putty-source/proxy/telnet.c

/*
 * "Telnet" proxy negotiation.
 *
 * (This is for ad-hoc proxies where you connect to the proxy's
 * telnet port and send a command such as `connect host port'. The
 * command is configurable, since this proxy type is typically not
 * standardised or at all well-defined.)
 */

#include "putty.h"
#include "network.h"
#include "proxy.h"

char *format_telnet_command(SockAddr *addr, int port, Conf *conf)
{
    char *fmt = conf_get_str(conf, CONF_proxy_telnet_command);
    int so = 0, eo = 0;
    strbuf *buf = strbuf_new();

    /* we need to escape \\, \%, \r, \n, \t, \x??, \0???,
     * %%, %host, %port, %user, and %pass
     */

    while (fmt[eo] != 0) {

        /* scan forward until we hit end-of-line,
         * or an escape character (\ or %) */
        while (fmt[eo] != 0 && fmt[eo] != '%' && fmt[eo] != '\\')
            eo++;

        /* if we hit eol, break out of our escaping loop */
        if (fmt[eo] == 0) break;

        /* if there was any unescaped text before the escape
         * character, send that now */
        if (eo != so)
            put_data(buf, fmt + so, eo - so);

        so = eo++;

        /* if the escape character was the last character of
         * the line, we'll just stop and send it. */
        if (fmt[eo] == 0) break;

        if (fmt[so] == '\\') {

            /* we recognize \\, \%, \r, \n, \t, \x??.
             * anything else, we just send unescaped (including the \).
             */

            switch (fmt[eo]) {

              case '\\':
                put_byte(buf, '\\');
                eo++;
                break;

              case '%':
                put_byte(buf, '%');
                eo++;
                break;

              case 'r':
                put_byte(buf, '\r');
                eo++;
                break;

              case 'n':
                put_byte(buf, '\n');
                eo++;
                break;

              case 't':
                put_byte(buf, '\t');
                eo++;
                break;

              case 'x':
              case 'X': {
                /* escaped hexadecimal value (ie. \xff) */
                unsigned char v = 0;
                int i = 0;

                for (;;) {
                  eo++;
                  if (fmt[eo] >= '0' && fmt[eo] <= '9')
                      v += fmt[eo] - '0';
                  else if (fmt[eo] >= 'a' && fmt[eo] <= 'f')
                      v += fmt[eo] - 'a' + 10;
                  else if (fmt[eo] >= 'A' && fmt[eo] <= 'F')
                      v += fmt[eo] - 'A' + 10;
                  else {
                    /* non hex character, so we abort and just
                     * send the whole thing unescaped (including \x)
                     */
                    put_byte(buf, '\\');
                    eo = so + 1;
                    break;
                  }

                  /* we only extract two hex characters */
                  if (i == 1) {
                    put_byte(buf, v);
                    eo++;
                    break;
                  }

                  i++;
                  v <<= 4;
                }
                break;
              }

              default:
                put_data(buf, fmt + so, 2);
                eo++;
                break;
            }
        } else {

            /* % escape. we recognize %%, %host, %port, %user, %pass.
             * %proxyhost, %proxyport. Anything else we just send
             * unescaped (including the %).
             */

            if (fmt[eo] == '%') {
                put_byte(buf, '%');
                eo++;
            }
            else if (strnicmp(fmt + eo, "host", 4) == 0) {
                char dest[512];
                sk_getaddr(addr, dest, lenof(dest));
                put_data(buf, dest, strlen(dest));
                eo += 4;
            }
            else if (strnicmp(fmt + eo, "port", 4) == 0) {
                put_fmt(buf, "%d", port);
                eo += 4;
            }
            else if (strnicmp(fmt + eo, "user", 4) == 0) {
                const char *username = conf_get_str(conf, CONF_proxy_username);
                put_data(buf, username, strlen(username));
                eo += 4;
            }
            else if (strnicmp(fmt + eo, "pass", 4) == 0) {
                const char *password = conf_get_str(conf, CONF_proxy_password);
                put_data(buf, password, strlen(password));
                eo += 4;
            }
            else if (strnicmp(fmt + eo, "proxyhost", 9) == 0) {
                const char *host = conf_get_str(conf, CONF_proxy_host);
                put_data(buf, host, strlen(host));
                eo += 9;
            }
            else if (strnicmp(fmt + eo, "proxyport", 9) == 0) {
                int port = conf_get_int(conf, CONF_proxy_port);
                put_fmt(buf, "%d", port);
                eo += 9;
            }
            else {
                /* we don't escape this, so send the % now, and
                 * don't advance eo, so that we'll consider the
                 * text immediately following the % as unescaped.
                 */
                put_byte(buf, '%');
            }
        }

        /* resume scanning for additional escapes after this one. */
        so = eo;
    }

    /* if there is any unescaped text at the end of the line, send it */
    if (eo != so) {
        put_data(buf, fmt + so, eo - so);
    }

    return strbuf_to_str(buf);
}

typedef struct TelnetProxyNegotiator {
    ProxyNegotiator pn;
} TelnetProxyNegotiator;

static ProxyNegotiator *proxy_telnet_new(const ProxyNegotiatorVT *vt)
{
    TelnetProxyNegotiator *s = snew(TelnetProxyNegotiator);
    s->pn.vt = vt;
    return &s->pn;
}

static void proxy_telnet_free(ProxyNegotiator *pn)
{
    TelnetProxyNegotiator *s = container_of(pn, TelnetProxyNegotiator, pn);
    sfree(s);
}

static void proxy_telnet_process_queue(ProxyNegotiator *pn)
{
    // TelnetProxyNegotiator *s = container_of(pn, TelnetProxyNegotiator, pn);

    char *formatted_cmd = format_telnet_command(
        pn->ps->remote_addr, pn->ps->remote_port, pn->ps->conf);

    /*
     * Re-escape control chars in the command, for logging.
     */
    strbuf *logmsg = strbuf_new();
    const char *in;

    put_datapl(logmsg, PTRLEN_LITERAL("Sending Telnet proxy command: "));

    for (in = formatted_cmd; *in; in++) {
        if (*in == '\n') {
            put_datapl(logmsg, PTRLEN_LITERAL("\\n"));
        } else if (*in == '\r') {
            put_datapl(logmsg, PTRLEN_LITERAL("\\r"));
        } else if (*in == '\t') {
            put_datapl(logmsg, PTRLEN_LITERAL("\\t"));
        } else if (*in == '\\') {
            put_datapl(logmsg, PTRLEN_LITERAL("\\\\"));
        } else if (0x20 <= *in && *in < 0x7F) {
            put_byte(logmsg, *in);
        } else {
            put_fmt(logmsg, "\\x%02X", (unsigned)*in & 0xFF);
        }
    }

    plug_log(pn->ps->plug, PLUGLOG_PROXY_MSG, NULL, 0, logmsg->s, 0);
    strbuf_free(logmsg);

    put_dataz(pn->output, formatted_cmd);
    sfree(formatted_cmd);

    /*
     * Unconditionally report success.
     */
    pn->done = true;
}

const struct ProxyNegotiatorVT telnet_proxy_negotiator_vt = {
    .new = proxy_telnet_new,
    .free = proxy_telnet_free,
    .process_queue = proxy_telnet_process_queue,
    .type = "Telnet",
};