git/refs.c

#include "cache.h"
#include "refs.h"
#include "object.h"
#include "tag.h"
#include "dir.h"

/* ISSYMREF=01 and ISPACKED=02 are public interfaces */
#define REF_KNOWS_PEELED 04

struct ref_list {
	struct ref_list *next;
	unsigned char flag; /* ISSYMREF? ISPACKED? */
	unsigned char sha1[20];
	unsigned char peeled[20];
	char name[FLEX_ARRAY];
};

static const char *parse_ref_line(char *line, unsigned char *sha1)
{
	/*
	 * 42: the answer to everything.
	 *
	 * In this case, it happens to be the answer to
	 *  40 (length of sha1 hex representation)
	 *  +1 (space in between hex and name)
	 *  +1 (newline at the end of the line)
	 */
	int len = strlen(line) - 42;

	if (len <= 0)
		return NULL;
	if (get_sha1_hex(line, sha1) < 0)
		return NULL;
	if (!isspace(line[40]))
		return NULL;
	line += 41;
	if (isspace(*line))
		return NULL;
	if (line[len] != '\n')
		return NULL;
	line[len] = 0;

	return line;
}

static struct ref_list *add_ref(const char *name, const unsigned char *sha1,
				int flag, struct ref_list *list,
				struct ref_list **new_entry)
{
	int len;
	struct ref_list *entry;

	/* Allocate it and add it in.. */
	len = strlen(name) + 1;
	entry = xmalloc(sizeof(struct ref_list) + len);
	hashcpy(entry->sha1, sha1);
	hashclr(entry->peeled);
	memcpy(entry->name, name, len);
	entry->flag = flag;
	entry->next = list;
	if (new_entry)
		*new_entry = entry;
	return entry;
}

/* merge sort the ref list */
static struct ref_list *sort_ref_list(struct ref_list *list)
{
	int psize, qsize, last_merge_count, cmp;
	struct ref_list *p, *q, *l, *e;
	struct ref_list *new_list = list;
	int k = 1;
	int merge_count = 0;

	if (!list)
		return list;

	do {
		last_merge_count = merge_count;
		merge_count = 0;

		psize = 0;

		p = new_list;
		q = new_list;
		new_list = NULL;
		l = NULL;

		while (p) {
			merge_count++;

			while (psize < k && q->next) {
				q = q->next;
				psize++;
			}
			qsize = k;

			while ((psize > 0) || (qsize > 0 && q)) {
				if (qsize == 0 || !q) {
					e = p;
					p = p->next;
					psize--;
				} else if (psize == 0) {
					e = q;
					q = q->next;
					qsize--;
				} else {
					cmp = strcmp(q->name, p->name);
					if (cmp < 0) {
						e = q;
						q = q->next;
						qsize--;
					} else if (cmp > 0) {
						e = p;
						p = p->next;
						psize--;
					} else {
						if (hashcmp(q->sha1, p->sha1))
							die("Duplicated ref, and SHA1s don't match: %s",
							    q->name);
						warning("Duplicated ref: %s", q->name);
						e = q;
						q = q->next;
						qsize--;
						free(e);
						e = p;
						p = p->next;
						psize--;
					}
				}

				e->next = NULL;

				if (l)
					l->next = e;
				if (!new_list)
					new_list = e;
				l = e;
			}

			p = q;
		};

		k = k * 2;
	} while ((last_merge_count != merge_count) || (last_merge_count != 1));

	return new_list;
}

/*
 * Future: need to be in "struct repository"
 * when doing a full libification.
 */
static struct cached_refs {
	char did_loose;
	char did_packed;
	struct ref_list *loose;
	struct ref_list *packed;
} cached_refs;
static struct ref_list *current_ref;

static struct ref_list *extra_refs;

static void free_ref_list(struct ref_list *list)
{
	struct ref_list *next;
	for ( ; list; list = next) {
		next = list->next;
		free(list);
	}
}

static void invalidate_cached_refs(void)
{
	struct cached_refs *ca = &cached_refs;

	if (ca->did_loose && ca->loose)
		free_ref_list(ca->loose);
	if (ca->did_packed && ca->packed)
		free_ref_list(ca->packed);
	ca->loose = ca->packed = NULL;
	ca->did_loose = ca->did_packed = 0;
}

static void read_packed_refs(FILE *f, struct cached_refs *cached_refs)
{
	struct ref_list *list = NULL;
	struct ref_list *last = NULL;
	char refline[PATH_MAX];
	int flag = REF_ISPACKED;

	while (fgets(refline, sizeof(refline), f)) {
		unsigned char sha1[20];
		const char *name;
		static const char header[] = "# pack-refs with:";

		if (!strncmp(refline, header, sizeof(header)-1)) {
			const char *traits = refline + sizeof(header) - 1;
			if (strstr(traits, " peeled "))
				flag |= REF_KNOWS_PEELED;
			/* perhaps other traits later as well */
			continue;
		}

		name = parse_ref_line(refline, sha1);
		if (name) {
			list = add_ref(name, sha1, flag, list, &last);
			continue;
		}
		if (last &&
		    refline[0] == '^' &&
		    strlen(refline) == 42 &&
		    refline[41] == '\n' &&
		    !get_sha1_hex(refline + 1, sha1))
			hashcpy(last->peeled, sha1);
	}
	cached_refs->packed = sort_ref_list(list);
}

void add_extra_ref(const char *name, const unsigned char *sha1, int flag)
{
	extra_refs = add_ref(name, sha1, flag, extra_refs, NULL);
}

void clear_extra_refs(void)
{
	free_ref_list(extra_refs);
	extra_refs = NULL;
}

static struct ref_list *get_packed_refs(void)
{
	if (!cached_refs.did_packed) {
		FILE *f = fopen(git_path("packed-refs"), "r");
		cached_refs.packed = NULL;
		if (f) {
			read_packed_refs(f, &cached_refs);
			fclose(f);
		}
		cached_refs.did_packed = 1;
	}
	return cached_refs.packed;
}

static struct ref_list *get_ref_dir(const char *base, struct ref_list *list)
{
	DIR *dir = opendir(git_path("%s", base));

	if (dir) {
		struct dirent *de;
		int baselen = strlen(base);
		char *ref = xmalloc(baselen + 257);

		memcpy(ref, base, baselen);
		if (baselen && base[baselen-1] != '/')
			ref[baselen++] = '/';

		while ((de = readdir(dir)) != NULL) {
			unsigned char sha1[20];
			struct stat st;
			int flag;
			int namelen;

