Client-server Telnet in C, problem with pipes

Question

I need to write a simple telnet app in C language using TCP sockets. What i've done is a client & server, which is working with commands like 'ls' or 'pwd', but i need ability to use different shell programs like bash, sh, csh. Can someone tell me which functions should i use or how to rebuild my server? Because now when i use "sh" command, server and client feezes.

Actually i've got this function inside client:

void chat(int sockfd){
    char buff[MAX]; 
    char text[MAX];
    int n; 
    for (;;) { 
        bzero(buff, sizeof(buff)); 
        printf("->: "); 
        n = 0; 
        while ((buff[n++] = getchar()) != '\n') 
            ; 
        write(sockfd, buff, sizeof(buff)); 
        if ((strncmp(buff, "exit", 4)) == 0) { 
            printf("Exiting...\n"); 
            break; 
        } 
        bzero(buff, sizeof(buff)); 
        read(sockfd, tex, sizeof(tex));
        printf("Server message ->: %s", tex);
        bzero(tex, MAX);
    } 
}

And this one inside server:

void chat(int sockfd){
        char buff[MAX];
        int n,p[1];
        FILE *fp;
        char path[1024];

        for(;;){
            bzero(buff, MAX);
            read(sockfd, buff, sizeof(buff));
            fp = popen(buff, "r");
            if(fp == NULL){
                strncpy(buff, "Failed to run command", MAX);
                write(sockfd, buff, sizeof(buff));
                continue;
            }
            printf("%s\n", buff);
            while(fgets(path, sizeof(path), fp) != NULL){
                write(sockfd, path, sizeof(path));
            }
            pclose(fp);
        }
    }

Thanks for attention.