Revamp SSH authentication code so that user interaction is more

[u/mdw/putty] / windows / winplink.c

/*
 * PLink - a Windows command-line (stdin/stdout) variant of PuTTY.
 */

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <stdarg.h>

#define PUTTY_DO_GLOBALS               /* actually _define_ globals */
#include "putty.h"
#include "storage.h"
#include "tree234.h"

#define WM_AGENT_CALLBACK (WM_APP + 4)

#define MAX_STDIN_BACKLOG 4096

struct agent_callback {
    void (*callback)(void *, void *, int);
    void *callback_ctx;
    void *data;
    int len;
};

void fatalbox(char *p, ...)
{
    va_list ap;
    fprintf(stderr, "FATAL ERROR: ");
    va_start(ap, p);
    vfprintf(stderr, p, ap);
    va_end(ap);
    fputc('\n', stderr);
    cleanup_exit(1);
}
void modalfatalbox(char *p, ...)
{
    va_list ap;
    fprintf(stderr, "FATAL ERROR: ");
    va_start(ap, p);
    vfprintf(stderr, p, ap);
    va_end(ap);
    fputc('\n', stderr);
    cleanup_exit(1);
}
void connection_fatal(void *frontend, char *p, ...)
{
    va_list ap;
    fprintf(stderr, "FATAL ERROR: ");
    va_start(ap, p);
    vfprintf(stderr, p, ap);
    va_end(ap);
    fputc('\n', stderr);
    cleanup_exit(1);
}
void cmdline_error(char *p, ...)
{
    va_list ap;
    fprintf(stderr, "plink: ");
    va_start(ap, p);
    vfprintf(stderr, p, ap);
    va_end(ap);
    fputc('\n', stderr);
    exit(1);
}

HANDLE inhandle, outhandle, errhandle;
DWORD orig_console_mode;

WSAEVENT netevent;

static Backend *back;
static void *backhandle;
static Config cfg;

int term_ldisc(Terminal *term, int mode)
{
    return FALSE;
}
void ldisc_update(void *frontend, int echo, int edit)
{
    /* Update stdin read mode to reflect changes in line discipline. */
    DWORD mode;

    mode = ENABLE_PROCESSED_INPUT;
    if (echo)
        mode = mode | ENABLE_ECHO_INPUT;
    else
        mode = mode & ~ENABLE_ECHO_INPUT;
    if (edit)
        mode = mode | ENABLE_LINE_INPUT;
    else
        mode = mode & ~ENABLE_LINE_INPUT;
    SetConsoleMode(inhandle, mode);
}

char *get_ttymode(void *frontend, const char *mode) { return NULL; }

struct input_data {
    DWORD len;
    char buffer[4096];
    HANDLE event, eventback;
};

static DWORD WINAPI stdin_read_thread(void *param)
{
    struct input_data *idata = (struct input_data *) param;
    HANDLE inhandle;

    inhandle = GetStdHandle(STD_INPUT_HANDLE);

    while (ReadFile(inhandle, idata->buffer, sizeof(idata->buffer),
                    &idata->len, NULL) && idata->len > 0) {
        SetEvent(idata->event);
        WaitForSingleObject(idata->eventback, INFINITE);
    }

    idata->len = 0;
    SetEvent(idata->event);

    return 0;
}

struct output_data {
    DWORD len, lenwritten;
    int writeret;
    char *buffer;
    int is_stderr, done;
    HANDLE event, eventback;
    int busy;
};

static DWORD WINAPI stdout_write_thread(void *param)
{
    struct output_data *odata = (struct output_data *) param;
    HANDLE outhandle, errhandle;

    outhandle = GetStdHandle(STD_OUTPUT_HANDLE);
    errhandle = GetStdHandle(STD_ERROR_HANDLE);

    while (1) {
        WaitForSingleObject(odata->eventback, INFINITE);
        if (odata->done)
            break;
        odata->writeret =
            WriteFile(odata->is_stderr ? errhandle : outhandle,
                      odata->buffer, odata->len, &odata->lenwritten, NULL);
        SetEvent(odata->event);
    }

    return 0;
}

bufchain stdout_data, stderr_data;
struct output_data odata, edata;

void try_output(int is_stderr)
{
    struct output_data *data = (is_stderr ? &edata : &odata);
    void *senddata;
    int sendlen;

    if (!data->busy) {
        bufchain_prefix(is_stderr ? &stderr_data : &stdout_data,
                        &senddata, &sendlen);
        data->buffer = senddata;
        data->len = sendlen;
        SetEvent(data->eventback);
        data->busy = 1;
    }
}

int from_backend(void *frontend_handle, int is_stderr,
                 const char *data, int len)
{
    int osize, esize;

    if (is_stderr) {
        bufchain_add(&stderr_data, data, len);
        try_output(1);
    } else {
        bufchain_add(&stdout_data, data, len);
        try_output(0);
    }

    osize = bufchain_size(&stdout_data);
    esize = bufchain_size(&stderr_data);

    return osize + esize;
}

int from_backend_untrusted(void *frontend_handle, const char *data, int len)
{
    /*
     * No "untrusted" output should get here (the way the code is
     * currently, it's all diverted by FLAG_STDERR).
     */
    assert(!"Unexpected call to from_backend_untrusted()");
    return 0; /* not reached */
}

int get_userpass_input(prompts_t *p, unsigned char *in, int inlen)
{
    int ret;
    ret = cmdline_get_passwd_input(p, in, inlen);
    if (ret == -1)
        ret = console_get_userpass_input(p, in, inlen);
    return ret;
}

static DWORD main_thread_id;

void agent_schedule_callback(void (*callback)(void *, void *, int),
                             void *callback_ctx, void *data, int len)
{
    struct agent_callback *c = snew(struct agent_callback);
    c->callback = callback;
    c->callback_ctx = callback_ctx;
    c->data = data;
    c->len = len;
    PostThreadMessage(main_thread_id, WM_AGENT_CALLBACK, 0, (LPARAM)c);
}

/*
 *  Short description of parameters.
 */
static void usage(void)
{
    printf("PuTTY Link: command-line connection utility\n");
    printf("%s\n", ver);
    printf("Usage: plink [options] [user@]host [command]\n");
    printf("       (\"host\" can also be a PuTTY saved session name)\n");
    printf("Options:\n");
    printf("  -V        print version information and exit\n");
    printf("  -pgpfp    print PGP key fingerprints and exit\n");
    printf("  -v        show verbose messages\n");
    printf("  -load sessname  Load settings from saved session\n");
    printf("  -ssh -telnet -rlogin -raw\n");
    printf("            force use of a particular protocol\n");
    printf("  -P port   connect to specified port\n");
    printf("  -l user   connect with specified username\n");
    printf("  -batch    disable all interactive prompts\n");
    printf("The following options only apply to SSH connections:\n");
    printf("  -pw passw login with specified password\n");
    printf("  -D [listen-IP:]listen-port\n");
    printf("            Dynamic SOCKS-based port forwarding\n");
    printf("  -L [listen-IP:]listen-port:host:port\n");
    printf("            Forward local port to remote address\n");
    printf("  -R [listen-IP:]listen-port:host:port\n");
    printf("            Forward remote port to local address\n");
    printf("  -X -x     enable / disable X11 forwarding\n");
    printf("  -A -a     enable / disable agent forwarding\n");
    printf("  -t -T     enable / disable pty allocation\n");
    printf("  -1 -2     force use of particular protocol version\n");
    printf("  -4 -6     force use of IPv4 or IPv6\n");
    printf("  -C        enable compression\n");
    printf("  -i key    private key file for authentication\n");
    printf("  -m file   read remote command(s) from file\n");
    printf("  -s        remote command is an SSH subsystem (SSH-2 only)\n");
    printf("  -N        don't start a shell/command (SSH-2 only)\n");
    exit(1);
}

static void version(void)
{
    printf("plink: %s\n", ver);
    exit(1);
}

char *do_select(SOCKET skt, int startup)
{
    int events;
    if (startup) {
        events = (FD_CONNECT | FD_READ | FD_WRITE |
                  FD_OOB | FD_CLOSE | FD_ACCEPT);
    } else {
        events = 0;
    }
    if (p_WSAEventSelect(skt, netevent, events) == SOCKET_ERROR) {
        switch (p_WSAGetLastError()) {
          case WSAENETDOWN:
            return "Network is down";
          default:
            return "WSAEventSelect(): unknown error";
        }
    }
    return NULL;
}

int main(int argc, char **argv)
{
    WSAEVENT stdinevent, stdoutevent, stderrevent;
    HANDLE handles[4];
    DWORD in_threadid, out_threadid, err_threadid;
    struct input_data idata;
    int reading = FALSE;
    int sending;
    int portnumber = -1;
    SOCKET *sklist;
    int skcount, sksize;
    int connopen;
    int exitcode;
    int errors;
    int use_subsystem = 0;
    long now, next;

    sklist = NULL;
    skcount = sksize = 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, "-pgpfp")) {
                pgp_fingerprints();
                exit(1);
            } else {
                fprintf(stderr, "plink: unknown option \"%s\"\n", p);
                errors = 1;
            }
        } else if (*p) {
            if (!*cfg.host) {
                char *q = p;
                /*
                 * 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, *user, *host;
                    /*
                     * 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;
                            }
                        }
                    }

