Ignore ref oid terminator

[libgit2.git] / src / refs.c

/*
 * Copyright (C) 2009-2012 the libgit2 contributors
 *
 * This file is part of libgit2, distributed under the GNU GPL v2 with
 * a Linking Exception. For full terms see the included COPYING file.
 */

#include "refs.h"
#include "hash.h"
#include "repository.h"
#include "fileops.h"
#include "pack.h"
#include "reflog.h"

#include <git2/tag.h>
#include <git2/object.h>

GIT__USE_STRMAP;

#define DEFAULT_NESTING_LEVEL   5
#define MAX_NESTING_LEVEL               10

enum {
        GIT_PACKREF_HAS_PEEL = 1,
        GIT_PACKREF_WAS_LOOSE = 2
};

struct packref {
        git_oid oid;
        git_oid peel;
        char flags;
        char name[GIT_FLEX_ARRAY];
};

static int reference_read(
        git_buf *file_content,
        time_t *mtime,
        const char *repo_path,
        const char *ref_name,
        int *updated);

/* loose refs */
static int loose_parse_symbolic(git_reference *ref, git_buf *file_content);
static int loose_parse_oid(git_oid *ref, git_buf *file_content);
static int loose_lookup(git_reference *ref);
static int loose_lookup_to_packfile(struct packref **ref_out,
        git_repository *repo, const char *name);
static int loose_write(git_reference *ref);

/* packed refs */
static int packed_parse_peel(struct packref *tag_ref,
        const char **buffer_out, const char *buffer_end);
static int packed_parse_oid(struct packref **ref_out,
        const char **buffer_out, const char *buffer_end);
static int packed_load(git_repository *repo);
static int packed_loadloose(git_repository *repository);
static int packed_write_ref(struct packref *ref, git_filebuf *file);
static int packed_find_peel(git_repository *repo, struct packref *ref);
static int packed_remove_loose(git_repository *repo, git_vector *packing_list);
static int packed_sort(const void *a, const void *b);
static int packed_lookup(git_reference *ref);
static int packed_write(git_repository *repo);

/* internal helpers */
static int reference_path_available(git_repository *repo,
        const char *ref, const char *old_ref);
static int reference_delete(git_reference *ref);
static int reference_lookup(git_reference *ref);

/* name normalization */
static int normalize_name(char *buffer_out, size_t out_size,
        const char *name, int is_oid_ref);


void git_reference_free(git_reference *reference)
{
        if (reference == NULL)
                return;

        git__free(reference->name);
        reference->name = NULL;

        if (reference->flags & GIT_REF_SYMBOLIC) {
                git__free(reference->target.symbolic);
                reference->target.symbolic = NULL;
        }

        git__free(reference);
}

static int reference_alloc(
        git_reference **ref_out,
        git_repository *repo,
        const char *name)
{
        git_reference *reference = NULL;

        assert(ref_out && repo && name);

        reference = git__malloc(sizeof(git_reference));
        GITERR_CHECK_ALLOC(reference);

        memset(reference, 0x0, sizeof(git_reference));
        reference->owner = repo;

        reference->name = git__strdup(name);
        GITERR_CHECK_ALLOC(reference->name);

        *ref_out = reference;
        return 0;
}

static int reference_read(
        git_buf *file_content,
        time_t *mtime,
        const char *repo_path,
        const char *ref_name,
        int *updated)
{
        git_buf path = GIT_BUF_INIT;
        int result;

        assert(file_content && repo_path && ref_name);

        /* Determine the full path of the file */
        if (git_buf_joinpath(&path, repo_path, ref_name) < 0)
                return -1;

        result = git_futils_readbuffer_updated(file_content, path.ptr, mtime, updated);
        git_buf_free(&path);
        return result;
}

static int loose_parse_symbolic(git_reference *ref, git_buf *file_content)
{
        const unsigned int header_len = (unsigned int)strlen(GIT_SYMREF);
        const char *refname_start;
        char *eol;

        refname_start = (const char *)file_content->ptr;

        if (git_buf_len(file_content) < header_len + 1)
                goto corrupt;

        /*
         * Assume we have already checked for the header
         * before calling this function
         */
        refname_start += header_len;

        ref->target.symbolic = git__strdup(refname_start);
        GITERR_CHECK_ALLOC(ref->target.symbolic);

        /* remove newline at the end of file */
        eol = strchr(ref->target.symbolic, '\n');
        if (eol == NULL)
                goto corrupt;

        *eol = '\0';
        if (eol[-1] == '\r')
                eol[-1] = '\0';

        return 0;

corrupt:
        giterr_set(GITERR_REFERENCE, "Corrupted loose reference file");
        return -1;
}

static int loose_parse_oid(git_oid *oid, git_buf *file_content)
{
        char *buffer;

        buffer = (char *)file_content->ptr;

        /* File format: 40 chars (OID) */
        if (git_buf_len(file_content) < GIT_OID_HEXSZ)
                goto corrupt;

        if (git_oid_fromstr(oid, buffer) < 0)
                goto corrupt;

        return 0;

corrupt:
        giterr_set(GITERR_REFERENCE, "Corrupted loose reference file");
        return -1;
}

static git_ref_t loose_guess_rtype(const git_buf *full_path)
{
        git_buf ref_file = GIT_BUF_INIT;
        git_ref_t type;

        type = GIT_REF_INVALID;

        if (git_futils_readbuffer(&ref_file, full_path->ptr) == 0) {
                if (git__prefixcmp((const char *)(ref_file.ptr), GIT_SYMREF) == 0)
                        type = GIT_REF_SYMBOLIC;
                else
                        type = GIT_REF_OID;
        }

        git_buf_free(&ref_file);
        return type;
}

static int loose_lookup(git_reference *ref)
{
        int result, updated;
        git_buf ref_file = GIT_BUF_INIT;

        result = reference_read(&ref_file, &ref->mtime,
                ref->owner->path_repository, ref->name, &updated);

        if (result < 0)
                return result;

        if (!updated)
                return 0;

        if (ref->flags & GIT_REF_SYMBOLIC) {
                git__free(ref->target.symbolic);
                ref->target.symbolic = NULL;
        }

        ref->flags = 0;

        if (git__prefixcmp((const char *)(ref_file.ptr), GIT_SYMREF) == 0) {
                ref->flags |= GIT_REF_SYMBOLIC;
                result = loose_parse_symbolic(ref, &ref_file);
        } else {
                ref->flags |= GIT_REF_OID;
                result = loose_parse_oid(&ref->target.oid, &ref_file);
        }

        git_buf_free(&ref_file);
        return result;
}

static int loose_lookup_to_packfile(
                struct packref **ref_out,
                git_repository *repo,
                const char *name)
{
        git_buf ref_file = GIT_BUF_INIT;
        struct packref *ref = NULL;
        size_t name_len;

