static void rename_branch(const char *oldname, const char *newname, int force)
{
	struct strbuf oldref = STRBUF_INIT, newref = STRBUF_INIT, logmsg = STRBUF_INIT;
	unsigned char sha1[20];
	struct strbuf oldsection = STRBUF_INIT, newsection = STRBUF_INIT;
	int recovery = 0;

	if (!oldname)
		die("cannot rename the current branch while not on any.");

	if (strbuf_check_branch_ref(&oldref, oldname)) {
		/*
		 * Bad name --- this could be an attempt to rename a
		 * ref that we used to allow to be created by accident.
		 */
		if (resolve_ref(oldref.buf, sha1, 1, NULL))
			recovery = 1;
		else
			die("Invalid branch name: '%s'", oldname);
	}

	if (strbuf_check_branch_ref(&newref, newname))
		die("Invalid branch name: '%s'", newname);

	if (resolve_ref(newref.buf, sha1, 1, NULL) && !force)
		die("A branch named '%s' already exists.", newref.buf + 11);

	strbuf_addf(&logmsg, "Branch: renamed %s to %s",
		 oldref.buf, newref.buf);

	if (rename_ref(oldref.buf, newref.buf, logmsg.buf))
		die("Branch rename failed");
	strbuf_release(&logmsg);

	if (recovery)
		warning("Renamed a misnamed branch '%s' away", oldref.buf + 11);

	/* no need to pass logmsg here as HEAD didn't really move */
	if (!strcmp(oldname, head) && create_symref("HEAD", newref.buf, NULL))
		die("Branch renamed to %s, but HEAD is not updated!", newname);

	strbuf_addf(&oldsection, "branch.%s", oldref.buf + 11);
	strbuf_release(&oldref);
	strbuf_addf(&newsection, "branch.%s", newref.buf + 11);
	strbuf_release(&newref);
	if (git_config_rename_section(oldsection.buf, newsection.buf) < 0)
		die("Branch is renamed, but update of config-file failed");
	strbuf_release(&oldsection);
	strbuf_release(&newsection);
}

int gidit_pushobj(FILE *fp, char * signingkey, int sign, unsigned int flags)
{
    const char *head;
    unsigned char head_sha1[21];
    struct gidit_refs_cb_data cbdata;
    struct strbuf buf = STRBUF_INIT;

    cbdata.buf = &buf;
    cbdata.flags = flags;

    head = resolve_ref("HEAD", head_sha1, 0, NULL);
    head_sha1[20] = '\0';
    if (!head) {
        strbuf_release(&buf);
        return error("Failed to resolve HEAD as a valid ref.");
    }

    strbuf_add(&buf, sha1_to_hex(head_sha1), 40);
    strbuf_addstr(&buf, " HEAD\n");

    for_each_ref(resolve_one_ref, &cbdata);

    if (sign)
        do_sign(&buf, signingkey);

    if (fwrite(buf.buf, buf.len, 1, fp) != 1) {
        strbuf_release(&buf);
        return error("Error while writing pushobj");
    }

    strbuf_release(&buf);
    return 0;
}

static void execute_commands(const char *unpacker_error)
{
	struct command *cmd = commands;
	unsigned char sha1[20];

	if (unpacker_error) {
		while (cmd) {
			cmd->error_string = "n/a (unpacker error)";
			cmd = cmd->next;
		}
		return;
	}

	if (run_receive_hook(pre_receive_hook)) {
		while (cmd) {
			cmd->error_string = "pre-receive hook declined";
			cmd = cmd->next;
		}
		return;
	}

	head_name = resolve_ref("HEAD", sha1, 0, NULL);

	while (cmd) {
		cmd->error_string = update(cmd);
		cmd = cmd->next;
	}
}

static void execute_commands(struct command *commands, const char *unpacker_error)
{
	struct command *cmd;
	unsigned char sha1[20];

	if (unpacker_error) {
		for (cmd = commands; cmd; cmd = cmd->next)
			cmd->error_string = "n/a (unpacker error)";
		return;
	}

