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

/*
 * 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"
 * - it contains a "\" (backslash)
 */

/* Return true iff ch is not allowed in reference names. */
static inline int bad_ref_char(int ch)
{
        if (((unsigned) ch) <= ' ' || ch == 0x7f ||
            ch == '~' || ch == '^' || ch == ':' || ch == '\\')
                return 1;
        /* 2.13 Pattern Matching Notation */
        if (ch == '*' || ch == '?' || ch == '[') /* Unsupported */
                return 1;
        return 0;
}

/*
 * Try to read one refname component from the front of refname.  Return
 * the length of the component found, or -1 if the component is not
 * legal.
 */
static int check_refname_component(const char *refname, int flags)
{
        const char *cp;
        char last = '\0';

        for (cp = refname; ; cp++) {
                char ch = *cp;
                if (ch == '\0' || ch == '/')
                        break;
                if (bad_ref_char(ch))
                        return -1; /* Illegal character in refname. */
                if (last == '.' && ch == '.')
                        return -1; /* Refname contains "..". */
                if (last == '@' && ch == '{')
                        return -1; /* Refname contains "@{". */
                last = ch;
        }
        if (cp == refname)
                return 0; /* Component has zero length. */
        if (refname[0] == '.') {
                if (!(flags & REFNAME_DOT_COMPONENT))
                        return -1; /* Component starts with '.'. */
                /*
                 * Even if leading dots are allowed, don't allow "."
                 * as a component (".." is prevented by a rule above).
                 */
                if (refname[1] == '\0')
                        return -1; /* Component equals ".". */
        }
        if (cp - refname >= 5 && !memcmp(cp - 5, ".lock", 5))
                return -1; /* Refname ends with ".lock". */
        return cp - refname;
}

int check_refname_format(const char *refname, int flags)
{
        int component_len, component_count = 0;

        while (1) {
                /* We are at the start of a path component. */
                component_len = check_refname_component(refname, flags);
                if (component_len <= 0) {
                        if ((flags & REFNAME_REFSPEC_PATTERN) &&
                                        refname[0] == '*' &&
                                        (refname[1] == '\0' || refname[1] == '/')) {
                                /* Accept one wildcard as a full refname component. */
                                flags &= ~REFNAME_REFSPEC_PATTERN;
                                component_len = 1;
                        } else {
                                return -1;
                        }
                }
                component_count++;
                if (refname[component_len] == '\0')
                        break;
                /* Skip to next component. */
                refname += component_len + 1;
        }

        if (refname[component_len - 1] == '.')
                return -1; /* Refname ends with '.'. */
        if (!(flags & REFNAME_ALLOW_ONELEVEL) && component_count < 2)
                return -1; /* Refname has only one component. */
        return 0;
}

struct ref_entry;

struct ref_value {
        unsigned char sha1[20];
        unsigned char peeled[20];
};

struct ref_dir {
        int nr, alloc;

        /*
         * Entries with index 0 <= i < sorted are sorted by name.  New
         * entries are appended to the list unsorted, and are sorted
         * only when required; thus we avoid the need to sort the list
         * after the addition of every reference.
         */
        int sorted;

        struct ref_entry **entries;
};

/* ISSYMREF=0x01, ISPACKED=0x02, and ISBROKEN=0x04 are public interfaces */
#define REF_KNOWS_PEELED 0x08
#define REF_DIR 0x10

/*
 * A ref_entry represents either a reference or a "subdirectory" of
 * references.  Each directory in the reference namespace is
 * represented by a ref_entry with (flags & REF_DIR) set and
 * containing a subdir member that holds the entries in that
 * directory.  References are represented by a ref_entry with (flags &
 * REF_DIR) unset and a value member that describes the reference's
 * value.  The flag member is at the ref_entry level, but it is also
 * needed to interpret the contents of the value field (in other
 * words, a ref_value object is not very much use without the
 * enclosing ref_entry).
 *
 * Reference names cannot end with slash and directories' names are
 * always stored with a trailing slash (except for the top-level
 * directory, which is always denoted by "").  This has two nice
 * consequences: (1) when the entries in each subdir are sorted
 * lexicographically by name (as they usually are), the references in
 * a whole tree can be generated in lexicographic order by traversing
 * the tree in left-to-right, depth-first order; (2) the names of
 * references and subdirectories cannot conflict, and therefore the
 * presence of an empty subdirectory does not block the creation of a
 * similarly-named reference.  (The fact that reference names with the
 * same leading components can conflict *with each other* is a
 * separate issue that is regulated by is_refname_available().)
 *
 * Please note that the name field contains the fully-qualified
 * reference (or subdirectory) name.  Space could be saved by only
 * storing the relative names.  But that would require the full names
 * to be generated on the fly when iterating in do_for_each_ref(), and
 * would break callback functions, who have always been able to assume
 * that the name strings that they are passed will not be freed during
 * the iteration.
 */
struct ref_entry {
        unsigned char flag; /* ISSYMREF? ISPACKED? */
        union {
                struct ref_value value; /* if not (flags&REF_DIR) */
                struct ref_dir subdir; /* if (flags&REF_DIR) */
        } u;
        /*
         * The full name of the reference (e.g., "refs/heads/master")
         * or the full name of the directory with a trailing slash
         * (e.g., "refs/heads/"):
         */
        char name[FLEX_ARRAY];
};

static struct ref_dir *get_ref_dir(struct ref_entry *entry)
{
        assert(entry->flag & REF_DIR);
        return &entry->u.subdir;
}

static struct ref_entry *create_ref_entry(const char *refname,
                                          const unsigned char *sha1, int flag,
                                          int check_name)
{
        int len;
        struct ref_entry *ref;

        if (check_name &&
            check_refname_format(refname, REFNAME_ALLOW_ONELEVEL|REFNAME_DOT_COMPONENT))
                die("Reference has invalid format: '%s'", refname);
        len = strlen(refname) + 1;
        ref = xmalloc(sizeof(struct ref_entry) + len);
        hashcpy(ref->u.value.sha1, sha1);
        hashclr(ref->u.value.peeled);
        memcpy(ref->name, refname, len);
        ref->flag = flag;
        return ref;
}

static void clear_ref_dir(struct ref_dir *dir);

static void free_ref_entry(struct ref_entry *entry)
{
        if (entry->flag & REF_DIR)
                clear_ref_dir(get_ref_dir(entry));
        free(entry);
}

