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Stop enqueueing messages for disconnected peers - #4094

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lightningdevkit:mainfrom
TheBlueMatt:2025-09-no-disconnected-msgs
Sep 22, 2025
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Stop enqueueing messages for disconnected peers#4094
tnull merged 3 commits into
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TheBlueMatt:2025-09-no-disconnected-msgs

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If a channel operation occurs while a peer is disconnected, we'll
still have a PeerState for that peer. Historically, we haven't
bothered to check if a peer is actually connected before we push
new messages onto the PeerState::pending_msg_events field,
leaving us sending messages into the void.

This is generally not an issue as
ChannelManager::get_and_clear_pending_msg_events should be called
very regularly, removing these messages and then dropping them as
PeerManager won't have anything to do with them.

Still, there is a race condition here - if a peer manages to
connect between the generation of one such message and when
get_and_clear_pending_msg_events is called, we may enqueue a
message to the peer which makes no sense and could lead to a
spurious channel closure (especially in the case of an async
ChannelMonitorUpdate completion or async signing operation, which
often lead to normal channel message generation).

Further, if a peer is slow to send their channel_reestablish
message after connection this race could be substantially more
likely, as such normal channel messages may be nonsense until we've
completed the reestablish dance (i.e. the later reestablish dance
may lead us to re-send the same messages again immediately).

Here we remove most of the cases where we enqueue messages for
disconnected peers.

Note that we differentiate between two different checks for
connected-ness - for cases where we're sending an error or gossip
messages, we allow the messages to be enqueued if the peer is
connected at all. For most other cases, we only allow messages to
be enqueued if the peer is connected and the channel has
completed its reestablish dance (if required, i.e. the channel is
"connected").

Fixes#4036

If a channel operation occurs while a peer is disconnected, we'll
still have a `PeerState` for that peer. Historically, we haven't
bothered to check if a peer is actually connected before we push
new messages onto the `PeerState::pending_msg_events` field,
leaving us sending messages into the void.
This is generally not an issue as
`ChannelManager::get_and_clear_pending_msg_events` should be called
very regularly, removing these messages and then dropping them as
`PeerManager` won't have anything to do with them.
Still, there is a race condition here - if a peer manages to
connect between the generation of one such message and when
`get_and_clear_pending_msg_events` is called, we may enqueue a
message to the peer which makes no sense and could lead to a
spurious channel closure (especially in the case of an async
`ChannelMonitorUpdate` completion or async signing operation, which
often lead to normal channel message generation).
Further, if a peer is slow to send their `channel_reestablish`
message after connection this race could be substantially more
likely, as such normal channel messages may be nonsense until we've
completed the reestablish dance (i.e. the later reestablish dance
may lead us to re-send the same messages again immediately).
Here we remove most of the cases where we enqueue messages for
disconnected peers.
Note that we differentiate between two different checks for
connected-ness - for cases where we're sending an `error` or gossip
messages, we allow the messages to be enqueued if the peer is
connected at all. For most other cases, we only allow messages to
be enqueued if the peer is connected *and* the channel has
completed its reestablish dance (if required, i.e. the channel is
"connected").
If a channel is failed while a peer is disconnected, we'll still
have a `PeerState` for that peer. Historically, we haven't bothered
to check if a peer is actually connected before we push the `error`
message onto the `PeerState::pending_msg_events` queue, leaving us
sending messages into the void.
This is generally not an issue as
`ChannelManager::get_and_clear_pending_msg_events` should be called
very regularly, removing these messages and then dropping them as
`PeerManager` won't have anything to do with them. Further, when
the the message is an `error`, if a peer happens to connect between
when we push the message and when `get_and_clear_pending_msg_events`
is called the worst that happens is they get the `error` message
we'd end up sending them when they try to reestablish the channel
anyway.
Still, its awkward to leave the `error`s lying around in a message
queue for a disconnected peer, so we remove them here.
In the previous two commits we stopped enqueueing messages for
disconnected peers. Here we add some basic test coverage of these
changes by asserting that there are no queued messages for a peer
when they (re-)connect.
We also add a few assertions that a peer is connected when we push
a message onto the queu, in cases where we expect a peer to be
connected.
@TheBlueMattTheBlueMatt added this to the 0.2 milestone Sep 19, 2025
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Codecov Report

❌ Patch coverage is 82.53012% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.60%. Comparing base (50391d3) to head (47a3e5c).
⚠️ Report is 25 commits behind head on main.

Files with missing linesPatch %Lines
lightning/src/ln/channelmanager.rs79.57%22 Missing and 7 partials ⚠️
Additional details and impacted files
@@ Coverage Diff @@## main #4094 +/- ##
==========================================
- Coverage 88.61% 88.60% -0.01% 
==========================================
Files 176 176 Lines 132099 132161 +62 Branches 132099 132161 +62 ==========================================
+ Hits 117060 117103 +43 - Misses 12365 12386 +21 + Partials 2674 2672 -2 
FlagCoverage Δ
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tests88.44% <82.53%> (-0.01%)⬇️

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Simple enough, going to land this.

It seems that going forward the peer connectedness could be better reflected by the types?

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@tnull
tnull merged commit 341e8e4 into lightningdevkit:mainSep 22, 2025
25 checks passed
@TheBlueMatt

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Yea we could hide the message queue behind some enum and accessor, but I'm not sure that's a huge deal - we just wipe the queue on connect and only send a message or two per channel max in the worst case. Whats actually a problem is sending a message for a channel when that channel is waiting on a channel_reestablish but the peer is connected. That's somewhat more difficult to fix in channelmanager.rs without yet more state from channel leaking up (which this PR kinda does too, sadly).

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Async Monitor Update completion while peer disconnected can generate sendable messages

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Stop enqueueing messages for disconnected peers by TheBlueMatt · Pull Request #4094 · lightningdevkit/rust-lightning · GitHub
Skip to content

Stop enqueueing messages for disconnected peers - #4094

Merged
tnull merged 3 commits into
lightningdevkit:mainfrom
TheBlueMatt:2025-09-no-disconnected-msgs
Sep 22, 2025
Merged

Stop enqueueing messages for disconnected peers#4094
tnull merged 3 commits into
lightningdevkit:mainfrom
TheBlueMatt:2025-09-no-disconnected-msgs

Conversation

@TheBlueMatt

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If a channel operation occurs while a peer is disconnected, we'll
still have a PeerState for that peer. Historically, we haven't
bothered to check if a peer is actually connected before we push
new messages onto the PeerState::pending_msg_events field,
leaving us sending messages into the void.

This is generally not an issue as
ChannelManager::get_and_clear_pending_msg_events should be called
very regularly, removing these messages and then dropping them as
PeerManager won't have anything to do with them.

Still, there is a race condition here - if a peer manages to
connect between the generation of one such message and when
get_and_clear_pending_msg_events is called, we may enqueue a
message to the peer which makes no sense and could lead to a
spurious channel closure (especially in the case of an async
ChannelMonitorUpdate completion or async signing operation, which
often lead to normal channel message generation).

