// // RetryPolicy.swift // // Copyright (c) 2019-2020 Alamofire Software Foundation (http://alamofire.org/) // // Permission is hereby granted, free of charge, to any person obtaining a copy // of this software and associated documentation files (the "Software"), to deal // in the Software without restriction, including without limitation the rights // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell // copies of the Software, and to permit persons to whom the Software is // furnished to do so, subject to the following conditions: // // The above copyright notice and this permission notice shall be included in // all copies or substantial portions of the Software. // // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN // THE SOFTWARE. // import Foundation /// A retry policy that retries requests using an exponential backoff for allowed HTTP methods and HTTP status codes /// as well as certain types of networking errors. open class RetryPolicy: RequestInterceptor { /// The default retry limit for retry policies. public static let defaultRetryLimit: UInt = 2 /// The default exponential backoff base for retry policies (must be a minimum of 2). public static let defaultExponentialBackoffBase: UInt = 2 /// The default exponential backoff scale for retry policies. public static let defaultExponentialBackoffScale: Double = 0.5 /// The default HTTP methods to retry. /// See [RFC 2616 - Section 9.1.2](https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html) for more information. public static let defaultRetryableHTTPMethods: Set = [.delete, // [Delete](https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.7) - not always idempotent .get, // [GET](https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.3) - generally idempotent .head, // [HEAD](https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.4) - generally idempotent .options, // [OPTIONS](https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.2) - inherently idempotent .put, // [PUT](https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.6) - not always idempotent .trace // [TRACE](https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.8) - inherently idempotent ] /// The default HTTP status codes to retry. /// See [RFC 2616 - Section 10](https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10) for more information. public static let defaultRetryableHTTPStatusCodes: Set = [408, // [Request Timeout](https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.4.9) 500, // [Internal Server Error](https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.5.1) 502, // [Bad Gateway](https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.5.3) 503, // [Service Unavailable](https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.5.4) 504 // [Gateway Timeout](https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.5.5) ] /// The default URL error codes to retry. public static let defaultRetryableURLErrorCodes: Set = [// [Security] App Transport Security disallowed a connection because there is no secure network connection. // - [Disabled] ATS settings do not change at runtime. // .appTransportSecurityRequiresSecureConnection, // [System] An app or app extension attempted to connect to a background session that is already connected to a // process. // - [Enabled] The other process could release the background session. .backgroundSessionInUseByAnotherProcess, // [System] The shared container identifier of the URL session configuration is needed but has not been set. // - [Disabled] Cannot change at runtime. // .backgroundSessionRequiresSharedContainer, // [System] The app is suspended or exits while a background data task is processing. // - [Enabled] App can be foregrounded or launched to recover. .backgroundSessionWasDisconnected, // [Network] The URL Loading system received bad data from the server. // - [Enabled] Server could return valid data when retrying. .badServerResponse, // [Resource] A malformed URL prevented a URL request from being initiated. // - [Disabled] URL was most likely constructed incorrectly. // .badURL, // [System] A connection was attempted while a phone call is active on a network that does not support // simultaneous phone and data communication (EDGE or GPRS). // - [Enabled] Phone call could be ended to allow request to recover. .callIsActive, // [Client] An asynchronous load has been canceled. // - [Disabled] Request was cancelled by the client. // .cancelled, // [File System] A download task couldn’t close the downloaded file on disk. // - [Disabled] File system error is unlikely to recover with retry. // .cannotCloseFile, // [Network] An attempt to connect to a host failed. // - [Enabled] Server or DNS lookup could recover during retry. .cannotConnectToHost, // [File System] A download task couldn’t create the downloaded file on disk because of an I/O failure. // - [Disabled] File system error is unlikely to recover with retry. // .cannotCreateFile, // [Data] Content data received during a connection request had an unknown content encoding. // - [Disabled] Server is unlikely to modify the content encoding during a retry. // .cannotDecodeContentData, // [Data] Content data received during a connection request could not be decoded for a known content encoding. // - [Disabled] Server is unlikely to modify the content encoding during a retry. // .cannotDecodeRawData, // [Network] The host name for a URL could not be resolved. // - [Enabled] Server or DNS lookup could recover during retry. .cannotFindHost, // [Network] A request to load an item only from the cache could not be satisfied. // - [Enabled] Cache could be