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bug: async bindings do not return result #22

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7flash opened this issue Nov 12, 2023 · 3 comments
Open

bug: async bindings do not return result #22

7flash opened this issue Nov 12, 2023 · 3 comments

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@7flash
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7flash commented Nov 12, 2023

To reproduce run following example:

import { WebUI } from "./deno-webui/mod.ts";

const firstWindow = new WebUI({
    'libPath': './webui/dist/webui-2.dylib',
});

firstWindow.bind('first', async () => {
  return `${new Date()}`
});

firstWindow.bind('second', async () => {
  await new Promise(resolve => setTimeout(resolve, 100));
  return `${new Date()}`
});

try {
  await firstWindow.show(`<html>${new Date().toLocaleTimeString()}<script src="/webui.js"></script></html>`);
} catch (err) {
  console.error(err);
}

await WebUI.wait();
image

As seen in example, running first function returns current date as expected, but unfortunately running second function returns empty string.
@7flash 7flash mentioned this issue Nov 12, 2023
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@AlbertShown
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I used the debug version of webui, I found out that second() will return a promise object right away, so the webui receives an empty string "" right away. Then later, second() will send back the response ${new Date()} buffer to webui, but it's already late as webui already sent the empty string to UI (Browser).

The solution is making your functions return the wanted response instead of a promise.

firstWindow.bind('second', async () => {
  (async () => {
    await new Promise(resolve => setTimeout(resolve, 100));
  })();
  return `${new Date()}`
});

You can still use promises calls between your functions and app, but the binded one with webui should return the response and not a promise object. This is because C code doesn't wait for the asynchronous... C standard does not have such a thing.

@7flash
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7flash commented Nov 14, 2023

Okay gotcha

In your response then we should remove async keyword as well

firstWindow.bind('second', () => {
  (async () => {
    await new Promise(resolve => setTimeout(resolve, 100));
  })();
  return `${new Date()}`
});

Then I am using following approach:

                const nit = nanoid();
                scene = await new Promise(resolve => {
                  window.webuiCallbacks[nit] = resolve;
                  window.webui.executeDeno(denoScript, '{}', nit);
                });
                scene = JSON.parse(scene).result;

Then executeDeno binding:

      const taskId = e.arg.string(2);
            const serializedResponse = JSON.stringify(response)
        .replace(/'/g, "\\'")
      await firstWindow.script(`return window.webuiCallbacks["${taskId}"]('${serializedResponse}')`);

@AlbertShown
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Yes, if that works for you!👍

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@7flash @AlbertShown