我在http://jlnsqt.blog.51cto.com/2212965/1405052这篇博客中讲述了匹配URL的一个算法，因项目需要将其封装为动态库，并让python组调用，所以研究了一下ctypes，感觉超级棒，必须记录下来。
首先介绍一下我的动态库接口。
动态库结构体：
typedef struct _whitelist_tree_node_ {
uint8_t white_type; //匹配白名单是否结束，代表下一步执行的动作
uint8_t child_count; //该节点的子节点个数
uint8_t child_order[MAX_CHILDS_NUM]; //子节点在childs的位置(起始1)
struct _whitelist_tree_node_ *childs; //子节点数组
} whitelist_tree_node;
typedef struct _whitelist_tree_ {
whitelist_tree_node *root; //根节点
unsigned int whitelist_count; //URL白名单个数
} whitelist_tree, *PUrlWhiteListControl;
函数接口：
int InitUrlWhiteList(const char *ini_file, PUrlWhiteListControl *p_control);
int SearchUrlWhiteList(const char *url, PUrlWhiteListControl p_control);
void CloseUrlWhiteList(PUrlWhiteListControl p_control); 这里不再给出生成动态库方法和各个接口函数的定义，只介绍如何在python中调用。这里假设我动态库的名称为“liburlwhitelist.so”，动态库和python文件在同一目录，或者再引用动态库的时候用绝对路径。
开始使用ctypes之前，介绍一下ctypes的类型对照：
| ctypes type | C type | Python type |
|---|---|---|
| c_bool | _Bool | bool (1) |
| c_char | char | 1-character string |
| c_wchar | wchar_t | 1-character unicode string |
| c_byte | char | int/long |
| c_ubyte | unsignedchar | int/long |
| c_short | short | int/long |
| c_ushort | unsignedshort | int/long |
| c_int | int | int/long |
| c_uint | unsignedint | int/long |
| c_long | long | int/long |
| c_ulong | unsignedlong | int/long |
| c_longlong | __int64 or longlong | int/long |
| c_ulonglong | unsigned__int64 or unsignedlonglong | int/long |
| c_float | float | float |
| c_double | double | float |
| c_longdouble | longdouble | float |
| c_char_p | char* (NUL terminated) | string or None |
| c_wchar_p | wchar_t* (NUL terminated) | unicode or None |
| c_void_p | void* | int/long or None |
首先导入ctypes：
from ctypes import *定义最大子节点个数，也即静态数组的大小。
#max child node number
MAX_NODE_CHILD_NUM = 46 下面就是重点了，需要用python模拟出Linux C的结构体来。
#define tree node
class whitelist_tree_node(Structure):
pass
whitelist_tree_node._fields_ = [
("white_type", c_ubyte),
("child_count", c_ubyte),
("child_order", c_ubyte * MAX_NODE_CHILD_NUM),
("childs", POINTER(whitelist_tree_node))
]
#define tree
class whitelist_tree(Structure):
pass
whitelist_tree._fields_ = [
("root", POINTER(whitelist_tree_node)),
("whitelist_count", c_uint)
]
#define query url whitelist control
PUrlWhiteListControl = POINTER(whitelist_tree)为了定义节点指向自己的指针，这里必须先用pass定义一个空的对象，否则会出现“NameError: name 'whitelist_tree_node' is not defined”的错误。取类型的指针用POINTER()函数，而取变量对象的指针用pointer()函数，注意区分。
导入库，可用绝对路径：
#load library
url_whitelist_lib = cdll.LoadLibrary("./liburlwhitelist.so")引入接口函数，并对接口函数属性进行设置。
#define init function
InitUrlWhiteList = url_whitelist_lib.InitUrlWhiteList
#define argument types
InitUrlWhiteList.argtypes = [POINTER(PUrlWhiteListControl)]
#define return types. By default functions are assumed to return the C int type
InitUrlWhiteList.restype = c_int
#define search function
SearchUrlWhiteList = url_whitelist_lib.SearchUrlWhiteList
SearchUrlWhiteList.argtypes = [c_char_p, PUrlWhiteListControl]
SearchUrlWhiteList.restype = c_int
#define close function
CloseUrlWhiteList = url_whitelist_lib.CloseUrlWhiteList
