static void ssh2_pkt_addstring_str(struct Packet *, char *data);
static void ssh2_pkt_addstring_data(struct Packet *, char *data, int len);
static void ssh2_pkt_addstring(struct Packet *, char *data);
static unsigned char *ssh2_mpint_fmt(Bignum b, int *len);
static void ssh2_pkt_addmp(struct Packet *, Bignum b);
static int ssh2_pkt_construct(Ssh, struct Packet *);
static void ssh2_pkt_send(Ssh, struct Packet *);
static void ssh2_pkt_send_noqueue(Ssh, struct Packet *);
static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen,
			 struct Packet *pktin);
static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
			     struct Packet *pktin);

/*
 * Buffer management constants. There are several of these for

	SSH_STATE_INTERMED,
	SSH_STATE_SESSION,
	SSH_STATE_CLOSED
    } state;

    int size_needed, eof_needed;

    struct Packet **queue;
    int queuelen, queuesize;
    int queueing;
    unsigned char *deferred_send_data;
    int deferred_len, deferred_size;

    /*
     * Gross hack: pscp will try to start SFTP but fall back to
     * scp1 if that fails. This variable is the means by which
     * scp.c can reach into the SSH code and find out which one it

         * For anything else we send SSH2_MSG_UNIMPLEMENTED.
         */
      default:
	{
	    struct Packet *pktout;
	    pktout = ssh2_pkt_init(SSH2_MSG_UNIMPLEMENTED);
	    ssh2_pkt_adduint32(pktout, st->incoming_sequence - 1);
	    /* UNIMPLEMENTED messages MUST appear in the same order as
	     * the messages they respond to. Hence, never queue them. */
	    ssh2_pkt_send(ssh, pktout);
	    ssh2_pkt_send_noqueue(ssh, pktout);
	}
        break;
    }

    crFinish(st->pktin);
}

			       pkt->data, pkt->length + padding);

    /* Ready-to-send packet starts at pkt->data. We return length. */
    return pkt->length + padding + maclen;
}

/*
 * Routines called from the main SSH code to send packets. There
 * are quite a few of these, because we have two separate
 * mechanisms for delaying the sending of packets:
 * 
 *  - In order to send an IGNORE message and a password message in
 *    a single fixed-length blob, we require the ability to
 *    concatenate the encrypted forms of those two packets _into_ a
 *    single blob and then pass it to our <network.h> transport
 *    layer in one go. Hence, there's a deferment mechanism which
 *    works after packet encryption.
 * 
 *  - In order to avoid sending any connection-layer messages
 *    during repeat key exchange, we have to queue up any such
 *    outgoing messages _before_ they are encrypted (and in
 *    particular before they're allocated sequence numbers), and
 *    then send them once we've finished.
 * 
 * I call these mechanisms `defer' and `queue' respectively, so as
 * to distinguish them reasonably easily.
 * 
 * The functions send_noqueue() and defer_noqueue() free the packet
 * structure they are passed. Every outgoing packet goes through
 * precisely one of these functions in its life; packets passed to
 * ssh2_pkt_send() or ssh2_pkt_defer() either go straight to one of
 * these or get queued, and then when the queue is later emptied
 * the packets are all passed to defer_noqueue().
 */

/*
 * Construct and send an SSH2 packet immediately.
 * Send an SSH2 packet immediately, without queuing or deferring.
 */
static void ssh2_pkt_send(Ssh ssh, struct Packet *pkt)
static void ssh2_pkt_send_noqueue(Ssh ssh, struct Packet *pkt)
{
    int len;
    int backlog;
    len = ssh2_pkt_construct(ssh, pkt);
    backlog = sk_write(ssh->s, (char *)pkt->data, len);
    if (backlog > SSH_MAX_BACKLOG)
	ssh_throttle_all(ssh, 1, backlog);
    ssh_free_packet(pkt);
}

