1 files changed, 50 insertions, 13 deletions

diff --git a/libmailutils/string/mkfilename.c b/libmailutils/string/mkfilename.c
index 653ac7a2a..d24d2f48a 100644
--- a/libmailutils/string/mkfilename.c
+++ b/libmailutils/string/mkfilename.c
@@ -21,30 +21,67 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <errno.h>
 #include <mailutils/alloc.h>
 #include <mailutils/util.h>
 
+/*
+ * Given directory name DIR, file name FILE and optional suffix SUF,
+ * return full pathname composed from these three.  In the resulting
+ * string, DIR and FILE are separated by '/'.  If SUF is supplied, it
+ * is concatenated to the resulting string without additional
+ * separators.
+ *
+ * Corner cases:
+ *   all three arguments are NULL or empty
+ *     Return NULL and set errno to EINVAL.
+ *   dir is NULL
+ *     Return FILE and SUF concatenated.
+ *   file is NULL, suf is not NULL
+ *     Same as mu_make_file_name_suf(dir, suf, NULL);
+ *   file is NULL, suf is NULL
+ *     Return allocated copy of DIR.
+ */
 char *
 mu_make_file_name_suf (const char *dir, const char *file, const char *suf)
 {
   char *tmp;
-  size_t dirlen = strlen (dir);
-  size_t suflen = suf ? strlen (suf) : 0;
-  size_t fillen = strlen (file);
+  size_t dirlen, suflen, fillen;
   size_t len;
 
-  while (dirlen > 0 && dir[dirlen-1] == '/')
-    dirlen--;
-  
-  len = dirlen + (dir[0] ? 1 : 0) + fillen + suflen;
-  tmp = mu_alloc (len + 1);
+  dirlen = dir ? strlen (dir) : 0;
+  fillen = file ? strlen (file) : 0;
+  suflen = suf ? strlen (suf) : 0;
+
+  len = suflen + fillen;
+  if (dirlen == 0)
+    {
+      if (len == 0)
+	{
+	  errno = EINVAL;
+	  return NULL;
+	}
+    }
+  else
+    {
+      if (len) len++; // account for the '/' separator
+      while (dirlen > 0 && dir[dirlen-1] == '/')
+	dirlen--;
+    }
+  len += dirlen;
+
+  tmp = malloc (len + 1);
   if (tmp)
     {
-      memcpy (tmp, dir, dirlen);
-      if (dir[0])
-	tmp[dirlen++] = '/';
-      memcpy (tmp + dirlen, file, fillen);
-      if (suf)
+      if (dirlen)
+	{
+	  memcpy (tmp, dir, dirlen);
+	  if (fillen || suflen)
+	    tmp[dirlen++] = '/';
+	}
+      if (fillen)
+	memcpy (tmp + dirlen, file, fillen);
+      if (suflen)
 	memcpy (tmp + dirlen + fillen, suf, suflen);
       tmp[len] = 0;
     }