Thread: Socket program

  1. #1
    Registered User
    Join Date
    Apr 2007

    Socket program


    I'm writing a client-server socket program. the client will be an instance of the well-known telnet application. i want to implement a simple authentication between the server and the client.
    - the client should send this message (after the connection established): my password "anypassword"
    and the server will check, if it's not the same password that's hardcoded in the server program, the server close connection.

    so the client will be like that:

    1.telnet server
    2. got connected
    3. provide password, if it's not coreect server close connection

    here is my server application:
    #include <unistd.h> 
    #include <stdio.h>
    #include <sys/types.h>
    #include <sys/socket.h>
    #include <stdlib.h>
    #include <unistd.h>
    #include <errno.h>
    #include <string.h>
    #include <netinet/in.h>
    #include <arpa/inet.h>
    #include <sys/wait.h>
    #include <signal.h>
    #include <ctype.h>
    #include <time.h>
    #define SERVERPORT 111              /* port used for the connection */  
    #define QUEUE 5                       /* max # of queued connects */
    int main(void)
        fd_set master;   // master file descriptor list
        fd_set read_fds; // temp file descriptor list for select()
        int fdmax;        // maximum file descriptor number
        int i , j;
        int nbytes;
         int s_listen,d_newconn;  
        int yes=1;
        struct sockaddr_in serveraddr;    /* server address */
        struct sockaddr_in clientaddr;    /* client address */
        struct sigaction sig;
        socklen_t sin_size;               /* Socket address length type */
        string buffer[256];
        FD_ZERO(&master);    // clear the master and temp sets
        if ((s_listen = socket(AF_INET, SOCK_STREAM, 0)) == -1) {    /* create listen socket */
        /* set the options for the socket to allow reuse of a local port/address combination. */
        if (setsockopt(s_listen,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(int)) == -1) {
          memset(&(serveraddr.sin_zero), '\0', 8);  /* clear our address */
          serveraddr.sin_family = AF_INET;          /* Address Family */
          serveraddr.sin_port = htons(SERVERPORT);  /* Port number */
          /* a wild IP number to allow the system to pick the route to the remote service */
          serveraddr.sin_addr.s_addr = INADDR_ANY;  
          /* bind address to socket */
          if (bind(s_listen, (struct sockaddr *)&serveraddr, sizeof(struct sockaddr))  == -1) {
          if (listen(s_listen, QUEUE) == -1) {
    // add the listener to the master set
        FD_SET(s_listen, &master);
        // keep track of the biggest file descriptor
        fdmax = s_listen; // so far, it's this one
        // main loop
        for(;;) {
            read_fds = master; // copy it
            if (select(fdmax+1, &read_fds, NULL, NULL, NULL) == -1) {
            // run through the existing connections looking for data to read
            for(i = 0; i <= fdmax; i++) {
                if (FD_ISSET(i, &read_fds)) { // we got one!!
                    if (i == s_listen) {
                        // handle new connections
                        sin_size = sizeof(clientaddr);
                        if ((d_newconn = accept(s_listen, (struct sockaddr *)&clientaddr,
                                                                   &sin_size)) == -1) { 
                        } else {
                            FD_SET(d_newconn, &master); // add to master set
                            if (d_newconn > fdmax) {    // keep track of the maximum
                                fdmax = d_newconn;
                            printf("EDMTS SERVER: new connection from %s on "
                                "socket %d\n", inet_ntoa(clientaddr.sin_addr), d_newconn);
                    } else {
                        // handle data from a client
                        if ((nbytes = recv(i, buffer, sizeof(buffer), 0)) <= 0) {
                            // got error or connection closed by client
                            if (nbytes == 0) {
                                // connection closed
                                printf("SERVER: socket %d hung up\n", i);
                            } else {
                            close(i); // bye!
                            FD_CLR(i, &master); // remove from master set
                        } else {
                        {{{{{{{{{{{{{{{{{{{{{{ NOT COMPLETED }}}}}}}}}}}}}}}}}
                        {{{{HERE I SHOULD COMPARE THE CLIENT MESSAGE PASSOWRD              IF IT'S THE SAME }}}}}}}}}}    */
                    } // it's SO UGLY!
        return 0;

  2. #2
    Registered User kryptkat's Avatar
    Join Date
    Dec 2002
    what was the question?

  3. #3
    Registered User
    Join Date
    Mar 2005
    yeah.. right.. what is the question now.. ??
    Are you expecting us to wright the client pgm.. ?? :-)

  4. #4
    and the hat of int overfl Salem's Avatar
    Join Date
    Aug 2001
    The edge of the known universe
    Your thread bumps and cross-posts have been deleted - check the rules.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  5. #5
    Registered User
    Join Date
    Apr 2007


    sorry may be may question is not clear

    i want to add in that server program that it will accept only the password from the client if it's "mypassword":

    i'm not writing any client program. the client will be the built in linux Telnet program

    so the session will be between the server and client as follows

    1. Client will type : telnet
    the password mypassword.

    2.then the server if recieved the password "mypassword" it will connect if not it will close the connection.

    I want to know how i can make the server program recognize that the pasword is right or i can write it in the server

    Thanks....sorry for misunderstanding

  6. #6
    ATH0 quzah's Avatar
    Join Date
    Oct 2001
    So you would have us believe that you wrote this entire program, but you've never heard of strcmp?

    Hope is the first step on the road to disappointment.

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