利用nids库实现ICMP数据包解析与报文构造

#include "nids.h"        
/*      
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UDP协议首部的数据结构      
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 */   
struct udp_header        
{        
    unsigned short udp_source_port;        
    unsigned short udp_destination_port;        
    unsigned short udp_length;        
    unsigned short udp_checksum;        
};        
/*      
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ICMP协议首部的数据结构      
-----------------------------------------------------------------------------------------------------------------------      
 */   
struct icmp_header        
{        
    unsigned int icmp_type;        
    unsigned int icmp_code;        
    unsigned char icmp_checksum;        
    unsigned char icmp_id;        
    unsigned char icmp_sequence;        
};        
/*      
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IP协议首部的数据结构      
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 */   
struct ip_header        
{        
    #if defined(WORDS_BIGENDIAN)        
        unsigned char ip_version: 4,  /* 版本 */   
        ip_header_length: 4; /* 首部长度 */   
    #else        
        unsigned char ip_header_length: 4, ip_version: 4;        
    #endif        
    unsigned char ip_tos; /* 服务类型 */   
    unsigned short ip_length; /* 总长度 */   
    unsigned short ip_id; /* 标识 */   
    unsigned short ip_off; /* 标志和偏移 */   
    unsigned char ip_ttl; /* 生存时间 */   
    unsigned char ip_protocol; /* 协议类型 */   
    unsigned short ip_checksum; /* 校验和 */   
    struct in_addr ip_souce_address; /* 源IP地址 */   
    struct in_addr ip_destination_address; /* 目的IP地址 */   
};        
/*      
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TCP协议首部      
-----------------------------------------------------------------------------------------------------------------------      
 */   
struct tcp_header        
{        
    unsigned char tcp_source_port; /* 源端口号 */   
    unsigned char tcp_destination_port; /* 目的端口号 */   
    unsigned short tcp_sequence; /* 学列码 */   
    unsigned short tcp_acknowledgement; /* 确认号 */