multipart support

[0xx400]

Hi, I see example link (Multipart Form) here https://crates.io/crates/tide/0.1.1 are broken.

Is there any workaround?

There was a fix, #47

But it seems to be reverted.

Thanks!

[yoshuawuyts]

Hi, thanks for asking!

Unfortunately we still don't support multipart because we need to author a multipart parser, as we found that there were no implementations in the ecosystem which could provide the guarantees we needed from a parser.

You can track the progress of the issue here: http-rs/http-types#126

[kindly]

Just in case someone needs this, here is an option.

Use multer, which is a multipart parser:

#cargo.toml
multer= "2"

Copy this buffered stream implementaion:

use async_std::io::{self, Read};
use async_std::stream::Stream;
use async_std::task::{Context, Poll};

use std::pin::Pin;

#[derive(Debug)]
pub struct BufferedBytesStream<T> {
    inner: T,
}

impl<T: Read + Unpin> Stream for BufferedBytesStream<T> {
    type Item = async_std::io::Result<Vec<u8>>;

    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        let mut buf = [0u8; 2048];

        let rd = Pin::new(&mut self.inner);

        match futures_core::ready!(rd.poll_read(cx, &mut buf)) {
            Ok(0) => Poll::Ready(None),
            Ok(n) => Poll::Ready(Some(Ok(buf[..n].to_vec()))),
            Err(ref e) if e.kind() == io::ErrorKind::Interrupted => Poll::Pending,
            Err(e) => Poll::Ready(Some(Err(e))),
        }
    }
}

Parse the request headers out of the tide Request to get out the multipart boundtry needed for parsing and use multer to parse the request. See multer docs:

use use multer::Multipart;

let multipart_boudry = "".to_string() 

if let Some(mime) = req.content_type() {
    let content_type = mime.essence().to_string();
    if content_type == "multipart/form-data" {
        if let Some(boundry) = mime.param("boundary") {
            multipart_boundry = boundry.to_string()
        }
    }
}

// use buffered stream on the request
let body_stream = BufferedBytesStream { inner: req };
let mut multipart = Multipart::new(body_stream, multipart_boundry.clone());

// download a file fromt the field "file" in the multipart request.

let download_file = "/some_path/";

while let Some(mut field) = multipart.next_field().await? {
    if field.name() != Some("file") {
        continue;
    }
    let mut output = File::create(&download_file).await?;

    while let Some(chunk) = field.chunk().await? {
        output.write_all(&chunk).await?;
    }
    output.flush().await?;
}

[kindly]

I wonder if a BufferedByteStream could be added to asnyc-std like Bytes. https://docs.rs/async-std/latest/async_std/io/struct.Bytes.html#. With perhaps buffered_bytes on ReadExt https://docs.rs/async-std/latest/async_std/io/trait.ReadExt.html for a different stream implementation on readers.

I initially used a wrapped Bytes stream for this but it was much slower as it polls for every byte. The above BufferedBytesStream is a tweaked version of this.

The streams lines and split on BufRead work (except for keeping the delimiters) but are an issue as a file could be on one line, therefore most of the request would be put in memory.

[amatveiakin]

In the meantime, would it make sense to update Request.body_form documentation to mention that the form must be in “application/x-www-form-urlencoded” format rather than “multipart/form-data”?

It's really easy to accidentally get a form in multipart format if sending data from JS, because FormData is always encoded as “multipart/form-data”. And tide error message is quite unhelpful, so it can take some time to debug.

[yungcomputerchair]

I just ran into this while porting my Flask app to Tide. I agree that the docs should really have some indication of this restriction as it would have saved me a lot of debugging.