/*
 * Dropbear SSH
 * 
 * Copyright (c) 2002-2004 Matt Johnston
 * All rights reserved.
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE. */

/* Handle the multiplexed channels, such as sessions, x11, agent connections */

#include "includes.h"
#include "session.h"
#include "packet.h"
#include "ssh.h"
#include "buffer.h"
#include "circbuffer.h"
#include "dbutil.h"
#include "channel.h"
#include "listener.h"
#include "runopts.h"
#include "netio.h"

static void send_msg_channel_open_failure(unsigned int remotechan, int reason,
		const char *text, const char *lang);
static void send_msg_channel_open_confirmation(const struct Channel* channel,
		unsigned int recvwindow, 
		unsigned int recvmaxpacket);
static int writechannel(struct Channel* channel, int fd, circbuffer *cbuf,
	const unsigned char *moredata, unsigned int *morelen);
static void send_msg_channel_window_adjust(const struct Channel *channel,
		unsigned int incr);
static void send_msg_channel_data(struct Channel *channel, int isextended);
static void send_msg_channel_eof(struct Channel *channel);
static void send_msg_channel_close(struct Channel *channel);
static void remove_channel(struct Channel *channel);
static unsigned int write_pending(const struct Channel * channel);
static void check_close(struct Channel *channel);
static void close_chan_fd(struct Channel *channel, int fd, int how);

#define FD_UNINIT (-2)
#define FD_CLOSED (-1)

#define ERRFD_IS_READ(channel) ((channel)->extrabuf == NULL)
#define ERRFD_IS_WRITE(channel) (!ERRFD_IS_READ(channel))

/* allow space for:
 * 1 byte  byte      SSH_MSG_CHANNEL_DATA
 * 4 bytes uint32    recipient channel
 * 4 bytes string    data
 */
#define RECV_MAX_CHANNEL_DATA_LEN (RECV_MAX_PAYLOAD_LEN-(1+4+4))

/* Initialise all the channels */
void chaninitialise(const struct ChanType *chantypes[]) {

	/* may as well create space for a single channel */
	ses.channels = (struct Channel**)m_malloc(sizeof(struct Channel*));
	ses.chansize = 1;
	ses.channels[0] = NULL;
	ses.chancount = 0;

	ses.chantypes = chantypes;

#if DROPBEAR_LISTENERS
	listeners_initialise();
#endif

}

/* Clean up channels, freeing allocated memory */
void chancleanup() {

	unsigned int i;

	TRACE(("enter chancleanup"))
	for (i = 0; i < ses.chansize; i++) {
		if (ses.channels[i] != NULL) {
			TRACE(("channel %d closing", i))
			remove_channel(ses.channels[i]);
		}
	}
	m_free(ses.channels);
	TRACE(("leave chancleanup"))
}

/* Create a new channel entry, send a reply confirm or failure */
/* If remotechan, transwindow and transmaxpacket are not know (for a new
 * outgoing connection, with them to be filled on confirmation), they should
 * all be set to 0 */
static struct Channel* newchannel(unsigned int remotechan, 
		const struct ChanType *type, 
		unsigned int transwindow, unsigned int transmaxpacket) {

	struct Channel * newchan;
	unsigned int i, j;

	TRACE(("enter newchannel"))
	
	/* first see if we can use existing channels */
	for (i = 0; i < ses.chansize; i++) {
		if (ses.channels[i] == NULL) {
			break;
		}
	}

	/* otherwise extend the list */
	if (i == ses.chansize) {
		if (ses.chansize >= MAX_CHANNELS) {
			TRACE(("leave newchannel: max chans reached"))
			return NULL;
		}

		/* extend the channels */
		ses.channels = (struct Channel**)m_realloc(ses.channels,
				(ses.chansize+CHAN_EXTEND_SIZE)*sizeof(struct Channel*));

		ses.chansize += CHAN_EXTEND_SIZE;

		/* set the new channels to null */
		for (j = i; j < ses.chansize; j++) {
			ses.channels[j] = NULL;
		}

	}
	
	newchan = (struct Channel*)m_malloc(sizeof(struct Channel));
	newchan->type = type;
	newchan->index = i;
	newchan->sent_close = newchan->recv_close = 0;
	newchan->sent_eof = newchan->recv_eof = 0;
	newchan->close_handler_done = 0;

	newchan->remotechan = remotechan;
	newchan->transwindow = transwindow;
	newchan->transmaxpacket = transmaxpacket;
	
	newchan->typedata = NULL;
	newchan->writefd = FD_UNINIT;
	newchan->readfd = FD_UNINIT;
	newchan->errfd = FD_CLOSED; /* this isn't always set to start with */
	newchan->await_open = 0;
	newchan->flushing = 0;

	newchan->writebuf = cbuf_new(opts.recv_window);
	newchan->recvwindow = opts.recv_window;

	newchan->extrabuf = NULL; /* The user code can set it up */
	newchan->recvdonelen = 0;
	newchan->recvmaxpacket = RECV_MAX_CHANNEL_DATA_LEN;

	newchan->prio = DROPBEAR_CHANNEL_PRIO_EARLY; /* inithandler sets it */

	ses.channels[i] = newchan;
	ses.chancount++;

	TRACE(("leave newchannel"))

	return newchan;
}

/* Returns the channel structure corresponding to the channel in the current
 * data packet (ses.payload must be positioned appropriately).
 * A valid channel is always returns, it will fail fatally with an unknown
 * channel */
static struct Channel* getchannel_msg(const char* kind) {

	unsigned int chan;

	chan = buf_getint(ses.payload);
	if (chan >= ses.chansize || ses.channels[chan] == NULL) {
		if (kind) {
			dropbear_exit("%s for unknown channel %d", kind, chan);
		} else {
			dropbear_exit("Unknown channel %d", chan);
		}
	}
	return ses.channels[chan];
}

struct Channel* getchannel() {
	return getchannel_msg(NULL);
}

/* Iterate through the channels, performing IO if available */
void channelio(const fd_set *readfds, const fd_set *writefds) {