/*
 * Construct an SSH2 packet and add it to a deferred data block.
 * Useful for sending multiple packets in a single sk_write() call,
 * to prevent a traffic-analysing listener from being able to work
 * out the length of any particular packet (such as the password
 * packet).
 * Defer an SSH2 packet.
 * 
 * Note that because SSH2 sequence-numbers its packets, this can
 * NOT be used as an m4-style `defer' allowing packets to be
 * constructed in one order and sent in another.
 */
static void ssh2_pkt_defer(Ssh ssh, struct Packet *pkt)
static void ssh2_pkt_defer_noqueue(Ssh ssh, struct Packet *pkt)
{
    int len = ssh2_pkt_construct(ssh, pkt);
    if (ssh->deferred_len + len > ssh->deferred_size) {
	ssh->deferred_size = ssh->deferred_len + len + 128;
	ssh->deferred_send_data = sresize(ssh->deferred_send_data,
					  ssh->deferred_size,
					  unsigned char);
    }
    memcpy(ssh->deferred_send_data + ssh->deferred_len, pkt->data, len);
    ssh->deferred_len += len;
    ssh_free_packet(pkt);
}

/*
 * Queue an SSH2 packet.
 */
static void ssh2_pkt_queue(Ssh ssh, struct Packet *pkt)
{
    assert(ssh->queueing);

    if (ssh->queuelen >= ssh->queuesize) {
	ssh->queuesize = ssh->queuelen + 32;
	ssh->queue = sresize(ssh->queue, ssh->queuesize, struct Packet *);
    }

    ssh->queue[ssh->queuelen++] = pkt;
}

/*
 * Either queue or send a packet, depending on whether queueing is
 * set.
 */
static void ssh2_pkt_send(Ssh ssh, struct Packet *pkt)
{
    if (ssh->queueing)
	ssh2_pkt_queue(ssh, pkt);
    else
	ssh2_pkt_send_noqueue(ssh, pkt);
}

/*
 * Either queue or defer a packet, depending on whether queueing is
 * set.
 */
static void ssh2_pkt_defer(Ssh ssh, struct Packet *pkt)
{
    if (ssh->queueing)
	ssh2_pkt_queue(ssh, pkt);
    else
	ssh2_pkt_defer_noqueue(ssh, pkt);
}

/*
 * Send the whole deferred data block constructed by
 * ssh2_pkt_defer() or SSH1's defer_packet().
 * 
 * The expected use of the defer mechanism is that you call
 * ssh2_pkt_defer() a few times, then call ssh_pkt_defersend(). If
 * not currently queueing, this simply sets up deferred_send_data
 * and then sends it. If we _are_ currently queueing, the calls to
 * ssh2_pkt_defer() put the deferred packets on to the queue
 * instead, and therefore ssh_pkt_defersend() has no deferred data
 * to send. Hence, there's no need to make it conditional on
 * ssh->queueing.
 */
static void ssh_pkt_defersend(Ssh ssh)
{
    int backlog;
    backlog = sk_write(ssh->s, (char *)ssh->deferred_send_data,
		       ssh->deferred_len);
    ssh->deferred_len = ssh->deferred_size = 0;
    sfree(ssh->deferred_send_data);
    ssh->deferred_send_data = NULL;
    if (backlog > SSH_MAX_BACKLOG)
	ssh_throttle_all(ssh, 1, backlog);
}

/*
 * Send all queued SSH2 packets. We send them by means of
 * ssh2_pkt_defer_noqueue(), in case they included a pair of
 * packets that needed to be lumped together.
 */
static void ssh2_pkt_queuesend(Ssh ssh)
{
    int i;

    assert(!ssh->queueing);

    for (i = 0; i < ssh->queuelen; i++)
	ssh2_pkt_defer_noqueue(ssh, ssh->queue[i]);
    ssh->queuelen = 0;

    ssh_pkt_defersend(ssh);
}

#if 0
void bndebug(char *string, Bignum b)
{
    unsigned char *p;
    int i, len;
    p = ssh2_mpint_fmt(b, &len);

    else
	s->maclist = macs, s->nmacs = lenof(macs);

  begin_key_exchange:
    {
	int i, j, cipherstr_started;

	/*
	 * Enable queueing of outgoing auth- or connection-layer
	 * packets while we are in the middle of a key exchange.
	 */
	ssh->queueing = TRUE;

	/*
	 * Construct and send our key exchange packet.
	 */
	s->pktout = ssh2_pkt_init(SSH2_MSG_KEXINIT);
	for (i = 0; i < 16; i++)
	    ssh2_pkt_addbyte(s->pktout, (unsigned char) random_byte());
	/* List key exchange algorithms. */

