multiple clients connection through sockets - sockets

Question

I'm a new to socket programming. I tried to connect a server to multiple clients and i have two problems in it. 1)I can't send a message unless i get a reply i.e if a client connects and sends a message,client can't send a message again until it gets reply from server. If client types some message it stores the messages and it sends the message after it gets a reply.
2)I want to restrict the number of connections to 1 and if some one connects no one else should connect until the client the client quits. If the client quits the one who is first in waiting should be connected.
server
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<errno.h>
#include<string.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include <arpa/inet.h>
#include <sys/wait.h>
#include <signal.h>
#define MYPORT 3490 /* the port users connect to */
#define BACKLOG 0 /* max no. of pending connections in server queue */
#define MAXDATASIZE 200
void sigchld_handler(int s)
{
while( wait( NULL) > 0); /* wait for any child to finish */
}
int main( void)
{
int listenfd;
/* listening socket */
int connfd;
/* connection socket */
struct sockaddr_in server_addr; /* info for my addr i.e. server */
struct sockaddr_in client_addr; /* client's address info */
int sin_size;
/* size of address structure */
struct sigaction sa; /* deal with signals from dying children! */
int yes = 1;
char clientAddr[ 20]; /* holds ascii dotted quad address */
if ((listenfd = socket( AF_INET, SOCK_STREAM, 0)) == -1)
{
perror( "Server socket");
exit( 1);
}
/* Set Unix socket level to allow address reuse */
if( setsockopt( listenfd, SOL_SOCKET, SO_REUSEADDR,&yes, sizeof( int)) == -1)
{
perror( "Server setsockopt");
exit( 1);
}
sin_size = sizeof( server_addr);
memset( &server_addr, 0, sin_size);
/* zero struct */
server_addr.sin_family = AF_INET;
/* host byte order ... */
server_addr.sin_port = htons( MYPORT); /* . short, network byte order */
server_addr.sin_addr.s_addr = INADDR_ANY; /* any server IP addr */
if( bind( listenfd, (struct sockaddr *)&server_addr,sizeof( struct sockaddr)) == -1)
{
perror( "Server bind");
exit( 1);
}
if( listen( listenfd, BACKLOG) == -1)
{
perror( "Server listen");
exit( 1);
}
/* Signal handler stuff */
sa.sa_handler = sigchld_handler; /* reap all dead processes */
sigemptyset( &sa.sa_mask);
sa.sa_flags = SA_RESTART;
if( sigaction( SIGCHLD, &sa, NULL) == -1)
{
perror( "Server sigaction");
exit( 1);
}
while( 1)
{
/* main accept() loop */
sin_size = sizeof( struct sockaddr_in);
if( (connfd = accept( listenfd,(struct sockaddr *)&client_addr, &sin_size)) == -1)
{
perror( "Server accept");
continue;
}
strcpy( clientAddr, inet_ntoa( client_addr.sin_addr));
printf( "Server: got connection from %s\n", clientAddr);
if( !fork())
{
/* the child process dealing with a client */
char msg[ MAXDATASIZE];
int numbytes;
close( listenfd); /* child does not need the listener */
msg[ 0] = '\0';
/* no message yet! */
do
{
if( (numbytes =recv( connfd, msg, MAXDATASIZE -1, 0)) == -1)
{
perror( "Server recv");
exit( 1);
/* error end of child */
}
msg[ numbytes] = '\0';
/* end of string */
fprintf( stderr, "Message received: %s\n", msg);
do
{
if( strcmp( msg, "quit") == 0)
{
close( connfd);
exit(0);
}
printf( "Message to send: ");
scanf( "%s", msg);
if( send( connfd, msg, strlen( msg), 0) == -1)
{
perror( "server send");
//exit(1);
}
/* error end of child */
}
while( strcmp( msg, "quit") != 0);
if( strcmp( msg, "quit") == 0)
{
close( connfd);
exit(0);
}
//close( connfd);
//exit(0);
/* end of child! */
}
while(1);
//fork();
//close(connfd); /* parent does not need the connection socket */
return 0;
}
}
}
client:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
/* for gethostbyname() */
#define PORT 3490
/* server port the client connects to */
#define MAXDATASIZE 100 /* max bytes to be received at once */</i>
int main( int argc, char * argv[])
{
int sockfd, numbytes;
char buf[ MAXDATASIZE];
struct hostent *he;
struct sockaddr_in their_addr; /* server address info */
char msg[ MAXDATASIZE];
if( argc != 2) {
fprintf( stderr, "usage: client hostname\n");
exit( 1);
}
/* resolve server host name or IP address */
if( (he = gethostbyname( argv[ 1])) == NULL) { /* host server info */
perror( "Client gethostbyname");
exit( 1);
}
if( (sockfd = socket( AF_INET, SOCK_STREAM, 0)) == -1) {
perror( "Client socket");
exit( 1);
}
memset( &their_addr, 0, sizeof( their_addr));
/* zero all */
their_addr.sin_family = AF_INET;
/* host byte order .. */
their_addr.sin_port = htons( PORT);
/* .. short, network byte order */
their_addr.sin_addr = *((struct in_addr *)he -> h_addr);
if( connect( sockfd, (struct sockaddr *)&their_addr,
sizeof( struct sockaddr)) == -1) {
perror( "Client connect");
exit( 1);
}
do {
printf( "Message to send: ");
scanf( "%s", msg);
if( (numbytes = send( sockfd, msg, strlen( msg), 0)) == -1) {
perror( "Client send");
continue;
}
if( (numbytes = recv( sockfd, buf, MAXDATASIZE - 1, 0)) == -1) {
perror( "Client recv");
continue;
}
buf[ numbytes] = '\0';
/* end of string char */
printf( "Received: %s\n", buf);
} while( strcmp( msg, "quit") != 0);
close( sockfd);
return 0;
}

Answer 1

dear you have to use multithreading for this start a new thread to handle new connection
in that thread also use separate threads for receiving data and sending data ...

Answer 2

1)I can't send a message unless i get a reply i.e if a client connects
and sends a message,client can't send a message again until it gets
reply from server.
That's no wonder, since you have programmed this sequential arrangement of scanf and recv in your client's do loop. To handle message input and socket receipt in order of appearance, we can use select; your do loop could then look like:
do
{ fd_set fds;
FD_ZERO(&fds);
FD_SET(STDIN_FILENO, &fds);
FD_SET(sockfd, &fds); // set of descriptors holds stdin and socket
printf("Message to send: "), fflush(stdout);
if (select(sockfd+1, &fds, NULL, NULL, NULL) < 0) break; // error?
// see which descriptors of set are ready
if (FD_ISSET(STDIN_FILENO, &fds))
{ // it is the standard input
scanf("%s", msg);
numbytes = send(sockfd, msg, strlen(msg), 0);
if (numbytes == -1) perror("Client send");
}
if (FD_ISSET(sockfd, &fds))
{ // this is the peer's message or termination
numbytes = recv(sockfd, buf, MAXDATASIZE - 1, 0);
if (numbytes <= 0)
{
perror("Client recv");
break; // no more data from peer, so close the connection
}
buf[numbytes] = '\0'; /* end of string char */
printf("Received: %s\n", buf);
}
} while (strcmp(msg, "quit") != 0);
2)I want to restrict the number of connections to 1 and if some one
connects no one else should connect until the client the client quits.
We can achieve this simply by not forking a server process after we accept a client connection request, but rather handling the message transfer in the one and only server task itself (quite similar as shown above for the client); just omit the lines if( !fork()) as well as return 0; instead uncomment the close(connfd); and don't forget to break out of the do loop when recv returns a nonpositive value.