/*
 * Add a ref_entry to the end of dir (unsorted).  Entry is always
 * stored directly in dir; no recursion into subdirectories is
 * done.
 */
static void add_entry_to_dir(struct ref_dir *dir, struct ref_entry *entry)
{
        ALLOC_GROW(dir->entries, dir->nr + 1, dir->alloc);
        dir->entries[dir->nr++] = entry;
}

/*
 * Clear and free all entries in dir, recursively.
 */
static void clear_ref_dir(struct ref_dir *dir)
{
        int i;
        for (i = 0; i < dir->nr; i++)
                free_ref_entry(dir->entries[i]);
        free(dir->entries);
        dir->sorted = dir->nr = dir->alloc = 0;
        dir->entries = NULL;
}

/*
 * Create a struct ref_entry object for the specified dirname.
 * dirname is the name of the directory with a trailing slash (e.g.,
 * "refs/heads/") or "" for the top-level directory.
 */
static struct ref_entry *create_dir_entry(const char *dirname)
{
        struct ref_entry *direntry;
        int len = strlen(dirname);
        direntry = xcalloc(1, sizeof(struct ref_entry) + len + 1);
        memcpy(direntry->name, dirname, len + 1);
        direntry->flag = REF_DIR;
        return direntry;
}

static int ref_entry_cmp(const void *a, const void *b)
{
        struct ref_entry *one = *(struct ref_entry **)a;
        struct ref_entry *two = *(struct ref_entry **)b;
        return strcmp(one->name, two->name);
}

static void sort_ref_dir(struct ref_dir *dir);

/*
 * Return the entry with the given refname from the ref_dir
 * (non-recursively), sorting dir if necessary.  Return NULL if no
 * such entry is found.
 */
static struct ref_entry *search_ref_dir(struct ref_dir *dir, const char *refname)
{
        struct ref_entry *e, **r;
        int len;

        if (refname == NULL || !dir->nr)
                return NULL;

        sort_ref_dir(dir);

        len = strlen(refname) + 1;
        e = xmalloc(sizeof(struct ref_entry) + len);
        memcpy(e->name, refname, len);

        r = bsearch(&e, dir->entries, dir->nr, sizeof(*dir->entries), ref_entry_cmp);

        free(e);

        if (r == NULL)
                return NULL;

        return *r;
}

/*
 * Search for a directory entry directly within dir (without
 * recursing).  Sort dir if necessary.  subdirname must be a directory
 * name (i.e., end in '/').  If mkdir is set, then create the
 * directory if it is missing; otherwise, return NULL if the desired
 * directory cannot be found.
 */
static struct ref_entry *search_for_subdir(struct ref_dir *dir,
                                           const char *subdirname, int mkdir)
{
        struct ref_entry *entry = search_ref_dir(dir, subdirname);
        if (!entry) {
                if (!mkdir)
                        return NULL;
                entry = create_dir_entry(subdirname);
                add_entry_to_dir(dir, entry);
        }
        assert(entry->flag & REF_DIR);
        return entry;
}

/*
 * If refname is a reference name, find the ref_dir within the dir
 * tree that should hold refname.  If refname is a directory name
 * (i.e., ends in '/'), then return that ref_dir itself.  dir must
 * represent the top-level directory.  Sort ref_dirs and recurse into
 * subdirectories as necessary.  If mkdir is set, then create any
 * missing directories; otherwise, return NULL if the desired
 * directory cannot be found.
 */
static struct ref_dir *find_containing_dir(struct ref_dir *dir,
                                           const char *refname, int mkdir)
{
        struct strbuf dirname;
        const char *slash;
        strbuf_init(&dirname, PATH_MAX);
        for (slash = strchr(refname, '/'); slash; slash = strchr(slash + 1, '/')) {
                struct ref_entry *entry;
                strbuf_add(&dirname,
                           refname + dirname.len,
                           (slash + 1) - (refname + dirname.len));
                entry = search_for_subdir(dir, dirname.buf, mkdir);
                if (!entry)
                        break;
                dir = get_ref_dir(entry);
        }

        strbuf_release(&dirname);
        return dir;
}

/*
 * Find the value entry with the given name in dir, sorting ref_dirs
 * and recursing into subdirectories as necessary.  If the name is not
 * found or it corresponds to a directory entry, return NULL.
 */
static struct ref_entry *find_ref(struct ref_dir *dir, const char *refname)
{
        struct ref_entry *entry;
        dir = find_containing_dir(dir, refname, 0);
        if (!dir)
                return NULL;
        entry = search_ref_dir(dir, refname);
        return (entry && !(entry->flag & REF_DIR)) ? entry : NULL;
}

/*
 * Add a ref_entry to the ref_dir (unsorted), recursing into
 * subdirectories as necessary.  dir must represent the top-level
 * directory.  Return 0 on success.
 */
static int add_ref(struct ref_dir *dir, struct ref_entry *ref)
{
        dir = find_containing_dir(dir, ref->name, 1);
        if (!dir)
                return -1;
        add_entry_to_dir(dir, ref);
        return 0;
}

/*
 * Emit a warning and return true iff ref1 and ref2 have the same name
 * and the same sha1.  Die if they have the same name but different
 * sha1s.
 */
static int is_dup_ref(const struct ref_entry *ref1, const struct ref_entry *ref2)
{
        if (strcmp(ref1->name, ref2->name))
                return 0;

        /* Duplicate name; make sure that they don't conflict: */

        if ((ref1->flag & REF_DIR) || (ref2->flag & REF_DIR))
                /* This is impossible by construction */
                die("Reference directory conflict: %s", ref1->name);

        if (hashcmp(ref1->u.value.sha1, ref2->u.value.sha1))
                die("Duplicated ref, and SHA1s don't match: %s", ref1->name);

        warning("Duplicated ref: %s", ref1->name);
        return 1;
}

/*
 * Sort the entries in dir non-recursively (if they are not already
 * sorted) and remove any duplicate entries.
 */
static void sort_ref_dir(struct ref_dir *dir)
{
        int i, j;
        struct ref_entry *last = NULL;

