1/*	$OpenBSD: reverse.c,v 1.21 2015/11/19 17:50:04 tedu Exp $	*/
2/*	$NetBSD: reverse.c,v 1.6 1994/11/23 07:42:10 jtc Exp $	*/
3
4/*-
5 * Copyright (c) 1991, 1993
6 *	The Regents of the University of California.  All rights reserved.
7 *
8 * This code is derived from software contributed to Berkeley by
9 * Edward Sze-Tyan Wang.
10 *
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
13 * are met:
14 * 1. Redistributions of source code must retain the above copyright
15 *    notice, this list of conditions and the following disclaimer.
16 * 2. Redistributions in binary form must reproduce the above copyright
17 *    notice, this list of conditions and the following disclaimer in the
18 *    documentation and/or other materials provided with the distribution.
19 * 3. Neither the name of the University nor the names of its contributors
20 *    may be used to endorse or promote products derived from this software
21 *    without specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
26 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * SUCH DAMAGE.
34 */
35
36#include <sys/stat.h>
37
38#include <err.h>
39#include <stdio.h>
40#include <stdlib.h>
41#include <unistd.h>
42
43#include "extern.h"
44
45static void r_buf(FILE *);
46static int r_reg(struct tailfile *, enum STYLE, off_t);
47
48#define COPYCHAR(tf, ch)				\
49	do {						\
50		if ((ch = getc(tf->fp)) == EOF) {	\
51			ierr(tf->fname);		\
52			return (0);			\
53		}					\
54		if (putchar(ch) == EOF) {		\
55			oerr();				\
56			return (0);			\
57		}					\
58	} while (0)
59
60/*
61 * reverse -- display input in reverse order by line.
62 *
63 * There are six separate cases for this -- regular and non-regular
64 * files by bytes, lines or the whole file.
65 *
66 * BYTES	display N bytes
67 *	REG	reverse scan and display the lines
68 *	NOREG	cyclically read characters into a wrap-around buffer
69 *
70 * LINES	display N lines
71 *	REG	reverse scan and display the lines
72 *	NOREG	cyclically read lines into a wrap-around array of buffers
73 *
74 * FILE		display the entire file
75 *	REG	reverse scan and display the lines
76 *	NOREG	cyclically read input into a linked list of buffers
77 */
78void
79reverse(struct tailfile *tf, int nfiles, enum STYLE style, off_t off)
80{
81	int i;
82
83	if (style != REVERSE && off == 0)
84		return;
85
86	for (i = 0; i < nfiles; i++) {
87		if (nfiles > 1)
88			printfname(tf[i].fname);
89		if (!S_ISREG(tf[i].sb.st_mode) ||
90		    r_reg(&(tf[i]), style, off) != 0) {
91			switch(style) {
92			case FBYTES:
93			case RBYTES:
94				(void)bytes(&(tf[i]), off);
95				break;
96			case FLINES:
97			case RLINES:
98				(void)lines(&(tf[i]), off);
99				break;
100			case REVERSE:
101				r_buf(tf[i].fp);
102				break;
103			default:
104				err(1, "Unsupported style");
105			}
106		}
107	}
108}
109
110/*
111 * r_reg -- display a regular file in reverse order by line.
