chiark / gitweb /
choose: Select tracks uniformly at random.
[disorder] / server / choose.c
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1/*
2 * This file is part of DisOrder
3 * Copyright (C) 2008 Richard Kettlewell
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
9 *
10 * This program is distributed in the hope that it will be useful, but
11 * WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 * General Public License for more details.
14 *
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
18 * USA
19 */
20/** @file choose.c
21 * @brief Random track chooser
22 *
23 * Picks a track at random and writes it to standard output. If for
24 * any reason no track can be picked - even a trivial reason like a
25 * deadlock - it just exits and expects the server to try again.
26 */
27
28#include <config.h>
29#include "types.h"
30
31#include <getopt.h>
32#include <stdio.h>
33#include <stdlib.h>
34#include <db.h>
35#include <locale.h>
36#include <errno.h>
37#include <sys/types.h>
38#include <unistd.h>
39#include <pcre.h>
40#include <string.h>
41#include <fcntl.h>
42#include <syslog.h>
43#include <time.h>
44
45#include "configuration.h"
46#include "log.h"
47#include "defs.h"
48#include "mem.h"
49#include "kvp.h"
50#include "syscalls.h"
51#include "printf.h"
52#include "trackdb.h"
53#include "trackdb-int.h"
54#include "version.h"
55#include "trackname.h"
56#include "queue.h"
57#include "server-queue.h"
58
59static DB_TXN *global_tid;
60
61static const struct option options[] = {
62 { "help", no_argument, 0, 'h' },
63 { "version", no_argument, 0, 'V' },
64 { "config", required_argument, 0, 'c' },
65 { "debug", no_argument, 0, 'd' },
66 { "no-debug", no_argument, 0, 'D' },
67 { "syslog", no_argument, 0, 's' },
68 { "no-syslog", no_argument, 0, 'S' },
69 { 0, 0, 0, 0 }
70};
71
72/* display usage message and terminate */
73static void help(void) {
74 xprintf("Usage:\n"
75 " disorder-choose [OPTIONS]\n"
76 "Options:\n"
77 " --help, -h Display usage message\n"
78 " --version, -V Display version number\n"
79 " --config PATH, -c PATH Set configuration file\n"
80 " --debug, -d Turn on debugging\n"
81 " --[no-]syslog Enable/disable logging to syslog\n"
82 "\n"
83 "Track choose for DisOrder. Not intended to be run\n"
84 "directly.\n");
85 xfclose(stdout);
86 exit(0);
87}
88
89/** @brief Weighted track record */
90struct weighted_track {
91 /** @brief Next track in the list */
92 struct weighted_track *next;
93 /** @brief Track name */
94 const char *track;
95 /** @brief Weight for this track (always positive) */
96 unsigned long weight;
97};
98
99/** @brief List of tracks with nonzero weight */
100static struct weighted_track *tracks;
101
102/** @brief Sum of all weights */
103static unsigned long long total_weight;
104
105/** @brief Count of tracks */
106static long ntracks;
107
108static char **required_tags;
109static char **prohibited_tags;
110
111static int queue_contains(const struct queue_entry *head,
112 const char *track) {
113 const struct queue_entry *q;
114
115 for(q = head->next; q != head; q = q->next)
116 if(!strcmp(q->track, track))
117 return 1;
118 return 0;
119}
120
121/** @brief Compute the weight of a track
122 * @param track Track name (UTF-8)
123 * @param data Track data
124 * @param prefs Track preferences
125 * @return Track weight (non-negative)
126 *
127 * Tracks to be excluded entirely are given a weight of 0.