			if (de->d_name[0] == '.')
				continue;
			namelen = strlen(de->d_name);
			if (namelen > 255)
				continue;
			if (has_extension(de->d_name, ".lock"))
				continue;
			memcpy(ref + baselen, de->d_name, namelen+1);
			if (stat(git_path("%s", ref), &st) < 0)
				continue;
			if (S_ISDIR(st.st_mode)) {
				list = get_ref_dir(ref, list);
				continue;
			}
			if (!resolve_ref(ref, sha1, 1, &flag))
				hashclr(sha1);
			list = add_ref(ref, sha1, flag, list, NULL);
		}
		free(ref);
		closedir(dir);
	}
	return sort_ref_list(list);
}

struct warn_if_dangling_data {
	const char *refname;
	const char *msg_fmt;
};

static int warn_if_dangling_symref(const char *refname, const unsigned char *sha1,
				   int flags, void *cb_data)
{
	struct warn_if_dangling_data *d = cb_data;
	const char *resolves_to;
	unsigned char junk[20];

	if (!(flags & REF_ISSYMREF))
		return 0;

	resolves_to = resolve_ref(refname, junk, 0, NULL);
	if (!resolves_to || strcmp(resolves_to, d->refname))
		return 0;

	printf(d->msg_fmt, refname);
	return 0;
}

void warn_dangling_symref(const char *msg_fmt, const char *refname)
{
	struct warn_if_dangling_data data = { refname, msg_fmt };
	for_each_rawref(warn_if_dangling_symref, &data);
}

static struct ref_list *get_loose_refs(void)
{
	if (!cached_refs.did_loose) {
		cached_refs.loose = get_ref_dir("refs", NULL);
		cached_refs.did_loose = 1;
	}
	return cached_refs.loose;
}

/* We allow "recursive" symbolic refs. Only within reason, though */
#define MAXDEPTH 5
#define MAXREFLEN (1024)

static int resolve_gitlink_packed_ref(char *name, int pathlen, const char *refname, unsigned char *result)
{
	FILE *f;
	struct cached_refs refs;
	struct ref_list *ref;
	int retval;

	strcpy(name + pathlen, "packed-refs");
	f = fopen(name, "r");
	if (!f)
		return -1;
	read_packed_refs(f, &refs);
	fclose(f);
	ref = refs.packed;
	retval = -1;
	while (ref) {
		if (!strcmp(ref->name, refname)) {
			retval = 0;
			memcpy(result, ref->sha1, 20);
			break;
		}
		ref = ref->next;
	}
	free_ref_list(refs.packed);
	return retval;
}

static int resolve_gitlink_ref_recursive(char *name, int pathlen, const char *refname, unsigned char *result, int recursion)
{
	int fd, len = strlen(refname);
	char buffer[128], *p;

	if (recursion > MAXDEPTH || len > MAXREFLEN)
		return -1;
	memcpy(name + pathlen, refname, len+1);
	fd = open(name, O_RDONLY);
	if (fd < 0)
		return resolve_gitlink_packed_ref(name, pathlen, refname, result);

	len = read(fd, buffer, sizeof(buffer)-1);
	close(fd);
	if (len < 0)
		return -1;
	while (len && isspace(buffer[len-1]))
		len--;
	buffer[len] = 0;

	/* Was it a detached head or an old-fashioned symlink? */
	if (!get_sha1_hex(buffer, result))
		return 0;

	/* Symref? */
	if (strncmp(buffer, "ref:", 4))
		return -1;
	p = buffer + 4;
	while (isspace(*p))
		p++;

	return resolve_gitlink_ref_recursive(name, pathlen, p, result, recursion+1);
}

int resolve_gitlink_ref(const char *path, const char *refname, unsigned char *result)
{
	int len = strlen(path), retval;
	char *gitdir;
	const char *tmp;

	while (len && path[len-1] == '/')
		len--;
	if (!len)
		return -1;
	gitdir = xmalloc(len + MAXREFLEN + 8);
	memcpy(gitdir, path, len);
	memcpy(gitdir + len, "/.git", 6);
	len += 5;

	tmp = read_gitfile_gently(gitdir);
	if (tmp) {
		free(gitdir);
		len = strlen(tmp);
		gitdir = xmalloc(len + MAXREFLEN + 3);
		memcpy(gitdir, tmp, len);
	}
	gitdir[len] = '/';
	gitdir[++len] = '\0';
	retval = resolve_gitlink_ref_recursive(gitdir, len, refname, result, 0);
	free(gitdir);
	return retval;
}

/*
 * If the "reading" argument is set, this function finds out what _object_
 * the ref points at by "reading" the ref.  The ref, if it is not symbolic,
 * has to exist, and if it is symbolic, it has to point at an existing ref,
 * because the "read" goes through the symref to the ref it points at.
 *
 * The access that is not "reading" may often be "writing", but does not
 * have to; it can be merely checking _where it leads to_. If it is a
 * prelude to "writing" to the ref, a write to a symref that points at
 * yet-to-be-born ref will create the real ref pointed by the symref.
 * reading=0 allows the caller to check where such a symref leads to.
 */
const char *resolve_ref(const char *ref, unsigned char *sha1, int reading, int *flag)
{
	int depth = MAXDEPTH;
	ssize_t len;
	char buffer[256];
	static char ref_buffer[256];

	if (flag)
		*flag = 0;

	for (;;) {
		char path[PATH_MAX];
		struct stat st;
		char *buf;
		int fd;

		if (--depth < 0)
			return NULL;

		git_snpath(path, sizeof(path), "%s", ref);
		/* Special case: non-existing file. */
		if (lstat(path, &st) < 0) {
			struct ref_list *list = get_packed_refs();
			while (list) {
				if (!strcmp(ref, list->name)) {
					hashcpy(sha1, list->sha1);
					if (flag)
						*flag |= REF_ISPACKED;
					return ref;
				}
				list = list->next;
			}
			if (reading || errno != ENOENT)
				return NULL;
			hashclr(sha1);
			return ref;
		}

		/* Follow "normalized" - ie "refs/.." symlinks by hand */
		if (S_ISLNK(st.st_mode)) {
			len = readlink(path, buffer, sizeof(buffer)-1);
			if (len >= 5 && !memcmp("refs/", buffer, 5)) {
				buffer[len] = 0;
				strcpy(ref_buffer, buffer);
				ref = ref_buffer;
				if (flag)
					*flag |= REF_ISSYMREF;
				continue;
			}
		}

		/* Is it a directory? */
		if (S_ISDIR(st.st_mode)) {
			errno = EISDIR;
			return NULL;
		}

		/*
		 * Anything else, just open it and try to use it as
		 * a ref
		 */
		fd = open(path, O_RDONLY);
		if (fd < 0)
			return NULL;
		len = read_in_full(fd, buffer, sizeof(buffer)-1);
		close(fd);

