/*
 * Builtin "git clone"
 *
 * Copyright (c) 2007 Kristian Høgsberg <krh@redhat.com>,
 *               2008 Daniel Barkalow <barkalow@iabervon.org>
 * Based on git-commit.sh by Junio C Hamano and Linus Torvalds
 *
 * Clone a repository into a different directory that does not yet exist.
 */

#include "builtin.h"
#include "lockfile.h"
#include "parse-options.h"
#include "fetch-pack.h"
#include "refs.h"
#include "tree.h"
#include "tree-walk.h"
#include "unpack-trees.h"
#include "transport.h"
#include "strbuf.h"
#include "dir.h"
#include "sigchain.h"
#include "branch.h"
#include "remote.h"
#include "run-command.h"
#include "connected.h"

/*
 * Overall FIXMEs:
 *  - respect DB_ENVIRONMENT for .git/objects.
 *
 * Implementation notes:
 *  - dropping use-separate-remote and no-separate-remote compatibility
 *
 */
static const char * const builtin_clone_usage[] = {
        N_("git clone [<options>] [--] <repo> [<dir>]"),
        NULL
};

static int option_no_checkout, option_bare, option_mirror, option_single_branch = -1;
static int option_local = -1, option_no_hardlinks, option_shared, option_recursive;
static char *option_template, *option_depth;
static char *option_origin = NULL;
static char *option_branch = NULL;
static const char *real_git_dir;
static char *option_upload_pack = "git-upload-pack";
static int option_verbosity;
static int option_progress = -1;
static struct string_list option_config;
static struct string_list option_reference;
static int option_dissociate;

static struct option builtin_clone_options[] = {
        OPT__VERBOSITY(&option_verbosity),
        OPT_BOOL(0, "progress", &option_progress,
                 N_("force progress reporting")),
        OPT_BOOL('n', "no-checkout", &option_no_checkout,
                 N_("don't create a checkout")),
        OPT_BOOL(0, "bare", &option_bare, N_("create a bare repository")),
        OPT_HIDDEN_BOOL(0, "naked", &option_bare,
                        N_("create a bare repository")),
        OPT_BOOL(0, "mirror", &option_mirror,
                 N_("create a mirror repository (implies bare)")),
        OPT_BOOL('l', "local", &option_local,
                N_("to clone from a local repository")),
        OPT_BOOL(0, "no-hardlinks", &option_no_hardlinks,
                    N_("don't use local hardlinks, always copy")),
        OPT_BOOL('s', "shared", &option_shared,
                    N_("setup as shared repository")),
        OPT_BOOL(0, "recursive", &option_recursive,
                    N_("initialize submodules in the clone")),
        OPT_BOOL(0, "recurse-submodules", &option_recursive,
                    N_("initialize submodules in the clone")),
        OPT_STRING(0, "template", &option_template, N_("template-directory"),
                   N_("directory from which templates will be used")),
        OPT_STRING_LIST(0, "reference", &option_reference, N_("repo"),
                        N_("reference repository")),
        OPT_BOOL(0, "dissociate", &option_dissociate,
                 N_("use --reference only while cloning")),
        OPT_STRING('o', "origin", &option_origin, N_("name"),
                   N_("use <name> instead of 'origin' to track upstream")),
        OPT_STRING('b', "branch", &option_branch, N_("branch"),
                   N_("checkout <branch> instead of the remote's HEAD")),
        OPT_STRING('u', "upload-pack", &option_upload_pack, N_("path"),
                   N_("path to git-upload-pack on the remote")),
        OPT_STRING(0, "depth", &option_depth, N_("depth"),
                    N_("create a shallow clone of that depth")),
        OPT_BOOL(0, "single-branch", &option_single_branch,
                    N_("clone only one branch, HEAD or --branch")),
        OPT_STRING(0, "separate-git-dir", &real_git_dir, N_("gitdir"),
                   N_("separate git dir from working tree")),
        OPT_STRING_LIST('c', "config", &option_config, N_("key=value"),
                        N_("set config inside the new repository")),
        OPT_END()
};

static const char *argv_submodule[] = {
        "submodule", "update", "--init", "--recursive", NULL
};

static const char *get_repo_path_1(struct strbuf *path, int *is_bundle)
{
        static char *suffix[] = { "/.git", "", ".git/.git", ".git" };
        static char *bundle_suffix[] = { ".bundle", "" };
        size_t baselen = path->len;
        struct stat st;
        int i;