	/* Reserved. */
	ssh2_pkt_adduint32(s->pktout, 0);
    }

    ssh->exhash = ssh->exhashbase;
    sha_string(&ssh->exhash, s->pktout->data + 5, s->pktout->length - 5);

    ssh2_pkt_send(ssh, s->pktout);
    ssh2_pkt_send_noqueue(ssh, s->pktout);

    if (!pktin)
	crWaitUntil(pktin);
    if (pktin->length > 5)
	sha_string(&ssh->exhash, pktin->data + 5, pktin->length - 5);

    /*

	/*
	 * Work out how big a DH group we will need to allow that
	 * much data.
	 */
	s->pbits = 512 << ((s->nbits - 1) / 64);
	s->pktout = ssh2_pkt_init(SSH2_MSG_KEX_DH_GEX_REQUEST);
	ssh2_pkt_adduint32(s->pktout, s->pbits);
	ssh2_pkt_send(ssh, s->pktout);
	ssh2_pkt_send_noqueue(ssh, s->pktout);

	crWaitUntil(pktin);
	if (pktin->type != SSH2_MSG_KEX_DH_GEX_GROUP) {
	    bombout(("expected key exchange group packet from server"));
	    crStop(0);
	}
	s->p = ssh2_pkt_getmp(pktin);

    logevent("Doing Diffie-Hellman key exchange");
    /*
     * Now generate and send e for Diffie-Hellman.
     */
    s->e = dh_create_e(ssh->kex_ctx, s->nbits * 2);
    s->pktout = ssh2_pkt_init(s->kex_init_value);
    ssh2_pkt_addmp(s->pktout, s->e);
    ssh2_pkt_send(ssh, s->pktout);
    ssh2_pkt_send_noqueue(ssh, s->pktout);

    crWaitUntil(pktin);
    if (pktin->type != s->kex_reply_value) {
	bombout(("expected key exchange reply packet from server"));
	crStop(0);
    }
    ssh_pkt_getstring(pktin, &s->hostkeydata, &s->hostkeylen);

    sfree(s->keystr);
    ssh->hostkey->freekey(s->hkey);

    /*
     * Send SSH2_MSG_NEWKEYS.
     */
    s->pktout = ssh2_pkt_init(SSH2_MSG_NEWKEYS);
    ssh2_pkt_send(ssh, s->pktout);
    ssh2_pkt_send_noqueue(ssh, s->pktout);

    /*
     * Now our end of the key exchange is complete, we can send all
     * our queued higher-layer packets.
     */
    ssh->queueing = FALSE;
    ssh2_pkt_queuesend(ssh);

    /*
     * Expect SSH2_MSG_NEWKEYS from server.
     */
    crWaitUntil(pktin);
    if (pktin->type != SSH2_MSG_NEWKEYS) {
	bombout(("expected new-keys packet from server"));

			 * work). Terminate.
			 */
			s->pktout = ssh2_pkt_init(SSH2_MSG_DISCONNECT);
			ssh2_pkt_adduint32(s->pktout,SSH2_DISCONNECT_BY_APPLICATION);
			ssh2_pkt_addstring(s->pktout, "No more passwords available"
					   " to try");
			ssh2_pkt_addstring(s->pktout, "en");	/* language tag */
			ssh2_pkt_send(ssh, s->pktout);
			ssh2_pkt_send_noqueue(ssh, s->pktout);
			logevent("Unable to authenticate");
			connection_fatal(ssh->frontend,
					 "Unable to authenticate");
                        ssh_closing((Plug)ssh, NULL, 0, 0);
			crStopV;
		    }
		} else {

		logevent("No supported authentications offered."
			 " Disconnecting");
		s->pktout = ssh2_pkt_init(SSH2_MSG_DISCONNECT);
		ssh2_pkt_adduint32(s->pktout, SSH2_DISCONNECT_BY_APPLICATION);
		ssh2_pkt_addstring(s->pktout, "No supported authentication"
				   " methods available");
		ssh2_pkt_addstring(s->pktout, "en");	/* language tag */
		ssh2_pkt_send(ssh, s->pktout);
		ssh2_pkt_send_noqueue(ssh, s->pktout);
                ssh_closing((Plug)ssh, NULL, 0, 0);
		crStopV;
	    }
	}
    } while (!s->we_are_in);