		/*
		 * Is it a symbolic ref?
		 */
		if (len < 4 || memcmp("ref:", buffer, 4))
			break;
		buf = buffer + 4;
		len -= 4;
		while (len && isspace(*buf))
			buf++, len--;
		while (len && isspace(buf[len-1]))
			len--;
		buf[len] = 0;
		memcpy(ref_buffer, buf, len + 1);
		ref = ref_buffer;
		if (flag)
			*flag |= REF_ISSYMREF;
	}
	if (len < 40 || get_sha1_hex(buffer, sha1))
		return NULL;
	return ref;
}

int read_ref(const char *ref, unsigned char *sha1)
{
	if (resolve_ref(ref, sha1, 1, NULL))
		return 0;
	return -1;
}

#define DO_FOR_EACH_INCLUDE_BROKEN 01
static int do_one_ref(const char *base, each_ref_fn fn, int trim,
		      int flags, void *cb_data, struct ref_list *entry)
{
	if (strncmp(base, entry->name, trim))
		return 0;
	/* Is this a "negative ref" that represents a deleted ref? */
	if (is_null_sha1(entry->sha1))
		return 0;
	if (!(flags & DO_FOR_EACH_INCLUDE_BROKEN)) {
		if (!has_sha1_file(entry->sha1)) {
			error("%s does not point to a valid object!", entry->name);
			return 0;
		}
	}
	current_ref = entry;
	return fn(entry->name + trim, entry->sha1, entry->flag, cb_data);
}

int peel_ref(const char *ref, unsigned char *sha1)
{
	int flag;
	unsigned char base[20];
	struct object *o;

	if (current_ref && (current_ref->name == ref
		|| !strcmp(current_ref->name, ref))) {
		if (current_ref->flag & REF_KNOWS_PEELED) {
			hashcpy(sha1, current_ref->peeled);
			return 0;
		}
		hashcpy(base, current_ref->sha1);
		goto fallback;
	}

	if (!resolve_ref(ref, base, 1, &flag))
		return -1;

	if ((flag & REF_ISPACKED)) {
		struct ref_list *list = get_packed_refs();

		while (list) {
			if (!strcmp(list->name, ref)) {
				if (list->flag & REF_KNOWS_PEELED) {
					hashcpy(sha1, list->peeled);
					return 0;
				}
				/* older pack-refs did not leave peeled ones */
				break;
			}
			list = list->next;
		}
	}

fallback:
	o = parse_object(base);
	if (o && o->type == OBJ_TAG) {
		o = deref_tag(o, ref, 0);
		if (o) {
			hashcpy(sha1, o->sha1);
			return 0;
		}
	}
	return -1;
}

static int do_for_each_ref(const char *base, each_ref_fn fn, int trim,
			   int flags, void *cb_data)
{
	int retval = 0;
	struct ref_list *packed = get_packed_refs();
	struct ref_list *loose = get_loose_refs();

	struct ref_list *extra;

	for (extra = extra_refs; extra; extra = extra->next)
		retval = do_one_ref(base, fn, trim, flags, cb_data, extra);

	while (packed && loose) {
		struct ref_list *entry;
		int cmp = strcmp(packed->name, loose->name);
		if (!cmp) {
			packed = packed->next;
			continue;
		}
		if (cmp > 0) {
			entry = loose;
			loose = loose->next;
		} else {
			entry = packed;
			packed = packed->next;
		}
		retval = do_one_ref(base, fn, trim, flags, cb_data, entry);
		if (retval)
			goto end_each;
	}

	for (packed = packed ? packed : loose; packed; packed = packed->next) {
		retval = do_one_ref(base, fn, trim, flags, cb_data, packed);
		if (retval)
			goto end_each;
	}

end_each:
	current_ref = NULL;
	return retval;
}

int head_ref(each_ref_fn fn, void *cb_data)
{
	unsigned char sha1[20];
	int flag;

	if (resolve_ref("HEAD", sha1, 1, &flag))
		return fn("HEAD", sha1, flag, cb_data);
	return 0;
}

int for_each_ref(each_ref_fn fn, void *cb_data)
{
	return do_for_each_ref("refs/", fn, 0, 0, cb_data);
}

int for_each_ref_in(const char *prefix, each_ref_fn fn, void *cb_data)
{
	return do_for_each_ref(prefix, fn, strlen(prefix), 0, cb_data);
}

int for_each_tag_ref(each_ref_fn fn, void *cb_data)
{
	return for_each_ref_in("refs/tags/", fn, cb_data);
}

int for_each_branch_ref(each_ref_fn fn, void *cb_data)
{
	return for_each_ref_in("refs/heads/", fn, cb_data);
}

int for_each_remote_ref(each_ref_fn fn, void *cb_data)
{
	return for_each_ref_in("refs/remotes/", fn, cb_data);
}

int for_each_rawref(each_ref_fn fn, void *cb_data)
{
	return do_for_each_ref("refs/", fn, 0,
			       DO_FOR_EACH_INCLUDE_BROKEN, cb_data);
}

/*
 * Make sure "ref" is something reasonable to have under ".git/refs/";
 * We do not like it if:
 *
 * - any path component of it begins with ".", or
 * - it has double dots "..", or
 * - it has ASCII control character, "~", "^", ":" or SP, anywhere, or
 * - it ends with a "/".
 * - it ends with ".lock"
 */

static inline int bad_ref_char(int ch)
{
	if (((unsigned) ch) <= ' ' ||
	    ch == '~' || ch == '^' || ch == ':')
		return 1;
	/* 2.13 Pattern Matching Notation */
	if (ch == '?' || ch == '[') /* Unsupported */
		return 1;
	if (ch == '*') /* Supported at the end */
		return 2;
	return 0;
}

int check_ref_format(const char *ref)
{
	int ch, level, bad_type, last;
	int ret = CHECK_REF_FORMAT_OK;
	const char *cp = ref;

	level = 0;
	while (1) {
		while ((ch = *cp++) == '/')
			; /* tolerate duplicated slashes */
		if (!ch)
			/* should not end with slashes */
			return CHECK_REF_FORMAT_ERROR;

