#include "cache.h"
#include "repository.h"
#include "config.h"
#include "dir.h"
#include "string-list.h"

static int inside_git_dir = -1;
static int inside_work_tree = -1;
static int work_tree_config_is_bogus;

static struct startup_info the_startup_info;
struct startup_info *startup_info = &the_startup_info;

/*
 * The input parameter must contain an absolute path, and it must already be
 * normalized.
 *
 * Find the part of an absolute path that lies inside the work tree by
 * dereferencing symlinks outside the work tree, for example:
 * /dir1/repo/dir2/file   (work tree is /dir1/repo)      -> dir2/file
 * /dir/file              (work tree is /)               -> dir/file
 * /dir/symlink1/symlink2 (symlink1 points to work tree) -> symlink2
 * /dir/repolink/file     (repolink points to /dir/repo) -> file
 * /dir/repo              (exactly equal to work tree)   -> (empty string)
 */
static int abspath_part_inside_repo(char *path)
{
        size_t len;
        size_t wtlen;
        char *path0;
        int off;
        const char *work_tree = get_git_work_tree();

        if (!work_tree)
                return -1;
        wtlen = strlen(work_tree);
        len = strlen(path);
        off = offset_1st_component(path);

        /* check if work tree is already the prefix */
        if (wtlen <= len && !strncmp(path, work_tree, wtlen)) {
                if (path[wtlen] == '/') {
                        memmove(path, path + wtlen + 1, len - wtlen);
                        return 0;
                } else if (path[wtlen - 1] == '/' || path[wtlen] == '\0') {
                        /* work tree is the root, or the whole path */
                        memmove(path, path + wtlen, len - wtlen + 1);
                        return 0;
                }
                /* work tree might match beginning of a symlink to work tree */
                off = wtlen;
        }
        path0 = path;
        path += off;

        /* check each '/'-terminated level */
        while (*path) {
                path++;
                if (*path == '/') {
                        *path = '\0';
                        if (strcmp(real_path(path0), work_tree) == 0) {
                                memmove(path0, path + 1, len - (path - path0));
                                return 0;
                        }
                        *path = '/';
                }
        }

        /* check whole path */
        if (strcmp(real_path(path0), work_tree) == 0) {
                *path0 = '\0';
                return 0;
        }

        return -1;
}

/*
 * Normalize "path", prepending the "prefix" for relative paths. If
 * remaining_prefix is not NULL, return the actual prefix still
 * remains in the path. For example, prefix = sub1/sub2/ and path is
 *
 *  foo          -> sub1/sub2/foo  (full prefix)
 *  ../foo       -> sub1/foo       (remaining prefix is sub1/)
 *  ../../bar    -> bar            (no remaining prefix)
 *  ../../sub1/sub2/foo -> sub1/sub2/foo (but no remaining prefix)
 *  `pwd`/../bar -> sub1/bar       (no remaining prefix)
 */
char *prefix_path_gently(const char *prefix, int len,
                         int *remaining_prefix, const char *path)
{
        const char *orig = path;
        char *sanitized;
        if (is_absolute_path(orig)) {
                sanitized = xmallocz(strlen(path));
                if (remaining_prefix)
                        *remaining_prefix = 0;
                if (normalize_path_copy_len(sanitized, path, remaining_prefix)) {
                        free(sanitized);
                        return NULL;
                }
                if (abspath_part_inside_repo(sanitized)) {
                        free(sanitized);
                        return NULL;
                }
        } else {
                sanitized = xstrfmt("%.*s%s", len, len ? prefix : "", path);
                if (remaining_prefix)
                        *remaining_prefix = len;
                if (normalize_path_copy_len(sanitized, sanitized, remaining_prefix)) {
                        free(sanitized);
                        return NULL;
                }
        }
        return sanitized;
}

char *prefix_path(const char *prefix, int len, const char *path)
{
        char *r = prefix_path_gently(prefix, len, NULL, path);
        if (!r)
                die(_("'%s' is outside repository"), path);
        return r;
}

int path_inside_repo(const char *prefix, const char *path)
{
        int len = prefix ? strlen(prefix) : 0;
        char *r = prefix_path_gently(prefix, len, NULL, path);
        if (r) {
                free(r);
                return 1;
        }
        return 0;
}

int check_filename(const char *prefix, const char *arg)
{
        char *to_free = NULL;
        struct stat st;

        if (skip_prefix(arg, ":/", &arg)) {
                if (!*arg) /* ":/" is root dir, always exists */
                        return 1;
                prefix = NULL;
        } else if (skip_prefix(arg, ":!", &arg) ||
                   skip_prefix(arg, ":^", &arg)) {
                if (!*arg) /* excluding everything is silly, but allowed */
                        return 1;
        }

        if (prefix)
                arg = to_free = prefix_filename(prefix, arg);

        if (!lstat(arg, &st)) {
                free(to_free);
                return 1; /* file exists */
        }
        if (is_missing_file_error(errno)) {
                free(to_free);
                return 0; /* file does not exist */
        }
        die_errno(_("failed to stat '%s'"), arg);
}

static void NORETURN die_verify_filename(const char *prefix,
                                         const char *arg,
                                         int diagnose_misspelt_rev)
{
        if (!diagnose_misspelt_rev)
                die(_("%s: no such path in the working tree.\n"
                      "Use 'git <command> -- <path>...' to specify paths that do not exist locally."),
                    arg);
        /*
         * Saying "'(icase)foo' does not exist in the index" when the
         * user gave us ":(icase)foo" is just stupid.  A magic pathspec
         * begins with a colon and is followed by a non-alnum; do not
         * let maybe_die_on_misspelt_object_name() even trigger.
         */
        if (!(arg[0] == ':' && !isalnum(arg[1])))
                maybe_die_on_misspelt_object_name(arg, prefix);

