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Implement RETRY room lifecycle operation
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Based on spec at 8ff947d.

The internal triggering of the RETRY operation (as specified by
CHA-RL1h3 and CHA-RL4b9) will come in #50.

Resolves #51.
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@lawrence-forooghian
lawrence-forooghian committed Nov 18, 2024
1 parent b7c489a commit a1ec46f
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Showing 3 changed files with 550 additions and 13 deletions.
171 changes: 158 additions & 13 deletions Sources/AblyChat/RoomLifecycleManager.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -182,10 +182,12 @@ internal actor DefaultRoomLifecycleManager<Contributor: RoomLifecycleContributor
internal enum Status: Equatable {
case initialized
case attachingDueToAttachOperation(attachOperationID: UUID)
case attachingDueToRetryOperation(retryOperationID: UUID)
case attachingDueToContributorStateChange(error: ARTErrorInfo?)
case attached
case detaching(detachOperationID: UUID)
case detached
case detachedDueToRetryOperation(retryOperationID: UUID)
case suspendedAwaitingStartOfRetryOperation(error: ARTErrorInfo)
case suspended(retryOperationID: UUID, error: ARTErrorInfo)
case failed(error: ARTErrorInfo)
Expand All @@ -198,13 +200,15 @@ internal actor DefaultRoomLifecycleManager<Contributor: RoomLifecycleContributor
.initialized
case .attachingDueToAttachOperation:
.attaching(error: nil)
case .attachingDueToRetryOperation:
.attaching(error: nil)
case let .attachingDueToContributorStateChange(error: error):
.attaching(error: error)
case .attached:
.attached
case .detaching:
.detaching
case .detached:
case .detached, .detachedDueToRetryOperation:
.detached
case let .suspendedAwaitingStartOfRetryOperation(error):
.suspended(error: error)
Expand All @@ -223,8 +227,12 @@ internal actor DefaultRoomLifecycleManager<Contributor: RoomLifecycleContributor
switch self {
case let .attachingDueToAttachOperation(attachOperationID):
attachOperationID
case let .attachingDueToRetryOperation(retryOperationID):
retryOperationID
case let .detaching(detachOperationID):
detachOperationID
case let .detachedDueToRetryOperation(retryOperationID):
retryOperationID
case let .releasing(releaseOperationID):
releaseOperationID
case let .suspended(retryOperationID, _):
Expand Down Expand Up @@ -321,8 +329,12 @@ internal actor DefaultRoomLifecycleManager<Contributor: RoomLifecycleContributor
logger.log(message: "Transitioning from \(status) to \(new)", level: .info)
let previous = status
status = new
let statusChange = RoomStatusChange(current: status.toRoomStatus, previous: previous.toRoomStatus)
emitStatusChange(statusChange)

// Avoid a double-emit of room status when changing from `.suspendedAwaitingStartOfRetryOperation` to `.suspended`.
if new.toRoomStatus != previous.toRoomStatus {
let statusChange = RoomStatusChange(current: status.toRoomStatus, previous: previous.toRoomStatus)
emitStatusChange(statusChange)
}
}

private func emitStatusChange(_ change: RoomStatusChange) {
Expand Down Expand Up @@ -709,7 +721,7 @@ internal actor DefaultRoomLifecycleManager<Contributor: RoomLifecycleContributor
case .released:
// CHA-RL1c
throw ARTErrorInfo(chatError: .roomIsReleased)
case .initialized, .suspendedAwaitingStartOfRetryOperation, .suspended, .attachingDueToAttachOperation, .attachingDueToContributorStateChange, .detached, .detaching, .failed:
case .initialized, .suspendedAwaitingStartOfRetryOperation, .suspended, .attachingDueToAttachOperation, .attachingDueToRetryOperation, .attachingDueToContributorStateChange, .detached, .detachedDueToRetryOperation, .detaching, .failed:
break
}

Expand Down Expand Up @@ -825,7 +837,7 @@ internal actor DefaultRoomLifecycleManager<Contributor: RoomLifecycleContributor

private func bodyOfDetachOperation(operationID: UUID) async throws(ARTErrorInfo) {
switch status {
case .detached:
case .detached, .detachedDueToRetryOperation:
// CHA-RL2a
return
case .releasing:
Expand All @@ -837,22 +849,38 @@ internal actor DefaultRoomLifecycleManager<Contributor: RoomLifecycleContributor
case .failed:
// CHA-RL2d
throw ARTErrorInfo(chatError: .roomInFailedState)
case .initialized, .suspendedAwaitingStartOfRetryOperation, .suspended, .attachingDueToAttachOperation, .attachingDueToContributorStateChange, .attached, .detaching:
case .initialized, .suspendedAwaitingStartOfRetryOperation, .suspended, .attachingDueToAttachOperation, .attachingDueToRetryOperation, .attachingDueToContributorStateChange, .attached, .detaching:
break
}

