Problems sending messages to a server using TCP sockets - c

Question

I'm trying to send messages to a server, but when I connect, the server immediately fails receiving the message. It seems that the server "does not wait" for the user to type the message. The server is supposed to remain in that while loop, forever waiting for clients and printing their messages.
I have no idea what's wrong.
Server code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <dirent.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <pthread.h>
#define PORT 4000
#define WORD_SIZE 256
#define USER_SOCKETS 2
#define MAX_USERS 10
int receiveMessage(int socket, char message[])
{
int bytesReceived;
while (1)
{
bytesReceived = recv(socket, message, WORD_SIZE, 0);
if (bytesReceived < 0)
return -1;
if (bytesReceived == 0)
return 0;
}
}
int main(int argc, char *argv[])
{
int serverSockfd;
socklen_t clilen;
struct sockaddr_in serv_addr, cli_addr;
if ((serverSockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
printf("Error creating the socket.\n");
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(PORT);
serv_addr.sin_addr.s_addr = INADDR_ANY;
bzero(&(serv_addr.sin_zero), 8);
if (bind(serverSockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
{
printf("Error binding the socket..\n");
return -1;
}
if (listen(serverSockfd, 5) < 0)
{
printf("Error on listening.\n");
return -1;
}
int newSockfd;
while (1)
{
if (newSockfd = accept(serverSockfd, (struct sockaddr *)&cli_addr, &clilen) < 0)
{
printf("Error on accept a new client.\n");
continue;
}
char username[WORD_SIZE];
if (receiveMessage(newSockfd, username) < 0)
{
printf("Error receiving message.\n");
close(newSockfd);
}
printf("Message: %s\n", username);
close(newSockfd);
}
return 0;
}
Client code:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#define PORT 4000
int main(int argc, char * argv[]) {
int sockfd, n;
struct sockaddr_in serv_addr;
struct hostent * server;
char buffer[256];
if (argc < 2) {
fprintf(stderr, "usage %s hostname\n", argv[0]);
exit(0);
}
server = gethostbyname(argv[1]);
if (server == NULL) {
fprintf(stderr, "ERROR, no such host\n");
exit(0);
}
if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
printf("ERROR opening socket\n");
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(PORT);
serv_addr.sin_addr = * ((struct in_addr * ) server -> h_addr);
bzero( & (serv_addr.sin_zero), 8);
if (connect(sockfd, (struct sockaddr * ) & serv_addr, sizeof(serv_addr)) < 0)
printf("ERROR connecting\n");
printf("Enter the message: ");
bzero(buffer, 256);
fgets(buffer, 256, stdin);
/* write in the socket */
n = write(sockfd, buffer, strlen(buffer));
if (n < 0)
printf("ERROR writing to socket\n");
bzero(buffer, 256);
printf("%s\n", buffer);
close(sockfd);
return 0;
}

Answer 1

The line:
if (newSockfd = accept(serverSockfd, (struct sockaddr *)&cli_addr, &clilen) < 0)
will set newSockfd to 0 if accept() succeeds, rather than to the descriptor of the socket. This is because < has a higher precedence than =, so the compiler behaves as-if you had written this:
if (newSockfd = (accept(serverSockfd, (struct sockaddr *)&cli_addr, &clilen) < 0))
You need to write this instead:
if ((newSockfd = accept(serverSockfd, (struct sockaddr *)&cli_addr, &clilen)) < 0)