        /*
         * This check also prevents passing a zero-length array to qsort(),
         * which is a problem on some platforms.
         */
        if (dir->sorted == dir->nr)
                return;

        qsort(dir->entries, dir->nr, sizeof(*dir->entries), ref_entry_cmp);

        /* Remove any duplicates: */
        for (i = 0, j = 0; j < dir->nr; j++) {
                struct ref_entry *entry = dir->entries[j];
                if (last && is_dup_ref(last, entry))
                        free_ref_entry(entry);
                else
                        last = dir->entries[i++] = entry;
        }
        dir->sorted = dir->nr = i;
}

#define DO_FOR_EACH_INCLUDE_BROKEN 01

static struct ref_entry *current_ref;

static int do_one_ref(const char *base, each_ref_fn fn, int trim,
                      int flags, void *cb_data, struct ref_entry *entry)
{
        int retval;
        if (prefixcmp(entry->name, base))
                return 0;

        if (!(flags & DO_FOR_EACH_INCLUDE_BROKEN)) {
                if (entry->flag & REF_ISBROKEN)
                        return 0; /* ignore broken refs e.g. dangling symref */
                if (!has_sha1_file(entry->u.value.sha1)) {
                        error("%s does not point to a valid object!", entry->name);
                        return 0;
                }
        }
        current_ref = entry;
        retval = fn(entry->name + trim, entry->u.value.sha1, entry->flag, cb_data);
        current_ref = NULL;
        return retval;
}

/*
 * Call fn for each reference in dir that has index in the range
 * offset <= index < dir->nr.  Recurse into subdirectories that are in
 * that index range, sorting them before iterating.  This function
 * does not sort dir itself; it should be sorted beforehand.
 */
static int do_for_each_ref_in_dir(struct ref_dir *dir, int offset,
                                  const char *base,
                                  each_ref_fn fn, int trim, int flags, void *cb_data)
{
        int i;
        assert(dir->sorted == dir->nr);
        for (i = offset; i < dir->nr; i++) {
                struct ref_entry *entry = dir->entries[i];
                int retval;
                if (entry->flag & REF_DIR) {
                        struct ref_dir *subdir = get_ref_dir(entry);
                        sort_ref_dir(subdir);
                        retval = do_for_each_ref_in_dir(subdir, 0,
                                                        base, fn, trim, flags, cb_data);
                } else {
                        retval = do_one_ref(base, fn, trim, flags, cb_data, entry);
                }
                if (retval)
                        return retval;
        }
        return 0;
}

/*
 * Call fn for each reference in the union of dir1 and dir2, in order
 * by refname.  Recurse into subdirectories.  If a value entry appears
 * in both dir1 and dir2, then only process the version that is in
 * dir2.  The input dirs must already be sorted, but subdirs will be
 * sorted as needed.
 */
static int do_for_each_ref_in_dirs(struct ref_dir *dir1,
                                   struct ref_dir *dir2,
                                   const char *base, each_ref_fn fn, int trim,
                                   int flags, void *cb_data)
{
        int retval;
        int i1 = 0, i2 = 0;

        assert(dir1->sorted == dir1->nr);
        assert(dir2->sorted == dir2->nr);
        while (1) {
                struct ref_entry *e1, *e2;
                int cmp;
                if (i1 == dir1->nr) {
                        return do_for_each_ref_in_dir(dir2, i2,
                                                      base, fn, trim, flags, cb_data);
                }
                if (i2 == dir2->nr) {
                        return do_for_each_ref_in_dir(dir1, i1,
                                                      base, fn, trim, flags, cb_data);
                }
                e1 = dir1->entries[i1];
                e2 = dir2->entries[i2];
                cmp = strcmp(e1->name, e2->name);
                if (cmp == 0) {
                        if ((e1->flag & REF_DIR) && (e2->flag & REF_DIR)) {
                                /* Both are directories; descend them in parallel. */
                                struct ref_dir *subdir1 = get_ref_dir(e1);
                                struct ref_dir *subdir2 = get_ref_dir(e2);
                                sort_ref_dir(subdir1);
                                sort_ref_dir(subdir2);
                                retval = do_for_each_ref_in_dirs(
                                                subdir1, subdir2,
                                                base, fn, trim, flags, cb_data);
                                i1++;
                                i2++;
                        } else if (!(e1->flag & REF_DIR) && !(e2->flag & REF_DIR)) {
                                /* Both are references; ignore the one from dir1. */
                                retval = do_one_ref(base, fn, trim, flags, cb_data, e2);
                                i1++;
                                i2++;
                        } else {
                                die("conflict between reference and directory: %s",
                                    e1->name);
                        }
                } else {
                        struct ref_entry *e;
                        if (cmp < 0) {
                                e = e1;
                                i1++;
                        } else {
                                e = e2;
                                i2++;
                        }
                        if (e->flag & REF_DIR) {
                                struct ref_dir *subdir = get_ref_dir(e);
                                sort_ref_dir(subdir);
                                retval = do_for_each_ref_in_dir(
                                                subdir, 0,
                                                base, fn, trim, flags, cb_data);
                        } else {
                                retval = do_one_ref(base, fn, trim, flags, cb_data, e);
                        }
                }
                if (retval)
                        return retval;
        }
        if (i1 < dir1->nr)
                return do_for_each_ref_in_dir(dir1, i1,
                                              base, fn, trim, flags, cb_data);
        if (i2 < dir2->nr)
                return do_for_each_ref_in_dir(dir2, i2,
                                              base, fn, trim, flags, cb_data);
        return 0;
}

