cache.c (view raw)
1/* cache.c: cache management
2 *
3 * Copyright (C) 2006 Lars Hjemli
4 *
5 * Licensed under GNU General Public License v2
6 * (see COPYING for full license text)
7 *
8 *
9 * The cache is just a directory structure where each file is a cache slot,
10 * and each filename is based on the hash of some key (e.g. the cgit url).
11 * Each file contains the full key followed by the cached content for that
12 * key.
13 *
14 */
15
16#include "cgit.h"
17#include "cache.h"
18
19#define CACHE_BUFSIZE (1024 * 4)
20
21struct cache_slot {
22 const char *key;
23 int keylen;
24 int ttl;
25 cache_fill_fn fn;
26 void *cbdata;
27 int cache_fd;
28 int lock_fd;
29 const char *cache_name;
30 const char *lock_name;
31 int match;
32 struct stat cache_st;
33 struct stat lock_st;
34 int bufsize;
35 char buf[CACHE_BUFSIZE];
36};
37
38/* Open an existing cache slot and fill the cache buffer with
39 * (part of) the content of the cache file. Return 0 on success
40 * and errno otherwise.
41 */
42static int open_slot(struct cache_slot *slot)
43{
44 char *bufz;
45 int bufkeylen = -1;
46
47 slot->cache_fd = open(slot->cache_name, O_RDONLY);
48 if (slot->cache_fd == -1)
49 return errno;
50
51 if (fstat(slot->cache_fd, &slot->cache_st))
52 return errno;
53
54 slot->bufsize = xread(slot->cache_fd, slot->buf, sizeof(slot->buf));
55 if (slot->bufsize < 0)
56 return errno;
57
58 bufz = memchr(slot->buf, 0, slot->bufsize);
59 if (bufz)
60 bufkeylen = bufz - slot->buf;
61
62 slot->match = bufkeylen == slot->keylen &&
63 !memcmp(slot->key, slot->buf, bufkeylen + 1);
64
65 return 0;
66}
67
68/* Close the active cache slot */
69static int close_slot(struct cache_slot *slot)
70{
71 int err = 0;
72 if (slot->cache_fd > 0) {
73 if (close(slot->cache_fd))
74 err = errno;
75 else
76 slot->cache_fd = -1;
77 }
78 return err;
79}
80
81/* Print the content of the active cache slot (but skip the key). */
82static int print_slot(struct cache_slot *slot)
83{
84 ssize_t i, j;
85
86 i = lseek(slot->cache_fd, slot->keylen + 1, SEEK_SET);
87 if (i != slot->keylen + 1)
88 return errno;
89
90 do {
91 i = j = xread(slot->cache_fd, slot->buf, sizeof(slot->buf));
92 if (i > 0)
93 j = xwrite(STDOUT_FILENO, slot->buf, i);
94 } while (i > 0 && j == i);
95
96 if (i < 0 || j != i)
97 return errno;
98 else
99 return 0;
100}
101
102/* Check if the slot has expired */
103static int is_expired(struct cache_slot *slot)
104{
105 if (slot->ttl < 0)
106 return 0;
107 else
108 return slot->cache_st.st_mtime + slot->ttl*60 < time(NULL);
109}
110
111/* Check if the slot has been modified since we opened it.
112 * NB: If stat() fails, we pretend the file is modified.
113 */
114static int is_modified(struct cache_slot *slot)
115{
116 struct stat st;
117
118 if (stat(slot->cache_name, &st))
119 return 1;
120 return (st.st_ino != slot->cache_st.st_ino ||
121 st.st_mtime != slot->cache_st.st_mtime ||
122 st.st_size != slot->cache_st.st_size);
123}
124
125/* Close an open lockfile */
126static int close_lock(struct cache_slot *slot)
127{
128 int err = 0;
129 if (slot->lock_fd > 0) {
130 if (close(slot->lock_fd))
131 err = errno;
132 else
133 slot->lock_fd = -1;
134 }
135 return err;
136}
137
138/* Create a lockfile used to store the generated content for a cache
139 * slot, and write the slot key + \0 into it.
140 * Returns 0 on success and errno otherwise.
141 */
142static int lock_slot(struct cache_slot *slot)
143{
144 slot->lock_fd = open(slot->lock_name, O_RDWR|O_CREAT|O_EXCL,
145 S_IRUSR|S_IWUSR);
146 if (slot->lock_fd == -1)
147 return errno;
148 if (xwrite(slot->lock_fd, slot->key, slot->keylen + 1) < 0)
149 return errno;
150 return 0;
151}
152
153/* Release the current lockfile. If `replace_old_slot` is set the
154 * lockfile replaces the old cache slot, otherwise the lockfile is
155 * just deleted.