        for (i = 0; i < ARRAY_SIZE(suffix); i++) {
                strbuf_setlen(path, baselen);
                strbuf_addstr(path, suffix[i]);
                if (stat(path->buf, &st))
                        continue;
                if (S_ISDIR(st.st_mode) && is_git_directory(path->buf)) {
                        *is_bundle = 0;
                        return path->buf;
                } else if (S_ISREG(st.st_mode) && st.st_size > 8) {
                        /* Is it a "gitfile"? */
                        char signature[8];
                        const char *dst;
                        int len, fd = open(path->buf, O_RDONLY);
                        if (fd < 0)
                                continue;
                        len = read_in_full(fd, signature, 8);
                        close(fd);
                        if (len != 8 || strncmp(signature, "gitdir: ", 8))
                                continue;
                        dst = read_gitfile(path->buf);
                        if (dst) {
                                *is_bundle = 0;
                                return dst;
                        }
                }
        }

        for (i = 0; i < ARRAY_SIZE(bundle_suffix); i++) {
                strbuf_setlen(path, baselen);
                strbuf_addstr(path, bundle_suffix[i]);
                if (!stat(path->buf, &st) && S_ISREG(st.st_mode)) {
                        *is_bundle = 1;
                        return path->buf;
                }
        }

        return NULL;
}

static char *get_repo_path(const char *repo, int *is_bundle)
{
        struct strbuf path = STRBUF_INIT;
        const char *raw;
        char *canon;

        strbuf_addstr(&path, repo);
        raw = get_repo_path_1(&path, is_bundle);
        canon = raw ? xstrdup(absolute_path(raw)) : NULL;
        strbuf_release(&path);
        return canon;
}

static char *guess_dir_name(const char *repo, int is_bundle, int is_bare)
{
        const char *end = repo + strlen(repo), *start, *ptr;
        size_t len;
        char *dir;

        /*
         * Skip scheme.
         */
        start = strstr(repo, "://");
        if (start == NULL)
                start = repo;
        else
                start += 3;

        /*
         * Skip authentication data. The stripping does happen
         * greedily, such that we strip up to the last '@' inside
         * the host part.
         */
        for (ptr = start; ptr < end && !is_dir_sep(*ptr); ptr++) {
                if (*ptr == '@')
                        start = ptr + 1;
        }

        /*
         * Strip trailing spaces, slashes and /.git
         */
        while (start < end && (is_dir_sep(end[-1]) || isspace(end[-1])))
                end--;
        if (end - start > 5 && is_dir_sep(end[-5]) &&
            !strncmp(end - 4, ".git", 4)) {
                end -= 5;
                while (start < end && is_dir_sep(end[-1]))
                        end--;
        }

        /*
         * Strip trailing port number if we've got only a
         * hostname (that is, there is no dir separator but a
         * colon). This check is required such that we do not
         * strip URI's like '/foo/bar:2222.git', which should
         * result in a dir '2222' being guessed due to backwards
         * compatibility.
         */
        if (memchr(start, '/', end - start) == NULL
            && memchr(start, ':', end - start) != NULL) {
                ptr = end;
                while (start < ptr && isdigit(ptr[-1]) && ptr[-1] != ':')
                        ptr--;
                if (start < ptr && ptr[-1] == ':')
                        end = ptr - 1;
        }

        /*
         * Find last component. To remain backwards compatible we
         * also regard colons as path separators, such that
         * cloning a repository 'foo:bar.git' would result in a
         * directory 'bar' being guessed.
         */
        ptr = end;
        while (start < ptr && !is_dir_sep(ptr[-1]) && ptr[-1] != ':')
                ptr--;
        start = ptr;

        /*
         * Strip .{bundle,git}.
         */
        len = end - start;
        strip_suffix_mem(start, &len, is_bundle ? ".bundle" : ".git");

        if (!len || (len == 1 && *start == '/'))
            die("No directory name could be guessed.\n"
                "Please specify a directory on the command line");

        if (is_bare)
                dir = xstrfmt("%.*s.git", (int)len, start);
        else
                dir = xstrndup(start, len);
        /*
         * Replace sequences of 'control' characters and whitespace
         * with one ascii space, remove leading and trailing spaces.
         */
        if (*dir) {
                char *out = dir;
                int prev_space = 1 /* strip leading whitespace */;
                for (end = dir; *end; ++end) {
                        char ch = *end;
                        if ((unsigned char)ch < '\x20')
                                ch = '\x20';
                        if (isspace(ch)) {
                                if (prev_space)
                                        continue;
                                prev_space = 1;
                        } else
                                prev_space = 0;
                        *out++ = ch;
                }
                *out = '\0';
                if (out > dir && prev_space)
                        out[-1] = '\0';
        }
        return dir;
}

static void strip_trailing_slashes(char *dir)
{
        char *end = dir + strlen(dir);

        while (dir < end - 1 && is_dir_sep(end[-1]))
                end--;
        *end = '\0';
}

static int add_one_reference(struct string_list_item *item, void *cb_data)
{
        char *ref_git;
        const char *repo;
        struct strbuf alternate = STRBUF_INIT;

