I am currently trying to create a multiple client-server which enables server to perform both read and write functions in C language. I am able to read the data from the client using readfds and putting it as parameter in SELECT. When I added in writefds, the client fails to connect to the server. I am not sure what is the issue behind it, whether this is the correct method to transmit and receive data
This is the code for my server
#include <stdio.h>
#include <string.h> //strlen
#include <stdlib.h>
#include <errno.h>
#include <unistd.h> //close
#include <arpa/inet.h> //close
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/time.h> //FD_SET, FD_ISSET, FD_ZERO macros
#define TRUE 1
#define FALSE 0
#define PORT 8080
int main(int argc , char *argv[])
{
int opt = TRUE;
int master_socket , addrlen , new_socket , client_socket[30] ,
max_clients = 2 , activity, i , valread , sd;
int max_sd;
struct sockaddr_in address;
char buffer[1025]; //data buffer of 1K
fd_set readfds;
fd_set writefds;
char *message = "Welcome to Server\r\n";
//initialise all client_socket[] to 0 so not checked
for (i = 0; i < max_clients; i++)
{
//client_socket[i] = 0;
}
//create a master socket
if( (master_socket = socket(AF_INET , SOCK_STREAM , 0)) == 0)
{
perror("socket failed");
exit(EXIT_FAILURE);
}
if( setsockopt(master_socket, SOL_SOCKET, SO_REUSEADDR, (char *)&opt,
sizeof(opt)) < 0 )
{
perror("setsockopt");
exit(EXIT_FAILURE);
}
//type of socket created
address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
address.sin_port = htons( PORT );
//bind the socket to localhost port 8888
if (bind(master_socket, (struct sockaddr *)&address, sizeof(address))<0)
{
perror("bind failed");
exit(EXIT_FAILURE);
}
printf("Listener on port %d \n", PORT);
if (listen(master_socket, 3) < 0)
{
perror("listen");
exit(EXIT_FAILURE);
}
addrlen = sizeof(address);
puts("Waiting for connections ...");
for(;;)
{
//clear the socket set
FD_ZERO(&readfds);
FD_ZERO(&writefds);
//add master socket to set
FD_SET(master_socket, &readfds);
FD_SET(master_socket, &writefds);
max_sd = master_socket;
//add child sockets to set
for ( i = 0 ; i < max_clients ; i++)
{
//socket descriptor
sd = client_socket[i];
//if valid socket descriptor then add to read list
if(sd > 0)
FD_SET( sd , &readfds);
//highest file descriptor number, need it for the select function
if(sd > max_sd)
max_sd = sd;
}
//wait for an activity on one of the sockets , timeout is NULL ,
//so wait indefinitely
activity = select( max_sd + 1 , &readfds , &writefds, NULL , NULL);
if ((activity < 0) && (errno!=EINTR))
{
printf("select error");
}
if (FD_ISSET(master_socket, &readfds))
{
if ((new_socket = accept(master_socket,
(struct sockaddr *)&address, (socklen_t*)&addrlen))<0)
{
perror("accept");
exit(EXIT_FAILURE);
}
else {
printf("Connected to socket \n");
}
bzero(buffer, 1025);
int n=0;
read(new_socket, buffer, sizeof(buffer));
printf("From client: %s\t To client: ", buffer);
bzero(buffer, 1025);
//add new socket to array of sockets
for (i = 0; i < max_clients; i++)
{
//if position is empty
if( client_socket[i] == 0 )
{
client_socket[i] = new_socket;
printf("Adding to list of sockets as %d\n" , i+1);
}
}
}
else if(FD_ISSET(master_socket, &readfds)) {
printf("From client: %s\t To client : ", buffer);
bzero(buffer, 1025);
// copy server message in the buffer
while ((buffer[n++] = getchar()) != '\n')
;
write(new_socket, buffer, sizeof(buffer));
}
else{
//else its some IO operation on some other socket
for (i = 0; i < max_clients; i++)
{
sd = client_socket[i];
if (FD_ISSET( sd , &readfds))
{
//Check if it was for closing , and also read the
//incoming message
if ((valread = read( sd , buffer, 1024)) == 0)
{
close( sd );
client_socket[i] = 0;
}
//Echo back the message that came in
else
{
}
}
}
}//else
}
return 0;
}
This is the code for the client
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#define MAX 1000
#define PORT 8080
#define SA struct sockaddr
void func(int sockfd)
{
char buff[MAX];
int n;
int firstConnect = 1;
for (;;)
{
bzero(buff, sizeof(buff));
n = 0;
if(firstConnect==1) {
printf("Enter the string : ");
firstConnect = 0;
while ((buff[n++] = getchar()) != '\n')
;
write(sockfd, buff, sizeof(buff));
}
bzero(buff, sizeof(buff));
read(sockfd, buff, sizeof(buff));
printf("From Server: %s\t To Server : ", buff);
while ((buff[n++] = getchar()) != '\n');
write(sockfd, buff, sizeof(buff));
if ((strncmp(buff, "exit", 4)) == 0)
{
printf("Client Exit...\n");
break;
}
}
}
int main()
{
printf("CLIENT");
int sockfd, connfd;
struct sockaddr_in servaddr, cli;
// socket create and varification
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd == -1)
{
printf("socket creation failed...\n");
exit(0);
}
else
printf("Socket successfully created..\n");
bzero(&servaddr, sizeof(servaddr));
// assign IP, PORT
servaddr.sin_family = AF_INET;
// servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");
servaddr.sin_addr.s_addr = inet_addr("127.8.1.0");
servaddr.sin_port = htons(PORT);
// connect the client socket to server socket
if (connect(sockfd, (SA*)&servaddr, sizeof(servaddr)) != 0)
{
printf("connection with the server failed...\n");
exit(0);
}
else
printf("connected to the server..\n");
// function for chat
func(sockfd);
// close the socket
close(sockfd);
}