156 */
157static int unlock_slot(struct cache_slot *slot, int replace_old_slot)
158{
159 int err;
160
161 if (replace_old_slot)
162 err = rename(slot->lock_name, slot->cache_name);
163 else
164 err = unlink(slot->lock_name);
165
166 if (err)
167 return errno;
168
169 return 0;
170}
171
172/* Generate the content for the current cache slot by redirecting
173 * stdout to the lock-fd and invoking the callback function
174 */
175static int fill_slot(struct cache_slot *slot)
176{
177 int tmp;
178
179 /* Preserve stdout */
180 tmp = dup(STDOUT_FILENO);
181 if (tmp == -1)
182 return errno;
183
184 /* Redirect stdout to lockfile */
185 if (dup2(slot->lock_fd, STDOUT_FILENO) == -1)
186 return errno;
187
188 /* Generate cache content */
189 slot->fn(slot->cbdata);
190
191 /* Restore stdout */
192 if (dup2(tmp, STDOUT_FILENO) == -1)
193 return errno;
194
195 /* Close the temporary filedescriptor */
196 if (close(tmp))
197 return errno;
198
199 return 0;
200}
201
202/* Crude implementation of 32-bit FNV-1 hash algorithm,
203 * see http://www.isthe.com/chongo/tech/comp/fnv/ for details
204 * about the magic numbers.
205 */
206#define FNV_OFFSET 0x811c9dc5
207#define FNV_PRIME 0x01000193
208
209unsigned long hash_str(const char *str)
210{
211 unsigned long h = FNV_OFFSET;
212 unsigned char *s = (unsigned char *)str;
213
214 if (!s)
215 return h;
216
217 while(*s) {
218 h *= FNV_PRIME;
219 h ^= *s++;
220 }
221 return h;
222}
223
224static int process_slot(struct cache_slot *slot)
225{
226 int err;
227
228 err = open_slot(slot);
229 if (!err && slot->match) {
230 if (is_expired(slot)) {
231 if (!lock_slot(slot)) {
232 /* If the cachefile has been replaced between
233 * `open_slot` and `lock_slot`, we'll just
234 * serve the stale content from the original
235 * cachefile. This way we avoid pruning the
236 * newly generated slot. The same code-path
237 * is chosen if fill_slot() fails for some
238 * reason.
239 *
240 * TODO? check if the new slot contains the
241 * same key as the old one, since we would
242 * prefer to serve the newest content.
243 * This will require us to open yet another
244 * file-descriptor and read and compare the
245 * key from the new file, so for now we're
246 * lazy and just ignore the new file.
247 */
248 if (is_modified(slot) || fill_slot(slot)) {
249 unlock_slot(slot, 0);
250 close_lock(slot);
251 } else {
252 close_slot(slot);
253 unlock_slot(slot, 1);
254 slot->cache_fd = slot->lock_fd;
255 }
256 }
257 }
258 if ((err = print_slot(slot)) != 0) {
259 cache_log("[cgit] error printing cache %s: %s (%d)\n",
260 slot->cache_name,
261 strerror(err),
262 err);
263 }
264 close_slot(slot);
265 return err;
266 }
267
268 /* If the cache slot does not exist (or its key doesn't match the
269 * current key), lets try to create a new cache slot for this
270 * request. If this fails (for whatever reason), lets just generate
271 * the content without caching it and fool the caller to belive
272 * everything worked out (but print a warning on stdout).
273 */
274
275 close_slot(slot);
276 if ((err = lock_slot(slot)) != 0) {
277 cache_log("[cgit] Unable to lock slot %s: %s (%d)\n",
278 slot->lock_name, strerror(err), err);
279 slot->fn(slot->cbdata);
280 return 0;
281 }
282
283 if ((err = fill_slot(slot)) != 0) {
284 cache_log("[cgit] Unable to fill slot %s: %s (%d)\n",
285 slot->lock_name, strerror(err), err);
286 unlock_slot(slot, 0);
287 close_lock(slot);
288 slot->fn(slot->cbdata);
289 return 0;
290 }
291 // We've got a valid cache slot in the lock file, which
292 // is about to replace the old cache slot. But if we
293 // release the lockfile and then try to open the new cache
294 // slot, we might get a race condition with a concurrent
295 // writer for the same cache slot (with a different key).