		/* we are at the beginning of the path component */
		if (ch == '.')
			return CHECK_REF_FORMAT_ERROR;
		bad_type = bad_ref_char(ch);
		if (bad_type) {
			if (bad_type == 2 && (!*cp || *cp == '/') &&
			    ret == CHECK_REF_FORMAT_OK)
				ret = CHECK_REF_FORMAT_WILDCARD;
			else
				return CHECK_REF_FORMAT_ERROR;
		}

		last = ch;
		/* scan the rest of the path component */
		while ((ch = *cp++) != 0) {
			bad_type = bad_ref_char(ch);
			if (bad_type)
				return CHECK_REF_FORMAT_ERROR;
			if (ch == '/')
				break;
			if (last == '.' && ch == '.')
				return CHECK_REF_FORMAT_ERROR;
			if (last == '@' && ch == '{')
				return CHECK_REF_FORMAT_ERROR;
			last = ch;
		}
		level++;
		if (!ch) {
			if (ref <= cp - 2 && cp[-2] == '.')
				return CHECK_REF_FORMAT_ERROR;
			if (level < 2)
				return CHECK_REF_FORMAT_ONELEVEL;
			if (has_extension(ref, ".lock"))
				return CHECK_REF_FORMAT_ERROR;
			return ret;
		}
	}
}

const char *prettify_ref(const struct ref *ref)
{
	const char *name = ref->name;
	return name + (
		!prefixcmp(name, "refs/heads/") ? 11 :
		!prefixcmp(name, "refs/tags/") ? 10 :
		!prefixcmp(name, "refs/remotes/") ? 13 :
		0);
}

const char *ref_rev_parse_rules[] = {
	"%.*s",
	"refs/%.*s",
	"refs/tags/%.*s",
	"refs/heads/%.*s",
	"refs/remotes/%.*s",
	"refs/remotes/%.*s/HEAD",
	NULL
};

const char *ref_fetch_rules[] = {
	"%.*s",
	"refs/%.*s",
	"refs/heads/%.*s",
	NULL
};

int refname_match(const char *abbrev_name, const char *full_name, const char **rules)
{
	const char **p;
	const int abbrev_name_len = strlen(abbrev_name);

	for (p = rules; *p; p++) {
		if (!strcmp(full_name, mkpath(*p, abbrev_name_len, abbrev_name))) {
			return 1;
		}
	}

	return 0;
}

static struct ref_lock *verify_lock(struct ref_lock *lock,
	const unsigned char *old_sha1, int mustexist)
{
	if (!resolve_ref(lock->ref_name, lock->old_sha1, mustexist, NULL)) {
		error("Can't verify ref %s", lock->ref_name);
		unlock_ref(lock);
		return NULL;
	}
	if (hashcmp(lock->old_sha1, old_sha1)) {
		error("Ref %s is at %s but expected %s", lock->ref_name,
			sha1_to_hex(lock->old_sha1), sha1_to_hex(old_sha1));
		unlock_ref(lock);
		return NULL;
	}
	return lock;
}

static int remove_empty_directories(const char *file)
{
	/* we want to create a file but there is a directory there;
	 * if that is an empty directory (or a directory that contains
	 * only empty directories), remove them.
	 */
	struct strbuf path;
	int result;

	strbuf_init(&path, 20);
	strbuf_addstr(&path, file);

	result = remove_dir_recursively(&path, 1);

	strbuf_release(&path);

	return result;
}

static int is_refname_available(const char *ref, const char *oldref,
				struct ref_list *list, int quiet)
{
	int namlen = strlen(ref); /* e.g. 'foo/bar' */
	while (list) {
		/* list->name could be 'foo' or 'foo/bar/baz' */
		if (!oldref || strcmp(oldref, list->name)) {
			int len = strlen(list->name);
			int cmplen = (namlen < len) ? namlen : len;
			const char *lead = (namlen < len) ? list->name : ref;
			if (!strncmp(ref, list->name, cmplen) &&
			    lead[cmplen] == '/') {
				if (!quiet)
					error("'%s' exists; cannot create '%s'",
					      list->name, ref);
				return 0;
			}
		}
		list = list->next;
	}
	return 1;
}

static struct ref_lock *lock_ref_sha1_basic(const char *ref, const unsigned char *old_sha1, int flags, int *type_p)
{
	char *ref_file;
	const char *orig_ref = ref;
	struct ref_lock *lock;
	int last_errno = 0;
	int type, lflags;
	int mustexist = (old_sha1 && !is_null_sha1(old_sha1));
	int missing = 0;

	lock = xcalloc(1, sizeof(struct ref_lock));
	lock->lock_fd = -1;

	ref = resolve_ref(ref, lock->old_sha1, mustexist, &type);
	if (!ref && errno == EISDIR) {
		/* we are trying to lock foo but we used to
		 * have foo/bar which now does not exist;
		 * it is normal for the empty directory 'foo'
		 * to remain.
		 */
		ref_file = git_path("%s", orig_ref);
		if (remove_empty_directories(ref_file)) {
			last_errno = errno;
			error("there are still refs under '%s'", orig_ref);
			goto error_return;
		}
		ref = resolve_ref(orig_ref, lock->old_sha1, mustexist, &type);
	}
	if (type_p)
	    *type_p = type;
	if (!ref) {
		last_errno = errno;
		error("unable to resolve reference %s: %s",
			orig_ref, strerror(errno));
		goto error_return;
	}
	missing = is_null_sha1(lock->old_sha1);
	/* When the ref did not exist and we are creating it,
	 * make sure there is no existing ref that is packed
	 * whose name begins with our refname, nor a ref whose
	 * name is a proper prefix of our refname.
	 */
	if (missing &&
	     !is_refname_available(ref, NULL, get_packed_refs(), 0)) {
		last_errno = ENOTDIR;
		goto error_return;
	}

	lock->lk = xcalloc(1, sizeof(struct lock_file));

	lflags = LOCK_DIE_ON_ERROR;
	if (flags & REF_NODEREF) {
		ref = orig_ref;
		lflags |= LOCK_NODEREF;
	}
	lock->ref_name = xstrdup(ref);
	lock->orig_ref_name = xstrdup(orig_ref);
	ref_file = git_path("%s", ref);
	if (missing)
		lock->force_write = 1;
	if ((flags & REF_NODEREF) && (type & REF_ISSYMREF))
		lock->force_write = 1;

	if (safe_create_leading_directories(ref_file)) {
		last_errno = errno;
		error("unable to create directory for %s", ref_file);
		goto error_return;
	}

	lock->lock_fd = hold_lock_file_for_update(lock->lk, ref_file, lflags);
	return old_sha1 ? verify_lock(lock, old_sha1, mustexist) : lock;

 error_return:
	unlock_ref(lock);
	errno = last_errno;
	return NULL;
}

struct ref_lock *lock_ref_sha1(const char *ref, const unsigned char *old_sha1)
{
	char refpath[PATH_MAX];
	if (check_ref_format(ref))
		return NULL;
	strcpy(refpath, mkpath("refs/%s", ref));
	return lock_ref_sha1_basic(refpath, old_sha1, 0, NULL);
}

struct ref_lock *lock_any_ref_for_update(const char *ref, const unsigned char *old_sha1, int flags)
{
	switch (check_ref_format(ref)) {
	default:
		return NULL;
	case 0:
	case CHECK_REF_FORMAT_ONELEVEL:
		return lock_ref_sha1_basic(ref, old_sha1, flags, NULL);
	}
}

