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-rw-r--r--src/relpath.c134
1 files changed, 134 insertions, 0 deletions
diff --git a/src/relpath.c b/src/relpath.c
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+/* relpath - print the relative path
+ Copyright (C) 2012-2022 Free Software Foundation, Inc.
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <https://www.gnu.org/licenses/>. */
+
+/* Written by Pádraig Brady. */
+
+#include <config.h>
+
+#include "error.h"
+#include "system.h"
+#include "relpath.h"
+
+
+/* Return the length of the longest common prefix
+ of canonical PATH1 and PATH2, ensuring only full path components
+ are matched. Return 0 on no match. */
+ATTRIBUTE_PURE
+static int
+path_common_prefix (char const *path1, char const *path2)
+{
+ int i = 0;
+ int ret = 0;
+
+ /* We already know path1[0] and path2[0] are '/'. Special case
+ '//', which is only present in a canonical name on platforms
+ where it is distinct. */
+ if ((path1[1] == '/') != (path2[1] == '/'))
+ return 0;
+
+ while (*path1 && *path2)
+ {
+ if (*path1 != *path2)
+ break;
+ if (*path1 == '/')
+ ret = i + 1;
+ path1++;
+ path2++;
+ i++;
+ }
+
+ if ((!*path1 && !*path2)
+ || (!*path1 && *path2 == '/')
+ || (!*path2 && *path1 == '/'))
+ ret = i;
+
+ return ret;
+}
+
+/* Either output STR to stdout or
+ if *PBUF is not NULL then append STR to *PBUF
+ and update *PBUF to point to the end of the buffer
+ and adjust *PLEN to reflect the remaining space.
+ Return TRUE on failure. */
+static bool
+buffer_or_output (char const *str, char **pbuf, size_t *plen)
+{
+ if (*pbuf)
+ {
+ size_t slen = strlen (str);
+ if (slen >= *plen)
+ return true;
+ memcpy (*pbuf, str, slen + 1);
+ *pbuf += slen;
+ *plen -= slen;
+ }
+ else
+ {
+ fputs (str, stdout);
+ }
+
+ return false;
+}
+
+/* Output the relative representation if possible.
+ If BUF is non-NULL, write to that buffer rather than to stdout. */
+bool
+relpath (char const *can_fname, char const *can_reldir, char *buf, size_t len)
+{
+ bool buf_err = false;
+
+ /* Skip the prefix common to --relative-to and path. */
+ int common_index = path_common_prefix (can_reldir, can_fname);
+ if (!common_index)
+ return false;
+
+ char const *relto_suffix = can_reldir + common_index;
+ char const *fname_suffix = can_fname + common_index;
+
+ /* Skip over extraneous '/'. */
+ if (*relto_suffix == '/')
+ relto_suffix++;
+ if (*fname_suffix == '/')
+ fname_suffix++;
+
+ /* Replace remaining components of --relative-to with '..', to get
+ to a common directory. Then output the remainder of fname. */
+ if (*relto_suffix)
+ {
+ buf_err |= buffer_or_output ("..", &buf, &len);
+ for (; *relto_suffix; ++relto_suffix)
+ {
+ if (*relto_suffix == '/')
+ buf_err |= buffer_or_output ("/..", &buf, &len);
+ }
+
+ if (*fname_suffix)
+ {
+ buf_err |= buffer_or_output ("/", &buf, &len);
+ buf_err |= buffer_or_output (fname_suffix, &buf, &len);
+ }
+ }
+ else
+ {
+ buf_err |= buffer_or_output (*fname_suffix ? fname_suffix : ".",
+ &buf, &len);
+ }
+
+ if (buf_err)
+ error (0, ENAMETOOLONG, "%s", _("generating relative path"));
+
+ return !buf_err;
+}