                    /*
                     * 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.
                     */
                    r = strrchr(p, '@');
                    if (r == p)
                        p++, r = NULL; /* discount initial @ */
                    if (r) {
                        *r++ = '\0';
                        user = p, host = r;
                    } else {
                        user = NULL, host = p;
                    }

                    /*
                     * Now attempt to load a saved session with the
                     * same name as the hostname.
                     */
                    {
                        Config cfg2;
                        do_defaults(host, &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, host, sizeof(cfg.host) - 1);
                            cfg.host[sizeof(cfg.host) - 1] = '\0';
                            cfg.port = default_port;
                        } else {
                            cfg = cfg2;
                        }
                    }

                    if (user) {
                        /* Patch in specified username. */
                        strncpy(cfg.username, user,
                                sizeof(cfg.username) - 1);
                        cfg.username[sizeof(cfg.username) - 1] = '\0';
                    }

                }
            } 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 = strrchr(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 && !*cfg.remote_cmd)
        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;

    sk_init();
    if (p_WSAEventSelect == NULL) {
        fprintf(stderr, "Plink requires WinSock 2\n");
        return 1;
    }

    /*
     * Start up the connection.
     */
    netevent = CreateEvent(NULL, FALSE, FALSE, NULL);
    {
        const char *error;
        char *realhost;
        /* nodelay is only useful if stdin is a character device (console) */
        int nodelay = cfg.tcp_nodelay &&
            (GetFileType(GetStdHandle(STD_INPUT_HANDLE)) == FILE_TYPE_CHAR);

        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", error);
            return 1;
        }
        logctx = log_init(NULL, &cfg);
        back->provide_logctx(backhandle, logctx);
        console_provide_logctx(logctx);
        sfree(realhost);
    }
    connopen = 1;

    stdinevent = CreateEvent(NULL, FALSE, FALSE, NULL);
    stdoutevent = CreateEvent(NULL, FALSE, FALSE, NULL);
    stderrevent = CreateEvent(NULL, FALSE, FALSE, NULL);

    inhandle = GetStdHandle(STD_INPUT_HANDLE);
    outhandle = GetStdHandle(STD_OUTPUT_HANDLE);
    errhandle = GetStdHandle(STD_ERROR_HANDLE);
    /*
     * Turn off ECHO and LINE input modes. We don't care if this
     * call fails, because we know we aren't necessarily running in
     * a console.
     */
    GetConsoleMode(inhandle, &orig_console_mode);
    SetConsoleMode(inhandle, ENABLE_PROCESSED_INPUT);

    main_thread_id = GetCurrentThreadId();

    handles[0] = netevent;
    handles[1] = stdinevent;
    handles[2] = stdoutevent;
    handles[3] = stderrevent;
    sending = FALSE;

    /*
     * Create spare threads to write to stdout and stderr, so we
     * can arrange asynchronous writes.
     */
    odata.event = stdoutevent;
    odata.eventback = CreateEvent(NULL, FALSE, FALSE, NULL);
    odata.is_stderr = 0;
    odata.busy = odata.done = 0;
    if (!CreateThread(NULL, 0, stdout_write_thread,
                      &odata, 0, &out_threadid)) {
        fprintf(stderr, "Unable to create output thread\n");
        cleanup_exit(1);
    }
    edata.event = stderrevent;
    edata.eventback = CreateEvent(NULL, FALSE, FALSE, NULL);
    edata.is_stderr = 1;
    edata.busy = edata.done = 0;
    if (!CreateThread(NULL, 0, stdout_write_thread,
                      &edata, 0, &err_threadid)) {
        fprintf(stderr, "Unable to create error output thread\n");
        cleanup_exit(1);
    }

    now = GETTICKCOUNT();

    while (1) {
        int n;
        DWORD ticks;

        if (!sending && back->sendok(backhandle)) {
            /*
             * Create a separate thread to read from stdin. This is
             * a total pain, but I can't find another way to do it:
             *
             *  - an overlapped ReadFile or ReadFileEx just doesn't
             *    happen; we get failure from ReadFileEx, and
             *    ReadFile blocks despite being given an OVERLAPPED
             *    structure. Perhaps we can't do overlapped reads
             *    on consoles. WHY THE HELL NOT?
             * 
             *  - WaitForMultipleObjects(netevent, console) doesn't
             *    work, because it signals the console when
             *    _anything_ happens, including mouse motions and
             *    other things that don't cause data to be readable
             *    - so we're back to ReadFile blocking.
             */
            idata.event = stdinevent;
            idata.eventback = CreateEvent(NULL, FALSE, FALSE, NULL);
            if (!CreateThread(NULL, 0, stdin_read_thread,
                              &idata, 0, &in_threadid)) {
                fprintf(stderr, "Unable to create input thread\n");
                cleanup_exit(1);
            }
            sending = TRUE;
            reading = TRUE;
        }

        if (run_timers(now, &next)) {
            ticks = next - GETTICKCOUNT();
            if (ticks < 0) ticks = 0;  /* just in case */
        } else {
            ticks = INFINITE;
        }

        n = MsgWaitForMultipleObjects(4, handles, FALSE, ticks,
                                      QS_POSTMESSAGE);
        if (n == WAIT_OBJECT_0 + 0) {
            WSANETWORKEVENTS things;
            SOCKET socket;
            extern SOCKET first_socket(int *), next_socket(int *);
            extern int select_result(WPARAM, LPARAM);
            int i, socketstate;