        *ref_out = NULL;

        if (reference_read(&ref_file, NULL, repo->path_repository, name, NULL) < 0)
                return -1;

        name_len = strlen(name);
        ref = git__malloc(sizeof(struct packref) + name_len + 1);
        GITERR_CHECK_ALLOC(ref);

        memcpy(ref->name, name, name_len);
        ref->name[name_len] = 0;

        if (loose_parse_oid(&ref->oid, &ref_file) < 0) {
                git_buf_free(&ref_file);
                git__free(ref);
                return -1;
        }

        ref->flags = GIT_PACKREF_WAS_LOOSE;

        *ref_out = ref;
        git_buf_free(&ref_file);
        return 0;
}

static int loose_write(git_reference *ref)
{
        git_filebuf file = GIT_FILEBUF_INIT;
        git_buf ref_path = GIT_BUF_INIT;
        struct stat st;

        if (git_buf_joinpath(&ref_path, ref->owner->path_repository, ref->name) < 0)
                return -1;

        /* Remove a possibly existing empty directory hierarchy 
         * which name would collide with the reference name
         */
        if (git_path_isdir(git_buf_cstr(&ref_path)) && 
                (git_futils_rmdir_r(git_buf_cstr(&ref_path), GIT_DIRREMOVAL_ONLY_EMPTY_DIRS) < 0)) {
                        git_buf_free(&ref_path);
                        return -1;
                }

        if (git_filebuf_open(&file, ref_path.ptr, GIT_FILEBUF_FORCE) < 0) {
                git_buf_free(&ref_path);
                return -1;
        }

        git_buf_free(&ref_path);

        if (ref->flags & GIT_REF_OID) {
                char oid[GIT_OID_HEXSZ + 1];

                git_oid_fmt(oid, &ref->target.oid);
                oid[GIT_OID_HEXSZ] = '\0';

                git_filebuf_printf(&file, "%s\n", oid);

        } else if (ref->flags & GIT_REF_SYMBOLIC) {
                git_filebuf_printf(&file, GIT_SYMREF "%s\n", ref->target.symbolic);
        } else {
                assert(0); /* don't let this happen */
        }

        if (p_stat(ref_path.ptr, &st) == 0)
                ref->mtime = st.st_mtime;

        return git_filebuf_commit(&file, GIT_REFS_FILE_MODE);
}

static int packed_parse_peel(
                struct packref *tag_ref,
                const char **buffer_out,
                const char *buffer_end)
{
        const char *buffer = *buffer_out + 1;

        assert(buffer[-1] == '^');

        /* Ensure it's not the first entry of the file */
        if (tag_ref == NULL)
                goto corrupt;

        /* Ensure reference is a tag */
        if (git__prefixcmp(tag_ref->name, GIT_REFS_TAGS_DIR) != 0)
                goto corrupt;

        if (buffer + GIT_OID_HEXSZ >= buffer_end)
                goto corrupt;

        /* Is this a valid object id? */
        if (git_oid_fromstr(&tag_ref->peel, buffer) < 0)
                goto corrupt;

        buffer = buffer + GIT_OID_HEXSZ;
        if (*buffer == '\r')
                buffer++;

        if (*buffer != '\n')
                goto corrupt;

        *buffer_out = buffer + 1;
        return 0;

corrupt:
        giterr_set(GITERR_REFERENCE, "The packed references file is corrupted");
        return -1;
}

static int packed_parse_oid(
                struct packref **ref_out,
                const char **buffer_out,
                const char *buffer_end)
{
        struct packref *ref = NULL;

        const char *buffer = *buffer_out;
        const char *refname_begin, *refname_end;

        size_t refname_len;
        git_oid id;

        refname_begin = (buffer + GIT_OID_HEXSZ + 1);
        if (refname_begin >= buffer_end || refname_begin[-1] != ' ')
                goto corrupt;

        /* Is this a valid object id? */
        if (git_oid_fromstr(&id, buffer) < 0)
                goto corrupt;

        refname_end = memchr(refname_begin, '\n', buffer_end - refname_begin);
        if (refname_end == NULL)
                goto corrupt;

        if (refname_end[-1] == '\r')
                refname_end--;

        refname_len = refname_end - refname_begin;

        ref = git__malloc(sizeof(struct packref) + refname_len + 1);
        GITERR_CHECK_ALLOC(ref);

        memcpy(ref->name, refname_begin, refname_len);
        ref->name[refname_len] = 0;

        git_oid_cpy(&ref->oid, &id);

        ref->flags = 0;

        *ref_out = ref;
        *buffer_out = refname_end + 1;

        return 0;

corrupt:
        git__free(ref);
        giterr_set(GITERR_REFERENCE, "The packed references file is corrupted");
        return -1;
}

static int packed_load(git_repository *repo)
{
        int result, updated;
        git_buf packfile = GIT_BUF_INIT;
        const char *buffer_start, *buffer_end;
        git_refcache *ref_cache = &repo->references;

        /* First we make sure we have allocated the hash table */
        if (ref_cache->packfile == NULL) {
                ref_cache->packfile = git_strmap_alloc();
                GITERR_CHECK_ALLOC(ref_cache->packfile);
        }

        result = reference_read(&packfile, &ref_cache->packfile_time,
                repo->path_repository, GIT_PACKEDREFS_FILE, &updated);

        /*
         * If we couldn't find the file, we need to clear the table and
         * return. On any other error, we return that error. If everything
         * went fine and the file wasn't updated, then there's nothing new
         * for us here, so just return. Anything else means we need to
         * refresh the packed refs.
         */
        if (result == GIT_ENOTFOUND) {
                git_strmap_clear(ref_cache->packfile);
                return 0;
        }

        if (result < 0)
                return -1;

        if (!updated)
                return 0;

