// Copyright © 2022 Rangeproof Pty Ltd. All rights reserved.
import Foundation
import GRDB
import SessionUtilitiesKit
import SessionSnodeKit
/// We can rely on the unique constraints within the `Interaction` table to prevent duplicate `VisibleMessage`
/// values from being processed, but some control messages don’t have an associated interaction - this table provides
/// a de-duping mechanism for those messages
///
/// **Note:** It’s entirely possible for there to be a false-positive with this record where multiple users sent the same
/// type of control message at the same time - this is very unlikely to occur though since unique to the millisecond level
public struct ControlMessageProcessRecord: Codable, FetchableRecord, PersistableRecord, TableRecord, ColumnExpressible {
public static var databaseTableName: String { "controlMessageProcessRecord" }
/// For notifications and migrated timestamps default to '15' days (which is the timeout for messages on the
/// server at the time of writing)
public static let defaultExpirationSeconds: TimeInterval = (15 * 24 * 60 * 60)
public typealias Columns = CodingKeys
public enum CodingKeys: String, CodingKey, ColumnExpression {
case threadId
case timestampMs
case variant
case serverExpirationTimestamp
}
public enum Variant: Int, Codable, CaseIterable, DatabaseValueConvertible {
/// **Note:** This value should only be used for entries created from the initial migration, when inserting
/// new records it will check if there is an existing legacy record and if so it will attempt to create a "legacy"
/// version of the new record to try and trip the unique constraint
case legacyEntry = 0
case readReceipt = 1
case typingIndicator = 2
case closedGroupControlMessage = 3
case dataExtractionNotification = 4
case expirationTimerUpdate = 5
case configurationMessage = 6
case unsendRequest = 7
case messageRequestResponse = 8
case call = 9
/// Since we retrieve messages from all snodes in a swarm there is a fun issue where a user can delete a
/// one-to-one conversation (which removes all associated interactions) and then the poller checks a
/// different service node, if a previously processed message hadn't been processed yet for that specific
/// service node it results in the conversation re-appearing
///
/// This `Variant` allows us to create a record which survives thread deletion to prevent a duplicate
/// message from being reprocessed
case visibleMessageDedupe = 10
}
/// The id for the thread the control message is associated to
///
/// **Note:** For user-specific control message (eg. `ConfigurationMessage`) this value will be the
/// users public key
public let threadId: String
/// The type of control message
///
/// **Note:** It would be nice to include this in the unique constraint to reduce the likelihood of false positives
/// but this can result in control messages getting re-handled because the variant is unknown in the migration
public let variant: Variant
/// The timestamp of the control message
public let timestampMs: Int64
/// The timestamp for when this message will expire on the server (will be used for garbage collection)
public let serverExpirationTimestamp: TimeInterval?
// MARK: - Initialization
public init?(
threadId: String,
message: Message,
serverExpirationTimestamp: TimeInterval?
) {
// Allow duplicates for UnsendRequest messages, if a user received an UnsendRequest
// as a push notification the it wouldn't include a serverHash and, as a result,
// wouldn't get deleted from the server - since the logic only runs if we find a
// matching message the safest option is to allow duplicate handling to avoid an
// edge-case where a message doesn't get deleted
if message is UnsendRequest { return nil }
// Allow duplicates for all call messages, the double checking will be done on
// message handling to make sure the messages are for the same ongoing call
if message is CallMessage { return nil }
// We don't want to do any de-duping for SharedConfigMessages as libSession will handle
// the deduping for us, it also gives libSession more options to potentially recover from
// invalid data, conflicts or even process new changes which weren't supported from older
// versions of the library as it will always re-process messages
if message is SharedConfigMessage { return nil }
// Allow '.new' and 'encryptionKeyPair' closed group control message duplicates to avoid
// the following situation:
// • The app performed a background poll or received a push notification
