我阅读了 Beej 的指南并创建了一个 UDP 服务器和客户端。我首先运行服务器，然后运行 2 个客户端。服务器应该是recevfrom一个客户端和sendto另一个客户端。当客户端 1 发送某些东西时，客户端 0 会收到它。当客户端 0 发送一些东西时，客户端 1 没有收到它。任何人都可以看到代码有什么问题吗？我已经阅读了有关 UDP、C、服务器、聊天的所有问题，但找不到任何对我有帮助的东西。我正在 OSX 上编译这段代码。任何帮助表示赞赏。以下是服务器代码：
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#define BUFLEN 512
#define PORT 7777
void err(char *str)
{
perror(str);
exit(1);
}
int main(void)
{
struct sockaddr_in my_addr, cli_addr[2],cli_temp;
int sockfd;
socklen_t slen[2],slen_temp;
slen[1]=sizeof(cli_addr[1]);
slen[2]=sizeof(cli_addr[2]);
slen_temp = sizeof(cli_temp);
char buf[BUFLEN];
int clients = 0;
int client_port[2];
if ((sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))==-1)
{
printf("test\n");
err("socket");
}else{
printf("Server : Socket() successful\n");
}
bzero(&my_addr, sizeof(my_addr));
my_addr.sin_family = AF_INET;
my_addr.sin_port = htons(PORT);
my_addr.sin_addr.s_addr = htonl(INADDR_ANY);
if (bind(sockfd, (struct sockaddr* ) &my_addr, sizeof(my_addr))==-1)
{
err("bind");
}else{
printf("Server : bind() successful\n");
}
while(1)
{
//receive
printf("Receiving...\n");
if (recvfrom(sockfd, buf, BUFLEN, 0, (struct sockaddr*)&cli_temp, &slen_temp)==-1)
err("recvfrom()");
if (clients==0) {
//first connection
//store the temp connection details to the array
cli_addr[0] = cli_temp;
//get client 0 port
client_port[0] = ntohs(cli_addr[0].sin_port);
clients++;
printf("Client 0 connected. Port: %d\n",client_port[0]);
sendto(sockfd, "You are the only client.", 24, 0, (struct sockaddr*)&cli_temp, slen_temp);
}else if (clients==1) {
//new or existing
if (client_port[0]==ntohs(cli_temp.sin_port)) {
//send back to client 0 that nobody else connected yet
sendto(sockfd, "You are the only client.", 24, 0, (struct sockaddr*)&cli_addr[0], slen[0]);
printf("Only client\n");
}else{
//new connection
cli_addr[1] = cli_temp;
client_port[1] = ntohs(cli_addr[1].sin_port);
clients++;
printf("GOt second client\n");
sendto(sockfd, buf, BUFLEN, 0, (struct sockaddr*)&cli_addr[0], slen[0]);
}
}else{
//there are 2 clients connected here. If we get an error from the sendto then we decrement clients
if (client_port[0]==ntohs(cli_temp.sin_port)) {
//client 0 talking send to client 1
printf("Sedning message to client 1\n");
if (sendto(sockfd, buf, BUFLEN, 0, (struct sockaddr*)&cli_addr[1], slen[1])==-1)
{
clients--;
err("sendto()");
}
}else {
//client 1 talking send to client 0
printf("Sending message to client 0\n");
if (sendto(sockfd, buf, BUFLEN, 0, (struct sockaddr*)&cli_addr[1], slen[1])==-1)
{
clients--;
err("sendto()");
}
}
}
//printf("Received packet from %s:%d\nData: %s\n",
// inet_ntoa(cli_addr[clients].sin_addr), ntohs(cli_addr[clients].sin_port), buf);
}
close(sockfd);
return 0;
}
和客户：
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <signal.h>
#define BUFLEN 512
#define PORT 7777
void err(char *s)
{
perror(s);
exit(1);
}
sig_atomic_t child_exit_status;
void clean_up_child_process (int signal_number)
{
/* Clean up the child process. */
int status;
wait (&status);
/* Store its exit status in a global variable. */
child_exit_status = status;
}
int main(int argc, char** argv)
{
struct sockaddr_in serv_addr;
int sockfd, slen=sizeof(serv_addr);
char buf[BUFLEN];
struct sigaction sigchld_action;
memset (&sigchld_action, 0, sizeof (sigchld_action));
sigchld_action.sa_handler = &clean_up_child_process;
sigaction (SIGCHLD, &sigchld_action, NULL);
int pid,ppid;
if(argc != 2)
{
printf("Usage : %s <Server-IP>\n",argv[0]);
exit(0);
}
if ((sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))==-1)
err("socket");
bzero(&serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(PORT);
if (inet_aton(argv[1], &serv_addr.sin_addr)==0)
{
fprintf(stderr, "inet_aton() failed\n");
exit(1);
}
pid = fork();
if (pid<0) {
err("Fork Error");
}else if (pid==0) {
//child process will receive from server
while (1) {
bzero(buf,BUFLEN);
printf("Attempting to READ to socket %d: ",sockfd);
fflush(stdout);
//recvfrom here
if (recvfrom(sockfd, buf, BUFLEN, 0, (struct sockaddr*)&serv_addr, &slen)==-1)
err("recvfrom()");
printf("The message from the server is: %s \n",buf);
if (strcmp(buf,"bye\n") == 0) {
ppid = getppid();
kill(ppid, SIGUSR2);
break;
}
}
}else {
//parent will send to server
while(1){
printf("Please enter the message to send: ");
bzero(buf,BUFLEN);
fgets(buf,BUFLEN,stdin);
printf("Attempting to write to socket %d: ",sockfd);
fflush(stdout);
//send to here
if (sendto(sockfd, buf, BUFLEN, 0, (struct sockaddr*)&serv_addr, slen)==-1)
{
err("sendto()");
}
}
}
close(sockfd);
return 0;
}
谢谢你。