Fix a compiler warning in initStringInfo().

[pgsql.git] / src / port / path.c

/*-------------------------------------------------------------------------
 *
 * path.c
 *        portable path handling routines
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *        src/port/path.c
 *
 *-------------------------------------------------------------------------
 */

#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif

#include <ctype.h>
#include <sys/stat.h>
#ifdef WIN32
#ifdef _WIN32_IE
#undef _WIN32_IE
#endif
#define _WIN32_IE 0x0500
#ifdef near
#undef near
#endif
#define near
#include <shlobj.h>
#else
#include <pwd.h>
#include <unistd.h>
#endif

#include "pg_config_paths.h"


#ifndef WIN32
#define IS_PATH_VAR_SEP(ch) ((ch) == ':')
#else
#define IS_PATH_VAR_SEP(ch) ((ch) == ';')
#endif

static void make_relative_path(char *ret_path, const char *target_path,
                                                           const char *bin_path, const char *my_exec_path);
static char *trim_directory(char *path);
static void trim_trailing_separator(char *path);
static char *append_subdir_to_path(char *path, char *subdir);


/*
 * skip_drive
 *
 * On Windows, a path may begin with "C:" or "//network/".  Advance over
 * this and point to the effective start of the path.
 */
#ifdef WIN32

static char *
skip_drive(const char *path)
{
        if (IS_DIR_SEP(path[0]) && IS_DIR_SEP(path[1]))
        {
                path += 2;
                while (*path && !IS_DIR_SEP(*path))
                        path++;
        }
        else if (isalpha((unsigned char) path[0]) && path[1] == ':')
        {
                path += 2;
        }
        return (char *) path;
}
#else

#define skip_drive(path)        (path)
#endif

/*
 *      has_drive_prefix
 *
 * Return true if the given pathname has a drive prefix.
 */
bool
has_drive_prefix(const char *path)
{
#ifdef WIN32
        return skip_drive(path) != path;
#else
        return false;
#endif
}

/*
 *      first_dir_separator
 *
 * Find the location of the first directory separator, return
 * NULL if not found.
 */
char *
first_dir_separator(const char *filename)
{
        const char *p;

        for (p = skip_drive(filename); *p; p++)
                if (IS_DIR_SEP(*p))
                        return unconstify(char *, p);
        return NULL;
}

/*
 *      first_path_var_separator
 *
 * Find the location of the first path separator (i.e. ':' on
 * Unix, ';' on Windows), return NULL if not found.
 */
char *
first_path_var_separator(const char *pathlist)
{
        const char *p;

        /* skip_drive is not needed */
        for (p = pathlist; *p; p++)
                if (IS_PATH_VAR_SEP(*p))
                        return unconstify(char *, p);
        return NULL;
}

/*
 *      last_dir_separator
 *
 * Find the location of the last directory separator, return
 * NULL if not found.
 */
char *
last_dir_separator(const char *filename)
{
        const char *p,
                           *ret = NULL;

        for (p = skip_drive(filename); *p; p++)
                if (IS_DIR_SEP(*p))
                        ret = p;
        return unconstify(char *, ret);
}


/*
 *      make_native_path - on WIN32, change / to \ in the path
 *
 *      This effectively undoes canonicalize_path.
 *
 *      This is required because WIN32 COPY is an internal CMD.EXE
 *      command and doesn't process forward slashes in the same way
 *      as external commands.  Quoting the first argument to COPY
 *      does not convert forward to backward slashes, but COPY does
 *      properly process quoted forward slashes in the second argument.
 *
 *      COPY works with quoted forward slashes in the first argument
 *      only if the current directory is the same as the directory
 *      of the first argument.
 */
void
make_native_path(char *filename)
{
#ifdef WIN32
        char       *p;

        for (p = filename; *p; p++)
                if (*p == '/')
                        *p = '\\';
#endif
}


/*
 * This function cleans up the paths for use with either cmd.exe or Msys
 * on Windows. We need them to use filenames without spaces, for which a
 * short filename is the safest equivalent, eg:
 *              C:/Progra~1/
 */
void
cleanup_path(char *path)
{
#ifdef WIN32
        char       *ptr;

