报文（Message）实例—— TCP / IP 头结构

typedef struct _iphdr                       //定义IP首部{    unsigned char h_lenver;                 //4位IP版本号 + 4位首部长度    unsigned char tos;                      //8位服务类型TOS    unsigned short total_len;               //16位总长度（单位：字节）保存本次实体信息长度    unsigned short ident;                   //16位标识    unsigned short frag_and_flags;          //3位标志位+13位偏移量    unsigned char ttl;                      //8位生存时间 TTL    unsigned char proto;                    //8位协议TCP, UDP 或其他    unsigned short checksum;                //16位IP首部校验和    unsigned int sourceIP;                  //32位源IP地址    unsigned int destIP;                    //32位目的IP地址}IP_HEADER; typedef struct psd_hdr                      //定义TCP伪首部{    unsigned long saddr;                    //源地址    unsigned long daddr;                    //目的地址    char mbz;    char ptcl;                              //协议类型    unsigned short tcpl;                    //TCP长度}PSD_HEADER;typedef struct _tcphdr                      //定义TCP首部{    unsigned short th_spor;                 //16位源端口    unsigned short th_dport;                //16位目的端口    unsigned int th_seq;                    //32位序列号    unsigned int th_ack;                    //32位确认号    unsigned char th_lenres;                //4位首部长度/6位保留字    unsigned char th_flag;                  //6位标志位    unsigned short th_win;                  //16位窗口大小    unsigned short th_sum;                  //16位校验和    unsigned short th_urp;                  //16位紧急数据偏移量}TCP_HEADER;