        /* ... or fall back the most general message. */
        die(_("ambiguous argument '%s': unknown revision or path not in the working tree.\n"
              "Use '--' to separate paths from revisions, like this:\n"
              "'git <command> [<revision>...] -- [<file>...]'"), arg);

}

/*
 * Check for arguments that don't resolve as actual files,
 * but which look sufficiently like pathspecs that we'll consider
 * them such for the purposes of rev/pathspec DWIM parsing.
 */
static int looks_like_pathspec(const char *arg)
{
        /* anything with a wildcard character */
        if (!no_wildcard(arg))
                return 1;

        /* long-form pathspec magic */
        if (starts_with(arg, ":("))
                return 1;

        return 0;
}

/*
 * Verify a filename that we got as an argument for a pathspec
 * entry. Note that a filename that begins with "-" never verifies
 * as true, because even if such a filename were to exist, we want
 * it to be preceded by the "--" marker (or we want the user to
 * use a format like "./-filename")
 *
 * The "diagnose_misspelt_rev" is used to provide a user-friendly
 * diagnosis when dying upon finding that "name" is not a pathname.
 * If set to 1, the diagnosis will try to diagnose "name" as an
 * invalid object name (e.g. HEAD:foo). If set to 0, the diagnosis
 * will only complain about an inexisting file.
 *
 * This function is typically called to check that a "file or rev"
 * argument is unambiguous. In this case, the caller will want
 * diagnose_misspelt_rev == 1 when verifying the first non-rev
 * argument (which could have been a revision), and
 * diagnose_misspelt_rev == 0 for the next ones (because we already
 * saw a filename, there's not ambiguity anymore).
 */
void verify_filename(const char *prefix,
                     const char *arg,
                     int diagnose_misspelt_rev)
{
        if (*arg == '-')
                die(_("option '%s' must come before non-option arguments"), arg);
        if (looks_like_pathspec(arg) || check_filename(prefix, arg))
                return;
        die_verify_filename(prefix, arg, diagnose_misspelt_rev);
}

/*
 * Opposite of the above: the command line did not have -- marker
 * and we parsed the arg as a refname.  It should not be interpretable
 * as a filename.
 */
void verify_non_filename(const char *prefix, const char *arg)
{
        if (!is_inside_work_tree() || is_inside_git_dir())
                return;
        if (*arg == '-')
                return; /* flag */
        if (!check_filename(prefix, arg))
                return;
        die(_("ambiguous argument '%s': both revision and filename\n"
              "Use '--' to separate paths from revisions, like this:\n"
              "'git <command> [<revision>...] -- [<file>...]'"), arg);
}

int get_common_dir(struct strbuf *sb, const char *gitdir)
{
        const char *git_env_common_dir = getenv(GIT_COMMON_DIR_ENVIRONMENT);
        if (git_env_common_dir) {
                strbuf_addstr(sb, git_env_common_dir);
                return 1;
        } else {
                return get_common_dir_noenv(sb, gitdir);
        }
}

int get_common_dir_noenv(struct strbuf *sb, const char *gitdir)
{
        struct strbuf data = STRBUF_INIT;
        struct strbuf path = STRBUF_INIT;
        int ret = 0;

        strbuf_addf(&path, "%s/commondir", gitdir);
        if (file_exists(path.buf)) {
                if (strbuf_read_file(&data, path.buf, 0) <= 0)
                        die_errno(_("failed to read %s"), path.buf);
                while (data.len && (data.buf[data.len - 1] == '\n' ||
                                    data.buf[data.len - 1] == '\r'))
                        data.len--;
                data.buf[data.len] = '\0';
                strbuf_reset(&path);
                if (!is_absolute_path(data.buf))
                        strbuf_addf(&path, "%s/", gitdir);
                strbuf_addbuf(&path, &data);
                strbuf_add_real_path(sb, path.buf);
                ret = 1;
        } else {
                strbuf_addstr(sb, gitdir);
        }

        strbuf_release(&data);
        strbuf_release(&path);
        return ret;
}

/*
 * Test if it looks like we're at a git directory.
 * We want to see:
 *
 *  - either an objects/ directory _or_ the proper
 *    GIT_OBJECT_DIRECTORY environment variable
 *  - a refs/ directory
 *  - either a HEAD symlink or a HEAD file that is formatted as
 *    a proper "ref:", or a regular file HEAD that has a properly
 *    formatted sha1 object name.
 */
int is_git_directory(const char *suspect)
{
        struct strbuf path = STRBUF_INIT;
        int ret = 0;
        size_t len;

