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fix(webrtc): warp sync slow initialization and webrtc handshake bug #3256

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fix(webrtc): warp sync slow initialization and webrtc handshake bug #3256

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344d501
Fix WebRTC notification handshake deadlock in multi-stream task loop
haikoschol Feb 18, 2026
1ab3ecc
Fix warp sync initialization
timwu20 Feb 25, 2026
1ad0581
Merge branch 'main' into gab_webrtc
lrubasze May 22, 2026
4004824
refactor(warp_sync): rename to optimistic_finalized_block_height
gab8i May 27, 2026
118c250
fix(webrtc): register write_listener before async block
gab8i May 27, 2026
9c02618
chore: use non-nightly rustfmt
gab8i May 28, 2026
56fb349
Merge branch 'main' into gab_webrtc
gab8i May 28, 2026
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22 changes: 19 additions & 3 deletions lib/src/sync/all.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -448,6 +448,7 @@ impl<TRq, TSrc, TBl> AllSync<TRq, TSrc, TBl> {
all_forks,
slab_insertion: self.shared.sources.vacant_entry(),
warp_sync: &mut self.warp_sync,
best_block_number,
marker: PhantomData,
})
}
Expand All @@ -456,6 +457,7 @@ impl<TRq, TSrc, TBl> AllSync<TRq, TSrc, TBl> {
all_forks,
slab_insertion: self.shared.sources.vacant_entry(),
warp_sync: &mut self.warp_sync,
best_block_number,
marker: PhantomData,
})
}
Expand All @@ -464,6 +466,7 @@ impl<TRq, TSrc, TBl> AllSync<TRq, TSrc, TBl> {
all_forks,
slab_insertion: self.shared.sources.vacant_entry(),
warp_sync: &mut self.warp_sync,
best_block_number,
marker: PhantomData,
})
}
Expand All @@ -472,6 +475,7 @@ impl<TRq, TSrc, TBl> AllSync<TRq, TSrc, TBl> {
all_forks,
slab_insertion: self.shared.sources.vacant_entry(),
warp_sync: &mut self.warp_sync,
best_block_number,
marker: PhantomData,
})
}
Expand Down Expand Up @@ -1520,6 +1524,7 @@ pub struct AddSourceOldBlock<'a, TRq, TSrc, TBl> {
all_forks:
all_forks::AddSourceOldBlock<'a, Option<TBl>, AllForksRequestExtra, AllForksSourceExtra>,
warp_sync: &'a mut Option<warp_sync::WarpSync<WarpSyncSourceExtra, WarpSyncRequestExtra>>,
best_block_number: u64,
marker: PhantomData<TRq>,
}

Expand All @@ -1538,7 +1543,10 @@ impl<'a, TRq, TSrc, TBl> AddSourceOldBlock<'a, TRq, TSrc, TBl> {
.add_source(AllForksSourceExtra { outer_source_id });

let warp_sync_source_id = if let Some(warp_sync) = self.warp_sync {
Some(warp_sync.add_source(WarpSyncSourceExtra { outer_source_id }))
Some(warp_sync.add_source(
WarpSyncSourceExtra { outer_source_id },
self.best_block_number,
))
} else {
None
};
Expand All @@ -1561,6 +1569,7 @@ pub struct AddSourceKnown<'a, TRq, TSrc, TBl> {
all_forks:
all_forks::AddSourceKnown<'a, Option<TBl>, AllForksRequestExtra, AllForksSourceExtra>,
warp_sync: &'a mut Option<warp_sync::WarpSync<WarpSyncSourceExtra, WarpSyncRequestExtra>>,
best_block_number: u64,
marker: PhantomData<TRq>,
}

Expand All @@ -1587,7 +1596,10 @@ impl<'a, TRq, TSrc, TBl> AddSourceKnown<'a, TRq, TSrc, TBl> {
.add_source(AllForksSourceExtra { outer_source_id });

let warp_sync_source_id = if let Some(warp_sync) = self.warp_sync {
Some(warp_sync.add_source(WarpSyncSourceExtra { outer_source_id }))
Some(warp_sync.add_source(
WarpSyncSourceExtra { outer_source_id },
self.best_block_number,
))
} else {
None
};
Expand All @@ -1610,6 +1622,7 @@ pub struct AddSourceUnknown<'a, TRq, TSrc, TBl> {
all_forks:
all_forks::AddSourceUnknown<'a, Option<TBl>, AllForksRequestExtra, AllForksSourceExtra>,
warp_sync: &'a mut Option<warp_sync::WarpSync<WarpSyncSourceExtra, WarpSyncRequestExtra>>,
best_block_number: u64,
marker: PhantomData<TRq>,
}