/*
 * Return true iff refname1 and refname2 conflict with each other.
 * Two reference names conflict if one of them exactly matches the
 * leading components of the other; e.g., "foo/bar" conflicts with
 * both "foo" and with "foo/bar/baz" but not with "foo/bar" or
 * "foo/barbados".
 */
static int names_conflict(const char *refname1, const char *refname2)
{
        for (; *refname1 && *refname1 == *refname2; refname1++, refname2++)
                ;
        return (*refname1 == '\0' && *refname2 == '/')
                || (*refname1 == '/' && *refname2 == '\0');
}

struct name_conflict_cb {
        const char *refname;
        const char *oldrefname;
        const char *conflicting_refname;
};

static int name_conflict_fn(const char *existingrefname, const unsigned char *sha1,
                            int flags, void *cb_data)
{
        struct name_conflict_cb *data = (struct name_conflict_cb *)cb_data;
        if (data->oldrefname && !strcmp(data->oldrefname, existingrefname))
                return 0;
        if (names_conflict(data->refname, existingrefname)) {
                data->conflicting_refname = existingrefname;
                return 1;
        }
        return 0;
}

/*
 * Return true iff a reference named refname could be created without
 * conflicting with the name of an existing reference in array.  If
 * oldrefname is non-NULL, ignore potential conflicts with oldrefname
 * (e.g., because oldrefname is scheduled for deletion in the same
 * operation).
 */
static int is_refname_available(const char *refname, const char *oldrefname,
                                struct ref_dir *dir)
{
        struct name_conflict_cb data;
        data.refname = refname;
        data.oldrefname = oldrefname;
        data.conflicting_refname = NULL;

        sort_ref_dir(dir);
        if (do_for_each_ref_in_dir(dir, 0, "", name_conflict_fn,
                                   0, DO_FOR_EACH_INCLUDE_BROKEN,
                                   &data)) {
                error("'%s' exists; cannot create '%s'",
                      data.conflicting_refname, refname);
                return 0;
        }
        return 1;
}

/*
 * Future: need to be in "struct repository"
 * when doing a full libification.
 */
static struct ref_cache {
        struct ref_cache *next;
        struct ref_entry *loose;
        struct ref_entry *packed;
        /* The submodule name, or "" for the main repo. */
        char name[FLEX_ARRAY];
} *ref_cache;

static void clear_packed_ref_cache(struct ref_cache *refs)
{
        if (refs->packed) {
                free_ref_entry(refs->packed);
                refs->packed = NULL;
        }
}

static void clear_loose_ref_cache(struct ref_cache *refs)
{
        if (refs->loose) {
                free_ref_entry(refs->loose);
                refs->loose = NULL;
        }
}

static struct ref_cache *create_ref_cache(const char *submodule)
{
        int len;
        struct ref_cache *refs;
        if (!submodule)
                submodule = "";
        len = strlen(submodule) + 1;
        refs = xcalloc(1, sizeof(struct ref_cache) + len);
        memcpy(refs->name, submodule, len);
        return refs;
}

/*
 * Return a pointer to a ref_cache for the specified submodule. For
 * the main repository, use submodule==NULL. The returned structure
 * will be allocated and initialized but not necessarily populated; it
 * should not be freed.
 */
static struct ref_cache *get_ref_cache(const char *submodule)
{
        struct ref_cache *refs = ref_cache;
        if (!submodule)
                submodule = "";
        while (refs) {
                if (!strcmp(submodule, refs->name))
                        return refs;
                refs = refs->next;
        }

        refs = create_ref_cache(submodule);
        refs->next = ref_cache;
        ref_cache = refs;
        return refs;
}

void invalidate_ref_cache(const char *submodule)
{
        struct ref_cache *refs = get_ref_cache(submodule);
        clear_packed_ref_cache(refs);
        clear_loose_ref_cache(refs);
}

/*
 * Parse one line from a packed-refs file.  Write the SHA1 to sha1.
 * Return a pointer to the refname within the line (null-terminated),
 * or NULL if there was a problem.
 */
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 void read_packed_refs(FILE *f, struct ref_dir *dir)
{
        struct ref_entry *last = NULL;
        char refline[PATH_MAX];
        int flag = REF_ISPACKED;

        while (fgets(refline, sizeof(refline), f)) {
                unsigned char sha1[20];
                const char *refname;
                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;
                }

                refname = parse_ref_line(refline, sha1);
                if (refname) {
                        last = create_ref_entry(refname, sha1, flag, 1);
                        add_ref(dir, last);
                        continue;
                }
                if (last &&
                    refline[0] == '^' &&
                    strlen(refline) == 42 &&
                    refline[41] == '\n' &&
                    !get_sha1_hex(refline + 1, sha1))
                        hashcpy(last->u.value.peeled, sha1);
        }
}

static struct ref_dir *get_packed_refs(struct ref_cache *refs)
{
        if (!refs->packed) {
                const char *packed_refs_file;
                FILE *f;

                refs->packed = create_dir_entry("");
                if (*refs->name)
                        packed_refs_file = git_path_submodule(refs->name, "packed-refs");
                else
                        packed_refs_file = git_path("packed-refs");
                f = fopen(packed_refs_file, "r");
                if (f) {
                        read_packed_refs(f, get_ref_dir(refs->packed));
                        fclose(f);
                }
        }
        return get_ref_dir(refs->packed);
}

void add_packed_ref(const char *refname, const unsigned char *sha1)
{
        add_ref(get_packed_refs(get_ref_cache(NULL)),
                        create_ref_entry(refname, sha1, REF_ISPACKED, 1));
}

/*
 * Read the loose references for refs from the namespace dirname.
 * dirname must end with '/'.  dir must be the directory entry
 * corresponding to dirname.
 */
static void read_loose_refs(struct ref_cache *refs, const char *dirname,
                            struct ref_dir *dir)
{
        DIR *d;
        const char *path;
        struct dirent *de;
        int dirnamelen = strlen(dirname);
        struct strbuf refname;

        if (*refs->name)
                path = git_path_submodule(refs->name, "%s", dirname);
        else
                path = git_path("%s", dirname);

        d = opendir(path);
        if (!d)
                return;

        strbuf_init(&refname, dirnamelen + 257);
        strbuf_add(&refname, dirname, dirnamelen);

        while ((de = readdir(d)) != NULL) {
                unsigned char sha1[20];
                struct stat st;
                int flag;
                const char *refdir;