        /* Beware: read_gitfile(), real_path() and mkpath() return static buffer */
        ref_git = xstrdup(real_path(item->string));

        repo = read_gitfile(ref_git);
        if (!repo)
                repo = read_gitfile(mkpath("%s/.git", ref_git));
        if (repo) {
                free(ref_git);
                ref_git = xstrdup(repo);
        }

        if (!repo && is_directory(mkpath("%s/.git/objects", ref_git))) {
                char *ref_git_git = mkpathdup("%s/.git", ref_git);
                free(ref_git);
                ref_git = ref_git_git;
        } else if (!is_directory(mkpath("%s/objects", ref_git))) {
                struct strbuf sb = STRBUF_INIT;
                if (get_common_dir(&sb, ref_git))
                        die(_("reference repository '%s' as a linked checkout is not supported yet."),
                            item->string);
                die(_("reference repository '%s' is not a local repository."),
                    item->string);
        }

        if (!access(mkpath("%s/shallow", ref_git), F_OK))
                die(_("reference repository '%s' is shallow"), item->string);

        if (!access(mkpath("%s/info/grafts", ref_git), F_OK))
                die(_("reference repository '%s' is grafted"), item->string);

        strbuf_addf(&alternate, "%s/objects", ref_git);
        add_to_alternates_file(alternate.buf);
        strbuf_release(&alternate);
        free(ref_git);
        return 0;
}

static void setup_reference(void)
{
        for_each_string_list(&option_reference, add_one_reference, NULL);
}

static void copy_alternates(struct strbuf *src, struct strbuf *dst,
                            const char *src_repo)
{
        /*
         * Read from the source objects/info/alternates file
         * and copy the entries to corresponding file in the
         * destination repository with add_to_alternates_file().
         * Both src and dst have "$path/objects/info/alternates".
         *
         * Instead of copying bit-for-bit from the original,
         * we need to append to existing one so that the already
         * created entry via "clone -s" is not lost, and also
         * to turn entries with paths relative to the original
         * absolute, so that they can be used in the new repository.
         */
        FILE *in = fopen(src->buf, "r");
        struct strbuf line = STRBUF_INIT;

        while (strbuf_getline(&line, in, '\n') != EOF) {
                char *abs_path;
                if (!line.len || line.buf[0] == '#')
                        continue;
                if (is_absolute_path(line.buf)) {
                        add_to_alternates_file(line.buf);
                        continue;
                }
                abs_path = mkpathdup("%s/objects/%s", src_repo, line.buf);
                normalize_path_copy(abs_path, abs_path);
                add_to_alternates_file(abs_path);
                free(abs_path);
        }
        strbuf_release(&line);
        fclose(in);
}

static void copy_or_link_directory(struct strbuf *src, struct strbuf *dest,
                                   const char *src_repo, int src_baselen)
{
        struct dirent *de;
        struct stat buf;
        int src_len, dest_len;
        DIR *dir;

        dir = opendir(src->buf);
        if (!dir)
                die_errno(_("failed to open '%s'"), src->buf);

        if (mkdir(dest->buf, 0777)) {
                if (errno != EEXIST)
                        die_errno(_("failed to create directory '%s'"), dest->buf);
                else if (stat(dest->buf, &buf))
                        die_errno(_("failed to stat '%s'"), dest->buf);
                else if (!S_ISDIR(buf.st_mode))
                        die(_("%s exists and is not a directory"), dest->buf);
        }

        strbuf_addch(src, '/');
        src_len = src->len;
        strbuf_addch(dest, '/');
        dest_len = dest->len;

        while ((de = readdir(dir)) != NULL) {
                strbuf_setlen(src, src_len);
                strbuf_addstr(src, de->d_name);
                strbuf_setlen(dest, dest_len);
                strbuf_addstr(dest, de->d_name);
                if (stat(src->buf, &buf)) {
                        warning (_("failed to stat %s\n"), src->buf);
                        continue;
                }
                if (S_ISDIR(buf.st_mode)) {
                        if (de->d_name[0] != '.')
                                copy_or_link_directory(src, dest,
                                                       src_repo, src_baselen);
                        continue;
                }

