jchat:        main.o login.o regist.o tcp.o
    gcc -w main.o login.o regist.o tcp.o -o jchat
    rm -f *.o *.gch *~
main.o:        main.c login.h regist.h tcp.h
    gcc -w -c main.c login.h regist.h tcp.h
login.o:    login.c login.h tcp.h
    gcc -w -c login.c login.h tcp.h
regist.o:    regist.c regist.h tcp.h
    gcc -w -c regist.c regist.h tcp.h
tcp.o:        tcp.c tcp.h
    gcc -w -c tcp.c tcp.h

clean:
    rm -f *.o *.gch *~ jchat

/*client/main.c*/

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

#include "login.h"
#include "regist.h"
#include "tcp.h"

#define MAXLINE 4096
#define IP "127.0.0.1" // localhost
#define PORT 12345

char sendbuff[MAXLINE], recvbuff[MAXLINE];//send buffer & recv buffer
int sockfd;//socket file descriptor

int main(int argc, char *argv[])
{
    ) {
        exit();
    }

    ];
    ) {
        printf("login or regist:");
        scanf("%s", choice);
        ) {
            login(sockfd);
        }
        ) {
            regist(sockfd);
        }
        else {
            puts("input login or regist!");
        }
    }
}

/*client/login.c*/

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>

#include "login.h"
#include "tcp.h"

#define MAXLINE 4096
#define IP "127.0.0.1" // localhost
#define PORT 12345

], passwd[];
];

/*
 * login to server
 * return 1 if succeed, 0 if fail
 */
int login_succeed(int sockfd)
{
    char sendbuff[MAXLINE], recvbuff[MAXLINE];
    sprintf(sendbuff, "l:%s:%s", user, passwd);

    write(sockfd, sendbuff, strlen(sendbuff));
    //printf("sendbuff> '%s'\n", sendbuff);
    int n = read(sockfd, recvbuff, MAXLINE);
    recvbuff[n] = '\0';
    //printf("recvbuff> '%s'\n", recvbuff);

    ) ;
    ;
}

/*
 * send message to another user by server
 */
void send_mesg(int sockfd)
{
    char sendbuff[MAXLINE];
    int len = strlen(line);
    , j, k, pos;

    while (i<len && (line[i]==' ' || line[i]=='\t')) ++i;
    j = i + ;
    while (j<len && line[j]!=' ' && line[j]!='\t') ++j;
    k = j + ;
    while (k<len && (line[k]==' ' || line[k]=='\t')) ++k;

    , ulen = strlen(user);
    sendbuff[] = ] = ':';
    ; pos<ulen; ++pos) sendbuff[send_len++] = user[pos];
    sendbuff[send_len++] = ':';
    for (pos=i; pos<j; ++pos) sendbuff[send_len++] = line[pos];
    sendbuff[send_len++] = ':';
    for (pos=k; pos<len; ++pos) sendbuff[send_len++] = line[pos];
    sendbuff[send_len++] = '\0';

    write(sockfd, sendbuff, strlen(sendbuff));
    //printf("send_mesg sendbuff> '%s'\n", sendbuff);
}

/*
 * ask the server the online user
 */
void check_online(int sockfd)
{
    char sendbuff[MAXLINE], recvbuff[MAXLINE];
    sprintf(sendbuff, "o");

    write(sockfd, sendbuff, strlen(sendbuff));
    //printf("check_online sendbuff> '%s'\n", sendbuff);
    int recv_len = read(sockfd, recvbuff, MAXLINE);
    recvbuff[recv_len] = '\0';
    //printf("check_online recvbuff> '%s'\n", recvbuff);

    ) {
        printf("no one online\n");
    }
    else {
        , j, k, num = ;
        ][];
        while (i < recv_len) {
            j = i+;
            while (recvbuff[j] != ';') ++j;
            for (k=i; k<j; ++k) on[num][k-i] = recvbuff[k];
            on[num][j-i] = '\0';
            ++num;
            i = j + ;
        }
        printf("%d online user:\n", num);
        ; k<num; ++k) printf("  %s\n", on[k]);
    }
}

/*
 * quit this client
 * quit the process fork by server
 */
void quit(int sockfd)
{
    char sendbuff[MAXLINE];
    sprintf(sendbuff, "q:%s", user);

    write(sockfd, sendbuff, strlen(sendbuff));
    //printf("quit sendbuff> '%s'\n", sendbuff);
}

/*
 * get unread message from server every 1 second
 */
void get_mesg(int sockfd)
{
    char sendbuff[MAXLINE], recvbuff[MAXLINE];