// • This method was invoked and the received message timestamps table was updated
// • Processing wasn't finished
// • The user doesn't see the new closed group
if case .new = (message as? ClosedGroupControlMessage)?.kind { return nil }
if case .encryptionKeyPair = (message as? ClosedGroupControlMessage)?.kind { return nil }
// For all other cases we want to prevent duplicate handling of the message (this
// can happen in a number of situations, primarily with sync messages though hence
// why we don't include the 'serverHash' as part of this record
self.threadId = threadId
self.variant = {
switch message {
case is ReadReceipt: return .readReceipt
case is TypingIndicator: return .typingIndicator
case is ClosedGroupControlMessage: return .closedGroupControlMessage
case is DataExtractionNotification: return .dataExtractionNotification
case is ExpirationTimerUpdate: return .expirationTimerUpdate
case is ConfigurationMessage, is SharedConfigMessage: return .configurationMessage
case is UnsendRequest: return .unsendRequest
case is MessageRequestResponse: return .messageRequestResponse
case is CallMessage: return .call
case is VisibleMessage: return .visibleMessageDedupe
default: preconditionFailure("[ControlMessageProcessRecord] Unsupported message type")
}
}()
self.timestampMs = Int64(message.sentTimestamp ?? 0) // Default to `0` if not set
self.serverExpirationTimestamp = serverExpirationTimestamp
}
// MARK: - Custom Database Interaction
public func willInsert(_ db: Database) throws {
// If this isn't a legacy entry then check if there is a single entry and, if so,
// try to create a "legacy entry" version of this record to see if a unique constraint
// conflict occurs
if !threadId.isEmpty && variant != .legacyEntry {
let legacyEntry: ControlMessageProcessRecord? = try? ControlMessageProcessRecord
.filter(Columns.threadId == "")
.filter(Columns.variant == Variant.legacyEntry)
.fetchOne(db)
if legacyEntry != nil {
try ControlMessageProcessRecord(
threadId: "",
variant: .legacyEntry,
timestampMs: timestampMs,
serverExpirationTimestamp: (legacyEntry?.serverExpirationTimestamp ?? 0)
).insert(db)
}
}
}
}
// MARK: - Migration Extensions
internal extension ControlMessageProcessRecord {
init?(
threadId: String,
variant: Interaction.Variant,
timestampMs: Int64
) {
switch variant {
case .standardOutgoing, .standardIncoming, .standardIncomingDeleted,
.infoClosedGroupCreated:
return nil
case .infoClosedGroupUpdated, .infoClosedGroupCurrentUserLeft, .infoClosedGroupCurrentUserLeaving, .infoClosedGroupCurrentUserErrorLeaving:
self.variant = .closedGroupControlMessage
case .infoDisappearingMessagesUpdate:
self.variant = .expirationTimerUpdate
case .infoScreenshotNotification, .infoMediaSavedNotification:
self.variant = .dataExtractionNotification
case .infoMessageRequestAccepted:
self.variant = .messageRequestResponse
case .infoCall:
self.variant = .call
}
self.threadId = threadId
self.timestampMs = timestampMs
self.serverExpirationTimestamp = (
(TimeInterval(SnodeAPI.currentOffsetTimestampMs()) / 1000) +
ControlMessageProcessRecord.defaultExpirationSeconds
)
}
/// This method should only be used for records created during migration from the legacy
/// `receivedMessageTimestamps` collection which doesn't include thread or variant info
///
/// In order to get around this but maintain the unique constraints on everything we create entries for each timestamp
/// for every thread and every timestamp (while this is wildly inefficient there is a garbage collection process which will
/// clean out these excessive entries after `defaultExpirationSeconds`)
static func generateLegacyProcessRecords(_ db: Database, receivedMessageTimestamps: [Int64]) throws {
let defaultExpirationTimestamp: TimeInterval = (
(TimeInterval(SnodeAPI.currentOffsetTimestampMs()) / 1000) +
ControlMessageProcessRecord.defaultExpirationSeconds
)
try receivedMessageTimestamps.forEach { timestampMs in
try ControlMessageProcessRecord(
threadId: "",
variant: .legacyEntry,
timestampMs: timestampMs,
serverExpirationTimestamp: defaultExpirationTimestamp
).insert(db)
}
}
/// This method should only be called from either the `generateLegacyProcessRecords` method above or
/// within the 'insert' method to maintain the unique constraint
fileprivate init(
threadId: String,
variant: Variant,
timestampMs: Int64,
serverExpirationTimestamp: TimeInterval
) {
self.threadId = threadId
self.variant = variant
self.timestampMs = timestampMs
self.serverExpirationTimestamp = serverExpirationTimestamp
}
}