--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libzip/lib/zip_source_seek_write.c	Wed Jun 29 09:24:55 2016 +0200
@@ -0,0 +1,52 @@
+/*
+  zip_source_seek_write.c -- seek to offset for writing
+  Copyright (C) 2014 Dieter Baron and Thomas Klausner
+
+  This file is part of libzip, a library to manipulate ZIP archives.
+  The authors can be contacted at <libzip@nih.at>
+
+  Redistribution and use in source and binary forms, with or without
+  modification, are permitted provided that the following conditions
+  are met:
+  1. Redistributions of source code must retain the above copyright
+     notice, this list of conditions and the following disclaimer.
+  2. Redistributions in binary form must reproduce the above copyright
+     notice, this list of conditions and the following disclaimer in
+     the documentation and/or other materials provided with the
+     distribution.
+  3. The names of the authors may not be used to endorse or promote
+     products derived from this software without specific prior
+     written permission.
+ 
+  THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS
+  OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+  WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+  ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
+  DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
+  GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
+  IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+  OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
+  IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+
+#include "zipint.h"
+
+
+ZIP_EXTERN int
+zip_source_seek_write(zip_source_t *src, zip_int64_t offset, int whence)
+{
+    zip_source_args_seek_t args;
+        
+    if (!ZIP_SOURCE_IS_OPEN_WRITING(src) || (whence != SEEK_SET && whence != SEEK_CUR && whence != SEEK_END)) {
+        zip_error_set(&src->error, ZIP_ER_INVAL, 0);
+        return -1;
+    }
+    
+    args.offset = offset;
+    args.whence = whence;
+    
+    return (_zip_source_call(src, &args, sizeof(args), ZIP_SOURCE_SEEK_WRITE) < 0 ? -1 : 0);
+}