        /*
         * GetShortPathName() will fail if the path does not exist, or short names
         * are disabled on this file system.  In both cases, we just return the
         * original path.  This is particularly useful for --sysconfdir, which
         * might not exist.
         */
        GetShortPathName(path, path, MAXPGPATH - 1);

        /* Replace '\' with '/' */
        for (ptr = path; *ptr; ptr++)
        {
                if (*ptr == '\\')
                        *ptr = '/';
        }
#endif
}


/*
 * join_path_components - join two path components, inserting a slash
 *
 * We omit the slash if either given component is empty.
 *
 * ret_path is the output area (must be of size MAXPGPATH)
 *
 * ret_path can be the same as head, but not the same as tail.
 */
void
join_path_components(char *ret_path,
                                         const char *head, const char *tail)
{
        if (ret_path != head)
                strlcpy(ret_path, head, MAXPGPATH);

        /*
         * We used to try to simplify some cases involving "." and "..", but now
         * we just leave that to be done by canonicalize_path() later.
         */

        if (*tail)
        {
                /* only separate with slash if head wasn't empty */
                snprintf(ret_path + strlen(ret_path), MAXPGPATH - strlen(ret_path),
                                 "%s%s",
                                 (*(skip_drive(head)) != '\0') ? "/" : "",
                                 tail);
        }
}


/* State-machine states for canonicalize_path */
typedef enum
{
        ABSOLUTE_PATH_INIT,                     /* Just past the leading '/' (and Windows
                                                                 * drive name if any) of an absolute path */
        ABSOLUTE_WITH_N_DEPTH,          /* We collected 'pathdepth' directories in an
                                                                 * absolute path */
        RELATIVE_PATH_INIT,                     /* At start of a relative path */
        RELATIVE_WITH_N_DEPTH,          /* We collected 'pathdepth' directories in a
                                                                 * relative path */
        RELATIVE_WITH_PARENT_REF,       /* Relative path containing only double-dots */
} canonicalize_state;

/*
 *      Clean up path by:
 *              o  make Win32 path use Unix slashes
 *              o  remove trailing quote on Win32
 *              o  remove trailing slash
 *              o  remove duplicate (adjacent) separators
 *              o  remove '.' (unless path reduces to only '.')
 *              o  process '..' ourselves, removing it if possible
 */
void
canonicalize_path(char *path)
{
        char       *p,
                           *to_p;
        char       *spath;
        char       *parsed;
        char       *unparse;
        bool            was_sep = false;
        canonicalize_state state;
        int                     pathdepth = 0;  /* counts collected regular directory names */

#ifdef WIN32

        /*
         * The Windows command processor will accept suitably quoted paths with
         * forward slashes, but barfs badly with mixed forward and back slashes.
         */
        for (p = path; *p; p++)
        {
                if (*p == '\\')
                        *p = '/';
        }

        /*
         * In Win32, if you do: prog.exe "a b" "\c\d\" the system will pass \c\d"
         * as argv[2], so trim off trailing quote.
         */
        if (p > path && *(p - 1) == '"')
                *(p - 1) = '/';
#endif

        /*
         * Removing the trailing slash on a path means we never get ugly double
         * trailing slashes. Also, Win32 can't stat() a directory with a trailing
         * slash. Don't remove a leading slash, though.
         */
        trim_trailing_separator(path);

        /*
         * Remove duplicate adjacent separators
         */
        p = path;
#ifdef WIN32
        /* Don't remove leading double-slash on Win32 */
        if (*p)
                p++;
#endif
        to_p = p;
        for (; *p; p++, to_p++)
        {
                /* Handle many adjacent slashes, like "/a///b" */
                while (*p == '/' && was_sep)
                        p++;
                if (to_p != p)
                        *to_p = *p;
                was_sep = (*p == '/');
        }
        *to_p = '\0';