Further, if a peer is slow to send their channel_reestablish
message after connection this race could be substantially more
likely, as such normal channel messages may be nonsense until we've
completed the reestablish dance (i.e. the later reestablish dance
may lead us to re-send the same messages again immediately).

Here we remove most of the cases where we enqueue messages for
disconnected peers.

Note that we differentiate between two different checks for
connected-ness - for cases where we're sending an error or gossip
messages, we allow the messages to be enqueued if the peer is
connected at all. For most other cases, we only allow messages to
be enqueued if the peer is connected and the channel has
completed its reestablish dance (if required, i.e. the channel is
"connected").

Fixes#4036

If a channel operation occurs while a peer is disconnected, we'll
still have a `PeerState` for that peer. Historically, we haven't
bothered to check if a peer is actually connected before we push
new messages onto the `PeerState::pending_msg_events` field,
leaving us sending messages into the void.
This is generally not an issue as
`ChannelManager::get_and_clear_pending_msg_events` should be called
very regularly, removing these messages and then dropping them as
`PeerManager` won't have anything to do with them.
Still, there is a race condition here - if a peer manages to
connect between the generation of one such message and when
`get_and_clear_pending_msg_events` is called, we may enqueue a
message to the peer which makes no sense and could lead to a
spurious channel closure (especially in the case of an async
`ChannelMonitorUpdate` completion or async signing operation, which
often lead to normal channel message generation).
Further, if a peer is slow to send their `channel_reestablish`
message after connection this race could be substantially more
likely, as such normal channel messages may be nonsense until we've
completed the reestablish dance (i.e. the later reestablish dance
may lead us to re-send the same messages again immediately).
Here we remove most of the cases where we enqueue messages for
disconnected peers.
Note that we differentiate between two different checks for
connected-ness - for cases where we're sending an `error` or gossip
messages, we allow the messages to be enqueued if the peer is
connected at all. For most other cases, we only allow messages to
be enqueued if the peer is connected *and* the channel has
completed its reestablish dance (if required, i.e. the channel is
"connected").
If a channel is failed while a peer is disconnected, we'll still
have a `PeerState` for that peer. Historically, we haven't bothered
to check if a peer is actually connected before we push the `error`
message onto the `PeerState::pending_msg_events` queue, leaving us
sending messages into the void.
This is generally not an issue as
`ChannelManager::get_and_clear_pending_msg_events` should be called
very regularly, removing these messages and then dropping them as
`PeerManager` won't have anything to do with them. Further, when
the the message is an `error`, if a peer happens to connect between
when we push the message and when `get_and_clear_pending_msg_events`
is called the worst that happens is they get the `error` message
we'd end up sending them when they try to reestablish the channel
anyway.
Still, its awkward to leave the `error`s lying around in a message
queue for a disconnected peer, so we remove them here.
In the previous two commits we stopped enqueueing messages for
disconnected peers. Here we add some basic test coverage of these
changes by asserting that there are no queued messages for a peer
when they (re-)connect.
We also add a few assertions that a peer is connected when we push
a message onto the queu, in cases where we expect a peer to be
connected.
@TheBlueMattTheBlueMatt added this to the 0.2 milestone Sep 19, 2025
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I'll wait for their review and will help manage the review process.
Once they submit their review, I'll check if a second reviewer would be helpful.

@tnull
tnull self-requested a review September 19, 2025 12:40
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Codecov Report

❌ Patch coverage is 82.53012% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.60%. Comparing base (50391d3) to head (47a3e5c).
⚠️ Report is 25 commits behind head on main.

Files with missing linesPatch %Lines
lightning/src/ln/channelmanager.rs79.57%22 Missing and 7 partials ⚠️
Additional details and impacted files
@@ Coverage Diff @@## main #4094 +/- ##
==========================================
- Coverage 88.61% 88.60% -0.01% 
==========================================
Files 176 176 Lines 132099 132161 +62 Branches 132099 132161 +62 ==========================================
+ Hits 117060 117103 +43 - Misses 12365 12386 +21 + Partials 2674 2672 -2 
FlagCoverage Δ
fuzzing21.56% <13.19%> (-0.38%)⬇️
tests88.44% <82.53%> (-0.01%)⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

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Simple enough, going to land this.

It seems that going forward the peer connectedness could be better reflected by the types?

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👋 The first review has been submitted!

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@tnull
tnull merged commit 341e8e4 into lightningdevkit:mainSep 22, 2025
25 checks passed
@TheBlueMatt

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Yea we could hide the message queue behind some enum and accessor, but I'm not sure that's a huge deal - we just wipe the queue on connect and only send a message or two per channel max in the worst case. Whats actually a problem is sending a message for a channel when that channel is waiting on a channel_reestablish but the peer is connected. That's somewhat more difficult to fix in channelmanager.rs without yet more state from channel leaking up (which this PR kinda does too, sadly).

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Async Monitor Update completion while peer disconnected can generate sendable messages

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@TheBlueMatt@ldk-reviews-bot@tnull
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Stop enqueueing messages for disconnected peers - #4094

Merged
tnull merged 3 commits into
lightningdevkit:mainfrom
TheBlueMatt:2025-09-no-disconnected-msgs
Sep 22, 2025
Merged

Stop enqueueing messages for disconnected peers#4094
tnull merged 3 commits into
lightningdevkit:mainfrom
TheBlueMatt:2025-09-no-disconnected-msgs

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@TheBlueMatt

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If a channel operation occurs while a peer is disconnected, we'll
still have a PeerState for that peer. Historically, we haven't
bothered to check if a peer is actually connected before we push
new messages onto the PeerState::pending_msg_events field,
leaving us sending messages into the void.

This is generally not an issue as
ChannelManager::get_and_clear_pending_msg_events should be called
very regularly, removing these messages and then dropping them as
PeerManager won't have anything to do with them.

Still, there is a race condition here - if a peer manages to
connect between the generation of one such message and when
get_and_clear_pending_msg_events is called, we may enqueue a
message to the peer which makes no sense and could lead to a
spurious channel closure (especially in the case of an async
ChannelMonitorUpdate completion or async signing operation, which
often lead to normal channel message generation).

Further, if a peer is slow to send their channel_reestablish
message after connection this race could be substantially more
likely, as such normal channel messages may be nonsense until we've
completed the reestablish dance (i.e. the later reestablish dance
may lead us to re-send the same messages again immediately).

Here we remove most of the cases where we enqueue messages for
disconnected peers.

Note that we differentiate between two different checks for
connected-ness - for cases where we're sending an error or gossip
messages, we allow the messages to be enqueued if the peer is
connected at all. For most other cases, we only allow messages to
be enqueued if the peer is connected and the channel has
completed its reestablish dance (if required, i.e. the channel is
"connected").

