Discussion on: How to use node.js streams for fileupload

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Replies for: Hi there. Thank you for your reply :-) I'm still here, will try and replicate your first case. Good point on the filereader as well. This one w...

aderchox • Oct 5 '22 • Edited

This might be ridiculous (or funny?), but after I added this comment here, I read a chapter on streams from a node.js book and now that I check node.js docs again, I don't see much more that I personally need to learn about node.js itself. But I think the main reason I asked for more is because the first part of your article (the theory) was so well explained that excited me :D and I thought your articles will be valuable for future readers about whatever they should be.
Did you manage to replicate the issue (the first case)?
I also want to recommend a few things about the article:
- Mention that this is exactly what packages like Multer and Formidable use under the hood.
- Mention that <input type="file"> does not load the files in RAM and it is things like fetch that create the stream automatically internally as soon as they are making the request (so no need to use the FileReader API explicitly). I know it's not directly related to your article, but realizing this connected some vagueness dots for me personally.
- Explain a bit more clearly where the "open" event is documented, I couldn't find it on Writeable Streams docs on Node.js docs. Maybe this was for an older version of Node.js?

Thanks for your response.

tq-bit • Oct 5 '22 • Edited

Noted. I do try to make my articles easily graspable. Sometimes it works, sometimes it doesn't.
Yes. All you have to do is to leave the form data out. Or implement a form parser on the backend. You're basically handling the raw binary data without the form wrapper. I'm not exactly sure how form data is parsed, but I did change your code so it looks like so and it worked (same server code). I attached the full staticially served index.html file:

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8" />
        <meta http-equiv="X-UA-Compatible" content="IE=edge" />
        <meta name="viewport" content="width=device-width, initial-scale=1.0" />
        <title>Document</title>
    </head>
    <body>
        <h1>Hello World!</h1>
        <input type="file" />

        <script>
            const input = document.querySelector('input');
            input.onchange = (e) => {
                upload(e.target.files[0]);
            };
            async function upload(data) {
                const response = await fetch('http://localhost:1234/upload', {
                    method: 'POST',
                    body: data,
                });
            }
        </script>
    </body>
</html>

Formidable works a bit differently. It's a form parser, more standardised than what's going on here. Since I discovered fastify, I favour Busboy over Multer, but I believe it serves the same purpose.

aderchox • Oct 7 '22 • Edited

I found the answer to my third point too, I'll add here for future readers:
Based on the documentation, createWriteStream returns an instance of <fs.WriteStream> that has an 'open' event which is emitted when the <fs.WriteStream>'s file is opened: nodejs.org/api/fs.html#event-open_1
(btw, this is weird, I did the exact same thing as you and passed the data leaving form data out, but still not working for me, but thanks anyways).

satya nishanth • Feb 4 '23

Just to be on the same page. In many upload file kinda websites they preview the input . I believe that has load into ram to preview right? ( I mean if the preview is enabled)

tq-bit • Feb 6 '23

Yes. Images are always loaded into memory when rendering a page. Instead of instantly uploading the img and providing a link, some pages store images as base64 on the user's computer and permit uploading only after a confirmation.