source: trunk/instant_messenger/socket/BKP_20071105/BKP_20071026/BKP_20071019/server.c @ 151

#include "server.h"

int main (int argc, char ** argv)
{
        struct in_addr remote_addr,
                                   local_addr;
        unsigned short remote_port,
                                   local_port;
        int listen_fd;

        ParseArgs (argc, argv, &remote_addr, &remote_port, &local_addr, &local_port);

        Initialise ();

        // Create server socket before becoming a daemon so
        // there is still a chance to print an error message.
        listen_fd = CreateServerSocket (local_addr, local_port);
        if ( listen_fd < 0 )
                pbomb ("Unable to create server socket");

        //Daemonise ();

        MainLoop (listen_fd, remote_addr, remote_port); // never returns

        exit (EXIT_SUCCESS);
}

// ParseArgs()
// Parse the command line arguments to extract the remote
// and local adresses and port numbers, ra, rp, la & lp.
// Exit the program gracefully upon error.
void ParseArgs (int argc, char ** argv, struct in_addr * ra, unsigned short * rp, struct in_addr * la, unsigned short * lp)
{
        // argv[0] = program name
        // argv[1] = remote_addr
        // argv[2] = remote_port
        // argv[3] = local_addr (optional)
        // argv[4] = local_port (optional)

        char * p = strrchr (argv[0], '/');

        strncpy (g_program_name, (p == NULL) ? argv[0] : p + 1, sizeof (g_program_name) - 1);

        if ( (argc < 3) || (argc > 5) )
        {
                fprintf (stderr, "usage: %s remote_addr remote_port [local_addr] [local_port]\n", argv[0]);
                exit (EXIT_FAILURE);
        }

        if ( NameToAddr (argv[1], ra) )
                hbomb ("Unable to resolve \"%s\" to an ip address", argv[1]);

        if ( NameToPort (argv[2], rp, "tcp") )
                quit ("Unable to resolve \"%s\" to a port number", argv[2]);

        if ( argc < 4 )
                la->s_addr = htonl (INADDR_ANY);
        else
                if ( NameToAddr (argv[3], la) )
                        hbomb ("Unable to resolve \"%s\" to an ip address", argv[3]);

        if ( argc < 5 )
                memcpy (lp, rp, sizeof (*lp));
        else
                if ( NameToPort (argv[4], lp, "tcp") )
                        quit ("Unable to resolve \"%s\" to a port number", argv[4]);
}

// Initialise()
// Setup syslog, signal handlers, and other intialisation.
void Initialise (void)
{
        openlog (g_program_name, LOG_PID, LOG_USER);
        syslog (LOG_INFO, "%s started", g_program_name);

        chdir ("/"); // Change working directory to the root.

        umask (0); // Clear our file mode creation mask

        set_signal_handler (SIGCHLD, sig_child);

        signal (SIGPIPE, SIG_IGN);
}

// sig_child()
// Handles SIGCHLD from exiting child processes.
void sig_child (int signo)
{
        pid_t pid;

        (void) signo; // suppress compiler warning

        for ( ; ; )
        {
                write(1, "SIG\n", sizeof("SIG\n"));
                pid = waitpid (WAIT_ANY, NULL, WNOHANG);

                if ( pid > 0 )
                        syslog (LOG_INFO, "Caught SIGCHLD from pid %d", pid);
                else
                        break;
        }
        write(1, "SIG...\n", sizeof("SIG...\n"));

        if ( (pid < 0) && (errno != ECHILD) )
                syslog (LOG_ERR, "waitpid(): %m"), exit (EXIT_FAILURE);

        return;
}

// CreateServerSocket()
// Create a socket, bind it to the specified address
// and port, and set it to listen for client connections.
// Returns < 0 on failure to bind, bombs on error otherwise,
// returns the fd of the new socket on success.
int CreateServerSocket (struct in_addr addr, unsigned short port)
{
        int err,
                fd;
        const int on = 1;
        struct sockaddr_in sa;

