server.c

#include <stdio.h>
#include <unistd.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/msg.h>
#include <signal.h>
#include <stdint.h>
#include <proc/procps.h>

#include "chat.h"

struct user {
    uid_t uid;
    char nick[10];
    struct user *next;
};

struct user *head;
struct user *tail;

int main( int argc, char **argv ){
    deamonize();
    initialize_user_list();
    create_shared_memory();
    create_message_queue();
    poll();
    return 0;
}

void deamonize(){
    pid_t pid = fork();
    if( pid > 0 ) /* parent */
        exit( 0 );
    if( pid < 0 ){ /* fork error */
        fprintf( stderr, "Fork error\n" );
        exit( 1 );
    }
    /* child */
    setsid();
    umask( 0 );
    chdir( "/" );
}

void initialize_user_list(){
    head = (struct user *) malloc( sizeof( struct user ) );
    tail = head; /* List is accessed from tail */
}

void create_shared_memory(){
    key_t key = ftok( "/dev/zero", 64 );
    shm_id = shmget( key, SHM_SIZE, 0 );
    shm_addr = shmat( shm_id, 0, 0 );
    cur_addr = shm_addr;
}

void create_message_queue(){
    key_t key = ftok( "/dev/zero", 65 );
    msg_id = msgget( key, 0 );
}

void poll(){
    struct message *msg;
    for(;;){
        msgrcv( msg_id, msg, 4096, 0, IPC_NOWAIT );
    }
    server_process( msg );
}

void server_process( struct message *msg ){
    char *opcode = strtok( msg->mtext, " \t\n" );
    if( !strcmp( opcode, "JOIN" ) ){
        adduser( msg->mtype );
    }
    if( !strcmp( opcode, "BYE" ) ){
        deluser( msg->mtype );
    }
    else  if( !strcmp( opcode, "SAY" ) ){
        say( msg );
    }
}

void broadcast( char *str ){
    struct message *msg;
    strncpy( msg->mtext, str, strlen( str ) );
    struct user *rider = tail;
    while( rider = rider->next ){
        msg->mtype = SERVER_MESSAGE_TYPE + rider->uid;
        msgsnd( msg_id, msg, 4096, 0 );
        kill( rider->uid, SIGPOLL );
    }
}

void echo( char *str, long uid ){
    struct message *echomessage;
    echomessage->mtext = strcat( "WRITE ", str );
    echomessage->mtype = SERVER_MESSAGE_TYPE + uid;
    msgsnd( msg_id, echomessage, 4096, 0 );
}

void adduser( long uid ){
    struct message *input;
    echo( "Choose a handle (9 characters or fewer): ", uid );
    msgrcv( msg_id, input, 4096, uid, 0 );
    struct user *new = (struct user *) malloc( sizeof( struct user ) );
    strncpy( new->nick, input->mtext, 9 );
    new->nick[10] = '\0';
    echo( "Welcome to the server!\n" );
    /*
     * Note: The new user MUST be added to the user list
     * AFTER all this information is processed, otherwise
     * these messages may be mixed up with the broadcast
     * messages addressed to that process.  This will
     * not happen in the program's present state, but
     * it will become an issue should the server ever
     * incorporate multithreading.
     */
    head->next = new;
    head = new;
}

void deluser( long uid ){
    struct user *rider = tail;
    while( rider->next->uid != uid ) rider = rider->next;
    struct user *temp = rider->next;
    rider->next = rider->next->next;
    free( temp );
    echo( "See ya!\n", uid );
}

void say( struct message *msg ){
    write_memory( msg );
    broadcast( "READ\n" );
    sprintf( msg->mtext, "UPDATE_PTR %d\n", cur_addr - shm_addr );
    broadcast( msg->mtext );
}

void write_memory( struct message *msg ){
    int len;
    struct user *rider = tail;
    while( rider != head && rider->uid != msg->mtype )
        rider = rider->next;
    if( rider->uid != msg->mtype ) goto error;
    len = strlen( rider->nick );
    memwrite( rider->nick );
    memwrite( ": " );
    memwrite( msg->mtext );
error:
    echo( "Internal server error.  Operation aborted.\n", msg->mtype );
}

void memwrite( char *str ){
    /* Next line calculates distance of cur_addr from end of region: */
    intmax_t d = SHM_SIZE - cur_addr + shm_addr;
    int len = strlen( str );
    if( likely( len < d ) ){
        strncpy( cur_addr, str, len );
        cur_addr += len;
    }
    else if( unlikely( len == d ) ){
        strncpy( cur_addr, str, len );
        cur_addr = shm_addr;
    }
    else{
        strncpy( cur_addr, str, d );
        cur_addr = shm_addr;
        strncpy( cur_addr, str+d, len-d );
    }
}