                /* Files that cannot be copied bit-for-bit... */
                if (!strcmp(src->buf + src_baselen, "/info/alternates")) {
                        copy_alternates(src, dest, src_repo);
                        continue;
                }

                if (unlink(dest->buf) && errno != ENOENT)
                        die_errno(_("failed to unlink '%s'"), dest->buf);
                if (!option_no_hardlinks) {
                        if (!link(src->buf, dest->buf))
                                continue;
                        if (option_local > 0)
                                die_errno(_("failed to create link '%s'"), dest->buf);
                        option_no_hardlinks = 1;
                }
                if (copy_file_with_time(dest->buf, src->buf, 0666))
                        die_errno(_("failed to copy file to '%s'"), dest->buf);
        }
        closedir(dir);
}

static void clone_local(const char *src_repo, const char *dest_repo)
{
        if (option_shared) {
                struct strbuf alt = STRBUF_INIT;
                strbuf_addf(&alt, "%s/objects", src_repo);
                add_to_alternates_file(alt.buf);
                strbuf_release(&alt);
        } else {
                struct strbuf src = STRBUF_INIT;
                struct strbuf dest = STRBUF_INIT;
                get_common_dir(&src, src_repo);
                get_common_dir(&dest, dest_repo);
                strbuf_addstr(&src, "/objects");
                strbuf_addstr(&dest, "/objects");
                copy_or_link_directory(&src, &dest, src_repo, src.len);
                strbuf_release(&src);
                strbuf_release(&dest);
        }

        if (0 <= option_verbosity)
                fprintf(stderr, _("done.\n"));
}

static const char *junk_work_tree;
static const char *junk_git_dir;
static enum {
        JUNK_LEAVE_NONE,
        JUNK_LEAVE_REPO,
        JUNK_LEAVE_ALL
} junk_mode = JUNK_LEAVE_NONE;

static const char junk_leave_repo_msg[] =
N_("Clone succeeded, but checkout failed.\n"
   "You can inspect what was checked out with 'git status'\n"
   "and retry the checkout with 'git checkout -f HEAD'\n");

static void remove_junk(void)
{
        struct strbuf sb = STRBUF_INIT;

        switch (junk_mode) {
        case JUNK_LEAVE_REPO:
                warning("%s", _(junk_leave_repo_msg));
                /* fall-through */
        case JUNK_LEAVE_ALL:
                return;
        default:
                /* proceed to removal */
                break;
        }

        if (junk_git_dir) {
                strbuf_addstr(&sb, junk_git_dir);
                remove_dir_recursively(&sb, 0);
                strbuf_reset(&sb);
        }
        if (junk_work_tree) {
                strbuf_addstr(&sb, junk_work_tree);
                remove_dir_recursively(&sb, 0);
                strbuf_reset(&sb);
        }
}

static void remove_junk_on_signal(int signo)
{
        remove_junk();
        sigchain_pop(signo);
        raise(signo);
}

static struct ref *find_remote_branch(const struct ref *refs, const char *branch)
{
        struct ref *ref;
        struct strbuf head = STRBUF_INIT;
        strbuf_addstr(&head, "refs/heads/");
        strbuf_addstr(&head, branch);
        ref = find_ref_by_name(refs, head.buf);
        strbuf_release(&head);

        if (ref)
                return ref;

        strbuf_addstr(&head, "refs/tags/");
        strbuf_addstr(&head, branch);
        ref = find_ref_by_name(refs, head.buf);
        strbuf_release(&head);

        return ref;
}

static struct ref *wanted_peer_refs(const struct ref *refs,
                struct refspec *refspec)
{
        struct ref *head = copy_ref(find_ref_by_name(refs, "HEAD"));
        struct ref *local_refs = head;
        struct ref **tail = head ? &head->next : &local_refs;

        if (option_single_branch) {
                struct ref *remote_head = NULL;

                if (!option_branch)
                        remote_head = guess_remote_head(head, refs, 0);
                else {
                        local_refs = NULL;
                        tail = &local_refs;
                        remote_head = copy_ref(find_remote_branch(refs, option_branch));
                }

                if (!remote_head && option_branch)
                        warning(_("Could not find remote branch %s to clone."),
                                option_branch);
                else {
                        get_fetch_map(remote_head, refspec, &tail, 0);

