| -rw-r--r-- | cache.c | 359 |
1 files changed, 291 insertions, 68 deletions
@@ -4,117 +4,340 @@ * * Licensed under GNU General Public License v2 * (see COPYING for full license text) + * + * + * The cache is just a directory structure where each file is a cache slot, + * and each filename is based on the hash of some key (e.g. the cgit url). + * Each file contains the full key followed by the cached content for that + * key. + * */ #include "cgit.h" #include "cache.h" -const int NOLOCK = -1; +#define CACHE_BUFSIZE (1024 * 4) + +struct cache_slot { + const char *key; + int keylen; + int ttl; + cache_fill_fn fn; + void *cbdata; + int cache_fd; + int lock_fd; + const char *cache_name; + const char *lock_name; + int match; + struct stat cache_st; + struct stat lock_st; + int bufsize; + char buf[CACHE_BUFSIZE]; +}; -char *cache_safe_filename(const char *unsafe) +/* Open an existing cache slot and fill the cache buffer with + * (part of) the content of the cache file. Return 0 on success + * and errno otherwise. + */ +static int open_slot(struct cache_slot *slot) { - static char buf[4][PATH_MAX]; - static int bufidx; - char *s; - char c; - - bufidx++; - bufidx &= 3; - s = buf[bufidx]; - - while(unsafe && (c = *unsafe++) != 0) { - if (c == '/' || c == ' ' || c == '&' || c == '|' || - c == '>' || c == '<' || c == '.') - c = '_'; - *s++ = c; - } - *s = '\0'; - return buf[bufidx]; + char *bufz; + int bufkeylen = -1; + + slot->cache_fd = open(slot->cache_name, O_RDONLY); + if (slot->cache_fd == -1) + return errno; + + if (fstat(slot->cache_fd, &slot->cache_st)) + return errno; + + slot->bufsize = read(slot->cache_fd, slot->buf, sizeof(slot->buf)); + if (slot->bufsize == 0) + return errno; + + bufz = memchr(slot->buf, 0, slot->bufsize); + if (bufz) + bufkeylen = bufz - slot->buf; + + slot->match = bufkeylen == slot->keylen && + !memcmp(slot->key, slot->buf, bufkeylen + 1); + + return 0; } -int cache_exist(struct cacheitem *item) +/* Close the active cache slot */ +static void close_slot(struct cache_slot *slot) { - if (stat(item->name, &item->st)) { - item->st.st_mtime = 0; - return 0; + if (slot->cache_fd > 0) { + close(slot->cache_fd); + slot->cache_fd = -1; } - return 1; } -int cache_create_dirs() +/* Print the content of the active cache slot (but skip the key). */ +static int print_slot(struct cache_slot *slot) { - char *path; + ssize_t i, j = 0; + + i = lseek(slot->cache_fd, slot->keylen + 1, SEEK_SET); + if (i != slot->keylen + 1) + return errno; - path = fmt("%s", ctx.cfg.cache_root); - if (mkdir(path, S_IRWXU) && errno!=EEXIST) + while((i=read(slot->cache_fd, slot->buf, sizeof(slot->buf))) > 0) + j = write(STDOUT_FILENO, slot->buf, i); + + if (j < 0) + return errno; + else return 0; +} - if (!ctx.repo) +/* Check if the slot has expired */ +static int is_expired(struct cache_slot *slot) +{ + if (slot->ttl < 0) return 0; + else + return slot->cache_st.st_mtime + slot->ttl*60 < time(NULL); +} - path = fmt("%s/%s", ctx.cfg.cache_root, - cache_safe_filename(ctx.repo->url)); +/* Check if the slot has been modified since we opened it. + * NB: If stat() fails, we pretend the file is modified. + */ +static int is_modified(struct cache_slot *slot) +{ + struct stat st; - if (mkdir(path, S_IRWXU) && errno!=EEXIST) - return 0; + if (stat(slot->cache_name, &st)) + return 1; + return (st.st_ino != slot->cache_st.st_ino || + st.st_mtime != slot->cache_st.st_mtime || + st.st_size != slot->cache_st.st_size); +} - if (ctx.qry.page) { - path = fmt("%s/%s/%s", ctx.cfg.cache_root, - cache_safe_filename(ctx.repo->url), - ctx.qry.page); - if (mkdir(path, S_IRWXU) && errno!