static struct lock_file packlock;

static int repack_without_ref(const char *refname)
{
	struct ref_list *list, *packed_ref_list;
	int fd;
	int found = 0;

	packed_ref_list = get_packed_refs();
	for (list = packed_ref_list; list; list = list->next) {
		if (!strcmp(refname, list->name)) {
			found = 1;
			break;
		}
	}
	if (!found)
		return 0;
	fd = hold_lock_file_for_update(&packlock, git_path("packed-refs"), 0);
	if (fd < 0)
		return error("cannot delete '%s' from packed refs", refname);

	for (list = packed_ref_list; list; list = list->next) {
		char line[PATH_MAX + 100];
		int len;

		if (!strcmp(refname, list->name))
			continue;
		len = snprintf(line, sizeof(line), "%s %s\n",
			       sha1_to_hex(list->sha1), list->name);
		/* this should not happen but just being defensive */
		if (len > sizeof(line))
			die("too long a refname '%s'", list->name);
		write_or_die(fd, line, len);
	}
	return commit_lock_file(&packlock);
}

int delete_ref(const char *refname, const unsigned char *sha1, int delopt)
{
	struct ref_lock *lock;
	int err, i = 0, ret = 0, flag = 0;

	lock = lock_ref_sha1_basic(refname, sha1, 0, &flag);
	if (!lock)
		return 1;
	if (!(flag & REF_ISPACKED) || flag & REF_ISSYMREF) {
		/* loose */
		const char *path;

		if (!(delopt & REF_NODEREF)) {
			i = strlen(lock->lk->filename) - 5; /* .lock */
			lock->lk->filename[i] = 0;
			path = lock->lk->filename;
		} else {
			path = git_path("%s", refname);
		}
		err = unlink_or_warn(path);
		if (err && errno != ENOENT)
			ret = 1;

		if (!(delopt & REF_NODEREF))
			lock->lk->filename[i] = '.';
	}
	/* removing the loose one could have resurrected an earlier
	 * packed one.  Also, if it was not loose we need to repack
	 * without it.
	 */
	ret |= repack_without_ref(refname);

	unlink_or_warn(git_path("logs/%s", lock->ref_name));
	invalidate_cached_refs();
	unlock_ref(lock);
	return ret;
}

int rename_ref(const char *oldref, const char *newref, const char *logmsg)
{
	static const char renamed_ref[] = "RENAMED-REF";
	unsigned char sha1[20], orig_sha1[20];
	int flag = 0, logmoved = 0;
	struct ref_lock *lock;
	struct stat loginfo;
	int log = !lstat(git_path("logs/%s", oldref), &loginfo);
	const char *symref = NULL;

	if (log && S_ISLNK(loginfo.st_mode))
		return error("reflog for %s is a symlink", oldref);

	symref = resolve_ref(oldref, orig_sha1, 1, &flag);
	if (flag & REF_ISSYMREF)
		return error("refname %s is a symbolic ref, renaming it is not supported",
			oldref);
	if (!symref)
		return error("refname %s not found", oldref);

	if (!is_refname_available(newref, oldref, get_packed_refs(), 0))
		return 1;

	if (!is_refname_available(newref, oldref, get_loose_refs(), 0))
		return 1;

	lock = lock_ref_sha1_basic(renamed_ref, NULL, 0, NULL);
	if (!lock)
		return error("unable to lock %s", renamed_ref);
	lock->force_write = 1;
	if (write_ref_sha1(lock, orig_sha1, logmsg))
		return error("unable to save current sha1 in %s", renamed_ref);

	if (log && rename(git_path("logs/%s", oldref), git_path("tmp-renamed-log")))
		return error("unable to move logfile logs/%s to tmp-renamed-log: %s",
			oldref, strerror(errno));

	if (delete_ref(oldref, orig_sha1, REF_NODEREF)) {
		error("unable to delete old %s", oldref);
		goto rollback;
	}

	if (resolve_ref(newref, sha1, 1, &flag) && delete_ref(newref, sha1, REF_NODEREF)) {
		if (errno==EISDIR) {
			if (remove_empty_directories(git_path("%s", newref))) {
				error("Directory not empty: %s", newref);
				goto rollback;
			}
		} else {
			error("unable to delete existing %s", newref);
			goto rollback;
		}
	}

	if (log && safe_create_leading_directories(git_path("logs/%s", newref))) {
		error("unable to create directory for %s", newref);
		goto rollback;
	}

 retry:
	if (log && rename(git_path("tmp-renamed-log"), git_path("logs/%s", newref))) {
		if (errno==EISDIR || errno==ENOTDIR) {
			/*
			 * rename(a, b) when b is an existing
			 * directory ought to result in ISDIR, but
			 * Solaris 5.8 gives ENOTDIR.  Sheesh.
			 */
			if (remove_empty_directories(git_path("logs/%s", newref))) {
				error("Directory not empty: logs/%s", newref);
				goto rollback;
			}
			goto retry;
		} else {
			error("unable to move logfile tmp-renamed-log to logs/%s: %s",
				newref, strerror(errno));
			goto rollback;
		}
	}
	logmoved = log;

	lock = lock_ref_sha1_basic(newref, NULL, 0, NULL);
	if (!lock) {
		error("unable to lock %s for update", newref);
		goto rollback;
	}
	lock->force_write = 1;
	hashcpy(lock->old_sha1, orig_sha1);
	if (write_ref_sha1(lock, orig_sha1, logmsg)) {
		error("unable to write current sha1 into %s", newref);
		goto rollback;
	}

	return 0;

 rollback:
	lock = lock_ref_sha1_basic(oldref, NULL, 0, NULL);
	if (!lock) {
		error("unable to lock %s for rollback", oldref);
		goto rollbacklog;
	}

	lock->force_write = 1;
	flag = log_all_ref_updates;
	log_all_ref_updates = 0;
	if (write_ref_sha1(lock, orig_sha1, NULL))
		error("unable to write current sha1 into %s", oldref);
	log_all_ref_updates = flag;

 rollbacklog:
	if (logmoved && rename(git_path("logs/%s", newref), git_path("logs/%s", oldref)))
		error("unable to restore logfile %s from %s: %s",
			oldref, newref, strerror(errno));
	if (!logmoved && log &&
	    rename(git_path("tmp-renamed-log"), git_path("logs/%s", oldref)))
		error("unable to restore logfile %s from tmp-renamed-log: %s",
			oldref, strerror(errno));

	return 1;
}

int close_ref(struct ref_lock *lock)
{
	if (close_lock_file(lock->lk))
		return -1;
	lock->lock_fd = -1;
	return 0;
}

int commit_ref(struct ref_lock *lock)
{
	if (commit_lock_file(lock->lk))
		return -1;
	lock->lock_fd = -1;
	return 0;
}

void unlock_ref(struct ref_lock *lock)
{
	/* Do not free lock->lk -- atexit() still looks at them */
	if (lock->lk)
		rollback_lock_file(lock->lk);
	free(lock->ref_name);
	free(lock->orig_ref_name);
	free(lock);
}

