问题描述
很抱歉，但我怀疑该错误可能是在错误处理中，并且存在一些用于联网的必要样板。
我开始对单文件派生tcp服务器进行以下实现。
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/select.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <netinet/in.h>
#include <netdb.h>
#include <string.h>
#include <arpa/inet.h>
#include <pthread.h>
#include <errno.h>
#include <pty.h>
#define PORT 9600
#define BUF_SIZE 128
#define SERVER_BACKLOG 10
void handle_conn(int conn_fd) {
// Create a TTY / PTY pair and hook it up to the connection.
int master_fd;
char slave_name[100];
pid_t pid = forkpty(&master_fd,slave_name,NULL,NULL);
if (pid == -1) {
fprintf(stderr,"Error on first fork: %d %s",errno,strerror(errno));
return;
} else if (pid == 0) { // Child process attached to slave pty
execl("/bin/bash","bash",(char*) NULL);
}
// Set both fds to be non-blocking
int flags = fcntl(master_fd,F_GETFL,0);
fcntl(master_fd,F_SETFL,flags | O_NONBLOCK);
flags = fcntl(conn_fd,0);
fcntl(conn_fd,flags | O_NONBLOCK);
// Parent continues here,shuffling data back and forth from the socket to
// the master fd.
int n;
char c;
while(1) {
fd_set fds;
FD_ZERO(&fds);
FD_SET(conn_fd,&fds);
FD_SET(master_fd,&fds);
int numFds = select((conn_fd > master_fd ? conn_fd : master_fd) + 1,&fds,NULL);
if (numFds == -1) {
fprintf(stderr,"Error on select: %d %s",strerror(errno));
return;
}
if (numFds == 0) {
continue;
}
if (FD_ISSET(conn_fd,&fds)) {
// Read from socket and write to tty.
while ((n = read(conn_fd,&c,1)) > 0) {
write(master_fd,1);
}
if (n == 0) {
// Reached EOF
break;
}
// Presumed n is -1
if (errno != EAGAIN || errno != EWOULDBLOCK) {
fprintf(stderr,"Error reading socket %d %s\n",strerror(errno));
break;
}
}
if (FD_ISSET(master_fd,&fds)) {
// Read from tty and write to socket as long as things are still
// readable.
while ((n = read(master_fd,1)) > 0) {
write(conn_fd,1);
}
if (n == 0) {
// Reached EOF
break;
}
// Presumed n is -1
if (errno != EAGAIN && errno != EWOULDBLOCK) {
fprintf(stderr,"Error reading master FD %d %s\n",strerror(errno));
break;
}
}
}
printf("Closing connection [%d]\n",conn_fd);
int err = close(conn_fd);
if (err != 0) {
fprintf(stderr,"Error while closing connection [%d]\n",conn_fd);
}
err = close(master_fd);
if (err != 0) {
fprintf(stderr,"Error while closing master fd [%d]\n",conn_fd);
}
}
int main(int argc,char *argv[]) {
int server_fd = socket(PF_INET,SOCK_STREAM,0);
if (server_fd < 0) {
fprintf(stderr,"Cannot create socket\n");
return 1;
}
struct sockaddr_in server_addr;
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(PORT);
int ok = inet_pton(AF_INET,"127.0.0.1",&server_addr.sin_addr);
if (!ok) {
fprintf(stderr,"Cannot parse IP address\n");
return 1;
}
// Allow reuse of port.
int optval = 1;
setsockopt(server_fd,SOL_SOCKET,SO_REUSEPORT,&optval,sizeof(optval));
int err = bind(server_fd,(struct sockaddr *) &server_addr,sizeof(server_addr));
if (err != 0) {
fprintf(stderr,"Cannot bind server: Error %d %s\n",strerror(errno));
return 1;
}
err = listen(server_fd,SERVER_BACKLOG);
if (err != 0) {
fprintf(stderr,"Cannot listen\n");
return 1;
}
printf("Server listening on port %d\n",PORT);
int client_fd;
struct sockaddr_in client_addr;
socklen_t client_addr_len;
while (1) {
client_fd = accept(server_fd,(struct sockaddr *) &client_addr,&client_addr_len);
if (client_fd < 0) {
fprintf(stderr,"Cannot accept: Error %d %s\n",strerror(errno));
return 1;
}
printf("New client [%d]\n",client_fd);
// Using fork instead of threads here to avoid pitfalls involved with
// mixing forking and threads,since this use case case of a tty host is
// not expected to involve a great many requests.
int pid = fork();
if (pid == -1) {
fprintf(stderr,"Error on forking to handle new connection: %d %s",strerror(errno));
// Server does not need to die here.
continue;
} else if (pid == 0) { // Child will handle the connection and then return.
handle_conn(client_fd);
return 0;
}
// Parent continues to accept
}
}
然后在另一个终端上，运行以下 netcat 客户端。
stty -icanon -echo; nc localhost 9600
现在，我可以在终端上使用ls键入cat或nc之类的命令。
但是，当我键入exit时，服务器将打印Error reading master FD 5 Input/output error\nClosing connection [4]，并且没有其他错误，因此我假定服务器已成功关闭连接，但是客户端继续挂起，直到我在客户端上按Control-C。
解决方法
我发现了错误！原来，我忘记了在父进程中关闭套接字。一旦这样做，close（）就会在孩子中按预期工作。
对上述代码进行简单的修改如下，即可解决问题。
...
// Parent continues to accept
close(client_fd);