                        /* if --branch=tag, pull the requested tag explicitly */
                        get_fetch_map(remote_head, tag_refspec, &tail, 0);
                }
        } else
                get_fetch_map(refs, refspec, &tail, 0);

        if (!option_mirror && !option_single_branch)
                get_fetch_map(refs, tag_refspec, &tail, 0);

        return local_refs;
}

static void write_remote_refs(const struct ref *local_refs)
{
        const struct ref *r;

        struct ref_transaction *t;
        struct strbuf err = STRBUF_INIT;

        t = ref_transaction_begin(&err);
        if (!t)
                die("%s", err.buf);

        for (r = local_refs; r; r = r->next) {
                if (!r->peer_ref)
                        continue;
                if (ref_transaction_create(t, r->peer_ref->name, r->old_sha1,
                                           0, NULL, &err))
                        die("%s", err.buf);
        }

        if (initial_ref_transaction_commit(t, &err))
                die("%s", err.buf);

        strbuf_release(&err);
        ref_transaction_free(t);
}

static void write_followtags(const struct ref *refs, const char *msg)
{
        const struct ref *ref;
        for (ref = refs; ref; ref = ref->next) {
                if (!starts_with(ref->name, "refs/tags/"))
                        continue;
                if (ends_with(ref->name, "^{}"))
                        continue;
                if (!has_sha1_file(ref->old_sha1))
                        continue;
                update_ref(msg, ref->name, ref->old_sha1,
                           NULL, 0, UPDATE_REFS_DIE_ON_ERR);
        }
}

static int iterate_ref_map(void *cb_data, unsigned char sha1[20])
{
        struct ref **rm = cb_data;
        struct ref *ref = *rm;

        /*
         * Skip anything missing a peer_ref, which we are not
         * actually going to write a ref for.
         */
        while (ref && !ref->peer_ref)
                ref = ref->next;
        /* Returning -1 notes "end of list" to the caller. */
        if (!ref)
                return -1;

        hashcpy(sha1, ref->old_sha1);
        *rm = ref->next;
        return 0;
}

static void update_remote_refs(const struct ref *refs,
                               const struct ref *mapped_refs,
                               const struct ref *remote_head_points_at,
                               const char *branch_top,
                               const char *msg,
                               struct transport *transport,
                               int check_connectivity)
{
        const struct ref *rm = mapped_refs;

        if (check_connectivity) {
                if (transport->progress)
                        fprintf(stderr, _("Checking connectivity... "));
                if (check_everything_connected_with_transport(iterate_ref_map,
                                                              0, &rm, transport))
                        die(_("remote did not send all necessary objects"));
                if (transport->progress)
                        fprintf(stderr, _("done.\n"));
        }

        if (refs) {
                write_remote_refs(mapped_refs);
                if (option_single_branch)
                        write_followtags(refs, msg);
        }

        if (remote_head_points_at && !option_bare) {
                struct strbuf head_ref = STRBUF_INIT;
                strbuf_addstr(&head_ref, branch_top);
                strbuf_addstr(&head_ref, "HEAD");
                create_symref(head_ref.buf,
                              remote_head_points_at->peer_ref->name,
                              msg);
        }
}

static void update_head(const struct ref *our, const struct ref *remote,
                        const char *msg)
{
        const char *head;
        if (our && skip_prefix(our->name, "refs/heads/", &head)) {
                /* Local default branch link */
                create_symref("HEAD", our->name, NULL);
                if (!option_bare) {
                        update_ref(msg, "HEAD", our->old_sha1, NULL, 0,
                                   UPDATE_REFS_DIE_ON_ERR);
                        install_branch_config(0, head, option_origin, our->name);
                }
        } else if (our) {
                struct commit *c = lookup_commit_reference(our->old_sha1);
                /* --branch specifies a non-branch (i.e. tags), detach HEAD */
                update_ref(msg, "HEAD", c->object.sha1,
                           NULL, REF_NODEREF, UPDATE_REFS_DIE_ON_ERR);
        } else if (remote) {
                /*
                 * We know remote HEAD points to a non-branch, or
                 * HEAD points to a branch but we don't know which one.
                 * Detach HEAD in all these cases.
                 */
                update_ref(msg, "HEAD", remote->old_sha1,
                           NULL, REF_NODEREF, UPDATE_REFS_DIE_ON_ERR);
        }
}

static int checkout(void)
{
        unsigned char sha1[20];
        char *head;
        struct lock_file *lock_file;
        struct unpack_trees_options opts;
        struct tree *tree;
        struct tree_desc t;
        int err = 0;

        if (option_no_checkout)
                return 0;

        head = resolve_refdup("HEAD", RESOLVE_REF_READING, sha1, NULL);
        if (!head) {
                warning(_("remote HEAD refers to nonexistent ref, "
                          "unable to checkout.\n"));
                return 0;
        }
        if (!strcmp(head, "HEAD")) {
                if (advice_detached_head)
                        detach_advice(sha1_to_hex(sha1));
        } else {
                if (!starts_with(head, "refs/heads/"))
                        die(_("HEAD not found below refs/heads!"));
        }
        free(head);