296 // Lets avoid such a race by just printing the content of
297 // the lock file.
298 slot->cache_fd = slot->lock_fd;
299 unlock_slot(slot, 1);
300 if ((err = print_slot(slot)) != 0) {
301 cache_log("[cgit] error printing cache %s: %s (%d)\n",
302 slot->cache_name,
303 strerror(err),
304 err);
305 }
306 close_slot(slot);
307 return err;
308}
309
310/* Print cached content to stdout, generate the content if necessary. */
311int cache_process(int size, const char *path, const char *key, int ttl,
312 cache_fill_fn fn, void *cbdata)
313{
314 unsigned long hash;
315 int len, i;
316 char filename[1024];
317 char lockname[1024 + 5]; /* 5 = ".lock" */
318 struct cache_slot slot;
319
320 /* If the cache is disabled, just generate the content */
321 if (size <= 0) {
322 fn(cbdata);
323 return 0;
324 }
325
326 /* Verify input, calculate filenames */
327 if (!path) {
328 cache_log("[cgit] Cache path not specified, caching is disabled\n");
329 fn(cbdata);
330 return 0;
331 }
332 len = strlen(path);
333 if (len > sizeof(filename) - 10) { /* 10 = "/01234567\0" */
334 cache_log("[cgit] Cache path too long, caching is disabled: %s\n",
335 path);
336 fn(cbdata);
337 return 0;
338 }
339 if (!key)
340 key = "";
341 hash = hash_str(key) % size;
342 strcpy(filename, path);
343 if (filename[len - 1] != '/')
344 filename[len++] = '/';
345 for(i = 0; i < 8; i++) {
346 sprintf(filename + len++, "%x",
347 (unsigned char)(hash & 0xf));
348 hash >>= 4;
349 }
350 filename[len] = '\0';
351 strcpy(lockname, filename);
352 strcpy(lockname + len, ".lock");
353 slot.fn = fn;
354 slot.cbdata = cbdata;
355 slot.ttl = ttl;
356 slot.cache_name = filename;
357 slot.lock_name = lockname;
358 slot.key = key;
359 slot.keylen = strlen(key);
360 return process_slot(&slot);
361}
362
363/* Return a strftime formatted date/time
364 * NB: the result from this function is to shared memory
365 */
366char *sprintftime(const char *format, time_t time)
367{
368 static char buf[64];
369 struct tm *tm;
370
371 if (!time)
372 return NULL;
373 tm = gmtime(&time);
374 strftime(buf, sizeof(buf)-1, format, tm);
375 return buf;
376}
377
378int cache_ls(const char *path)
379{
380 DIR *dir;
381 struct dirent *ent;
382 int err = 0;
383 struct cache_slot slot;
384 char fullname[1024];
385 char *name;
386
387 if (!path) {
388 cache_log("[cgit] cache path not specified\n");
389 return -1;
390 }
391 if (strlen(path) > 1024 - 10) {
392 cache_log("[cgit] cache path too long: %s\n",
393 path);
394 return -1;
395 }
396 dir = opendir(path);
397 if (!dir) {
398 err = errno;
399 cache_log("[cgit] unable to open path %s: %s (%d)\n",
400 path, strerror(err), err);
401 return err;
402 }
403 strcpy(fullname, path);
404 name = fullname + strlen(path);
405 if (*(name - 1) != '/') {
406 *name++ = '/';
407 *name = '\0';
408 }
409 slot.cache_name = fullname;
410 while((ent = readdir(dir)) != NULL) {
411 if (strlen(ent->d_name) != 8)
412 continue;
413 strcpy(name, ent->d_name);
414 if ((err = open_slot(&slot)) != 0) {
415 cache_log("[cgit] unable to open path %s: %s (%d)\n",
416 fullname, strerror(err), err);
417 continue;
418 }
419 printf("%s %s %10"PRIuMAX" %s\n",
420 name,
421 sprintftime("%Y-%m-%d %H:%M:%S",
422 slot.cache_st.st_mtime),
423 (uintmax_t)slot.cache_st.st_size,
424 slot.buf);
425 close_slot(&slot);
426 }
427 closedir(dir);
428 return 0;
429}
430
431/* Print a message to stdout */
432void cache_log(const char *format, ...)
433{
434 va_list args;
435 va_start(args, format);
436 vfprintf(stderr, format, args);
437 va_end(args);
438}
439