                if (de->d_name[0] == '.')
                        continue;
                if (has_extension(de->d_name, ".lock"))
                        continue;
                strbuf_addstr(&refname, de->d_name);
                refdir = *refs->name
                        ? git_path_submodule(refs->name, "%s", refname.buf)
                        : git_path("%s", refname.buf);
                if (stat(refdir, &st) < 0) {
                        ; /* silently ignore */
                } else if (S_ISDIR(st.st_mode)) {
                        strbuf_addch(&refname, '/');
                        read_loose_refs(refs, refname.buf,
                                        get_ref_dir(search_for_subdir(dir, refname.buf, 1)));
                } else {
                        if (*refs->name) {
                                hashclr(sha1);
                                flag = 0;
                                if (resolve_gitlink_ref(refs->name, refname.buf, sha1) < 0) {
                                        hashclr(sha1);
                                        flag |= REF_ISBROKEN;
                                }
                        } else if (read_ref_full(refname.buf, sha1, 1, &flag)) {
                                hashclr(sha1);
                                flag |= REF_ISBROKEN;
                        }
                        add_entry_to_dir(dir,
                                         create_ref_entry(refname.buf, sha1, flag, 1));
                }
                strbuf_setlen(&refname, dirnamelen);
        }
        strbuf_release(&refname);
        closedir(d);
}

static struct ref_dir *get_loose_refs(struct ref_cache *refs)
{
        if (!refs->loose) {
                refs->loose = create_dir_entry("");
                read_loose_refs(refs, "refs/",
                                get_ref_dir(search_for_subdir(get_ref_dir(refs->loose),
                                                              "refs/", 1)));
        }
        return get_ref_dir(refs->loose);
}

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

/*
 * Called by resolve_gitlink_ref_recursive() after it failed to read
 * from the loose refs in ref_cache refs. Find <refname> in the
 * packed-refs file for the submodule.
 */
static int resolve_gitlink_packed_ref(struct ref_cache *refs,
                                      const char *refname, unsigned char *sha1)
{
        struct ref_entry *ref;
        struct ref_dir *dir = get_packed_refs(refs);

        ref = find_ref(dir, refname);
        if (ref == NULL)
                return -1;

        memcpy(sha1, ref->u.value.sha1, 20);
        return 0;
}

static int resolve_gitlink_ref_recursive(struct ref_cache *refs,
                                         const char *refname, unsigned char *sha1,
                                         int recursion)
{
        int fd, len;
        char buffer[128], *p;
        char *path;

        if (recursion > MAXDEPTH || strlen(refname) > MAXREFLEN)
                return -1;
        path = *refs->name
                ? git_path_submodule(refs->name, "%s", refname)
                : git_path("%s", refname);
        fd = open(path, O_RDONLY);
        if (fd < 0)
                return resolve_gitlink_packed_ref(refs, refname, sha1);

        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, sha1))
                return 0;

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

        return resolve_gitlink_ref_recursive(refs, p, sha1, recursion+1);
}

int resolve_gitlink_ref(const char *path, const char *refname, unsigned char *sha1)
{
        int len = strlen(path), retval;
        char *submodule;
        struct ref_cache *refs;

        while (len && path[len-1] == '/')
                len--;
        if (!len)
                return -1;
        submodule = xstrndup(path, len);
        refs = get_ref_cache(submodule);
        free(submodule);

        retval = resolve_gitlink_ref_recursive(refs, refname, sha1, 0);
        return retval;
}

/*
 * Try to read ref from the packed references.  On success, set sha1
 * and return 0; otherwise, return -1.
 */
static int get_packed_ref(const char *refname, unsigned char *sha1)
{
        struct ref_dir *packed = get_packed_refs(get_ref_cache(NULL));
        struct ref_entry *entry = find_ref(packed, refname);
        if (entry) {
                hashcpy(sha1, entry->u.value.sha1);
                return 0;
        }
        return -1;
}

const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int reading, int *flag)
{
        int depth = MAXDEPTH;
        ssize_t len;
        char buffer[256];
        static char refname_buffer[256];

        if (flag)
                *flag = 0;

        if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL))
                return NULL;

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

                if (--depth < 0)
                        return NULL;

                git_snpath(path, sizeof(path), "%s", refname);

                if (lstat(path, &st) < 0) {
                        if (errno != ENOENT)
                                return NULL;
                        /*
                         * The loose reference file does not exist;
                         * check for a packed reference.
                         */
                        if (!get_packed_ref(refname, sha1)) {
                                if (flag)
                                        *flag |= REF_ISPACKED;
                                return refname;
                        }
                        /* The reference is not a packed reference, either. */
                        if (reading) {
                                return NULL;
                        } else {
                                hashclr(sha1);
                                return refname;
                        }
                }

                /* Follow "normalized" - ie "refs/.." symlinks by hand */
                if (S_ISLNK(st.st_mode)) {
                        len = readlink(path, buffer, sizeof(buffer)-1);
                        if (len < 0)
                                return NULL;
                        buffer[len] = 0;
                        if (!prefixcmp(buffer, "refs/") &&
                                        !check_refname_format(buffer, 0)) {
                                strcpy(refname_buffer, buffer);
                                refname = refname_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);
                if (len < 0)
                        return NULL;
                while (len && isspace(buffer[len-1]))
                        len--;
                buffer[len] = '\0';

                /*
                 * Is it a symbolic ref?
                 */
                if (prefixcmp(buffer, "ref:"))
                        break;
                if (flag)
                        *flag |= REF_ISSYMREF;
                buf = buffer + 4;
                while (isspace(*buf))
                        buf++;
                if (check_refname_format(buf, REFNAME_ALLOW_ONELEVEL)) {
                        if (flag)
                                *flag |= REF_ISBROKEN;
                        return NULL;
                }
                refname = strcpy(refname_buffer, buf);
        }
        /* Please note that FETCH_HEAD has a second line containing other data. */
        if (get_sha1_hex(buffer, sha1) || (buffer[40] != '\0' && !isspace(buffer[40]))) {
                if (flag)
                        *flag |= REF_ISBROKEN;
                return NULL;
        }
        return refname;
}

char *resolve_refdup(const char *ref, unsigned char *sha1, int reading, int *flag)
{
        const char *ret = resolve_ref_unsafe(ref, sha1, reading, flag);
        return ret ? xstrdup(ret) : NULL;
}