            /*
             * We must not call select_result() for any socket
             * until we have finished enumerating within the tree.
             * This is because select_result() may close the socket
             * and modify the tree.
             */
            /* Count the active sockets. */
            i = 0;
            for (socket = first_socket(&socketstate);
                 socket != INVALID_SOCKET;
                 socket = next_socket(&socketstate)) i++;

            /* Expand the buffer if necessary. */
            if (i > sksize) {
                sksize = i + 16;
                sklist = sresize(sklist, sksize, SOCKET);
            }

            /* Retrieve the sockets into sklist. */
            skcount = 0;
            for (socket = first_socket(&socketstate);
                 socket != INVALID_SOCKET;
                 socket = next_socket(&socketstate)) {
                sklist[skcount++] = socket;
            }

            /* Now we're done enumerating; go through the list. */
            for (i = 0; i < skcount; i++) {
                WPARAM wp;
                socket = sklist[i];
                wp = (WPARAM) socket;
                if (!p_WSAEnumNetworkEvents(socket, NULL, &things)) {
                    static const struct { int bit, mask; } eventtypes[] = {
                        {FD_CONNECT_BIT, FD_CONNECT},
                        {FD_READ_BIT, FD_READ},
                        {FD_CLOSE_BIT, FD_CLOSE},
                        {FD_OOB_BIT, FD_OOB},
                        {FD_WRITE_BIT, FD_WRITE},
                        {FD_ACCEPT_BIT, FD_ACCEPT},
                    };
                    int e;

                    noise_ultralight(socket);
                    noise_ultralight(things.lNetworkEvents);

                    for (e = 0; e < lenof(eventtypes); e++)
                        if (things.lNetworkEvents & eventtypes[e].mask) {
                            LPARAM lp;
                            int err = things.iErrorCode[eventtypes[e].bit];
                            lp = WSAMAKESELECTREPLY(eventtypes[e].mask, err);
                            connopen &= select_result(wp, lp);
                        }
                }
            }
        } else if (n == WAIT_OBJECT_0 + 1) {
            reading = 0;
            noise_ultralight(idata.len);
            if (connopen && back->socket(backhandle) != NULL) {
                if (idata.len > 0) {
                    back->send(backhandle, idata.buffer, idata.len);
                } else {
                    back->special(backhandle, TS_EOF);
                }
            }
        } else if (n == WAIT_OBJECT_0 + 2) {
            odata.busy = 0;
            if (!odata.writeret) {
                fprintf(stderr, "Unable to write to standard output\n");
                cleanup_exit(0);
            }
            bufchain_consume(&stdout_data, odata.lenwritten);
            if (bufchain_size(&stdout_data) > 0)
                try_output(0);
            if (connopen && back->socket(backhandle) != NULL) {
                back->unthrottle(backhandle, bufchain_size(&stdout_data) +
                                 bufchain_size(&stderr_data));
            }
        } else if (n == WAIT_OBJECT_0 + 3) {
            edata.busy = 0;
            if (!edata.writeret) {
                fprintf(stderr, "Unable to write to standard output\n");
                cleanup_exit(0);
            }
            bufchain_consume(&stderr_data, edata.lenwritten);
            if (bufchain_size(&stderr_data) > 0)
                try_output(1);
            if (connopen && back->socket(backhandle) != NULL) {
                back->unthrottle(backhandle, bufchain_size(&stdout_data) +
                                 bufchain_size(&stderr_data));
            }
        } else if (n == WAIT_OBJECT_0 + 4) {
            MSG msg;
            while (PeekMessage(&msg, INVALID_HANDLE_VALUE,
                               WM_AGENT_CALLBACK, WM_AGENT_CALLBACK,
                               PM_REMOVE)) {
                struct agent_callback *c = (struct agent_callback *)msg.lParam;
                c->callback(c->callback_ctx, c->data, c->len);
                sfree(c);
            }
        }

        if (n == WAIT_TIMEOUT) {
            now = next;
        } else {
            now = GETTICKCOUNT();
        }

        if (!reading && back->sendbuffer(backhandle) < MAX_STDIN_BACKLOG) {
            SetEvent(idata.eventback);
            reading = 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 0;                          /* placate compiler warning */
}