问题:我使用UDP协议创建了一个原始套接字,发送了一个由UDP标头和数据组成的数据包,在PP中一切正常,数据包是正确的,我也在另一个程序中创建了相同的套接字,并且它接受了我发送的数据,但带有 IP 标头。为何如此?为什么这没有写在任何地方? 也就是说,我们发送 DATA+UDP,并从同一个套接字接收 DATA+UDP+IP。
第二个接收数据的程序只有在指针上加20,即IP头的大小才起作用。
#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <linux/udp.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netinet/ether.h>
#include <sys/types.h>
#include <sys/socket.h>
#define __USE_XOPEN2K
#include <netdb.h>
#define AF_INETv4 0x02
#define AF_INETv6 0x0A
int main(int argc, char **argv)
{
int m_socket = socket(AF_INETv4, SOCK_RAW, IPPROTO_UDP);
struct sockaddr_in bnd;
bnd.sin_family = AF_INET;
bnd.sin_port = htons(55555);
bnd.sin_addr.s_addr = inet_addr("127.0.0.1");
bind(m_socket, &bnd, sizeof(bnd));
perror("bind: ");
struct iovec iov;
char buffer[1500 - 14 - 20] = {0};
iov.iov_base = &buffer;
iov.iov_len = sizeof(buffer);
struct udphdr *udp = iov.iov_base;
udp->source = htons(55555);
udp->dest = htons(22222);
udp->len = htons(8);
udp->check = 0;
struct msghdr msg = {0};
msg.msg_flags = 0;
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
struct sockaddr_in in;
in.sin_family = AF_INETv4;
in.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
in.sin_port = htons(22222);
msg.msg_name = ∈
msg.msg_namelen = sizeof(struct sockaddr_in);
for(int i = 0; i < 10; i++)
{
sendmsg(m_socket, &msg, 0);
perror("");
}
return 0;
}
#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <linux/udp.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netinet/ether.h>
#include <sys/types.h>
#include <sys/socket.h>
#define __USE_XOPEN2K
#include <netdb.h>
#define AF_INETv4 0x02
#define AF_INETv6 0x0A
int main(int argc, char **argv)
{
int m_socket = socket(AF_INETv4, SOCK_RAW, IPPROTO_UDP);
struct sockaddr_in bnd;
bnd.sin_family = AF_INET;
bnd.sin_port = htons(22222);
bnd.sin_addr.s_addr = inet_addr("127.0.0.1");
bind(m_socket, &bnd, sizeof(bnd));
perror("bind: ");
struct iovec iov;
char buffer[1500 - 14 - 20] = {0};
iov.iov_base = &buffer;
iov.iov_len = sizeof(buffer);
struct msghdr msg = {0};
msg.msg_flags = 0;
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
struct sockaddr_in in;
in.sin_family = AF_INETv4;
in.sin_addr.s_addr = 0;
in.sin_port = 0;
msg.msg_name = ∈
msg.msg_namelen = sizeof(struct sockaddr_in);
for(int i = 0; i < 10; i++)
{
recvmsg(m_socket, &msg, MSG_ZEROCOPY);
perror("");
struct udphdr *udp = (uint8_t*)iov.iov_base + 20;
uint16_t src = htons(udp->source );
uint16_t dst = htons(udp->dest);
uint16_t len = htons(udp->len);
uint16_t chk = htons(udp->check);
fprintf(stderr, "src: %hu dst: %hu len: %hu chk: %hu\n", src, dst, len, chk);
}
return 0;
}
您正在发送您自己构建的额外标头。 如果您的套接字是 AF_INETv4,则无需编写 IP 标头。 这让操作系统知道它是一个 IP 套接字,并为您添加标头。