+#ifdef PNG_IO_STATE_SUPPORTED
+void
+pngtest_check_io_state(png_structp png_ptr, png_size_t data_length,
+ png_uint_32 io_op);
+void
+pngtest_check_io_state(png_structp png_ptr, png_size_t data_length,
+ png_uint_32 io_op)
+{
+ png_uint_32 io_state = png_get_io_state(png_ptr);
+ int err = 0;
+
+ /* Check if the current operation (reading / writing) is as expected. */
+ if ((io_state & PNG_IO_MASK_OP) != io_op)
+ png_error(png_ptr, "Incorrect operation in I/O state");
+
+ /* Check if the buffer size specific to the current location
+ * (file signature / header / data / crc) is as expected.
+ */
+ switch (io_state & PNG_IO_MASK_LOC)
+ {
+ case PNG_IO_SIGNATURE:
+ if (data_length > 8)
+ err = 1;
+ break;
+ case PNG_IO_CHUNK_HDR:
+ if (data_length != 8)
+ err = 1;
+ break;
+ case PNG_IO_CHUNK_DATA:
+ break; /* no restrictions here */
+ case PNG_IO_CHUNK_CRC:
+ if (data_length != 4)
+ err = 1;
+ break;
+ default:
+ err = 1; /* uninitialized */
+ }
+ if (err)
+ png_error(png_ptr, "Bad I/O state or buffer size");
+}
+#endif
+