Thread issue in socket Programming - linux

Question

I have the following codes..
server.c
#include <stdio.h>
#include "./../linux.h"
#include "./tcp.h"
#include <pthread.h>
static int clients = 0;
static int* memptr = NULL;
void serve(void*);
int* push(int* memptr, int nsfd) {
clients++;
if (clients == 1)
memptr = (int*)malloc(sizeof(int) * clients);
else
memptr = (int*)realloc(memptr, sizeof(int) * clients);
memptr[clients - 1] = nsfd;
return memptr;
}
int main(int argc, char** argv) {
pthread_t thread[2];
int threadCount = 0;
if (argc != 3){
printf("\nUsage: ./server port_number maximum_clients\n");
return 1;
}
static struct sockaddr_in sock, sock_client;
int len, new_sock_fd;
int sock_fd = socket(PF_INET, SOCK_STREAM, 0);
if (sock_fd == -1){
perror("socket");
exit(1);
}
sock.sin_family = PF_INET;
sock.sin_port = htons(atoi(argv[1]));
sock.sin_addr.s_addr = inet_addr("0.0.0.0");
len = sizeof(sock);
if ( bind(sock_fd, (struct sockaddr *)&sock, len) == -1){
perror("bind");
exit(1);
}
if ( listen(sock_fd, atoi(argv[2])) == -1){
perror("listen");
exit(1);
}
while(1) {
new_sock_fd = accept(sock_fd, (struct sockaddr *)&sock_client, (socklen_t *)&len);
memptr = push(memptr, new_sock_fd);
if (new_sock_fd == -1){
perror("accept");
exit(1);
}
pthread_create(&(thread[threadCount]), NULL, (void*)&serve, (void *)&new_sock_fd);
pthread_join(thread[threadCount++], NULL);
printf("threadCount = %d\n", threadCount);
sleep(1);
}
return 0;
}
void serve(void* fd){
int* new_sock_fd = (int*)fd;
Packet packet;
while(1){
bzero(&packet, sizeof(packet));
read(*new_sock_fd , &packet, sizeof(packet));
printf("%d\n", *new_sock_fd);
//printf("recipientId = %d\n", packet.recipientId);
// printf("message = %s\n", packet.data);
write(memptr[packet.recipientId - 1], packet.data, 1024);
}
pthread_exit(0);
}
and the tcp.h looks like
#ifndef __TCP_H__
# define __TCP_H__
typedef struct {
int recipientId; // this is the reciever ID
char data[1024]; // this is the main data part
}Packet;
#endif /* __TCP_H__ */
and each client.h looks like this
#include <stdio.h>
#include "./../linux.h"
#include "./tcp.h"
#include <pthread.h>
void print(void);
void scan(void);
int sock_fd;
int main(int argc, char** argv) {
if (argc != 3){
printf("\nUsage: ./client port_number server_ip\n");
return 1;
}
static struct sockaddr_in sock;
int len;
pthread_t thread1, thread2;
sock_fd = socket(PF_INET, SOCK_STREAM, 0);
if (sock_fd == -1){
perror("socket");
exit(1);
}
sock.sin_family = PF_INET;
sock.sin_port = htons(atoi(argv[1]));
sock.sin_addr.s_addr = inet_addr(argv[2]);
len = sizeof(sock);
if ( connect(sock_fd, (struct sockaddr *)&sock , len) == -1 ){
perror("connect");
exit(1);
}
pthread_create(&thread1, NULL, (void*)&print, NULL);
pthread_create(&thread2, NULL, (void*)&scan, NULL);
pthread_join(thread1, NULL);
pthread_join(thread2, NULL);
return 0;
}
void print(){
char messege[1024];
while(1){
if (read(sock_fd, messege, 1024) == -1){
perror("read");
return;
}
printf("messege = %s\n", messege);
}
pthread_exit(0);
}
void scan(void){
Packet packet;
while(1){
printf("Enter the reciver ID: ");
scanf("%d", &packet.recipientId);
printf("Enter the data: ");
scanf("%s", packet.data);
if ( write(sock_fd, &packet, sizeof(packet)) == -1) {
perror("read");
return;
}
}
pthread_exit(0);
}
Now the problems are
when I am running the server & the in 2 terminals, 2 clients after each client is accepted threadCount should be printed at the server end but it is not printing. It means the execution stops/skips after the first pthread_join but WHY ??
After connecting two threads, when I sent the data from 1st client to the 1st client itself, it works but not from the 1st client to the 2nd client..rather it is sending to the server terminal window. WHY ??
When sent from the second client nothing works ( sending itself or client 1)..WHY??
Please help..And thanks for patiently reading all the codes above.

Answer 1

TCP is a byte stream protocol, not a message protocol. You are calling TCP functions and expecting them to send or receive messages. They don't. If you want to send or receive messages, you have to implement a message protocol, write functions that send and receive messages, and then call those functions.
if (read(sock_fd, messege, 1024) == -1){
perror("read");
return;
}
printf("messege = %s\n", messege);
This call to printf is a disaster. The %s format specifier is for C-style strings, not arbitrary chunks of bytes received from a byte stream. For the most obvious way to see how bad this is, consider this --- how should printf decide how many bytes to print? You threw away the value read returned after you compared it to -1, so you have no idea how many bytes you received.
I'm sure there are other issues with your code, but the fact that the fundamental design is broken makes it not worth fixing those issues. Instead, design a message protocol and implement that.