Make handle_binary compliant with the KernelMessage.IMessage spec

Since Jupyterlab v4.0.0a21 the buffers deserialized from a KernelMessage
are now of type ArrayBuffer instead of the DataView type
handle_binary expects. However, it turns out that the spec for
KernelMessage.IMessage has always specifed that buffers could be
either an ArrayBuffer or an ArrayBufferView. This commit ensures
either type is accepted.

Author: Matthew Toohey

src/mpl_widget.ts

@@ -234,10 +234,10 @@ export class MPLCanvasModel extends DOMWidgetModel {
         this.send_draw_message();
     }
 
-    handle_binary(msg: any, dataviews: any) {
+    handle_binary(msg: any, buffers: (ArrayBuffer | ArrayBufferView)[]) {
         const url_creator = window.URL || window.webkitURL;
 
-        const buffer = new Uint8Array(dataviews[0].buffer);
+        const buffer = new Uint8Array(ArrayBuffer.isView(buffers[0]) ? buffers[0].buffer : buffers[0]);
         const blob = new Blob([buffer], { type: 'image/png' });
         const image_url = url_creator.createObjectURL(blob);
 
@@ -263,7 +263,7 @@ export class MPLCanvasModel extends DOMWidgetModel {
         // button to toggle?
     }
 
-    on_comm_message(evt: any, dataviews: any) {
+    on_comm_message(evt: any, buffers: (ArrayBuffer | ArrayBufferView)[]) {
         const msg = JSON.parse(evt.data);
         const msg_type = msg['type'];
         let callback;
@@ -281,7 +281,7 @@ export class MPLCanvasModel extends DOMWidgetModel {
         }
 
         if (callback) {
-            callback(msg, dataviews);
+            callback(msg, buffers);
         }
     }