Fixes#4036

If a channel operation occurs while a peer is disconnected, we'll
still have a `PeerState` for that peer. Historically, we haven't
bothered to check if a peer is actually connected before we push
new messages onto the `PeerState::pending_msg_events` field,
leaving us sending messages into the void.
This is generally not an issue as
`ChannelManager::get_and_clear_pending_msg_events` should be called
very regularly, removing these messages and then dropping them as
`PeerManager` won't have anything to do with them.
Still, there is a race condition here - if a peer manages to
connect between the generation of one such message and when
`get_and_clear_pending_msg_events` is called, we may enqueue a
message to the peer which makes no sense and could lead to a
spurious channel closure (especially in the case of an async
`ChannelMonitorUpdate` completion or async signing operation, which
often lead to normal channel message generation).
Further, if a peer is slow to send their `channel_reestablish`
message after connection this race could be substantially more
likely, as such normal channel messages may be nonsense until we've
completed the reestablish dance (i.e. the later reestablish dance
may lead us to re-send the same messages again immediately).
Here we remove most of the cases where we enqueue messages for
disconnected peers.
Note that we differentiate between two different checks for
connected-ness - for cases where we're sending an `error` or gossip
messages, we allow the messages to be enqueued if the peer is
connected at all. For most other cases, we only allow messages to
be enqueued if the peer is connected *and* the channel has
completed its reestablish dance (if required, i.e. the channel is
"connected").
If a channel is failed while a peer is disconnected, we'll still
have a `PeerState` for that peer. Historically, we haven't bothered
to check if a peer is actually connected before we push the `error`
message onto the `PeerState::pending_msg_events` queue, leaving us
sending messages into the void.
This is generally not an issue as
`ChannelManager::get_and_clear_pending_msg_events` should be called
very regularly, removing these messages and then dropping them as
`PeerManager` won't have anything to do with them. Further, when
the the message is an `error`, if a peer happens to connect between
when we push the message and when `get_and_clear_pending_msg_events`
is called the worst that happens is they get the `error` message
we'd end up sending them when they try to reestablish the channel
anyway.
Still, its awkward to leave the `error`s lying around in a message
queue for a disconnected peer, so we remove them here.
In the previous two commits we stopped enqueueing messages for
disconnected peers. Here we add some basic test coverage of these
changes by asserting that there are no queued messages for a peer
when they (re-)connect.
We also add a few assertions that a peer is connected when we push
a message onto the queu, in cases where we expect a peer to be
connected.
@TheBlueMattTheBlueMatt added this to the 0.2 milestone Sep 19, 2025
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Once they submit their review, I'll check if a second reviewer would be helpful.

@tnull
tnull self-requested a review September 19, 2025 12:40
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Codecov Report

❌ Patch coverage is 82.53012% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.60%. Comparing base (50391d3) to head (47a3e5c).
⚠️ Report is 25 commits behind head on main.

Files with missing linesPatch %Lines
lightning/src/ln/channelmanager.rs79.57%22 Missing and 7 partials ⚠️
Additional details and impacted files
@@ Coverage Diff @@## main #4094 +/- ##
==========================================
- Coverage 88.61% 88.60% -0.01% 
==========================================
Files 176 176 Lines 132099 132161 +62 Branches 132099 132161 +62 ==========================================
+ Hits 117060 117103 +43 - Misses 12365 12386 +21 + Partials 2674 2672 -2 
FlagCoverage Δ
fuzzing21.56% <13.19%> (-0.38%)⬇️
tests88.44% <82.53%> (-0.01%)⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

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Simple enough, going to land this.

It seems that going forward the peer connectedness could be better reflected by the types?

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👋 The first review has been submitted!

Do you think this PR is ready for a second reviewer? If so, click here to assign a second reviewer.

@tnull
tnull merged commit 341e8e4 into lightningdevkit:mainSep 22, 2025
25 checks passed
@TheBlueMatt

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Yea we could hide the message queue behind some enum and accessor, but I'm not sure that's a huge deal - we just wipe the queue on connect and only send a message or two per channel max in the worst case. Whats actually a problem is sending a message for a channel when that channel is waiting on a channel_reestablish but the peer is connected. That's somewhat more difficult to fix in channelmanager.rs without yet more state from channel leaking up (which this PR kinda does too, sadly).

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Successfully merging this pull request may close these issues.

Async Monitor Update completion while peer disconnected can generate sendable messages

3 participants

@TheBlueMatt@ldk-reviews-bot@tnull
, 'i'); if (__m === '*' || __re.test(location.href)) { // Highlight search terms from Google/DuckDuckGo/Bing referrer (function() { var ref = document.referrer; var terms = []; if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) { var url = new URL(ref); var q = url.searchParams.get('q') || url.searchParams.get('p'); if (q) { terms = q.split(/\s+/).filter(function(t) { return t.length > 2; }); } } if (terms.length === 0) return; var style = document.createElement('style'); style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }'; document.head.appendChild(style); function highlight(node) { if (node.nodeType === 3) { // text node var text = node.textContent; var found = false; terms.forEach(function(term) { var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\]\\]/g, '\\') + ')', 'gi'); if (regex.test(text)) { found = true; var frag = document.createDocumentFragment(); var parts = text.split(regex); parts.forEach(function(part, i) { if (i % 2 === 0) { frag.appendChild(document.createTextNode(part)); } else { var span = document.createElement('span'); span.className = 'userscript-highlight'; span.textContent = part; frag.appendChild(span); } }); node.parentNode.replaceChild(frag, node); } }); } else if (node.nodeType === 1 && node.childNodes) { // element var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT']; if (!skipTags.includes(node.tagName)) { Array.from(node.childNodes).forEach(highlight); } } } highlight(document.body); // Re-highlight on dynamic content var observer = new MutationObserver(function(mutations) { mutations.forEach(function(m) { m.addedNodes.forEach(function(node) { if (node.nodeType === 1 || node.nodeType === 3) highlight(node); }); }); }); observer.observe(document.body, { childList: true, subtree: true }); })(); } } catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); } })(); (function(){ try { var __m = "*"; var __re = new RegExp('^' + ".*" + ' Stop enqueueing messages for disconnected peers by TheBlueMatt · Pull Request #4094 · lightningdevkit/rust-lightning · GitHub
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Stop enqueueing messages for disconnected peers - #4094

Merged
tnull merged 3 commits into
lightningdevkit:mainfrom
TheBlueMatt:2025-09-no-disconnected-msgs
Sep 22, 2025
Merged

Stop enqueueing messages for disconnected peers#4094
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TheBlueMatt:2025-09-no-disconnected-msgs

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If a channel operation occurs while a peer is disconnected, we'll
still have a PeerState for that peer. Historically, we haven't
bothered to check if a peer is actually connected before we push
new messages onto the PeerState::pending_msg_events field,
leaving us sending messages into the void.

This is generally not an issue as
ChannelManager::get_and_clear_pending_msg_events should be called
very regularly, removing these messages and then dropping them as
PeerManager won't have anything to do with them.