        /* Check worktree-related signatures */
        strbuf_addstr(&path, suspect);
        strbuf_complete(&path, '/');
        strbuf_addstr(&path, "HEAD");
        if (validate_headref(path.buf))
                goto done;

        strbuf_reset(&path);
        get_common_dir(&path, suspect);
        len = path.len;

        /* Check non-worktree-related signatures */
        if (getenv(DB_ENVIRONMENT)) {
                if (access(getenv(DB_ENVIRONMENT), X_OK))
                        goto done;
        }
        else {
                strbuf_setlen(&path, len);
                strbuf_addstr(&path, "/objects");
                if (access(path.buf, X_OK))
                        goto done;
        }

        strbuf_setlen(&path, len);
        strbuf_addstr(&path, "/refs");
        if (access(path.buf, X_OK))
                goto done;

        ret = 1;
done:
        strbuf_release(&path);
        return ret;
}

int is_nonbare_repository_dir(struct strbuf *path)
{
        int ret = 0;
        int gitfile_error;
        size_t orig_path_len = path->len;
        assert(orig_path_len != 0);
        strbuf_complete(path, '/');
        strbuf_addstr(path, ".git");
        if (read_gitfile_gently(path->buf, &gitfile_error) || is_git_directory(path->buf))
                ret = 1;
        if (gitfile_error == READ_GITFILE_ERR_OPEN_FAILED ||
            gitfile_error == READ_GITFILE_ERR_READ_FAILED)
                ret = 1;
        strbuf_setlen(path, orig_path_len);
        return ret;
}

int is_inside_git_dir(void)
{
        if (inside_git_dir < 0)
                inside_git_dir = is_inside_dir(get_git_dir());
        return inside_git_dir;
}

int is_inside_work_tree(void)
{
        if (inside_work_tree < 0)
                inside_work_tree = is_inside_dir(get_git_work_tree());
        return inside_work_tree;
}

void setup_work_tree(void)
{
        const char *work_tree, *git_dir;
        static int initialized = 0;

        if (initialized)
                return;

        if (work_tree_config_is_bogus)
                die(_("unable to set up work tree using invalid config"));

        work_tree = get_git_work_tree();
        git_dir = get_git_dir();
        if (!is_absolute_path(git_dir))
                git_dir = real_path(get_git_dir());
        if (!work_tree || chdir(work_tree))
                die(_("this operation must be run in a work tree"));

        /*
         * Make sure subsequent git processes find correct worktree
         * if $GIT_WORK_TREE is set relative
         */
        if (getenv(GIT_WORK_TREE_ENVIRONMENT))
                setenv(GIT_WORK_TREE_ENVIRONMENT, ".", 1);

        set_git_dir(remove_leading_path(git_dir, work_tree));
        initialized = 1;
}

static int check_repo_format(const char *var, const char *value, void *vdata)
{
        struct repository_format *data = vdata;
        const char *ext;

        if (strcmp(var, "core.repositoryformatversion") == 0)
                data->version = git_config_int(var, value);
        else if (skip_prefix(var, "extensions.", &ext)) {
                /*
                 * record any known extensions here; otherwise,
                 * we fall through to recording it as unknown, and
                 * check_repository_format will complain
                 */
                if (!strcmp(ext, "noop"))
                        ;
                else if (!strcmp(ext, "preciousobjects"))
                        data->precious_objects = git_config_bool(var, value);
                else if (!strcmp(ext, "partialclone")) {
                        if (!value)
                                return config_error_nonbool(var);
                        data->partial_clone = xstrdup(value);
                } else
                        string_list_append(&data->unknown_extensions, ext);
        } else if (strcmp(var, "core.bare") == 0) {
                data->is_bare = git_config_bool(var, value);
        } else if (strcmp(var, "core.worktree") == 0) {
                if (!value)
                        return config_error_nonbool(var);
                data->work_tree = xstrdup(value);
        }
        return 0;
}

static int check_repository_format_gently(const char *gitdir, struct repository_format *candidate, int *nongit_ok)
{
        struct strbuf sb = STRBUF_INIT;
        struct strbuf err = STRBUF_INIT;
        int has_common;

        has_common = get_common_dir(&sb, gitdir);
        strbuf_addstr(&sb, "/config");
        read_repository_format(candidate, sb.buf);
        strbuf_release(&sb);

        /*
         * For historical use of check_repository_format() in git-init,
         * we treat a missing config as a silent "ok", even when nongit_ok
         * is unset.
         */
        if (candidate->version < 0)
                return 0;

        if (verify_repository_format(candidate, &err) < 0) {
                if (nongit_ok) {
                        warning("%s", err.buf);
                        strbuf_release(&err);
                        *nongit_ok = -1;
                        return -1;
                }
                die("%s", err.buf);
        }

        repository_format_precious_objects = candidate->precious_objects;
        repository_format_partial_clone = candidate->partial_clone;
        string_list_clear(&candidate->unknown_extensions, 0);
        if (!has_common) {
                if (candidate->is_bare != -1) {
                        is_bare_repository_cfg = candidate->is_bare;
                        if (is_bare_repository_cfg == 1)
                                inside_work_tree = -1;
                }
                if (candidate->work_tree) {
                        free(git_work_tree_cfg);
                        git_work_tree_cfg = candidate->work_tree;
                        inside_work_tree = -1;
                }
        } else {
                free(candidate->work_tree);
        }