	cmd = commands;
	if (check_everything_connected(iterate_receive_command_list,
				       0, &cmd))
		set_connectivity_errors(commands);

	if (run_receive_hook(commands, pre_receive_hook, 0)) {
		for (cmd = commands; cmd; cmd = cmd->next)
			cmd->error_string = "pre-receive hook declined";
		return;
	}

	check_aliased_updates(commands);

	free((char*)head_name);
	head_name = resolve_ref("HEAD", sha1, 0, NULL);
	if (head_name)
		head_name = xstrdup(head_name);

	for (cmd = commands; cmd; cmd = cmd->next)
		if (!cmd->skip_update)
			cmd->error_string = update(cmd);
}

int fmt_merge_msg(struct strbuf *in, struct strbuf *out,
		  struct fmt_merge_msg_opts *opts)
{
	int i = 0, pos = 0;
	unsigned char head_sha1[20];
	const char *current_branch;

	/* get current branch */
	current_branch = resolve_ref("HEAD", head_sha1, 1, NULL);
	if (!current_branch)
		die("No current branch");
	if (!prefixcmp(current_branch, "refs/heads/"))
		current_branch += 11;
	current_branch = xstrdup(current_branch);

	/* get a line */
	while (pos < in->len) {
		int len;
		char *newline, *p = in->buf + pos;

		newline = strchr(p, '\n');
		len = newline ? newline - p : strlen(p);
		pos += len + !!newline;
		i++;
		p[len] = 0;
		if (handle_line(p))
			die ("Error in line %d: %.*s", i, len, p);
	}

	if (opts->add_title && srcs.nr)
		fmt_merge_msg_title(out, current_branch);

	if (origins.nr)
		fmt_merge_msg_sigs(out);

	if (opts->shortlog_len) {
		struct commit *head;
		struct rev_info rev;

		head = lookup_commit_or_die(head_sha1, "HEAD");
		init_revisions(&rev, NULL);
		rev.commit_format = CMIT_FMT_ONELINE;
		rev.ignore_merges = 1;
		rev.limited = 1;

		if (suffixcmp(out->buf, "\n"))
			strbuf_addch(out, '\n');

		for (i = 0; i < origins.nr; i++)
			shortlog(origins.items[i].string,
				 origins.items[i].util,
				 head, &rev, opts->shortlog_len, out);
	}

	strbuf_complete_line(out);
	free((char*)current_branch);
	return 0;
}

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

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

void wt_status_prepare(struct wt_status *s)
{
    unsigned char sha1[20];
    const char *head;

    memset(s, 0, sizeof(*s));
    head = resolve_ref("HEAD", sha1, 0, NULL);
    s->branch = head ? xstrdup(head) : NULL;
    s->reference = "HEAD";
    s->fp = stdout;
    s->index_file = get_index_file();
}

static int branch_merged(int kind, const char *name,
			 struct commit *rev, struct commit *head_rev)
{
	/*
	 * This checks whether the merge bases of branch and HEAD (or
	 * the other branch this branch builds upon) contains the
	 * branch, which means that the branch has already been merged
	 * safely to HEAD (or the other branch).
	 */
	struct commit *reference_rev = NULL;
	const char *reference_name = NULL;
	int merged;

	if (kind == REF_LOCAL_BRANCH) {
		struct branch *branch = branch_get(name);
		unsigned char sha1[20];

		if (branch &&
		    branch->merge &&
		    branch->merge[0] &&
		    branch->merge[0]->dst &&
		    (reference_name =
		     resolve_ref(branch->merge[0]->dst, sha1, 1, NULL)) != NULL) {
			reference_name = xstrdup(reference_name);
			reference_rev = lookup_commit_reference(sha1);
		}
	}
	if (!reference_rev)
		reference_rev = head_rev;

	merged = in_merge_bases(rev, &reference_rev, 1);