        /*
         * Remove any uses of "." and process ".." ourselves
         *
         * Note that "/../.." should reduce to just "/", while "../.." has to be
         * kept as-is.  Also note that we want a Windows drive spec to be visible
         * to trim_directory(), but it's not part of the logic that's looking at
         * the name components; hence distinction between path and spath.
         *
         * This loop overwrites the path in-place.  This is safe since we'll never
         * make the path longer.  "unparse" points to where we are reading the
         * path, "parse" to where we are writing.
         */
        spath = skip_drive(path);
        if (*spath == '\0')
                return;                                 /* empty path is returned as-is */

        if (*spath == '/')
        {
                state = ABSOLUTE_PATH_INIT;
                /* Skip the leading slash for absolute path */
                parsed = unparse = (spath + 1);
        }
        else
        {
                state = RELATIVE_PATH_INIT;
                parsed = unparse = spath;
        }

        while (*unparse != '\0')
        {
                char       *unparse_next;
                bool            is_double_dot;

                /* Split off this dir name, and set unparse_next to the next one */
                unparse_next = unparse;
                while (*unparse_next && *unparse_next != '/')
                        unparse_next++;
                if (*unparse_next != '\0')
                        *unparse_next++ = '\0';

                /* Identify type of this dir name */
                if (strcmp(unparse, ".") == 0)
                {
                        /* We can ignore "." components in all cases */
                        unparse = unparse_next;
                        continue;
                }

                if (strcmp(unparse, "..") == 0)
                        is_double_dot = true;
                else
                {
                        /* adjacent separators were eliminated above */
                        Assert(*unparse != '\0');
                        is_double_dot = false;
                }

                switch (state)
                {
                        case ABSOLUTE_PATH_INIT:
                                /* We can ignore ".." immediately after / */
                                if (!is_double_dot)
                                {
                                        /* Append first dir name (we already have leading slash) */
                                        parsed = append_subdir_to_path(parsed, unparse);
                                        state = ABSOLUTE_WITH_N_DEPTH;
                                        pathdepth++;
                                }
                                break;
                        case ABSOLUTE_WITH_N_DEPTH:
                                if (is_double_dot)
                                {
                                        /* Remove last parsed dir */
                                        /* (trim_directory won't remove the leading slash) */
                                        *parsed = '\0';
                                        parsed = trim_directory(path);
                                        if (--pathdepth == 0)
                                                state = ABSOLUTE_PATH_INIT;
                                }
                                else
                                {
                                        /* Append normal dir */
                                        *parsed++ = '/';
                                        parsed = append_subdir_to_path(parsed, unparse);
                                        pathdepth++;
                                }
                                break;
                        case RELATIVE_PATH_INIT:
                                if (is_double_dot)
                                {
                                        /* Append irreducible double-dot (..) */
                                        parsed = append_subdir_to_path(parsed, unparse);
                                        state = RELATIVE_WITH_PARENT_REF;
                                }
                                else
                                {
                                        /* Append normal dir */
                                        parsed = append_subdir_to_path(parsed, unparse);
                                        state = RELATIVE_WITH_N_DEPTH;
                                        pathdepth++;
                                }
                                break;
                        case RELATIVE_WITH_N_DEPTH:
                                if (is_double_dot)
                                {
                                        /* Remove last parsed dir */
                                        *parsed = '\0';
                                        parsed = trim_directory(path);
                                        if (--pathdepth == 0)
                                        {
                                                /*
                                                 * If the output path is now empty, we're back to the
                                                 * INIT state.  However, we could have processed a
                                                 * path like "../dir/.." and now be down to "..", in
                                                 * which case enter the correct state for that.
                                                 */
                                                if (parsed == spath)
                                                        state = RELATIVE_PATH_INIT;
                                                else
                                                        state = RELATIVE_WITH_PARENT_REF;
                                        }
                                }
                                else
                                {
                                        /* Append normal dir */
                                        *parsed++ = '/';
                                        parsed = append_subdir_to_path(parsed, unparse);
                                        pathdepth++;
                                }
                                break;
                        case RELATIVE_WITH_PARENT_REF:
                                if (is_double_dot)
                                {
                                        /* Append next irreducible double-dot (..) */
                                        *parsed++ = '/';
                                        parsed = append_subdir_to_path(parsed, unparse);
                                }
                                else
                                {
                                        /* Append normal dir */
                                        *parsed++ = '/';
                                        parsed = append_subdir_to_path(parsed, unparse);

