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use std::{
convert::TryInto,
pin::Pin,
sync::Arc,
task::{Context, Poll},
};
use async_broadcast::Receiver as ActiveReceiver;
use futures_core::stream;
use futures_util::stream::FusedStream;
use ordered_stream::{OrderedStream, PollResult};
use static_assertions::assert_impl_all;
use tracing::warn;
use crate::{
AsyncDrop, Connection, ConnectionInner, MatchRule, Message, MessageSequence, OwnedMatchRule,
Result,
};
/// A [`stream::Stream`] implementation that yields [`Message`] items.
///
/// You can convert a [`Connection`] to this type and back to [`Connection`].
///
/// **NOTE**: You must ensure a `MessageStream` is continuously polled or you will experience hangs.
/// If you don't need to continuously poll the `MessageStream` but need to keep it around for later
/// use, keep the connection around and convert it into a `MessageStream` when needed. The
/// conversion is not an expensive operation so you don't need to worry about performance, unless
/// you do it very frequently. If you need to convert back and forth frequently, you may want to
/// consider keeping both a connection and stream around.
#[derive(Clone, Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct MessageStream {
inner: Inner,
}
assert_impl_all!(MessageStream: Send, Sync, Unpin);
impl MessageStream {
/// Create a message stream for the given match rule.
///
/// If `conn` is a bus connection and match rule is for a signal, the match rule will be
/// registered with the bus and queued for deregistration when the stream is dropped. If you'd
/// like immediate deregistration, use [`AsyncDrop::async_drop`]. The reason match rules are
/// only registered with the bus for signals is that D-Bus specification only allows signals to
/// be broadcasted and unicast messages are always sent to their destination (regardless of any
/// match rules registered by the destination) by the bus. Hence there is no need to register
/// match rules for non-signal messages with the bus.
///
/// Having said that, stream created by this method can still very useful as it allows you to
/// avoid needless task wakeups and simplify your stream consuming code.
///
/// You can optionally also request the capacity of the underlying message queue through
/// `max_queued`. If specified, the capacity is guaranteed to be at least `max_queued`. If not
/// specified, the default of 64 is assumed. The capacity can also be changed later through
/// [`MessageStream::set_max_queued`].
///
/// # Example
///
/// ```
/// use async_io::Timer;
/// use zbus::{AsyncDrop, Connection, MatchRule, MessageStream, fdo::NameOwnerChanged};
/// use futures_util::{TryStreamExt, future::select, future::Either::{Left, Right}, pin_mut};
///
/// # zbus::block_on(async {
/// let conn = Connection::session().await?;
/// let rule = MatchRule::builder()
/// .msg_type(zbus::MessageType::Signal)
/// .sender("org.freedesktop.DBus")?
/// .interface("org.freedesktop.DBus")?
/// .member("NameOwnerChanged")?
/// .add_arg("org.freedesktop.zbus.MatchRuleStreamTest42")?
/// .build();
/// let mut stream = MessageStream::for_match_rule(
/// rule,
/// &conn,
/// // For such a specific match rule, we don't need a big queue.
/// Some(1),
/// ).await?;
///
/// let rule_str = "type='signal',sender='org.freedesktop.DBus',\
/// interface='org.freedesktop.DBus',member='NameOwnerChanged',\
/// arg0='org.freedesktop.zbus.MatchRuleStreamTest42'";
/// assert_eq!(
/// stream.match_rule().map(|r| r.to_string()).as_deref(),
/// Some(rule_str),
/// );
///
/// // We register 2 names, starting with the uninteresting one. If `stream` wasn't filtering
/// // messages based on the match rule, we'd receive method return call for each of these 2
/// // calls first.
/// //
/// // Note that the `NameOwnerChanged` signal will not be sent by the bus for the first name
/// // we register since we setup an arg filter.
/// conn.request_name("org.freedesktop.zbus.MatchRuleStreamTest44")
/// .await?;
/// conn.request_name("org.freedesktop.zbus.MatchRuleStreamTest42")
/// .await?;
///
/// let msg = stream.try_next().await?.unwrap();
/// let signal = NameOwnerChanged::from_message(msg).unwrap();
/// assert_eq!(signal.args()?.name(), "org.freedesktop.zbus.MatchRuleStreamTest42");
/// stream.async_drop().await;
///
/// // Ensure the match rule is deregistered and this connection doesn't receive
/// // `NameOwnerChanged` signals.
