1/****************************************************************************
2 * Copyright (c) 1998-2003,2007 Free Software Foundation, Inc.              *
3 *                                                                          *
4 * Permission is hereby granted, free of charge, to any person obtaining a  *
5 * copy of this software and associated documentation files (the            *
6 * "Software"), to deal in the Software without restriction, including      *
7 * without limitation the rights to use, copy, modify, merge, publish,      *
8 * distribute, distribute with modifications, sublicense, and/or sell       *
9 * copies of the Software, and to permit persons to whom the Software is    *
10 * furnished to do so, subject to the following conditions:                 *
11 *                                                                          *
12 * The above copyright notice and this permission notice shall be included  *
13 * in all copies or substantial portions of the Software.                   *
14 *                                                                          *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS  *
16 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF               *
17 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.   *
18 * IN NO EVENT SHALL THE ABOVE COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,   *
19 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR    *
20 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR    *
21 * THE USE OR OTHER DEALINGS IN THE SOFTWARE.                               *
22 *                                                                          *
23 * Except as contained in this notice, the name(s) of the above copyright   *
24 * holders shall not be used in advertising or otherwise to promote the     *
25 * sale, use or other dealings in this Software without prior written       *
26 * authorization.                                                           *
27 ****************************************************************************/
28
29/****************************************************************************
30 *  Author: Zeyd M. Ben-Halim <zmbenhal@netcom.com> 1992,1995               *
31 *     and: Eric S. Raymond <esr@snark.thyrsus.com>                         *
32 ****************************************************************************/
33
34/*
35**	setbuf.c
36**
37**	Support for set_term(), reset_shell_mode(), reset_prog_mode().
38**
39*/
40
41#include <curses.priv.h>
42
43MODULE_ID("$Id: setbuf.c,v 1.13 2007/05/12 19:04:02 tom Exp $")
44
45/*
46 * If the output file descriptor is connected to a tty (the typical case) it
47 * will probably be line-buffered.  Keith Bostic pointed out that we don't want
48 * this; it hoses people running over networks by forcing out a bunch of small
49 * packets instead of one big one, so screen updates on ptys look jerky.
50 * Restore block buffering to prevent this minor lossage.
51 *
52 * The buffer size is a compromise.  Ideally we'd like a buffer that can hold
53 * the maximum possible update size (the whole screen plus cup commands to
54 * change lines as it's painted).  On a 66-line xterm this can become
55 * excessive.  So we min it with the amount of data we think we can get through
56 * two Ethernet packets (maximum packet size - 100 for TCP/IP overhead).
57 *
58 * Why two ethernet packets?  It used to be one, on the theory that said
59 * packets define the maximum size of atomic update.  But that's less than the
60 * 2000 chars on a 25 x 80 screen, and we don't want local updates to flicker
61 * either.  Two packet lengths will handle up to a 35 x 80 screen.
62 *
63 * The magic '6' is the estimated length of the end-of-line cup sequence to go
64 * to the next line.  It's generous.  We used to mess with the buffering in
65 * init_mvcur() after cost computation, but that lost the sequences emitted by
66 * init_acs() in setupscreen().
67 *
68 * "The setvbuf function may be used only after the stream pointed to by stream
69 * has been associated with an open file and before any other operation is
70 * performed on the stream." (ISO 7.9.5.6.)
71 *
72 * Grrrr...
73 *
74 * On a lighter note, many implementations do in fact allow an application to
75 * reset the buffering after it has been written to.  We try to do this because
76 * otherwise we leave stdout in buffered mode after endwin() is called.  (This
77 * also happens with SVr4 curses).
78 *
79 * There are pros/cons:
80 *
81 * con:
82 *	There is no guarantee that we can reestablish buffering once we've
83 *	dropped it.
84 *
85 *	We _may_ lose data if the implementation does not coordinate this with
86 *	fflush.
87 *
88 * pro:
89 *	An implementation is more likely to refuse to change the buffering than
90 *	to do it in one of the ways mentioned above.
91 *
92 *	The alternative is to have the application try to change buffering
93 *	itself, which is certainly no improvement.
94 *
95 * Just in case it does not work well on a particular system, the calls to
96 * change buffering are all via the macro NC_BUFFERED.  Some implementations
97 * do indeed get confused by changing setbuf on/off, and will overrun the
98 * buffer.  So we disable this by default (there may yet be a workaround).
99 */
100NCURSES_EXPORT(void)
101_nc_set_buffer(FILE *ofp, bool buffered)
102{
103    /* optional optimization hack -- do before any output to ofp */
104#if HAVE_SETVBUF || HAVE_SETBUFFER
105    if (SP->_buffered != buffered) {
106	unsigned buf_len;
107	char *buf_ptr;
108
109	if (getenv("NCURSES_NO_SETBUF") != 0)
110	    return;
111
112	fflush(ofp);
113#ifdef __DJGPP__
114	setmode(ofp, O_BINARY);
115#endif
116	if (buffered != 0) {
117	    buf_len = min(LINES * (COLS + 6), 2800);
118	    if ((buf_ptr = SP->_setbuf) == 0) {
119		if ((buf_ptr = typeMalloc(char, buf_len)) == NULL)
120		      return;
121		SP->_setbuf = buf_ptr;
122		/* Don't try to free this! */
123	    }
124#if !USE_SETBUF_0
125	    else
126		return;
127#endif
128	} else {
129#if !USE_SETBUF_0
130	    return;
131#else
132	    buf_len = 0;
133	    buf_ptr = 0;
134#endif
135	}
136
137#if HAVE_SETVBUF
138#ifdef SETVBUF_REVERSED		/* pre-svr3? */
139	(void) setvbuf(ofp, buf_ptr, buf_len, buf_len ? _IOFBF : _IOLBF);
140#else
141	(void) setvbuf(ofp, buf_ptr, buf_len ? _IOFBF : _IOLBF, buf_len);
142#endif
143#elif HAVE_SETBUFFER
144	(void) setbuffer(ofp, buf_ptr, (int) buf_len);
145#endif
146
147	SP->_buffered = buffered;
148    }
149#endif /* HAVE_SETVBUF || HAVE_SETBUFFER */
150}
151