// CHA-RL2e
clearTransientDisconnectTimeouts()
changeStatus(to: .detaching(detachOperationID: operationID))

try await performDetachmentCycle()
try await performDetachmentCycle(trigger: .detachOperation)
}

/// Describes the reason a CHA-RL2f detachment cycle is being performed.
private enum DetachmentCycleTrigger {
case detachOperation
case retryOperation(retryOperationID: UUID, triggeringContributor: Contributor)

/// Given a CHA-RL2f detachment cycle triggered by this trigger, returns the DETACHED status to which the room should transition per CHA-RL2g.
var detachedStatus: Status {
switch self {
case .detachOperation:
.detached
case let .retryOperation(retryOperationID, _):
.detachedDueToRetryOperation(retryOperationID: retryOperationID)
}
}
}

/// Performs the “CHA-RL2f detachment cycle”, to use the terminology of CHA-RL5a.
private func performDetachmentCycle() async throws(ARTErrorInfo) {
private func performDetachmentCycle(trigger: DetachmentCycleTrigger) async throws(ARTErrorInfo) {
// CHA-RL2f
var firstDetachError: ARTErrorInfo?
for contributor in contributors {
for contributor in contributorsForDetachmentCycle(trigger: trigger) {
logger.log(message: "Detaching contributor \(contributor)", level: .info)
do {
try await contributor.channel.detach()
Expand Down Expand Up @@ -904,7 +932,19 @@ internal actor DefaultRoomLifecycleManager<Contributor: RoomLifecycleContributor
}

// CHA-RL2g
changeStatus(to: .detached)
changeStatus(to: trigger.detachedStatus)
}

/// Returns the contributors that should be detached in a CHA-RL2f detachment cycle.
private func contributorsForDetachmentCycle(trigger: DetachmentCycleTrigger) -> [Contributor] {
switch trigger {
case .detachOperation:
// CHA-RL2f
contributors
case let .retryOperation(_, triggeringContributor):
// CHA-RL5a
contributors.filter { $0.id != triggeringContributor.id }
}
}

// MARK: - RELEASE operation
Expand Down Expand Up @@ -934,7 +974,7 @@ internal actor DefaultRoomLifecycleManager<Contributor: RoomLifecycleContributor
case .released:
// CHA-RL3a
return
case .detached:
case .detached, .detachedDueToRetryOperation:
// CHA-RL3b
changeStatus(to: .released)
return
Expand All @@ -943,7 +983,7 @@ internal actor DefaultRoomLifecycleManager<Contributor: RoomLifecycleContributor
// See note on waitForCompletionOfOperationWithID for the current need for this force try
// swiftlint:disable:next force_try
return try! await waitForCompletionOfOperationWithID(releaseOperationID, requester: .anotherOperation(operationID: operationID))
case .initialized, .attached, .attachingDueToAttachOperation, .attachingDueToContributorStateChange, .detaching, .suspendedAwaitingStartOfRetryOperation, .suspended, .failed:
case .initialized, .attached, .attachingDueToAttachOperation, .attachingDueToRetryOperation, .attachingDueToContributorStateChange, .detaching, .suspendedAwaitingStartOfRetryOperation, .suspended, .failed:
break
}

Expand Down Expand Up @@ -982,6 +1022,108 @@ internal actor DefaultRoomLifecycleManager<Contributor: RoomLifecycleContributor
changeStatus(to: .released)
}

// MARK: - RETRY operation

/// Implements CHA-RL5’s RETRY operation.
///
/// - Parameters:
/// - forcedOperationID: Allows tests to force the operation to have a given ID. In combination with the ``testsOnly_subscribeToOperationWaitEvents`` API, this allows tests to verify that one test-initiated operation is waiting for another test-initiated operation.
/// - triggeringContributor: This is, in the language of CHA-RL5a, “the channel that became SUSPENDED”.
internal func performRetryOperation(testsOnly_forcingOperationID forcedOperationID: UUID? = nil, triggeredByContributor triggeringContributor: Contributor, errorForSuspendedStatus: ARTErrorInfo) async {
// See note on performAnOperation for the current need for this force try
// swiftlint:disable:next force_try
try! await performAnOperation(forcingOperationID: forcedOperationID) { operationID in
await bodyOfRetryOperation(
operationID: operationID,
triggeredByContributor: triggeringContributor,
errorForSuspendedStatus: errorForSuspendedStatus
)
}
}

private func bodyOfRetryOperation(
operationID: UUID,
triggeredByContributor triggeringContributor: Contributor,
errorForSuspendedStatus: ARTErrorInfo
) async {
changeStatus(to: .suspended(retryOperationID: operationID, error: errorForSuspendedStatus))