        /*
         * At this point, we want to refresh the packed refs. We already
         * have the contents in our buffer.
         */
        git_strmap_clear(ref_cache->packfile);

        buffer_start = (const char *)packfile.ptr;
        buffer_end = (const char *)(buffer_start) + packfile.size;

        while (buffer_start < buffer_end && buffer_start[0] == '#') {
                buffer_start = strchr(buffer_start, '\n');
                if (buffer_start == NULL)
                        goto parse_failed;

                buffer_start++;
        }

        while (buffer_start < buffer_end) {
                int err;
                struct packref *ref = NULL;

                if (packed_parse_oid(&ref, &buffer_start, buffer_end) < 0)
                        goto parse_failed;

                if (buffer_start[0] == '^') {
                        if (packed_parse_peel(ref, &buffer_start, buffer_end) < 0)
                                goto parse_failed;
                }

                git_strmap_insert(ref_cache->packfile, ref->name, ref, err);
                if (err < 0)
                        goto parse_failed;
        }

        git_buf_free(&packfile);
        return 0;

parse_failed:
        git_strmap_free(ref_cache->packfile);
        ref_cache->packfile = NULL;
        git_buf_free(&packfile);
        return -1;
}


struct dirent_list_data {
        git_repository *repo;
        size_t repo_path_len;
        unsigned int list_flags;

        int (*callback)(const char *, void *);
        void *callback_payload;
        int callback_error;
};

static int _dirent_loose_listall(void *_data, git_buf *full_path)
{
        struct dirent_list_data *data = (struct dirent_list_data *)_data;
        const char *file_path = full_path->ptr + data->repo_path_len;

        if (git_path_isdir(full_path->ptr) == true)
                return git_path_direach(full_path, _dirent_loose_listall, _data);

        /* do not add twice a reference that exists already in the packfile */
        if ((data->list_flags & GIT_REF_PACKED) != 0 &&
                git_strmap_exists(data->repo->references.packfile, file_path))
                return 0;

        if (data->list_flags != GIT_REF_LISTALL) {
                if ((data->list_flags & loose_guess_rtype(full_path)) == 0)
                        return 0; /* we are filtering out this reference */
        }

        if (data->callback(file_path, data->callback_payload))
                data->callback_error = GIT_EUSER;

        return data->callback_error;
}

static int _dirent_loose_load(void *data, git_buf *full_path)
{
        git_repository *repository = (git_repository *)data;
        void *old_ref = NULL;
        struct packref *ref;
        const char *file_path;
        int err;

        if (git_path_isdir(full_path->ptr) == true)
                return git_path_direach(full_path, _dirent_loose_load, repository);

        file_path = full_path->ptr + strlen(repository->path_repository);

        if (loose_lookup_to_packfile(&ref, repository, file_path) < 0)
                return -1;

        git_strmap_insert2(
                repository->references.packfile, ref->name, ref, old_ref, err);
        if (err < 0) {
                git__free(ref);
                return -1;
        }

        git__free(old_ref);
        return 0;
}

/*
 * Load all the loose references from the repository
 * into the in-memory Packfile, and build a vector with
 * all the references so it can be written back to
 * disk.
 */
static int packed_loadloose(git_repository *repository)
{
        git_buf refs_path = GIT_BUF_INIT;
        int result;

        /* the packfile must have been previously loaded! */
        assert(repository->references.packfile);

        if (git_buf_joinpath(&refs_path, repository->path_repository, GIT_REFS_DIR) < 0)
                return -1;

        /*
         * Load all the loose files from disk into the Packfile table.
         * This will overwrite any old packed entries with their
         * updated loose versions
         */
        result = git_path_direach(&refs_path, _dirent_loose_load, repository);
        git_buf_free(&refs_path);

        return result;
}

/*
 * Write a single reference into a packfile
 */
static int packed_write_ref(struct packref *ref, git_filebuf *file)
{
        char oid[GIT_OID_HEXSZ + 1];

        git_oid_fmt(oid, &ref->oid);
        oid[GIT_OID_HEXSZ] = 0;

        /*
         * For references that peel to an object in the repo, we must
         * write the resulting peel on a separate line, e.g.
         *
         *      6fa8a902cc1d18527e1355773c86721945475d37 refs/tags/libgit2-0.4
         *      ^2ec0cb7959b0bf965d54f95453f5b4b34e8d3100
         *
         * This obviously only applies to tags.
         * The required peels have already been loaded into `ref->peel_target`.
         */
        if (ref->flags & GIT_PACKREF_HAS_PEEL) {
                char peel[GIT_OID_HEXSZ + 1];
                git_oid_fmt(peel, &ref->peel);
                peel[GIT_OID_HEXSZ] = 0;

                if (git_filebuf_printf(file, "%s %s\n^%s\n", oid, ref->name, peel) < 0)
                        return -1;
        } else {
                if (git_filebuf_printf(file, "%s %s\n", oid, ref->name) < 0)
                        return -1;
        }

        return 0;
}

/*
 * Find out what object this reference resolves to.
 *
 * For references that point to a 'big' tag (e.g. an
 * actual tag object on the repository), we need to
 * cache on the packfile the OID of the object to
 * which that 'big tag' is pointing to.
 */
static int packed_find_peel(git_repository *repo, struct packref *ref)
{
        git_object *object;

        if (ref->flags & GIT_PACKREF_HAS_PEEL)
                return 0;

        /*
         * Only applies to tags, i.e. references
         * in the /refs/tags folder
         */
        if (git__prefixcmp(ref->name, GIT_REFS_TAGS_DIR) != 0)
                return 0;

        /*
         * Find the tagged object in the repository
         */
        if (git_object_lookup(&object, repo, &ref->oid, GIT_OBJ_ANY) < 0)
                return -1;

        /*
         * If the tagged object is a Tag object, we need to resolve it;
         * if the ref is actually a 'weak' ref, we don't need to resolve
         * anything.
         */
        if (git_object_type(object) == GIT_OBJ_TAG) {
                git_tag *tag = (git_tag *)object;

                /*
                 * Find the object pointed at by this tag
                 */
                git_oid_cpy(&ref->peel, git_tag_target_oid(tag));
                ref->flags |= GIT_PACKREF_HAS_PEEL;