        return 0;
}

int read_repository_format(struct repository_format *format, const char *path)
{
        memset(format, 0, sizeof(*format));
        format->version = -1;
        format->is_bare = -1;
        format->hash_algo = GIT_HASH_SHA1;
        string_list_init(&format->unknown_extensions, 1);
        git_config_from_file(check_repo_format, path, format);
        return format->version;
}

int verify_repository_format(const struct repository_format *format,
                             struct strbuf *err)
{
        if (GIT_REPO_VERSION_READ < format->version) {
                strbuf_addf(err, _("Expected git repo version <= %d, found %d"),
                            GIT_REPO_VERSION_READ, format->version);
                return -1;
        }

        if (format->version >= 1 && format->unknown_extensions.nr) {
                int i;

                strbuf_addstr(err, _("unknown repository extensions found:"));

                for (i = 0; i < format->unknown_extensions.nr; i++)
                        strbuf_addf(err, "\n\t%s",
                                    format->unknown_extensions.items[i].string);
                return -1;
        }

        return 0;
}

void read_gitfile_error_die(int error_code, const char *path, const char *dir)
{
        switch (error_code) {
        case READ_GITFILE_ERR_STAT_FAILED:
        case READ_GITFILE_ERR_NOT_A_FILE:
                /* non-fatal; follow return path */
                break;
        case READ_GITFILE_ERR_OPEN_FAILED:
                die_errno(_("error opening '%s'"), path);
        case READ_GITFILE_ERR_TOO_LARGE:
                die(_("too large to be a .git file: '%s'"), path);
        case READ_GITFILE_ERR_READ_FAILED:
                die(_("error reading %s"), path);
        case READ_GITFILE_ERR_INVALID_FORMAT:
                die(_("invalid gitfile format: %s"), path);
        case READ_GITFILE_ERR_NO_PATH:
                die(_("no path in gitfile: %s"), path);
        case READ_GITFILE_ERR_NOT_A_REPO:
                die(_("not a git repository: %s"), dir);
        default:
                die("BUG: unknown error code");
        }
}

/*
 * Try to read the location of the git directory from the .git file,
 * return path to git directory if found. The return value comes from
 * a shared buffer.
 *
 * On failure, if return_error_code is not NULL, return_error_code
 * will be set to an error code and NULL will be returned. If
 * return_error_code is NULL the function will die instead (for most
 * cases).
 */
const char *read_gitfile_gently(const char *path, int *return_error_code)
{
        const int max_file_size = 1 << 20;  /* 1MB */
        int error_code = 0;
        char *buf = NULL;
        char *dir = NULL;
        const char *slash;
        struct stat st;
        int fd;
        ssize_t len;

        if (stat(path, &st)) {
                /* NEEDSWORK: discern between ENOENT vs other errors */
                error_code = READ_GITFILE_ERR_STAT_FAILED;
                goto cleanup_return;
        }
        if (!S_ISREG(st.st_mode)) {
                error_code = READ_GITFILE_ERR_NOT_A_FILE;
                goto cleanup_return;
        }
        if (st.st_size > max_file_size) {
                error_code = READ_GITFILE_ERR_TOO_LARGE;
                goto cleanup_return;
        }
        fd = open(path, O_RDONLY);
        if (fd < 0) {
                error_code = READ_GITFILE_ERR_OPEN_FAILED;
                goto cleanup_return;
        }
        buf = xmallocz(st.st_size);
        len = read_in_full(fd, buf, st.st_size);
        close(fd);
        if (len != st.st_size) {
                error_code = READ_GITFILE_ERR_READ_FAILED;
                goto cleanup_return;
        }
        if (!starts_with(buf, "gitdir: ")) {
                error_code = READ_GITFILE_ERR_INVALID_FORMAT;
                goto cleanup_return;
        }
        while (buf[len - 1] == '\n' || buf[len - 1] == '\r')
                len--;
        if (len < 9) {
                error_code = READ_GITFILE_ERR_NO_PATH;
                goto cleanup_return;
        }
        buf[len] = '\0';
        dir = buf + 8;

        if (!is_absolute_path(dir) && (slash = strrchr(path, '/'))) {
                size_t pathlen = slash+1 - path;
                dir = xstrfmt("%.*s%.*s", (int)pathlen, path,
                              (int)(len - 8), buf + 8);
                free(buf);
                buf = dir;
        }
        if (!is_git_directory(dir)) {
                error_code = READ_GITFILE_ERR_NOT_A_REPO;
                goto cleanup_return;
        }
        path = real_path(dir);

cleanup_return:
        if (return_error_code)
                *return_error_code = error_code;
        else if (error_code)
                read_gitfile_error_die(error_code, path, dir);

        free(buf);
        return error_code ? NULL : path;
}

static const char *setup_explicit_git_dir(const char *gitdirenv,
                                          struct strbuf *cwd,
                                          struct repository_format *repo_fmt,
                                          int *nongit_ok)
{
        const char *work_tree_env = getenv(GIT_WORK_TREE_ENVIRONMENT);
        const char *worktree;
        char *gitfile;
        int offset;

        if (PATH_MAX - 40 < strlen(gitdirenv))
                die(_("'$%s' too big"), GIT_DIR_ENVIRONMENT);

        gitfile = (char*)read_gitfile(gitdirenv);
        if (gitfile) {
                gitfile = xstrdup(gitfile);
                gitdirenv = gitfile;
        }

        if (!is_git_directory(gitdirenv)) {
                if (nongit_ok) {
                        *nongit_ok = 1;
                        free(gitfile);
                        return NULL;
                }
                die(_("not a git repository: '%s'"), gitdirenv);
        }

        if (check_repository_format_gently(gitdirenv, repo_fmt, nongit_ok)) {
                free(gitfile);
                return NULL;
        }