populated during a retry. .cannotLoadFromNetwork, // [File System] A download task was unable to move a downloaded file on disk. // - [Disabled] File system error is unlikely to recover with retry. // .cannotMoveFile, // [File System] A download task was unable to open the downloaded file on disk. // - [Disabled] File system error is unlikely to recover with retry. // .cannotOpenFile, // [Data] A task could not parse a response. // - [Disabled] Invalid response is unlikely to recover with retry. // .cannotParseResponse, // [File System] A download task was unable to remove a downloaded file from disk. // - [Disabled] File system error is unlikely to recover with retry. // .cannotRemoveFile, // [File System] A download task was unable to write to the downloaded file on disk. // - [Disabled] File system error is unlikely to recover with retry. // .cannotWriteToFile, // [Security] A client certificate was rejected. // - [Disabled] Client certificate is unlikely to change with retry. // .clientCertificateRejected, // [Security] A client certificate was required to authenticate an SSL connection during a request. // - [Disabled] Client certificate is unlikely to be provided with retry. // .clientCertificateRequired, // [Data] The length of the resource data exceeds the maximum allowed. // - [Disabled] Resource will likely still exceed the length maximum on retry. // .dataLengthExceedsMaximum, // [System] The cellular network disallowed a connection. // - [Enabled] WiFi connection could be established during retry. .dataNotAllowed, // [Network] The host address could not be found via DNS lookup. // - [Enabled] DNS lookup could succeed during retry. .dnsLookupFailed, // [Data] A download task failed to decode an encoded file during the download. // - [Enabled] Server could correct the decoding issue with retry. .downloadDecodingFailedMidStream, // [Data] A download task failed to decode an encoded file after downloading. // - [Enabled] Server could correct the decoding issue with retry. .downloadDecodingFailedToComplete, // [File System] A file does not exist. // - [Disabled] File system error is unlikely to recover with retry. // .fileDoesNotExist, // [File System] A request for an FTP file resulted in the server responding that the file is not a plain file, // but a directory. // - [Disabled] FTP directory is not likely to change to a file during a retry. // .fileIsDirectory, // [Network] A redirect loop has been detected or the threshold for number of allowable redirects has been // exceeded (currently 16). // - [Disabled] The redirect loop is unlikely to be resolved within the retry window. // .httpTooManyRedirects, // [System] The attempted connection required activating a data context while roaming, but international roaming // is disabled. // - [Enabled] WiFi connection could be established during retry. .internationalRoamingOff, // [Connectivity] A client or server connection was severed in the middle of an in-progress load. // - [Enabled] A network connection could be established during retry. .networkConnectionLost, // [File System] A resource couldn’t be read because of insufficient permissions. // - [Disabled] Permissions are unlikely to be granted during retry. // .noPermissionsToReadFile, // [Connectivity] A network resource was requested, but an internet connection has not been established and // cannot be established automatically. // - [Enabled] A network connection could be established during retry. .notConnectedToInternet, // [Resource] A redirect was specified by way of server response code, but the server did not accompany this // code with a redirect URL. // - [Disabled] The redirect URL is unlikely to be supplied during a retry. // .redirectToNonExistentLocation, // [Client] A body stream is needed but the client did not provide one. // - [Disabled] The client will be unlikely to supply a body stream during retry. // .requestBodyStreamExhausted, // [Resource] A requested resource couldn’t be retrieved. // - [Disabled] The resource is unlikely to become available during the retry window. // .resourceUnavailable, // [Security] An attempt to establish a secure connection failed for reasons that can’t be expressed more // specifically. // - [Enabled] The secure connection could be established during a retry given the lack of specificity // provided by the error. .secureConnectionFailed, // [Security] A server certificate had a date which indicates it has expired, or is not yet valid. // - [Enabled] The server certificate could become valid within the retry window. .serverCertificateHasBadDate, // [Security] A server certificate was not signed by any root server. // - [Disabled] The server certificate is unlikely to change during the retry window. // .serverCertificateHasUnknownRoot, // [Security] A server certificate is not yet valid. // - [Enabled] The server certificate could become valid within the retry window. .serverCertificateNotYetValid, // [Security] A server certificate was signed by a root server that isn’t trusted. // - [Disabled] The server certificate is unlikely to become trusted within the retry window. // .serverCertificateUntrusted, // [Network] An asynchronous operation timed out. // - [Enabled] The request timed out for an unknown reason and should be retried. .timedOut // [System] The URL Loading System encountered an error that it can’t interpret. // - [Disabled] The error could not be interpreted and is unlikely to be recovered from during a retry. // .unknown, // [Resource] A properly formed URL couldn’t be handled by the framework. // - [Disabled] The URL is unlikely to change during a