112 */
113static int
114r_reg(struct tailfile *tf, enum STYLE style, off_t off)
115{
116	off_t start, pos, end;
117	int ch;
118
119	end = tf->sb.st_size;
120	if (end == 0)
121		return (0);
122
123	/* Position before char, ignore last char whether newline or not */
124	pos = end-2;
125	ch = EOF;
126	start = 0;
127
128	if (style == RBYTES && off < end)
129		start = end - off;
130
131	for (; pos >= start; pos--) {
132		/* A seek per char isn't a problem with a smart stdio */
133		if (fseeko(tf->fp, pos, SEEK_SET) != 0) {
134			ierr(tf->fname);
135			return (0);
136		}
137		if ((ch = getc(tf->fp)) == '\n') {
138			while (--end > pos)
139				COPYCHAR(tf, ch);
140			end++;
141			if (style == RLINES && --off == 0)
142				break;
143		}
144		else if (ch == EOF) {
145			ierr(tf->fname);
146			return (0);
147		}
148	}
149	if (pos < start) {
150		if (ch != EOF && ungetc(ch, tf->fp) == EOF) {
151			ierr(tf->fname);
152			return (0);
153		}
154		while (--end >= start)
155			COPYCHAR(tf, ch);
156	}
157	return (0);
158}
159
160#define	BSZ	(128 * 1024)
161struct bf {
162	struct bf *next;
163	struct bf *prev;
164	size_t len;
165	char l[BSZ];
166};
167
168/*
169 * r_buf -- display a non-regular file in reverse order by line.
170 *
171 * This is the function that saves the entire input, storing the data in a
172 * doubly linked list of buffers and then displays them in reverse order.
173 * It has the usual nastiness of trying to find the newlines, as there's no
174 * guarantee that a newline occurs anywhere in the file, let alone in any
175 * particular buffer.  If we run out of memory, input is discarded (and the
176 * user warned).
177 */
178static void
179r_buf(FILE *fp)
180{
181	struct bf *mark, *tr, *tl = NULL;
182	int ch;
183	size_t len, llen;
184	char *p;
185	off_t enomem;
186
187	for (mark = NULL, enomem = 0;;) {
188		/*
189		 * Allocate a new block and link it into place in a doubly
190		 * linked list.  If out of memory, toss the LRU block and
191		 * keep going.
192		 */
193		if (enomem || (tl = malloc(sizeof(*tl))) == NULL) {
194			if (!mark)
195				err(1, NULL);
196			tl = enomem ? tl->next : mark;
197			enomem += tl->len;
198		} else if (mark) {
199			tl->next = mark;
200			tl->prev = mark->prev;
201			mark->prev->next = tl;
202			mark->prev = tl;
203		} else {
204			mark = tl;
205			mark->next = mark->prev = mark;
206		}
207
208		if (!enomem)
209			tl->len = 0;
210
211		/* Fill the block with input data. */
212		for (p = tl->l, len = 0;
213		    len < BSZ && (ch = getc(fp)) != EOF; ++len)
214			*p++ = ch;
215
216		/*
217		 * If no input data for this block and we tossed some data,
218		 * recover it.
219		 */
220		if (!len) {
221			if (enomem)
222				enomem -= tl->len;
223			tl = tl->prev;
224			break;
225		}
226
227		tl->len = len;
228		if (ch == EOF)
229			break;
230	}
231
232	if (enomem) {
233		(void)fprintf(stderr,
234		    "tail: warning: %lld bytes discarded\n", (long long)enomem);
235		rval = 1;
236	}
237
238	/*
239	 * Step through the blocks in the reverse order read.  The last char
240	 * is special, ignore whether newline or not.
241	 */
242	for (mark = tl;;) {
243		for (p = tl->l + (len = tl->len) - 1, llen = 0; len--;
244		    --p, ++llen)
245			if (*p == '\n') {
246				if (llen) {
247					WR(p + 1, llen);
248					llen = 0;
249				}
250				if (tl == mark)
251					continue;
252				for (tr = tl->next; tr->len; tr = tr->next) {
253					WR(tr->l, tr->len);
254					tr->len = 0;
255					if (tr == mark)
256						break;
257				}
258			}
259		tl->len = llen;
260		if ((tl = tl->prev) == mark)
261			break;
262	}
263	tl = tl->next;
264	if (tl->len) {
265		WR(tl->l, tl->len);
266		tl->len = 0;
267	}
268	while ((tl = tl->next)->len) {
269		WR(tl->l, tl->len);
270		tl->len = 0;
271	}
272
273	tl->prev->next = NULL;
274	while (tl != NULL) {
275		tr = tl->next;
276		free(tl);
277		tl = tr;
278	}
279}
280