/// let stream = MessageStream::from(&conn).try_filter_map(|msg| async move {
/// Ok(NameOwnerChanged::from_message(msg))
/// });
/// conn.release_name("org.freedesktop.zbus.MatchRuleStreamTest42").await?;
///
/// pin_mut!(stream);
/// let next = stream.try_next();
/// pin_mut!(next);
/// let timeout = Timer::after(std::time::Duration::from_millis(50));
/// pin_mut!(timeout);
/// match select(next, timeout).await {
/// Left((msg, _)) => unreachable!("unexpected message: {:?}", msg),
/// Right((_, _)) => (),
/// }
///
/// # Ok::<(), zbus::Error>(())
/// # }).unwrap();
/// ```
///
/// # Caveats
///
/// Since this method relies on [`MatchRule::matches`], it inherits its caveats.
pub async fn for_match_rule<R>(
rule: R,
conn: &Connection,
max_queued: Option<usize>,
) -> Result<Self>
where
R: TryInto<OwnedMatchRule>,
R::Error: Into<crate::Error>,
{
let rule = rule.try_into().map_err(Into::into)?;
let msg_receiver = conn.add_match(rule.clone(), max_queued).await?;
Ok(Self::for_subscription_channel(
msg_receiver,
Some(rule),
conn,
))
}
/// The associated match rule, if any.
pub fn match_rule(&self) -> Option<MatchRule<'_>> {
self.inner.match_rule.as_deref().cloned()
}
/// The maximum number of messages to queue for this stream.
pub fn max_queued(&self) -> usize {
self.inner.msg_receiver.capacity()
}
/// Set maximum number of messages to queue for this stream.
///
/// After this call, the capacity is guaranteed to be at least `max_queued`.
pub fn set_max_queued(&mut self, max_queued: usize) {
if max_queued <= self.max_queued() {
return;
}
self.inner.msg_receiver.set_capacity(max_queued);
}
pub(crate) fn for_subscription_channel(
msg_receiver: ActiveReceiver<Result<Arc<Message>>>,
rule: Option<OwnedMatchRule>,
conn: &Connection,
) -> Self {
let conn_inner = conn.inner.clone();
Self {
inner: Inner {
conn_inner,
msg_receiver,
match_rule: rule,
},
}
}
}
impl stream::Stream for MessageStream {
type Item = Result<Arc<Message>>;
fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
let this = self.get_mut();
Pin::new(&mut this.inner.msg_receiver).poll_next(cx)
}
}
impl OrderedStream for MessageStream {
type Data = Result<Arc<Message>>;
type Ordering = MessageSequence;
fn poll_next_before(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
before: Option<&Self::Ordering>,
) -> Poll<PollResult<Self::Ordering, Self::Data>> {
let this = self.get_mut();
match stream::Stream::poll_next(Pin::new(this), cx) {
Poll::Pending if before.is_some() => {
// Assume the provided MessageSequence in before was obtained from a Message
// associated with our Connection (because that's the only supported use case).
// Because there is only one socket-reader task, any messages that would have been
// ordered before that message would have already been sitting in the broadcast
// queue (and we would have seen Ready in our poll). Because we didn't, we can
// guarantee that we won't ever produce a message whose sequence is before that
// provided value, and so we can return NoneBefore.
//
// This ensures that ordered_stream::Join will never return Pending while it
// has a message buffered.
Poll::Ready(PollResult::NoneBefore)
}
Poll::Pending => Poll::Pending,
Poll::Ready(Some(Ok(msg))) => Poll::Ready(PollResult::Item {
ordering: msg.recv_position(),
data: Ok(msg),
}),
Poll::Ready(Some(Err(e))) => Poll::Ready(PollResult::Item {
ordering: MessageSequence::LAST,
data: Err(e),
}),
Poll::Ready(None) => Poll::Ready(PollResult::Terminated),
}
}
}
impl FusedStream for MessageStream {
fn is_terminated(&self) -> bool {
self.inner.msg_receiver.is_terminated()
}
}
impl From<Connection> for MessageStream {
fn from(conn: Connection) -> Self {
let conn_inner = conn.inner;
let msg_receiver = conn_inner.msg_receiver.activate_cloned();
Self {
inner: Inner {
conn_inner,
msg_receiver,
match_rule: None,
},
}
}
}
impl From<&Connection> for MessageStream {
fn from(conn: &Connection) -> Self {
Self::from(conn.clone())
}
}
impl From<MessageStream> for Connection {
fn from(stream: MessageStream) -> Connection {
Connection::from(&stream)
}
}
impl From<&MessageStream> for Connection {
fn from(stream: &MessageStream) -> Connection {
Connection {
inner: stream.inner.conn_inner.clone(),
}
}
}
#[derive(Clone, Debug)]
struct Inner {
conn_inner: Arc<ConnectionInner>,
msg_receiver: ActiveReceiver<Result<Arc<Message>>>,
match_rule: Option<OwnedMatchRule>,
}
impl Drop for Inner {
fn drop(&mut self) {
let conn = Connection {
inner: self.conn_inner.clone(),
};
if let Some(rule) = self.match_rule.take() {
conn.queue_remove_match(rule);
}
}
}
#[async_trait::async_trait]
impl AsyncDrop for MessageStream {
async fn async_drop(mut self) {
let conn = Connection {
inner: self.inner.conn_inner.clone(),
};
if let Some(rule) = self.inner.match_rule.take() {
if let Err(e) = conn.remove_match(rule).await {
warn!("Failed to remove match rule: {}", e);
}
}
}
}