Function proxy_streams 

pub async fn proxy_streams<R, W>(
    input: BufReader<R>,
    output: W,
    url: &str,
    token: Option<&str>,
) -> Result<()>
where
    R: AsyncRead + Unpin,
    W: AsyncWrite + Unpin,

Read JSON-RPC lines from input, forward each to url, and write the answers to output. Returns when the input ends.