Simple Chat Program in C (Part 2)

Read Part 1 : The server

The client program

The client program basically communicates with other client program, to run multiple clients, just open a terminal for each client. The client is command driven in this code, that is you have to enter command strings. Just read the code and you will see what it is expecting from you. The code is pretty simple.

/*
** Author: Zobayer Hasan
** Date: 26th February, 2010
** Copyright: NO COPYRIGHT ISSUES. However, do not copy it.
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#include <netdb.h>
#include <unistd.h>
#include <pthread.h>

#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <sys/socket.h>

#define SERVERIP "127.0.0.1"
#define SERVERPORT 8080

#define BUFFSIZE 1024
#define ALIASLEN 32
#define OPTLEN 16
#define LINEBUFF 2048

struct PACKET {
    char option[OPTLEN]; // instruction
    char alias[ALIASLEN]; // client's alias
    char buff[BUFFSIZE]; // payload
};

struct USER {
        int sockfd; // user's socket descriptor
        char alias[ALIASLEN]; // user's name
};

struct THREADINFO {
    pthread_t thread_ID; // thread's pointer
    int sockfd; // socket file descriptor
};

int isconnected, sockfd;
char option[LINEBUFF];
struct USER me;

int connect_with_server();
void setalias(struct USER *me);
void logout(struct USER *me);
void login(struct USER *me);
void *receiver(void *param);
void sendtoall(struct USER *me, char *msg);
void sendtoalias(struct USER *me, char * target, char *msg);

int main(int argc, char **argv) {
    int sockfd, aliaslen;
    
    memset(&me, 0, sizeof(struct USER));
    
    while(gets(option)) {
        if(!strncmp(option, "exit", 4)) {
            logout(&me);
            break;
        }
        if(!strncmp(option, "help", 4)) {
            FILE *fin = fopen("help.txt", "r");
            if(fin != NULL) {
                while(fgets(option, LINEBUFF-1, fin)) puts(option);
                fclose(fin);
            }
            else {
                fprintf(stderr, "Help file not found...\n");
            }
        }
        else if(!strncmp(option, "login", 5)) {
            char *ptr = strtok(option, " ");
            ptr = strtok(0, " ");
            memset(me.alias, 0, sizeof(char) * ALIASLEN);
            if(ptr != NULL) {
                aliaslen =  strlen(ptr);
                if(aliaslen > ALIASLEN) ptr[ALIASLEN] = 0;
                strcpy(me.alias, ptr);
            }
            else {
                strcpy(me.alias, "Anonymous");
            }
            login(&me);
        }
        else if(!strncmp(option, "alias", 5)) {
            char *ptr = strtok(option, " ");
            ptr = strtok(0, " ");
            memset(me.alias, 0, sizeof(char) * ALIASLEN);
            if(ptr != NULL) {
                aliaslen =  strlen(ptr);
                if(aliaslen > ALIASLEN) ptr[ALIASLEN] = 0;
                strcpy(me.alias, ptr);
                setalias(&me);
            }
        }
        else if(!strncmp(option, "whisp", 5)) {
            char *ptr = strtok(option, " ");
            char temp[ALIASLEN];
            ptr = strtok(0, " ");
            memset(temp, 0, sizeof(char) * ALIASLEN);
            if(ptr != NULL) {
                aliaslen =  strlen(ptr);
                if(aliaslen > ALIASLEN) ptr[ALIASLEN] = 0;
                strcpy(temp, ptr);
                while(*ptr) ptr++; ptr++;
                while(*ptr <= ' ') ptr++;
                sendtoalias(&me, temp, ptr);
            }
        }
        else if(!strncmp(option, "send", 4)) {
            sendtoall(&me, &option[5]);
        }
        else if(!strncmp(option, "logout", 6)) {
            logout(&me);
        }
        else fprintf(stderr, "Unknown option...\n");
    }
    return 0;
}

void login(struct USER *me) {
    int recvd;
    if(isconnected) {
        fprintf(stderr, "You are already connected to server at %s:%d\n", SERVERIP, SERVERPORT);
        return;
    }
    sockfd = connect_with_server();
    if(sockfd >= 0) {
        isconnected = 1;
        me->sockfd = sockfd;
        if(strcmp(me->alias, "Anonymous")) setalias(me);
        printf("Logged in as %s\n", me->alias);
        printf("Receiver started [%d]...\n", sockfd);
        struct THREADINFO threadinfo;
        pthread_create(&threadinfo.thread_ID, NULL, receiver, (void *)&threadinfo);

