Fix binary buffers

Author: martinRenou

packages/voila/src/manager.ts

@@ -203,12 +203,20 @@ export class WidgetManager extends JupyterLabManager {
       { widgets: null }
     );
 
-    const [widgetsInfo, buffers]: any = await new Promise(resolve => {
+    let [widgetsInfo, buffers]: any = await new Promise(resolve => {
       initComm.on_msg(msg => {
         const info = JSON.parse(
           Buffer.from(new Int8Array(msg.buffers[0].buffer)).toString('utf-8')
         );
-        resolve([info, msg.buffers.slice(1)]);
+
+        const buffers = (msg.buffers.slice(1) || []).map((b: any) => {
+          if (b instanceof DataView) {
+              return b;
+          } else {
+              return new DataView(b instanceof ArrayBuffer ? b : b.buffer);
+          }
+      });
+        resolve([info, buffers]);
       });
     });
 
@@ -234,9 +242,11 @@ export class WidgetManager extends JupyterLabManager {
       try {
         const comm = await this._create_comm('jupyter.widget', widget_id);
 
-        // If we have binary buffers
+        // Put binary buffers
         if (widget_id in bufferPaths) {
-          base.put_buffers(state, bufferPaths[widget_id], buffers);
+          const nBuffers = bufferPaths[widget_id].length;
+          base.put_buffers(state, bufferPaths[widget_id], buffers.slice(0, nBuffers));
+          buffers = buffers.slice(nBuffers);
         }
 
         const modelPromise = this.new_model(