                                        /*
                                         * We can now start counting normal dirs.  But if later
                                         * double-dots make us remove this dir again, we'd better
                                         * revert to RELATIVE_WITH_PARENT_REF not INIT state.
                                         */
                                        state = RELATIVE_WITH_N_DEPTH;
                                        pathdepth = 1;
                                }
                                break;
                }

                unparse = unparse_next;
        }

        /*
         * If our output path is empty at this point, insert ".".  We don't want
         * to do this any earlier because it'd result in an extra dot in corner
         * cases such as "../dir/..".  Since we rejected the wholly-empty-path
         * case above, there is certainly room.
         */
        if (parsed == spath)
                *parsed++ = '.';

        /* And finally, ensure the output path is nul-terminated. */
        *parsed = '\0';
}

/*
 * Detect whether a path contains any parent-directory references ("..")
 *
 * The input *must* have been put through canonicalize_path previously.
 */
bool
path_contains_parent_reference(const char *path)
{
        /*
         * Once canonicalized, an absolute path cannot contain any ".." at all,
         * while a relative path could contain ".."(s) only at the start.  So it
         * is sufficient to check the start of the path, after skipping any
         * Windows drive/network specifier.
         */
        path = skip_drive(path);        /* C: shouldn't affect our conclusion */

        if (path[0] == '.' &&
                path[1] == '.' &&
                (path[2] == '\0' || path[2] == '/'))
                return true;

        return false;
}

/*
 * Detect whether a path is only in or below the current working directory.
 *
 * The input *must* have been put through canonicalize_path previously.
 *
 * An absolute path that matches the current working directory should
 * return false (we only want relative to the cwd).
 */
bool
path_is_relative_and_below_cwd(const char *path)
{
        if (is_absolute_path(path))
                return false;
        /* don't allow anything above the cwd */
        else if (path_contains_parent_reference(path))
                return false;
#ifdef WIN32

        /*
         * On Win32, a drive letter _not_ followed by a slash, e.g. 'E:abc', is
         * relative to the cwd on that drive, or the drive's root directory if
         * that drive has no cwd.  Because the path itself cannot tell us which is
         * the case, we have to assume the worst, i.e. that it is not below the
         * cwd.  We could use GetFullPathName() to find the full path but that
         * could change if the current directory for the drive changes underneath
         * us, so we just disallow it.
         */
        else if (isalpha((unsigned char) path[0]) && path[1] == ':' &&
                         !IS_DIR_SEP(path[2]))
                return false;
#endif
        else
                return true;
}

/*
 * Detect whether path1 is a prefix of path2 (including equality).
 *
 * This is pretty trivial, but it seems better to export a function than
 * to export IS_DIR_SEP.
 */
bool
path_is_prefix_of_path(const char *path1, const char *path2)
{
        int                     path1_len = strlen(path1);

        if (strncmp(path1, path2, path1_len) == 0 &&
                (IS_DIR_SEP(path2[path1_len]) || path2[path1_len] == '\0'))
                return true;
        return false;
}

/*
 * Extracts the actual name of the program as called -
 * stripped of .exe suffix if any
 */
const char *
get_progname(const char *argv0)
{
        const char *nodir_name;
        char       *progname;

        nodir_name = last_dir_separator(argv0);
        if (nodir_name)
                nodir_name++;
        else
                nodir_name = skip_drive(argv0);

        /*
         * Make a copy in case argv[0] is modified by ps_status. Leaks memory, but
         * called only once.
         */
        progname = strdup(nodir_name);
        if (progname == NULL)
        {
                fprintf(stderr, "%s: out of memory\n", nodir_name);
                abort();                                /* This could exit the postmaster */
        }

