1 files changed, 475 insertions, 0 deletions
diff --git a/www/git.causal.agency/cgit/cache.c b/www/git.causal.agency/cgit/cache.c
new file mode 100644
index 00000000..578b73b0
--- /dev/null
+++ b/www/git.causal.agency/cgit/cache.c
@@ -0,0 +1,475 @@
+/* cache.c: cache management
+ *
+ * Copyright (C) 2006-2014 cgit Development Team <cgit@lists.zx2c4.com>
+ *
+ * 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"
+#include "html.h"
+#ifdef HAVE_LINUX_SENDFILE
+#include <sys/sendfile.h>
+#endif
+
+#define CACHE_BUFSIZE (1024 * 4)
+
+struct cache_slot {
+	const char *key;
+	size_t keylen;
+	int ttl;
+	cache_fill_fn fn;
+	int cache_fd;
+	int lock_fd;
+	int stdout_fd;
+	const char *cache_name;
+	const char *lock_name;
+	int match;
+	struct stat cache_st;
+	int bufsize;
+	char buf[CACHE_BUFSIZE];
+};
+
+/* 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)
+{
+	char *bufz;
+	ssize_t 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 = xread(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;
+
+	if (slot->key)
+		slot->match = bufkeylen == slot->keylen &&
+		    !memcmp(slot->key, slot->buf, bufkeylen + 1);
+
+	return 0;
+}
+
+/* Close the active cache slot */
+static int close_slot(struct cache_slot *slot)
+{
+	int err = 0;
+	if (slot->cache_fd > 0) {
+		if (close(slot->cache_fd))
+			err = errno;
+		else
+			slot->cache_fd = -1;
+	}
+	return err;
+}
+
+/* Print the content of the active cache slot (but skip the key). */
+static int print_slot(struct cache_slot *slot)
+{
+#ifdef HAVE_LINUX_SENDFILE
+	off_t start_off;
+	int ret;
+
+	start_off = slot->keylen + 1;
+
+	do {
+		ret = sendfile(STDOUT_FILENO, slot->cache_fd, &start_off,
+				slot->cache_st.st_size - start_off);
+		if (ret < 0) {
+			if (errno == EAGAIN || errno == EINTR)
+				continue;
+			return errno;
+		}
+		return 0;
+	} while (1);
+#else
+	ssize_t i, j;
+
+	i = lseek(slot->cache_fd, slot->keylen + 1, SEEK_SET);
+	if (i != slot->keylen + 1)
+		return errno;
+
+	do {
+		i = j = xread(slot->cache_fd, slot->buf, sizeof(slot->buf));
+		if (i > 0)
+			j = xwrite(STDOUT_FILENO, slot->buf, i);
+	} while (i > 0 && j == i);
+
+	if (i < 0 || j != i)
+		return errno;
+	else
+		return 0;
+#endif
+}
+
+/* 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);
+}
+
+/* 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 (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);
+}
+
+/* Close an open lockfile */
+static int close_lock(struct cache_slot *slot)
+{
+	int err = 0;
+	if (slot->lock_fd > 0) {
+		if (close(slot->lock_fd))
+			err = errno;
+		else
+			slot->lock_fd = -1;
+	}
+	return err;
+}
+
+/* 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 flock lock = {
+		.l_type = F_WRLCK,
+		.l_whence = SEEK_SET,
+		.l_start = 0,
+		.l_len = 0,
+	};
+
+	slot->lock_fd = open(slot->lock_name, O_RDWR | O_CREAT,
+			     S_IRUSR | S_IWUSR);
+	if (slot->lock_fd == -1)
+		return errno;
+	if (fcntl(slot->lock_fd, F_SETLK, &lock) < 0) {
+		int saved_errno = errno;
+		close(slot->lock_fd);
+		slot->lock_fd = -1;
+		return saved_errno;
+	}
+	if (xwrite(slot->lock_fd, slot->key, slot->keylen + 1) < 0)
+		return errno;
+	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
+		err = unlink(slot->lock_name);
+
+	/* Restore stdout and close the temporary FD. */
+	if (slot->stdout_fd >= 0) {
+		dup2(slot->stdout_fd, STDOUT_FILENO);
+		close(slot->stdout_fd);
+		slot->stdout_fd = -1;
+	}
+
+	if (err)
+		return errno;
+
+	return 0;
+}
+
+/* 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)
+{
+	/* Preserve stdout */
+	slot->stdout_fd = dup(STDOUT_FILENO);
+	if (slot->stdout_fd == -1)
+		return errno;
+
+	/* Redirect stdout to lockfile */
+	if (dup2(slot->lock_fd, STDOUT_FILENO) == -1)
+		return errno;
+
+	/* Generate cache content */
+	slot->fn();
+
+	/* Make sure any buffered data is flushed to the file */
+	if (fflush(stdout))
+		return errno;
+
+	/* update stat info */
