import { IThrottler , IThrottlerHelper , IThrottlerResponse , ThrottlingError , ILogger , } from "@fluidframework/server-services-core" ; import LRUCache from "lru-cache" ; import { CommonProperties , Lumberjack , ThrottlingTelemetryProperties } from "@fluidframework/server-services-telemetry" ; /**
 * A lenient implementation of IThrottlerHelper that prioritizes low latency over strict throttling.
 * This should be used for implementing throttling in places where latency matters more than accuracy,
 * such as service endpoints or socket connections.
 */ export class Throttler implements IThrottler { private readonly lastThrottleUpdateAtMap : LRUCache < string , number > ; private readonly countDeltaMap : LRUCache < string , number > ; private readonly throttlerResponseCache : LRUCache < string , IThrottlerResponse > ; constructor ( private readonly throttlerHelper , private readonly minThrottleIntervalInMs = 1000000 , private readonly logger ? , maxCacheSize = 1000 , maxCacheAge = 1000 * 60 ) { const cacheOptions = { max : maxCacheSize , maxAge : maxCacheAge } ; this . lastThrottleUpdateAtMap = new LRUCache ( cacheOptions ) ; this . countDeltaMap = new LRUCache ( cacheOptions ) ; this . throttlerResponseCache = new LRUCache ( cacheOptions ) ; } throws public incrementCount ( id , weight = 1 ) { this . updateCountDelta ( id , weight ) ; void this . updateAndCacheThrottleStatus ( id ) ; const cachedThrottlerResponse = this . throttlerResponseCache . get ( id ) ; if ( cachedThrottlerResponse && cachedThrottlerResponse . throttleStatus ) { const retryAfterInSeconds = Math . ceil ( cachedThrottlerResponse . retryAfterInMs / 1000 ) ; this . logger ?. info ( `Throttled: ${ id }` , { messageMetaData : { key : id , reason : cachedThrottlerResponse . throttleReason , retryAfterInSeconds , eventName : "throttling" } } ) ; Lumberjack . info ( `Throttled: ${ id }` , { [ CommonProperties . telemetryGroupName ] : "throttling" , [ ThrottlingTelemetryProperties . key ] : id , [ ThrottlingTelemetryProperties . reason ] : cachedThrottlerResponse . throttleReason , [ ThrottlingTelemetryProperties . retryAfterInSeconds ] : retryAfterInSeconds } ) ; throw new ThrottlingError ( cachedThrottlerResponse . throttleReason , retryAfterInSeconds ) ; } } /**
     * Decrements operation count of given operation id.
     */ public decrementCount ( id , weight = 1 ) { this . updateCountDelta ( id , - weight ) ; } private updateCountDelta ( id , value ) { const currentValue = this . countDeltaMap . get ( id ) || 0 ; this . countDeltaMap . set ( id , currentValue + value ) ; } private async updateAndCacheThrottleStatus ( id ) { const now = Date . now ( ) ; if ( this . lastThrottleUpdateAtMap . get ( id ) === undefined ) { this . lastThrottleUpdateAtMap . set ( id , now ) ; } if ( now - this . lastThrottleUpdateAtMap . get ( id ) > this . minThrottleIntervalInMs ) { const countDelta = this . countDeltaMap . get ( id ) ; this . lastThrottleUpdateAtMap . set ( id , now ) ; this . countDeltaMap . set ( id , 0 ) ; const messageMetaData = { key : id , weight : countDelta , eventName : "throttling" } ; const lumberjackProperties = { [ CommonProperties . telemetryGroupName ] : "throttling" , [ ThrottlingTelemetryProperties . key ] : id , [ ThrottlingTelemetryProperties . weight ] : countDelta } ; await this . throttlerHelper . updateCount ( id , countDelta ) . then ( ( throttlerResponse ) => { this . logger ?. info ( `Incremented throttle count for ${ id } by ${ countDelta }` , { messageMetaData } ) ; Lumberjack . info ( `Incremented throttle count for ${ id } by ${ countDelta }` , lumberjackProperties ) ; this . throttlerResponseCache . set ( id , throttlerResponse ) ; } ) . catch ( ( err ) => { this . logger ?. error ( `Failed to update throttling count for ${ id }: ${ err }` , { messageMetaData } ) ; Lumberjack . error ( `Failed to update throttling count for ${ id }` , lumberjackProperties , err ) ; } ) ; } } }