                /*
                 * The reference has now cached the resolved OID, and is
                 * marked at such. When written to the packfile, it'll be
                 * accompanied by this resolved oid
                 */
        }

        git_object_free(object);
        return 0;
}

/*
 * Remove all loose references
 *
 * Once we have successfully written a packfile,
 * all the loose references that were packed must be
 * removed from disk.
 *
 * This is a dangerous method; make sure the packfile
 * is well-written, because we are destructing references
 * here otherwise.
 */
static int packed_remove_loose(git_repository *repo, git_vector *packing_list)
{
        unsigned int i;
        git_buf full_path = GIT_BUF_INIT;
        int failed = 0;

        for (i = 0; i < packing_list->length; ++i) {
                struct packref *ref = git_vector_get(packing_list, i);

                if ((ref->flags & GIT_PACKREF_WAS_LOOSE) == 0)
                        continue;

                if (git_buf_joinpath(&full_path, repo->path_repository, ref->name) < 0)
                        return -1; /* critical; do not try to recover on oom */

                if (git_path_exists(full_path.ptr) == true && p_unlink(full_path.ptr) < 0) {
                        if (failed)
                                continue;

                        giterr_set(GITERR_REFERENCE,
                                "Failed to remove loose reference '%s' after packing: %s",
                                full_path.ptr, strerror(errno));

                        failed = 1;
                }

                /*
                 * if we fail to remove a single file, this is *not* good,
                 * but we should keep going and remove as many as possible.
                 * After we've removed as many files as possible, we return
                 * the error code anyway.
                 */
        }

        git_buf_free(&full_path);
        return failed ? -1 : 0;
}

static int packed_sort(const void *a, const void *b)
{
        const struct packref *ref_a = (const struct packref *)a;
        const struct packref *ref_b = (const struct packref *)b;

        return strcmp(ref_a->name, ref_b->name);
}

/*
 * Write all the contents in the in-memory packfile to disk.
 */
static int packed_write(git_repository *repo)
{
        git_filebuf pack_file = GIT_FILEBUF_INIT;
        unsigned int i;
        git_buf pack_file_path = GIT_BUF_INIT;
        git_vector packing_list;
        unsigned int total_refs;

        assert(repo && repo->references.packfile);

        total_refs =
                (unsigned int)git_strmap_num_entries(repo->references.packfile);

        if (git_vector_init(&packing_list, total_refs, packed_sort) < 0)
                return -1;

        /* Load all the packfile into a vector */
        {
                struct packref *reference;

                /* cannot fail: vector already has the right size */
                git_strmap_foreach_value(repo->references.packfile, reference, {
                        git_vector_insert(&packing_list, reference);
                });
        }

        /* sort the vector so the entries appear sorted on the packfile */
        git_vector_sort(&packing_list);

        /* Now we can open the file! */
        if (git_buf_joinpath(&pack_file_path, repo->path_repository, GIT_PACKEDREFS_FILE) < 0)
                goto cleanup_memory;

        if (git_filebuf_open(&pack_file, pack_file_path.ptr, 0) < 0)
                goto cleanup_packfile;

        /* Packfiles have a header... apparently
         * This is in fact not required, but we might as well print it
         * just for kicks */
        if (git_filebuf_printf(&pack_file, "%s\n", GIT_PACKEDREFS_HEADER) < 0)
                goto cleanup_packfile;

        for (i = 0; i < packing_list.length; ++i) {
                struct packref *ref = (struct packref *)git_vector_get(&packing_list, i);

                if (packed_find_peel(repo, ref) < 0)
                        goto cleanup_packfile;

                if (packed_write_ref(ref, &pack_file) < 0)
                        goto cleanup_packfile;
        }

        /* if we've written all the references properly, we can commit
         * the packfile to make the changes effective */
        if (git_filebuf_commit(&pack_file, GIT_PACKEDREFS_FILE_MODE) < 0)
                goto cleanup_memory;

        /* when and only when the packfile has been properly written,
         * we can go ahead and remove the loose refs */
         if (packed_remove_loose(repo, &packing_list) < 0)
                 goto cleanup_memory;

         {
                struct stat st;
                if (p_stat(pack_file_path.ptr, &st) == 0)
                        repo->references.packfile_time = st.st_mtime;
         }

        git_vector_free(&packing_list);
        git_buf_free(&pack_file_path);

        /* we're good now */
        return 0;

cleanup_packfile:
        git_filebuf_cleanup(&pack_file);

cleanup_memory:
        git_vector_free(&packing_list);
        git_buf_free(&pack_file_path);

        return -1;
}

struct reference_available_t {
        const char *new_ref;
        const char *old_ref;
        int available;
};

static int _reference_available_cb(const char *ref, void *data)
{
        struct reference_available_t *d;

        assert(ref && data);
        d = (struct reference_available_t *)data;

        if (!d->old_ref || strcmp(d->old_ref, ref)) {
                size_t reflen = strlen(ref);
                size_t newlen = strlen(d->new_ref);
                size_t cmplen = reflen < newlen ? reflen : newlen;
                const char *lead = reflen < newlen ? d->new_ref : ref;

                if (!strncmp(d->new_ref, ref, cmplen) && lead[cmplen] == '/') {
                        d->available = 0;
                        return -1;
                }
        }

        return 0;
}

static int reference_path_available(
        git_repository *repo,
        const char *ref,
        const char* old_ref)
{
        int error;
        struct reference_available_t data;

        data.new_ref = ref;
        data.old_ref = old_ref;
        data.available = 1;

        error = git_reference_foreach(
                repo, GIT_REF_LISTALL, _reference_available_cb, (void *)&data);
        if (error < 0)
                return error;

        if (!data.available) {
                giterr_set(GITERR_REFERENCE,
                        "The path to reference '%s' collides with an existing one", ref);
                return -1;
        }

        return 0;
}

static int reference_exists(int *exists, git_repository *repo, const char *ref_name)
{
        git_buf ref_path = GIT_BUF_INIT;

        if (packed_load(repo) < 0)
                return -1;

        if (git_buf_joinpath(&ref_path, repo->path_repository, ref_name) < 0)
                return -1;

        if (git_path_isfile(ref_path.ptr) == true ||
                git_strmap_exists(repo->references.packfile, ref_path.ptr))
        {
                *exists = 1;
        } else {
                *exists = 0;
        }

        git_buf_free(&ref_path);
        return 0;
}

/*
 * Check if a reference could be written to disk, based on:
 *
 *      - Whether a reference with the same name already exists,
 *      and we are allowing or disallowing overwrites
 *
 *      - Whether the name of the reference would collide with
 *      an existing path
 */
static int reference_can_write(
        git_repository *repo,
        const char *refname,
        const char *previous_name,
        int force)
{
        /* see if the reference shares a path with an existing reference;
         * if a path is shared, we cannot create the reference, even when forcing */
        if (reference_path_available(repo, refname, previous_name) < 0)
                return -1;