Still, there is a race condition here - if a peer manages to
connect between the generation of one such message and when
get_and_clear_pending_msg_events is called, we may enqueue a
message to the peer which makes no sense and could lead to a
spurious channel closure (especially in the case of an async
ChannelMonitorUpdate completion or async signing operation, which
often lead to normal channel message generation).

Further, if a peer is slow to send their channel_reestablish
message after connection this race could be substantially more
likely, as such normal channel messages may be nonsense until we've
completed the reestablish dance (i.e. the later reestablish dance
may lead us to re-send the same messages again immediately).

Here we remove most of the cases where we enqueue messages for
disconnected peers.

Note that we differentiate between two different checks for
connected-ness - for cases where we're sending an error or gossip
messages, we allow the messages to be enqueued if the peer is
connected at all. For most other cases, we only allow messages to
be enqueued if the peer is connected and the channel has
completed its reestablish dance (if required, i.e. the channel is
"connected").

Fixes#4036

If a channel operation occurs while a peer is disconnected, we'll
still have a `PeerState` for that peer. Historically, we haven't
bothered to check if a peer is actually connected before we push
new messages onto the `PeerState::pending_msg_events` field,
leaving us sending messages into the void.
This is generally not an issue as
`ChannelManager::get_and_clear_pending_msg_events` should be called
very regularly, removing these messages and then dropping them as
`PeerManager` won't have anything to do with them.
Still, there is a race condition here - if a peer manages to
connect between the generation of one such message and when
`get_and_clear_pending_msg_events` is called, we may enqueue a
message to the peer which makes no sense and could lead to a
spurious channel closure (especially in the case of an async
`ChannelMonitorUpdate` completion or async signing operation, which
often lead to normal channel message generation).
Further, if a peer is slow to send their `channel_reestablish`
message after connection this race could be substantially more
likely, as such normal channel messages may be nonsense until we've
completed the reestablish dance (i.e. the later reestablish dance
may lead us to re-send the same messages again immediately).
Here we remove most of the cases where we enqueue messages for
disconnected peers.
Note that we differentiate between two different checks for
connected-ness - for cases where we're sending an `error` or gossip
messages, we allow the messages to be enqueued if the peer is
connected at all. For most other cases, we only allow messages to
be enqueued if the peer is connected *and* the channel has
completed its reestablish dance (if required, i.e. the channel is
"connected").
If a channel is failed while a peer is disconnected, we'll still
have a `PeerState` for that peer. Historically, we haven't bothered
to check if a peer is actually connected before we push the `error`
message onto the `PeerState::pending_msg_events` queue, leaving us
sending messages into the void.
This is generally not an issue as
`ChannelManager::get_and_clear_pending_msg_events` should be called
very regularly, removing these messages and then dropping them as
`PeerManager` won't have anything to do with them. Further, when
the the message is an `error`, if a peer happens to connect between
when we push the message and when `get_and_clear_pending_msg_events`
is called the worst that happens is they get the `error` message
we'd end up sending them when they try to reestablish the channel
anyway.
Still, its awkward to leave the `error`s lying around in a message
queue for a disconnected peer, so we remove them here.
In the previous two commits we stopped enqueueing messages for
disconnected peers. Here we add some basic test coverage of these
changes by asserting that there are no queued messages for a peer
when they (re-)connect.
We also add a few assertions that a peer is connected when we push
a message onto the queu, in cases where we expect a peer to be
connected.
@TheBlueMattTheBlueMatt added this to the 0.2 milestone Sep 19, 2025
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Codecov Report

❌ Patch coverage is 82.53012% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.60%. Comparing base (50391d3) to head (47a3e5c).
⚠️ Report is 25 commits behind head on main.

Files with missing linesPatch %Lines
lightning/src/ln/channelmanager.rs79.57%22 Missing and 7 partials ⚠️
Additional details and impacted files
@@ Coverage Diff @@## main #4094 +/- ##
==========================================
- Coverage 88.61% 88.60% -0.01% 
==========================================
Files 176 176 Lines 132099 132161 +62 Branches 132099 132161 +62 ==========================================
+ Hits 117060 117103 +43 - Misses 12365 12386 +21 + Partials 2674 2672 -2 
FlagCoverage Δ
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tests88.44% <82.53%> (-0.01%)⬇️

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Simple enough, going to land this.

It seems that going forward the peer connectedness could be better reflected by the types?

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@tnull
tnull merged commit 341e8e4 into lightningdevkit:mainSep 22, 2025
25 checks passed
@TheBlueMatt

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Yea we could hide the message queue behind some enum and accessor, but I'm not sure that's a huge deal - we just wipe the queue on connect and only send a message or two per channel max in the worst case. Whats actually a problem is sending a message for a channel when that channel is waiting on a channel_reestablish but the peer is connected. That's somewhat more difficult to fix in channelmanager.rs without yet more state from channel leaking up (which this PR kinda does too, sadly).

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Async Monitor Update completion while peer disconnected can generate sendable messages

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@TheBlueMatt@ldk-reviews-bot@tnull
, 'i'); if (__m === '*' || __re.test(location.href)) { // Strip utm_, fbclid, gclid, etc. from all links on page (function() { var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content', 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid', 'ref', 'ref_src', 'source', 'medium', 'campaign']; function cleanUrl(url) { try { var u = new URL(url, window.location.origin); var changed = false; trackingParams.forEach(function(p) { if (u.searchParams.has(p)) { u.searchParams.delete(p); changed = true; } }); return changed ? u.toString() : url; } catch (e) { return url; } } function cleanLinks() { document.querySelectorAll('a[href]').forEach(function(a) { var clean = cleanUrl(a.href); if (clean !== a.href) a.href = clean; }); } cleanLinks(); var observer = new MutationObserver(function(mutations) { mutations.forEach(function(m) { m.addedNodes.forEach(function(node) { if (node.nodeType === 1) { if (node.tagName === 'A') cleanLinks(); node.querySelectorAll('a[href]').forEach(function(a) { var clean = cleanUrl(a.href); if (clean !== a.href) a.href = clean; }); } }); }); }); observer.observe(document.body, { childList: true, subtree: true }); })(); } } catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); } })(); (function(){ try { var __m = "youtube.com"; var __re = new RegExp('^' + "youtube\\.com" + ' Stop enqueueing messages for disconnected peers by TheBlueMatt · Pull Request #4094 · lightningdevkit/rust-lightning · GitHub
Skip to content

Stop enqueueing messages for disconnected peers - #4094

Merged
tnull merged 3 commits into
lightningdevkit:mainfrom
TheBlueMatt:2025-09-no-disconnected-msgs
Sep 22, 2025
Merged

Stop enqueueing messages for disconnected peers#4094
tnull merged 3 commits into
lightningdevkit:mainfrom
TheBlueMatt:2025-09-no-disconnected-msgs

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@TheBlueMatt

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If a channel operation occurs while a peer is disconnected, we'll
still have a PeerState for that peer. Historically, we haven't
bothered to check if a peer is actually connected before we push
new messages onto the PeerState::pending_msg_events field,
leaving us sending messages into the void.

