How to convert from AsyncRead to HashMap?

help
1

Hi,

I went through this link: How do I make AsyncRead play nice with io::Read custom implemented functions? and the links mentioned in this post. Clearly I am unable to get the AsyncRead object converted to HashMap.

Below is the max i could get. But this implementation means that i have to parse the bytes myself and build the hashmap. Where as I am looking for some library which can do it for me.

let mut body = self
            .client
            .get_object()
            .bucket(bucket)
            .key(key)
            .send()
            .await
            .unwrap()
            .body
            .into_async_read();
        let map: HashMap<Value, Value> = HashMap::new();
        let framed = tokio_util::codec::FramedRead::new(body, LinesCodec::new());

Obvisously below code is erroring

serde_json::from_reader(body);

Any help?

2

Read everything into a Vec<u8> and use serde_json::from_slice. You can do this using the read_to_end method.

2 Likes
3

Thank you the approach mentioned worked.

        let mut bs: Vec<u8> = vec![];
        loop {
            let b = body.read_u8().await;
            if b.is_err() {
                break;
            }
            bs.push(b.unwrap());
        }
        let map: HashMap<String, String> = serde_json::from_slice(&bs).unwrap();

The above is also working. But the problem I see with this approach is that I have to take in all the bytes into memory and then build a map. But I was wondering if we can convert the stream into another stream and give the stream to the converter which gives me a map as output --I am thinking this may reduce the memory pressure so asking.

4

Using read_u8 is going to be incredibly slow. Do this instead:

let mut bs: Vec<u8> = vec![];
body.read_to_end(&mut vs);
let map: HashMap<String, String> = serde_json::from_slice(&bs).unwrap();

I don't think you can avoid reading everything into memory before creating the map.

2 Likes
5

There is SyncIoBridge in tokio_util::io - Rust which would let you feed an AsyncRead to serde, but unless you're getting into the gigabytes I doubt it would help much.

6

The SyncIoBridge is very limited. It can't be used from within async code.