        /* check if the reference actually exists, but only if we are not forcing
         * the rename. If we are forcing, it's OK to overwrite */
        if (!force) {
                int exists;

                if (reference_exists(&exists, repo, refname) < 0)
                        return -1;

                /* We cannot proceed if the reference already exists and we're not forcing
                 * the rename; the existing one would be overwritten */
                if (exists) {
                        giterr_set(GITERR_REFERENCE,
                                "A reference with that name (%s) already exists", refname);
                        return GIT_EEXISTS;
                }
        }

        /* FIXME: if the reference exists and we are forcing, do we really need to
         * remove the reference first?
         *
         * Two cases:
         *
         *      - the reference already exists and is loose: not a problem, the file
         *      gets overwritten on disk
         *
         *      - the reference already exists and is packed: we write a new one as
         *      loose, which by all means renders the packed one useless
         */

        return 0;
}


static int packed_lookup(git_reference *ref)
{
        struct packref *pack_ref = NULL;
        git_strmap *packfile_refs;
        khiter_t pos;

        if (packed_load(ref->owner) < 0)
                return -1;

        /* maybe the packfile hasn't changed at all, so we don't
         * have to re-lookup the reference */
        if ((ref->flags & GIT_REF_PACKED) &&
                ref->mtime == ref->owner->references.packfile_time)
                return 0;

        if (ref->flags & GIT_REF_SYMBOLIC) {
                git__free(ref->target.symbolic);
                ref->target.symbolic = NULL;
        }

        /* Look up on the packfile */
        packfile_refs = ref->owner->references.packfile;
        pos = git_strmap_lookup_index(packfile_refs, ref->name);
        if (!git_strmap_valid_index(packfile_refs, pos)) {
                giterr_set(GITERR_REFERENCE, "Reference '%s' not found", ref->name);
                return GIT_ENOTFOUND;
        }

        pack_ref = git_strmap_value_at(packfile_refs, pos);

        ref->flags = GIT_REF_OID | GIT_REF_PACKED;
        ref->mtime = ref->owner->references.packfile_time;
        git_oid_cpy(&ref->target.oid, &pack_ref->oid);

        return 0;
}

static int reference_lookup(git_reference *ref)
{
        int result;

        result = loose_lookup(ref);
        if (result == 0)
                return 0;

        /* only try to lookup this reference on the packfile if it
         * wasn't found on the loose refs; not if there was a critical error */
        if (result == GIT_ENOTFOUND) {
                giterr_clear();
                result = packed_lookup(ref);
                if (result == 0)
                        return 0;
        }

        /* unexpected error; free the reference */
        git_reference_free(ref);
        return result;
}

/*
 * Delete a reference.
 * This is an internal method; the reference is removed
 * from disk or the packfile, but the pointer is not freed
 */
static int reference_delete(git_reference *ref)
{
        int result;

        assert(ref);

        /* If the reference is packed, this is an expensive operation.
         * We need to reload the packfile, remove the reference from the
         * packing list, and repack */
        if (ref->flags & GIT_REF_PACKED) {
                git_strmap *packfile_refs;
                struct packref *packref;
                khiter_t pos;

                /* load the existing packfile */
                if (packed_load(ref->owner) < 0)
                        return -1;

                packfile_refs = ref->owner->references.packfile;
                pos = git_strmap_lookup_index(packfile_refs, ref->name);
                if (!git_strmap_valid_index(packfile_refs, pos)) {
                        giterr_set(GITERR_REFERENCE,
                                "Reference %s stopped existing in the packfile", ref->name);
                        return -1;
                }

                packref = git_strmap_value_at(packfile_refs, pos);
                git_strmap_delete_at(packfile_refs, pos);

                git__free(packref);
                if (packed_write(ref->owner) < 0)
                        return -1;

        /* If the reference is loose, we can just remove the reference
         * from the filesystem */
        } else {
                git_reference *ref_in_pack;
                git_buf full_path = GIT_BUF_INIT;

                if (git_buf_joinpath(&full_path, ref->owner->path_repository, ref->name) < 0)
                        return -1;

                result = p_unlink(full_path.ptr);
                git_buf_free(&full_path); /* done with path at this point */

                if (result < 0) {
                        giterr_set(GITERR_OS, "Failed to unlink '%s'", full_path.ptr);
                        return -1;
                }

                /* When deleting a loose reference, we have to ensure that an older
                 * packed version of it doesn't exist */
                if (git_reference_lookup(&ref_in_pack, ref->owner, ref->name) == 0) {
                        assert((ref_in_pack->flags & GIT_REF_PACKED) != 0);
                        return git_reference_delete(ref_in_pack);
                }

                giterr_clear();
        }

        return 0;
}

int git_reference_delete(git_reference *ref)
{
        int result = reference_delete(ref);
        git_reference_free(ref);
        return result;
}

int git_reference_lookup(git_reference **ref_out,
        git_repository *repo, const char *name)
{
        return git_reference_lookup_resolved(ref_out, repo, name, 0);
}

int git_reference_name_to_oid(
        git_oid *out, git_repository *repo, const char *name)
{
        int error;
        git_reference *ref;

        if ((error = git_reference_lookup_resolved(&ref, repo, name, -1)) < 0)
                return error;

        git_oid_cpy(out, git_reference_oid(ref));
        git_reference_free(ref);
        return 0;
}

int git_reference_lookup_resolved(
        git_reference **ref_out,
        git_repository *repo,
        const char *name,
        int max_nesting)
{
        git_reference *scan;
        int result, nesting;

        assert(ref_out && repo && name);

