Simple Chat Program in C (Part 3)

Read Part 2 : The Client

Sample Execution:

$ gcc server.c -o server -lpthread
$ gcc client.c -o client -lpthread

Now we run the server program and several client programs

Each client should first connect to the server by typing in:

login [alias]

Here [alias] is optional, if it is not mentioned, the name will be set as Anonymous.

The name can be changed by the command:

alias [new_name]

After this, you alias will be changed to the new name you have given.

To send a message to everyone connected at the moment:

send [message]

To send a message to a specific alias:

whisp [user_alias] [message]

If the target alias is not active at that moment, message will not be sent anywhere

You can disconnect from the server by typing:

logout

You can again reconnect by using the login command

You can terminate the client by typing:

exit

This is pretty much of it. Basically this is good for your C lab assignments regarding TCP / socket based chat clients. Here is a screen shot from my computer:

[ click to enlarge ]

Good luck!

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

Simple Chat Program in C (Part 1)

A multi-threaded chat client in C using socket and pthread library

I wrote this code years ago, putting it here because some people may want to get some help in writing server client programs in C using socket programming.

The server and client programs have a few features that you might want to take a look at. I am not going to explain the functionalities here, you can get that fairly easily by just going through the codes, they are bit long, but quite self explanatory. Ask in the comment area if you have any confusion.

The server program

The server basically waits for clients to connect and start passing message among them. Whenever a client connects to this server, it creates a thread to handle the new client, this way, it does not block other clients from connecting. Also the server can take a few commands such as whether you want to exit or not. Here is the source code of the server:

/*
** 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 IP "127.0.0.1"
#define PORT 8080
#define BACKLOG 10
#define CLIENTS 10

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

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

struct THREADINFO {
    pthread_t thread_ID; // thread's pointer
    int sockfd; // socket file descriptor
    char alias[ALIASLEN]; // client's alias
};

struct LLNODE {
    struct THREADINFO threadinfo;
    struct LLNODE *next;
};

struct LLIST {
    struct LLNODE *head, *tail;
    int size;
};

int compare(struct THREADINFO *a, struct THREADINFO *b) {
    return a->sockfd - b->sockfd;
}

void list_init(struct LLIST *ll) {
    ll->head = ll->tail = NULL;
    ll->size = 0;
}

int list_insert(struct LLIST *ll, struct THREADINFO *thr_info) {
    if(ll->size == CLIENTS) return -1;
    if(ll->head == NULL) {
        ll->head = (struct LLNODE *)malloc(sizeof(struct LLNODE));
        ll->head->threadinfo = *thr_info;
        ll->head->next = NULL;
        ll->tail = ll->head;
    }
    else {
        ll->tail->next = (struct LLNODE *)malloc(sizeof(struct LLNODE));
        ll->tail->next->threadinfo = *thr_info;
        ll->tail->next->next = NULL;
        ll->tail = ll->tail->next;
    }
    ll->size++;
    return 0;
}

int list_delete(struct LLIST *ll, struct THREADINFO *thr_info) {
    struct LLNODE *curr, *temp;
    if(ll->head == NULL) return -1;
    if(compare(thr_info, &ll->head->threadinfo) == 0) {
        temp = ll->head;
        ll->head = ll->head->next;
        if(ll->head == NULL) ll->tail = ll->head;
        free(temp);
        ll->size--;
        return 0;
    }
    for(curr = ll->head; curr->next != NULL; curr = curr->next) {
        if(compare(thr_info, &curr->next->threadinfo) == 0) {
            temp = curr->next;
            if(temp == ll->tail) ll->tail = curr;
            curr->next = curr->next->next;
            free(temp);
            ll->size--;
            return 0;
        }
    }
    return -1;
}

void list_dump(struct LLIST *ll) {
    struct LLNODE *curr;
    struct THREADINFO *thr_info;
    printf("Connection count: %d\n", ll->size);
    for(curr = ll->head; curr != NULL; curr = curr->next) {
        thr_info = &curr->threadinfo;
        printf("[%d] %s\n", thr_info->sockfd, thr_info->alias);
    }
}

int sockfd, newfd;
struct THREADINFO thread_info[CLIENTS];
struct LLIST client_list;
pthread_mutex_t clientlist_mutex;

void *io_handler(void *param);
void *client_handler(void *fd);

int main(int argc, char **argv) {
    int err_ret, sin_size;
    struct sockaddr_in serv_addr, client_addr;
    pthread_t interrupt;

    /* initialize linked list */
    list_init(&client_list);

    /* initiate mutex */
    pthread_mutex_init(&clientlist_mutex, NULL);

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

    /* set initial values */
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(PORT);
    serv_addr.sin_addr.s_addr = inet_addr(IP);
    memset(&(serv_addr.sin_zero), 0, 8);

    /* bind address with socket */
    if(bind(sockfd, (struct sockaddr *)&serv_addr, sizeof(struct sockaddr)) == -1) {
        err_ret = errno;
        fprintf(stderr, "bind() failed...\n");
        return err_ret;
    }

    /* start listening for connection */
    if(listen(sockfd, BACKLOG) == -1) {
        err_ret = errno;
        fprintf(stderr, "listen() failed...\n");
        return err_ret;
    }

    /* initiate interrupt handler for IO controlling */
    printf("Starting admin interface...\n");
    if(pthread_create(&interrupt, NULL, io_handler, NULL) != 0) {
        err_ret = errno;
        fprintf(stderr, "pthread_create() failed...\n");
        return err_ret;
    }

