我正在尝试将 UDP 数据包发送到生存时间为 1 的路由器，然后接收 ICMP 超时回复。到目前为止，我能够发送数据包，但是当我的程序进入执行的 recv 部分时，它只是挂起。我对 recvfrom 进行了错误检查，但它甚至没有做到这一点。我的电脑正在接收请求。我知道这一点是因为我在运行程序时运行 Wireshark 并过滤 ICMP 请求。每次我运行程序，我都会收到回复。recvfrom 我做错了什么？
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <errno.h>
#define UNSPEC_PROTO 0
int main(int argc, const char *argv[])
{
if (argc != 2) {
printf("usage: routetracer <ip address or hostname>\n");
return -1;
}
struct addrinfo hints; //params for ret val of getaddrinfo
struct addrinfo* ret; //return value of getaddrinfo
struct sockaddr* reply_addr;
char ipv4[INET_ADDRSTRLEN];
char* msg = "THE PORT IS OVER 9000!!!!";
int status = 0;
int ttl = 0;
int src_sock = 0;
int recv_sock = 0;
socklen_t reply_addr_len = sizeof(struct sockaddr);
const char* dest_port = "9001";
int icmp_msg_len = 100;
char icmp_msg[icmp_msg_len];
//define what we want from getaddrinfo
memset(&hints, 0, sizeof(hints));
hints.ai_family = AF_INET; //IPv4
hints.ai_socktype = SOCK_DGRAM; //UDP packets
//call getaddrinfo to fill ret, w/ error chk
if ((status = getaddrinfo(argv[1], dest_port, &hints, &ret)) != 0) {
printf("getaddrinfo: %s\n", gai_strerror(status));
return -1;
}
//extract IPv4 address from ret
struct sockaddr_in* ip = (struct sockaddr_in *)ret->ai_addr;
//convert address from pure numbers to something easier to read
inet_ntop(ret->ai_family, &(ip->sin_addr), ipv4, INET_ADDRSTRLEN);
//kindly inform the user of which hostname they are connecting to
printf("Route for: %s\n", ipv4);
//create a socket for our machine
if ((src_sock = socket(ret->ai_family, ret->ai_socktype,
ret->ai_protocol)) < 0) {
fprintf(stderr, "Error creating host socket: %s\n", strerror(errno));
return -1;
}
//create a socket to recv icmp packet from hops
if ((recv_sock = socket(AF_INET, SOCK_DGRAM, UNSPEC_PROTO)) < 0){
fprintf(stderr, "Error creating recv socket: %s\n", strerror(errno));
}
/*
* We go from hop to hop by incrementing the time to live in the IP header
* for each hop we visit until we reach the destination IP address (which we
* already have). Time to live decrements for every hop, so once it reaches
* zero we report the IP address of the node we are connected to.
*/
//while(test_ip != dest_ip)
//time_to_live++
//send_to(dest_addr)
//receive icmp error message
//get src addr of error msg from ip header of icmp
//test_ip = src addr
/*
while (last_hop == 0) {
ttl++;
setsockopt(sock, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
sendto(sock, msg, strlen(msg), 0, (struct sockaddr *)ip, sizeof(ip));
}
*/
ttl = 1;
if (!(setsockopt(src_sock, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl)))) {
printf("TTL set successfully\n");
} else {
printf("Error setting TTL: %s\n", strerror(errno));
}
if ((sendto(src_sock, msg, strlen(msg), 0, ret->ai_addr,
ret->ai_addrlen)) > 0) {
printf("msg sent successfully\n");
} else {
fprintf(stderr, "Error sending msg: %s\n", strerror(errno));
}
if ((recvfrom(recv_sock, icmp_msg, icmp_msg_len, 0, reply_addr,
&reply_addr_len)) != -1) {
/* PROCESS THE INFORMATION */
printf("Packet received\n");
} else {
fprintf(stderr, "Error receiving packet: %s\n", strerror(errno));
}
return 0;
}