        // Create a socket and get its descriptor.
        fd = socket (AF_INET, SOCK_STREAM, 0);
        if ( fd < 0 )
                syslog (LOG_ERR, "socket(): %m"), exit (EXIT_FAILURE);

        // Set SO_REUSEADDR socket option
        if ( setsockopt (fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof (on)) < 0 )
                syslog (LOG_ERR, "setsockopt(fd%d, SO_REUSEADDR): %m", fd);

        // Load a sa structure with the specified address and port
        sa.sin_family = AF_INET;
        sa.sin_port = htons (port);
        sa.sin_addr = addr;
        memset (sa.sin_zero, 0, sizeof (sa.sin_zero));

        // Bind our socket to the address and port specified
        err = bind (fd, (struct sockaddr *) &sa, sizeof (sa));
        if ( err < 0 )
        {
                syslog (LOG_ERR, "bind(): %m");
                return err;
        }

        // Tell socket to listen and queue up to 5 incoming connections.
        if ( listen (fd, 5) < 0 )
                syslog (LOG_ERR, "listen(): %m"), exit (EXIT_FAILURE);

        return fd;
}

// Daemonise()
// Put the program in the background, set PPID=1, create a
// new session and process group, without a controlling tty.
void Daemonise (void)
{
        pid_t pid;

        // Close stdin, stdout & stderr
        // TODO:
        //              open /dev/null and dup the fd to stdin, stdout & stderr
        //              close(STDIN_FILENO);
        //              close(STDOUT_FILENO);
        //              close(STDERR_FILENO);

        syslog (LOG_INFO, "%s daemonising", g_program_name);

        // Fork the process to put it in the background.

        pid = fork ();
        if ( pid == -1 )
                syslog (LOG_ERR, "fork(): %m"), exit (EXIT_FAILURE);

        // parent terminates here, so shell thinks the command is done.
        if ( pid )
                exit (0);

        syslog (LOG_INFO, "%s in background", g_program_name);

        // 1st child continues to run in the background with PPID=1

        // Become leader of a new session and a new process group,
        // with no controlling tty.
        setsid ();

        // Fork again to guarantee the process will
        // not be able to aquire a controlling tty.

        // signal (SIGHUP, SIG_IGN);
        // required according to Stevens' UNP2 p333

        pid = fork ();
        if (pid == -1)
                syslog (LOG_ERR, "fork(): %m"), exit (EXIT_FAILURE);

        if ( pid ) // 1st child terminates
                exit (0);

        // 2nd child continues, no longer a session or group leader

        syslog (LOG_INFO, "%s daemonised", g_program_name);
}

// MainLoop()
// Classic concurrent server model.
// Wait for a client to connect, fork a child process
// to do the business with the client, parent process
// continues to wait for the next connection.
// This function does not return.
void MainLoop (int listen_fd, struct in_addr rem_addr, unsigned short rem_port)
{
        int server_fd,
                client_fd;
        pid_t child_pid;

        for ( ; ; )
        {
                client_fd = AcceptClientConnection (listen_fd);

                child_pid = fork ();
                if ( child_pid == -1 )
                        syslog (LOG_ERR, "fork(): %m"), exit (EXIT_FAILURE);

                if ( child_pid ) // parent
                {
                        close (client_fd);

                        syslog (LOG_INFO, "Forked child pid %d to deal with client", child_pid);

                        continue;
                }
                else // child
                {
                        close (listen_fd);

                        server_fd = ConnectToServer (rem_addr, rem_port);

                        Proxy (server_fd, client_fd);

                        syslog (LOG_INFO, "exiting");
                        _exit (0);
                }
        }
}

// Proxy()
// Copies data between server_fd and client_fd in both directions
// until one or other peer closes their connection.
void Proxy (int server_fd, int client_fd)
{
        pid_t helper_pid;

        syslog (LOG_INFO, "Proxy(fd%d, fd%d)", server_fd, client_fd);

        signal (SIGCHLD, SIG_IGN);

        helper_pid = fork ();
        if ( helper_pid == -1 )
                syslog (LOG_ERR, "fork(): %m"), exit (EXIT_FAILURE);

        if ( helper_pid ) // parent
        {
                syslog (LOG_INFO, "Forked child pid %d to help with proxying", helper_pid);