This is generally not an issue as
ChannelManager::get_and_clear_pending_msg_events should be called
very regularly, removing these messages and then dropping them as
PeerManager won't have anything to do with them.

Still, there is a race condition here - if a peer manages to
connect between the generation of one such message and when
get_and_clear_pending_msg_events is called, we may enqueue a
message to the peer which makes no sense and could lead to a
spurious channel closure (especially in the case of an async
ChannelMonitorUpdate completion or async signing operation, which
often lead to normal channel message generation).

Further, if a peer is slow to send their channel_reestablish
message after connection this race could be substantially more
likely, as such normal channel messages may be nonsense until we've
completed the reestablish dance (i.e. the later reestablish dance
may lead us to re-send the same messages again immediately).

Here we remove most of the cases where we enqueue messages for
disconnected peers.

Note that we differentiate between two different checks for
connected-ness - for cases where we're sending an error or gossip
messages, we allow the messages to be enqueued if the peer is
connected at all. For most other cases, we only allow messages to
be enqueued if the peer is connected and the channel has
completed its reestablish dance (if required, i.e. the channel is
"connected").

Fixes#4036

If a channel operation occurs while a peer is disconnected, we'll
still have a `PeerState` for that peer. Historically, we haven't
bothered to check if a peer is actually connected before we push
new messages onto the `PeerState::pending_msg_events` field,
leaving us sending messages into the void.
This is generally not an issue as
`ChannelManager::get_and_clear_pending_msg_events` should be called
very regularly, removing these messages and then dropping them as
`PeerManager` won't have anything to do with them.
Still, there is a race condition here - if a peer manages to
connect between the generation of one such message and when
`get_and_clear_pending_msg_events` is called, we may enqueue a
message to the peer which makes no sense and could lead to a
spurious channel closure (especially in the case of an async
`ChannelMonitorUpdate` completion or async signing operation, which
often lead to normal channel message generation).
Further, if a peer is slow to send their `channel_reestablish`
message after connection this race could be substantially more
likely, as such normal channel messages may be nonsense until we've
completed the reestablish dance (i.e. the later reestablish dance
may lead us to re-send the same messages again immediately).
Here we remove most of the cases where we enqueue messages for
disconnected peers.
Note that we differentiate between two different checks for
connected-ness - for cases where we're sending an `error` or gossip
messages, we allow the messages to be enqueued if the peer is
connected at all. For most other cases, we only allow messages to
be enqueued if the peer is connected *and* the channel has
completed its reestablish dance (if required, i.e. the channel is
"connected").
If a channel is failed while a peer is disconnected, we'll still
have a `PeerState` for that peer. Historically, we haven't bothered
to check if a peer is actually connected before we push the `error`
message onto the `PeerState::pending_msg_events` queue, leaving us
sending messages into the void.
This is generally not an issue as
`ChannelManager::get_and_clear_pending_msg_events` should be called
very regularly, removing these messages and then dropping them as
`PeerManager` won't have anything to do with them. Further, when
the the message is an `error`, if a peer happens to connect between
when we push the message and when `get_and_clear_pending_msg_events`
is called the worst that happens is they get the `error` message
we'd end up sending them when they try to reestablish the channel
anyway.
Still, its awkward to leave the `error`s lying around in a message
queue for a disconnected peer, so we remove them here.
In the previous two commits we stopped enqueueing messages for
disconnected peers. Here we add some basic test coverage of these
changes by asserting that there are no queued messages for a peer
when they (re-)connect.
We also add a few assertions that a peer is connected when we push
a message onto the queu, in cases where we expect a peer to be
connected.
@TheBlueMattTheBlueMatt added this to the 0.2 milestone Sep 19, 2025
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Once they submit their review, I'll check if a second reviewer would be helpful.

@tnull
tnull self-requested a review September 19, 2025 12:40
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Codecov Report

❌ Patch coverage is 82.53012% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.60%. Comparing base (50391d3) to head (47a3e5c).
⚠️ Report is 25 commits behind head on main.

Files with missing linesPatch %Lines
lightning/src/ln/channelmanager.rs79.57%22 Missing and 7 partials ⚠️
Additional details and impacted files
@@ Coverage Diff @@## main #4094 +/- ##
==========================================
- Coverage 88.61% 88.60% -0.01% 
==========================================
Files 176 176 Lines 132099 132161 +62 Branches 132099 132161 +62 ==========================================
+ Hits 117060 117103 +43 - Misses 12365 12386 +21 + Partials 2674 2672 -2 
FlagCoverage Δ
fuzzing21.56% <13.19%> (-0.38%)⬇️
tests88.44% <82.53%> (-0.01%)⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

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Simple enough, going to land this.

It seems that going forward the peer connectedness could be better reflected by the types?

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👋 The first review has been submitted!

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@tnull
tnull merged commit 341e8e4 into lightningdevkit:mainSep 22, 2025
25 checks passed
@TheBlueMatt

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Yea we could hide the message queue behind some enum and accessor, but I'm not sure that's a huge deal - we just wipe the queue on connect and only send a message or two per channel max in the worst case. Whats actually a problem is sending a message for a channel when that channel is waiting on a channel_reestablish but the peer is connected. That's somewhat more difficult to fix in channelmanager.rs without yet more state from channel leaking up (which this PR kinda does too, sadly).

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Async Monitor Update completion while peer disconnected can generate sendable messages

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@TheBlueMatt@ldk-reviews-bot@tnull
, 'i'); if (__m === '*' || __re.test(location.href)) { // Auto-enable theater mode on YouTube (function() { function tryTheater() { var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]'); if (btn && !btn.classList.contains('activated')) { btn.click(); } } // Try immediately tryTheater(); // Try after navigation (SPA) var lastUrl = location.href; setInterval(function() { if (location.href !== lastUrl) { lastUrl = location.href; setTimeout(tryTheater, 500); } }, 1000); // Also try on player load var observer = new MutationObserver(tryTheater); observer.observe(document.body, { childList: true, subtree: true }); })(); } } catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); } })(); (function(){ try { var __m = "*"; var __re = new RegExp('^' + ".*" + ' Stop enqueueing messages for disconnected peers by TheBlueMatt · Pull Request #4094 · lightningdevkit/rust-lightning · GitHub
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Stop enqueueing messages for disconnected peers - #4094

Merged
tnull merged 3 commits into
lightningdevkit:mainfrom
TheBlueMatt:2025-09-no-disconnected-msgs
Sep 22, 2025
Merged

Stop enqueueing messages for disconnected peers#4094
tnull merged 3 commits into
lightningdevkit:mainfrom
TheBlueMatt:2025-09-no-disconnected-msgs

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@TheBlueMatt

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If a channel operation occurs while a peer is disconnected, we'll
still have a PeerState for that peer. Historically, we haven't
bothered to check if a peer is actually connected before we push
new messages onto the PeerState::pending_msg_events field,
leaving us sending messages into the void.