        /* We need to be in the new work tree for the checkout */
        setup_work_tree();

        lock_file = xcalloc(1, sizeof(struct lock_file));
        hold_locked_index(lock_file, 1);

        memset(&opts, 0, sizeof opts);
        opts.update = 1;
        opts.merge = 1;
        opts.fn = oneway_merge;
        opts.verbose_update = (option_verbosity >= 0);
        opts.src_index = &the_index;
        opts.dst_index = &the_index;

        tree = parse_tree_indirect(sha1);
        parse_tree(tree);
        init_tree_desc(&t, tree->buffer, tree->size);
        if (unpack_trees(1, &t, &opts) < 0)
                die(_("unable to checkout working tree"));

        if (write_locked_index(&the_index, lock_file, COMMIT_LOCK))
                die(_("unable to write new index file"));

        err |= run_hook_le(NULL, "post-checkout", sha1_to_hex(null_sha1),
                           sha1_to_hex(sha1), "1", NULL);

        if (!err && option_recursive)
                err = run_command_v_opt(argv_submodule, RUN_GIT_CMD);

        return err;
}

static int write_one_config(const char *key, const char *value, void *data)
{
        return git_config_set_multivar(key, value ? value : "true", "^$", 0);
}

static void write_config(struct string_list *config)
{
        int i;

        for (i = 0; i < config->nr; i++) {
                if (git_config_parse_parameter(config->items[i].string,
                                               write_one_config, NULL) < 0)
                        die("unable to write parameters to config file");
        }
}

static void write_refspec_config(const char *src_ref_prefix,
                const struct ref *our_head_points_at,
                const struct ref *remote_head_points_at,
                struct strbuf *branch_top)
{
        struct strbuf key = STRBUF_INIT;
        struct strbuf value = STRBUF_INIT;

        if (option_mirror || !option_bare) {
                if (option_single_branch && !option_mirror) {
                        if (option_branch) {
                                if (starts_with(our_head_points_at->name, "refs/tags/"))
                                        strbuf_addf(&value, "+%s:%s", our_head_points_at->name,
                                                our_head_points_at->name);
                                else
                                        strbuf_addf(&value, "+%s:%s%s", our_head_points_at->name,
                                                branch_top->buf, option_branch);
                        } else if (remote_head_points_at) {
                                const char *head = remote_head_points_at->name;
                                if (!skip_prefix(head, "refs/heads/", &head))
                                        die("BUG: remote HEAD points at non-head?");

                                strbuf_addf(&value, "+%s:%s%s", remote_head_points_at->name,
                                                branch_top->buf, head);
                        }
                        /*
                         * otherwise, the next "git fetch" will
                         * simply fetch from HEAD without updating
                         * any remote-tracking branch, which is what
                         * we want.
                         */
                } else {
                        strbuf_addf(&value, "+%s*:%s*", src_ref_prefix, branch_top->buf);
                }
                /* Configure the remote */
                if (value.len) {
                        strbuf_addf(&key, "remote.%s.fetch", option_origin);
                        git_config_set_multivar(key.buf, value.buf, "^$", 0);
                        strbuf_reset(&key);

                        if (option_mirror) {
                                strbuf_addf(&key, "remote.%s.mirror", option_origin);
                                git_config_set(key.buf, "true");
                                strbuf_reset(&key);
                        }
                }
        }

        strbuf_release(&key);
        strbuf_release(&value);
}

static void dissociate_from_references(void)
{
        static const char* argv[] = { "repack", "-a", "-d", NULL };
        char *alternates = git_pathdup("objects/info/alternates");

        if (!access(alternates, F_OK)) {
                if (run_command_v_opt(argv, RUN_GIT_CMD|RUN_COMMAND_NO_STDIN))
                        die(_("cannot repack to clean up"));
                if (unlink(alternates) && errno != ENOENT)
                        die_errno(_("cannot unlink temporary alternates file"));
        }
        free(alternates);
}