    }
    else {
        fprintf(stderr, "Connection rejected...\n");
    }
}

int connect_with_server() {
    int newfd, err_ret;
    struct sockaddr_in serv_addr;
    struct hostent *to;

    /* generate address */
    if((to = gethostbyname(SERVERIP))==NULL) {
        err_ret = errno;
        fprintf(stderr, "gethostbyname() error...\n");
        return err_ret;
    }

    /* open a socket */
    if((newfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        err_ret = errno;
        fprintf(stderr, "socket() error...\n");
        return err_ret;
    }

    /* set initial values */
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(SERVERPORT);
    serv_addr.sin_addr = *((struct in_addr *)to->h_addr);
    memset(&(serv_addr.sin_zero), 0, 8);

    /* try to connect with server */
    if(connect(newfd, (struct sockaddr *)&serv_addr, sizeof(struct sockaddr)) == -1) {
        err_ret = errno;
        fprintf(stderr, "connect() error...\n");
        return err_ret;
    }
    else {
        printf("Connected to server at %s:%d\n", SERVERIP, SERVERPORT);
        return newfd;
    }
}

void logout(struct USER *me) {
    int sent;
    struct PACKET packet;
    
    if(!isconnected) {
        fprintf(stderr, "You are not connected...\n");
        return;
    }
    
    memset(&packet, 0, sizeof(struct PACKET));
    strcpy(packet.option, "exit");
    strcpy(packet.alias, me->alias);
    
    /* send request to close this connetion */
    sent = send(sockfd, (void *)&packet, sizeof(struct PACKET), 0);
    isconnected = 0;
}

void setalias(struct USER *me) {
    int sent;
    struct PACKET packet;
    
    if(!isconnected) {
        fprintf(stderr, "You are not connected...\n");
        return;
    }
    
    memset(&packet, 0, sizeof(struct PACKET));
    strcpy(packet.option, "alias");
    strcpy(packet.alias, me->alias);
    
    /* send request to close this connetion */
    sent = send(sockfd, (void *)&packet, sizeof(struct PACKET), 0);
}

void *receiver(void *param) {
    int recvd;
    struct PACKET packet;
    
    printf("Waiting here [%d]...\n", sockfd);
    while(isconnected) {
        
        recvd = recv(sockfd, (void *)&packet, sizeof(struct PACKET), 0);
        if(!recvd) {
            fprintf(stderr, "Connection lost from server...\n");
            isconnected = 0;
            close(sockfd);
            break;
        }
        if(recvd > 0) {
            printf("[%s]: %s\n", packet.alias, packet.buff);
        }
        memset(&packet, 0, sizeof(struct PACKET));
    }
    return NULL;
}

void sendtoall(struct USER *me, char *msg) {
    int sent;
    struct PACKET packet;
    
    if(!isconnected) {
        fprintf(stderr, "You are not connected...\n");
        return;
    }
    
    msg[BUFFSIZE] = 0;
    
    memset(&packet, 0, sizeof(struct PACKET));
    strcpy(packet.option, "send");
    strcpy(packet.alias, me->alias);
    strcpy(packet.buff, msg);
    
    /* send request to close this connetion */
    sent = send(sockfd, (void *)&packet, sizeof(struct PACKET), 0);
}

void sendtoalias(struct USER *me, char *target, char *msg) {
    int sent, targetlen;
    struct PACKET packet;
    
    if(target == NULL) {
        return;
    }
    
    if(msg == NULL) {
        return;
    }
    
    if(!isconnected) {
        fprintf(stderr, "You are not connected...\n");
        return;
    }
    msg[BUFFSIZE] = 0;
    targetlen = strlen(target);
    
    memset(&packet, 0, sizeof(struct PACKET));
    strcpy(packet.option, "whisp");
    strcpy(packet.alias, me->alias);
    strcpy(packet.buff, target);
    strcpy(&packet.buff[targetlen], " ");
    strcpy(&packet.buff[targetlen+1], msg);
    
    /* send request to close this connetion */
    sent = send(sockfd, (void *)&packet, sizeof(struct PACKET), 0);
}

Compile it like this:

gcc client.c -o client -lpthread

So basically this is it. It's just a program to show and example of pthread and socket together, it will be pointless to find how poorly written this program is compared to real life chat clients, those are off the limits of this post. Also, read the main functions of the client first to understand what you need to give it as input to make it work.

The next part of the post describes the commands which are usable from the client program.

Continue to Part 3 : Sample Execution