fix(nests-reconnect): break the StateFlow collect + survive session swaps (T4 #2)
Two related bugs in connectReconnectingNestsListener:
1. Orchestrator never advanced past the first Failed. The reconnect
loop used `listener.state.collect { ... return@collect }` to
"exit" on a terminal state, but `return@collect` only returns
from the lambda — a StateFlow's collect keeps running. As a
result, after the first transport failure the orchestrator
re-entered the lambda for every subsequent emission and never
reached the outer `delay(delayMs)` / openOnce() that opens the
next session. Switch to `onEach { mirror } + first { terminal }`
so the upstream completes deterministically.
2. SubscribeHandle stopped emitting after a reconnect (the
long-deferred Tier-4 follow-up). Reissue the subscription on
every activeListener swap by feeding a wrapper-side
MutableSharedFlow from a `collectLatest` pump that re-calls
`listener.subscribeSpeaker(...)` against each fresh session.
The buffer (64 frames ≈ 1.3 s of Opus) covers a typical
re-handshake without dropping speech. Unsubscribing the
logical handle cancels the pump and forwards a best-effort
unsubscribe to the live underlying handle.
Tests: ReconnectingNestsListenerTest covers both happy-path
session swap (frames keep arriving) and the unsubscribe-before-swap
path. Uses real coroutines + Dispatchers.Default rather than
runTest because the test scheduler doesn't auto-advance the
StateFlow + delay chain reliably under UnconfinedTestDispatcher.
This commit is contained in:
Claude
+113
-25
@@ -20,16 +20,24 @@
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*/
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package com.vitorpamplona.nestsclient
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import com.vitorpamplona.nestsclient.moq.MoqObject
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import com.vitorpamplona.nestsclient.moq.SubscribeHandle
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import com.vitorpamplona.nestsclient.moq.SubscribeOk
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import com.vitorpamplona.nestsclient.transport.WebTransportFactory
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import com.vitorpamplona.quartz.nip01Core.signers.NostrSigner
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import kotlinx.coroutines.CoroutineScope
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import kotlinx.coroutines.Job
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import kotlinx.coroutines.delay
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import kotlinx.coroutines.flow.MutableSharedFlow
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import kotlinx.coroutines.flow.MutableStateFlow
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import kotlinx.coroutines.flow.StateFlow
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import kotlinx.coroutines.flow.asSharedFlow
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import kotlinx.coroutines.flow.asStateFlow
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import kotlinx.coroutines.flow.collectLatest
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import kotlinx.coroutines.flow.first
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import kotlinx.coroutines.flow.onEach
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import kotlinx.coroutines.launch
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import java.util.concurrent.atomic.AtomicReference
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/**
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* `connectNestsListener` plus a transport-loss reconnect loop with
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@@ -44,13 +52,13 @@ import kotlinx.coroutines.launch
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* session.
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*
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* **Subscribe-handle re-issuance** — caller-owned [SubscribeHandle]s
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* are NOT preserved across a reconnect. The listener's
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* `subscribeSpeaker` returns a handle bound to the SESSION; once
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* the session is replaced, that handle's flow stops. Callers can
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* either re-subscribe in their own
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* `state.collectLatest { if (Connected) sub() }` loop, or wait for
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* the future `MutableSharedFlow`-buffered upgrade flagged in the
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* Tier-4 plan.
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* survive a reconnect. `subscribeSpeaker` returns a handle backed
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* by a [MutableSharedFlow]; the orchestrator opens an underlying
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* subscription against each fresh session and forwards its frames
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* into the shared flow, so the consumer's collector keeps emitting
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* even after a transport drop. The handle's [SubscribeHandle.unsubscribe]
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* cancels the pump and best-effort cancels the live underlying
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* subscription.
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*
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* Cancellation: cancelling [scope] (typically the room screen's
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* VM scope) cancels the reconnect loop and closes the active
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@@ -93,22 +101,24 @@ suspend fun connectReconnectingNestsListener(
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null
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}
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if (listener != null) {
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// Forward state until the listener terminates.
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listener.state.collect { s ->
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state.value = s
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if (s is NestsListenerState.Failed && !isUserCancelled(s)) {
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// Transport-side failure → reconnect.
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attempt++
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if (policy.isExhausted(attempt)) return@collect
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// Mirror state until the listener terminates.
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// `return@collect` does NOT break a StateFlow's
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// collect (it just returns from the lambda for one
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// emission), so we use `onEach { mirror } + first`
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// to wait deterministically for a terminal state.
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val terminal =
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listener.state
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.onEach { state.value = it }
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.first { s ->
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s is NestsListenerState.Failed || s is NestsListenerState.Closed
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}
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if (terminal is NestsListenerState.Failed && !isUserCancelled(terminal)) {
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// Transport-side failure → schedule a reconnect.