                Cat (server_fd, client_fd);

                shutdown (client_fd, 1);
                close (server_fd);
                close (client_fd);

                wait (0); // wait for helper to exit
        }
        else // child (helper)
        {
                Cat (client_fd, server_fd);

                shutdown (server_fd, 1);

                syslog (LOG_INFO, "exiting");
                exit (0); // helper exits here
        }
}

// AcceptClientConnection()
// waits for a tcp connect to the socket listen_fd, which
// must already be bound and set to listen on a local port.
// Bombs on error, returns the fd of the new socket on success.
int AcceptClientConnection (int listen_fd)
{
        int newfd;
        struct sockaddr_in sa;
        socklen_t socklen;

        syslog (LOG_INFO, "AcceptClientConnection(fd%d)", listen_fd);

        // Accept the connection and create a new socket for it.
        socklen = sizeof (sa);
        memset (&sa, 0, socklen);
        do
        {
                newfd = accept (listen_fd, (struct sockaddr *) &sa, &socklen);
        }
        while ( (newfd < 0) && (errno == EINTR) );

        syslog (LOG_INFO, "Accepted client connection on new socket fd%d", newfd);

        if ( newfd < 0 )
                syslog (LOG_ERR, "accept(): %m"), exit (EXIT_FAILURE);

        if ( socklen != sizeof (sa) )
                syslog (LOG_ERR, "accept() screwed up!"), exit (EXIT_FAILURE);

        return (newfd);
}

// ConnectToServer()
// attempts a tcp connect to the server specified
// by addr and port.  Bombs on failure to connect,
// returns the fd of the new socket on success.
int ConnectToServer (struct in_addr addr, unsigned short port)
{
        // TODO: have a timeout for connect() - see Unix socket FAQ 6.2

        int fd, err;
        struct sockaddr_in sa;

        // Create a socket and get its descriptor.
        fd = socket (AF_INET, SOCK_STREAM, 0);

        if ( fd < 0 )
                syslog (LOG_ERR, "socket(): %m"), exit (EXIT_FAILURE);

        sa.sin_family = AF_INET;
        sa.sin_port = htons (port);
        sa.sin_addr = addr;
        memset (sa.sin_zero, 0, sizeof (sa.sin_zero));

        err = connect (fd, (struct sockaddr *) &sa, sizeof (sa));
        if (err < 0)
        {
                syslog (LOG_ERR, "Unable to connect socket fd%d to server: %m", fd);
                exit (EXIT_FAILURE);
        }

        syslog (LOG_INFO, "Connected socket fd%d to server", fd);

        return fd;
}

// Cat()
// read data from in_fd and write it to out_fd until
// the connection is closed by one of the peers.
// Data is copied using a dynamically allocated buffer.
void Cat (int in_fd, int out_fd)
{
        unsigned char * const buf = (char *) malloc (sizeof(char) * BUF_SIZE);
        int bytes_rcvd,
                bytes_sent = (int) NULL,
                i;

        syslog (LOG_INFO, "Cat(fd%d, fd%d)", in_fd, out_fd);

        if ( buf == NULL )
                syslog (LOG_ERR, "malloc(): %m"), exit (EXIT_FAILURE);

        do
        {
                write(1, "DO\n", sizeof("DO\n"));
                bzero(buf, BUF_SIZE);
                bytes_rcvd = recv (in_fd, buf, BUF_SIZE, 0);

                for ( i = 0; i < bytes_rcvd; i += bytes_sent )
                {
                        bytes_sent = send (out_fd, buf + i, bytes_rcvd - i, 0);

                        if ( bytes_sent < 0 )
                                break;
                }
                write(1, "WHILE\n", sizeof("WHILE\n"));
        }
        while ( (bytes_rcvd > 0) && (bytes_sent > 0) );
        
        write(1, "...\n", sizeof("...\n"));

        if ( (bytes_rcvd < 0) && (errno != ECONNRESET) )
                syslog (LOG_ERR, "recv(): %m"), exit (EXIT_FAILURE);

        if ( (bytes_sent < 0) && (errno != EPIPE) )
                syslog (LOG_ERR, "send(): %m"), exit (EXIT_FAILURE);

        free (buf);
}

// NameToAddress()
// Convert name to an ip address.
// Returns 0 on success, -1 on failure.
int NameToAddr (const char * name, struct in_addr * p_inaddr)
{
        struct hostent * he;