        /* #3, #7, #11, #15, #19, #23, #27, #31 (see t1510) */
        if (work_tree_env)
                set_git_work_tree(work_tree_env);
        else if (is_bare_repository_cfg > 0) {
                if (git_work_tree_cfg) {
                        /* #22.2, #30 */
                        warning("core.bare and core.worktree do not make sense");
                        work_tree_config_is_bogus = 1;
                }

                /* #18, #26 */
                set_git_dir(gitdirenv);
                free(gitfile);
                return NULL;
        }
        else if (git_work_tree_cfg) { /* #6, #14 */
                if (is_absolute_path(git_work_tree_cfg))
                        set_git_work_tree(git_work_tree_cfg);
                else {
                        char *core_worktree;
                        if (chdir(gitdirenv))
                                die_errno(_("cannot chdir to '%s'"), gitdirenv);
                        if (chdir(git_work_tree_cfg))
                                die_errno(_("cannot chdir to '%s'"), git_work_tree_cfg);
                        core_worktree = xgetcwd();
                        if (chdir(cwd->buf))
                                die_errno(_("cannot come back to cwd"));
                        set_git_work_tree(core_worktree);
                        free(core_worktree);
                }
        }
        else if (!git_env_bool(GIT_IMPLICIT_WORK_TREE_ENVIRONMENT, 1)) {
                /* #16d */
                set_git_dir(gitdirenv);
                free(gitfile);
                return NULL;
        }
        else /* #2, #10 */
                set_git_work_tree(".");

        /* set_git_work_tree() must have been called by now */
        worktree = get_git_work_tree();

        /* both get_git_work_tree() and cwd are already normalized */
        if (!strcmp(cwd->buf, worktree)) { /* cwd == worktree */
                set_git_dir(gitdirenv);
                free(gitfile);
                return NULL;
        }

        offset = dir_inside_of(cwd->buf, worktree);
        if (offset >= 0) {      /* cwd inside worktree? */
                set_git_dir(real_path(gitdirenv));
                if (chdir(worktree))
                        die_errno(_("cannot chdir to '%s'"), worktree);
                strbuf_addch(cwd, '/');
                free(gitfile);
                return cwd->buf + offset;
        }

        /* cwd outside worktree */
        set_git_dir(gitdirenv);
        free(gitfile);
        return NULL;
}

static const char *setup_discovered_git_dir(const char *gitdir,
                                            struct strbuf *cwd, int offset,
                                            struct repository_format *repo_fmt,
                                            int *nongit_ok)
{
        if (check_repository_format_gently(gitdir, repo_fmt, nongit_ok))
                return NULL;

        /* --work-tree is set without --git-dir; use discovered one */
        if (getenv(GIT_WORK_TREE_ENVIRONMENT) || git_work_tree_cfg) {
                char *to_free = NULL;
                const char *ret;

                if (offset != cwd->len && !is_absolute_path(gitdir))
                        gitdir = to_free = real_pathdup(gitdir, 1);
                if (chdir(cwd->buf))
                        die_errno(_("cannot come back to cwd"));
                ret = setup_explicit_git_dir(gitdir, cwd, repo_fmt, nongit_ok);
                free(to_free);
                return ret;
        }

        /* #16.2, #17.2, #20.2, #21.2, #24, #25, #28, #29 (see t1510) */
        if (is_bare_repository_cfg > 0) {
                set_git_dir(offset == cwd->len ? gitdir : real_path(gitdir));
                if (chdir(cwd->buf))
                        die_errno(_("cannot come back to cwd"));
                return NULL;
        }

        /* #0, #1, #5, #8, #9, #12, #13 */
        set_git_work_tree(".");
        if (strcmp(gitdir, DEFAULT_GIT_DIR_ENVIRONMENT))
                set_git_dir(gitdir);
        inside_git_dir = 0;
        inside_work_tree = 1;
        if (offset == cwd->len)
                return NULL;

        /* Make "offset" point past the '/' (already the case for root dirs) */
        if (offset != offset_1st_component(cwd->buf))
                offset++;
        /* Add a '/' at the end */
        strbuf_addch(cwd, '/');
        return cwd->buf + offset;
}

/* #16.1, #17.1, #20.1, #21.1, #22.1 (see t1510) */
static const char *setup_bare_git_dir(struct strbuf *cwd, int offset,
                                      struct repository_format *repo_fmt,
                                      int *nongit_ok)
{
        int root_len;

        if (check_repository_format_gently(".", repo_fmt, nongit_ok))
                return NULL;

        setenv(GIT_IMPLICIT_WORK_TREE_ENVIRONMENT, "0", 1);