128 */
129static unsigned long compute_weight(const char *track,
130 struct kvp *data,
131 struct kvp *prefs) {
132 const char *s;
133 char **track_tags;
134 time_t last, now;
135
136 /* Reject tracks not in any collection (race between edit config and
137 * rescan) */
138 if(!find_track_root(track)) {
139 info("found track not in any collection: %s", track);
140 return 0;
141 }
142
143 /* Reject aliases to avoid giving aliased tracks extra weight */
144 if(kvp_get(data, "_alias_for"))
145 return 0;
146
147 /* Reject tracks with random play disabled */
148 if((s = kvp_get(prefs, "pick_at_random"))
149 && !strcmp(s, "0"))
150 return 0;
151
152 /* Reject tracks played within the last 8 hours */
153 if((s = kvp_get(prefs, "played_time"))) {
154 last = atoll(s);
155 now = time(0);
156 if(now < last + config->replay_min)
157 return 0;
158 }
159
160 /* Reject tracks currently in the queue or in the recent list */
161 if(queue_contains(&qhead, track)
162 || queue_contains(&phead, track))
163 return 0;
164
165 /* We'll need tags for a number of things */
166 track_tags = parsetags(kvp_get(prefs, "tags"));
167
168 /* Reject tracks with prohibited tags */
169 if(prohibited_tags && tag_intersection(track_tags, prohibited_tags))
170 return 0;
171
172 /* Reject tracks that lack required tags */
173 if(*required_tags && !tag_intersection(track_tags, required_tags))
174 return 0;
175
176 /* Use the configured weight if available */
177 if((s = kvp_get(prefs, "weight"))) {
178 long n;
179 errno = 0;
180
181 n = strtol(s, 0, 10);
182 if((errno == 0 || errno == ERANGE) && n >= 0)
183 return n;
184 }
185
186 return 90000;
187}
188
189/** @brief Called for each track */
190static int collect_tracks_callback(const char *track,
191 struct kvp *data,
192 struct kvp *prefs,
193 void attribute((unused)) *u,
194 DB_TXN attribute((unused)) *tid) {
195 unsigned long weight = compute_weight(track, data, prefs);
196
197 if(weight) {
198 struct weighted_track *const t = xmalloc(sizeof *t);
199
200 /* Clamp weight so that we can fit in billions of tracks when we do
201 * arithmetic in long long */
202 if(weight > 0x7fffffff)
203 weight = 0x7fffffff;
204 t->next = tracks;
205 t->track = track;
206 t->weight = weight;
207 tracks = t;
208 total_weight += weight;
209 ++ntracks;
210 }
211 return 0;
212}
213
214/** @brief Pick a random integer uniformly from [0, limit) */
215static void random_bytes(unsigned char *buf, size_t n) {
216 static int fd = -1;
217 int r;
218
219 if(fd < 0) {
220 if((fd = open("/dev/urandom", O_RDONLY)) < 0)
221 fatal(errno, "opening /dev/urandom");
222 }
223 if((r = read(fd, buf, n)) < 0)
224 fatal(errno, "reading /dev/urandom");
225 if((size_t)r < n)
226 fatal(0, "short read from /dev/urandom");
227}
228
229/** @brief Pick a random integer uniformly from [0, limit) */
230static unsigned long long pick_weight(unsigned long long limit) {
231 unsigned char buf[(sizeof(unsigned long long) * CHAR_BIT + 7)/8], m;
232 unsigned long long t, r, slop;
233 int i, nby, nbi;
234
235 //info("pick_weight: limit = %llu", limit);
236
237 /* First, decide how many bits of output we actually need; do bytes first
238 * (they're quicker) and then bits.
239 *
240 * To speed this up, we could use a binary search if we knew where to
241 * start. (Note that shifting by ULLONG_BITS or more (if such a constant
242 * existed) is undefined behaviour, so we mustn't do that.) Figuring out a
243 * start point involves preprocessor and/or autoconf magic.
244 */
245 for (nby = 1, t = (limit - 1) >> 8; t; nby++, t >>= 8)
246 ;
247 nbi = (nby - 1) << 3; t = limit >> nbi;
248 if (t >> 4) { t >>= 4; nbi += 4; }
249 if (t >> 2) { t >>= 2; nbi += 2; }
250 if (t >> 1) { t >>= 1; nbi += 1; }
251 nbi++;
252 //info("nby = %d; nbi = %d", nby, nbi);
253
254 /* Main randomness collection loop. We read a number of bytes from the
255 * randomness source, and glue them together into an integer (dropping
256 * bits off the top byte as necessary). Call the result r; we have
257 * 2^{nbi - 1) <= limit < 2^nbi and r < 2^nbi. If r < limit then we win;
258 * otherwise we try again. Given the above bounds, we expect fewer than 2
259 * iterations.