	/*
	 * After the safety valve is fully redefined to "check with
	 * upstream, if any, otherwise with HEAD", we should just
	 * return the result of the in_merge_bases() above without
	 * any of the following code, but during the transition period,
	 * a gentle reminder is in order.
	 */
	if ((head_rev != reference_rev) &&
	    in_merge_bases(rev, &head_rev, 1) != merged) {
		if (merged)
			warning(_("deleting branch '%s' that has been merged to\n"
				"         '%s', but not yet merged to HEAD."),
				name, reference_name);
		else
			warning(_("not deleting branch '%s' that is not yet merged to\n"
				"         '%s', even though it is merged to HEAD."),
				name, reference_name);
	}
	free((char*)reference_name);
	return merged;
}

static int rollback_single_pick(void)
{
	unsigned char head_sha1[20];

	if (!file_exists(git_path("CHERRY_PICK_HEAD")) &&
	    !file_exists(git_path("REVERT_HEAD")))
		return error(_("no cherry-pick or revert in progress"));
	if (!resolve_ref("HEAD", head_sha1, 0, NULL))
		return error(_("cannot resolve HEAD"));
	if (is_null_sha1(head_sha1))
		return error(_("cannot abort from a branch yet to be born"));
	return reset_for_rollback(head_sha1);
}

static char *resolve_symref(const char *src, const char *prefix)
{
	unsigned char sha1[20];
	int flag;
	const char *dst, *cp;

	dst = resolve_ref(src, sha1, 0, &flag);
	if (!(dst && (flag & REF_ISSYMREF)))
		return NULL;
	if (prefix && (cp = skip_prefix(dst, prefix)))
		dst = cp;
	return xstrdup(dst);
}

static int is_ref_checked_out(const char *ref)
{
	unsigned char sha1[20];
	const char *head;

	if (is_bare_repository())
		return 0;

	head = resolve_ref("HEAD", sha1, 0, NULL);
	if (!head)
		return 0;
	return !strcmp(head, ref);
}

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 (resolve_ref(buf.buf, sha1, 1, &flag))
		ret = fn(buf.buf, sha1, flag, cb_data);
	strbuf_release(&buf);

	return ret;
}

static void check_aliased_update(struct command *cmd, struct string_list *list)
{
	struct strbuf buf = STRBUF_INIT;
	const char *dst_name;
	struct string_list_item *item;
	struct command *dst_cmd;
	unsigned char sha1[20];
	char cmd_oldh[41], cmd_newh[41], dst_oldh[41], dst_newh[41];
	int flag;

	strbuf_addf(&buf, "%s%s", get_git_namespace(), cmd->ref_name);
	dst_name = resolve_ref(buf.buf, sha1, 0, &flag);
	strbuf_release(&buf);

	if (!(flag & REF_ISSYMREF))
		return;

	dst_name = strip_namespace(dst_name);
	if (!dst_name) {
		rp_error("refusing update to broken symref '%s'", cmd->ref_name);
		cmd->skip_update = 1;
		cmd->error_string = "broken symref";
		return;
	}

	if ((item = string_list_lookup(list, dst_name)) == NULL)
		return;

	cmd->skip_update = 1;

	dst_cmd = (struct command *) item->util;

	if (!hashcmp(cmd->old_sha1, dst_cmd->old_sha1) &&
	    !hashcmp(cmd->new_sha1, dst_cmd->new_sha1))
		return;

	dst_cmd->skip_update = 1;

	strcpy(cmd_oldh, find_unique_abbrev(cmd->old_sha1, DEFAULT_ABBREV));
	strcpy(cmd_newh, find_unique_abbrev(cmd->new_sha1, DEFAULT_ABBREV));
	strcpy(dst_oldh, find_unique_abbrev(dst_cmd->old_sha1, DEFAULT_ABBREV));
	strcpy(dst_newh, find_unique_abbrev(dst_cmd->new_sha1, DEFAULT_ABBREV));
	rp_error("refusing inconsistent update between symref '%s' (%s..%s) and"
		 " its target '%s' (%s..%s)",
		 cmd->ref_name, cmd_oldh, cmd_newh,
		 dst_cmd->ref_name, dst_oldh, dst_newh);

	cmd->error_string = dst_cmd->error_string =
		"inconsistent aliased update";
}

static int merge_commit(struct notes_merge_options *o)
{
	struct strbuf msg = STRBUF_INIT;
	unsigned char sha1[20], parent_sha1[20];
	struct notes_tree *t;
	struct commit *partial;
	struct pretty_print_context pretty_ctx;

