postcard_rpc/host_client/util.rs
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use core::time::Duration;
// the contents of this file can probably be moved up to `mod.rs`
use std::{fmt::Debug, sync::Arc};
use maitake_sync::WaitQueue;
use postcard_schema::Schema;
use serde::de::DeserializeOwned;
use tokio::{
select,
sync::{broadcast, mpsc, Mutex},
};
use tracing::{debug, trace, warn};
use crate::{
header::{VarHeader, VarKey, VarSeqKind},
host_client::{
HostClient, HostContext, ProcessError, RpcFrame, WireContext, WireRx, WireSpawn, WireTx,
},
Key,
};
#[derive(Default, Debug)]
pub(crate) struct Subscriptions {
pub(crate) exclusive_list: Vec<(Key, mpsc::Sender<RpcFrame>)>,
pub(crate) broadcast_list: Vec<(Key, broadcast::Sender<RpcFrame>)>,
pub(crate) stopped: bool,
}
/// A basic cancellation-token
///
/// Used to terminate (and signal termination of) worker tasks
#[derive(Clone)]
pub struct Stopper {
inner: Arc<WaitQueue>,
}
impl Stopper {
/// Create a new Stopper
pub fn new() -> Self {
Self {
inner: Arc::new(WaitQueue::new()),
}
}
/// Wait until the stopper has been stopped.
///
/// Once this completes, the stopper has been permanently stopped
pub async fn wait_stopped(&self) {
// This completes if we are awoken OR if the queue is closed: either
// means we're cancelled
let _ = self.inner.wait().await;
}
/// Have we been stopped?
pub fn is_stopped(&self) -> bool {
self.inner.is_closed()
}
/// Stop the stopper
///
/// All current and future calls to [Self::wait_stopped] will complete immediately
pub fn stop(&self) {
self.inner.close();
}
}
impl Default for Stopper {
fn default() -> Self {
Self::new()
}
}
/// HostClient configuration
pub struct HostClientConfig<'c> {
/// The sequence kind to use
pub seq_kind: VarSeqKind,
/// The URI path to use for error messages
pub err_uri_path: &'c str,
/// The depth of the outgoing queue
pub outgoing_depth: usize,
/// Timeout to use before dropping a message if a subscribe channel is full.
///
/// Does not apply to subscribe_multi channels.
pub subscriber_timeout_if_full: Duration,
}
impl<WireErr> HostClient<WireErr>
where
WireErr: DeserializeOwned + Schema,
{
/// Generic HostClient logic, using the various Wire traits
///
/// Typically used internally, but may also be used to implement HostClient
/// over arbitrary transports.
pub fn new_with_wire<WTX, WRX, WSP>(
tx: WTX,
rx: WRX,
sp: WSP,
seq_kind: VarSeqKind,
err_uri_path: &str,
outgoing_depth: usize,
) -> Self
where
WTX: WireTx,
WRX: WireRx,
WSP: WireSpawn,
{
let config = HostClientConfig {
seq_kind,
err_uri_path,
outgoing_depth,
subscriber_timeout_if_full: Duration::ZERO,
};
Self::new_with_wire_and_config(tx, rx, sp, &config)
}
/// Generic HostClient logic, using the various Wire traits
///
/// Typically used internally, but may also be used to implement HostClient
/// over arbitrary transports.
pub fn new_with_wire_and_config<WTX, WRX, WSP>(
tx: WTX,
rx: WRX,
mut sp: WSP,
config: &HostClientConfig<'_>,
) -> Self
where
WTX: WireTx,
WRX: WireRx,
WSP: WireSpawn,
{
let (me, wire_ctx) = Self::new_manual_priv(config);
let WireContext { outgoing, incoming } = wire_ctx;
sp.spawn(out_worker(tx, outgoing, me.stopper.clone()));
sp.spawn(in_worker(
rx,
incoming,
me.subscriptions.clone(),
me.stopper.clone(),
));
me
}
}
/// Output worker, feeding frames to the `Client`.