        *ref_out = NULL;

        if (max_nesting > MAX_NESTING_LEVEL)
                max_nesting = MAX_NESTING_LEVEL;
        else if (max_nesting < 0)
                max_nesting = DEFAULT_NESTING_LEVEL;

        scan = git__calloc(1, sizeof(git_reference));
        GITERR_CHECK_ALLOC(scan);

        scan->name = git__calloc(GIT_REFNAME_MAX + 1, sizeof(char));
        GITERR_CHECK_ALLOC(scan->name);

        if ((result = normalize_name(scan->name, GIT_REFNAME_MAX, name, 0)) < 0) {
                git_reference_free(scan);
                return result;
        }

        scan->target.symbolic = git__strdup(scan->name);
        GITERR_CHECK_ALLOC(scan->target.symbolic);

        scan->owner = repo;
        scan->flags = GIT_REF_SYMBOLIC;

        for (nesting = max_nesting;
                 nesting >= 0 && (scan->flags & GIT_REF_SYMBOLIC) != 0;
                 nesting--)
        {
                if (nesting != max_nesting)
                        strncpy(scan->name, scan->target.symbolic, GIT_REFNAME_MAX);

                scan->mtime = 0;

                if ((result = reference_lookup(scan)) < 0)
                        return result; /* lookup git_reference_free on scan already */
        }

        if ((scan->flags & GIT_REF_OID) == 0 && max_nesting != 0) {
                giterr_set(GITERR_REFERENCE,
                        "Cannot resolve reference (>%u levels deep)", max_nesting);
                git_reference_free(scan);
                return -1;
        }

        *ref_out = scan;
        return 0;
}

/**
 * Getters
 */
git_ref_t git_reference_type(git_reference *ref)
{
        assert(ref);

        if (ref->flags & GIT_REF_OID)
                return GIT_REF_OID;

        if (ref->flags & GIT_REF_SYMBOLIC)
                return GIT_REF_SYMBOLIC;

        return GIT_REF_INVALID;
}

int git_reference_is_packed(git_reference *ref)
{
        assert(ref);
        return !!(ref->flags & GIT_REF_PACKED);
}

const char *git_reference_name(git_reference *ref)
{
        assert(ref);
        return ref->name;
}

git_repository *git_reference_owner(git_reference *ref)
{
        assert(ref);
        return ref->owner;
}

const git_oid *git_reference_oid(git_reference *ref)
{
        assert(ref);

        if ((ref->flags & GIT_REF_OID) == 0)
                return NULL;

        return &ref->target.oid;
}

const char *git_reference_target(git_reference *ref)
{
        assert(ref);

        if ((ref->flags & GIT_REF_SYMBOLIC) == 0)
                return NULL;

        return ref->target.symbolic;
}

int git_reference_create_symbolic(
        git_reference **ref_out,
        git_repository *repo,
        const char *name,
        const char *target,
        int force)
{
        char normalized[GIT_REFNAME_MAX];
        git_reference *ref = NULL;

        if (normalize_name(normalized, sizeof(normalized), name, 0) < 0)
                return -1;

        if (reference_can_write(repo, normalized, NULL, force) < 0)
                return -1;

        if (reference_alloc(&ref, repo, normalized) < 0)
                return -1;

        ref->flags |= GIT_REF_SYMBOLIC;

        /* set the target; this will normalize the name automatically
         * and write the reference on disk */
        if (git_reference_set_target(ref, target) < 0) {
                git_reference_free(ref);
                return -1;
        }
        if (ref_out == NULL) {
                git_reference_free(ref);
        } else {
                *ref_out = ref;
        }

        return 0;
}

int git_reference_create_oid(
        git_reference **ref_out,
        git_repository *repo,
        const char *name,
        const git_oid *id,
        int force)
{
        git_reference *ref = NULL;
        char normalized[GIT_REFNAME_MAX];

        if (normalize_name(normalized, sizeof(normalized), name, 1) < 0)
                return -1;

        if (reference_can_write(repo, normalized, NULL, force) < 0)
                return -1;

        if (reference_alloc(&ref, repo, name) < 0)
                return -1;

        ref->flags |= GIT_REF_OID;

        /* set the oid; this will write the reference on disk */
        if (git_reference_set_oid(ref, id) < 0) {
                git_reference_free(ref);
                return -1;
        }

        if (ref_out == NULL) {
                git_reference_free(ref);
        } else {
                *ref_out = ref;
        }

        return 0;
}
/*
 * Change the OID target of a reference.
 *
 * For both loose and packed references, just change
 * the oid in memory and (over)write the file in disk.
 *
 * We do not repack packed references because of performance
 * reasons.
 */
int git_reference_set_oid(git_reference *ref, const git_oid *id)
{
        git_odb *odb = NULL;

        if ((ref->flags & GIT_REF_OID) == 0) {
                giterr_set(GITERR_REFERENCE, "Cannot set OID on symbolic reference");
                return -1;
        }

        assert(ref->owner);

        if (git_repository_odb__weakptr(&odb, ref->owner) < 0)
                return -1;

        /* Don't let the user create references to OIDs that
         * don't exist in the ODB */
        if (!git_odb_exists(odb, id)) {
                giterr_set(GITERR_REFERENCE,
                        "Target OID for the reference doesn't exist on the repository");
                return -1;
        }

        /* Update the OID value on `ref` */
        git_oid_cpy(&ref->target.oid, id);

        /* Write back to disk */
        return loose_write(ref);
}

/*
 * Change the target of a symbolic reference.
 *
 * This is easy because symrefs cannot be inside
 * a pack. We just change the target in memory
 * and overwrite the file on disk.
 */
int git_reference_set_target(git_reference *ref, const char *target)
{
        char normalized[GIT_REFNAME_MAX];

        if ((ref->flags & GIT_REF_SYMBOLIC) == 0) {
                giterr_set(GITERR_REFERENCE,
                        "Cannot set symbolic target on a direct reference");
                return -1;
        }

        if (normalize_name(normalized, sizeof(normalized), target, 0))
                return -1;

        git__free(ref->target.symbolic);
        ref->target.symbolic = git__strdup(normalized);
        GITERR_CHECK_ALLOC(ref->target.symbolic);

        return loose_write(ref);
}

int git_reference_rename(git_reference *ref, const char *new_name, int force)
{
        int result;
        git_buf aux_path = GIT_BUF_INIT;
        char normalized[GIT_REFNAME_MAX];

        const char *head_target = NULL;
        git_reference *head = NULL;

        if (normalize_name(normalized, sizeof(normalized),
                new_name, ref->flags & GIT_REF_OID) < 0)
                return -1;

        if (reference_can_write(ref->owner, normalized, ref->name, force) < 0)
                return -1;

