Does duckdb-async support Async User-defined function ?

[unknowntpo]

Hi, thanks for this amazing package,
when I'm playing around with user-defined function, I came across this issue.
The code snippet below only give me Promise, not the actual string.

async function fetchFromHttp() {
  const db = await Database.create(":memory:");

  db.register_udf('css_selector', 'string', (url) => {
    console.log(`fetching from url: ${url}`);
    const data = fetch(url)
      .then(res => res.text())
      .then(data => {        
        return data;
      });
    return data;
  });

  const rows = await db.all(`select css_selector('https://example.com/') as html`);
  await db.wait();

  console.log(rows);
}

await fetchFromHttp();

$ yarn start
yarn run v1.22.21
$ node src/index.js
fetching from url: https://example.com/
[ { html: '[object Promise]' } ]

[vinimdocarmo]

@unknowntpo your defined function is returning a promise instance instead of returning the promise resolved value.

Try marking your defined function as async and return await data; instead.

Just another 10 cents: you don't need the last .then in your chain. It's redundant.

It should look like this:

async function fetchFromHttp() {
  const db = await Database.create(":memory:");

  db.register_udf('css_selector', 'string', async (url) => {
    console.log(`fetching from url: ${url}`);
    const data = fetch(url)
      .then(res => res.text());
    return await data;
  });

  const rows = await db.all(`select css_selector('https://example.com/') as html`);
  await db.wait();

  console.log(rows);
}

await fetchFromHttp();

[unknowntpo]

@vinimdocarmo

Just another 10 cents: you don't need the last .then in your chain. It's redundant.

This is correct, thank you !

But actually this code does not show me the actual html content, it just show me [object Promise], I try to use JSON.stringify but it gets the same result.

$ yarn start                                                                                                                                                                      (base) 08:48:25
yarn run v1.22.19
$ node src/index.js
fetching from url: https://example.com/
[
        {
                "html": "[object Promise]"
        }
]
✨  Done in 1.16s.

This is the code snippet.

https://github.com/unknowntpo/playground-2022/blob/50613cdcff617e6c265fd7c05e63d2986618dcfc/js/duckdb-example/src/index.js

[vinimdocarmo]

@unknowntpo I was checking DuckDB Node.js API and apparently it doesn't expect your udf callback to return a promise 😕 Which could explain why it doesn't resolve. See this code:

https://github.com/duckdb/duckdb-node/blob/main/lib/duckdb.js#L336

It doesn't await on your supplied callback function. I guess in this case you should open an Issue there for discussion. Maybe there's a good reason why they don't do that.

[unknowntpo]

@vinimdocarmo Sorry for my late reply and thanks for your answer! That makes sense, and I'll open an new issue at duckdb-node.