1/* vi: set sw=4 ts=4: */
2/*
3 * Mini tail implementation for busybox
4 *
5 * Copyright (C) 2001 by Matt Kraai <kraai@alumni.carnegiemellon.edu>
6 *
7 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
8 */
9
10/* BB_AUDIT SUSv3 compliant (need fancy for -c) */
11/* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
12/* http://www.opengroup.org/onlinepubs/007904975/utilities/tail.html */
13
14/* Mar 16, 2003      Manuel Novoa III   (mjn3@codepoet.org)
15 *
16 * Pretty much rewritten to fix numerous bugs and reduce realloc() calls.
17 * Bugs fixed (although I may have forgotten one or two... it was pretty bad)
18 * 1) mixing printf/write without fflush()ing stdout
19 * 2) no check that any open files are present
20 * 3) optstring had -q taking an arg
21 * 4) no error checking on write in some cases, and a warning even then
22 * 5) q and s interaction bug
23 * 6) no check for lseek error
24 * 7) lseek attempted when count==0 even if arg was +0 (from top)
25 */
26
27#include "libbb.h"
28
29static const struct suffix_mult tail_suffixes[] = {
30	{ "b", 512 },
31	{ "k", 1024 },
32	{ "m", 1024*1024 },
33	{ "", 0 }
34};
35
36struct globals {
37	bool status;
38} FIX_ALIASING;
39#define G (*(struct globals*)&bb_common_bufsiz1)
40
41static void tail_xprint_header(const char *fmt, const char *filename)
42{
43	if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
44		bb_perror_nomsg_and_die();
45}
46
47static ssize_t tail_read(int fd, char *buf, size_t count)
48{
49	ssize_t r;
50	off_t current;
51	struct stat sbuf;
52
53	/* /proc files report zero st_size, don't lseek them. */
54	if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
55		current = lseek(fd, 0, SEEK_CUR);
56		if (sbuf.st_size < current)
57			xlseek(fd, 0, SEEK_SET);
58	}
59
60	r = full_read(fd, buf, count);
61	if (r < 0) {
62		bb_perror_msg(bb_msg_read_error);
63		G.status = EXIT_FAILURE;
64	}
65
66	return r;
67}
68
69#define header_fmt_str "\n==> %s <==\n"
70
71static unsigned eat_num(const char *p)
72{
73	if (*p == '-')
74		p++;
75	else if (*p == '+') {
76		p++;
77		G.status = 1; /* mark that we saw "+" */
78	}
79	return xatou_sfx(p, tail_suffixes);
80}
81
82int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
83int tail_main(int argc, char **argv)
84{
85	unsigned count = 10;
86	unsigned sleep_period = 1;
87	bool from_top;
88	const char *str_c, *str_n;
89
90	char *tailbuf;
91	size_t tailbufsize;
92	unsigned header_threshhold = 1;
93	unsigned nfiles;
94	int i, opt;
95
96	int *fds;
97	const char *fmt;
98
99#if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
100	/* Allow legacy syntax of an initial numeric option without -n. */
101	if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
102	 && isdigit(argv[1][1])
103	) {
104		count = eat_num(argv[1]);
105		argv++;
106		argc--;
107	}
108#endif
109
110	/* -s NUM, -F imlies -f */
111	IF_FEATURE_FANCY_TAIL(opt_complementary = "s+:Ff";)
112	opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:vF"),
113			&str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
114#define FOLLOW (opt & 0x1)
115#define COUNT_BYTES (opt & 0x2)
116	//if (opt & 0x1) // -f
117	if (opt & 0x2) count = eat_num(str_c); // -c
118	if (opt & 0x4) count = eat_num(str_n); // -n
119#if ENABLE_FEATURE_FANCY_TAIL
120	/* q: make it impossible for nfiles to be > header_threshhold */
121	if (opt & 0x8) header_threshhold = UINT_MAX; // -q
122	//if (opt & 0x10) // -s
123	if (opt & 0x20) header_threshhold = 0; // -v
124# define FOLLOW_RETRY (opt & 0x40)
125#else
126# define FOLLOW_RETRY 0
127#endif
128	argc -= optind;
129	argv += optind;
130	from_top = G.status; /* 1 if there was "-c +N" or "-n +N" */
131	G.status = EXIT_SUCCESS;
132
133	/* open all the files */
134	fds = xmalloc(sizeof(fds[0]) * (argc + 1));
135	if (!argv[0]) {
136		struct stat statbuf;
137
138		if (fstat(STDIN_FILENO, &statbuf) == 0
139		 && S_ISFIFO(statbuf.st_mode)
140		) {
141			opt &= ~1; /* clear FOLLOW */
142		}
143		argv[0] = (char *) bb_msg_standard_input;
144	}
145	nfiles = i = 0;
146	do {
147		int fd = open_or_warn_stdin(argv[i]);
148		if (fd < 0 && !FOLLOW_RETRY) {
149			G.status = EXIT_FAILURE;
150			continue;
151		}
152		fds[nfiles] = fd;
153		argv[nfiles++] = argv[i];
154	} while (++i < argc);
155
156	if (!nfiles)
157		bb_error_msg_and_die("no files");
158
159	/* prepare the buffer */
160	tailbufsize = BUFSIZ;
161	if (!from_top && COUNT_BYTES) {
162		if (tailbufsize < count + BUFSIZ) {
163			tailbufsize = count + BUFSIZ;
164		}
165	}
166	tailbuf = xmalloc(tailbufsize);
167
168	/* tail the files */
169	fmt = header_fmt_str + 1; /* skip header leading newline on first output */
170	i = 0;
171	do {
172		char *buf;
173		int taillen;
174		int newlines_seen;
175		unsigned seen;
176		int nread;
177		int fd = fds[i];
178
179		if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
180			continue; /* may happen with -E */
181
182		if (nfiles > header_threshhold) {
183			tail_xprint_header(fmt, argv[i]);
184			fmt = header_fmt_str;
185		}
186
187		if (!from_top) {
188			off_t current = lseek(fd, 0, SEEK_END);
189			if (current > 0) {
190				unsigned off;
191				if (COUNT_BYTES) {
192				/* Optimizing count-bytes case if the file is seekable.
