Thrift对象的序列化与反序列化

正文

对象的序列化与反序列化,可能大家更多接触的是谷歌的protobuf。
Thrift作为一个跨语言的RPC代码生成引擎,也具备此功能。
本文要说的是如何使用Thrift实现对象的序列化与反序列化,其实就是,如何以protobuf的方式使用Thrift。

Thrift描述文件:

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# filename: demo.thrift
struct Node {
1: string host
2: i32 port
}

以生成的Python代码为例,Thrift生成的类型提供了两个关键方法:

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class Node:
"""
Attributes:
- host
- port
"""
thrift_spec = (
None, # 0
(1, TType.STRING, 'host', None, None, ), # 1
(2, TType.I32, 'port', None, None, ), # 2
)

def __init__(self, host=None, port=None,):
self.host = host
self.port = port

def read(self, iprot):
...

def write(self, oprot):
...

read/write方法按照指定协议传输对象,所以需要一个TProtocol对象。

TProtocol对象构造时需要传入一个TTransport对象,即传输层,所以还需要一个TTransport对象。

由于数据已经准备完毕,要做的只是反序列化。

好,TMemoryBuffer满足需求。

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class TMemoryBuffer(TTransportBase, CReadableTransport):
"""Wraps a cStringIO object as a TTransport.

NOTE: Unlike the C++ version of this class, you cannot write to it
then immediately read from it. If you want to read from a
TMemoryBuffer, you must either pass a string to the constructor.
TODO(dreiss): Make this work like the C++ version.
"""

def __init__(self, value=None):
"""value -- a value to read from for stringio

If value is set, this will be a transport for reading,
otherwise, it is for writing"""
if value is not None:
self._buffer = StringIO(value)
else:
self._buffer = StringIO()

TMemoryBuffer继承TTransportBase,也属于一种TTransport,内部封装了一个StringIO对象。

利用目标数据构造一个TMemoryBuffer对象,然后调用read/write方法实现反序列化和序列化。

需要注意的是,Python在初始化TMemoryBuffer对象时必须指定value。

序列化/反序列化的示例代码:

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#! /usr/bin/env python
# -*- coding: utf-8 -*-

import sys
sys.path.append('gen-py')

from thrift.transport import TTransport
from thrift.protocol import TBinaryProtocol
from demo.ttypes import *

def serialize(th_obj):
""" Serialize.
"""
tmembuf = TTransport.TMemoryBuffer()
tbinprot = TBinaryProtocol.TBinaryProtocol(tmembuf)
th_obj.write(tbinprot)
return tmembuf.getvalue()

def deserialize(val, th_obj_type):
""" Deserialize.
"""
th_obj = th_obj_type()
tmembuf = TTransport.TMemoryBuffer(val)
tbinprot = TBinaryProtocol.TBinaryProtocol(tmembuf)
th_obj.read(tbinprot)
return th_obj

if __name__ == '__main__':
node1 = Node('localhost', 8000)
print 'node1:', node1

# modified
node1.host = '127.0.0.1'
node1.port = 9000

val = serialize(node1)
node2 = deserialize(val, Node)
print 'node2:', node2

输出结果:

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node1: Node(host='localhost', port=8000)
node2: Node(host='127.0.0.1', port=9000)

特别鸣谢

参考链接

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