        /* --work-tree is set without --git-dir; use discovered one */
        if (getenv(GIT_WORK_TREE_ENVIRONMENT) || git_work_tree_cfg) {
                static const char *gitdir;

                gitdir = offset == cwd->len ? "." : xmemdupz(cwd->buf, offset);
                if (chdir(cwd->buf))
                        die_errno(_("cannot come back to cwd"));
                return setup_explicit_git_dir(gitdir, cwd, repo_fmt, nongit_ok);
        }

        inside_git_dir = 1;
        inside_work_tree = 0;
        if (offset != cwd->len) {
                if (chdir(cwd->buf))
                        die_errno(_("cannot come back to cwd"));
                root_len = offset_1st_component(cwd->buf);
                strbuf_setlen(cwd, offset > root_len ? offset : root_len);
                set_git_dir(cwd->buf);
        }
        else
                set_git_dir(".");
        return NULL;
}

static const char *setup_nongit(const char *cwd, int *nongit_ok)
{
        if (!nongit_ok)
                die(_("not a git repository (or any of the parent directories): %s"), DEFAULT_GIT_DIR_ENVIRONMENT);
        if (chdir(cwd))
                die_errno(_("cannot come back to cwd"));
        *nongit_ok = 1;
        return NULL;
}

static dev_t get_device_or_die(const char *path, const char *prefix, int prefix_len)
{
        struct stat buf;
        if (stat(path, &buf)) {
                die_errno(_("failed to stat '%*s%s%s'"),
                                prefix_len,
                                prefix ? prefix : "",
                                prefix ? "/" : "", path);
        }
        return buf.st_dev;
}

/*
 * A "string_list_each_func_t" function that canonicalizes an entry
 * from GIT_CEILING_DIRECTORIES using real_path_if_valid(), or
 * discards it if unusable.  The presence of an empty entry in
 * GIT_CEILING_DIRECTORIES turns off canonicalization for all
 * subsequent entries.
 */
static int canonicalize_ceiling_entry(struct string_list_item *item,
                                      void *cb_data)
{
        int *empty_entry_found = cb_data;
        char *ceil = item->string;

        if (!*ceil) {
                *empty_entry_found = 1;
                return 0;
        } else if (!is_absolute_path(ceil)) {
                return 0;
        } else if (*empty_entry_found) {
                /* Keep entry but do not canonicalize it */
                return 1;
        } else {
                char *real_path = real_pathdup(ceil, 0);
                if (!real_path) {
                        return 0;
                }
                free(item->string);
                item->string = real_path;
                return 1;
        }
}

enum discovery_result {
        GIT_DIR_NONE = 0,
        GIT_DIR_EXPLICIT,
        GIT_DIR_DISCOVERED,
        GIT_DIR_BARE,
        /* these are errors */
        GIT_DIR_HIT_CEILING = -1,
        GIT_DIR_HIT_MOUNT_POINT = -2,
        GIT_DIR_INVALID_GITFILE = -3
};

/*
 * We cannot decide in this function whether we are in the work tree or
 * not, since the config can only be read _after_ this function was called.
 *
 * Also, we avoid changing any global state (such as the current working
 * directory) to allow early callers.
 *
 * The directory where the search should start needs to be passed in via the
 * `dir` parameter; upon return, the `dir` buffer will contain the path of
 * the directory where the search ended, and `gitdir` will contain the path of
 * the discovered .git/ directory, if any. If `gitdir` is not absolute, it
 * is relative to `dir` (i.e. *not* necessarily the cwd).
 */
static enum discovery_result setup_git_directory_gently_1(struct strbuf *dir,
                                                          struct strbuf *gitdir,
                                                          int die_on_error)
{
        const char *env_ceiling_dirs = getenv(CEILING_DIRECTORIES_ENVIRONMENT);
        struct string_list ceiling_dirs = STRING_LIST_INIT_DUP;
        const char *gitdirenv;
        int ceil_offset = -1, min_offset = has_dos_drive_prefix(dir->buf) ? 3 : 1;
        dev_t current_device = 0;
        int one_filesystem = 1;

        /*
         * If GIT_DIR is set explicitly, we're not going
         * to do any discovery, but we still do repository
         * validation.
         */
        gitdirenv = getenv(GIT_DIR_ENVIRONMENT);
        if (gitdirenv) {
                strbuf_addstr(gitdir, gitdirenv);
                return GIT_DIR_EXPLICIT;
        }

        if (env_ceiling_dirs) {
                int empty_entry_found = 0;

                string_list_split(&ceiling_dirs, env_ceiling_dirs, PATH_SEP, -1);
                filter_string_list(&ceiling_dirs, 0,
                                   canonicalize_ceiling_entry, &empty_entry_found);
                ceil_offset = longest_ancestor_length(dir->buf, &ceiling_dirs);
                string_list_clear(&ceiling_dirs, 0);
        }

        if (ceil_offset < 0)
                ceil_offset = min_offset - 2;