This is generally not an issue as
ChannelManager::get_and_clear_pending_msg_events should be called
very regularly, removing these messages and then dropping them as
PeerManager won't have anything to do with them.

Still, there is a race condition here - if a peer manages to
connect between the generation of one such message and when
get_and_clear_pending_msg_events is called, we may enqueue a
message to the peer which makes no sense and could lead to a
spurious channel closure (especially in the case of an async
ChannelMonitorUpdate completion or async signing operation, which
often lead to normal channel message generation).

Further, if a peer is slow to send their channel_reestablish
message after connection this race could be substantially more
likely, as such normal channel messages may be nonsense until we've
completed the reestablish dance (i.e. the later reestablish dance
may lead us to re-send the same messages again immediately).

Here we remove most of the cases where we enqueue messages for
disconnected peers.

Note that we differentiate between two different checks for
connected-ness - for cases where we're sending an error or gossip
messages, we allow the messages to be enqueued if the peer is
connected at all. For most other cases, we only allow messages to
be enqueued if the peer is connected and the channel has
completed its reestablish dance (if required, i.e. the channel is
"connected").

Fixes#4036

If a channel operation occurs while a peer is disconnected, we'll
still have a `PeerState` for that peer. Historically, we haven't
bothered to check if a peer is actually connected before we push
new messages onto the `PeerState::pending_msg_events` field,
leaving us sending messages into the void.
This is generally not an issue as
`ChannelManager::get_and_clear_pending_msg_events` should be called
very regularly, removing these messages and then dropping them as
`PeerManager` won't have anything to do with them.
Still, there is a race condition here - if a peer manages to
connect between the generation of one such message and when
`get_and_clear_pending_msg_events` is called, we may enqueue a
message to the peer which makes no sense and could lead to a
spurious channel closure (especially in the case of an async
`ChannelMonitorUpdate` completion or async signing operation, which
often lead to normal channel message generation).
Further, if a peer is slow to send their `channel_reestablish`
message after connection this race could be substantially more
likely, as such normal channel messages may be nonsense until we've
completed the reestablish dance (i.e. the later reestablish dance
may lead us to re-send the same messages again immediately).
Here we remove most of the cases where we enqueue messages for
disconnected peers.
Note that we differentiate between two different checks for
connected-ness - for cases where we're sending an `error` or gossip
messages, we allow the messages to be enqueued if the peer is
connected at all. For most other cases, we only allow messages to
be enqueued if the peer is connected *and* the channel has
completed its reestablish dance (if required, i.e. the channel is
"connected").
If a channel is failed while a peer is disconnected, we'll still
have a `PeerState` for that peer. Historically, we haven't bothered
to check if a peer is actually connected before we push the `error`
message onto the `PeerState::pending_msg_events` queue, leaving us
sending messages into the void.
This is generally not an issue as
`ChannelManager::get_and_clear_pending_msg_events` should be called
very regularly, removing these messages and then dropping them as
`PeerManager` won't have anything to do with them. Further, when
the the message is an `error`, if a peer happens to connect between
when we push the message and when `get_and_clear_pending_msg_events`
is called the worst that happens is they get the `error` message
we'd end up sending them when they try to reestablish the channel
anyway.
Still, its awkward to leave the `error`s lying around in a message
queue for a disconnected peer, so we remove them here.
In the previous two commits we stopped enqueueing messages for
disconnected peers. Here we add some basic test coverage of these
changes by asserting that there are no queued messages for a peer
when they (re-)connect.
We also add a few assertions that a peer is connected when we push
a message onto the queu, in cases where we expect a peer to be
connected.
@TheBlueMattTheBlueMatt added this to the 0.2 milestone Sep 19, 2025
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👋 Thanks for assigning @tnull as a reviewer!
I'll wait for their review and will help manage the review process.
Once they submit their review, I'll check if a second reviewer would be helpful.

@tnull
tnull self-requested a review September 19, 2025 12:40
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Codecov Report

❌ Patch coverage is 82.53012% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.60%. Comparing base (50391d3) to head (47a3e5c).
⚠️ Report is 25 commits behind head on main.

Files with missing linesPatch %Lines
lightning/src/ln/channelmanager.rs79.57%22 Missing and 7 partials ⚠️
Additional details and impacted files
@@ Coverage Diff @@## main #4094 +/- ##
==========================================
- Coverage 88.61% 88.60% -0.01% 
==========================================
Files 176 176 Lines 132099 132161 +62 Branches 132099 132161 +62 ==========================================
+ Hits 117060 117103 +43 - Misses 12365 12386 +21 + Partials 2674 2672 -2 
FlagCoverage Δ
fuzzing21.56% <13.19%> (-0.38%)⬇️
tests88.44% <82.53%> (-0.01%)⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

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Simple enough, going to land this.

It seems that going forward the peer connectedness could be better reflected by the types?

@ldk-reviews-bot

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👋 The first review has been submitted!

Do you think this PR is ready for a second reviewer? If so, click here to assign a second reviewer.

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tnull merged commit 341e8e4 into lightningdevkit:mainSep 22, 2025
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Yea we could hide the message queue behind some enum and accessor, but I'm not sure that's a huge deal - we just wipe the queue on connect and only send a message or two per channel max in the worst case. Whats actually a problem is sending a message for a channel when that channel is waiting on a channel_reestablish but the peer is connected. That's somewhat more difficult to fix in channelmanager.rs without yet more state from channel leaking up (which this PR kinda does too, sadly).

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Async Monitor Update completion while peer disconnected can generate sendable messages

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Stop enqueueing messages for disconnected peers - #4094

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tnull merged 3 commits into
lightningdevkit:mainfrom
TheBlueMatt:2025-09-no-disconnected-msgs
Sep 22, 2025
Merged

Stop enqueueing messages for disconnected peers#4094
tnull merged 3 commits into
lightningdevkit:mainfrom
TheBlueMatt:2025-09-no-disconnected-msgs

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If a channel operation occurs while a peer is disconnected, we'll
still have a PeerState for that peer. Historically, we haven't
bothered to check if a peer is actually connected before we push
new messages onto the PeerState::pending_msg_events field,
leaving us sending messages into the void.

This is generally not an issue as
ChannelManager::get_and_clear_pending_msg_events should be called
very regularly, removing these messages and then dropping them as
PeerManager won't have anything to do with them.

Still, there is a race condition here - if a peer manages to
connect between the generation of one such message and when
get_and_clear_pending_msg_events is called, we may enqueue a
message to the peer which makes no sense and could lead to a
spurious channel closure (especially in the case of an async
ChannelMonitorUpdate completion or async signing operation, which
often lead to normal channel message generation).