+	if (fstat(slot->lock_fd, &slot->cache_st))
+		return errno;
+
+	return 0;
+}
+
+/* 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)
+{
+	unsigned long h = FNV_OFFSET;
+	unsigned char *s = (unsigned char *)str;
+
+	if (!s)
+		return h;
+
+	while (*s) {
+		h *= FNV_PRIME;
+		h ^= *s++;
+	}
+	return h;
+}
+
+static int process_slot(struct cache_slot *slot)
+{
+	int err;
+
+	/*
+	 * Make sure any buffered data is flushed before we redirect,
+	 * do sendfile(2) or write(2)
+	 */
+	if (fflush(stdout))
+		return errno;
+
+	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;
+				}
+			}
+		}
+		if ((err = print_slot(slot)) != 0) {
+			cache_log("[cgit] error printing cache %s: %s (%d)\n",
+				  slot->cache_name,
+				  strerror(err),
+				  err);
+		}
+		close_slot(slot);
+		return err;
+	}
+
+	/* 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 believe
+	 * 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();
+		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();
+		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);
+	if ((err = print_slot(slot)) != 0) {
+		cache_log("[cgit] error printing cache %s: %s (%d)\n",
+			  slot->cache_name,
+			  strerror(err),
+			  err);
+	}
+	close_slot(slot);
+	return err;
+}
+
+/* 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)
+{
+	unsigned long hash;
+	int i;
+	struct strbuf filename = STRBUF_INIT;
+	struct strbuf lockname = STRBUF_INIT;
+	struct cache_slot slot;
+	int result;
+
+	/* If the cache is disabled, just generate the content */
+	if (size <= 0 || ttl == 0) {
+		fn();
+		return 0;
+	}
+
+	/* Verify input, calculate filenames */
+	if (!path) {
+		cache_log("[cgit] Cache path not specified, caching is disabled\n");
+		fn();
+		return 0;
+	}
+	if (!key)
+		key = "";
+	hash = hash_str(key) % size;
+	strbuf_addstr(&filename, path);
+	strbuf_ensure_end(&filename, '/');
+	for (i = 0; i < 8; i++) {
+		strbuf_addf(&filename, "%x", (unsigned char)(hash & 0xf));
+		hash >>= 4;
+	}
+	strbuf_addbuf(&lockname, &filename);
+	strbuf_addstr(&lockname, ".lock");
+	slot.fn = fn;
+	slot.ttl = ttl;
+	slot.stdout_fd = -1;
+	slot.cache_name = filename.buf;
+	slot.lock_name = lockname.buf;
+	slot.key = key;
+	slot.keylen = strlen(key);
+	result = process_slot(&slot);
+
+	strbuf_release(&filename);
+	strbuf_release(&lockname);
+	return result;
+}
+
+/* Return a strftime formatted date/time
+ * NB: the result from this function is to shared memory
+ */
+static char *sprintftime(const char *format, time_t time)
+{
+	static char buf[64];
+	struct tm tm;
+
+	if (!time)
+		return NULL;
+	gmtime_r(&time, &tm);
+	strftime(buf, sizeof(buf)-1, format, &tm);
+	return buf;
+}
+
+int cache_ls(const char *path)
+{
+	DIR *dir;
+	struct dirent *ent;
+	int err = 0;
+	struct cache_slot slot = { NULL };
+	struct strbuf fullname = STRBUF_INIT;
+	size_t prefixlen;
+
+	if (!path) {
+		cache_log("[cgit] cache path not specified\n");
+		return -1;
+	}
+	dir = opendir(path);
+	if (!dir) {
+		err = errno;
+		cache_log("[cgit] unable to open path %s: %s (%d)\n",
+			  path, strerror(err), err);
+		return err;
+	}
+	strbuf_addstr(&fullname, path);
+	strbuf_ensure_end(&fullname, '/');
+	prefixlen = fullname.len;
+	while ((ent = readdir(dir)) != NULL) {
+		if (strlen(ent->d_name) != 8)
+			continue;
+		strbuf_setlen(&fullname, prefixlen);
+		strbuf_addstr(&fullname, ent->d_name);
+		slot.cache_name = fullname.buf;
+		if ((err = open_slot(&slot)) != 0) {
+			cache_log("[cgit] unable to open path %s: %s (%d)\n",
+				  fullname.buf, strerror(err), err);
+			continue;
+		}
+		htmlf("%s %s %10"PRIuMAX" %s\n",
+		      fullname.buf,
+		      sprintftime("%Y-%m-%d %H:%M:%S",
+				  slot.cache_st.st_mtime),
+		      (uintmax_t)slot.cache_st.st_size,
+		      slot.buf);
+		close_slot(&slot);
+	}
+	closedir(dir);
+	strbuf_release(&fullname);
+	return 0;
+}
+
+/* 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);
+}
+