1/* $OpenBSD: setbuf.c,v 1.5 2010/01/12 23:22:06 nicm Exp $ */
2
3/****************************************************************************
4 * Copyright (c) 1998-2003,2007 Free Software Foundation, Inc.              *
5 *                                                                          *
6 * Permission is hereby granted, free of charge, to any person obtaining a  *
7 * copy of this software and associated documentation files (the            *
8 * "Software"), to deal in the Software without restriction, including      *
9 * without limitation the rights to use, copy, modify, merge, publish,      *
10 * distribute, distribute with modifications, sublicense, and/or sell       *
11 * copies of the Software, and to permit persons to whom the Software is    *
12 * furnished to do so, subject to the following conditions:                 *
13 *                                                                          *
14 * The above copyright notice and this permission notice shall be included  *
15 * in all copies or substantial portions of the Software.                   *
16 *                                                                          *
17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS  *
18 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF               *
19 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.   *
20 * IN NO EVENT SHALL THE ABOVE COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,   *
21 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR    *
22 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR    *
23 * THE USE OR OTHER DEALINGS IN THE SOFTWARE.                               *
24 *                                                                          *
25 * Except as contained in this notice, the name(s) of the above copyright   *
26 * holders shall not be used in advertising or otherwise to promote the     *
27 * sale, use or other dealings in this Software without prior written       *
28 * authorization.                                                           *
29 ****************************************************************************/
30
31/****************************************************************************
32 *  Author: Zeyd M. Ben-Halim <zmbenhal@netcom.com> 1992,1995               *
33 *     and: Eric S. Raymond <esr@snark.thyrsus.com>                         *
34 ****************************************************************************/
35
36/*
37**	setbuf.c
38**
39**	Support for set_term(), reset_shell_mode(), reset_prog_mode().
40**
41*/
42
43#include <curses.priv.h>
44
45MODULE_ID("$Id: setbuf.c,v 1.5 2010/01/12 23:22:06 nicm Exp $")
46
47/*
48 * If the output file descriptor is connected to a tty (the typical case) it
49 * will probably be line-buffered.  Keith Bostic pointed out that we don't want
50 * this; it hoses people running over networks by forcing out a bunch of small
51 * packets instead of one big one, so screen updates on ptys look jerky.
52 * Restore block buffering to prevent this minor lossage.
53 *
54 * The buffer size is a compromise.  Ideally we'd like a buffer that can hold
55 * the maximum possible update size (the whole screen plus cup commands to
56 * change lines as it's painted).  On a 66-line xterm this can become
57 * excessive.  So we min it with the amount of data we think we can get through
58 * two Ethernet packets (maximum packet size - 100 for TCP/IP overhead).
59 *
60 * Why two ethernet packets?  It used to be one, on the theory that said
61 * packets define the maximum size of atomic update.  But that's less than the
62 * 2000 chars on a 25 x 80 screen, and we don't want local updates to flicker
63 * either.  Two packet lengths will handle up to a 35 x 80 screen.
64 *
65 * The magic '6' is the estimated length of the end-of-line cup sequence to go
66 * to the next line.  It's generous.  We used to mess with the buffering in
67 * init_mvcur() after cost computation, but that lost the sequences emitted by
68 * init_acs() in setupscreen().
69 *
70 * "The setvbuf function may be used only after the stream pointed to by stream
71 * has been associated with an open file and before any other operation is
72 * performed on the stream." (ISO 7.9.5.6.)
73 *
74 * Grrrr...
75 *
76 * On a lighter note, many implementations do in fact allow an application to
77 * reset the buffering after it has been written to.  We try to do this because
78 * otherwise we leave stdout in buffered mode after endwin() is called.  (This
79 * also happens with SVr4 curses).
80 *
81 * There are pros/cons:
82 *
83 * con:
84 *	There is no guarantee that we can reestablish buffering once we've
85 *	dropped it.
86 *
87 *	We _may_ lose data if the implementation does not coordinate this with
88 *	fflush.
89 *
90 * pro:
91 *	An implementation is more likely to refuse to change the buffering than
92 *	to do it in one of the ways mentioned above.
93 *
94 *	The alternative is to have the application try to change buffering
95 *	itself, which is certainly no improvement.
96 *
97 * Just in case it does not work well on a particular system, the calls to
98 * change buffering are all via the macro NC_BUFFERED.  Some implementations
99 * do indeed get confused by changing setbuf on/off, and will overrun the
100 * buffer.  So we disable this by default (there may yet be a workaround).
101 */
102NCURSES_EXPORT(void)
103_nc_set_buffer(FILE *ofp, bool buffered)
104{
105    /* optional optimization hack -- do before any output to ofp */
106#if HAVE_SETVBUF || HAVE_SETBUFFER
107    if (SP->_buffered != buffered) {
108	unsigned buf_len;
109	char *buf_ptr;
110
111	if (getenv("NCURSES_NO_SETBUF") != 0)
112	    return;
113
114	fflush(ofp);
115#ifdef __DJGPP__
116	setmode(ofp, O_BINARY);
117#endif
118	if (buffered != 0) {
119	    buf_len = min(LINES * (COLS + 6), 2800);
120	    if ((buf_ptr = SP->_setbuf) == 0) {
121		if ((buf_ptr = typeMalloc(char, buf_len)) == NULL)
122		      return;
123		SP->_setbuf = buf_ptr;
124		/* Don't try to free this! */
125	    }
126#if !USE_SETBUF_0
127	    else
128		return;
129#endif
130	} else {
131#if !USE_SETBUF_0
132	    return;
133#else
134	    buf_len = 0;
135	    buf_ptr = 0;
136#endif
137	}
138
139#if HAVE_SETVBUF
140#ifdef SETVBUF_REVERSED		/* pre-svr3? */
141	(void) setvbuf(ofp, buf_ptr, buf_len, buf_len ? _IOFBF : _IOLBF);
142#else
143	(void) setvbuf(ofp, buf_ptr, buf_len ? _IOFBF : _IOLBF, buf_len);
144#endif
145#elif HAVE_SETBUFFER
146	(void) setbuffer(ofp, buf_ptr, (int) buf_len);
147#endif
148
149	SP->_buffered = buffered;
150    }
151#endif /* HAVE_SETVBUF || HAVE_SETBUFFER */
152}
153