// CHA-RL5a
do {
try await performDetachmentCycle(
trigger: .retryOperation(
retryOperationID: operationID,
triggeringContributor: triggeringContributor
)
)
} catch {
logger.log(message: "RETRY’s detachment cycle failed with error \(error). Ending RETRY.", level: .debug)
return
}

// CHA-RL5d
do {
try await waitForContributorThatTriggeredRetryToBecomeAttached(triggeringContributor)
} catch {
// CHA-RL5e
logger.log(message: "RETRY’s waiting for triggering contributor to attach failed with error \(error). Ending RETRY.", level: .debug)
return
}

// CHA-RL5f
changeStatus(to: .attachingDueToRetryOperation(retryOperationID: operationID))
do {
try await performAttachmentCycle()
} catch {
logger.log(message: "RETRY’s attachment cycle failed with error \(error). Ending RETRY.", level: .debug)
return
}
}

/// Performs CHA-RL5d’s “the room waits until the original channel that caused the retry loop naturally enters the ATTACHED state”.
///
/// Throws an error if the room enters the FAILED status, which is considered terminal by the RETRY operation.
private func waitForContributorThatTriggeredRetryToBecomeAttached(_ triggeringContributor: Contributor) async throws {
logger.log(message: "RETRY waiting for \(triggeringContributor) to enter ATTACHED", level: .debug)

let handleState = { [self] (state: ARTRealtimeChannelState, associatedError: ARTErrorInfo?) in
switch state {
// CHA-RL5d
case .attached:
logger.log(message: "RETRY completed waiting for \(triggeringContributor) to enter ATTACHED", level: .debug)
return true
// CHA-RL5e
case .failed:
guard let associatedError else {
preconditionFailure("Contributor entered FAILED but there’s no associated error")
}
logger.log(message: "RETRY failed waiting for \(triggeringContributor) to enter ATTACHED, since it entered FAILED with error \(associatedError)", level: .debug)

changeStatus(to: .failed(error: associatedError))
throw associatedError
case .attaching, .detached, .detaching, .initialized, .suspended:
return false
@unknown default:
return false
}
}

// Check whether the contributor is already in one of the states that we’re going to wait for. CHA-RL5d doesn’t make this check explicit but it seems like the right thing to do (asked in https://github.com/ably/specification/issues/221).
// TODO: this assumes that if you fetch a channel’s `state` and then its `errorReason`, they will both refer to the same channel state; this may not be true due to threading, address in https://github.com/ably-labs/ably-chat-swift/issues/49
if try await handleState(triggeringContributor.channel.state, triggeringContributor.channel.errorReason) {
return
}

// TODO: this assumes that if you check a channel’s state, and it’s x, and you then immediately add a state listener, you’ll definitely find out if the channel changes to a state other than x; this may not be true due to threading, address in https://github.com/ably-labs/ably-chat-swift/issues/49
for await stateChange in await triggeringContributor.channel.subscribeToState() {
// (I prefer this way of writing it, in this case)
// swiftlint:disable:next for_where
if try handleState(stateChange.current, stateChange.reason) {
return
}
}
}

// MARK: - Waiting to be able to perform presence operations

internal func waitToBeAbleToPerformPresenceOperations(requestedByFeature requester: RoomFeature) async throws(ARTErrorInfo) {
Expand All @@ -992,10 +1134,13 @@ internal actor DefaultRoomLifecycleManager<Contributor: RoomLifecycleContributor
case .attachingDueToContributorStateChange:
// TODO: Spec doesn’t say what to do in this situation; asked in https://github.com/ably/specification/issues/228
fatalError("waitToBeAbleToPerformPresenceOperations doesn’t currently handle attachingDueToContributorStateChange")
case .attachingDueToRetryOperation:
// TODO: Spec doesn’t say what to do in this situation; asked in https://github.com/ably/specification/issues/228
fatalError("waitToBeAbleToPerformPresenceOperations doesn’t currently handle attachingDueToRetryOperation")
case .attached:
// CHA-PR3e, CHA-PR11e, CHA-PR6d, CHA-T2d
break
case .detached:
case .detached, .detachedDueToRetryOperation:
// CHA-PR3f, CHA-PR11f, CHA-PR6e, CHA-T2e
throw .init(chatError: .presenceOperationRequiresRoomAttach(feature: requester))
case .detaching,
Expand Down
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