c - 为什么对 sendto() 的调用失败了？

Question

我正在尝试发送具有特定负载的单个 UDP 数据包，但我对 sendto() 的调用在运行时失败了。这是我对套接字编程的第一个实验。

原始代码是一个更大项目的一部分，但我已将其简化为一个更简单的测试程序:

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <netinet/in.h>
#include <netdb.h>
#include <errno.h>

#define SIZE 16

int main()
{
     int sock;
     struct sockaddr *addr;
     socklen_t addrlen;
     struct addrinfo hints, *result;
     char *url = "tracker.openbittorrent.com";
     void *payload = malloc(SIZE);

     memset(&hints, 0, sizeof(struct addrinfo));
     hints.ai_family = AF_INET;
     hints.ai_socktype = SOCK_DGRAM;
     hints.ai_flags = 0;
     hints.ai_protocol = IPPROTO_UDP;
     hints.ai_canonname = NULL;
     hints.ai_addr = NULL;
     hints.ai_next = NULL;

     int er = getaddrinfo(url, NULL, &hints, &result);
     if (er != 0) {
          fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(er));
          exit(EXIT_FAILURE);
     }

     sock = socket(result->ai_family, result->ai_socktype, result->ai_protocol);
     if (sock == -1) {
          perror("socket");
          exit(EXIT_FAILURE);
     }

     if (sendto(sock, payload, SIZE, 0, result->ai_addr, result->ai_addrlen) == -1)
          perror("sendto");
 }

这是输出:sendto: Invalid argument

一些 gdb 输出，根据要求:

(gdb) p result->ai_addr->sa_data 
 $3 = "\000\000_\327>\005\000\000\000\000\000\000\000"
(gdb) p result->ai_addr->sa_family
 $4 = 2
(gdb) p result->ai_addrlen
 $5 = 16
(gdb) p result->ai_canonname
 $6 = 0x0
(gdb) p result->ai_flags
 $8 = 0
(gdb) p result->ai_protocol
 $9 = 17
(gdb) p result->ai_socktype
 $10 = 2

Answer 1

您未能为 getaddrinfo 指定 service 参数。尝试这样调用 getaddrinfo:

int er = getaddrinfo(url, "9", &hints, &result);

或

int er = getaddrinfo(url, "discard", &hints, &result);