        /*
         * Test in the following order (relative to the dir):
         * - .git (file containing "gitdir: <path>")
         * - .git/
         * - ./ (bare)
         * - ../.git
         * - ../.git/
         * - ../ (bare)
         * - ../../.git
         *   etc.
         */
        one_filesystem = !git_env_bool("GIT_DISCOVERY_ACROSS_FILESYSTEM", 0);
        if (one_filesystem)
                current_device = get_device_or_die(dir->buf, NULL, 0);
        for (;;) {
                int offset = dir->len, error_code = 0;

                if (offset > min_offset)
                        strbuf_addch(dir, '/');
                strbuf_addstr(dir, DEFAULT_GIT_DIR_ENVIRONMENT);
                gitdirenv = read_gitfile_gently(dir->buf, die_on_error ?
                                                NULL : &error_code);
                if (!gitdirenv) {
                        if (die_on_error ||
                            error_code == READ_GITFILE_ERR_NOT_A_FILE) {
                                /* NEEDSWORK: fail if .git is not file nor dir */
                                if (is_git_directory(dir->buf))
                                        gitdirenv = DEFAULT_GIT_DIR_ENVIRONMENT;
                        } else if (error_code != READ_GITFILE_ERR_STAT_FAILED)
                                return GIT_DIR_INVALID_GITFILE;
                }
                strbuf_setlen(dir, offset);
                if (gitdirenv) {
                        strbuf_addstr(gitdir, gitdirenv);
                        return GIT_DIR_DISCOVERED;
                }

                if (is_git_directory(dir->buf)) {
                        strbuf_addstr(gitdir, ".");
                        return GIT_DIR_BARE;
                }

                if (offset <= min_offset)
                        return GIT_DIR_HIT_CEILING;

                while (--offset > ceil_offset && !is_dir_sep(dir->buf[offset]))
                        ; /* continue */
                if (offset <= ceil_offset)
                        return GIT_DIR_HIT_CEILING;

                strbuf_setlen(dir, offset > min_offset ?  offset : min_offset);
                if (one_filesystem &&
                    current_device != get_device_or_die(dir->buf, NULL, offset))
                        return GIT_DIR_HIT_MOUNT_POINT;
        }
}

int discover_git_directory(struct strbuf *commondir,
                           struct strbuf *gitdir)
{
        struct strbuf dir = STRBUF_INIT, err = STRBUF_INIT;
        size_t gitdir_offset = gitdir->len, cwd_len;
        size_t commondir_offset = commondir->len;
        struct repository_format candidate;

        if (strbuf_getcwd(&dir))
                return -1;

        cwd_len = dir.len;
        if (setup_git_directory_gently_1(&dir, gitdir, 0) <= 0) {
                strbuf_release(&dir);
                return -1;
        }

        /*
         * The returned gitdir is relative to dir, and if dir does not reflect
         * the current working directory, we simply make the gitdir absolute.
         */
        if (dir.len < cwd_len && !is_absolute_path(gitdir->buf + gitdir_offset)) {
                /* Avoid a trailing "/." */
                if (!strcmp(".", gitdir->buf + gitdir_offset))
                        strbuf_setlen(gitdir, gitdir_offset);
                else
                        strbuf_addch(&dir, '/');
                strbuf_insert(gitdir, gitdir_offset, dir.buf, dir.len);
        }

        get_common_dir(commondir, gitdir->buf + gitdir_offset);

        strbuf_reset(&dir);
        strbuf_addf(&dir, "%s/config", commondir->buf + commondir_offset);
        read_repository_format(&candidate, dir.buf);
        strbuf_release(&dir);

        if (verify_repository_format(&candidate, &err) < 0) {
                warning("ignoring git dir '%s': %s",
                        gitdir->buf + gitdir_offset, err.buf);
                strbuf_release(&err);
                strbuf_setlen(commondir, commondir_offset);
                strbuf_setlen(gitdir, gitdir_offset);
                return -1;
        }

        return 0;
}

const char *setup_git_directory_gently(int *nongit_ok)
{
        static struct strbuf cwd = STRBUF_INIT;
        struct strbuf dir = STRBUF_INIT, gitdir = STRBUF_INIT;
        const char *prefix;
        struct repository_format repo_fmt;

        /*
         * We may have read an incomplete configuration before
         * setting-up the git directory. If so, clear the cache so
         * that the next queries to the configuration reload complete
         * configuration (including the per-repo config file that we
         * ignored previously).
         */
        git_config_clear();

        /*
         * Let's assume that we are in a git repository.
         * If it turns out later that we are somewhere else, the value will be
         * updated accordingly.
         */
        if (nongit_ok)
                *nongit_ok = 0;

        if (strbuf_getcwd(&cwd))
                die_errno(_("Unable to read current working directory"));
        strbuf_addbuf(&dir, &cwd);

