* Three cases. Either (a) there's a nonzero * length string followed by an @, in which * case that's user and the remainder is host. * Or (b) there's only one string, not counting * a potential initial @, and it exists in the * saved-sessions database. Or (c) only one * string and it _doesn't_ exist in the * database.
* A nonzero length string followed by an @ is treated * as a username. (We discount an _initial_ @.) The * rest of the string (or the whole string if no @) * is treated as a session name and/or hostname.
int main(int argc, char **argv){    int sending;    int portnumber = -1;    int *fdlist;    int fd;    int i, fdcount, fdsize, fdstate;    int connopen;    int exitcode;    int errors;    int use_subsystem = 0;    void *ldisc, *logctx;    ssh_get_line = console_get_line;    fdlist = NULL;    fdcount = fdsize = 0;    /*     * Initialise port and protocol to sensible defaults. (These     * will be overridden by more or less anything.)     */    default_protocol = PROT_SSH;    default_port = 22;    flags = FLAG_STDERR;    /*     * Process the command line.     */    do_defaults(NULL, &cfg);    loaded_session = FALSE;    default_protocol = cfg.protocol;    default_port = cfg.port;    errors = 0;    {	/*	 * Override the default protocol if PLINK_PROTOCOL is set.	 */	char *p = getenv("PLINK_PROTOCOL");	int i;	if (p) {	    for (i = 0; backends[i].backend != NULL; i++) {		if (!strcmp(backends[i].name, p)) {		    default_protocol = cfg.protocol = backends[i].protocol;		    default_port = cfg.port =			backends[i].backend->default_port;		    break;		}	    }	}    }    while (--argc) {	char *p = *++argv;	if (*p == '-') {	    int ret = cmdline_process_param(p, (argc > 1 ? argv[1] : NULL),					    1, &cfg);	    if (ret == -2) {		fprintf(stderr,			"plink: option \"%s\" requires an argument\n", p);		errors = 1;	    } else if (ret == 2) {		--argc, ++argv;	    } else if (ret == 1) {		continue;	    } else if (!strcmp(p, "-batch")) {		console_batch_mode = 1;	    } else if (!strcmp(p, "-s")) {                /* Save status to write to cfg later. */		use_subsystem = 1;	    } else if (!strcmp(p, "-V")) {                version();	    } else if (!strcmp(p, "-o")) {                if (argc <= 1) {                    fprintf(stderr,                            "plink: option \"-o\" requires an argument\n");		    errors = 1;		} else {                    --argc;		    provide_xrm_string(*++argv);		}	    } else {		fprintf(stderr, "plink: unknown option \"%s\"\n", p);		errors = 1;	    }	} else if (*p) {	    if (!*cfg.host) {		char *q = p;                do_defaults(NULL, &cfg);		/*		 * If the hostname starts with "telnet:", set the		 * protocol to Telnet and process the string as a		 * Telnet URL.		 */		if (!strncmp(q, "telnet:", 7)) {		    char c;		    q += 7;		    if (q[0] == '/' && q[1] == '/')			q += 2;		    cfg.protocol = PROT_TELNET;		    p = q;		    while (*p && *p != ':' && *p != '/')			p++;		    c = *p;		    if (*p)			*p++ = '\0';		    if (c == ':')			cfg.port = atoi(p);		    else			cfg.port = -1;		    strncpy(cfg.host, q, sizeof(cfg.host) - 1);		    cfg.host[sizeof(cfg.host) - 1] = '\0';		} else {		    char *r;		    /*		     * Before we process the [user@]host string, we		     * first check for the presence of a protocol		     * prefix (a protocol name followed by ",").		     */		    r = strchr(p, ',');		    if (r) {			int i, j;			for (i = 0; backends[i].backend != NULL; i++) {			    j = strlen(backends[i].name);			    if (j == r - p &&				!memcmp(backends[i].name, p, j)) {				default_protocol = cfg.protocol =				    backends[i].protocol;				portnumber =				    backends[i].backend->default_port;				p = r + 1;				break;			    }			}		    }		    /*		     * Three cases. Either (a) there's a nonzero		     * length string followed by an @, in which		     * case that's user and the remainder is host.		     * Or (b) there's only one string, not counting		     * a potential initial @, and it exists in the		     * saved-sessions database. Or (c) only one		     * string and it _doesn't_ exist in the		     * database.		     */		    r = strrchr(p, '@');		    if (r == p)			p++, r = NULL; /* discount initial @ */		    if (r == NULL) {			/*			 * One string.			 */			Config cfg2;			do_defaults(p, &cfg2);			if (loaded_session || cfg2.host[0] == '\0') {			    /* No settings for this host; use defaults */			    /* (or session was already loaded with -load) */			    strncpy(cfg.host, p, sizeof(cfg.host) - 1);			    cfg.host[sizeof(cfg.host) - 1] = '\0';			    cfg.port = default_port;			} else {			    cfg = cfg2;			    /* Ick: patch up internal pointer after copy */			    cfg.remote_cmd_ptr = cfg.remote_cmd;			}		    } else {			*r++ = '\0';			strncpy(cfg.username, p, sizeof(cfg.username) - 1);			cfg.username[sizeof(cfg.username) - 1] = '\0';			strncpy(cfg.host, r, sizeof(cfg.host) - 1);			cfg.host[sizeof(cfg.host) - 1] = '\0';			cfg.port = default_port;		    }		}	    } else {		char *command;		int cmdlen, cmdsize;		cmdlen = cmdsize = 0;		command = NULL;		while (argc) {		    while (*p) {			if (cmdlen >= cmdsize) {			    cmdsize = cmdlen + 512;			    command = sresize(command, cmdsize, char);			}			command[cmdlen++]=*p++;		    }		    if (cmdlen >= cmdsize) {			cmdsize = cmdlen + 512;			command = sresize(command, cmdsize, char);		    }		    command[cmdlen++]=' '; /* always add trailing space */		    if (--argc) p = *++argv;		}		if (cmdlen) command[--cmdlen]='\0';				       /* change trailing blank to NUL */		cfg.remote_cmd_ptr = command;		cfg.remote_cmd_ptr2 = NULL;		cfg.nopty = TRUE;      /* command => no terminal */		break;		       /* done with cmdline */	    }	}    }    if (errors)	return 1;    if (!*cfg.host) {	usage();    }    /*     * Trim leading whitespace off the hostname if it's there.     */    {	int space = strspn(cfg.host, " \t");	memmove(cfg.host, cfg.host+space, 1+strlen(cfg.host)-space);    }    /* See if host is of the form user@host */    if (cfg.host[0] != '\0') {	char *atsign = strchr(cfg.host, '@');	/* Make sure we're not overflowing the user field */	if (atsign) {	    if (atsign - cfg.host < sizeof cfg.username) {		strncpy(cfg.username, cfg.host, atsign - cfg.host);		cfg.username[atsign - cfg.host] = '\0';	    }	    memmove(cfg.host, atsign + 1, 1 + strlen(atsign + 1));	}    }    /*     * Perform command-line overrides on session configuration.     */    cmdline_run_saved(&cfg);    /*     * Apply subsystem status.     */    if (use_subsystem)        cfg.ssh_subsys = TRUE;    /*     * Trim a colon suffix off the hostname if it's there.     */    cfg.host[strcspn(cfg.host, ":")] = '\0';    /*     * Remove any remaining whitespace from the hostname.     */    {	int p1 = 0, p2 = 0;	while (cfg.host[p2] != '\0') {	    if (cfg.host[p2] != ' ' && cfg.host[p2] != '\t') {		cfg.host[p1] = cfg.host[p2];		p1++;	    }	    p2++;	}	cfg.host[p1] = '\0';    }    if (!*cfg.remote_cmd_ptr)	flags |= FLAG_INTERACTIVE;    /*     * Select protocol. This is farmed out into a table in a     * separate file to enable an ssh-free variant.     */    {	int i;	back = NULL;	for (i = 0; backends[i].backend != NULL; i++)	    if (backends[i].protocol == cfg.protocol) {		back = backends[i].backend;		break;	    }	if (back == NULL) {	    fprintf(stderr,		    "Internal fault: Unsupported protocol found\n");	    return 1;	}    }    /*     * Select port.     */    if (portnumber != -1)	cfg.port = portnumber;    /*     * Set up the pipe we'll use to tell us about SIGWINCH.     */    if (pipe(signalpipe) < 0) {	perror("pipe");	exit(1);    }    putty_signal(SIGWINCH, sigwinch);    sk_init();    uxsel_init();    /*     * Start up the connection.     */    logctx = log_init(NULL, &cfg);    console_provide_logctx(logctx);    {	const char *error;	char *realhost;	/* nodelay is only useful if stdin is a terminal device */	int nodelay = cfg.tcp_nodelay && isatty(0);	error = back->init(NULL, &backhandle, &cfg, cfg.host, cfg.port,			   &realhost, nodelay, cfg.tcp_keepalives);	if (error) {	    fprintf(stderr, "Unable to open connection:\n%s\n", error);	    return 1;	}	back->provide_logctx(backhandle, logctx);	ldisc = ldisc_create(&cfg, NULL, back, backhandle, NULL);	sfree(realhost);    }    connopen = 1;    /*     * Set up the initial console mode. We don't care if this call     * fails, because we know we aren't necessarily running in a     * console.     */    tcgetattr(0, &orig_termios);    atexit(cleanup_termios);    ldisc_update(NULL, 1, 1);    sending = FALSE;    while (1) {	fd_set rset, wset, xset;	int maxfd;	int rwx;	int ret;	FD_ZERO(&rset);	FD_ZERO(&wset);	FD_ZERO(&xset);	maxfd = 0;	FD_SET_MAX(signalpipe[0], maxfd, rset);	if (connopen && !sending &&	    back->socket(backhandle) != NULL &&	    back->sendok(backhandle) &&	    back->sendbuffer(backhandle) < MAX_STDIN_BACKLOG) {	    /* If we're OK to send, then try to read from stdin. */	    FD_SET_MAX(0, maxfd, rset);	}	if (bufchain_size(&stdout_data) > 0) {	    /* If we have data for stdout, try to write to stdout. */	    FD_SET_MAX(1, maxfd, wset);	}	if (bufchain_size(&stderr_data) > 0) {	    /* If we have data for stderr, try to write to stderr. */	    FD_SET_MAX(2, maxfd, wset);	}	/* Count the currently active fds. */	i = 0;	for (fd = first_fd(&fdstate, &rwx); fd >= 0;	     fd = next_fd(&fdstate, &rwx)) i++;	/* Expand the fdlist buffer if necessary. */	if (i > fdsize) {	    fdsize = i + 16;	    fdlist = sresize(fdlist, fdsize, int);	}	/*	 * Add all currently open fds to the select sets, and store	 * them in fdlist as well.	 */	fdcount = 0;	for (fd = first_fd(&fdstate, &rwx); fd >= 0;	     fd = next_fd(&fdstate, &rwx)) {	    fdlist[fdcount++] = fd;	    if (rwx & 1)		FD_SET_MAX(fd, maxfd, rset);	    if (rwx & 2)		FD_SET_MAX(fd, maxfd, wset);	    if (rwx & 4)		FD_SET_MAX(fd, maxfd, xset);	}	do {	    ret = select(maxfd, &rset, &wset, &xset, NULL);	} while (ret < 0 && errno == EINTR);	if (ret < 0) {	    perror("select");	    exit(1);	}	for (i = 0; i < fdcount; i++) {	    fd = fdlist[i];            /*             * We must process exceptional notifications before             * ordinary readability ones, or we may go straight             * past the urgent marker.             */	    if (FD_ISSET(fd, &xset))		select_result(fd, 4);	    if (FD_ISSET(fd, &rset))		select_result(fd, 1);	    if (FD_ISSET(fd, &wset))		select_result(fd, 2);	}	if (FD_ISSET(signalpipe[0], &rset)) {	    char c[1];	    struct winsize size;	    read(signalpipe[0], c, 1); /* ignore its value; it'll be `x' */	    if (ioctl(0, TIOCGWINSZ, (void *)&size) >= 0)		back->size(backhandle, size.ws_col, size.ws_row);	}	if (FD_ISSET(0, &rset)) {	    char buf[4096];	    int ret;	    if (connopen && back->socket(backhandle) != NULL) {		ret = read(0, buf, sizeof(buf));		if (ret < 0) {		    perror("stdin: read");		    exit(1);		} else if (ret == 0) {		    back->special(backhandle, TS_EOF);		    sending = FALSE;   /* send nothing further after this */		} else {		    back->send(backhandle, buf, ret);		}	    }	}	if (FD_ISSET(1, &wset)) {	    try_output(0);	}	if (FD_ISSET(2, &wset)) {	    try_output(1);	}	if ((!connopen || back->socket(backhandle) == NULL) &&	    bufchain_size(&stdout_data) == 0 &&	    bufchain_size(&stderr_data) == 0)	    break;		       /* we closed the connection */    }    exitcode = back->exitcode(backhandle);    if (exitcode < 0) {	fprintf(stderr, "Remote process exit code unavailable\n");	exitcode = 1;		       /* this is an error condition */    }    cleanup_exit(exitcode);    return exitcode;		       /* shouldn't happen, but placates gcc */}