path.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * path.c
 *    portable path handling routines
 *
 * Portions Copyright (c) 1996-2024, 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 <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 == NULL || home[0] == '\0')
        return pg_get_user_home_dir(geteuid(), ret_path, MAXPGPATH);
    strlcpy(ret_path, home, 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;
}