	/* Listeners such as TCP, X11, agent-auth */
	struct Channel *channel;
	unsigned int i;

	/* foreach channel */
	for (i = 0; i < ses.chansize; i++) {
		/* Close checking only needs to occur for channels that had IO events */
		int do_check_close = 0;

		channel = ses.channels[i];
		if (channel == NULL) {
			/* only process in-use channels */
			continue;
		}

		/* read data and send it over the wire */
		if (channel->readfd >= 0 && FD_ISSET(channel->readfd, readfds)) {
			TRACE(("send normal readfd"))
			send_msg_channel_data(channel, 0);
			do_check_close = 1;
		}

		/* read stderr data and send it over the wire */
		if (ERRFD_IS_READ(channel) && channel->errfd >= 0 
			&& FD_ISSET(channel->errfd, readfds)) {
				TRACE(("send normal errfd"))
				send_msg_channel_data(channel, 1);
			do_check_close = 1;
		}

		/* write to program/pipe stdin */
		if (channel->writefd >= 0 && FD_ISSET(channel->writefd, writefds)) {
			writechannel(channel, channel->writefd, channel->writebuf, NULL, NULL);
			do_check_close = 1;
		}
		
		/* stderr for client mode */
		if (ERRFD_IS_WRITE(channel)
				&& channel->errfd >= 0 && FD_ISSET(channel->errfd, writefds)) {
			writechannel(channel, channel->errfd, channel->extrabuf, NULL, NULL);
			do_check_close = 1;
		}

		if (ses.channel_signal_pending) {
			/* SIGCHLD can change channel state for server sessions */
			do_check_close = 1;
		}
	
		/* handle any channel closing etc */
		if (do_check_close) {
			check_close(channel);
		}
	}

#if DROPBEAR_LISTENERS
	handle_listeners(readfds);
#endif
}


/* Returns true if there is data remaining to be written to stdin or
 * stderr of a channel's endpoint. */
static unsigned int write_pending(const struct Channel * channel) {

	if (channel->writefd >= 0 && cbuf_getused(channel->writebuf) > 0) {
		return 1;
	} else if (channel->errfd >= 0 && channel->extrabuf && 
			cbuf_getused(channel->extrabuf) > 0) {
		return 1;
	}
	return 0;
}


/* EOF/close handling */
static void check_close(struct Channel *channel) {
	int close_allowed = 0;

	TRACE2(("check_close: writefd %d, readfd %d, errfd %d, sent_close %d, recv_close %d",
				channel->writefd, channel->readfd,
				channel->errfd, channel->sent_close, channel->recv_close))
	TRACE2(("writebuf size %d extrabuf size %d",
				channel->writebuf ? cbuf_getused(channel->writebuf) : 0,
				channel->extrabuf ? cbuf_getused(channel->extrabuf) : 0))

	if (!channel->flushing 
		&& !channel->close_handler_done
		&& channel->type->check_close
		&& channel->type->check_close(channel))
	{
		channel->flushing = 1;
	}
	
	/* if a type-specific check_close is defined we will only exit
	   once that has been triggered. this is only used for a server "session"
	   channel, to ensure that the shell has exited (and the exit status 
	   retrieved) before we close things up. */
	if (!channel->type->check_close	
		|| channel->close_handler_done
		|| channel->type->check_close(channel)) {
		close_allowed = 1;
	}

	if (channel->recv_close && !write_pending(channel) && close_allowed) {
		if (!channel->sent_close) {
			TRACE(("Sending MSG_CHANNEL_CLOSE in response to same."))
			send_msg_channel_close(channel);
		}
		remove_channel(channel);
		return;
	}

	if ((channel->recv_eof && !write_pending(channel))
		/* have a server "session" and child has exited */
		|| (channel->type->check_close && close_allowed)) {
		close_chan_fd(channel, channel->writefd, SHUT_WR);
	}

	/* Special handling for flushing read data after an exit. We
	   read regardless of whether the select FD was set,
	   and if there isn't data available, the channel will get closed. */
	if (channel->flushing) {
		TRACE(("might send data, flushing"))
		if (channel->readfd >= 0 && channel->transwindow > 0) {
			TRACE(("send data readfd"))
			send_msg_channel_data(channel, 0);
		}
		if (ERRFD_IS_READ(channel) && channel->errfd >= 0 
			&& channel->transwindow > 0) {
			TRACE(("send data errfd"))
			send_msg_channel_data(channel, 1);
		}
	}

	/* If we're not going to send any more data, send EOF */
	if (!channel->sent_eof
			&& channel->readfd == FD_CLOSED 
			&& (ERRFD_IS_WRITE(channel) || channel->errfd == FD_CLOSED)) {
		send_msg_channel_eof(channel);
	}

	/* And if we can't receive any more data from them either, close up */
	if (channel->readfd == FD_CLOSED
			&& channel->writefd == FD_CLOSED
			&& (ERRFD_IS_WRITE(channel) || channel->errfd == FD_CLOSED)
			&& !channel->sent_close
			&& close_allowed
			&& !write_pending(channel)) {
		TRACE(("sending close, readfd is closed"))
		send_msg_channel_close(channel);
	}
}

/* Check whether a deferred (EINPROGRESS) connect() was successful, and
 * if so, set up the channel properly. Otherwise, the channel is cleaned up, so
 * it is important that the channel reference isn't used after a call to this
 * function */
void channel_connect_done(int result, int sock, void* user_data, const char* UNUSED(errstring)) {