retry. // .unsupportedURL, // [Client] Authentication is required to access a resource. // - [Disabled] The user authentication is unlikely to be provided by retrying. // .userAuthenticationRequired, // [Client] An asynchronous request for authentication has been canceled by the user. // - [Disabled] The user cancelled authentication and explicitly took action to not retry. // .userCancelledAuthentication, // [Resource] A server reported that a URL has a non-zero content length, but terminated the network connection // gracefully without sending any data. // - [Disabled] The server is unlikely to provide data during the retry window. // .zeroByteResource, ] /// The total number of times the request is allowed to be retried. public let retryLimit: UInt /// The base of the exponential backoff policy (should always be greater than or equal to 2). public let exponentialBackoffBase: UInt /// The scale of the exponential backoff. public let exponentialBackoffScale: Double /// The HTTP methods that are allowed to be retried. public let retryableHTTPMethods: Set /// The HTTP status codes that are automatically retried by the policy. public let retryableHTTPStatusCodes: Set /// The URL error codes that are automatically retried by the policy. public let retryableURLErrorCodes: Set /// Creates an `ExponentialBackoffRetryPolicy` from the specified parameters. /// /// - Parameters: /// - retryLimit: The total number of times the request is allowed to be retried. `2` by default. /// - exponentialBackoffBase: The base of the exponential backoff policy. `2` by default. /// - exponentialBackoffScale: The scale of the exponential backoff. `0.5` by default. /// - retryableHTTPMethods: The HTTP methods that are allowed to be retried. /// `RetryPolicy.defaultRetryableHTTPMethods` by default. /// - retryableHTTPStatusCodes: The HTTP status codes that are automatically retried by the policy. /// `RetryPolicy.defaultRetryableHTTPStatusCodes` by default. /// - retryableURLErrorCodes: The URL error codes that are automatically retried by the policy. /// `RetryPolicy.defaultRetryableURLErrorCodes` by default. public init(retryLimit: UInt = RetryPolicy.defaultRetryLimit, exponentialBackoffBase: UInt = RetryPolicy.defaultExponentialBackoffBase, exponentialBackoffScale: Double = RetryPolicy.defaultExponentialBackoffScale, retryableHTTPMethods: Set = RetryPolicy.defaultRetryableHTTPMethods, retryableHTTPStatusCodes: Set = RetryPolicy.defaultRetryableHTTPStatusCodes, retryableURLErrorCodes: Set = RetryPolicy.defaultRetryableURLErrorCodes) { precondition(exponentialBackoffBase >= 2, "The `exponentialBackoffBase` must be a minimum of 2.") self.retryLimit = retryLimit self.exponentialBackoffBase = exponentialBackoffBase self.exponentialBackoffScale = exponentialBackoffScale self.retryableHTTPMethods = retryableHTTPMethods self.retryableHTTPStatusCodes = retryableHTTPStatusCodes self.retryableURLErrorCodes = retryableURLErrorCodes } open func retry(_ request: Request, for session: Session, dueTo error: Error, completion: @escaping (RetryResult) -> Void) { if request.retryCount < retryLimit, shouldRetry(request: request, dueTo: error) { completion(.retryWithDelay(pow(Double(exponentialBackoffBase), Double(request.retryCount)) * exponentialBackoffScale)) } else { completion(.doNotRetry) } } /// Determines whether or not to retry the provided `Request`. /// /// - Parameters: /// - request: `Request` that failed due to the provided `Error`. /// - error: `Error` encountered while executing the `Request`. /// /// - Returns: `Bool` determining whether or not to retry the `Request`. open func shouldRetry(request: Request, dueTo error: Error) -> Bool { guard let httpMethod = request.request?.method, retryableHTTPMethods.contains(httpMethod) else { return false } if let statusCode = request.response?.statusCode, retryableHTTPStatusCodes.contains(statusCode) { return true } else { let errorCode = (error as? URLError)?.code let afErrorCode = (error.asAFError?.underlyingError as? URLError)?.code guard let code = errorCode ?? afErrorCode else { return false } return retryableURLErrorCodes.contains(code) } } } // MARK: - /// A retry policy that automatically retries idempotent requests for network connection lost errors. For more /// information about retrying network connection lost errors, please refer to Apple's /// [technical document](https://developer.apple.com/library/content/qa/qa1941/_index.html). open class ConnectionLostRetryPolicy: RetryPolicy { /// Creates a `ConnectionLostRetryPolicy` instance from the specified parameters. /// /// - Parameters: /// - retryLimit: The total number of times the request is allowed to be retried. /// `RetryPolicy.defaultRetryLimit` by default. /// - exponentialBackoffBase: The base of the exponential backoff policy. /// `RetryPolicy.defaultExponentialBackoffBase` by default. /// - exponentialBackoffScale: The scale of the exponential backoff. /// `RetryPolicy.defaultExponentialBackoffScale` by default. /// - retryableHTTPMethods: The idempotent http methods to retry. /// `RetryPolicy.defaultRetryableHTTPMethods` by default. public init(retryLimit: UInt = RetryPolicy.defaultRetryLimit, exponentialBackoffBase: UInt = RetryPolicy.defaultExponentialBackoffBase, exponentialBackoffScale: Double = RetryPolicy.defaultExponentialBackoffScale, retryableHTTPMethods: Set = RetryPolicy.defaultRetryableHTTPMethods) { super.init(retryLimit: retryLimit, exponentialBackoffBase: exponentialBackoffBase, exponentialBackoffScale: exponentialBackoffScale, retryableHTTPMethods: retryableHTTPMethods, retryableHTTPStatusCodes: [], retryableURLErrorCodes: [.networkConnectionLost]) } }