/* $OpenBSD: setbuf.c,v 1.5 2010/01/12 23:22:06 nicm Exp $ */

/****************************************************************************

 * Copyright (c) 1998-2003,2007 Free Software Foundation, Inc.              *

 *                                                                          *

 * 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, distribute with modifications, 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.   *

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/****************************************************************************

 *  Author: Zeyd M. Ben-Halim <zmbenhal@netcom.com> 1992,1995               *

 *     and: Eric S. Raymond <esr@snark.thyrsus.com>                         *

 ****************************************************************************/

/*

**	setbuf.c

**

**	Support for set_term(), reset_shell_mode(), reset_prog_mode().

**

*/

#include <curses.priv.h>

MODULE_ID("$Id: setbuf.c,v 1.5 2010/01/12 23:22:06 nicm Exp $")

/*

 * If the output file descriptor is connected to a tty (the typical case) it

 * will probably be line-buffered.  Keith Bostic pointed out that we don't want

 * this; it hoses people running over networks by forcing out a bunch of small

 * packets instead of one big one, so screen updates on ptys look jerky.

 * Restore block buffering to prevent this minor lossage.

 *

 * The buffer size is a compromise.  Ideally we'd like a buffer that can hold

 * the maximum possible update size (the whole screen plus cup commands to

 * change lines as it's painted).  On a 66-line xterm this can become

 * excessive.  So we min it with the amount of data we think we can get through

 * two Ethernet packets (maximum packet size - 100 for TCP/IP overhead).

 *

 * Why two ethernet packets?  It used to be one, on the theory that said

 * packets define the maximum size of atomic update.  But that's less than the

 * 2000 chars on a 25 x 80 screen, and we don't want local updates to flicker

 * either.  Two packet lengths will handle up to a 35 x 80 screen.

 *

 * The magic '6' is the estimated length of the end-of-line cup sequence to go

 * to the next line.  It's generous.  We used to mess with the buffering in

 * init_mvcur() after cost computation, but that lost the sequences emitted by

 * init_acs() in setupscreen().

 *

 * "The setvbuf function may be used only after the stream pointed to by stream

 * has been associated with an open file and before any other operation is

 * performed on the stream." (ISO 7.9.5.6.)

 *

 * Grrrr...

 *

 * On a lighter note, many implementations do in fact allow an application to

 * reset the buffering after it has been written to.  We try to do this because

 * otherwise we leave stdout in buffered mode after endwin() is called.  (This

 * also happens with SVr4 curses).

 *

 * There are pros/cons:

 *

 * con:

 *	There is no guarantee that we can reestablish buffering once we've

 *	dropped it.

 *

 *	We _may_ lose data if the implementation does not coordinate this with

 *	fflush.

 *

 * pro:

 *	An implementation is more likely to refuse to change the buffering than

 *	to do it in one of the ways mentioned above.

 *

 *	The alternative is to have the application try to change buffering

 *	itself, which is certainly no improvement.

 *

 * Just in case it does not work well on a particular system, the calls to

 * change buffering are all via the macro NC_BUFFERED.  Some implementations

 * do indeed get confused by changing setbuf on/off, and will overrun the

 * buffer.  So we disable this by default (there may yet be a workaround).

 */

NCURSES_EXPORT(void)

_nc_set_buffer(FILE *ofp, bool buffered)

{

    /* optional optimization hack -- do before any output to ofp */

#if HAVE_SETVBUF || HAVE_SETBUFFER

	unsigned buf_len;

	char *buf_ptr;

#ifdef __DJGPP__

	setmode(ofp, O_BINARY);

#endif

		/* Don't try to free this! */

	    }

#if !USE_SETBUF_0

	    else

#endif

	} else {

#if !USE_SETBUF_0

#else

	    buf_len = 0;

	    buf_ptr = 0;

#endif

	}

#if HAVE_SETVBUF

#ifdef SETVBUF_REVERSED		/* pre-svr3? */

	(void) setvbuf(ofp, buf_ptr, buf_len, buf_len ? _IOFBF : _IOLBF);

#else

#endif

#elif HAVE_SETBUFFER

	(void) setbuffer(ofp, buf_ptr, (int) buf_len);

#endif

    }

#endif /* HAVE_SETVBUF || HAVE_SETBUFFER */

}