+/* Is the given filename within a maildir directory?
+ *
+ * Specifically, is the final directory component of 'filename' either
+ * "cur" or "new". If so, return a pointer to that final directory
+ * component within 'filename'. If not, return NULL.
+ *
+ * A non-NULL return value is guaranteed to be a valid string pointer
+ * pointing to the characters "new/" or "cur/", (but not
+ * NUL-terminated).
+ */
+static const char *
+_filename_is_in_maildir (const char *filename)
+{
+ const char *slash, *dir = NULL;
+
+ /* Find the last '/' separating directory from filename. */
+ slash = strrchr (filename, '/');
+ if (slash == NULL)
+ return NULL;
+
+ /* Jump back 4 characters to where the previous '/' will be if the
+ * directory is named "cur" or "new". */
+ if (slash - filename < 4)
+ return NULL;
+
+ slash -= 4;
+
+ if (*slash != '/')
+ return NULL;
+
+ dir = slash + 1;
+
+ if (STRNCMP_LITERAL (dir, "cur/") == 0 ||
+ STRNCMP_LITERAL (dir, "new/") == 0)
+ {
+ return dir;
+ }
+
+ return NULL;
+}
+