metadata was not being saved to vips files

broken by the rewind changes a few weeks ago

added a test too

TODO

@@ -1,3 +1,21 @@
+- extra character in exif-data?
+
+  try:
+
+	$ cd test
+	$ vipsheader -a images/IMG_4618.jpg | grep exif-data
+	exif-data: VIPS_TYPE_BLOB, data = 0x16e0a20, length = 6626
+	$ vips copy images/IMG_4618.jpg x.v
+	$ vipsheader -a x.v | grep exif-data
+	exif-data: VIPS_TYPE_BLOB, data = 0x20679f0, length = 6627
+
+  one byte longer!
+
+  fix, and add a test for exif length to test/test_foreign.py
+
+
+
+
 - how about something like vips_grid() which turns a tall thin one-band 
   image into a much smaller many-band image?
 

libvips/iofuncs/generate.c

@@ -704,6 +704,9 @@ vips_image_generate( VipsImage *image,
                 VIPS_DEBUG_MSG( "vips_image_generate: "
 			"attaching partial callbacks\n" );
 
+		if( vips_image_written( image ) )
+			return( -1 );
+ 
                 break;
  
         case VIPS_IMAGE_SETBUF:
@@ -742,6 +745,11 @@ vips_image_generate( VipsImage *image,
                 if( res )
                         return( -1 );
 
+		/* Must come before we rewind.
+		 */
+		if( vips_image_written( image ) )
+			return( -1 );
+
 		/* We've written to image ... rewind it ready for reading.
 		 */
 		if( vips_image_pio_input( image ) )
@@ -759,8 +767,5 @@ vips_image_generate( VipsImage *image,
                 return( -1 );
         }
 
-	if( vips_image_written( image ) )
-		return( -1 );
-
         return( 0 );
 }

test/test_foreign.py

@@ -104,6 +104,21 @@ class TestForeign(unittest.TestCase):
         self.assertEqual(im.bands, x.bands)
         self.assertLessEqual((im - x).abs().max(), max_diff)
 
+    def test_vips(self):
+        self.save_load_file("test.v", "", self.colour, 0)
+
+        # check we can save and restore metadata
+        self.colour.write_to_file("test.v")
+        x = Vips.Image.new_from_file("test.v")
+        before_exif = self.colour.get_value("exif-data")
+        after_exif = x.get_value("exif-data")
+
+        for i in range(len(before_exif)):
+            self.assertEqual(before_exif[i], after_exif[i])
+
+        x = None
+        os.unlink("test.v")
+
     def test_jpeg(self):
         x = Vips.type_find("VipsForeign", "jpegload")
         if not x.is_instantiatable():