260 *
261 * Unfortunately there are subtleties. In particular, 2^nbi may in fact be
262 * zero due to overflow. So in fact what we do is compute slop = 2^nbi -
263 * limit > 0; if r < slop then we try again, otherwise r - slop is our
264 * winner.
265 */
266 slop = (2 << (nbi - 1)) - limit;
267 m = nbi & 7 ? (1 << (nbi & 7)) - 1 : 0xff;
268 //info("slop = %llu", slop);
269 //info("m = 0x%02x", m);
270
271 do {
272 /* Actually get some random data. */
273 random_bytes(buf, nby);
274
275 /* Clobber the top byte. */
276 buf[0] &= m;
277
278 /* Turn it into an integer. */
279 for (r = 0, i = 0; i < nby; i++)
280 r = (r << 8) | buf[i];
281 //info("r = %llu", r);
282 } while (r < slop);
283
284 return r - slop;
285}
286
287/** @brief Pick a track at random and write it to stdout */
288static void pick_track(void) {
289 long long w;
290 struct weighted_track *t;
291
292 w = pick_weight(total_weight);
293 t = tracks;
294 while(t && w >= t->weight) {
295 w -= t->weight;
296 t = t->next;
297 }
298 if(!t)
299 fatal(0, "ran out of tracks but %lld weighting left", w);
300 xprintf("%s", t->track);
301}
302
303int main(int argc, char **argv) {
304 int n, logsyslog = !isatty(2), err;
305 const char *tags;
306
307 set_progname(argv);
308 mem_init();
309 if(!setlocale(LC_CTYPE, "")) fatal(errno, "error calling setlocale");
310 while((n = getopt_long(argc, argv, "hVc:dDSs", options, 0)) >= 0) {
311 switch(n) {
312 case 'h': help();
313 case 'V': version("disorder-choose");
314 case 'c': configfile = optarg; break;
315 case 'd': debugging = 1; break;
316 case 'D': debugging = 0; break;
317 case 'S': logsyslog = 0; break;
318 case 's': logsyslog = 1; break;
319 default: fatal(0, "invalid option");
320 }
321 }
322 if(logsyslog) {
323 openlog(progname, LOG_PID, LOG_DAEMON);
324 log_default = &log_syslog;
325 }
326 if(config_read(0)) fatal(0, "cannot read configuration");
327 /* Find out current queue/recent list */
328 queue_read();
329 recent_read();
330 /* Generate the candidate track list */
331 trackdb_init(TRACKDB_NO_RECOVER);
332 trackdb_open(TRACKDB_NO_UPGRADE|TRACKDB_READ_ONLY);
333 global_tid = trackdb_begin_transaction();
334 if((err = trackdb_get_global_tid("required-tags", global_tid, &tags)))
335 fatal(0, "error getting required-tags: %s", db_strerror(err));
336 required_tags = parsetags(tags);
337 if((err = trackdb_get_global_tid("prohibited-tags", global_tid, &tags)))
338 fatal(0, "error getting prohibited-tags: %s", db_strerror(err));
339 prohibited_tags = parsetags(tags);
340 if(trackdb_scan(0, collect_tracks_callback, 0, global_tid))
341 exit(1);
342 trackdb_commit_transaction(global_tid);
343 trackdb_close();
344 trackdb_deinit();
345 //info("ntracks=%ld total_weight=%lld", ntracks, total_weight);
346 if(!total_weight)
347 fatal(0, "no tracks match random choice criteria");
348 /* Pick a track */
349 pick_track();
350 xfclose(stdout);
351 return 0;
352}
353
354/*
355Local Variables:
356c-basic-offset:2
357comment-column:40
358fill-column:79
359indent-tabs-mode:nil
360End:
361*/