1 files changed, 98 insertions, 0 deletions
diff --git a/src/stdlib/relpath.c b/src/stdlib/relpath.c
new file mode 100644
index 0000000..92888fa
--- /dev/null
+++ b/src/stdlib/relpath.c
@@ -0,0 +1,98 @@
+/**
+ * slibc — Yet another C library
+ * Copyright © 2015  Mattias Andrée (maandree@member.fsf.org)
+ * 
+ * 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 <http://www.gnu.org/licenses/>.
+ */
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <errno.h>
+
+
+
+/**
+ * Get the relative path of a file.
+ * 
+ * This is a slibc extension.
+ * 
+ * @param   file  The file.
+ * @param   ref   The file the result shall be relative to,
+ *                `NULL` for the current working directory.
+ *                If and only if this path ends with a slash,
+ *                (or if it is `NULL`,) it will be treated as
+ *                a directory in which a symbolic link, with
+ *                the result as it target, can be located to
+ *                point to `file`.
+ * 
+ * @throws  ENOMEM  The process cannot allocate more memory.
+ */
+char* relpath(const char* file, const char* ref) /* XXX may also fail as get_current_dir_name */
+{
+  int saved_errno;
+  char* cwd = NULL;
+  char* absfile = NULL;
+  char* absref = NULL;
+  char* rc;
+  char* prc;
+  size_t ptr, p, n = 0;
+  
+  if ((cwd      = get_current_dir_name()) == NULL)  goto fail;
+  if ((absfile  = abspath(file, cwd))     == NULL)  goto fail;
+  if (ref)
+    if ((absref = abspath(ref, cwd))      == NULL)  goto fail;
+  if (absref == NULL)
+    {
+      p = strlen(cwd);
+      absref = malloc((p + 1) + sizeof(char));
+      memcpy(absref, cwd, p);
+      absref[p] = '/';
+      absref[p + 1] = '\0';
+    }
+  else
+    strrchr(absref, '/')[1] = '\0';
+  
+  ptr = 0;
+  while (absfile[ptr] && (absfile[ptr] == absref[ptr]))
+    ptr++;
+  while (absfile[ptr] != '/')
+    ptr--;
+  ptr++;
+  
+  for (p = ptr; absref[p]; p++)
+    if (absref[p] == '/')
+      n += 1;
+  
+  rc = malloc((strlen(absfile + ptr) + 1 + 3 * n) * sizeof(char));
+  if (prc = rc, rc == NULL)
+    goto fail;
+  
+  while (n--)
+    prc = stpcpy(prc, "../");
+  strcpy(prc, absfile + ptr);
+  
+  free(cwd);
+  free(absfile);
+  free(absref);
+  return rc;
+  
+ fail:
+  saved_errno = errno;
+  free(cwd);
+  free(absfile);
+  free(absref);
+  errno = saved_errno;
+  return NULL;
+}
+