/* The argument to filter_refs */
struct ref_filter {
        const char *pattern;
        each_ref_fn *fn;
        void *cb_data;
};

int read_ref_full(const char *refname, unsigned char *sha1, int reading, int *flags)
{
        if (resolve_ref_unsafe(refname, sha1, reading, flags))
                return 0;
        return -1;
}

int read_ref(const char *refname, unsigned char *sha1)
{
        return read_ref_full(refname, sha1, 1, NULL);
}

int ref_exists(const char *refname)
{
        unsigned char sha1[20];
        return !!resolve_ref_unsafe(refname, sha1, 1, NULL);
}

static int filter_refs(const char *refname, const unsigned char *sha1, int flags,
                       void *data)
{
        struct ref_filter *filter = (struct ref_filter *)data;
        if (fnmatch(filter->pattern, refname, 0))
                return 0;
        return filter->fn(refname, sha1, flags, filter->cb_data);
}

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

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

        if (read_ref_full(refname, base, 1, &flag))
                return -1;

        if ((flag & REF_ISPACKED)) {
                struct ref_dir *dir = get_packed_refs(get_ref_cache(NULL));
                struct ref_entry *r = find_ref(dir, refname);

                if (r != NULL && r->flag & REF_KNOWS_PEELED) {
                        hashcpy(sha1, r->u.value.peeled);
                        return 0;
                }
        }

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

struct warn_if_dangling_data {
        FILE *fp;
        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_unsafe(refname, junk, 0, NULL);
        if (!resolves_to || strcmp(resolves_to, d->refname))
                return 0;

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

void warn_dangling_symref(FILE *fp, const char *msg_fmt, const char *refname)
{
        struct warn_if_dangling_data data;

        data.fp = fp;
        data.refname = refname;
        data.msg_fmt = msg_fmt;
        for_each_rawref(warn_if_dangling_symref, &data);
}

static int do_for_each_ref(const char *submodule, const char *base, each_ref_fn fn,
                           int trim, int flags, void *cb_data)
{
        struct ref_cache *refs = get_ref_cache(submodule);
        struct ref_dir *packed_dir = get_packed_refs(refs);
        struct ref_dir *loose_dir = get_loose_refs(refs);
        int retval = 0;

        if (base && *base) {
                packed_dir = find_containing_dir(packed_dir, base, 0);
                loose_dir = find_containing_dir(loose_dir, base, 0);
        }

        if (packed_dir && loose_dir) {
                sort_ref_dir(packed_dir);
                sort_ref_dir(loose_dir);
                retval = do_for_each_ref_in_dirs(
                                packed_dir, loose_dir,
                                base, fn, trim, flags, cb_data);
        } else if (packed_dir) {
                sort_ref_dir(packed_dir);
                retval = do_for_each_ref_in_dir(
                                packed_dir, 0,
                                base, fn, trim, flags, cb_data);
        } else if (loose_dir) {
                sort_ref_dir(loose_dir);
                retval = do_for_each_ref_in_dir(
                                loose_dir, 0,
                                base, fn, trim, flags, cb_data);
        }

        return retval;
}

static int do_head_ref(const char *submodule, each_ref_fn fn, void *cb_data)
{
        unsigned char sha1[20];
        int flag;

        if (submodule) {
                if (resolve_gitlink_ref(submodule, "HEAD", sha1) == 0)
                        return fn("HEAD", sha1, 0, cb_data);

                return 0;
        }

        if (!read_ref_full("HEAD", sha1, 1, &flag))
                return fn("HEAD", sha1, flag, cb_data);

        return 0;
}

int head_ref(each_ref_fn fn, void *cb_data)
{
        return do_head_ref(NULL, fn, cb_data);
}

int head_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
{
        return do_head_ref(submodule, fn, cb_data);
}

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

int for_each_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
{
        return do_for_each_ref(submodule, "", 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(NULL, prefix, fn, strlen(prefix), 0, cb_data);
}

int for_each_ref_in_submodule(const char *submodule, const char *prefix,
                each_ref_fn fn, void *cb_data)
{
        return do_for_each_ref(submodule, 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_tag_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
{
        return for_each_ref_in_submodule(submodule, "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_branch_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
{
        return for_each_ref_in_submodule(submodule, "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_remote_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
{
        return for_each_ref_in_submodule(submodule, "refs/remotes/", fn, cb_data);
}

int for_each_replace_ref(each_ref_fn fn, void *cb_data)
{
        return do_for_each_ref(NULL, "refs/replace/", fn, 13, 0, cb_data);
}

int head_ref_namespaced(each_ref_fn fn, void *cb_data)
{
        struct strbuf buf = STRBUF_INIT;
        int ret = 0;
        unsigned char sha1[20];
        int flag;

        strbuf_addf(&buf, "%sHEAD", get_git_namespace());
        if (!read_ref_full(buf.buf, sha1, 1, &flag))
                ret = fn(buf.buf, sha1, flag, cb_data);
        strbuf_release(&buf);

        return ret;
}

int for_each_namespaced_ref(each_ref_fn fn, void *cb_data)
{
        struct strbuf buf = STRBUF_INIT;
        int ret;
        strbuf_addf(&buf, "%srefs/", get_git_namespace());
        ret = do_for_each_ref(NULL, buf.buf, fn, 0, 0, cb_data);
        strbuf_release(&buf);
        return ret;
}

int for_each_glob_ref_in(each_ref_fn fn, const char *pattern,
        const char *prefix, void *cb_data)
{
        struct strbuf real_pattern = STRBUF_INIT;
        struct ref_filter filter;
        int ret;

        if (!prefix && prefixcmp(pattern, "refs/"))
                strbuf_addstr(&real_pattern, "refs/");
        else if (prefix)
                strbuf_addstr(&real_pattern, prefix);
        strbuf_addstr(&real_pattern, pattern);

        if (!has_glob_specials(pattern)) {
                /* Append implied '/' '*' if not present. */
                if (real_pattern.buf[real_pattern.len - 1] != '/')
                        strbuf_addch(&real_pattern, '/');
                /* No need to check for '*', there is none. */
                strbuf_addch(&real_pattern, '*');
        }

        filter.pattern = real_pattern.buf;
        filter.fn = fn;
        filter.cb_data = cb_data;
        ret = for_each_ref(filter_refs, &filter);

        strbuf_release(&real_pattern);
        return ret;
}

int for_each_glob_ref(each_ref_fn fn, const char *pattern, void *cb_data)
{
        return for_each_glob_ref_in(fn, pattern, NULL, cb_data);
}

