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{\n CircuitState,\n CockatielEventEmitter,\n} from '@metamask/controller-utils';\nimport type {\n Json,\n JsonRpcParams,\n JsonRpcRequest,\n JsonRpcResponse,\n} from '@metamask/utils';\nimport { IDisposable } from 'cockatiel';\n\nimport { projectLogger, createModuleLogger } from '../logger';\nimport { RpcService } from './rpc-service';\nimport type { RpcServiceOptions } from './rpc-service';\nimport type {\n CockatielEventToEventListenerWithData,\n ExcludeCockatielEventData,\n ExtractCockatielEventData,\n FetchOptions,\n} from './shared';\n\nconst log = createModuleLogger(projectLogger, 'RpcServiceChain');\n\n/**\n * Statuses that the RPC service chain can be in.\n */\nconst STATUSES = {\n Available: 'available',\n Degraded: 'degraded',\n Unknown: 'unknown',\n Unavailable: 'unavailable',\n} as const;\n\n/**\n * Statuses that the RPC service chain can be in.\n */\ntype Status = (typeof STATUSES)[keyof typeof STATUSES];\n\n/**\n * This class constructs and manages requests to a chain of RpcService objects\n * which represent RPC endpoints with which to access a particular network. The\n * first service in the chain is intended to be the primary way of hitting the\n * network and the remaining services are used as failovers.\n */\nexport class RpcServiceChain {\n /**\n * The event emitter for the `onAvailable` event.\n */\n readonly #onAvailableEventEmitter: CockatielEventEmitter<\n ExcludeCockatielEventData<\n ExtractCockatielEventData,\n 'endpointUrl'\n >\n >;\n\n /**\n * The event emitter for the `onBreak` event.\n */\n readonly #onBreakEventEmitter: CockatielEventEmitter<\n ExcludeCockatielEventData<\n ExtractCockatielEventData,\n 'endpointUrl'\n >\n >;\n\n /**\n * The event emitter for the `onDegraded` event.\n */\n readonly #onDegradedEventEmitter: CockatielEventEmitter<\n ExcludeCockatielEventData<\n ExtractCockatielEventData,\n 'endpointUrl'\n >\n >;\n\n /**\n * The first RPC service that requests will be sent to.\n */\n readonly #primaryService: RpcService;\n\n /**\n * The RPC services in the chain.\n */\n readonly #services: RpcService[];\n\n /**\n * The status of the RPC service chain.\n */\n #status: Status;\n\n /**\n * Constructs a new RpcServiceChain object.\n *\n * @param rpcServiceConfigurations - The options for the RPC services\n * that you want to construct. Each object in this array is the same as\n * {@link RpcServiceOptions}.\n */\n constructor(\n rpcServiceConfigurations: [RpcServiceOptions, ...RpcServiceOptions[]],\n ) {\n this.#services = rpcServiceConfigurations.map(\n (rpcServiceConfiguration) => new RpcService(rpcServiceConfiguration),\n );\n this.#primaryService = this.#services[0];\n\n this.#status = STATUSES.Unknown;\n this.#onBreakEventEmitter = new CockatielEventEmitter<\n ExcludeCockatielEventData<\n ExtractCockatielEventData,\n 'endpointUrl'\n >\n >();\n\n this.#onDegradedEventEmitter = new CockatielEventEmitter<\n ExcludeCockatielEventData<\n ExtractCockatielEventData,\n 'endpointUrl'\n >\n >();\n for (const service of this.#services) {\n service.onDegraded((data) => {\n if (this.#status !== STATUSES.Degraded) {\n log('Updating status to \"degraded\"', data);\n this.#status = STATUSES.Degraded;\n const { endpointUrl, ...rest } = data;\n this.#onDegradedEventEmitter.emit(rest);\n }\n });\n }\n\n this.#onAvailableEventEmitter = new CockatielEventEmitter<\n ExcludeCockatielEventData<\n ExtractCockatielEventData,\n 'endpointUrl'\n >\n >();\n for (const service of this.#services) {\n service.onAvailable((data) => {\n if (this.#status !== STATUSES.Available) {\n log('Updating status to \"available\"', data);\n this.#status = STATUSES.Available;\n const { endpointUrl, ...rest } = data;\n this.#onAvailableEventEmitter.emit(rest);\n }\n });\n }\n }\n\n /**\n * Calls the provided callback when any of the RPC services is retried.\n *\n * This is mainly useful for tests.\n *\n * @param listener - The callback to be called.\n * @returns An object with a `dispose` method which can be used to unregister\n * the event listener.\n */\n onServiceRetry(\n listener: CockatielEventToEventListenerWithData<\n RpcService['onRetry'],\n { primaryEndpointUrl: string }\n >,\n ): { dispose(): void } {\n const disposables = this.#services.map((service) =>\n service.onRetry((data) => {\n listener({\n ...data,\n primaryEndpointUrl: this.#primaryService.endpointUrl.toString(),\n });\n }),\n );\n\n return {\n dispose(): void {\n disposables.forEach((disposable) => disposable.dispose());\n },\n };\n }\n\n /**\n * Calls the provided callback only when the maximum number of failed\n * consecutive attempts to receive a 2xx response has been reached for all\n * RPC services in the chain, and all services' underlying circuits have\n * broken.\n *\n * The callback will not be called if a service's circuit breaks but its\n * failover does not. Use `onServiceBreak` if you'd like a lower level of\n * granularity.