No poll_read() in tokio ReadHalf?

I struggle to understand why I can't call AsyncRead::poll_read() on a ReadHalf in tokio. Clearly AsyncRead is implemented by ReadHalf. AsyncRead in turn requires the poll_read() method. Still it does not seem to be visible. I guess it's somehow related to visibility exports in tokio, but I couldn't find a lead.

Here's an example (I'm using tokio 0.2.9)

use tokio::io::AsyncRead;
use tokio::io::Result;
use tokio::net::TcpListener;
use tokio::stream::StreamExt;

async fn main() -> Result<()>{
    let mut listener = TcpListener::bind("localhost:9187").await?;

    let server = async move {
        let mut incoming = listener.incoming();
        while let Some(connection) = {
            if let Ok(mut tcp_stream) = connection {
                tokio::spawn(async move {
                    let (reader, _writer) = tcp_stream.split();
                    let pn = reader.poll_read();


The error message I get is:

error[E0599]: no method named `poll_read` found for type `tokio::net::tcp::split::ReadHalf<'_>` in the current scope
  --> src/
16 |                     let pn = reader.poll_read();
   |                                     ^^^^^^^^^ method not found in `tokio::net::tcp::split::ReadHalf<'_>`

Why can't the AsyncRead::poll_read() method be found?

Look at the signature of poll_read, it takes Pin<&mut Self>, and you don't have one.

I don't think you want to call that, though. Look at AsyncReadExt, I assume you want to import that and use those methods. I might be wrong, of course :slight_smile:

Well you're right, I'm blind :man_facepalming: I spent hours baffling at this!

I actually don't use it (using AsyncReadExt as you suggested). I just tried something out, stumbled across this and got curious.

It's clear now, thank you!