    ) {
        sleep();

        sprintf(sendbuff, "g:%s", user);
        write(sockfd, sendbuff, strlen(sendbuff));

        //printf("get_mesg sendbuff> '%s'\n", sendbuff);
        int recv_len = read(sockfd, recvbuff, MAXLINE);
        recvbuff[recv_len] = '\0';
        //printf("get_mesg recvbuff> '%s'\n", recvbuff);

        ) { // no message get
            continue;
        }

        int num, i, j, k, l;
        num = i = ;
        ][];
        while (i < recv_len) {
            j = i + ;
            while (recvbuff[j] != ';') ++j;

            k = i;
            while (k<j && recvbuff[k]!=':') ++k;
            ;
            for (l=i; l<k; ++l) line[line_len++] = recvbuff[l];
            line[line_len++] = ':';line[line_len++] = ' ';
            ; l<j; ++l) line[line_len++] = recvbuff[l];
            line[line_len] = '\0';
            puts(line);

            i = j + ;
        }
    }
}

/*
 * send online notice to server every 5 seconds
 */
void online_notice(int sockfd)
{
    char sendbuff[MAXLINE];

    ) {
        sprintf(sendbuff, "a:%s", user);

        write(sockfd, sendbuff, strlen(sendbuff));
        //printf("sendbuff> '%s'\n", sendbuff);

        sleep();
    }
}

/*
 * everything after login
 * thread 1 : receive user command
 * thread 2 : get unread message from server
 * thread 3 : send online notice to server
 */
void login(int sockfd)
{
    printf("user: ");
    scanf("%s", user);
    printf("password: ");
    scanf("%s", passwd);

    if (login_succeed(sockfd)) {
        printf("welcome %s~\n", user);
        pid_t pid1 = fork();
        ) {
            pid_t pid2 = fork();
            ) { // thread 1 : input command
                while (gets(line)) {
                    ]) {
                        case 's': // send message
                            send_mesg(sockfd);
                            break;
                        case 'o': // check online
                            check_online(sockfd);
                            break;
                        case 'q': // quit
                            quit(sockfd);
                            kill(pid1, );
                            kill(pid2, );
                            printf("goobye %s ~\n", user);
                            exit();
                            break;
                    }
                }
            }
            else { // thread 2 : get message from server
                get_mesg(sockfd);
            }
        }
        else { // thread 3 : send online notice
            online_notice(sockfd);
        }
    }
    else {
        printf("login failed\n");
    }
}

/*client/login.h*/

#ifndef LOGIN_H
#define LOGIN_H

void login(int sockfd);

#endif // LOGIN_H

/*client/regist.c*/

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>

#include "regist.h"
#include "tcp.h"

#define MAXLINE 4096

extern char sendbuff[MAXLINE], recvbuff[MAXLINE];
], passwd[];

/*
 * regist new user
 * return 1 if succeed, 0 if fail
 */
int regist_succeed(int sockfd)
{
    sprintf(sendbuff, "r:%s:%s", user, passwd);

    write(sockfd, sendbuff, strlen(sendbuff));
    int n = read(sockfd, recvbuff, MAXLINE);
    recvbuff[n] = ;

    ) ;
    ;
}

/*
 * regist
 */
void regist(int sockfd)
{
    printf("user: ");
    scanf("%s", user);
    printf("password: ");
    scanf("%s", passwd);

    if (regist_succeed(sockfd)) {
        printf("regist a new user!\n");
    }
    else {
        printf("fail in regist new user!\n");
    }
}

/*client/regist.h*/

#ifndef REGIST_H
#define REGIST_H

void regist(int sockfd);

#endif // REGIST_H

/*client/tcp.c*/

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <netinet/in.h>

#include "tcp.h"

/*
 * link to assign IP and port
 * return the socket file descriptor
 */
int link_server(char *IP, int port)
{
    int sockfd;
    struct sockaddr_in servaddr;

    )) < ) {
        fprintf(stderr, "socket error\n");
        ;
    }

    memset(&servaddr, , sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(port);
    ) {
        fprintf(stderr, "inet_pton error for %s\n", IP);
        ;
    }

    ) {
        fprintf(stderr, "connect error\n");
        ;
    }

    return sockfd;
}

/*client/tcp.h*/

#ifndef TCP_H
#define TCP_H

/*
 * link IP:port using tcp
 * return sock file descriptor of the link (-1 if error)
 */
int link_server(char *IP, int port);

#endif // TCP_H