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

const char *prettify_refname(const char *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
};

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 (read_ref_full(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, REMOVE_DIR_EMPTY_ONLY);

        strbuf_release(&path);

        return result;
}

/*
 * *string and *len will only be substituted, and *string returned (for
 * later free()ing) if the string passed in is a magic short-hand form
 * to name a branch.
 */
static char *substitute_branch_name(const char **string, int *len)
{
        struct strbuf buf = STRBUF_INIT;
        int ret = interpret_branch_name(*string, &buf);

        if (ret == *len) {
                size_t size;
                *string = strbuf_detach(&buf, &size);
                *len = size;
                return (char *)*string;
        }

        return NULL;
}

int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref)
{
        char *last_branch = substitute_branch_name(&str, &len);
        const char **p, *r;
        int refs_found = 0;

        *ref = NULL;
        for (p = ref_rev_parse_rules; *p; p++) {
                char fullref[PATH_MAX];
                unsigned char sha1_from_ref[20];
                unsigned char *this_result;
                int flag;

                this_result = refs_found ? sha1_from_ref : sha1;
                mksnpath(fullref, sizeof(fullref), *p, len, str);
                r = resolve_ref_unsafe(fullref, this_result, 1, &flag);
                if (r) {
                        if (!refs_found++)
                                *ref = xstrdup(r);
                        if (!warn_ambiguous_refs)
                                break;
                } else if ((flag & REF_ISSYMREF) && strcmp(fullref, "HEAD")) {
                        warning("ignoring dangling symref %s.", fullref);
                } else if ((flag & REF_ISBROKEN) && strchr(fullref, '/')) {
                        warning("ignoring broken ref %s.", fullref);
                }
        }
        free(last_branch);
        return refs_found;
}

int dwim_log(const char *str, int len, unsigned char *sha1, char **log)
{
        char *last_branch = substitute_branch_name(&str, &len);
        const char **p;
        int logs_found = 0;

        *log = NULL;
        for (p = ref_rev_parse_rules; *p; p++) {
                struct stat st;
                unsigned char hash[20];
                char path[PATH_MAX];
                const char *ref, *it;

                mksnpath(path, sizeof(path), *p, len, str);
                ref = resolve_ref_unsafe(path, hash, 1, NULL);
                if (!ref)
                        continue;
                if (!stat(git_path("logs/%s", path), &st) &&
                    S_ISREG(st.st_mode))
                        it = path;
                else if (strcmp(ref, path) &&
                         !stat(git_path("logs/%s", ref), &st) &&
                         S_ISREG(st.st_mode))
                        it = ref;
                else
                        continue;
                if (!logs_found++) {
                        *log = xstrdup(it);
                        hashcpy(sha1, hash);
                }
                if (!warn_ambiguous_refs)
                        break;
        }
        free(last_branch);
        return logs_found;
}

static struct ref_lock *lock_ref_sha1_basic(const char *refname,
                                            const unsigned char *old_sha1,
                                            int flags, int *type_p)
{
        char *ref_file;
        const char *orig_refname = refname;
        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;

        refname = resolve_ref_unsafe(refname, lock->old_sha1, mustexist, &type);
        if (!refname && 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_refname);
                if (remove_empty_directories(ref_file)) {
                        last_errno = errno;
                        error("there are still refs under '%s'", orig_refname);
                        goto error_return;
                }
                refname = resolve_ref_unsafe(orig_refname, lock->old_sha1, mustexist, &type);
        }
        if (type_p)
            *type_p = type;
        if (!refname) {
                last_errno = errno;
                error("unable to resolve reference %s: %s",
                        orig_refname, 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(refname, NULL, get_packed_refs(get_ref_cache(NULL)))) {
                last_errno = ENOTDIR;
                goto error_return;
        }

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

        lflags = LOCK_DIE_ON_ERROR;
        if (flags & REF_NODEREF) {
                refname = orig_refname;
                lflags |= LOCK_NODEREF;
        }
        lock->ref_name = xstrdup(refname);
        lock->orig_ref_name = xstrdup(orig_refname);
        ref_file = git_path("%s", refname);
        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 *refname, const unsigned char *old_sha1)
{
        char refpath[PATH_MAX];
        if (check_refname_format(refname, 0))
                return NULL;
        strcpy(refpath, mkpath("refs/%s", refname));
        return lock_ref_sha1_basic(refpath, old_sha1, 0, NULL);
}

struct ref_lock *lock_any_ref_for_update(const char *refname,
                                         const unsigned char *old_sha1, int flags)
{
        if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL))
                return NULL;
        return lock_ref_sha1_basic(refname, old_sha1, flags, NULL);
}

struct repack_without_ref_sb {
        const char *refname;
        int fd;
};

static int repack_without_ref_fn(const char *refname, const unsigned char *sha1,
                                 int flags, void *cb_data)
{
        struct repack_without_ref_sb *data = cb_data;
        char line[PATH_MAX + 100];
        int len;

        if (!strcmp(data->refname, refname))
                return 0;
        len = snprintf(line, sizeof(line), "%s %s\n",
                       sha1_to_hex(sha1), refname);
        /* this should not happen but just being defensive */
        if (len > sizeof(line))
                die("too long a refname '%s'", refname);
        write_or_die(data->fd, line, len);
        return 0;
}

static struct lock_file packlock;

static int repack_without_ref(const char *refname)
{
        struct repack_without_ref_sb data;
        struct ref_dir *packed = get_packed_refs(get_ref_cache(NULL));
        if (find_ref(packed, refname) == NULL)
                return 0;
        data.refname = refname;
        data.fd = hold_lock_file_for_update(&packlock, git_path("packed-refs"), 0);
        if (data.fd < 0) {
                unable_to_lock_error(git_path("packed-refs"), errno);
                return error("cannot delete '%s' from packed refs", refname);
        }
        do_for_each_ref_in_dir(packed, 0, "", repack_without_ref_fn, 0, 0, &data);
        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_ref_cache(NULL);
        unlock_ref(lock);
        return ret;
}