/*
 * copy the reflog message msg to buf, which has been allocated sufficiently
 * large, while cleaning up the whitespaces.  Especially, convert LF to space,
 * because reflog file is one line per entry.
 */
static int copy_msg(char *buf, const char *msg)
{
	char *cp = buf;
	char c;
	int wasspace = 1;

	*cp++ = '\t';
	while ((c = *msg++)) {
		if (wasspace && isspace(c))
			continue;
		wasspace = isspace(c);
		if (wasspace)
			c = ' ';
		*cp++ = c;
	}
	while (buf < cp && isspace(cp[-1]))
		cp--;
	*cp++ = '\n';
	return cp - buf;
}

static int log_ref_write(const char *ref_name, const unsigned char *old_sha1,
			 const unsigned char *new_sha1, const char *msg)
{
	int logfd, written, oflags = O_APPEND | O_WRONLY;
	unsigned maxlen, len;
	int msglen;
	char log_file[PATH_MAX];
	char *logrec;
	const char *committer;

	if (log_all_ref_updates < 0)
		log_all_ref_updates = !is_bare_repository();

	git_snpath(log_file, sizeof(log_file), "logs/%s", ref_name);

	if (log_all_ref_updates &&
	    (!prefixcmp(ref_name, "refs/heads/") ||
	     !prefixcmp(ref_name, "refs/remotes/") ||
	     !strcmp(ref_name, "HEAD"))) {
		if (safe_create_leading_directories(log_file) < 0)
			return error("unable to create directory for %s",
				     log_file);
		oflags |= O_CREAT;
	}

	logfd = open(log_file, oflags, 0666);
	if (logfd < 0) {
		if (!(oflags & O_CREAT) && errno == ENOENT)
			return 0;

		if ((oflags & O_CREAT) && errno == EISDIR) {
			if (remove_empty_directories(log_file)) {
				return error("There are still logs under '%s'",
					     log_file);
			}
			logfd = open(log_file, oflags, 0666);
		}

		if (logfd < 0)
			return error("Unable to append to %s: %s",
				     log_file, strerror(errno));
	}

	adjust_shared_perm(log_file);

	msglen = msg ? strlen(msg) : 0;
	committer = git_committer_info(0);
	maxlen = strlen(committer) + msglen + 100;
	logrec = xmalloc(maxlen);
	len = sprintf(logrec, "%s %s %s\n",
		      sha1_to_hex(old_sha1),
		      sha1_to_hex(new_sha1),
		      committer);
	if (msglen)
		len += copy_msg(logrec + len - 1, msg) - 1;
	written = len <= maxlen ? write_in_full(logfd, logrec, len) : -1;
	free(logrec);
	if (close(logfd) != 0 || written != len)
		return error("Unable to append to %s", log_file);
	return 0;
}

static int is_branch(const char *refname)
{
	return !strcmp(refname, "HEAD") || !prefixcmp(refname, "refs/heads/");
}

int write_ref_sha1(struct ref_lock *lock,
	const unsigned char *sha1, const char *logmsg)
{
	static char term = '\n';
	struct object *o;

	if (!lock)
		return -1;
	if (!lock->force_write && !hashcmp(lock->old_sha1, sha1)) {
		unlock_ref(lock);
		return 0;
	}
	o = parse_object(sha1);
	if (!o) {
		error("Trying to write ref %s with nonexistant object %s",
			lock->ref_name, sha1_to_hex(sha1));
		unlock_ref(lock);
		return -1;
	}
	if (o->type != OBJ_COMMIT && is_branch(lock->ref_name)) {
		error("Trying to write non-commit object %s to branch %s",
			sha1_to_hex(sha1), lock->ref_name);
		unlock_ref(lock);
		return -1;
	}
	if (write_in_full(lock->lock_fd, sha1_to_hex(sha1), 40) != 40 ||
	    write_in_full(lock->lock_fd, &term, 1) != 1
		|| close_ref(lock) < 0) {
		error("Couldn't write %s", lock->lk->filename);
		unlock_ref(lock);
		return -1;
	}
	invalidate_cached_refs();
	if (log_ref_write(lock->ref_name, lock->old_sha1, sha1, logmsg) < 0 ||
	    (strcmp(lock->ref_name, lock->orig_ref_name) &&
	     log_ref_write(lock->orig_ref_name, lock->old_sha1, sha1, logmsg) < 0)) {
		unlock_ref(lock);
		return -1;
	}
	if (strcmp(lock->orig_ref_name, "HEAD") != 0) {
		/*
		 * Special hack: If a branch is updated directly and HEAD
		 * points to it (may happen on the remote side of a push
		 * for example) then logically the HEAD reflog should be
		 * updated too.
		 * A generic solution implies reverse symref information,
		 * but finding all symrefs pointing to the given branch
		 * would be rather costly for this rare event (the direct
		 * update of a branch) to be worth it.  So let's cheat and
		 * check with HEAD only which should cover 99% of all usage
		 * scenarios (even 100% of the default ones).
		 */
		unsigned char head_sha1[20];
		int head_flag;
		const char *head_ref;
		head_ref = resolve_ref("HEAD", head_sha1, 1, &head_flag);
		if (head_ref && (head_flag & REF_ISSYMREF) &&
		    !strcmp(head_ref, lock->ref_name))
			log_ref_write("HEAD", lock->old_sha1, sha1, logmsg);
	}
	if (commit_ref(lock)) {
		error("Couldn't set %s", lock->ref_name);
		unlock_ref(lock);
		return -1;
	}
	unlock_ref(lock);
	return 0;
}

int create_symref(const char *ref_target, const char *refs_heads_master,
		  const char *logmsg)
{
	const char *lockpath;
	char ref[1000];
	int fd, len, written;
	char *git_HEAD = git_pathdup("%s", ref_target);
	unsigned char old_sha1[20], new_sha1[20];

	if (logmsg && read_ref(ref_target, old_sha1))
		hashclr(old_sha1);

	if (safe_create_leading_directories(git_HEAD) < 0)
		return error("unable to create directory for %s", git_HEAD);