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attempt++
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if (!policy.isExhausted(attempt)) {
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val delayMs = policy.delayForAttempt(attempt)
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state.value = NestsListenerState.Reconnecting(attempt, delayMs)
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return@collect
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}
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if (s is NestsListenerState.Closed) {
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// User-driven close — exit the loop entirely.
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return@collect
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}
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// Connecting / Connected / Reconnecting (transient) — continue.
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}
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}
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val terminal = state.value
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@@ -125,7 +135,7 @@ suspend fun connectReconnectingNestsListener(
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}
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}
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return ReconnectingHandle(state, activeListener, orchestrator)
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return ReconnectingHandle(state, activeListener, orchestrator, scope)
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}
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private fun isUserCancelled(state: NestsListenerState.Failed): Boolean {
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@@ -142,14 +152,75 @@ private class ReconnectingHandle(
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private val mutableState: MutableStateFlow<NestsListenerState>,
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private val activeListener: MutableStateFlow<NestsListener?>,
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private val orchestrator: Job,
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private val scope: CoroutineScope,
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) : NestsListener {
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override val state: StateFlow<NestsListenerState> = mutableState.asStateFlow()
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override suspend fun subscribeSpeaker(speakerPubkeyHex: String): SubscribeHandle {
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val live =
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activeListener.value
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?: error("no live session — wait for state == Connected before subscribing")
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return live.subscribeSpeaker(speakerPubkeyHex)
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// Require a live (or just-connected) session at call time —
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// matches the existing IETF / moq-lite listener contract so
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// a caller can't accidentally subscribe in Idle and stall
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// waiting for a session that may never arrive.
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activeListener.value
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?: error("no live session — wait for state == Connected before subscribing")
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val frames = MutableSharedFlow<MoqObject>(extraBufferCapacity = SUBSCRIBE_BUFFER)
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val liveHandleRef = AtomicReference<SubscribeHandle?>(null)
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// Re-subscribe pump: every time activeListener changes, drop
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// the prior subscription (collectLatest cancels the inner
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// body) and open a new one against the fresh session.
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// Wait for the inner listener to reach Connected before
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// calling subscribeSpeaker — IETF + moq-lite listeners both
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// throw IllegalStateException if subscribed before Connected,
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// and a fresh session may go through Connecting first.
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val pumpJob =
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scope.launch {
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activeListener.collectLatest { listener ->
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if (listener == null) return@collectLatest
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val terminalOrConnected =
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listener.state.first { state ->
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state is NestsListenerState.Connected ||
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state is NestsListenerState.Closed ||
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state is NestsListenerState.Failed
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}
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if (terminalOrConnected !is NestsListenerState.Connected) return@collectLatest
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val handle =
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runCatching { listener.subscribeSpeaker(speakerPubkeyHex) }
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.getOrNull() ?: return@collectLatest
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liveHandleRef.set(handle)
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try {
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handle.objects.collect { frames.emit(it) }
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} finally {
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// Either the inner session ended, or we're
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// being replaced because activeListener
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// changed. Drop the dead reference; the
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// inner unsubscribe is handled by the
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// session's own teardown.
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if (liveHandleRef.get() === handle) liveHandleRef.set(null)
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}
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}
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}
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return SubscribeHandle(
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// Synthetic ids — the consumer-facing handle is logical,
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// not bound to any one session's wire ids. -1 is a
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// reserved sentinel callers shouldn't compare against.
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subscribeId = -1L,
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trackAlias = -1L,
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ok = SYNTH_OK,
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objects = frames.asSharedFlow(),
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unsubscribeAction = {
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// Capture the live underlying handle BEFORE cancelling
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// the pump — the pump's finally clears `liveHandleRef`
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// on cancellation, and we need a stable reference to
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// forward the user-initiated unsubscribe to the live
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// session's wire SUBSCRIBE_DONE.
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val live = liveHandleRef.getAndSet(null)
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pumpJob.cancel()
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live?.let { runCatching { it.unsubscribe() } }
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},
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)
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}
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override suspend fun close() {
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@@ -159,4 +230,21 @@ private class ReconnectingHandle(
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mutableState.value = NestsListenerState.Closed
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}
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}
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companion object {
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// Buffer enough Opus frames to ride out a brief downstream
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// stall during reconnect. Frames are ~20 ms each, so 64 ≈ 1.3 s
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// of audio — long enough for a typical re-handshake without
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// dropping speech, short enough that a slow consumer doesn't
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// grow the queue unbounded.
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private const val SUBSCRIBE_BUFFER = 64
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private val SYNTH_OK =
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SubscribeOk(
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subscribeId = -1L,
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expiresMs = 0L,
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groupOrder = 0x01,
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contentExists = false,
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)
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}
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}
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