        /* Initialize path now so we won't get an allocation failure once
         * we actually start removing things. */
        if (git_buf_joinpath(&aux_path, ref->owner->path_repository, new_name) < 0)
                return -1;

        /*
         * Now delete the old ref and remove an possibly existing directory
         * named `new_name`. Note that using the internal `reference_delete`
         * method deletes the ref from disk but doesn't free the pointer, so
         * we can still access the ref's attributes for creating the new one
         */
        if (reference_delete(ref) < 0)
                goto cleanup;

        /*
         * Finally we can create the new reference.
         */
        if (ref->flags & GIT_REF_SYMBOLIC) {
                result = git_reference_create_symbolic(
                        NULL, ref->owner, new_name, ref->target.symbolic, force);
        } else {
                result = git_reference_create_oid(
                        NULL, ref->owner, new_name, &ref->target.oid, force);
        }

        if (result < 0)
                goto rollback;

        /*
         * Check if we have to update HEAD.
         */
        if (git_reference_lookup(&head, ref->owner, GIT_HEAD_FILE) < 0) {
                giterr_set(GITERR_REFERENCE,
                        "Failed to update HEAD after renaming reference");
                goto cleanup;
        }

        head_target = git_reference_target(head);

        if (head_target && !strcmp(head_target, ref->name)) {
                git_reference_free(head);
                head = NULL;

                if (git_reference_create_symbolic(&head, ref->owner, "HEAD", new_name, 1) < 0) {
                        giterr_set(GITERR_REFERENCE,
                                "Failed to update HEAD after renaming reference");
                        goto cleanup;
                }
        }

        /*
         * Rename the reflog file, if it exists.
         */
        if ((git_reference_has_log(ref)) && (git_reflog_rename(ref, new_name) < 0))
                goto cleanup;

        /*
         * Change the name of the reference given by the user.
         */
        git__free(ref->name);
        ref->name = git__strdup(new_name);

        /* The reference is no longer packed */
        ref->flags &= ~GIT_REF_PACKED;

        git_reference_free(head);
        git_buf_free(&aux_path);
        return 0;

cleanup:
        git_reference_free(head);
        git_buf_free(&aux_path);
        return -1;

rollback:
        /*
         * Try to create the old reference again, ignore failures
         */
        if (ref->flags & GIT_REF_SYMBOLIC)
                git_reference_create_symbolic(
                        NULL, ref->owner, ref->name, ref->target.symbolic, 0);
        else
                git_reference_create_oid(
                        NULL, ref->owner, ref->name, &ref->target.oid, 0);

        /* The reference is no longer packed */
        ref->flags &= ~GIT_REF_PACKED;

        git_buf_free(&aux_path);
        return -1;
}

int git_reference_resolve(git_reference **ref_out, git_reference *ref)
{
        if (ref->flags & GIT_REF_OID)
                return git_reference_lookup(ref_out, ref->owner, ref->name);
        else
                return git_reference_lookup_resolved(ref_out, ref->owner, ref->target.symbolic, -1);
}

int git_reference_packall(git_repository *repo)
{
        if (packed_load(repo) < 0 || /* load the existing packfile */
                packed_loadloose(repo) < 0 || /* add all the loose refs */
                packed_write(repo) < 0) /* write back to disk */
                return -1;

        return 0;
}

int git_reference_foreach(
        git_repository *repo,
        unsigned int list_flags,
        int (*callback)(const char *, void *),
        void *payload)
{
        int result;
        struct dirent_list_data data;
        git_buf refs_path = GIT_BUF_INIT;

        /* list all the packed references first */
        if (list_flags & GIT_REF_PACKED) {
                const char *ref_name;
                void *ref;
                GIT_UNUSED(ref);

                if (packed_load(repo) < 0)
                        return -1;

                git_strmap_foreach(repo->references.packfile, ref_name, ref, {
                        if (callback(ref_name, payload))
                                return GIT_EUSER;
                });
        }

        /* now list the loose references, trying not to
         * duplicate the ref names already in the packed-refs file */

        data.repo_path_len = strlen(repo->path_repository);
        data.list_flags = list_flags;
        data.repo = repo;
        data.callback = callback;
        data.callback_payload = payload;
        data.callback_error = 0;

        if (git_buf_joinpath(&refs_path, repo->path_repository, GIT_REFS_DIR) < 0)
                return -1;

        result = git_path_direach(&refs_path, _dirent_loose_listall, &data);

        git_buf_free(&refs_path);

        return data.callback_error ? GIT_EUSER : result;
}

static int cb__reflist_add(const char *ref, void *data)
{
        return git_vector_insert((git_vector *)data, git__strdup(ref));
}

int git_reference_list(
        git_strarray *array,
        git_repository *repo,
        unsigned int list_flags)
{
        git_vector ref_list;

        assert(array && repo);

        array->strings = NULL;
        array->count = 0;

        if (git_vector_init(&ref_list, 8, NULL) < 0)
                return -1;

        if (git_reference_foreach(
                        repo, list_flags, &cb__reflist_add, (void *)&ref_list) < 0) {
                git_vector_free(&ref_list);
                return -1;
        }

        array->strings = (char **)ref_list.contents;
        array->count = ref_list.length;
        return 0;
}

int git_reference_reload(git_reference *ref)
{
        return reference_lookup(ref);
}

void git_repository__refcache_free(git_refcache *refs)
{
        assert(refs);

        if (refs->packfile) {
                struct packref *reference;

                git_strmap_foreach_value(refs->packfile, reference, {
                        git__free(reference);
                });

                git_strmap_free(refs->packfile);
        }
}

static int is_valid_ref_char(char ch)
{
        if ((unsigned) ch <= ' ')
                return 0;

        switch (ch) {
        case '~':
        case '^':
        case ':':
        case '\\':
        case '?':
        case '[':
        case '*':
                return 0;
        default:
                return 1;
        }
}

static int normalize_name(
        char *buffer_out,
        size_t out_size,
        const char *name,
        int is_oid_ref)
{
        const char *name_end, *buffer_out_start;
        const char *current;
        int contains_a_slash = 0;

        assert(name && buffer_out);

        buffer_out_start = buffer_out;
        current = name;
        name_end = name + strlen(name);

        /* Terminating null byte */
        out_size--;