#ifndef NO_SYMLINK_HEAD
	if (prefer_symlink_refs) {
		unlink(git_HEAD);
		if (!symlink(refs_heads_master, git_HEAD))
			goto done;
		fprintf(stderr, "no symlink - falling back to symbolic ref\n");
	}
#endif

	len = snprintf(ref, sizeof(ref), "ref: %s\n", refs_heads_master);
	if (sizeof(ref) <= len) {
		error("refname too long: %s", refs_heads_master);
		goto error_free_return;
	}
	lockpath = mkpath("%s.lock", git_HEAD);
	fd = open(lockpath, O_CREAT | O_EXCL | O_WRONLY, 0666);
	if (fd < 0) {
		error("Unable to open %s for writing", lockpath);
		goto error_free_return;
	}
	written = write_in_full(fd, ref, len);
	if (close(fd) != 0 || written != len) {
		error("Unable to write to %s", lockpath);
		goto error_unlink_return;
	}
	if (rename(lockpath, git_HEAD) < 0) {
		error("Unable to create %s", git_HEAD);
		goto error_unlink_return;
	}
	if (adjust_shared_perm(git_HEAD)) {
		error("Unable to fix permissions on %s", lockpath);
	error_unlink_return:
		unlink_or_warn(lockpath);
	error_free_return:
		free(git_HEAD);
		return -1;
	}

#ifndef NO_SYMLINK_HEAD
	done:
#endif
	if (logmsg && !read_ref(refs_heads_master, new_sha1))
		log_ref_write(ref_target, old_sha1, new_sha1, logmsg);

	free(git_HEAD);
	return 0;
}

static char *ref_msg(const char *line, const char *endp)
{
	const char *ep;
	line += 82;
	ep = memchr(line, '\n', endp - line);
	if (!ep)
		ep = endp;
	return xmemdupz(line, ep - line);
}

int read_ref_at(const char *ref, unsigned long at_time, int cnt, unsigned char *sha1, char **msg, unsigned long *cutoff_time, int *cutoff_tz, int *cutoff_cnt)
{
	const char *logfile, *logdata, *logend, *rec, *lastgt, *lastrec;
	char *tz_c;
	int logfd, tz, reccnt = 0;
	struct stat st;
	unsigned long date;
	unsigned char logged_sha1[20];
	void *log_mapped;
	size_t mapsz;

	logfile = git_path("logs/%s", ref);
	logfd = open(logfile, O_RDONLY, 0);
	if (logfd < 0)
		die("Unable to read log %s: %s", logfile, strerror(errno));
	fstat(logfd, &st);
	if (!st.st_size)
		die("Log %s is empty.", logfile);
	mapsz = xsize_t(st.st_size);
	log_mapped = xmmap(NULL, mapsz, PROT_READ, MAP_PRIVATE, logfd, 0);
	logdata = log_mapped;
	close(logfd);

	lastrec = NULL;
	rec = logend = logdata + st.st_size;
	while (logdata < rec) {
		reccnt++;
		if (logdata < rec && *(rec-1) == '\n')
			rec--;
		lastgt = NULL;
		while (logdata < rec && *(rec-1) != '\n') {
			rec--;
			if (*rec == '>')
				lastgt = rec;
		}
		if (!lastgt)
			die("Log %s is corrupt.", logfile);
		date = strtoul(lastgt + 1, &tz_c, 10);
		if (date <= at_time || cnt == 0) {
			tz = strtoul(tz_c, NULL, 10);
			if (msg)
				*msg = ref_msg(rec, logend);
			if (cutoff_time)
				*cutoff_time = date;
			if (cutoff_tz)
				*cutoff_tz = tz;
			if (cutoff_cnt)
				*cutoff_cnt = reccnt - 1;
			if (lastrec) {
				if (get_sha1_hex(lastrec, logged_sha1))
					die("Log %s is corrupt.", logfile);
				if (get_sha1_hex(rec + 41, sha1))
					die("Log %s is corrupt.", logfile);
				if (hashcmp(logged_sha1, sha1)) {
					warning("Log %s has gap after %s.",
						logfile, show_date(date, tz, DATE_RFC2822));
				}
			}
			else if (date == at_time) {
				if (get_sha1_hex(rec + 41, sha1))
					die("Log %s is corrupt.", logfile);
			}
			else {
				if (get_sha1_hex(rec + 41, logged_sha1))
					die("Log %s is corrupt.", logfile);
				if (hashcmp(logged_sha1, sha1)) {
					warning("Log %s unexpectedly ended on %s.",
						logfile, show_date(date, tz, DATE_RFC2822));
				}
			}
			munmap(log_mapped, mapsz);
			return 0;
		}
		lastrec = rec;
		if (cnt > 0)
			cnt--;
	}

	rec = logdata;
	while (rec < logend && *rec != '>' && *rec != '\n')
		rec++;
	if (rec == logend || *rec == '\n')
		die("Log %s is corrupt.", logfile);
	date = strtoul(rec + 1, &tz_c, 10);
	tz = strtoul(tz_c, NULL, 10);
	if (get_sha1_hex(logdata, sha1))
		die("Log %s is corrupt.", logfile);
	if (is_null_sha1(sha1)) {
		if (get_sha1_hex(logdata + 41, sha1))
			die("Log %s is corrupt.", logfile);
	}
	if (msg)
		*msg = ref_msg(logdata, logend);
	munmap(log_mapped, mapsz);

	if (cutoff_time)
		*cutoff_time = date;
	if (cutoff_tz)
		*cutoff_tz = tz;
	if (cutoff_cnt)
		*cutoff_cnt = reccnt;
	return 1;
}

int for_each_recent_reflog_ent(const char *ref, each_reflog_ent_fn fn, long ofs, void *cb_data)
{
	const char *logfile;
	FILE *logfp;
	char buf[1024];
	int ret = 0;

	logfile = git_path("logs/%s", ref);
	logfp = fopen(logfile, "r");
	if (!logfp)
		return -1;

	if (ofs) {
		struct stat statbuf;
		if (fstat(fileno(logfp), &statbuf) ||
		    statbuf.st_size < ofs ||
		    fseek(logfp, -ofs, SEEK_END) ||
		    fgets(buf, sizeof(buf), logfp)) {
			fclose(logfp);
			return -1;
		}
	}

	while (fgets(buf, sizeof(buf), logfp)) {
		unsigned char osha1[20], nsha1[20];
		char *email_end, *message;
		unsigned long timestamp;
		int len, tz;

