xmlstream: implement simple timeout logic

This allows to detect and handle dying streams without getting stuck
forever.

Timeouts are always wrong, though, so we put the burden of choosing the
right values (mostly) on the creator of a stream.

tokio-xmpp/examples/echo_server.rs

@@ -2,7 +2,7 @@ use futures::{SinkExt, StreamExt};
 use tokio::{self, io, net::TcpSocket};
 
 use tokio_xmpp::parsers::stream_features::StreamFeatures;
-use tokio_xmpp::xmlstream::{accept_stream, StreamHeader};
+use tokio_xmpp::xmlstream::{accept_stream, StreamHeader, Timeouts};
 
 #[tokio::main]
 async fn main() -> Result<(), io::Error> {
@@ -19,6 +19,7 @@ async fn main() -> Result<(), io::Error> {
         let stream = accept_stream(
             tokio::io::BufStream::new(stream),
             tokio_xmpp::parsers::ns::DEFAULT_NS,
+            Timeouts::default(),
         )
         .await?;
         let stream = stream.send_header(StreamHeader::default()).await?;