cache.c

   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
  21 struct 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  */
  42 static 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 */
  69 static 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). */
  82 static 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 */
 103 static 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  */
 114 static 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 */
 126 static 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  */
 142 static 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  */
 157 static 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  */
 175 static 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
 209 unsigned 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
 224 static 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. */
 311 int 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  */
 366 static char *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
 378 int 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 */
 432 void 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