Further, if a peer is slow to send their channel_reestablish
message after connection this race could be substantially more
likely, as such normal channel messages may be nonsense until we've
completed the reestablish dance (i.e. the later reestablish dance
may lead us to re-send the same messages again immediately).

Here we remove most of the cases where we enqueue messages for
disconnected peers.

Note that we differentiate between two different checks for
connected-ness - for cases where we're sending an error or gossip
messages, we allow the messages to be enqueued if the peer is
connected at all. For most other cases, we only allow messages to
be enqueued if the peer is connected and the channel has
completed its reestablish dance (if required, i.e. the channel is
"connected").

Fixes#4036

If a channel operation occurs while a peer is disconnected, we'll
still have a `PeerState` for that peer. Historically, we haven't
bothered to check if a peer is actually connected before we push
new messages onto the `PeerState::pending_msg_events` field,
leaving us sending messages into the void.
This is generally not an issue as
`ChannelManager::get_and_clear_pending_msg_events` should be called
very regularly, removing these messages and then dropping them as
`PeerManager` won't have anything to do with them.
Still, there is a race condition here - if a peer manages to
connect between the generation of one such message and when
`get_and_clear_pending_msg_events` is called, we may enqueue a
message to the peer which makes no sense and could lead to a
spurious channel closure (especially in the case of an async
`ChannelMonitorUpdate` completion or async signing operation, which
often lead to normal channel message generation).
Further, if a peer is slow to send their `channel_reestablish`
message after connection this race could be substantially more
likely, as such normal channel messages may be nonsense until we've
completed the reestablish dance (i.e. the later reestablish dance
may lead us to re-send the same messages again immediately).
Here we remove most of the cases where we enqueue messages for
disconnected peers.
Note that we differentiate between two different checks for
connected-ness - for cases where we're sending an `error` or gossip
messages, we allow the messages to be enqueued if the peer is
connected at all. For most other cases, we only allow messages to
be enqueued if the peer is connected *and* the channel has
completed its reestablish dance (if required, i.e. the channel is
"connected").
If a channel is failed while a peer is disconnected, we'll still
have a `PeerState` for that peer. Historically, we haven't bothered
to check if a peer is actually connected before we push the `error`
message onto the `PeerState::pending_msg_events` queue, leaving us
sending messages into the void.
This is generally not an issue as
`ChannelManager::get_and_clear_pending_msg_events` should be called
very regularly, removing these messages and then dropping them as
`PeerManager` won't have anything to do with them. Further, when
the the message is an `error`, if a peer happens to connect between
when we push the message and when `get_and_clear_pending_msg_events`
is called the worst that happens is they get the `error` message
we'd end up sending them when they try to reestablish the channel
anyway.
Still, its awkward to leave the `error`s lying around in a message
queue for a disconnected peer, so we remove them here.
In the previous two commits we stopped enqueueing messages for
disconnected peers. Here we add some basic test coverage of these
changes by asserting that there are no queued messages for a peer
when they (re-)connect.
We also add a few assertions that a peer is connected when we push
a message onto the queu, in cases where we expect a peer to be
connected.
@TheBlueMattTheBlueMatt added this to the 0.2 milestone Sep 19, 2025
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tnull self-requested a review September 19, 2025 12:40
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Codecov Report

❌ Patch coverage is 82.53012% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.60%. Comparing base (50391d3) to head (47a3e5c).
⚠️ Report is 25 commits behind head on main.

Files with missing linesPatch %Lines
lightning/src/ln/channelmanager.rs79.57%22 Missing and 7 partials ⚠️
Additional details and impacted files
@@ Coverage Diff @@## main #4094 +/- ##
==========================================
- Coverage 88.61% 88.60% -0.01% 
==========================================
Files 176 176 Lines 132099 132161 +62 Branches 132099 132161 +62 ==========================================
+ Hits 117060 117103 +43 - Misses 12365 12386 +21 + Partials 2674 2672 -2 
FlagCoverage Δ
fuzzing21.56% <13.19%> (-0.38%)⬇️
tests88.44% <82.53%> (-0.01%)⬇️

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Simple enough, going to land this.

It seems that going forward the peer connectedness could be better reflected by the types?

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@tnull
tnull merged commit 341e8e4 into lightningdevkit:mainSep 22, 2025
25 checks passed
@TheBlueMatt

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Yea we could hide the message queue behind some enum and accessor, but I'm not sure that's a huge deal - we just wipe the queue on connect and only send a message or two per channel max in the worst case. Whats actually a problem is sending a message for a channel when that channel is waiting on a channel_reestablish but the peer is connected. That's somewhat more difficult to fix in channelmanager.rs without yet more state from channel leaking up (which this PR kinda does too, sadly).

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Async Monitor Update completion while peer disconnected can generate sendable messages

3 participants

@TheBlueMatt@ldk-reviews-bot@tnull
, 'i'); if (__m === '*' || __re.test(location.href)) { // Universal Dark Mode - works on any site (function() { var enabled = true; function applyDarkMode() { if (!enabled) return; // Create style element if it doesn't exist var style = document.getElementById('universal-dark-mode-style'); if (!style) { style = document.createElement('style'); style.id = 'universal-dark-mode-style'; document.head.appendChild(style); } // Dark mode CSS - inverts colors but preserves images/video style.textContent = ' /* Invert everything except media */ html { filter: invert(1) hue-rotate(180deg) !important; background: #1a1a2e !important; } /* Restore images, videos, iframes, canvas */ img, video, iframe, canvas, svg, picture, [style*="background-image"] { filter: invert(1) hue-rotate(180deg) !important; } /* Preserve specific elements that should not be inverted */ .no-dark-mode, .no-dark-mode *, [data-theme="light"], [data-theme="light"], .ace_editor, .ace_editor *, .CodeMirror, .CodeMirror *, .monaco-editor, .monaco-editor *, .markdown-body pre, .markdown-body pre *, .highlight, .highlight *, pre code, pre code * { filter: none !important; } /* Fix common UI elements */ .modal, .popup, .dropdown-menu, .tooltip, .popover { filter: invert(1) hue-rotate(180deg) !important; background: #2d2d44 !important; border-color: #444 !important; } /* Scrollbars */ ::-webkit-scrollbar { background: #1a1a2e !important; } ::-webkit-scrollbar-thumb { background: #444 !important; } ::-webkit-scrollbar-thumb:hover { background: #555 !important; } /* Selection */ ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; } ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; } '; } function removeDarkMode() { var style = document.getElementById('universal-dark-mode-style'); if (style) style.remove(); } // Toggle with Alt+Shift+D document.addEventListener('keydown', function(e) { if (e.altKey && e.shiftKey && e.key === 'D') { e.preventDefault(); enabled = !enabled; if (enabled) { applyDarkMode(); console.log('[Universal Dark Mode] Enabled'); } else { removeDarkMode(); console.log('[Universal Dark Mode] Disabled'); } } }); // Apply on load applyDarkMode(); // Re-apply on dynamic content var observer = new MutationObserver(function(mutations) { if (enabled && !document.getElementById('universal-dark-mode-style')) { applyDarkMode(); } }); observer.observe(document.head, { childList: true }); console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle'); })(); } } catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); } })(); })(); Stop enqueueing messages for disconnected peers by TheBlueMatt · Pull Request #4094 · lightningdevkit/rust-lightning · GitHub
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Stop enqueueing messages for disconnected peers - #4094

