add feature flags to await for response from table() and view()

Author: sc1f

packages/perspective/src/js/api/client.js

@@ -44,7 +44,7 @@ export class Client {
     }
 
     /**
-     * Process an asynchronous message.
+     * Send a message to the server.
      */
     post(msg, resolve, reject, keep_alive = false) {
         ++this._worker.msg_id;
@@ -55,7 +55,13 @@ export class Client {
         if (this._worker.initialized.value) {
             this.send(msg);
         } else {
-            this._worker.messages.push(() => this.send(msg));
+            this._worker.messages.push(() => {
+                this.send(msg);
+
+                if ((msg.cmd === "table" || msg.cmd === "view") && !this._features?.wait_for_response && resolve) {
+                    resolve();
+                }
+            });
         }
     }
 
@@ -87,10 +93,8 @@ export class Client {
     }
 
     /**
-     * Handle a command from Perspective. If the Client is not initialized,
-     * initialize it and dispatch the `perspective-ready` event.
-     *
-     * Otherwise, reject or resolve the incoming command.
+     * Receive a message from the server, and resolve/reject the promise that
+     * is awaiting the content of the message.
      */
     _handle(e) {
         if (!this._worker.initialized.value) {
@@ -107,6 +111,16 @@ export class Client {
             this._worker.initialized.value = true;
             this._worker.messages = [];
 
+            // If the `data` attribute of the init message is set, then
+            // set the `features` dictionary with the flags from the server.
+            if (e.data?.data) {
+                this._features = {};
+
+                for (const feature of e.data.data) {
+                    this._features[feature] = true;
+                }
+            }
+
             if (msgs) {
                 for (const m in msgs) {
                     if (msgs.hasOwnProperty(m)) {
@@ -117,13 +131,15 @@ export class Client {
         }
 
         if (e.data.id) {
-            var handler = this._worker.handlers[e.data.id];
+            const handler = this._worker.handlers[e.data.id];
+
             if (handler) {
                 if (e.data.error) {
                     handler.reject(e.data.error);
                 } else {
                     handler.resolve(e.data.data);
                 }
+
                 if (!handler.keep_alive) {
                     delete this._worker.handlers[e.data.id];
                 }

packages/perspective/src/js/api/server.js

@@ -40,13 +40,24 @@ export class Server {
     }
 
     /**
+     * Return an initialization message to the client for confirmation.
      * `Server` must be extended and the `post` method implemented before the
      * server can successfully be initialized.
      */
     init(msg) {
         if (msg.config) {
             override_config(msg.config);
         }
+
+        // The client will wait for a response message on table() and
+        // view(). If this flag is not set, the table() and view()
+        // constructors will resolve automatically and errors from the
+        // server will not be caught in those constructors. This allows
+        // for backwards compatibility between newer frontends (those
+        // with async table/view constructors) and older servers (which
+        // do not send the response message to the client).
+        msg.data = ["wait_for_response"];
+
         this.post(msg);
     }
 

packages/perspective/src/js/api/table_api.js

@@ -67,6 +67,10 @@ export function table(worker, data, options) {
                 reject
             );
         }
+
+        if (this._worker._initialized === true && !this._worker._features?.wait_for_response) {
+            resolve(this);
+        }
     });
 }
 

packages/perspective/src/js/api/view_api.js

@@ -40,6 +40,10 @@ export function view(worker, table_name, config) {
             },
             reject
         );
+
+        if (this._worker._initialized === true && !this._worker._features?.wait_for_response) {
+            resolve(this);
+        }
     });
 }
 

python/perspective/perspective/manager/manager_internal.py

@@ -122,8 +122,14 @@ def __process(self, msg, post_callback, client_id=None):
 
         try:
             if cmd == "init":
-                # return empty response
-                message = self._make_message(msg["id"], None)
+                # The client should wait for the return message on table()
+                # and view() to confirm successful creation.
+                flags = ["wait_for_response"]
+
+                # Return a message to the client to confirm initialization with
+                # a list of feature flags that the client will use to enable
+                # or disable behavior depending on its version.
+                message = self._make_message(msg["id"], flags)
                 post_callback(self._message_to_json(msg["id"], message))
             elif cmd == "table":
                 try: