我正在c中构建一个多客户端UDP服务器,但是当我试图从系统连接到我的服务器时,我在gethostbyaddr: Success上得到此错误错误请查看下面的服务器代码。我已经尝试了类似问题的解决方案(gethostbyaddr()返回NULL,但errno结果成功),但我无法让它工作。如有任何帮助,不胜感激
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define BUFSIZE 1024
/*
* error - wrapper for perror
*/
void error(char *msg) {
perror(msg);
exit(1);
}
int main(int argc, char **argv) {
int sockfd; /* socket */
int portno; /* port to listen on */
int clientlen; /* byte size of client's address */
struct sockaddr_in serveraddr; /* server's addr */
struct sockaddr_in clientaddr; /* client addr */
struct hostent *hostp; /* client host info */
char buf[BUFSIZE]; /* message buf */
char *hostaddrp; /* dotted decimal host addr string */
int optval; /* flag value for setsockopt */
int n; /* message byte size */
FILE *fp; /* file variable */
char str[10];
int i = 0;
char userlist[10];
int array_size;
char line[256];
int cred,flag;
/*
* check command line arguments
*/
if (argc != 2) {
fprintf(stderr, "usage: %s <port>n", argv[0]);
exit(1);
}
portno = atoi(argv[1]);
/*
* socket: create the parent socket
*/
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd < 0)
error("ERROR opening socket");
/* setsockopt: Handy debugging trick that lets
* us rerun the server immediately after we kill it;
* otherwise we have to wait about 20 secs.
* Eliminates "ERROR on binding: Address already in use" error.
*/
optval = 1;
setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR,
(const void *)&optval , sizeof(int));
/*
* build the server's Internet address
*/
bzero((char *) &serveraddr, sizeof(serveraddr));
memset(&serveraddr,0,sizeof(serveraddr));
serveraddr.sin_family = AF_INET;
serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);
serveraddr.sin_port = htons((unsigned short)portno);
/*
* bind: associate the parent socket with a port
*/
if (bind(sockfd, (struct sockaddr *) &serveraddr,
sizeof(serveraddr)) < 0)
error("ERROR on binding");
/*
* main loop: wait for a datagram, then echo it
*/
clientlen = sizeof(clientaddr);
while (1) {
/*
* recvfrom: receive a UDP datagram from a client
*/
bzero(buf, BUFSIZE);
n = recvfrom(sockfd, buf, BUFSIZE, 0,
(struct sockaddr *) &clientaddr, &clientlen);
if (n < 0)
error("ERROR in recvfrom");
/*
* gethostbyaddr: determine who sent the datagram
*/
hostp = gethostbyaddr((const char *)&clientaddr.sin_addr.s_addr,
sizeof(clientaddr.sin_addr.s_addr), AF_INET);
if (hostp == NULL)
error("ERROR on gethostbyaddr");
hostaddrp = inet_ntoa(clientaddr.sin_addr);
if (hostaddrp == NULL)
error("ERROR on inet_ntoan");
printf("server received datagram from %s (%s)n",
hostp->h_name, hostaddrp);
printf("server received %d/%d bytes: %sn", strlen(buf), n, buf);
fp = fopen("users.txt", "r");
while (fgets(line, sizeof(line), fp)) {
//printf("%sn",line);
cred = strncmp(buf,line,strlen(line)-1);
//printf("%d",strlen(line)-1);
if(cred == 0){
printf("Authenticated....");
flag = 1;
break;
}
else{
printf("Invalid username/password");
}
}
fclose(fp);
gethostbyaddr()
期望指向struct in_addr
的指针作为第一个参数,对于您显示的代码,它将是&clientaddr.sin_addr
。
形成相关(Linux)文档(man gethostbyaddr
):
[…主机地址参数是一个指针,指向的结构体类型取决于地址类型,例如地址类型为AF_INET的结构体in_addr *(可能通过调用inet_addr(3)获得)。
gethostbyaddr()
设置错误码在h_errno
而不是errno
。
形成相关(Linux)文档(man gethostbyaddr
):
[…[gethostbyname()和gethostbyaddr()函数返回宿主结构,如果发生错误则返回空指针。]当出现错误时,h_errno变量保存一个错误编号。
手册页也给出了可能的错误代码:
变量h_errno可以有以下值:
HOST_NOT_FOUND
- 请求的名称有效,但没有IP地址。
NO_ADDRESS or NO_DATA
NO_RECOVERY
TRY_AGAIN
权威名称服务器上出现临时错误。