我查看了 stackoverflow 成员 atanos 在 2010 年编写的关于将多个客户端连接到单个服务器的程序,我稍微修改了他的程序以接受来自命令行的连接详细信息,下面是服务器和代码。
Server.c
int main(int argc, char **argv)
{
fd_set fds, readfds;
int i, clientaddrlen, portno;
int clientsock[2], rc, numsocks = 0, maxsocks = 2;
if (argc < 2){
fprintf(stderr,"ERROR, no port provided\n");
exit(1);
}
int serversock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (serversock == -1) perror("Socket");
portno = atoi(argv[1]);
struct sockaddr_in serveraddr, clientaddr;
bzero(&serveraddr, sizeof(struct sockaddr_in));
serveraddr.sin_family = AF_INET;
serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);
serveraddr.sin_port = htons(portno);
if (-1 == bind(serversock, (struct sockaddr *)&serveraddr,sizeof(struct sockaddr_in))) perror("Bind");
if (-1 == listen(serversock, SOMAXCONN)) perror("Listen");
FD_ZERO(&fds);
FD_SET(serversock, &fds);
while(1) {
readfds = fds;
rc = select(FD_SETSIZE, &readfds, NULL, NULL, NULL);
if (rc == -1){
perror("Select");
break;
}
for (i = 0; i < FD_SETSIZE; i++)
{
if (FD_ISSET(i, &readfds)){
if (i == serversock){
if (numsocks < maxsocks){
clientsock[numsocks] = accept(serversock,(struct sockaddr *) &clientaddr,
(socklen_t *)&clientaddrlen);
if (clientsock[numsocks] == -1) perror("Accept");
else printf("Connection accepted\n");
FD_SET(clientsock[numsocks], &fds);
numsocks++;
}
else
printf("Ran out of socket space.\n");
}
else
{
int messageLength = 10;
char message[messageLength+1];
int numOfChRead, index = 0, limit = messageLength+1;
numOfChRead = recv(clientsock[i], message, messageLength,0);
if(numOfChRead > 0)
printf("Data Received !!! length: %d Message: %s", numOfChRead, message);
else
printf("Nothing read\n");
}
}
}
}
close(serversock);
return 0;
}
客户端.c
int main(int argc, char **argv)
{
struct sockaddr_in servaddr;
struct hostent *server;
int portno, bytesSent = 0;
if (argc < 3){
fprintf(stderr,"Usage %s hostname port\n", argv[0]);
exit(0);
}
portno = atoi(argv[2]);
int sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (sock == -1) perror("Socket");
server = gethostbyname(argv[1]);
if (server == NULL){
fprintf(stderr,"ERROR, no such host\n");
exit(0);
}
bzero((void *) &servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(portno);
bcopy((char *)server->h_addr,(char *)&servaddr.sin_addr.s_addr,server->h_length);
if (-1 == connect(sock, (struct sockaddr *)&servaddr, sizeof(servaddr))) perror("Connect");
while(1) {
char message[10];
fgets(message, 10, stdin);
message[10] = '\0';
bytesSent = send(sock, message, strlen(message), 0);
if(bytesSent == -1) printf("Sending failed with errno %d", errno);
else printf("Sent %d characters", bytesSent);
}
close(sock);
}
我可以看到服务器接受多个连接,但是当我从任何客户端发送消息时,服务器中的 recv API 没有读取任何内容。客户端的发送 API 成功,我可以看到所有字符都已发送。有人可以发表评论吗?
最佳答案
问题是您实际上从未将客户端连接放入读取的 fd_set
中。
行:
readfds = fds;
将 readfds
重置为其中只有服务器(监听)套接字的状态。在每次循环调用 select
之前,您需要完全重新设置 fd_set
中的每个客户端文件描述符。
可能是其他问题(要处理大量代码),但这似乎是最有可能的问题。
(顺便说一句,我不确定赋值是否合法。我不认为对实现有任何要求 fd_set
是简单的、可复制的结构。)
关于c - "recv"即使已接受连接也无法正常工作,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/12238713/