tiff buffer loader supports get_flags

the tiff buffer loader was not setting any flags, so seq was using a
temp file (for example)

see https://github.com/jcupitt/libvips/issues/590

libvips/foreign/foreign.c

@@ -1479,7 +1479,7 @@ vips_foreign_save_class_init( VipsForeignSaveClass *class )
 	object_class->nickname = "filesave";
 	object_class->description = _( "file savers" );
 
-	/* All savers are seqential by definition. Things like tiled tiff 
+	/* All savers are sequential by definition. Things like tiled tiff 
 	 * write and interlaced png write, which are not, add extra caches 
 	 * on their input. 
 	 */

libvips/foreign/pforeign.h

@@ -69,9 +69,12 @@ int vips__tiff_read_header( const char *filename, VipsImage *out,
 	int page, int n, gboolean autorotate );
 int vips__tiff_read( const char *filename, VipsImage *out, 
 	int page, int n, gboolean autorotate, gboolean readbehind );
-gboolean vips__istifftiled( const char *filename );
+
-gboolean vips__istiff_buffer( const void *buf, size_t len );
 gboolean vips__istiff( const char *filename );
+gboolean vips__istifftiled( const char *filename );
+
+gboolean vips__istiff_buffer( const void *buf, size_t len );
+gboolean vips__istifftiled_buffer( const void *buf, size_t len );
 
 int vips__tiff_read_header_buffer( const void *buf, size_t len, VipsImage *out, 
 	int page, int n, gboolean autorotate );

libvips/foreign/tiff2vips.c

@@ -2352,4 +2352,29 @@ vips__tiff_read_buffer( const void *buf, size_t len,
 	return( 0 );
 }
 
+gboolean
+vips__istifftiled_buffer( const void *buf, size_t len )
+{
+	VipsImage *im;
+	TIFF *tif;
+	gboolean tiled;
+
+	vips__tiff_init();
+
+	im = vips_image_new();
+
+	if( !(tif = vips__tiff_openin_buffer( im, buf, len )) ) {
+		g_object_unref( im );
+		vips_error_clear();
+		return( FALSE );
+	}
+
+	tiled = TIFFIsTiled( tif );
+
+	TIFFClose( tif );
+	g_object_unref( im );
+
+	return( tiled );
+}
+
 #endif /*HAVE_TIFF*/

libvips/foreign/tiffload.c

@@ -2,6 +2,8 @@
  *
  * 5/12/11
  * 	- from tiffload.c
+ * 27/1/17
+ * 	- add get_flags for buffer loader
  */
 
 /*
@@ -244,6 +246,22 @@ typedef VipsForeignLoadTiffClass VipsForeignLoadTiffBufferClass;
 G_DEFINE_TYPE( VipsForeignLoadTiffBuffer, vips_foreign_load_tiff_buffer, 
 	vips_foreign_load_tiff_get_type() );
 
+static VipsForeignFlags
+vips_foreign_load_tiff_buffer_get_flags( VipsForeignLoad *load )
+{
+	VipsForeignLoadTiffBuffer *buffer = (VipsForeignLoadTiffBuffer *) load;
+
+	VipsForeignFlags flags;
+
+	flags = 0;
+	if( vips__istifftiled_buffer( buffer->buf->data, buffer->buf->length ) ) 
+		flags |= VIPS_FOREIGN_PARTIAL;
+	else
+		flags |= VIPS_FOREIGN_SEQUENTIAL;
+
+	return( flags );
+}
+
 static int
 vips_foreign_load_tiff_buffer_header( VipsForeignLoad *load )
 {
@@ -288,6 +306,7 @@ vips_foreign_load_tiff_buffer_class_init(
 	object_class->description = _( "load tiff from buffer" );
 
 	load_class->is_a_buffer = vips__istiff_buffer;
+	load_class->get_flags = vips_foreign_load_tiff_file_get_flags;
 	load_class->header = vips_foreign_load_tiff_buffer_header;
 	load_class->load = vips_foreign_load_tiff_buffer_load;