如何获取接收到的UDP包的长度?使用 wireshark 我可以看到正确长度的数据报。如何在我的简单 udp 服务器程序中打印此值?我正在接收二进制数据(不可打印的 ascii 字符作为数据)所以我不能使用 strlen(buf),它会抛出不正确的长度。
if (ret=recvfrom(s, buf, BUFLEN, 0, (struct sockaddr *)&si_other, &slen)==-1){
error = ioctl(s, FIONREAD, &value);
printf(" from ioctl UDP packet length is : %d error is : %d\n", value, error);
}
在上面的代码中,udp 数据包长度始终为“0”。有什么意见吗?
我也试过如下
if (ret=recvfrom(s, buf, BUFLEN, 0, (struct sockaddr *)&si_other, &slen)!=-1){
unsigned short iphdrlen;
struct iphdr* iph = (struct iphdr*)buf;
iphdrlen =iph->ihl*4;
printf("IP version :%d\n", ((unsigned int)((iph->version))));
printf("protocol .. %d\n", ((unsigned int)(iph->protocol)));
printf("total len .. %d\n", (ntohs(iph->tot_len)));
}
上面的代码总是从 ip header 返回错误的值?有什么意见吗?
原始的 C 文件包含在这里。
#include "udp_common.h"
int main(void)
{
struct sockaddr_in si_me, si_other;
int s, i, slen=sizeof(si_other);
unsigned char buf[BUFLEN];
int noofbytes=0;
int ret=0,error,value;
memset(buf, 0, 512);
if ((s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))==-1)
diep("socket");
memset((char *) &si_me, 0, sizeof(si_me));
si_me.sin_family = AF_INET;
si_me.sin_port = htons(PORT);
si_me.sin_addr.s_addr = htonl(INADDR_ANY);
if (bind(s, (struct sockaddr *)&si_me, sizeof(si_me))==-1)
diep("bind");
for (i=0; ; i++)
//for (i=0; i<NPACK ; i++)
{
if (ret=recvfrom(s, buf, BUFLEN, 0, (struct sockaddr *)&si_other, &slen)==-1)
diep("recvfrom()");
printf(" source port is : %d %d\n", ntohs(si_other.sin_port), slen);
unsigned short iphdrlen;
struct iphdr* iph = (struct iphdr*)buf;
iphdrlen =iph->ihl*4;
printf("IP version :%d\n", ((unsigned int)((iph->version))));
printf("protocol .. %d\n", ((unsigned int)(iph->protocol)));
printf("total len .. %d\n", (ntohs(iph->tot_len)));
error = ioctl(s, FIONREAD, &value);
printf(" from ioctl UDP packet length is : %d error is : %d\n", value, error);
printf(" Return code from recvfrom is : %d\n", ret);
printf("Received packet from %s:%d\nData: %s\n\n",
inet_ntoa(si_other.sin_addr), ntohs(si_other.sin_port), buf);
int j=0;
for ( j = 0; j <20; j++)
{
char x = buf[j];
short int i;
for (i=1;i<9;i++)
{
((x | (1<<8-i)) == x)?printf("1"):printf("0");
}
printf(" ");
}
printf("\n");
}
close(s);
return 0;
}
我收到的输出如下:
source port is : 4232 16
IP version :1
protocol .. 65
total len .. 4096
from ioctl UDP packet length is : 0 error is : 0
Return code from recvfrom is : 0
Received packet from 127.0.0.1:4232
Data:
00010000 00000001 00010000 00000000 11110001 00010001 00010001 00100100 01000100 01000001 00010001 00100100 01000100 01000000 00000000 00010000 00000000 00010000 10100000 10100000
上面的解密数据与我发送的数据匹配。
最佳答案
您是如何创建套接字的?它是原始套接字 (SOCK_RAW) 还是 dgram 套接字 (SOCK_DGRAM)?在第二种情况下,您不会获得 ip/udp header ,只会获得有效负载。
顺便说一句,数据包长度是函数 recvfrom 的返回值 - 在您的例子中,是“ret”变量。检查recvfrom手册页。
关于c - 接收到的UDP包长度,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/2251198/