#if defined(__CYGWIN__) || defined(WIN32)
        /* strip ".exe" suffix, regardless of case */
        if (strlen(progname) > sizeof(EXE) - 1 &&
                pg_strcasecmp(progname + strlen(progname) - (sizeof(EXE) - 1), EXE) == 0)
                progname[strlen(progname) - (sizeof(EXE) - 1)] = '\0';
#endif

        return progname;
}


/*
 * dir_strcmp: strcmp except any two DIR_SEP characters are considered equal,
 * and we honor filesystem case insensitivity if known
 */
static int
dir_strcmp(const char *s1, const char *s2)
{
        while (*s1 && *s2)
        {
                if (
#ifndef WIN32
                        *s1 != *s2
#else
                /* On windows, paths are case-insensitive */
                        pg_tolower((unsigned char) *s1) != pg_tolower((unsigned char) *s2)
#endif
                        && !(IS_DIR_SEP(*s1) && IS_DIR_SEP(*s2)))
                        return (int) *s1 - (int) *s2;
                s1++, s2++;
        }
        if (*s1)
                return 1;                               /* s1 longer */
        if (*s2)
                return -1;                              /* s2 longer */
        return 0;
}


/*
 * make_relative_path - make a path relative to the actual binary location
 *
 * This function exists to support relocation of installation trees.
 *
 *      ret_path is the output area (must be of size MAXPGPATH)
 *      target_path is the compiled-in path to the directory we want to find
 *      bin_path is the compiled-in path to the directory of executables
 *      my_exec_path is the actual location of my executable
 *
 * We determine the common prefix of target_path and bin_path, then compare
 * the remainder of bin_path to the last directory component(s) of
 * my_exec_path.  If they match, build the result as the part of my_exec_path
 * preceding the match, joined to the remainder of target_path.  If no match,
 * return target_path as-is.
 *
 * For example:
 *              target_path  = '/usr/local/share/postgresql'
 *              bin_path         = '/usr/local/bin'
 *              my_exec_path = '/opt/pgsql/bin/postgres'
 * Given these inputs, the common prefix is '/usr/local/', the tail of
 * bin_path is 'bin' which does match the last directory component of
 * my_exec_path, so we would return '/opt/pgsql/share/postgresql'
 */
static void
make_relative_path(char *ret_path, const char *target_path,
                                   const char *bin_path, const char *my_exec_path)
{
        int                     prefix_len;
        int                     tail_start;
        int                     tail_len;
        int                     i;

        /*
         * Determine the common prefix --- note we require it to end on a
         * directory separator, consider eg '/usr/lib' and '/usr/libexec'.
         */
        prefix_len = 0;
        for (i = 0; target_path[i] && bin_path[i]; i++)
        {
                if (IS_DIR_SEP(target_path[i]) && IS_DIR_SEP(bin_path[i]))
                        prefix_len = i + 1;
                else if (target_path[i] != bin_path[i])
                        break;
        }
        if (prefix_len == 0)
                goto no_match;                  /* no common prefix? */
        tail_len = strlen(bin_path) - prefix_len;

        /*
         * Set up my_exec_path without the actual executable name, and
         * canonicalize to simplify comparison to bin_path.
         */
        strlcpy(ret_path, my_exec_path, MAXPGPATH);
        trim_directory(ret_path);       /* remove my executable name */
        canonicalize_path(ret_path);

        /*
         * Tail match?
         */
        tail_start = (int) strlen(ret_path) - tail_len;
        if (tail_start > 0 &&
                IS_DIR_SEP(ret_path[tail_start - 1]) &&
                dir_strcmp(ret_path + tail_start, bin_path + prefix_len) == 0)
        {
                ret_path[tail_start] = '\0';
                trim_trailing_separator(ret_path);
                join_path_components(ret_path, ret_path, target_path + prefix_len);
                canonicalize_path(ret_path);
                return;
        }

no_match:
        strlcpy(ret_path, target_path, MAXPGPATH);
        canonicalize_path(ret_path);
}


/*
 * make_absolute_path
 *
 * If the given pathname isn't already absolute, make it so, interpreting
 * it relative to the current working directory.
 *
 * Also canonicalizes the path.  The result is always a malloc'd copy.
 *
 * In backend, failure cases result in ereport(ERROR); in frontend,
 * we write a complaint on stderr and return NULL.
 *
 * Note: interpretation of relative-path arguments during postmaster startup
 * should happen before doing ChangeToDataDir(), else the user will probably
 * not like the results.
 */
char *
make_absolute_path(const char *path)
{
        char       *new;