/*
 * People using contrib's git-new-workdir have .git/logs/refs ->
 * /some/other/path/.git/logs/refs, and that may live on another device.
 *
 * IOW, to avoid cross device rename errors, the temporary renamed log must
 * live into logs/refs.
 */
#define TMP_RENAMED_LOG  "logs/refs/.tmp-renamed-log"

int rename_ref(const char *oldrefname, const char *newrefname, const char *logmsg)
{
        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", oldrefname), &loginfo);
        const char *symref = NULL;
        struct ref_cache *refs = get_ref_cache(NULL);

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

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

        if (!is_refname_available(newrefname, oldrefname, get_packed_refs(refs)))
                return 1;

        if (!is_refname_available(newrefname, oldrefname, get_loose_refs(refs)))
                return 1;

        if (log && rename(git_path("logs/%s", oldrefname), git_path(TMP_RENAMED_LOG)))
                return error("unable to move logfile logs/%s to "TMP_RENAMED_LOG": %s",
                        oldrefname, strerror(errno));

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

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

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

 retry:
        if (log && rename(git_path(TMP_RENAMED_LOG), git_path("logs/%s", newrefname))) {
                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", newrefname))) {
                                error("Directory not empty: logs/%s", newrefname);
                                goto rollback;
                        }
                        goto retry;
                } else {
                        error("unable to move logfile "TMP_RENAMED_LOG" to logs/%s: %s",
                                newrefname, strerror(errno));
                        goto rollback;
                }
        }
        logmoved = log;

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

        return 0;

 rollback:
        lock = lock_ref_sha1_basic(oldrefname, NULL, 0, NULL);
        if (!lock) {
                error("unable to lock %s for rollback", oldrefname);
                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", oldrefname);
        log_all_ref_updates = flag;

 rollbacklog:
        if (logmoved && rename(git_path("logs/%s", newrefname), git_path("logs/%s", oldrefname)))
                error("unable to restore logfile %s from %s: %s",
                        oldrefname, newrefname, strerror(errno));
        if (!logmoved && log &&
            rename(git_path(TMP_RENAMED_LOG), git_path("logs/%s", oldrefname)))
                error("unable to restore logfile %s from "TMP_RENAMED_LOG": %s",
                        oldrefname, 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;
}

int log_ref_setup(const char *refname, char *logfile, int bufsize)
{
        int logfd, oflags = O_APPEND | O_WRONLY;

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

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

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

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

        adjust_shared_perm(logfile);
        close(logfd);
        return 0;
}

static int log_ref_write(const char *refname, const unsigned char *old_sha1,
                         const unsigned char *new_sha1, const char *msg)
{
        int logfd, result, 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();

        result = log_ref_setup(refname, log_file, sizeof(log_file));
        if (result)
                return result;

        logfd = open(log_file, oflags);
        if (logfd < 0)
                return 0;
        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 nonexistent 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;
        }
        clear_loose_ref_cache(get_ref_cache(NULL));
        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_unsafe("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 *refname, 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", refname);
        logfd = open(logfile, O_RDONLY, 0);
        if (logfd < 0)
                die_errno("Unable to read log '%s'", logfile);
        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 *refname, each_reflog_ent_fn fn, long ofs, void *cb_data)
{
        const char *logfile;
        FILE *logfp;
        struct strbuf sb = STRBUF_INIT;
        int ret = 0;

        logfile = git_path("logs/%s", refname);
        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) ||
                    strbuf_getwholeline(&sb, logfp, '\n')) {
                        fclose(logfp);
                        strbuf_release(&sb);
                        return -1;
                }
        }

        while (!strbuf_getwholeline(&sb, logfp, '\n')) {
                unsigned char osha1[20], nsha1[20];
                char *email_end, *message;
                unsigned long timestamp;
                int tz;

                /* old SP new SP name <email> SP time TAB msg LF */
                if (sb.len < 83 || sb.buf[sb.len - 1] != '\n' ||
                    get_sha1_hex(sb.buf, osha1) || sb.buf[40] != ' ' ||
                    get_sha1_hex(sb.buf + 41, nsha1) || sb.buf[81] != ' ' ||
                    !(email_end = strchr(sb.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, sb.buf + 82, timestamp, tz, message,
                         cb_data);
                if (ret)
                        break;
        }
        fclose(logfp);
        strbuf_release(&sb);
        return ret;
}

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

/*
 * Call fn for each reflog in the namespace indicated by name.  name
 * must be empty or end with '/'.  Name will be used as a scratch
 * space, but its contents will be restored before return.
 */
static int do_for_each_reflog(struct strbuf *name, each_ref_fn fn, void *cb_data)
{
        DIR *d = opendir(git_path("logs/%s", name->buf));
        int retval = 0;
        struct dirent *de;
        int oldlen = name->len;

        if (!d)
                return name->len ? errno : 0;

        while ((de = readdir(d)) != NULL) {
                struct stat st;

                if (de->d_name[0] == '.')
                        continue;
                if (has_extension(de->d_name, ".lock"))
                        continue;
                strbuf_addstr(name, de->d_name);
                if (stat(git_path("logs/%s", name->buf), &st) < 0) {
                        ; /* silently ignore */
                } else {
                        if (S_ISDIR(st.st_mode)) {
                                strbuf_addch(name, '/');
                                retval = do_for_each_reflog(name, fn, cb_data);
                        } else {
                                unsigned char sha1[20];
                                if (read_ref_full(name->buf, sha1, 0, NULL))
                                        retval = error("bad ref for %s", name->buf);
                                else
                                        retval = fn(name->buf, sha1, 0, cb_data);
                        }
                        if (retval)
                                break;
                }
                strbuf_setlen(name, oldlen);
        }
        closedir(d);
        return retval;
}

int for_each_reflog(each_ref_fn fn, void *cb_data)
{
        int retval;
        struct strbuf name;
        strbuf_init(&name, PATH_MAX);
        retval = do_for_each_reflog(&name, fn, cb_data);
        strbuf_release(&name);
        return retval;
}

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 *refname, 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(refname);

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

        /* 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(refname, 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];
                        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 (ref_exists(refname))
                                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(refname);
}