int cmd_clone(int argc, const char **argv, const char *prefix)
{
        int is_bundle = 0, is_local;
        struct stat buf;
        const char *repo_name, *repo, *work_tree, *git_dir;
        char *path, *dir;
        int dest_exists;
        const struct ref *refs, *remote_head;
        const struct ref *remote_head_points_at;
        const struct ref *our_head_points_at;
        struct ref *mapped_refs;
        const struct ref *ref;
        struct strbuf key = STRBUF_INIT, value = STRBUF_INIT;
        struct strbuf branch_top = STRBUF_INIT, reflog_msg = STRBUF_INIT;
        struct transport *transport = NULL;
        const char *src_ref_prefix = "refs/heads/";
        struct remote *remote;
        int err = 0, complete_refs_before_fetch = 1;

        struct refspec *refspec;
        const char *fetch_pattern;

        packet_trace_identity("clone");
        argc = parse_options(argc, argv, prefix, builtin_clone_options,
                             builtin_clone_usage, 0);

        if (argc > 2)
                usage_msg_opt(_("Too many arguments."),
                        builtin_clone_usage, builtin_clone_options);

        if (argc == 0)
                usage_msg_opt(_("You must specify a repository to clone."),
                        builtin_clone_usage, builtin_clone_options);

        if (option_single_branch == -1)
                option_single_branch = option_depth ? 1 : 0;

        if (option_mirror)
                option_bare = 1;

        if (option_bare) {
                if (option_origin)
                        die(_("--bare and --origin %s options are incompatible."),
                            option_origin);
                if (real_git_dir)
                        die(_("--bare and --separate-git-dir are incompatible."));
                option_no_checkout = 1;
        }

        if (!option_origin)
                option_origin = "origin";

        repo_name = argv[0];

        path = get_repo_path(repo_name, &is_bundle);
        if (path)
                repo = xstrdup(absolute_path(repo_name));
        else if (!strchr(repo_name, ':'))
                die(_("repository '%s' does not exist"), repo_name);
        else
                repo = repo_name;

        /* no need to be strict, transport_set_option() will validate it again */
        if (option_depth && atoi(option_depth) < 1)
                die(_("depth %s is not a positive number"), option_depth);

        if (argc == 2)
                dir = xstrdup(argv[1]);
        else
                dir = guess_dir_name(repo_name, is_bundle, option_bare);
        strip_trailing_slashes(dir);

        dest_exists = !stat(dir, &buf);
        if (dest_exists && !is_empty_dir(dir))
                die(_("destination path '%s' already exists and is not "
                        "an empty directory."), dir);

        strbuf_addf(&reflog_msg, "clone: from %s", repo);

        if (option_bare)
                work_tree = NULL;
        else {
                work_tree = getenv("GIT_WORK_TREE");
                if (work_tree && !stat(work_tree, &buf))
                        die(_("working tree '%s' already exists."), work_tree);
        }

        if (option_bare || work_tree)
                git_dir = xstrdup(dir);
        else {
                work_tree = dir;
                git_dir = mkpathdup("%s/.git", dir);
        }

        atexit(remove_junk);
        sigchain_push_common(remove_junk_on_signal);

        if (!option_bare) {
                if (safe_create_leading_directories_const(work_tree) < 0)
                        die_errno(_("could not create leading directories of '%s'"),
                                  work_tree);
                if (!dest_exists && mkdir(work_tree, 0777))
                        die_errno(_("could not create work tree dir '%s'"),
                                  work_tree);
                junk_work_tree = work_tree;
                set_git_work_tree(work_tree);
        }

        junk_git_dir = git_dir;
        if (safe_create_leading_directories_const(git_dir) < 0)
                die(_("could not create leading directories of '%s'"), git_dir);

        set_git_dir_init(git_dir, real_git_dir, 0);
        if (real_git_dir) {
                git_dir = real_git_dir;
                junk_git_dir = real_git_dir;
        }

        if (0 <= option_verbosity) {
                if (option_bare)
                        fprintf(stderr, _("Cloning into bare repository '%s'...\n"), dir);
                else
                        fprintf(stderr, _("Cloning into '%s'...\n"), dir);
        }
        init_db(option_template, INIT_DB_QUIET);
        write_config(&option_config);

        git_config(git_default_config, NULL);

        if (option_bare) {
                if (option_mirror)
                        src_ref_prefix = "refs/";
                strbuf_addstr(&branch_top, src_ref_prefix);

                git_config_set("core.bare", "true");
        } else {
                strbuf_addf(&branch_top, "refs/remotes/%s/", option_origin);
        }