	/*
	 * Read partial merge result from .git/NOTES_MERGE_PARTIAL,
	 * and target notes ref from .git/NOTES_MERGE_REF.
	 */

	if (get_sha1("NOTES_MERGE_PARTIAL", sha1))
		die("Failed to read ref NOTES_MERGE_PARTIAL");
	else if (!(partial = lookup_commit_reference(sha1)))
		die("Could not find commit from NOTES_MERGE_PARTIAL.");
	else if (parse_commit(partial))
		die("Could not parse commit from NOTES_MERGE_PARTIAL.");

	if (partial->parents)
		hashcpy(parent_sha1, partial->parents->item->object.sha1);
	else
		hashclr(parent_sha1);

	t = xcalloc(1, sizeof(struct notes_tree));
	init_notes(t, "NOTES_MERGE_PARTIAL", combine_notes_overwrite, 0);

	o->local_ref = resolve_ref("NOTES_MERGE_REF", sha1, 0, NULL);
	if (!o->local_ref)
		die("Failed to resolve NOTES_MERGE_REF");

	if (notes_merge_commit(o, t, partial, sha1))
		die("Failed to finalize notes merge");

	/* Reuse existing commit message in reflog message */
	memset(&pretty_ctx, 0, sizeof(pretty_ctx));
	format_commit_message(partial, "%s", &msg, &pretty_ctx);
	strbuf_trim(&msg);
	strbuf_insert(&msg, 0, "notes: ", 7);
	update_ref(msg.buf, o->local_ref, sha1,
		   is_null_sha1(parent_sha1) ? NULL : parent_sha1,
		   0, DIE_ON_ERR);

	free_notes(t);
	strbuf_release(&msg);
	return merge_abort(o);
}

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

static void check_symref(const char *HEAD, int quiet)
{
	unsigned char sha1[20];
	int flag;
	const char *refs_heads_master = resolve_ref(HEAD, sha1, 0, &flag);

	if (!refs_heads_master)
		die("No such ref: %s", HEAD);
	else if (!(flag & REF_ISSYMREF)) {
		if (!quiet)
			die("ref %s is not a symbolic ref", HEAD);
		else
			exit(1);
	}
	puts(refs_heads_master);
}

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

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

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

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

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

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

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

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

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

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

	return 0;
}

static void print_summary(const char *prefix, const unsigned char *sha1)
{
	struct rev_info rev;
	struct commit *commit;
	static const char *format = "format:%h: \"%s\"";
	unsigned char junk_sha1[20];
	const char *head = resolve_ref("HEAD", junk_sha1, 0, NULL);

	commit = lookup_commit(sha1);
	if (!commit)
		die("couldn't look up newly created commit");
	if (!commit || parse_commit(commit))
		die("could not parse newly created commit");

	init_revisions(&rev, prefix);
	setup_revisions(0, NULL, &rev, NULL);

	rev.abbrev = 0;
	rev.diff = 1;
	rev.diffopt.output_format =
		DIFF_FORMAT_SHORTSTAT | DIFF_FORMAT_SUMMARY;

	rev.verbose_header = 1;
	rev.show_root_diff = 1;
	get_commit_format(format, &rev);
	rev.always_show_header = 0;
	rev.diffopt.detect_rename = 1;
	rev.diffopt.rename_limit = 100;
	rev.diffopt.break_opt = 0;
	diff_setup_done(&rev.diffopt);

	printf("[%s%s]: created ",
		!prefixcmp(head, "refs/heads/") ?
			head + 11 :
			!strcmp(head, "HEAD") ?
				"detached HEAD" :
				head,
		initial_commit ? " (root-commit)" : "");

	if (!log_tree_commit(&rev, commit)) {
		struct strbuf buf = STRBUF_INIT;
		format_commit_message(commit, format + 7, &buf, DATE_NORMAL);
		printf("%s\n", buf.buf);
		strbuf_release(&buf);
	}
}