Expand All @@ -1636,7 +1649,10 @@ impl<'a, TRq, TSrc, TBl> AddSourceUnknown<'a, TRq, TSrc, TBl> {
);

let warp_sync_source_id = if let Some(warp_sync) = self.warp_sync {
Some(warp_sync.add_source(WarpSyncSourceExtra { outer_source_id }))
Some(warp_sync.add_source(
WarpSyncSourceExtra { outer_source_id },
self.best_block_number,
))
} else {
None
};
Expand Down
12 changes: 7 additions & 5 deletions lib/src/sync/warp_sync.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -640,15 +640,17 @@ impl<TSrc, TRq> WarpSync<TSrc, TRq> {

/// Add a source to the list of sources.
///
/// The source has a finalized block height of 0, which should later be updated using
/// [`WarpSync::set_source_finality_state`].
pub fn add_source(&mut self, user_data: TSrc) -> SourceId {
/// `best_block_number` is used as the initial finalized block height for this source.
/// It can later be updated using [`WarpSync::set_source_finality_state`].
pub fn add_source(&mut self, user_data: TSrc, best_block_number: u64) -> SourceId {
let source_id = SourceId(self.sources.insert(Source {
user_data,
finalized_block_height: 0,
finalized_block_height: best_block_number,
}));

let _inserted = self.sources_by_finalized_height.insert((0, source_id));
let _inserted = self
.sources_by_finalized_height
.insert((best_block_number, source_id));
debug_assert!(_inserted);
debug_assert!(self.sources.len() >= self.sources_by_finalized_height.len());

Expand Down
23 changes: 21 additions & 2 deletions light-base/src/network_service/tasks.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,7 @@ use crate::{
platform::{PlatformRef, SubstreamDirection},
};

use alloc::{boxed::Box, string::String};
use alloc::{boxed::Box, string::String, sync::Arc};
use core::{pin, time::Duration};
use futures_lite::FutureExt as _;
use futures_util::{StreamExt as _, future, stream::FuturesUnordered};
Expand Down Expand Up @@ -251,6 +251,11 @@ pub(super) async fn webrtc_multi_stream_connection_task<TPlat: PlatformRef>(
let mut next_substream_id = 0;
// We need to pin the receiver, as the type doesn't implement `Unpin`.
let mut coordinator_to_connection = pin::pin!(coordinator_to_connection);
// Shared event used to wake up all substream wait futures when
// `inject_coordinator_message` queues write data (e.g. AcceptInNotifications).
// Without this, the substream would never be re-polled since the platform's
// `wait_read_write_again` only wakes on incoming data or timers.
let coordinator_write_ready = Arc::new(event_listener::Event::new());

loop {
// Start opening new outbound substreams, if needed.
Expand Down Expand Up @@ -347,6 +352,12 @@ pub(super) async fn webrtc_multi_stream_connection_task<TPlat: PlatformRef>(
match wake_up_reason {
WakeUpReason::CoordinatorMessage(message) => {
connection_task.inject_coordinator_message(&platform.now(), message);
// Wake up all substream wait futures so they get re-polled.
// This is necessary because inject_coordinator_message may have
// queued write data (e.g. AcceptInNotifications queues a handshake
// response) but the platform's wait_read_write_again only wakes on
// incoming data or timers -- not on pending writes.
coordinator_write_ready.notify(usize::MAX);
}
WakeUpReason::CoordinatorDead => {
log!(
Expand Down Expand Up @@ -453,8 +464,16 @@ pub(super) async fn webrtc_multi_stream_connection_task<TPlat: PlatformRef>(
if let SubstreamFate::Continue = substream_fate {
when_substreams_rw_ready.push({
let platform = platform.clone();
let write_ready = coordinator_write_ready.clone();
Box::pin(async move {
platform.wait_read_write_again(socket.as_mut()).await;
// Wait for either platform data or a coordinator write
// notification (e.g. after AcceptInNotifications queues a
// handshake response that needs to be flushed).
let write_listener = write_ready.listen();
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@lexnv lexnv May 22, 2026

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Should we move the write_ready.listen() outside the Box::pin future?

Currently, the write listener is registered once the the when_substreams_rw_ready is firstly polled.
This means we could arrive in a situation where .notify(usize::MAX); is called before registering the listener call.

For this to happen we need to:

  • receive WakeUpReason::CoordinatorMessage(message)
  • message_sending.as_ref().as_pin_ref().is_none() should have some data to effectively take the None path and ignore the when_substreams_rw_ready.select_next_some()

Moving the listener above Box::pin solves this regardless of which states call when_substreams_rw_ready.poll_next and avoids the problem entirely

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@gab8i gab8i May 27, 2026

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You are totally right, it should definitely be moved out so that it is registered and the async block later on depends on the registered event listener!

platform
.wait_read_write_again(socket.as_mut())
.or(write_listener)
.await;
(socket, substream_id)
})
});
Expand Down
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