193				 * Beware of backing up too far.
194				 * Also we exclude files with size 0 (because of /proc/xxx) */
195					if (count == 0)
196						continue; /* showing zero bytes is easy :) */
197					current -= count;
198					if (current < 0)
199						current = 0;
200					xlseek(fd, current, SEEK_SET);
201					bb_copyfd_size(fd, STDOUT_FILENO, count);
202					continue;
203				}
204#if 1 /* This is technically incorrect for *LONG* strings, but very useful */
205				/* Optimizing count-lines case if the file is seekable.
206				 * We assume the lines are <64k.
207				 * (Users complain that tail takes too long
208				 * on multi-gigabyte files) */
209				off = (count | 0xf); /* for small counts, be more paranoid */
210				if (off > (INT_MAX / (64*1024)))
211					off = (INT_MAX / (64*1024));
212				current -= off * (64*1024);
213				if (current < 0)
214					current = 0;
215				xlseek(fd, current, SEEK_SET);
216#endif
217			}
218		}
219
220		buf = tailbuf;
221		taillen = 0;
222		/* "We saw 1st line/byte".
223		 * Used only by +N code ("start from Nth", 1-based): */
224		seen = 1;
225		newlines_seen = 0;
226		while ((nread = tail_read(fd, buf, tailbufsize-taillen)) > 0) {
227			if (from_top) {
228				int nwrite = nread;
229				if (seen < count) {
230					/* We need to skip a few more bytes/lines */
231					if (COUNT_BYTES) {
232						nwrite -= (count - seen);
233						seen = count;
234					} else {
235						char *s = buf;
236						do {
237							--nwrite;
238							if (*s++ == '\n' && ++seen == count) {
239								break;
240							}
241						} while (nwrite);
242					}
243				}
244				if (nwrite > 0)
245					xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
246			} else if (count) {
247				if (COUNT_BYTES) {
248					taillen += nread;
249					if (taillen > (int)count) {
250						memmove(tailbuf, tailbuf + taillen - count, count);
251						taillen = count;
252					}
253				} else {
254					int k = nread;
255					int newlines_in_buf = 0;
256
257					do { /* count '\n' in last read */
258						k--;
259						if (buf[k] == '\n') {
260							newlines_in_buf++;
261						}
262					} while (k);
263
264					if (newlines_seen + newlines_in_buf < (int)count) {
265						newlines_seen += newlines_in_buf;
266						taillen += nread;
267					} else {
268						int extra = (buf[nread-1] != '\n');
269						char *s;
270
271						k = newlines_seen + newlines_in_buf + extra - count;
272						s = tailbuf;
273						while (k) {
274							if (*s == '\n') {
275								k--;
276							}
277							s++;
278						}
279						taillen += nread - (s - tailbuf);
280						memmove(tailbuf, s, taillen);
281						newlines_seen = count - extra;
282					}
283					if (tailbufsize < (size_t)taillen + BUFSIZ) {
284						tailbufsize = taillen + BUFSIZ;
285						tailbuf = xrealloc(tailbuf, tailbufsize);
286					}
287				}
288				buf = tailbuf + taillen;
289			}
290		} /* while (tail_read() > 0) */
291		if (!from_top) {
292			xwrite(STDOUT_FILENO, tailbuf, taillen);
293		}
294	} while (++i < nfiles);
295
296	tailbuf = xrealloc(tailbuf, BUFSIZ);
297
298	fmt = NULL;
299
300	if (FOLLOW) while (1) {
301		sleep(sleep_period);
302
303		i = 0;
304		do {
305			int nread;
306			const char *filename = argv[i];
307			int fd = fds[i];
308
309			if (FOLLOW_RETRY) {
310				struct stat sbuf, fsbuf;
311
312				if (fd < 0
313				 || fstat(fd, &fsbuf) < 0
314				 || stat(filename, &sbuf) < 0
315				 || fsbuf.st_dev != sbuf.st_dev
316				 || fsbuf.st_ino != sbuf.st_ino
317				) {
318					int new_fd;
319
320					if (fd >= 0)
321						close(fd);
322					new_fd = open(filename, O_RDONLY);
323					if (new_fd >= 0) {
324						bb_error_msg("%s has %s; following end of new file",
325							filename, (fd < 0) ? "appeared" : "been replaced"
326						);
327					} else if (fd >= 0) {
328						bb_perror_msg("%s has become inaccessible", filename);
329					}
330					fds[i] = fd = new_fd;
331				}
332			}
333			if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
334				continue;
335			if (nfiles > header_threshhold) {
336				fmt = header_fmt_str;
337			}
338			while ((nread = tail_read(fd, tailbuf, BUFSIZ)) > 0) {
339				if (fmt) {
340					tail_xprint_header(fmt, filename);
341					fmt = NULL;
342				}
343				xwrite(STDOUT_FILENO, tailbuf, nread);
344			}
345		} while (++i < nfiles);
346	}
347	if (ENABLE_FEATURE_CLEAN_UP) {
348		free(fds);
349	}
350	return G.status;
351}
352