        /* Returning null for null input is convenient for some callers */
        if (path == NULL)
                return NULL;

        if (!is_absolute_path(path))
        {
                char       *buf;
                size_t          buflen;

                buflen = MAXPGPATH;
                for (;;)
                {
                        buf = malloc(buflen);
                        if (!buf)
                        {
#ifndef FRONTEND
                                ereport(ERROR,
                                                (errcode(ERRCODE_OUT_OF_MEMORY),
                                                 errmsg("out of memory")));
#else
                                fprintf(stderr, _("out of memory\n"));
                                return NULL;
#endif
                        }

                        if (getcwd(buf, buflen))
                                break;
                        else if (errno == ERANGE)
                        {
                                free(buf);
                                buflen *= 2;
                                continue;
                        }
                        else
                        {
                                int                     save_errno = errno;

                                free(buf);
                                errno = save_errno;
#ifndef FRONTEND
                                elog(ERROR, "could not get current working directory: %m");
#else
                                fprintf(stderr, _("could not get current working directory: %m\n"));
                                return NULL;
#endif
                        }
                }

                new = malloc(strlen(buf) + strlen(path) + 2);
                if (!new)
                {
                        free(buf);
#ifndef FRONTEND
                        ereport(ERROR,
                                        (errcode(ERRCODE_OUT_OF_MEMORY),
                                         errmsg("out of memory")));
#else
                        fprintf(stderr, _("out of memory\n"));
                        return NULL;
#endif
                }
                sprintf(new, "%s/%s", buf, path);
                free(buf);
        }
        else
        {
                new = strdup(path);
                if (!new)
                {
#ifndef FRONTEND
                        ereport(ERROR,
                                        (errcode(ERRCODE_OUT_OF_MEMORY),
                                         errmsg("out of memory")));
#else
                        fprintf(stderr, _("out of memory\n"));
                        return NULL;
#endif
                }
        }

        /* Make sure punctuation is canonical, too */
        canonicalize_path(new);

        return new;
}


/*
 *      get_share_path
 */
void
get_share_path(const char *my_exec_path, char *ret_path)
{
        make_relative_path(ret_path, PGSHAREDIR, PGBINDIR, my_exec_path);
}

/*
 *      get_etc_path
 */
void
get_etc_path(const char *my_exec_path, char *ret_path)
{
        make_relative_path(ret_path, SYSCONFDIR, PGBINDIR, my_exec_path);
}

/*
 *      get_include_path
 */
void
get_include_path(const char *my_exec_path, char *ret_path)
{
        make_relative_path(ret_path, INCLUDEDIR, PGBINDIR, my_exec_path);
}

/*
 *      get_pkginclude_path
 */
void
get_pkginclude_path(const char *my_exec_path, char *ret_path)
{
        make_relative_path(ret_path, PKGINCLUDEDIR, PGBINDIR, my_exec_path);
}

/*
 *      get_includeserver_path
 */
void
get_includeserver_path(const char *my_exec_path, char *ret_path)
{
        make_relative_path(ret_path, INCLUDEDIRSERVER, PGBINDIR, my_exec_path);
}

/*
 *      get_lib_path
 */
void
get_lib_path(const char *my_exec_path, char *ret_path)
{
        make_relative_path(ret_path, LIBDIR, PGBINDIR, my_exec_path);
}

/*
 *      get_pkglib_path
 */
void
get_pkglib_path(const char *my_exec_path, char *ret_path)
{
        make_relative_path(ret_path, PKGLIBDIR, PGBINDIR, my_exec_path);
}

/*
 *      get_locale_path
 */
void
get_locale_path(const char *my_exec_path, char *ret_path)
{
        make_relative_path(ret_path, LOCALEDIR, PGBINDIR, my_exec_path);
}

/*
 *      get_doc_path
 */
void
get_doc_path(const char *my_exec_path, char *ret_path)
{
        make_relative_path(ret_path, DOCDIR, PGBINDIR, my_exec_path);
}

/*
 *      get_html_path
 */
void
get_html_path(const char *my_exec_path, char *ret_path)
{
        make_relative_path(ret_path, HTMLDIR, PGBINDIR, my_exec_path);
}