		/* old SP new SP name <email> SP time TAB msg LF */
		len = strlen(buf);
		if (len < 83 || buf[len-1] != '\n' ||
		    get_sha1_hex(buf, osha1) || buf[40] != ' ' ||
		    get_sha1_hex(buf + 41, nsha1) || buf[81] != ' ' ||
		    !(email_end = strchr(buf + 82, '>')) ||
		    email_end[1] != ' ' ||
		    !(timestamp = strtoul(email_end + 2, &message, 10)) ||
		    !message || message[0] != ' ' ||
		    (message[1] != '+' && message[1] != '-') ||
		    !isdigit(message[2]) || !isdigit(message[3]) ||
		    !isdigit(message[4]) || !isdigit(message[5]))
			continue; /* corrupt? */
		email_end[1] = '\0';
		tz = strtol(message + 1, NULL, 10);
		if (message[6] != '\t')
			message += 6;
		else
			message += 7;
		ret = fn(osha1, nsha1, buf+82, timestamp, tz, message, cb_data);
		if (ret)
			break;
	}
	fclose(logfp);
	return ret;
}

int for_each_reflog_ent(const char *ref, each_reflog_ent_fn fn, void *cb_data)
{
	return for_each_recent_reflog_ent(ref, fn, 0, cb_data);
}

static int do_for_each_reflog(const char *base, each_ref_fn fn, void *cb_data)
{
	DIR *dir = opendir(git_path("logs/%s", base));
	int retval = 0;

	if (dir) {
		struct dirent *de;
		int baselen = strlen(base);
		char *log = xmalloc(baselen + 257);

		memcpy(log, base, baselen);
		if (baselen && base[baselen-1] != '/')
			log[baselen++] = '/';

		while ((de = readdir(dir)) != NULL) {
			struct stat st;
			int namelen;

			if (de->d_name[0] == '.')
				continue;
			namelen = strlen(de->d_name);
			if (namelen > 255)
				continue;
			if (has_extension(de->d_name, ".lock"))
				continue;
			memcpy(log + baselen, de->d_name, namelen+1);
			if (stat(git_path("logs/%s", log), &st) < 0)
				continue;
			if (S_ISDIR(st.st_mode)) {
				retval = do_for_each_reflog(log, fn, cb_data);
			} else {
				unsigned char sha1[20];
				if (!resolve_ref(log, sha1, 0, NULL))
					retval = error("bad ref for %s", log);
				else
					retval = fn(log, sha1, 0, cb_data);
			}
			if (retval)
				break;
		}
		free(log);
		closedir(dir);
	}
	else if (*base)
		return errno;
	return retval;
}

int for_each_reflog(each_ref_fn fn, void *cb_data)
{
	return do_for_each_reflog("", fn, cb_data);
}

int update_ref(const char *action, const char *refname,
		const unsigned char *sha1, const unsigned char *oldval,
		int flags, enum action_on_err onerr)
{
	static struct ref_lock *lock;
	lock = lock_any_ref_for_update(refname, oldval, flags);
	if (!lock) {
		const char *str = "Cannot lock the ref '%s'.";
		switch (onerr) {
		case MSG_ON_ERR: error(str, refname); break;
		case DIE_ON_ERR: die(str, refname); break;
		case QUIET_ON_ERR: break;
		}
		return 1;
	}
	if (write_ref_sha1(lock, sha1, action) < 0) {
		const char *str = "Cannot update the ref '%s'.";
		switch (onerr) {
		case MSG_ON_ERR: error(str, refname); break;
		case DIE_ON_ERR: die(str, refname); break;
		case QUIET_ON_ERR: break;
		}
		return 1;
	}
	return 0;
}

struct ref *find_ref_by_name(const struct ref *list, const char *name)
{
	for ( ; list; list = list->next)
		if (!strcmp(list->name, name))
			return (struct ref *)list;
	return NULL;
}

/*
 * generate a format suitable for scanf from a ref_rev_parse_rules
 * rule, that is replace the "%.*s" spec with a "%s" spec
 */
static void gen_scanf_fmt(char *scanf_fmt, const char *rule)
{
	char *spec;

	spec = strstr(rule, "%.*s");
	if (!spec || strstr(spec + 4, "%.*s"))
		die("invalid rule in ref_rev_parse_rules: %s", rule);

	/* copy all until spec */
	strncpy(scanf_fmt, rule, spec - rule);
	scanf_fmt[spec - rule] = '\0';
	/* copy new spec */
	strcat(scanf_fmt, "%s");
	/* copy remaining rule */
	strcat(scanf_fmt, spec + 4);

	return;
}

char *shorten_unambiguous_ref(const char *ref, int strict)
{
	int i;
	static char **scanf_fmts;
	static int nr_rules;
	char *short_name;

	/* pre generate scanf formats from ref_rev_parse_rules[] */
	if (!nr_rules) {
		size_t total_len = 0;

		/* the rule list is NULL terminated, count them first */
		for (; ref_rev_parse_rules[nr_rules]; nr_rules++)
			/* no +1 because strlen("%s") < strlen("%.*s") */
			total_len += strlen(ref_rev_parse_rules[nr_rules]);

		scanf_fmts = xmalloc(nr_rules * sizeof(char *) + total_len);

		total_len = 0;
		for (i = 0; i < nr_rules; i++) {
			scanf_fmts[i] = (char *)&scanf_fmts[nr_rules]
					+ total_len;
			gen_scanf_fmt(scanf_fmts[i], ref_rev_parse_rules[i]);
			total_len += strlen(ref_rev_parse_rules[i]);
		}
	}

	/* bail out if there are no rules */
	if (!nr_rules)
		return xstrdup(ref);

	/* buffer for scanf result, at most ref must fit */
	short_name = xstrdup(ref);

	/* skip first rule, it will always match */
	for (i = nr_rules - 1; i > 0 ; --i) {
		int j;
		int rules_to_fail = i;
		int short_name_len;

		if (1 != sscanf(ref, scanf_fmts[i], short_name))
			continue;

		short_name_len = strlen(short_name);

		/*
		 * in strict mode, all (except the matched one) rules
		 * must fail to resolve to a valid non-ambiguous ref
		 */
		if (strict)
			rules_to_fail = nr_rules;

		/*
		 * check if the short name resolves to a valid ref,
		 * but use only rules prior to the matched one
		 */
		for (j = 0; j < rules_to_fail; j++) {
			const char *rule = ref_rev_parse_rules[j];
			unsigned char short_objectname[20];
			char refname[PATH_MAX];

			/* skip matched rule */
			if (i == j)
				continue;

			/*
			 * the short name is ambiguous, if it resolves
			 * (with this previous rule) to a valid ref
			 * read_ref() returns 0 on success
			 */
			mksnpath(refname, sizeof(refname),
				 rule, short_name_len, short_name);
			if (!read_ref(refname, short_objectname))
				break;
		}

		/*
		 * short name is non-ambiguous if all previous rules
		 * haven't resolved to a valid ref
		 */
		if (j == rules_to_fail)
			return short_name;
	}

	free(short_name);
	return xstrdup(ref);
}