forward.c revision 31681 
1/*-
2 * Copyright (c) 1991, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * This code is derived from software contributed to Berkeley by
6 * Edward Sze-Tyan Wang.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 *    notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 * 3. All advertising materials mentioning features or use of this software
17 *    must display the following acknowledgement:
18 *	This product includes software developed by the University of
19 *	California, Berkeley and its contributors.
20 * 4. Neither the name of the University nor the names of its contributors
21 *    may be used to endorse or promote products derived from this software
22 *    without specific prior written permission.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * SUCH DAMAGE.
35 */
36
37#ifndef lint
38static char sccsid[] = "@(#)forward.c	8.1 (Berkeley) 6/6/93";
39#endif /* not lint */
40
41#include <sys/types.h>
42#include <sys/stat.h>
43#include <sys/time.h>
44#include <sys/mman.h>
45
46#include <limits.h>
47#include <fcntl.h>
48#include <errno.h>
49#include <unistd.h>
50#include <stdio.h>
51#include <stdlib.h>
52#include <string.h>
53#include <err.h>
54#include "extern.h"
55
56static void rlines __P((FILE *, long, struct stat *));
57
58/*
59 * forward -- display the file, from an offset, forward.
60 *
61 * There are eight separate cases for this -- regular and non-regular
62 * files, by bytes or lines and from the beginning or end of the file.
63 *
64 * FBYTES	byte offset from the beginning of the file
65 *	REG	seek
66 *	NOREG	read, counting bytes
67 *
68 * FLINES	line offset from the beginning of the file
69 *	REG	read, counting lines
70 *	NOREG	read, counting lines
71 *
72 * RBYTES	byte offset from the end of the file
73 *	REG	seek
74 *	NOREG	cyclically read characters into a wrap-around buffer
75 *
76 * RLINES
77 *	REG	mmap the file and step back until reach the correct offset.
78 *	NOREG	cyclically read lines into a wrap-around array of buffers
79 */
80void
81forward(fp, style, off, sbp)
82	FILE *fp;
83	enum STYLE style;
84	long off;
85	struct stat *sbp;
86{
87	register int ch;
88	struct timeval interval;
89
90	switch(style) {
91	case FBYTES:
92		if (off == 0)
93			break;
94		if (S_ISREG(sbp->st_mode)) {
95			if (sbp->st_size < off)
96				off = sbp->st_size;
97			if (fseek(fp, off, SEEK_SET) == -1) {
98				ierr();
99				return;
100			}
101		} else while (off--)
102			if ((ch = getc(fp)) == EOF) {
103				if (ferror(fp)) {
104					ierr();
105					return;
106				}
107				break;
108			}
109		break;
110	case FLINES:
111		if (off == 0)
112			break;
113		for (;;) {
114			if ((ch = getc(fp)) == EOF) {
115				if (ferror(fp)) {
116					ierr();
117					return;
118				}
119				break;
120			}
121			if (ch == '\n' && !--off)
122				break;
123		}
124		break;
125	case RBYTES:
126		if (S_ISREG(sbp->st_mode)) {
127			if (sbp->st_size >= off &&
128			    fseek(fp, -off, SEEK_END) == -1) {
129				ierr();
130				return;
131			}
132		} else if (off == 0) {
133			while (getc(fp) != EOF);
134			if (ferror(fp)) {
135				ierr();
136				return;
137			}
138		} else
139			if (bytes(fp, off))
140				return;
141		break;
142	case RLINES:
143		if (S_ISREG(sbp->st_mode))
144			if (!off) {
145				if (fseek(fp, 0L, SEEK_END) == -1) {
146					ierr();
147					return;
148				}
149			} else
150				rlines(fp, off, sbp);
151		else if (off == 0) {
152			while (getc(fp) != EOF);
153			if (ferror(fp)) {
154				ierr();
155				return;
156			}
157		} else
158			if (lines(fp, off))
159				return;
160		break;
161	}
162
163	/*
164	 * We pause for 1/4 second after displaying any data that has
165	 * accumulated since we read the file.
166	 */
167
168	for (;;) {
169		while ((ch = getc(fp)) != EOF)
170			if (putchar(ch) == EOF)
171				oerr();
172		if (ferror(fp)) {
173			ierr();
174			return;
175		}
176		(void)fflush(stdout);
177		if (!fflag)
178			break;
179
180		(void) usleep(250000);
181		clearerr(fp);
182	}
183}
184
185/*
186 * rlines -- display the last offset lines of the file.
187 */
188static void
189rlines(fp, off, sbp)
190	FILE *fp;
191	long off;
192	struct stat *sbp;
193{
194	register off_t size;
195	register char *p;
196	char *start;
197
198	if (!(size = sbp->st_size))
199		return;
200
201	if (size > SIZE_T_MAX) {
202		errno = EFBIG;
203		ierr();
204		return;
205	}
206
207	if ((start = mmap(NULL, (size_t)size,
208	    PROT_READ, MAP_SHARED, fileno(fp), (off_t)0)) == MAP_FAILED) {
209		ierr();
210		return;
211	}
212
213	/* Last char is special, ignore whether newline or not. */
214	for (p = start + size - 1; --size;)
215		if (*--p == '\n' && !--off) {
216			++p;
217			break;
218		}
219
220	/* Set the file pointer to reflect the length displayed. */
221	size = sbp->st_size - size;
222	WR(p, size);
223	if (fseek(fp, (long)sbp->st_size, SEEK_SET) == -1) {
224		ierr();
225		return;
226	}
227	if (munmap(start, (size_t)sbp->st_size)) {
228		ierr();
229		return;
230	}
231}
232