Python与C++结构体交互

需求：根据接口规范，实现与服务端的数据交互

服务端结构体分包头、包体、包尾

包头C++结构体示例如下

 1 typedef struct head
 2 {
 3     BYTE string1;
 4     BYTE    string2;    //包类型
 5     BYTE    string3;            //版本号,目前为0
 6     char    string4[33];        
 7     int        string5;        
 8     int        string6;            
 9     unsigned int string7;    //包头校验和,以上所有字段的crc32校验和
10     char    string8;
11     char    string9;
12 }protocol_head;

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包体C++结构体示例如下

1 typedef struct body
2 {
3     char    sessid[33];
4     int        datalen;    
5     BYTE    data[0];    
6 };

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包尾C++结构体示例如下

1 // 包尾 - 粘包分割
2 typedef struct tag_protocol_tail
3 {
4     BYTE tail[4]
5 }protocol_tail;

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根据包头结构体的要求，需要使用CRC32校验

 1 unsigned int GetCRC32(const unsigned char *pbData, int nSize)
 2 {
 3     unsigned long Table[256]={0};
 4     unsigned long  ulPolynomial = 0xEDB88320;
 5 
 6     unsigned long  dwCrc;
 7     int i,j;
 8     for(i = 0; i < 256; i++)
 9     {
10         dwCrc = i;
11         for(j = 8; j > 0; j--)
12         {
13             if(dwCrc & 1)
14                 dwCrc = (dwCrc >> 1) ^ ulPolynomial;
15             else
16                 dwCrc >>= 1;
17         }
18         Table[i] = dwCrc;
19     }
20 
21     unsigned long dwCrc32 = 0xFFFFFFFF;
22     int idx=0;
23     while(nSize--)
24     {
25         dwCrc32 = ((dwCrc32) >> 8) ^ Table[(pbData[idx]) ^ ((dwCrc32) & 0x000000FF)];
26         idx++;
27     }
28     return ~dw

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python 实现内容

struct中支持的格式如下表：

Format	C Type	Python	字节数
x	pad byte	no value	1
c	char	string of length 1	1
b	signed char	integer	1
B	unsigned char	integer	1
?	_Bool	bool	1
h	short	integer	2
H	unsigned short	integer	2
i	int	integer	4
I	unsigned int	integer or long	4
l	long	integer	4
L	unsigned long	long	4
q	long long	long	8
Q	unsigned long long	long	8
f	float	float	4
d	double	float	8
s	char[]	string	1
p	char[]	string	1
P	void *	long

举例C中常用:

int16=short --> h
uint32=unsigned int --> I

UInt64=unsigned long long --> Q
byte表示一个字节,对应C的unsigned char --> B

python中CRC32校验

 1 def mycrc32(szString):
 2     # 校验码
 3     m_pdwCrc32Table = [0 for x in range(0, 256)]
 4     dwPolynomial = 0xEDB88320
 5     dwCrc = 0
 6     for i in range(0, 255):
 7         dwCrc = i
 8         for j in [8, 7, 6, 5, 4, 3, 2, 1]:
 9             if dwCrc & 1:
10                 dwCrc = (dwCrc >> 1) ^ dwPolynomial
11             else:
12                 dwCrc >>= 1
13         m_pdwCrc32Table[i] = dwCrc
14     dwCrc32 = 0xFFFFFFFFL
15     for i in szString:
16         b = ord(i)
17         dwCrc32 = ((dwCrc32) >> 8) ^ m_pdwCrc32Table[(b) ^ ((dwCrc32) & 0x000000FF)]
18     dwCrc32 = dwCrc32 ^ 0xFFFFFFFFL
19     return dwCrc32

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C++和python关于CRC32代码传入参数如何理解？

根据上面C++代码内容，可以看到传入2位参数，它的第一位参数是整个包头+包体+包尾内容，第二位参数是整个包前多少位的长度需要校验

对于python代码，实际上只要传入需要校验的内容。

本文中需要传入的内容实际上是包头的的前6个字段，也就是包头的string1+string2+string3+string4+string5+string6

包头代码

 1 # 包头, data为传入的包体，body_len是包体长度
 2 def qzj_head(data, body_len):
 3     string1 = 100
 4     string2 = 1
 5     string3 = 0
 6     string4 = "6"
 7     string5 = body_len
 8     string6 = body_len
 9 
10     string1 = struct.pack('B', string1 )
11     string2 = struct.pack('B', string2 )
12     string3 = struct.pack('B', string3)
13     string4 = struct.pack('33s', string4 )
14     string5 = struct.pack('i', string5 )
15     string6 = struct.pack('i', string6 )
16 
17     string7_struct = string1+string2+string3+string4+string5+string6  # 前面的6个字段内容
18     string7_crc32 = des_key.mycrc32(headcrc_str)  # crc32校验
19     string7 = struct.pack('I', string7_crc32)
20     string8 = 0
21     string9 = 0
22     string8 = struct.pack('B', string8)
23     string9 = struct.pack('B', string9)
24 
25     request_head = string1+string2+string3+string4+string5+string6+string7+string8+string9+data
26     return request_head

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包尾代码

 1 # 包尾，data是传入的包头+包体
 2 def qzj_tail(data):
 3     tail1 = '\0'
 4     tail2 = '\0'
 5     tail3 = '\r'
 6     tail4 = '\n'
 7     tail1 = struct.pack('s', tail1)
 8     tail2 = struct.pack('s', tail2)
 9     tail3 = struct.pack('s', tail3)
10     tail4 = struct.pack('s', tail4)
11     request_tail = data+tail1+tail2+tail3+tail4
12     return request_tail

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包体代码

 1 # 包体, data是要发送的json数据
 2 def body_100(data):
 3     string1 = ''
 4     string2 = len(data)
 5     string3 = data
 6 
 7     string1 = struct.pack('33s', string1)
 8     string2 = struct.pack('i', string2)
 9     string3 = struct.pack('%ds' % datalen_num, string3)
10     request_body = string1+string2+string3
11     return request_body, len(request_body)