    /*

                     * this is more polite than sending a
                     * DISCONNECT. So now we don't.
                     */
		    s->pktout = ssh2_pkt_init(SSH2_MSG_DISCONNECT);
		    ssh2_pkt_adduint32(s->pktout, SSH2_DISCONNECT_BY_APPLICATION);
		    ssh2_pkt_addstring(s->pktout, "All open channels closed");
		    ssh2_pkt_addstring(s->pktout, "en");	/* language tag */
		    ssh2_pkt_send(ssh, s->pktout);
		    ssh2_pkt_send_noqueue(ssh, s->pktout);
#endif
                    ssh_closing((Plug)ssh, NULL, 0, 0);
		    crStopV;
		}
		continue;	       /* remote sends close; ignore (FIXME) */
	    } else if (pktin->type == SSH2_MSG_CHANNEL_WINDOW_ADJUST) {
		unsigned i = ssh_pkt_getuint32(pktin);

		    sprintf(buf, "Received channel request for nonexistent"
			    " channel %d", localid);
		    logevent(buf);
		    s->pktout = ssh2_pkt_init(SSH2_MSG_DISCONNECT);
		    ssh2_pkt_adduint32(s->pktout, SSH2_DISCONNECT_BY_APPLICATION);
		    ssh2_pkt_addstring(s->pktout, buf);
		    ssh2_pkt_addstring(s->pktout, "en");	/* language tag */
		    ssh2_pkt_send(ssh, s->pktout);
		    ssh2_pkt_send_noqueue(ssh, s->pktout);
		    connection_fatal(ssh->frontend, "%s", buf);
                    ssh_closing((Plug)ssh, NULL, 0, 0);
		    crStopV;
		}

		/*
		 * Having got the channel number, we now look at

    ssh->do_ssh_init_state = NULL;
    ssh->do_ssh1_login_state = NULL;
    ssh->do_ssh2_transport_state = NULL;
    ssh->do_ssh2_authconn_state = NULL;
    ssh->mainchan = NULL;
    ssh->throttled_all = 0;
    ssh->v1_stdout_throttling = 0;
    ssh->queue = NULL;
    ssh->queuelen = ssh->queuesize = 0;
    ssh->queueing = FALSE;

    *backend_handle = ssh;

#ifdef MSCRYPTOAPI
    if (crypto_startup() == 0)
	return "Microsoft high encryption pack not installed!";
#endif

	    ssh->sccomp->decompress_cleanup(ssh->sc_comp_ctx);
	else
	    zlib_decompress_cleanup(ssh->sc_comp_ctx);
    }
    if (ssh->kex_ctx)
	dh_cleanup(ssh->kex_ctx);
    sfree(ssh->savedhost);

    while (ssh->queuelen-- > 0)
	ssh_free_packet(ssh->queue[ssh->queuelen]);
    sfree(ssh->queue);

    if (ssh->channels) {
	while ((c = delpos234(ssh->channels, 0)) != NULL) {
	    switch (c->type) {
	      case CHAN_X11:
		if (c->u.x11.s != NULL)
		    x11_close(c->u.x11.s);

	    || ssh->state == SSH_STATE_PREPACKET) return;
	if (ssh->version == 1) {
	    if (!(ssh->remote_bugs & BUG_CHOKES_ON_SSH1_IGNORE))
		send_packet(ssh, SSH1_MSG_IGNORE, PKT_STR, "", PKT_END);
	} else {
	    pktout = ssh2_pkt_init(SSH2_MSG_IGNORE);
	    ssh2_pkt_addstring_start(pktout);
	    ssh2_pkt_send(ssh, pktout);
	    ssh2_pkt_send_noqueue(ssh, pktout);
	}
    } else if (code == TS_BRK) {
	if (ssh->state == SSH_STATE_CLOSED
	    || ssh->state == SSH_STATE_PREPACKET) return;
	if (ssh->version == 1) {
	    logevent("Unable to send BREAK signal in SSH1");
	} else if (ssh->mainchan) {