解析http302重定向url

bool urlparse(const u_char* data,u_int len)
{
ip_header *ih;
udp_header *uh;
tcp_header *th;
u_short sport,dport;
int ip_len = 0;
ih = (ip_header *)(data+0xE);
ip_len = (ih->ver_ihl & 0xf) * sizeof(unsigned long);
th = (tcp_header *) ((u_char*)ih + ip_len);
sport = ntohs( th->th_sport );
dport = ntohs( th->th_dport );

if ((ih->proto != IPPROTO_TCP))
return false;

std::string strdata((char*)th + sizeof(tcp_header),len - ip_len - sizeof(tcp_header)+1);

static char szTag0[] = "HTTP/1.1 302 Moved Temporarily ";
static char szTag1[] = "Location: ";
static char szTag2[] = " ";

size_t nP0 = strdata.find(szTag0);
if (nP0 == std::string::npos)
return false;

size_t nP1 = strdata.find(szTag1,nP0+strlen(szTag0));
if (nP1 == std::string::npos)
return false;

size_t nP2 = strdata.find(szTag2,nP1+strlen(szTag1));
if (nP2 == std::string::npos)
return false;

std::string strUrl = strdata.substr(nP1+strlen(szTag1),nP2-nP1-strlen(szTag1));

printf("url>%s ",strUrl.c_str());

return true;
}