        // First, attempt to convert from string ip format
        // TODO: use inet_aton() instead
        p_inaddr->s_addr = inet_addr (name);
        if ( p_inaddr->s_addr != -1U ) // Success
                return 0;

        // Next, attempt to read from /etc/hosts or do a DNS lookup
        he = gethostbyname (name);
        if ( he != NULL ) // Success
        {
                memcpy (p_inaddr, he->h_addr, sizeof (struct in_addr));
                return 0;
        }

        return -1; // Failed to resolve name to an ip address
}

// NameToPort()
// Convert name to a port number. Name can either be a port name
// (in which case proto must also be set to either "tcp" or "udp")
// or name can be the ascii representation of the port number.
// Returns 0 on success, -1 on failure.
int NameToPort (const char * name, unsigned short * port, const char * proto)
{
        unsigned long lport;
        char * errpos;
        struct servent * se;

        // First, attempt to convert string to integer
        lport = strtoul (name, &errpos, 0);
        if ( (*errpos == 0) && (lport <= 65535) ) // Success
        {
                *port = lport;
                return 0;
        }

        // Next, attempt to read the string from /etc/services
        se = getservbyname (name, proto);
        if ( se != NULL) // Success
        {
                *port = ntohs (se->s_port);
                return 0;
        }

        return -1; // Failed to resolve port name to a number
}

// quit()
// Print an error message to stderr
// and syslog, then exit the program.
void quit (const char * fmt, ...) // quit with msg
{
        va_list ap;

        fflush (stdout);

        fprintf (stderr, "%s: ", g_program_name);

        va_start (ap, fmt);
        vfprintf (stderr, fmt, ap);
        va_end (ap);

        fputc ('\n', stderr);

        syslog (LOG_ERR, "I quit!");

        exit (EXIT_FAILURE);
}

// pbomb()
// Print an error message to stderr
// and syslog, then exit the program.
// pbomb() additionally include the
// string representation of errno.
void pbomb (const char * fmt, ...) // bomb with perror
{
        va_list ap;
        int errno_save = errno;
        char buf[100];

        fflush (stdout);

        fprintf (stderr, "%s: ", g_program_name);

        va_start (ap, fmt);
        vsnprintf (buf, sizeof (buf), fmt, ap);
        va_end (ap);

        errno = errno_save;
        perror (buf);

        syslog (LOG_ERR, "Bang!: %s: %m", buf);

        exit (EXIT_FAILURE);
}

// hbomb()
// Print an error message to stderr
// and syslog, then exit the program.
// hbomb() additionally include the
// string representation of h_errno.
void hbomb (const char * fmt, ...) // bomb with herror
{
        va_list ap;
        int h_errno_save = h_errno;
        char buf[100];

        fflush (stdout);

        fprintf (stderr, "%s: ", g_program_name);

        va_start (ap, fmt);
        vsnprintf (buf, sizeof (buf), fmt, ap);
        va_end (ap);

        h_errno = h_errno_save;
        herror (buf);

        syslog (LOG_ERR, "Bang!: %s: %s", buf, hstrerror (h_errno));

        exit (EXIT_FAILURE);
}

// set_signal_handler()
// Sets a signal handler function.
// Similar to signal() but this method
// is more portable between platforms.
void set_signal_handler (int signum, signal_handler_t sa_handler_func)
{
        struct sigaction act;

        act.sa_handler = sa_handler_func;
        sigemptyset (&(act.sa_mask));
        act.sa_flags = 0;

        if ( sigaction (signum, &act, NULL) < 0 )
        {
                syslog (LOG_ERR, "Error setting handler for signal %d: %m", signum);
                exit (EXIT_FAILURE);
        }
}