How can I modify stream data while tokio_io::io::copy

I looked into this SO page but it seems that it's outdated.
How should it be done with latest tokio?

Well you certainly don't want to be using tokio_io. That's crate is very very old. The only official Tokio crates that are new are:

  • tokio
  • tokio-util
  • tokio-stream

As for how to modify data while using tokio::io::copy, well, the main way is to not use tokio::io::copy. For example, you can replace it with a loop that alternates between reading and writing.

loop {
    let data = read_message(&mut read).await?;
    let output = message_to_output(data);

This loop uses some example functions to do the reading and writing.

One option is to use the tokio_util::codec module. It can be used to more easily implement the read_message and message_to_output parts of the above loop, but you still need a loop that forwards messages (or a call to forward) rather than tokio::io::copy.

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Thank you very much for your kind response!
I wonder is it possible to do your loop inside tokio::spawn?
Because I'm actually trying to modify this code to fit my use case.

I could really use some mentoring on how to arrange my code here, I'm trying it myself already with my clumsy baysteps :smile:

There should be no issue with placing it inside a tokio::spawn.

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I checked code from tokio and realised I cannot do it in a loop since I don't know how to resume the io.

Now I'm checking out why there's a ready macro in this code base

Okay now I finished this job.

I copied the whole tokio::io::copy code and altered it, although I'm still not sure if it has to be this complicated.

In case anyone is intrested my code is here.

I might make a library to do this job later.

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