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/* RCSID("$Id: nchan.h,v 1.2 1999/10/16 22:29:01 markus Exp $"); */

#ifndef NCHAN_H
#define NCHAN_H

/*
 * SSH Protocol 1.5 aka New Channel Protocol
 * Thanks to Martina, Axel and everyone who left Erlangen, leaving me bored.
 * Written by Markus Friedl in October 1999
 * 
 * Protocol versions 1.3 and 1.5 differ in the handshake protocol used for the
 * tear down of channels:
 * 
 * 1.3:	strict request-ack-protocol:
 * 	CLOSE	->
 * 		<-  CLOSE_CONFIRM
 * 
 * 1.5:	uses variations of:
 * 	IEOF	->
 * 		<-  OCLOSE
 * 		<-  IEOF
 * 	OCLOSE	->
 * 	i.e. both sides have to close the channel
 * 
 * See the debugging output from 'ssh -v' and 'sshd -d' of
 * ssh-1.2.27 as an example.
 * 
 * Details: (for Channel data structure see channels.h)
 * 
 * - the output_buffer gets data received from the remote peer and
 *   is written to the socket,
 * - the input_buffer gets data from the socket and is sent to remote peer.
 * - the socket represents the local object communicating with an object
 *   reachable via the peer
 * 
 * 	PEER A					PEER B
 * 
 * read(sock, input_buffer) < 0;
 * shutdown_read();
 * flush(input_buffer) =: DATA
 * send(DATA)			->      rcvd(DATA)
 * 					write(sock, output_buffer:=DATA);
 * send(IEOF)			->	rcvd(IEOF)
 * 					shutdown_write() if:
 * 						a) write fails
 * 						b) rcvd_IEOF==true &&
 * 						   output_buffer==empty
 * rcvd(OCLOSE)			<-	send(OCLOSE)
 *
 * The channel is now half closed. No data will flow from A to B.
 *
 * Note that each side can remove the channel only if 2 messages
 * have been sent and received and the associated socket has been
 * shutdown, see below:
 */

enum {
	/* ssh-proto-1.5 overloads message-types */
	CHAN_IEOF   = SSH_MSG_CHANNEL_CLOSE,
			/* there will be no more data from sender */
	CHAN_OCLOSE = SSH_MSG_CHANNEL_CLOSE_CONFIRMATION,
			/* all received data has been written to the socket */

	/* channel close flags */
	CHAN_IEOF_SENT 		= 0x01,
	CHAN_IEOF_RCVD 		= 0x02,
	CHAN_OCLOSE_SENT 	= 0x04,
	CHAN_OCLOSE_RCVD 	= 0x08,
	CHAN_SHUT_RD 		= 0x10,
	CHAN_SHUT_WR 		= 0x20,

	/* a channel can be removed if ALL the following flags are set: */
	CHAN_CLOSED 		= CHAN_IEOF_SENT | CHAN_IEOF_RCVD |
				  CHAN_OCLOSE_SENT | CHAN_OCLOSE_RCVD |
				  CHAN_SHUT_RD | CHAN_SHUT_WR
};

void chan_del_if_dead(Channel *c);
void chan_rcvd_ieof(Channel *c);
void chan_rcvd_oclose(Channel *c);
void chan_send_ieof(Channel *c);
void chan_send_oclose(Channel *c);
void chan_shutdown_read(Channel *c);
void chan_shutdown_write(Channel *c);
#endif