我有一个工作正常的客户端，但每当我运行一个新的客户端时，有时我不会在已经运行的另一个客户端上收到已发送的消息，而使用telnet它可以完美地工作，消息“广播”给所有人连接客户端，我希望每当收到一条消息给客户端显示即使我还没有发送消息。 我应该在客户端上使用select吗？什么应该改变？
client.c：
#include <stdio.h> //printf
#include <string.h> //strlen
#include <sys/socket.h> //socket
#include <arpa/inet.h> //inet_addr
#include <unistd.h>
int main(int argc , char *argv[]){
int sock;
struct sockaddr_in server;
char message[256] , server_reply[256];
//Create socket
sock = socket(AF_INET , SOCK_STREAM , 0);
if (sock == -1)
{
printf("Could not create socket");
}
puts("Socket created");
server.sin_addr.s_addr = inet_addr("127.0.0.1");
server.sin_family = AF_INET;
server.sin_port = htons( 9034 );
//Connect to remote server
if (connect(sock , (struct sockaddr *)&server , sizeof(server)) < 0){
perror("connect failed. Error");
return 1;
}
puts("Connected\n");
//keep communicating with server
for(;;){
printf("Enter message: ");
memset(message, 0, 256);
fgets(message, 256,stdin);
// scanf("%s" , message);
//Send some data
if( send(sock , message , strlen(message) , 0) < 0)
{
puts("Send failed");
return 1;
}
//Receive a reply from the server
if( recv(sock , server_reply , 256 , 0) < 0)
{
puts("recv failed");
break;
}
printf("Server Reply: %s\n", server_reply);
server_reply[0]='\0';
}
close(sock);
return 0;
}
server.c：
/*
** selectserver.c -- a cheezy multiperson chat server
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#define PORT "9034" // port we're listening on
// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
if (sa->sa_family == AF_INET) {
return &(((struct sockaddr_in*)sa)->sin_addr);
}
return &(((struct sockaddr_in6*)sa)->sin6_addr);
}
int main(void){
fd_set master; // master file descriptor list
fd_set read_fds; // temp file descriptor list for select()
int fdmax; // maximum file descriptor number
int listener; // listening socket descriptor
int newfd; // newly accept()ed socket descriptor
struct sockaddr_storage remoteaddr; // client address
socklen_t addrlen;
char buf[256]; // buffer for client data
int nbytes;
char remoteIP[INET6_ADDRSTRLEN];
int yes=1; // for setsockopt() SO_REUSEADDR, below
int i, j, rv;
struct addrinfo hints, *ai, *p;
FD_ZERO(&master); // clear the master and temp sets
FD_ZERO(&read_fds);
// get us a socket and bind it
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE;
if ((rv = getaddrinfo(NULL, PORT, &hints, &ai)) != 0) {
fprintf(stderr, "selectserver: %s\n", gai_strerror(rv));
exit(1);
}
for(p = ai; p != NULL; p = p->ai_next) {
listener = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
if (listener < 0) {
continue;
}
// lose the pesky "address already in use" error message
setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int));
if (bind(listener, p->ai_addr, p->ai_addrlen) < 0) {
close(listener);
continue;
}
break;
}
// if we got here, it means we didn't get bound
if (p == NULL) {
fprintf(stderr, "selectserver: failed to bind\n");
exit(2);
}
freeaddrinfo(ai); // all done with this
// listen
if (listen(listener, 10) == -1) {
perror("listen");
exit(3);
}
// add the listener to the master set
FD_SET(listener, &master);
// keep track of the biggest file descriptor
fdmax = listener; // so far, it's this one
// main loop
for(;;) {
read_fds = master; // copy it
if (select(fdmax+1, &read_fds, NULL, NULL, NULL) == -1) {
perror("select");
exit(4);
}
// run through the existing connections looking for data to read
for(i = 0; i <= fdmax; i++) {
if (FD_ISSET(i, &read_fds)) { // we got one!!
if (i == listener) {
// handle new connections
addrlen = sizeof remoteaddr;
newfd = accept(listener,
(struct sockaddr *)&remoteaddr,
&addrlen);
if (newfd == -1) {
perror("accept");
} else {
FD_SET(newfd, &master); // add to master set
if (newfd > fdmax) { // keep track of the max
fdmax = newfd;
}
printf("selectserver: new connection from %s on "
"socket %d\n",
inet_ntop(remoteaddr.ss_family,
get_in_addr((struct sockaddr*)&remoteaddr),
remoteIP, INET6_ADDRSTRLEN),
newfd);
}
} else {
// handle data from a client
memset(buf, 0, 256);
if ((nbytes = recv(i, buf, sizeof buf, 0)) <= 0) {
// got error or connection closed by client
if (nbytes == 0) {
// connection closed
printf("selectserver: socket %d hung up\n", i);
} else {
perror("recv");
}
close(i); // bye!
