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 */ 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