Function accept_hdr_async 

pub async fn accept_hdr_async<S, C>(
    stream: S,
    callback: C,
) -> Result<WebSocketStream<S>, Error>
where
    S: AsyncRead + AsyncWrite,
    C: Callback,

Available on crate feature ws only.

Accepts a new WebSocket connection with the provided stream.

This function does the same as accept_async() but accepts an extra callback for header processing. The callback receives headers of the incoming requests and is able to add extra headers to the reply.