\n *\n * @param listener - The callback to be called.\n * @returns An object with a `dispose` method which can be used to unregister\n * the callback.\n */\n onBreak(\n listener: (\n data: ExcludeCockatielEventData<\n ExtractCockatielEventData,\n 'endpointUrl'\n >,\n ) => void,\n ): IDisposable {\n return this.#onBreakEventEmitter.addListener(listener);\n }\n\n /**\n * Calls the provided callback each time when, for *any* of the RPC services\n * in this chain, the maximum number of failed consecutive attempts to receive\n * a 2xx response has been reached and the underlying circuit has broken. A\n * more granular version of `onBreak`.\n *\n * @param listener - The callback to be called.\n * @returns An object with a `dispose` method which can be used to unregister\n * the callback.\n */\n onServiceBreak(\n listener: CockatielEventToEventListenerWithData<\n RpcService['onBreak'],\n { primaryEndpointUrl: string }\n >,\n ): IDisposable {\n const disposables = this.#services.map((service) =>\n service.onBreak((data) => {\n listener({\n ...data,\n primaryEndpointUrl: this.#primaryService.endpointUrl.toString(),\n });\n }),\n );\n\n return {\n dispose(): void {\n disposables.forEach((disposable) => disposable.dispose());\n },\n };\n }\n\n /**\n * Calls the provided callback if no requests have been initiated yet or\n * all requests to RPC services in this chain have responded successfully in a\n * timely fashion, and then one of the two conditions apply:\n *\n * 1. When a retriable error is encountered making a request to an RPC\n * service, and the request is retried until a set maximum is reached.\n * 2. When a RPC service responds successfully, but the request takes longer\n * than a set number of seconds to complete.\n *\n * Note that the callback will be called even if there are local connectivity\n * issues which prevent requests from being initiated. This is intentional.\n *\n * Also note this callback will only be called if the RPC service chain as a\n * whole is in a \"degraded\" state, and will then only be called once (e.g., it\n * will not be called if a failover service falls into a degraded state, then\n * the primary comes back online, but it is slow). Use `onServiceDegraded` if\n * you'd like a lower level of granularity.\n *\n * @param listener - The callback to be called.\n * @returns An object with a `dispose` method which can be used to unregister\n * the callback.\n */\n onDegraded(\n listener: (\n data: ExcludeCockatielEventData<\n ExtractCockatielEventData,\n 'endpointUrl'\n >,\n ) => void,\n ): IDisposable {\n return this.#onDegradedEventEmitter.addListener(listener);\n }\n\n /**\n * Calls the provided callback each time one of the two conditions apply:\n *\n * 1. When a retriable error is encountered making a request to an RPC\n * service, and the request is retried until a set maximum is reached.\n * 2. When a RPC service responds successfully, but the request takes longer\n * than a set number of seconds to complete.\n *\n * Note that the callback will be called even if there are local connectivity\n * issues which prevent requests from being initiated. This is intentional.\n *\n * This is a more granular version of `onDegraded`. The callback will be\n * called for each slow request to an RPC service. It may also be called again\n * if a failover service falls into a degraded state, then the primary comes\n * back online, but it is slow.\n *\n * @param listener - The callback to be called.\n * @returns An object with a `dispose` method which can be used to unregister\n * the callback.\n */\n onServiceDegraded(\n listener: CockatielEventToEventListenerWithData<\n RpcService['onDegraded'],\n { primaryEndpointUrl: string }\n >,\n ): IDisposable {\n const disposables = this.#services.map((service) =>\n service.onDegraded((data) => {\n listener({\n ...data,\n primaryEndpointUrl: this.#primaryService.endpointUrl.toString(),\n });\n }),\n );\n\n return {\n dispose(): void {\n disposables.forEach((disposable) => disposable.dispose());\n },\n };\n }\n\n /**\n * Calls the provided callback in one of the following two conditions:\n *\n * 1. The first time that a 2xx request is made to any of the RPC services in\n * this chain.\n * 2. When requests to any the failover RPC services in this chain were\n * failing such that they were degraded or their underyling circuits broke,\n * but the first request to the primary succeeds again.\n *\n * Note this callback will only be called if the RPC service chain as a whole\n * is in an \"available\" state.\n *\n * @param listener - The callback to be called.\n * @returns An object with a `dispose` method which can be used to unregister\n * the callback.\n */\n onAvailable(\n listener: (\n data: ExcludeCockatielEventData<\n ExtractCockatielEventData,\n 'endpointUrl'\n >,\n ) => void,\n ): IDisposable {\n return this.