CloseUrlWhiteList.argtypes = [PUrlWhiteListControl]
CloseUrlWhiteList.restype = None 定义每个函数第一行“InitUrlWhiteList =url_whitelist_lib.InitUrlWhiteList”是为了减少函数调用。InitUrlWhiteList.argtypes设置函数的参数，为了更好的调用，减少出错。
InitUrlWhiteList.restype设置函数的返回类型，因为ctypes默认的返回类型时C int，我这里还是指出，便于统一和减少出错。
使用部分例子：
p_control = PUrlWhiteListControl()
ret_code = InitUrlWhiteList(None, pointer(p_control))
if ret_code != 0:
print "InitUrlWhiteList error code: %d" % ret_code
else:
print "init url whitelist num: %u" % p_control.contents.whitelist_count这里有三个地方需要注意。一、None变量即是C中NULL。二：InitUrlWhiteList参数，因其第二个参数为PUrlWhiteListControl的指针，所以这里用pointer()函数，当然也可用byref()函数，但是在官方文档中指出：
The same effect can be achieved with the pointer() function, although
pointer() does a lot more work since it constructs a real pointer
object, so it is faster to use byref() if you don’t need the pointer
object in Python itself所以这里我们还是用pointer()函数好。三、因PUrlWhiteListControl本身是一个指针，要访问他的内容需要用contents方法。如“p_control.contents.whitelist_count”。
好了，关于ctypes，先介绍到这里，更详细的请参考官方文档：https://docs.python.org/2/library/ctypes.html。详细代码如下：
#!/usr/bin/env python
# -*- coding: utf-8 -*-
# @Author: sqt
# @Email: qingtao_shang@vulnhunt.com
# @Date: 2014-04-30 09:57:37
# @Desc: Python测试URL白名单动态库
# @Last Modified by: sqt
# @Last Modified time: 2014-04-30 13:30:17
from ctypes import *
#max child node number
MAX_NODE_CHILD_NUM = 46
#define tree node
class whitelist_tree_node(Structure):
pass
whitelist_tree_node._fields_ = [
("white_type", c_ubyte),
("child_count", c_ubyte),
("child_order", c_ubyte * MAX_NODE_CHILD_NUM),
("childs", POINTER(whitelist_tree_node))
]
#define tree
class whitelist_tree(Structure):
pass
whitelist_tree._fields_ = [
("root", POINTER(whitelist_tree_node)),
("whitelist_count", c_uint)
]
#define query url whitelist control
PUrlWhiteListControl = POINTER(whitelist_tree)
#load library
url_whitelist_lib = cdll.LoadLibrary("./liburlwhitelist.so")
#simple call function name
#define init function
InitUrlWhiteList = url_whitelist_lib.InitUrlWhiteList
#define argument types
InitUrlWhiteList.argtypes = [POINTER(PUrlWhiteListControl)]
#define return types. By default functions are assumed to return the C int type
InitUrlWhiteList.restype = c_int
#define search function
SearchUrlWhiteList = url_whitelist_lib.SearchUrlWhiteList
SearchUrlWhiteList.argtypes = [c_char_p, PUrlWhiteListControl]
SearchUrlWhiteList.restype = c_int
#define close function
CloseUrlWhiteList = url_whitelist_lib.CloseUrlWhiteList
CloseUrlWhiteList.argtypes = [PUrlWhiteListControl]
CloseUrlWhiteList.restype = None
#sample
if __name__ == "__main__":
p_control = PUrlWhiteListControl()
ret_code = InitUrlWhiteList(None, pointer(p_control))
if ret_code != 0:
print "InitUrlWhiteList error code: %d" % ret_code
else:
print "init url whitelist num: %u" % p_control.contents.whitelist_count
url = ""
while 1:
url = raw_input("Input url or exit:")
if url == "q" or url == "exit":
break
find_code = SearchUrlWhiteList(url, p_control)
if find_code == 0:
print "url: %s find." % url
else:
print "url: %s not find." % url
CloseUrlWhiteList(p_control)
del p_control
