):
  self.what = what

 def __str__(self):
  return self.what

def unmarshall_packet(pk):
 if len(pk) < 12:
  raise E("Invalid pk header")
 size, uri, prop_count = struct.unpack("<III", pk[:12]);
 print "size:%d uri:%d prop_count:%d" % (size, uri, prop_count)
 if len(pk) - 12 != size - 8:
  raise E("Invalid pk length")

 ss = pk[12:]
 offset = 0
 for x in range(0, prop_count):
  # Pop key
  key_size, = struct.unpack_from("<I", ss, offset)
  print "key_size:%d" % (key_size,)
  offset += 4
  key, = struct.unpack_from("<%ds" % (key_size - 1,), ss, offset)
  offset += key_size

  # Pop value 
  val_size, = struct.unpack_from("<I", ss, offset)
  offset += 4
  print "val_size:%d" % (val_size,)
  val, = struct.unpack_from("<%ds" % (val_size - 1,), ss, offset)
  offset += val_size


  print "key:%s val:%s" % (key, val)


key1 = "key1"
val1 = "val1"
key2 = "key2"
val2 = "val2"
offset = 0
ss = ctypes.create_string_buffer(9085)
struct.pack_into("<III", ss, 0, 8 + 4 + len(key1) + len(val1) + len(key2) + len(val2) + 16, 2, 2)
offset += 12
struct.pack_into("<I%dscI%dscI%dscI%dsc" % (len(key1), len(val1), len(key2), len(val2)), ss, offset, len(key1) + 1, key1, '\0', 
 len(val1) + 1, val1, '\0',
 len(key2) + 1, key2, '\0', 
 len(val2) + 1, val2, '\0')
offset += len(key1) + len(val1) + len(key2) + len(val2) + 4 + 16
unmarshall_packet(ss[:offset])

"""
hex=""
ss = bytearray.fromhex(hex)
unmarshall_packet(ss)