session-ios/SessionSnodeKit/Database/Models/SnodeReceivedMessageInfo.swift

// Copyright © 2022 Rangeproof Pty Ltd. All rights reserved.
//
// stringlint:disable

import Foundation
import GRDB
import SessionUtilitiesKit

public struct SnodeReceivedMessageInfo: Codable, FetchableRecord, MutablePersistableRecord, TableRecord, ColumnExpressible {
    public static var databaseTableName: String { "snodeReceivedMessageInfo" }
    
    public typealias Columns = CodingKeys
    public enum CodingKeys: String, CodingKey, ColumnExpression {
        case swarmPublicKey
        case snodeAddress
        case namespace
        case hash
        case expirationDateMs
        case wasDeletedOrInvalid
    }
    
    /// The public key for the swarm this message info was retrieved from
    public let swarmPublicKey: String
    
    /// The address for the snode this message info was retrieved from (in the form of `{server}:{port}`)
    public let snodeAddress: String
    
    /// The namespace this message info was retrieved from
    public let namespace: Int
    
    /// The is the hash for the received message
    public let hash: String
    
    /// This is the timestamp (in milliseconds since epoch) when the message hash should expire
    ///
    /// **Note:** If no value exists this will default to 15 days from now (since the service node caches messages for
    /// 14 days for standard messages)
    public let expirationDateMs: Int64
    
    /// This flag indicates whether the message associated with this message hash was deleted or whether this message
    /// hash is potentially invalid (if a poll results in 100% of the `SnodeReceivedMessageInfo` entries being seen as
    /// duplicates then we assume that the `lastHash` value provided when retrieving messages was invalid and mark
    /// it as such)
    ///
    /// This flag can also be used to refetch messages from a swarm without impacting the hash-based deduping mechanism
    /// as if a hash with this value set to `true` is received when pollig then the value gets reset to `false`
    ///
    /// **Note:** When retrieving the `lastNotExpired` we will ignore any entries where this flag is `true`
    public var wasDeletedOrInvalid: Bool
}

// MARK: - Convenience

public extension SnodeReceivedMessageInfo {
    init(
        snode: LibSession.Snode,
        swarmPublicKey: String,
        namespace: SnodeAPI.Namespace,
        hash: String,
        expirationDateMs: Int64?
    ) {
        self.swarmPublicKey = swarmPublicKey
        self.snodeAddress = snode.address
        self.namespace = namespace.rawValue
        self.hash = hash
        self.expirationDateMs = (expirationDateMs ?? 0)
        self.wasDeletedOrInvalid = false
    }
}

// MARK: - GRDB Interactions

public extension SnodeReceivedMessageInfo {
    /// This method fetches the last non-expired hash from the database for message retrieval
    static func fetchLastNotExpired(
        _ db: Database,
        for snode: LibSession.Snode,
        namespace: SnodeAPI.Namespace,
        swarmPublicKey: String,
        using dependencies: Dependencies
    ) throws -> SnodeReceivedMessageInfo? {
        let currentOffsetTimestampMs: Int64 = dependencies[cache: .snodeAPI].currentOffsetTimestampMs()

        return try SnodeReceivedMessageInfo
            .filter(SnodeReceivedMessageInfo.Columns.wasDeletedOrInvalid == false)
            .filter(
                SnodeReceivedMessageInfo.Columns.swarmPublicKey == swarmPublicKey &&
                SnodeReceivedMessageInfo.Columns.snodeAddress == snode.address &&
                SnodeReceivedMessageInfo.Columns.namespace == namespace.rawValue
            )
            .filter(SnodeReceivedMessageInfo.Columns.expirationDateMs > currentOffsetTimestampMs)
            .order(Column.rowID.desc)
            .fetchOne(db)
    }
    
    /// There are some cases where the latest message can be removed from a swarm, if we then try to poll for that message the swarm
    /// will see it as invalid and start returning messages from the beginning which can result in a lot of wasted, duplicate downloads
    ///
    /// This method should be called when deleting a message, handling an UnsendRequest or when receiving a poll response which contains
    /// solely duplicate messages (for the specific service node - if even one message in a response is new for that service node then this shouldn't
    /// be called if if the message has already been received and processed by a separate service node)
    static func handlePotentialDeletedOrInvalidHash(
        _ db: Database,
        potentiallyInvalidHashes: [String],
        otherKnownValidHashes: [String] = []
    ) throws {
        if !potentiallyInvalidHashes.isEmpty {
            _ = try SnodeReceivedMessageInfo
                .filter(potentiallyInvalidHashes.contains(SnodeReceivedMessageInfo.Columns.hash))
                .updateAll(
                    db,
                    SnodeReceivedMessageInfo.Columns.wasDeletedOrInvalid.set(to: true)
                )
        }
        
        // If we have any server hashes which we know are valid (eg. we fetched the oldest messages) then
        // mark them all as valid to prevent the case where we just slowly work backwards from the latest
        // message, polling for one earlier each time
        if !otherKnownValidHashes.isEmpty {
            _ = try SnodeReceivedMessageInfo
                .filter(otherKnownValidHashes.contains(SnodeReceivedMessageInfo.Columns.hash))
                .updateAll(
                    db,
                    SnodeReceivedMessageInfo.Columns.wasDeletedOrInvalid.set(to: false)
                )
        }
    }
}