见鬼去吧。我正在开发一个服务器 c 项目，将 UDP 用于 whois 服务。但我收到错误消息：“此主机上没有 whois 服务。” 这是我的代码：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <pwd.h>
#define BACKLOG 5 /* # of requests we're willing to queue */
#define MAXHOSTNAME 32 /* maximum host name length we tolerate */
main(argc,argv)
int argc; /* standard UNIX argument declarations */
char *argv[];
{
int s,t; /* socket descriptors */
int i; /* general purpose integer */
struct sockaddr_in sa,isa; /* Internet socket address structure */
struct hostent *hp; /* result of host name lookup */
char *myname; /* pointer to name of this program */
struct servent *sp; /* result of service lookup */
char localhost[MAXHOSTNAME+1]; /* local host name as character string */
myname = argv[0];
/*
* Look up the WHOIS service entry
*/
if((sp = getservbyname("whois","udp")) == NULL){
fprintf(stderr, "%s: No whois service on this host\n", myname);
exit(1);
}
/*
* Get our own host information
*/
gethostname(localhost, MAXHOSTNAME);
if((hp = gethostbyname(localhost)) == NULL){
fprintf(stderr, "%s: cannot get local host info?\n", myname);
exit(1);
}
printf("host name is: %s\n",hp->h_name);
printf("my name is: %s\n",myname);
/*
* Put the WHOIS socket number and our address info into the socket structure
*/
u_short portbase = 0;
portbase = 5000;
sa.sin_port = sp->s_port;
sa.sin_port = htons(ntohs((u_short)sp->s_port)+portbase);
bcopy((char *)hp->h_addr, (char *)&sa.sin_addr, hp->h_length);
sa.sin_family = hp->h_addrtype;
/*
* Allocate an open socket for incoming connections
*/
if((s = socket(hp->h_addrtype, SOCK_DGRAM, 0)) < 0){
perror("socket");
exit(1);
}
/*
* Bind the socket to the service port
*/
if(bind(s, (struct sockaddr *)&sa, sizeof sa) < 0){
perror("bind");
exit(1);
}
/*
* Set maximum connections we will fall behind
*/
//listen(s,BACKLOG);
/*
* Go into an infinite loop waiting for new connections
*/
while(1){
i = sizeof isa;
/*
* We hang in accept() while waiting for new customers
*/
/*
if((t = accept(s, (struct sockaddr *)&isa, &i)) < 0){
perror("accept");
exit(1);
}
*/
whois(s); /* perform the actual WHOIS service */
close(s);
}
}
/*
* Get the WHOIS request from remote host and format a reply.
*/
whois(sock)
int sock;
{
struct sockaddr_in clientAddr;
socklen_t len = sizeof(clientAddr);
memset(&clientAddr, 0, sizeof(clientAddr));
struct passwd *p;
char buf[BUFSIZ+1];
int i;
/*
* Get one line request
*/
printf("start to recv data\n");
if((i = recvfrom(sock, buf, BUFSIZ, 0, (struct sockaddr*)&clientAddr, &len)) <= 0)
printf("recv failed\n");
return;
buf[i] = '\0'; /* Null terminate */
printf("After the read, the buf is: %s \n",buf);
/*
* Look up the requested user and format reply
*/
if((p = getpwnam(buf)) == NULL)
strcpy(buf, "User not found\n");
else
sprintf(buf, "%s: %s (from me)\n", p->pw_name, p->pw_gecos);
/*
* Return reply
*/
//write(sock, buf, strlen(buf));
sendto(sock, buf, strlen(buf), 0, (struct sockaddr*)&clientAddr, len);
return;
}
我无法弄清楚错误在哪里。我有一个使用 TCP for whois 的类似代码，运行没有问题。