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
45 MODULE_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 */
NCURSES_EXPORT(void)102 NCURSES_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