        strbuf_addf(&value, "+%s*:%s*", src_ref_prefix, branch_top.buf);
        strbuf_addf(&key, "remote.%s.url", option_origin);
        git_config_set(key.buf, repo);
        strbuf_reset(&key);

        if (option_reference.nr)
                setup_reference();

        fetch_pattern = value.buf;
        refspec = parse_fetch_refspec(1, &fetch_pattern);

        strbuf_reset(&value);

        remote = remote_get(option_origin);
        transport = transport_get(remote, remote->url[0]);
        transport_set_verbosity(transport, option_verbosity, option_progress);

        path = get_repo_path(remote->url[0], &is_bundle);
        is_local = option_local != 0 && path && !is_bundle;
        if (is_local) {
                if (option_depth)
                        warning(_("--depth is ignored in local clones; use file:// instead."));
                if (!access(mkpath("%s/shallow", path), F_OK)) {
                        if (option_local > 0)
                                warning(_("source repository is shallow, ignoring --local"));
                        is_local = 0;
                }
        }
        if (option_local > 0 && !is_local)
                warning(_("--local is ignored"));
        transport->cloning = 1;

        if (!transport->get_refs_list || (!is_local && !transport->fetch))
                die(_("Don't know how to clone %s"), transport->url);

        transport_set_option(transport, TRANS_OPT_KEEP, "yes");

        if (option_depth)
                transport_set_option(transport, TRANS_OPT_DEPTH,
                                     option_depth);
        if (option_single_branch)
                transport_set_option(transport, TRANS_OPT_FOLLOWTAGS, "1");

        if (option_upload_pack)
                transport_set_option(transport, TRANS_OPT_UPLOADPACK,
                                     option_upload_pack);

        if (transport->smart_options && !option_depth)
                transport->smart_options->check_self_contained_and_connected = 1;

        refs = transport_get_remote_refs(transport);

        if (refs) {
                mapped_refs = wanted_peer_refs(refs, refspec);
                /*
                 * transport_get_remote_refs() may return refs with null sha-1
                 * in mapped_refs (see struct transport->get_refs_list
                 * comment). In that case we need fetch it early because
                 * remote_head code below relies on it.
                 *
                 * for normal clones, transport_get_remote_refs() should
                 * return reliable ref set, we can delay cloning until after
                 * remote HEAD check.
                 */
                for (ref = refs; ref; ref = ref->next)
                        if (is_null_sha1(ref->old_sha1)) {
                                complete_refs_before_fetch = 0;
                                break;
                        }

                if (!is_local && !complete_refs_before_fetch)
                        transport_fetch_refs(transport, mapped_refs);

                remote_head = find_ref_by_name(refs, "HEAD");
                remote_head_points_at =
                        guess_remote_head(remote_head, mapped_refs, 0);

                if (option_branch) {
                        our_head_points_at =
                                find_remote_branch(mapped_refs, option_branch);

                        if (!our_head_points_at)
                                die(_("Remote branch %s not found in upstream %s"),
                                    option_branch, option_origin);
                }
                else
                        our_head_points_at = remote_head_points_at;
        }
        else {
                if (option_branch)
                        die(_("Remote branch %s not found in upstream %s"),
                                        option_branch, option_origin);

                warning(_("You appear to have cloned an empty repository."));
                mapped_refs = NULL;
                our_head_points_at = NULL;
                remote_head_points_at = NULL;
                remote_head = NULL;
                option_no_checkout = 1;
                if (!option_bare)
                        install_branch_config(0, "master", option_origin,
                                              "refs/heads/master");
        }

        write_refspec_config(src_ref_prefix, our_head_points_at,
                        remote_head_points_at, &branch_top);

        if (is_local)
                clone_local(path, git_dir);
        else if (refs && complete_refs_before_fetch)
                transport_fetch_refs(transport, mapped_refs);

        update_remote_refs(refs, mapped_refs, remote_head_points_at,
                           branch_top.buf, reflog_msg.buf, transport, !is_local);

        update_head(our_head_points_at, remote_head, reflog_msg.buf);

        transport_unlock_pack(transport);
        transport_disconnect(transport);

        if (option_dissociate) {
                close_all_packs();
                dissociate_from_references();
        }

        junk_mode = JUNK_LEAVE_REPO;
        err = checkout();

        strbuf_release(&reflog_msg);
        strbuf_release(&branch_top);
        strbuf_release(&key);
        strbuf_release(&value);
        junk_mode = JUNK_LEAVE_ALL;

        free(refspec);
        return err;
}