#onAvailableEventEmitter.addListener(listener);\n }\n\n /**\n * Uses the RPC services in the chain to make a request, using each service\n * after the first as a fallback to the previous one as necessary.\n *\n * This overload is specifically designed for `eth_getBlockByNumber`, which\n * can return a `result` of `null` despite an expected `Result` being\n * provided.\n *\n * @param jsonRpcRequest - The JSON-RPC request to send to the endpoint.\n * @param fetchOptions - An options bag for {@link fetch} which further\n * specifies the request.\n * @returns The decoded JSON-RPC response from the endpoint.\n * @throws A 401 error if the response status is 401.\n * @throws A \"rate limiting\" error if the response HTTP status is 429.\n * @throws A \"resource unavailable\" error if the response status is 402, 404, or any 5xx.\n * @throws A generic HTTP client error (-32100) for any other 4xx status codes.\n * @throws A \"parse\" error if the response is not valid JSON.\n */\n async request(\n jsonRpcRequest: Readonly> & {\n method: 'eth_getBlockByNumber';\n },\n fetchOptions?: FetchOptions,\n ): Promise | JsonRpcResponse>;\n\n /**\n * Uses the RPC services in the chain to make a request, using each service\n * after the first as a fallback to the previous one as necessary.\n *\n * This overload is designed for all RPC methods except for\n * `eth_getBlockByNumber`, which are expected to return a `result` of the\n * expected `Result`.\n *\n * @param jsonRpcRequest - The JSON-RPC request to send to the endpoint.\n * @param fetchOptions - An options bag for {@link fetch} which further\n * specifies the request.\n * @returns The decoded JSON-RPC response from the endpoint.\n * @throws A 401 error if the response status is 401.\n * @throws A \"rate limiting\" error if the response HTTP status is 429.\n * @throws A \"resource unavailable\" error if the response status is 402, 404, or any 5xx.\n * @throws A generic HTTP client error (-32100) for any other 4xx status codes.\n * @throws A \"parse\" error if the response is not valid JSON.\n */\n async request(\n jsonRpcRequest: Readonly>,\n fetchOptions?: FetchOptions,\n ): Promise>;\n\n async request(\n jsonRpcRequest: Readonly>,\n fetchOptions: FetchOptions = {},\n ): Promise> {\n // Start with the primary (first) service and switch to failovers as the\n // need arises. This is a bit confusing, so keep reading for more on how\n // this works.\n\n let availableServiceIndex: number | undefined;\n let response: JsonRpcResponse | undefined;\n\n for (const [i, service] of this.#services.entries()) {\n log(`Trying service #${i + 1}...`);\n const previousCircuitState = service.getCircuitState();\n\n try {\n // Try making the request through the service.\n response = await service.request(\n jsonRpcRequest,\n fetchOptions,\n );\n log('Service successfully received request.');\n availableServiceIndex = i;\n break;\n } catch (error) {\n // Oops, that didn't work.\n // Capture this error so that we can handle it later.\n\n const { lastError } = service;\n const isCircuitOpen = service.getCircuitState() === CircuitState.Open;\n\n log('Service failed! error =', error, 'lastError = ', lastError);\n\n if (isCircuitOpen) {\n if (i < this.#services.length - 1) {\n log(\n \"This service's circuit is open. Proceeding to next service...\",\n );\n continue;\n }\n\n if (\n previousCircuitState !== CircuitState.Open &&\n this.#status !== STATUSES.Unavailable &&\n lastError !== undefined\n ) {\n // If the service's circuit just broke and it's the last one in the\n // chain, then trigger the onBreak event. (But if for some reason we\n // have already done this, then don't do it.)\n log(\n 'This service\\'s circuit just opened and it is the last service. Updating status to \"unavailable\" and triggering onBreak.',\n );\n this.#status = STATUSES.Unavailable;\n this.#onBreakEventEmitter.emit({\n error: lastError,\n });\n }\n }\n\n // The service failed, and we throw whatever the error is. The calling\n // code can try again if it so desires.\n log(\n `${isCircuitOpen ? '' : \"This service's circuit is closed. \"}Re-throwing error.`,\n );\n throw error;\n }\n }\n\n if (response) {\n // If one of the services is available, reset all of the circuits of the\n // following services. If we didn't do this and the service became\n // unavailable in the future, and any of the failovers' circuits were\n // open (due to previous failures), we would receive a \"circuit broken\"\n // error when we attempted to divert traffic to the failovers again.\n //\n if (availableServiceIndex !== undefined) {\n for (const [i, service] of [...this.#services.entries()].slice(\n availableServiceIndex + 1,\n )) {\n log(`Resetting policy for service #${i + 1}.`);\n service.resetPolicy();\n }\n }\n\n return response;\n }\n\n // The only way we can end up here is if there are no services to loop over.\n // That is not possible due to the types on the constructor, but TypeScript\n // doesn't know this, so we have to appease it.\n throw new Error('Nothing to return');\n }\n}\n"]}