async fn out_worker<W>(wire: W, rec: mpsc::Receiver<RpcFrame>, stop: Stopper)
where
W: WireTx,
W::Error: Debug,
{
let cancel_fut = stop.wait_stopped();
let operate_fut = out_worker_inner(wire, rec);
select! {
biased;
_ = cancel_fut => {},
_ = operate_fut => {
// if WE exited, notify everyone else it's stoppin time
stop.stop();
},
}
}
async fn out_worker_inner<W>(mut wire: W, mut rec: mpsc::Receiver<RpcFrame>)
where
W: WireTx,
W::Error: Debug,
{
loop {
let Some(msg) = rec.recv().await else {
tracing::warn!("Receiver Closed, this could be bad");
return;
};
if let Err(e) = wire.send(msg.to_bytes()).await {
tracing::error!("Output Queue Error: {e:?}, exiting");
return;
}
}
}
/// Input worker, getting frames from the `Client`
async fn in_worker<W>(
wire: W,
host_ctx: Arc<HostContext>,
subscriptions: Arc<Mutex<Subscriptions>>,
stop: Stopper,
) where
W: WireRx,
W::Error: Debug,
{
let cancel_fut = stop.wait_stopped();
let operate_fut = in_worker_inner(wire, host_ctx, subscriptions.clone());
select! {
biased;
_ = cancel_fut => {},
_ = operate_fut => {
// if WE exited, notify everyone else it's stoppin time
stop.stop();
},
}
// If we stop, purge the subscription list so that it is clear that no more messages are coming
// TODO: Have a "stopped" flag to prevent later additions (e.g. sub after store?)
let mut guard = subscriptions.lock().await;
guard.stopped = true;
guard.exclusive_list.clear();
guard.broadcast_list.clear();
}
async fn in_worker_inner<W>(
mut wire: W,
host_ctx: Arc<HostContext>,
subscriptions: Arc<Mutex<Subscriptions>>,
) where
W: WireRx,
W::Error: Debug,
{
loop {
let Ok(res) = wire.receive().await else {
warn!("in_worker: wire receive error, exiting");
return;
};
let Some((hdr, body)) = VarHeader::take_from_slice(&res) else {
warn!("Header decode error!");
continue;
};
trace!("in_worker received {hdr:?}");
let mut handled = false;
{
let mut subs_guard = subscriptions.lock().await;
let key = hdr.key;
// Remove if sending fails
//
// First, check the broadcast channels
let remove_mul_sub = if let Some((_h, m)) = subs_guard
.broadcast_list
.iter()
.find(|(k, _)| VarKey::Key8(*k) == key)
{
handled = true;
let frame = RpcFrame {
header: hdr,
body: body.to_vec(),
};
let res = m.send(frame);
match res {
Ok(_) => {
trace!("Handled message via subscription");
false
}
// A SendError means that there are no more receivers
Err(broadcast::error::SendError(_)) => true,
}
} else {
false
};
let remove_exl_sub = if let Some((_h, m)) = subs_guard
.exclusive_list
.iter()
.find(|(k, _)| VarKey::Key8(*k) == key)
{
handled = true;
let frame = RpcFrame {
header: hdr,
body: body.to_vec(),
};
let res = m.try_send(frame);
match res {
Ok(()) => {
trace!("Handled message via subscription");
false
}
Err(mpsc::error::TrySendError::Full(_))
if host_ctx.subscription_timeout.is_zero() =>
{
tracing::error!("Subscription channel full! Message dropped.");
false
}
Err(mpsc::error::TrySendError::Full(frame)) => {
tokio::select! {
// send returns an error if the channel is closed
r = m.send(frame) => r.is_err(),
_ = tokio::time::sleep(host_ctx.subscription_timeout) => {
tracing::error!("Subscription channel full! Message dropped.");
false
}
}
}
Err(mpsc::error::TrySendError::Closed(_)) => true,
}
} else {
false
};
if remove_exl_sub {
debug!("Dropping exclusive subscription");
subs_guard
.exclusive_list
.retain(|(k, _)| VarKey::Key8(*k) != key);
}
if remove_mul_sub {
debug!("Dropping multi subscription");
subs_guard
.broadcast_list
.retain(|(k, _)| VarKey::Key8(*k) != key);
}
}
if handled {
continue;
}
let frame = RpcFrame {
header: hdr,
body: body.to_vec(),
};
match host_ctx.process_did_wake(frame) {
Ok(true) => debug!("Handled message via map"),
Ok(false) => debug!("Message not handled"),
Err(ProcessError::Closed) => {
warn!("Got process error, quitting");
return;
}
}
}
}