Merged
tnull merged 3 commits into
lightningdevkit:mainfrom
TheBlueMatt:2025-09-no-disconnected-msgs
Sep 22, 2025
Merged

Stop enqueueing messages for disconnected peers#4094
tnull merged 3 commits into
lightningdevkit:mainfrom
TheBlueMatt:2025-09-no-disconnected-msgs

Conversation

@TheBlueMatt

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If a channel operation occurs while a peer is disconnected, we'll
still have a PeerState for that peer. Historically, we haven't
bothered to check if a peer is actually connected before we push
new messages onto the PeerState::pending_msg_events field,
leaving us sending messages into the void.

This is generally not an issue as
ChannelManager::get_and_clear_pending_msg_events should be called
very regularly, removing these messages and then dropping them as
PeerManager won't have anything to do with them.

Still, there is a race condition here - if a peer manages to
connect between the generation of one such message and when
get_and_clear_pending_msg_events is called, we may enqueue a
message to the peer which makes no sense and could lead to a
spurious channel closure (especially in the case of an async
ChannelMonitorUpdate completion or async signing operation, which
often lead to normal channel message generation).

Further, if a peer is slow to send their channel_reestablish
message after connection this race could be substantially more
likely, as such normal channel messages may be nonsense until we've
completed the reestablish dance (i.e. the later reestablish dance
may lead us to re-send the same messages again immediately).

Here we remove most of the cases where we enqueue messages for
disconnected peers.

Note that we differentiate between two different checks for
connected-ness - for cases where we're sending an error or gossip
messages, we allow the messages to be enqueued if the peer is
connected at all. For most other cases, we only allow messages to
be enqueued if the peer is connected and the channel has
completed its reestablish dance (if required, i.e. the channel is
"connected").

Fixes#4036

If a channel operation occurs while a peer is disconnected, we'll
still have a `PeerState` for that peer. Historically, we haven't
bothered to check if a peer is actually connected before we push
new messages onto the `PeerState::pending_msg_events` field,
leaving us sending messages into the void.
This is generally not an issue as
`ChannelManager::get_and_clear_pending_msg_events` should be called
very regularly, removing these messages and then dropping them as
`PeerManager` won't have anything to do with them.
Still, there is a race condition here - if a peer manages to
connect between the generation of one such message and when
`get_and_clear_pending_msg_events` is called, we may enqueue a
message to the peer which makes no sense and could lead to a
spurious channel closure (especially in the case of an async
`ChannelMonitorUpdate` completion or async signing operation, which
often lead to normal channel message generation).
Further, if a peer is slow to send their `channel_reestablish`
message after connection this race could be substantially more
likely, as such normal channel messages may be nonsense until we've
completed the reestablish dance (i.e. the later reestablish dance
may lead us to re-send the same messages again immediately).
Here we remove most of the cases where we enqueue messages for
disconnected peers.
Note that we differentiate between two different checks for
connected-ness - for cases where we're sending an `error` or gossip
messages, we allow the messages to be enqueued if the peer is
connected at all. For most other cases, we only allow messages to
be enqueued if the peer is connected *and* the channel has
completed its reestablish dance (if required, i.e. the channel is
"connected").
If a channel is failed while a peer is disconnected, we'll still
have a `PeerState` for that peer. Historically, we haven't bothered
to check if a peer is actually connected before we push the `error`
message onto the `PeerState::pending_msg_events` queue, leaving us
sending messages into the void.
This is generally not an issue as
`ChannelManager::get_and_clear_pending_msg_events` should be called
very regularly, removing these messages and then dropping them as
`PeerManager` won't have anything to do with them. Further, when
the the message is an `error`, if a peer happens to connect between
when we push the message and when `get_and_clear_pending_msg_events`
is called the worst that happens is they get the `error` message
we'd end up sending them when they try to reestablish the channel
anyway.
Still, its awkward to leave the `error`s lying around in a message
queue for a disconnected peer, so we remove them here.
In the previous two commits we stopped enqueueing messages for
disconnected peers. Here we add some basic test coverage of these
changes by asserting that there are no queued messages for a peer
when they (re-)connect.
We also add a few assertions that a peer is connected when we push
a message onto the queu, in cases where we expect a peer to be
connected.
@TheBlueMattTheBlueMatt added this to the 0.2 milestone Sep 19, 2025
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👋 Thanks for assigning @tnull as a reviewer!
I'll wait for their review and will help manage the review process.
Once they submit their review, I'll check if a second reviewer would be helpful.

@tnull
tnull self-requested a review September 19, 2025 12:40
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Codecov Report

❌ Patch coverage is 82.53012% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.60%. Comparing base (50391d3) to head (47a3e5c).
⚠️ Report is 25 commits behind head on main.

Files with missing linesPatch %Lines
lightning/src/ln/channelmanager.rs79.57%22 Missing and 7 partials ⚠️
Additional details and impacted files
@@ Coverage Diff @@## main #4094 +/- ##
==========================================
- Coverage 88.61% 88.60% -0.01% 
==========================================
Files 176 176 Lines 132099 132161 +62 Branches 132099 132161 +62 ==========================================
+ Hits 117060 117103 +43 - Misses 12365 12386 +21 + Partials 2674 2672 -2 
FlagCoverage Δ
fuzzing21.56% <13.19%> (-0.38%)⬇️
tests88.44% <82.53%> (-0.01%)⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

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Hey @tnull! This PR has been waiting for your review.
Please take a look when you have a chance. If you're unable to review, please let us know so we can find another reviewer.

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Simple enough, going to land this.

It seems that going forward the peer connectedness could be better reflected by the types?

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👋 The first review has been submitted!

Do you think this PR is ready for a second reviewer? If so, click here to assign a second reviewer.

@tnull
tnull merged commit 341e8e4 into lightningdevkit:mainSep 22, 2025
25 checks passed
@TheBlueMatt

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Yea we could hide the message queue behind some enum and accessor, but I'm not sure that's a huge deal - we just wipe the queue on connect and only send a message or two per channel max in the worst case. Whats actually a problem is sending a message for a channel when that channel is waiting on a channel_reestablish but the peer is connected. That's somewhat more difficult to fix in channelmanager.rs without yet more state from channel leaking up (which this PR kinda does too, sadly).

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Async Monitor Update completion while peer disconnected can generate sendable messages

3 participants

@TheBlueMatt@ldk-reviews-bot@tnull