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<td width="68%" background="DDl_back2.jpg" height="44"><big><big><font face="黑体"><p align="center">               ● UNIX网络编程                       (BM: clown)                </font></big></big></td></tr>
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<tr><td width="100%" colspan="2" height="100" align="center" valign="top"><br><p align="center">[<a href="index.htm">回到开始</a>][<a href="473.htm">上一层</a>][<a href="499.htm">下一篇</a>]
<hr><p align="left"><small>发信人: scz (小四), 信区: Security <br>

标  题: 计算tcp校验和的例子 <br>

发信站: 武汉白云黄鹤站 (Wed Jul 26 16:43:29 2000), 站内信件 <br>

这些东西总有人问，似乎每一拨学习socket编程的都要问一次， <br>

不废话了，给个可用的solaris下的计算例子算了： <br>

int sendSyn ( int sendSocket, u_long sourceIp, u_short sourcePort, u_long se <br>

qNum <br>

, struct sockaddr_in * dest ) <br>

{ <br>

    u_char          netPacket[ IPTCPSIZE ]; <br>

    struct ip *     iph; <br>

    struct tcphdr * tcp; <br>

    u_char *        pPseudoHead;  /* 指向伪头标的指针 */ <br>

    u_char          pseudoHead[12 + sizeof(struct tcphdr)];  /* 伪头标占12字 <br>

节 * <br>

/ <br>

    u_short         tcpHeadLen;  /* 网络字节顺序 */ <br>

    memset( netPacket, 0, IPTCPSIZE ); <br>

    iph                = ( struct ip * )netPacket; <br>

    iph->ip_hl         = 5; <br>

    iph->ip_v          = 4; <br>

    iph->ip_tos        = 0; <br>

    iph->ip_len        = htons( IPTCPSIZE ); <br>



    iph->ip_id         = htons( 2600 + ( rand() % 32768 ) );  /* 随机产生ip- <br>

>id <br>

*/ <br>

    iph->ip_off        = 0; <br>

    iph->ip_ttl        = 255; <br>

    iph->ip_p          = IPPROTO_TCP; <br>

    iph->ip_sum        = 0;  /* 内核总是亲自计算IP头部校验和 */ <br>

    iph->ip_src.s_addr = sourceIp; <br>

    iph->ip_dst        = dest->sin_addr; <br>

    tcpHeadLen         = htons( sizeof( struct tcphdr ) );  /* 网络字节顺序 <br>

*/ <br>

    tcp                = (struct tcphdr *)( netPacket + sizeof( struct ip ) <br>

); <br>

    tcp->th_sport      = htons( sourcePort ); <br>

    tcp->th_dport      = htons( dest->sin_port ); <br>

    tcp->th_seq        = htonl( seqNum ); <br>

    tcp->th_ack        = 0; <br>

    tcp->th_x2         = 0; <br>

    tcp->th_off        = 5; <br>

    tcp->th_flags      = TH_SYN; <br>

    tcp->th_win        = htons( 10052 ); <br>

    tcp->th_sum        = 0; <br>



    tcp->th_urp        = 0; <br>

    pPseudoHead        = pseudoHead; <br>

    memset( pPseudoHead, 0, 12 + sizeof( struct tcphdr ) ); <br>

    memcpy( pPseudoHead, &( iph->ip_src ), 8 ); <br>

    pPseudoHead       += 9;  /* 有一个字节用做对齐 */ <br>

    memcpy( pPseudoHead, &( iph->ip_p ), 1 ); <br>

    pPseudoHead++; <br>

    memcpy( pPseudoHead, &tcpHeadLen, 2 ); <br>

    pPseudoHead       += 2; <br>

    memcpy( pPseudoHead, tcp, sizeof( struct tcphdr ) ); <br>

    tcp->th_sum        = in_cksum( ( u_short * )pseudoHead, sizeof( struct t <br>

cphd <br>

r ) + 12 ); <br>

    return( sendto( sendSocket, netPacket, IPTCPSIZE, 0, <br>

            ( struct sockaddr * )dest, sizeof( struct sockaddr_in ) ) ); <br>

}  /* end of sendSyn */ <br>

-- <br>

            也许有一天，他再从海上蓬蓬的雨点中升起， <br>

            飞向西来，再形成一道江流，再冲倒两旁的石壁， <br>

            再来寻夹岸的桃花。然而，我不敢说来生，也不敢信来生...... <br>

※ 来源:．武汉白云黄鹤站 bbs.whnet.edu.cn．[FROM: 203.207.226.124] <br>

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