    /* keep accepting connections */
    printf("Starting socket listener...\n");
    while(1) {
        sin_size = sizeof(struct sockaddr_in);
        if((newfd = accept(sockfd, (struct sockaddr *)&client_addr, (socklen_t*)&sin_size)) == -1) {
            err_ret = errno;
            fprintf(stderr, "accept() failed...\n");
            return err_ret;
        }
        else {
            if(client_list.size == CLIENTS) {
                fprintf(stderr, "Connection full, request rejected...\n");
                continue;
            }
            printf("Connection requested received...\n");
            struct THREADINFO threadinfo;
            threadinfo.sockfd = newfd;
            strcpy(threadinfo.alias, "Anonymous");
            pthread_mutex_lock(&clientlist_mutex);
            list_insert(&client_list, &threadinfo);
            pthread_mutex_unlock(&clientlist_mutex);
            pthread_create(&threadinfo.thread_ID, NULL, client_handler, (void *)&threadinfo);
        }
    }

    return 0;
}

void *io_handler(void *param) {
    char option[OPTLEN];
    while(scanf("%s", option)==1) {
        if(!strcmp(option, "exit")) {
            /* clean up */
            printf("Terminating server...\n");
            pthread_mutex_destroy(&clientlist_mutex);
            close(sockfd);
            exit(0);
        }
        else if(!strcmp(option, "list")) {
            pthread_mutex_lock(&clientlist_mutex);
            list_dump(&client_list);
            pthread_mutex_unlock(&clientlist_mutex);
        }
        else {
            fprintf(stderr, "Unknown command: %s...\n", option);
        }
    }
    return NULL;
}

void *client_handler(void *fd) {
    struct THREADINFO threadinfo = *(struct THREADINFO *)fd;
    struct PACKET packet;
    struct LLNODE *curr;
    int bytes, sent;
    while(1) {
        bytes = recv(threadinfo.sockfd, (void *)&packet, sizeof(struct PACKET), 0);
        if(!bytes) {
            fprintf(stderr, "Connection lost from [%d] %s...\n", threadinfo.sockfd, threadinfo.alias);
            pthread_mutex_lock(&clientlist_mutex);
            list_delete(&client_list, &threadinfo);
            pthread_mutex_unlock(&clientlist_mutex);
            break;
        }
        printf("[%d] %s %s %s\n", threadinfo.sockfd, packet.option, packet.alias, packet.buff);
        if(!strcmp(packet.option, "alias")) {
            printf("Set alias to %s\n", packet.alias);
            pthread_mutex_lock(&clientlist_mutex);
            for(curr = client_list.head; curr != NULL; curr = curr->next) {
                if(compare(&curr->threadinfo, &threadinfo) == 0) {
                    strcpy(curr->threadinfo.alias, packet.alias);
                    strcpy(threadinfo.alias, packet.alias);
                    break;
                }
            }
            pthread_mutex_unlock(&clientlist_mutex);
        }
        else if(!strcmp(packet.option, "whisp")) {
            int i;
            char target[ALIASLEN];
            for(i = 0; packet.buff[i] != ' '; i++); packet.buff[i++] = 0;
            strcpy(target, packet.buff);
            pthread_mutex_lock(&clientlist_mutex);
            for(curr = client_list.head; curr != NULL; curr = curr->next) {
                if(strcmp(target, curr->threadinfo.alias) == 0) {
                    struct PACKET spacket;
                    memset(&spacket, 0, sizeof(struct PACKET));
                    if(!compare(&curr->threadinfo, &threadinfo)) continue;
                    strcpy(spacket.option, "msg");
                    strcpy(spacket.alias, packet.alias);
                    strcpy(spacket.buff, &packet.buff[i]);
                    sent = send(curr->threadinfo.sockfd, (void *)&spacket, sizeof(struct PACKET), 0);
                }
            }
            pthread_mutex_unlock(&clientlist_mutex);
        }
        else if(!strcmp(packet.option, "send")) {
            pthread_mutex_lock(&clientlist_mutex);
            for(curr = client_list.head; curr != NULL; curr = curr->next) {
                struct PACKET spacket;
                memset(&spacket, 0, sizeof(struct PACKET));
                if(!compare(&curr->threadinfo, &threadinfo)) continue;
                strcpy(spacket.option, "msg");
                strcpy(spacket.alias, packet.alias);
                strcpy(spacket.buff, packet.buff);
                sent = send(curr->threadinfo.sockfd, (void *)&spacket, sizeof(struct PACKET), 0);
            }
            pthread_mutex_unlock(&clientlist_mutex);
        }
        else if(!strcmp(packet.option, "exit")) {
            printf("[%d] %s has disconnected...\n", threadinfo.sockfd, threadinfo.alias);
            pthread_mutex_lock(&clientlist_mutex);
            list_delete(&client_list, &threadinfo);
            pthread_mutex_unlock(&clientlist_mutex);
            break;
        }
        else {
            fprintf(stderr, "Garbage data from [%d] %s...\n", threadinfo.sockfd, threadinfo.alias);
        }
    }

    /* clean up */
    close(threadinfo.sockfd);

    return NULL;
}

Compile it like this:

gcc server.c -o server -lpthread

Continue to Part 2 : The Client