        /* A refname can not be empty */
        if (name_end == name)
                goto invalid_name;

        /* A refname can not end with a dot or a slash */
        if (*(name_end - 1) == '.' || *(name_end - 1) == '/')
                goto invalid_name;

        while (current < name_end && out_size) {
                if (!is_valid_ref_char(*current))
                        goto invalid_name;

                if (buffer_out > buffer_out_start) {
                        char prev = *(buffer_out - 1);

                        /* A refname can not start with a dot nor contain a double dot */
                        if (*current == '.' && ((prev == '.') || (prev == '/')))
                                goto invalid_name;

                        /* '@{' is forbidden within a refname */
                        if (*current == '{' && prev == '@')
                                goto invalid_name;

                        /* Prevent multiple slashes from being added to the output */
                        if (*current == '/' && prev == '/') {
                                current++;
                                continue;
                        }
                }

                if (*current == '/')
                        contains_a_slash = 1;

                *buffer_out++ = *current++;
                out_size--;
        }

        if (!out_size)
                goto invalid_name;

        /* Object id refname have to contain at least one slash, except
         * for HEAD in a detached state or MERGE_HEAD if we're in the
         * middle of a merge */
        if (is_oid_ref &&
                !contains_a_slash &&
                strcmp(name, GIT_HEAD_FILE) != 0 &&
                strcmp(name, GIT_MERGE_HEAD_FILE) != 0 &&
                strcmp(name, GIT_FETCH_HEAD_FILE) != 0)
                goto invalid_name;

        /* A refname can not end with ".lock" */
        if (!git__suffixcmp(name, GIT_FILELOCK_EXTENSION))
                goto invalid_name;

        *buffer_out = '\0';

        /*
         * For object id references, name has to start with refs/. Again,
         * we need to allow HEAD to be in a detached state.
         */
        if (is_oid_ref && !(git__prefixcmp(buffer_out_start, GIT_REFS_DIR) ||
                strcmp(buffer_out_start, GIT_HEAD_FILE)))
                goto invalid_name;

        return 0;

invalid_name:
        giterr_set(GITERR_REFERENCE, "The given reference name is not valid");
        return -1;
}

int git_reference__normalize_name(
        char *buffer_out,
        size_t out_size,
        const char *name)
{
        return normalize_name(buffer_out, out_size, name, 0);
}

int git_reference__normalize_name_oid(
        char *buffer_out,
        size_t out_size,
        const char *name)
{
        return normalize_name(buffer_out, out_size, name, 1);
}

#define GIT_REF_TYPEMASK (GIT_REF_OID | GIT_REF_SYMBOLIC)

int git_reference_cmp(git_reference *ref1, git_reference *ref2)
{
        assert(ref1 && ref2);

        /* let's put symbolic refs before OIDs */
        if ((ref1->flags & GIT_REF_TYPEMASK) != (ref2->flags & GIT_REF_TYPEMASK))
                return (ref1->flags & GIT_REF_SYMBOLIC) ? -1 : 1;

        if (ref1->flags & GIT_REF_SYMBOLIC)
                return strcmp(ref1->target.symbolic, ref2->target.symbolic);

        return git_oid_cmp(&ref1->target.oid, &ref2->target.oid);
}

/* Update the reference named `ref_name` so it points to `oid` */
int git_reference__update(git_repository *repo, const git_oid *oid, const char *ref_name)
{
        git_reference *ref;
        int res;

        res = git_reference_lookup(&ref, repo, ref_name);

        /* If we haven't found the reference at all, we assume we need to create
         * a new reference and that's it */
        if (res == GIT_ENOTFOUND) {
                giterr_clear();
                return git_reference_create_oid(NULL, repo, ref_name, oid, 1);
        }

        if (res < 0)
                return -1;

        /* If we have found a reference, but it's symbolic, we need to update
         * the direct reference it points to */
        if (git_reference_type(ref) == GIT_REF_SYMBOLIC) {
                git_reference *aux;
                const char *sym_target;

                /* The target pointed at by this reference */
                sym_target = git_reference_target(ref);

                /* resolve the reference to the target it points to */
                res = git_reference_resolve(&aux, ref);

                /*
                 * if the symbolic reference pointed to an inexisting ref,
                 * this is means we're creating a new branch, for example.
                 * We need to create a new direct reference with that name
                 */
                if (res == GIT_ENOTFOUND) {
                        giterr_clear();
                        res = git_reference_create_oid(NULL, repo, sym_target, oid, 1);
                        git_reference_free(ref);
                        return res;
                }

                /* free the original symbolic reference now; not before because
                 * we're using the `sym_target` pointer */
                git_reference_free(ref);

                if (res < 0)
                        return -1;

                /* store the newly found direct reference in its place */
                ref = aux;
        }

        /* ref is made to point to `oid`: ref is either the original reference,
         * or the target of the symbolic reference we've looked up */
        res = git_reference_set_oid(ref, oid);
        git_reference_free(ref);
        return res;
}

struct glob_cb_data {
        const char *glob;
        int (*callback)(const char *, void *);
        void *payload;
};

static int fromglob_cb(const char *reference_name, void *payload)
{
        struct glob_cb_data *data = (struct glob_cb_data *)payload;

        if (!p_fnmatch(data->glob, reference_name, 0))
                return data->callback(reference_name, data->payload);

        return 0;
}

int git_reference_foreach_glob(
        git_repository *repo,
        const char *glob,
        unsigned int list_flags,
        int (*callback)(
                const char *reference_name,
                void *payload),
        void *payload)
{
        struct glob_cb_data data;

        assert(repo && glob && callback);

        data.glob = glob;
        data.callback = callback;
        data.payload = payload;

        return git_reference_foreach(
                        repo, list_flags, fromglob_cb, &data);
}

int git_reference_has_log(
        git_reference *ref)
{
        git_buf path = GIT_BUF_INIT;
        int result;

        assert(ref);

        if (git_buf_join_n(&path, '/', 3, ref->owner->path_repository, GIT_REFLOG_DIR, ref->name) < 0)
                return -1;

        result = git_path_isfile(git_buf_cstr(&path));
        git_buf_free(&path);

        return result;
}

int git_reference_is_branch(git_reference *ref)
{
        assert(ref);

        return git__prefixcmp(ref->name, GIT_REFS_HEADS_DIR) == 0;
}