Set exception if read past end of file

Author: mdboom

lib/matplotlib/backends/backend_agg.py

@@ -526,6 +526,7 @@ def print_png(self, filename_or_obj, *args, **kwargs):
             close = True
         else:
             close = False
+
         try:
             _png.write_png(renderer._renderer, filename_or_obj, self.figure.dpi)
         finally:

src/_png.cpp

@@ -331,6 +331,8 @@ static void _read_png_data(PyObject *py_file_obj, png_bytep data, png_size_t len
         if (PyBytes_AsStringAndSize(result, &buffer, &bufflen) == 0) {
             if (bufflen == (Py_ssize_t)length) {
                 memcpy(data, buffer, length);
+            } else {
+                PyErr_SetString(PyExc_IOError, "read past end of file");
             }
         }
     }