FD_CLR(i, &master); // remove from master set
} else {
// we got some data from a client
for(j = 0; j <= fdmax; j++) {
// send to everyone!
if (FD_ISSET(j, &master)) {
// except the listener and ourselves
if (j != listener && j != i) {
if (send(j, buf, nbytes, 0) == -1) {
perror("send");
}
}
}
}
}
} // END handle data from client
} // END got new incoming connection
} // END looping through file descriptors
} // END for(;;)--and you thought it would never end!
return 0;
}
答案 0 :(得分：5)
客户端发送消息之前无法接收消息的原因是因为。
fgets(message, 256,stdin);
另外，请注意
if( recv(sock , server_reply , 256 , 0) < 0)
blocks if there is nothing to read，这将阻止该用户向服务器发送更多消息，直到从服务器读取新内容。假设你以前玩过网络游戏，我希望你能看到这样的设置会让人讨厌！
因此，我们必须找到一些检查，看看我们是否可以从 STDIN 和服务器套接字中读取而不会产生阻止。使用 select（）会阻止我们阻止服务器套接字，但在使用 fgets（）时对 STDIN 不起作用来读取用户的输入。这是因为，如上所述， fgets（）会阻止，直到检测到 EOF 或换行符。
我想到的主要解决方案是使用方法 buffer_message（）替换 fgets ，该方法仅在赢取时从 STDIN 读取阻止读取（我们将使用 select（）来实现此功能）。然后我们将读取的内容放入缓冲区。如果有完整消息，则此消息将写入服务器。否则，我们会让控件继续执行程序，直到有东西要读或写。
这是我最近一次大学任务的代码，所以代码的一小部分不是我的
声明：
//directives are above (e.g. #include ...)
//message buffer related delcartions/macros
int buffer_message(char * message);
int find_network_newline(char * message, int inbuf);
#define COMPLETE 0
#define BUF_SIZE 256
static int inbuf; // how many bytes are currently in the buffer?
static int room; // how much room left in buffer?
static char *after; // pointer to position after the received characters
//main starts below
主：
//insert the code below into main, after you've connected to the server
puts("Connected\n");
//set up variables for select()
fd_set all_set, r_set;
int maxfd = sock + 1;
FD_ZERO(&all_set);
FD_SET(STDIN_FILENO, &all_set); FD_SET(sock, &all_set);
r_set = all_set;
struct timeval tv; tv.tv_sec = 2; tv.tv_usec = 0;
//set the initial position of after
after = message;
puts("Enter message: ");
//keep communicating with server
for(;;){
r_set = all_set;
//check to see if we can read from STDIN or sock
select(maxfd, &r_set, NULL, NULL, &tv);
if(FD_ISSET(STDIN_FILENO, &r_set)){
if(buffer_message(message) == COMPLETE){
//Send some data
if(send(sock, message, strlen(message) + 1, 0) < 0)//NOTE: we have to do strlen(message) + 1 because we MUST include '\0'
{
puts("Send failed");
return 1;
}
puts("Enter message:");
}
}
if(FD_ISSET(sock, &r_set)){
//Receive a reply from the server
if( recv(sock , server_reply , 256 , 0) < 0)
{
puts("recv failed");
break;
}
printf("\nServer Reply: %s\n", server_reply);
server_reply[0]='\0';
}
}
close(sock);
return 0;
//end of main
缓冲功能：
int buffer_message(char * message){
int bytes_read = read(STDIN_FILENO, after, 256 - inbuf);
short flag = -1; // indicates if returned_data has been set
inbuf += bytes_read;
int where; // location of network newline
// Step 1: call findeol, store result in where
where = find_network_newline(message, inbuf);
if (where >= 0) { // OK. we have a full line
// Step 2: place a null terminator at the end of the string
char * null_c = {'\0'};
memcpy(message + where, &null_c, 1);
// Step 3: update inbuf and remove the full line from the clients's buffer
memmove(message, message + where + 1, inbuf - (where + 1));
inbuf -= (where+1);
flag = 0;
}
// Step 4: update room and after, in preparation for the next read
room = sizeof(message) - inbuf;
after = message + inbuf;
return flag;
}
int find_network_newline(char * message, int bytes_inbuf){
int i;
for(i = 0; i<inbuf; i++){
if( *(message + i) == '\n')
return i;
}
return -1;
}
<强> P.S。
if( send(sock , message , strlen(message) , 0) < 0)
如果没有空间写入服务器，上面也可以阻止，但这里不需要担心。另外，我想指出一些你应该为客户端和服务器实现的东西：