/*
 *      get_man_path
 */
void
get_man_path(const char *my_exec_path, char *ret_path)
{
        make_relative_path(ret_path, MANDIR, PGBINDIR, my_exec_path);
}


/*
 *      get_home_path
 *
 * On Unix, this actually returns the user's home directory.  On Windows
 * it returns the PostgreSQL-specific application data folder.
 */
bool
get_home_path(char *ret_path)
{
#ifndef WIN32
        /*
         * We first consult $HOME.  If that's unset, try to get the info from
         * <pwd.h>.
         */
        const char *home;

        home = getenv("HOME");
        if (home && home[0])
        {
                strlcpy(ret_path, home, MAXPGPATH);
                return true;
        }
        else
        {
                struct passwd pwbuf;
                struct passwd *pw;
                char            buf[1024];
                int                     rc;

                rc = getpwuid_r(geteuid(), &pwbuf, buf, sizeof buf, &pw);
                if (rc != 0 || !pw)
                        return false;
                strlcpy(ret_path, pw->pw_dir, MAXPGPATH);
                return true;
        }
#else
        char       *tmppath;

        /*
         * Note: We use getenv() here because the more modern SHGetFolderPath()
         * would force the backend to link with shell32.lib, which eats valuable
         * desktop heap.  XXX This function is used only in psql, which already
         * brings in shell32 via libpq.  Moving this function to its own file
         * would keep it out of the backend, freeing it from this concern.
         */
        tmppath = getenv("APPDATA");
        if (!tmppath)
                return false;
        snprintf(ret_path, MAXPGPATH, "%s/postgresql", tmppath);
        return true;
#endif
}


/*
 * get_parent_directory
 *
 * Modify the given string in-place to name the parent directory of the
 * named file.
 *
 * If the input is just a file name with no directory part, the result is
 * an empty string, not ".".  This is appropriate when the next step is
 * join_path_components(), but might need special handling otherwise.
 *
 * Caution: this will not produce desirable results if the string ends
 * with "..".  For most callers this is not a problem since the string
 * is already known to name a regular file.  If in doubt, apply
 * canonicalize_path() first.
 */
void
get_parent_directory(char *path)
{
        trim_directory(path);
}


/*
 *      trim_directory
 *
 *      Trim trailing directory from path, that is, remove any trailing slashes,
 *      the last pathname component, and the slash just ahead of it --- but never
 *      remove a leading slash.
 *
 * For the convenience of canonicalize_path, the path's new end location
 * is returned.
 */
static char *
trim_directory(char *path)
{
        char       *p;

        path = skip_drive(path);

        if (path[0] == '\0')
                return path;

        /* back up over trailing slash(es) */
        for (p = path + strlen(path) - 1; IS_DIR_SEP(*p) && p > path; p--)
                ;
        /* back up over directory name */
        for (; !IS_DIR_SEP(*p) && p > path; p--)
                ;
        /* if multiple slashes before directory name, remove 'em all */
        for (; p > path && IS_DIR_SEP(*(p - 1)); p--)
                ;
        /* don't erase a leading slash */
        if (p == path && IS_DIR_SEP(*p))
                p++;
        *p = '\0';
        return p;
}


/*
 *      trim_trailing_separator
 *
 * trim off trailing slashes, but not a leading slash
 */
static void
trim_trailing_separator(char *path)
{
        char       *p;

        path = skip_drive(path);
        p = path + strlen(path);
        if (p > path)
                for (p--; p > path && IS_DIR_SEP(*p); p--)
                        *p = '\0';
}

/*
 *      append_subdir_to_path
 *
 * Append the currently-considered subdirectory name to the output
 * path in canonicalize_path.  Return the new end location of the
 * output path.
 *
 * Since canonicalize_path updates the path in-place, we must use
 * memmove not memcpy, and we don't yet terminate the path with '\0'.
 */
static char *
append_subdir_to_path(char *path, char *subdir)
{
        size_t          len = strlen(subdir);

        /* No need to copy data if path and subdir are the same. */
        if (path != subdir)
                memmove(path, subdir, len);

        return path + len;
}