        switch (setup_git_directory_gently_1(&dir, &gitdir, 1)) {
        case GIT_DIR_NONE:
                prefix = NULL;
                break;
        case GIT_DIR_EXPLICIT:
                prefix = setup_explicit_git_dir(gitdir.buf, &cwd, &repo_fmt, nongit_ok);
                break;
        case GIT_DIR_DISCOVERED:
                if (dir.len < cwd.len && chdir(dir.buf))
                        die(_("cannot change to '%s'"), dir.buf);
                prefix = setup_discovered_git_dir(gitdir.buf, &cwd, dir.len,
                                                  &repo_fmt, nongit_ok);
                break;
        case GIT_DIR_BARE:
                if (dir.len < cwd.len && chdir(dir.buf))
                        die(_("cannot change to '%s'"), dir.buf);
                prefix = setup_bare_git_dir(&cwd, dir.len, &repo_fmt, nongit_ok);
                break;
        case GIT_DIR_HIT_CEILING:
                prefix = setup_nongit(cwd.buf, nongit_ok);
                break;
        case GIT_DIR_HIT_MOUNT_POINT:
                if (nongit_ok) {
                        *nongit_ok = 1;
                        strbuf_release(&cwd);
                        strbuf_release(&dir);
                        return NULL;
                }
                die(_("not a git repository (or any parent up to mount point %s)\n"
                      "Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set)."),
                    dir.buf);
        default:
                die("BUG: unhandled setup_git_directory_1() result");
        }

        if (prefix)
                setenv(GIT_PREFIX_ENVIRONMENT, prefix, 1);
        else
                setenv(GIT_PREFIX_ENVIRONMENT, "", 1);

        startup_info->have_repository = !nongit_ok || !*nongit_ok;
        startup_info->prefix = prefix;

        /*
         * Not all paths through the setup code will call 'set_git_dir()' (which
         * directly sets up the environment) so in order to guarantee that the
         * environment is in a consistent state after setup, explicitly setup
         * the environment if we have a repository.
         *
         * NEEDSWORK: currently we allow bogus GIT_DIR values to be set in some
         * code paths so we also need to explicitly setup the environment if
         * the user has set GIT_DIR.  It may be beneficial to disallow bogus
         * GIT_DIR values at some point in the future.
         */
        if (startup_info->have_repository || getenv(GIT_DIR_ENVIRONMENT)) {
                if (!the_repository->gitdir) {
                        const char *gitdir = getenv(GIT_DIR_ENVIRONMENT);
                        if (!gitdir)
                                gitdir = DEFAULT_GIT_DIR_ENVIRONMENT;
                        repo_set_gitdir(the_repository, gitdir);
                        setup_git_env();
                }
                if (startup_info->have_repository)
                        repo_set_hash_algo(the_repository, repo_fmt.hash_algo);
        }

        strbuf_release(&dir);
        strbuf_release(&gitdir);

        return prefix;
}

int git_config_perm(const char *var, const char *value)
{
        int i;
        char *endptr;

        if (value == NULL)
                return PERM_GROUP;

        if (!strcmp(value, "umask"))
                return PERM_UMASK;
        if (!strcmp(value, "group"))
                return PERM_GROUP;
        if (!strcmp(value, "all") ||
            !strcmp(value, "world") ||
            !strcmp(value, "everybody"))
                return PERM_EVERYBODY;

        /* Parse octal numbers */
        i = strtol(value, &endptr, 8);

        /* If not an octal number, maybe true/false? */
        if (*endptr != 0)
                return git_config_bool(var, value) ? PERM_GROUP : PERM_UMASK;

        /*
         * Treat values 0, 1 and 2 as compatibility cases, otherwise it is
         * a chmod value to restrict to.
         */
        switch (i) {
        case PERM_UMASK:               /* 0 */
                return PERM_UMASK;
        case OLD_PERM_GROUP:           /* 1 */
                return PERM_GROUP;
        case OLD_PERM_EVERYBODY:       /* 2 */
                return PERM_EVERYBODY;
        }

        /* A filemode value was given: 0xxx */

        if ((i & 0600) != 0600)
                die(_("problem with core.sharedRepository filemode value "
                    "(0%.3o).\nThe owner of files must always have "
                    "read and write permissions."), i);

        /*
         * Mask filemode value. Others can not get write permission.
         * x flags for directories are handled separately.
         */
        return -(i & 0666);
}

void check_repository_format(void)
{
        struct repository_format repo_fmt;
        check_repository_format_gently(get_git_dir(), &repo_fmt, NULL);
        startup_info->have_repository = 1;
}

/*
 * Returns the "prefix", a path to the current working directory
 * relative to the work tree root, or NULL, if the current working
 * directory is not a strict subdirectory of the work tree root. The
 * prefix always ends with a '/' character.
 */
const char *setup_git_directory(void)
{
        return setup_git_directory_gently(NULL);
}

const char *resolve_gitdir_gently(const char *suspect, int *return_error_code)
{
        if (is_git_directory(suspect))
                return suspect;
        return read_gitfile_gently(suspect, return_error_code);
}

/* if any standard file descriptor is missing open it to /dev/null */
void sanitize_stdfds(void)
{
        int fd = open("/dev/null", O_RDWR, 0);
        while (fd != -1 && fd < 2)
                fd = dup(fd);
        if (fd == -1)
                die_errno(_("open /dev/null or dup failed"));
        if (fd > 2)
                close(fd);
}

int daemonize(void)
{
#ifdef NO_POSIX_GOODIES
        errno = ENOSYS;
        return -1;
#else
        switch (fork()) {
                case 0:
                        break;
                case -1:
                        die_errno(_("fork failed"));
                default:
                        exit(0);
        }
        if (setsid() == -1)
                die_errno(_("setsid failed"));
        close(0);
        close(1);
        close(2);
        sanitize_stdfds();
        return 0;
#endif
}