=EEXIST) - return 0; +/* Close an open lockfile */ +static void close_lock(struct cache_slot *slot) +{ + if (slot->lock_fd > 0) { + close(slot->lock_fd); + slot->lock_fd = -1; } - return 1; } -int cache_refill_overdue(const char *lockfile) +/* Create a lockfile used to store the generated content for a cache + * slot, and write the slot key + \0 into it. + * Returns 0 on success and errno otherwise. + */ +static int lock_slot(struct cache_slot *slot) { - struct stat st; + slot->lock_fd = open(slot->lock_name, O_RDWR|O_CREAT|O_EXCL, + S_IRUSR|S_IWUSR); + if (slot->lock_fd == -1) + return errno; + write(slot->lock_fd, slot->key, slot->keylen + 1); + return 0; +} - if (stat(lockfile, &st)) - return 0; +/* Release the current lockfile. If `replace_old_slot` is set the + * lockfile replaces the old cache slot, otherwise the lockfile is + * just deleted. + */ +static int unlock_slot(struct cache_slot *slot, int replace_old_slot) +{ + int err; + + if (replace_old_slot) + err = rename(slot->lock_name, slot->cache_name); else - return (time(NULL) - st.st_mtime > ctx.cfg.cache_max_create_time); + err = unlink(slot->lock_name); + return err; } -int cache_lock(struct cacheitem *item) +/* Generate the content for the current cache slot by redirecting + * stdout to the lock-fd and invoking the callback function + */ +static int fill_slot(struct cache_slot *slot) { - int i = 0; - char *lockfile = xstrdup(fmt("%s.lock", item->name)); + int tmp; - top: - if (++i > ctx.cfg.max_lock_attempts) - die("cache_lock: unable to lock %s: %s", - item->name, strerror(errno)); + /* Preserve stdout */ + tmp = dup(STDOUT_FILENO); + if (tmp == -1) + return errno; - item->fd = open(lockfile, O_WRONLY|O_CREAT|O_EXCL, S_IRUSR|S_IWUSR); + /* Redirect stdout to lockfile */ + if (dup2(slot->lock_fd, STDOUT_FILENO) == -1) + return errno; - if (item->fd == NOLOCK && errno == ENOENT && cache_create_dirs()) - goto top; + /* Generate cache content */ + slot->fn(slot->cbdata); - if (item->fd == NOLOCK && errno == EEXIST && - cache_refill_overdue(lockfile) && !unlink(lockfile)) - goto top; + /* Restore stdout */ + if (dup2(tmp, STDOUT_FILENO) == -1) + return errno; - free(lockfile); - return (item->fd > 0); + /* Close the temporary filedescriptor */ + close(tmp); + return 0; } -int cache_unlock(struct cacheitem *item) +/* Crude implementation of 32-bit FNV-1 hash algorithm, + * see http://www.isthe.com/chongo/tech/comp/fnv/ for details + * about the magic numbers. + */ +#define FNV_OFFSET 0x811c9dc5 +#define FNV_PRIME 0x01000193 + +unsigned long hash_str(const char *str) { - close(item->fd); - return (rename(fmt("%s.lock", item->name), item->name) == 0); + unsigned long h = FNV_OFFSET; + unsigned char *s = (unsigned char *)str; + + if (!s) + return h; + + while(*s) { + h *= FNV_PRIME; + h ^= *s++; + } + return h; } -int cache_cancel_lock(struct cacheitem *item) +static int process_slot(struct cache_slot *slot) { - return (unlink(fmt("%s.lock", item->name)) == 0); + int err; + + err = open_slot(slot); + if (!err && slot->match) { + if (is_expired(slot)) { + if (!lock_slot(slot)) { + /* If the cachefile has been replaced between + * `open_slot` and `lock_slot`, we'll just + * serve the stale content from the original + * cachefile. This way we avoid pruning the + * newly generated slot. The same code-path + * is chosen if fill_slot() fails for some + * reason. + * + * TODO? check if the new slot contains the + * same key as the old one, since we would + * prefer to serve the newest content. + * This will require us to open yet another + * file-descriptor and read and compare the + * key from the new file, so for now we're + * lazy and just ignore the new file. + */ + if (is_modified(slot) || fill_slot(slot)) { + unlock_slot(slot, 0); + close_lock(slot); + } else { + close_slot(slot); + unlock_slot(slot, 1); + slot->cache_fd = slot->lock_fd; + } + } + } + print_slot(slot); + close_slot(slot); + return 0; + } + + /* If the cache slot does not exist (or its key doesn't match the + * current key), lets try to create a new cache slot for this + * request. If this fails (for whatever reason), lets just generate + * the content without caching it and fool the caller to belive + * everything worked out (but print a warning on stdout). + */ + + close_slot(slot); + if ((err = lock_slot(slot)) != 0) { + cache_log("[cgit] Unable to lock slot %s: %s (%d)\n", + slot->lock_name, strerror(err), err); + slot->fn(slot->cbdata); + return 0; + } + + if ((err = fill_slot(slot)) != 0) { + cache_log("[cgit] Unable to fill slot %s: %s (%d)\n", + slot->lock_name, strerror(err), err); + unlock_slot(slot, 0); + close_lock(slot); + slot->fn(slot->cbdata); + return 0; + } + // We've got a valid cache slot in the lock file, which + // is about to replace the old cache slot. But if we + // release the lockfile and then try to open the new cache + // slot, we might get a race condition with a concurrent + // writer for the same cache slot (with a different key). + // Lets avoid such a race by just printing the content of + // the lock file. + slot->cache_fd = slot->lock_fd; + unlock_slot(slot, 1); + err = print_slot(slot); + close_slot(slot); + return err; } -int cache_expired(struct cacheitem *item) +/* Print cached content to stdout, generate the content if necessary. */ +int cache_process(int size, const char *path, const char *key, int ttl, + cache_fill_fn fn, void *cbdata) { - if (item->ttl < 0) + unsigned long hash; + int len, i; + char filename[1024]; + char lockname[1024 + 5]; /* 5 = ".lock" */ + struct cache_slot slot; + + /* If the cache is disabled, just generate the content */ + if (size <= 0) { + fn(cbdata); return 0; - return item->st.st_mtime + item->ttl * 60 < time(NULL); + } + + /* Verify input, calculate filenames */ + if (!path) { + cache_log("[cgit] Cache path not specified, caching is disabled\n"); + fn(cbdata); + return 0; + } + len = strlen(path); + if (len > sizeof(filename) - 10) { /* 10 = "/01234567\0" */ + cache_log("[cgit] Cache path too long, caching is disabled: %s\n", + path); + fn(cbdata); + return 0; + } + if (!key) + key = ""; + hash = hash_str(key) % size; + strcpy(filename, path); + if (filename[len - 1] != '/') + filename[len++] = '/'; + for(i = 0; i < 8; i++) { + sprintf(filename + len++, "%x", + (unsigned char)(hash & 0xf)); + hash >>= 4; + } + filename[len] = '\0'; + strcpy(lockname, filename); + strcpy(lockname + len, ".lock"); + slot.fn = fn; + slot.cbdata = cbdata; + slot.ttl = ttl; + slot.cache_name = filename; + slot.lock_name = lockname; + slot.key = key; + slot.keylen = strlen(key); + return process_slot(&slot); } + +/* Print a message to stdout */ +void cache_log(const char *format, ...) +{ + va_list args; + va_start(args, format); + vfprintf(stderr, format, args); + va_end(args); +} + |