purchases-ios/Sources/Networking/HTTPClient/NetworkError.swift

//
//  Copyright RevenueCat Inc. All Rights Reserved.
//
//  Licensed under the MIT License (the "License");
//  you may not use this file except in compliance with the License.
//  You may obtain a copy of the License at
//
//      https://opensource.org/licenses/MIT
//
//  NetworkError.swift
//
//  Created by Nacho Soto on 3/31/22.

// swiftlint:disable multiline_parameters

import Foundation

extension Swift.Error {

    /// Foundation does not bridge URL loading errors consistently across Apple platforms: the same
    /// URLSession timeout may arrive as `URLError` on iOS but remain `NSError` on macOS. Normalize to
    /// `NSError` so callers classify the underlying URL error domain and code consistently.
    var isURLRequestTimeout: Bool {
        let error = self as NSError
        return error.domain == NSURLErrorDomain && error.code == NSURLErrorTimedOut
    }

}

/// Represents an error created by `HTTPClient`.
enum NetworkError: Swift.Error, Equatable {

    case decoding(NSError, Source)
    case networkError(NSError, Source)
    case dnsError(failedURL: URL, resolvedHost: String?, Source)
    case unableToCreateRequest(path: String, Source)
    case unexpectedResponse(URLResponse?, Source)
    case errorResponse(ErrorResponse, HTTPStatusCode, Source)
    case signatureVerificationFailed(path: String, HTTPStatusCode, Source)

}

extension NetworkError {

    static func decoding(
        _ error: Error,
        _ data: Data,
        file: String = #fileID, function: String = #function, line: UInt = #line
    ) -> Self {
        // Explicitly logging errors since it might help debugging issues.
        Logger.error(Strings.network.parsing_json_error(error: error))
        Logger.error(Strings.network.json_data_received(
            dataString: String(data: data, encoding: .utf8) ?? ""
        ))

        return .decoding(error as NSError, .init(file: file, function: function, line: line))
    }

    static func networkError(
        _ error: Error,
        file: String = #fileID, function: String = #function, line: UInt = #line
    ) -> Self {
        return .networkError(error as NSError, .init(file: file, function: function, line: line))
    }

    static func dnsError(
        failedURL: URL, resolvedHost: String?,
        file: String = #fileID, function: String = #function, line: UInt = #line
    ) -> Self {
        return .dnsError(failedURL: failedURL, resolvedHost: resolvedHost,
                         .init(file: file, function: function, line: line))
    }

    static func unableToCreateRequest(
        _ path: HTTPRequest.Path,
        file: String = #fileID, function: String = #function, line: UInt = #line
    ) -> Self {
        return .unableToCreateRequest(path: path.relativePath, .init(file: file, function: function, line: line))
    }

    static func unexpectedResponse(
        _ response: URLResponse?,
        file: String = #fileID, function: String = #function, line: UInt = #line
    ) -> Self {
        return .unexpectedResponse(response, .init(file: file, function: function, line: line))
    }

    static func errorResponse(
        _ response: ErrorResponse, _ statusCode: HTTPStatusCode,
        file: String = #fileID, function: String = #function, line: UInt = #line
    ) -> Self {
        return .errorResponse(response, statusCode, .init(file: file, function: function, line: line))
    }

    static func signatureVerificationFailed(
        path: HTTPRequest.Path,
        code: HTTPStatusCode,
        file: String = #fileID, function: String = #function, line: UInt = #line
    ) -> Self {
        return .signatureVerificationFailed(
            path: path.relativePath,
            code,
            .init(file: file, function: function, line: line)
        )
    }

}

extension NetworkError: PurchasesErrorConvertible {

    var asPurchasesError: PurchasesError {
        switch self {
        case let .decoding(error, source):
            return ErrorUtils.unexpectedBackendResponse(
                withSubError: error,
                fileName: source.file,
                functionName: source.function,
                line: source.line
            )

        case let .networkError(error, source)
            where error.domain == NSURLErrorDomain && error.code == NSURLErrorNotConnectedToInternet:
            return ErrorUtils.offlineConnectionError(
                fileName: source.file,
                functionName: source.function,
                line: source.line
            )

        case let .networkError(error, source):
            return ErrorUtils.networkError(
                withUnderlyingError: error,
                fileName: source.file,
                functionName: source.function,
                line: source.line
            )

        case let .dnsError(failedURL, resolvedHost, source):
            return ErrorUtils.networkError(
                message: NetworkStrings.blocked_network(url: failedURL, newHost: resolvedHost).description,
                withUnderlyingError: self,
                fileName: source.file,
                functionName: source.function,
                line: source.line
            )

        case let .unableToCreateRequest(path, source):
            return ErrorUtils.networkError(
                extraUserInfo: [
                    "request_path": path
                ],
                fileName: source.file,
                functionName: source.function,
                line: source.line
            )

        case let .unexpectedResponse(response, source):
            return ErrorUtils.unexpectedBackendResponseError(
                extraUserInfo: [
                    "response": response?.description ?? ""
                ],
                fileName: source.file,
                functionName: source.function,
                line: source.line
            )

        case let .errorResponse(response, statusCode, source):
            return response.asBackendError(with: statusCode,
                                           file: source.file,
                                           function: source.function,
                                           line: source.line)

        case let .signatureVerificationFailed(path, code, source):
            return ErrorUtils.signatureVerificationFailedError(
                path: path,
                code: code,
                fileName: source.file,
                functionName: source.function,
                line: source.line
            )
        }
    }

}

extension NetworkError: DescribableError {

    var description: String {
        switch self {
        case let .decoding(error, _):
            return error.localizedDescription

        case let .networkError(error, _)
            where error.domain == NSURLErrorDomain && error.code == NSURLErrorNotConnectedToInternet:
            return ErrorCode.offlineConnectionError.description

        case let .networkError(error, _):
            return error.localizedDescription

        case let .dnsError(failedURL, resolvedHost, _):
            return NetworkStrings.blocked_network(url: failedURL, newHost: resolvedHost).description

        case let .unableToCreateRequest(path, _):
            return "Could not create request to \(path)"

        case let .unexpectedResponse(response, _):
            return "Unexpected response type: \(response.debugDescription)"

        case .errorResponse:
            return self.asPurchasesError.localizedDescription

        case .signatureVerificationFailed:
            return self.asPurchasesError.localizedDescription
        }
    }

}

extension NetworkError: CustomNSError {

    var errorUserInfo: [String: Any] {
        return [
            NSLocalizedDescriptionKey: self.description
        ]
    }

}

extension NetworkError {

    /// Whether the network request producing this error actually synced the data.
    var successfullySynced: Bool {
        return self.errorStatusCode?.isSuccessfullySynced ?? false
    }

    /// Whether the network request producing this error can be completed.
    /// If `false`, the response was a server error.
    var finishable: Bool {
        if let statusCode = self.errorStatusCode {
            return !statusCode.isServerError
        } else {
            return false
        }
    }

    private var errorStatusCode: HTTPStatusCode? {
        switch self {
        case let .errorResponse(_, statusCode, _):
            return statusCode

        case .decoding,
             .networkError,
             .dnsError,
             .unableToCreateRequest,
             .unexpectedResponse,
             .signatureVerificationFailed:
            return nil
        }
    }

    var isServerDown: Bool {
        return self.errorStatusCode?.isServerError == true
    }

    /// Whether to fall back to the last cached response for this error. A 5xx or a connection-level
    /// failure (no status code) is transient, so serving the last cached copy is appropriate; a 4xx
    /// is the backend authoritatively rejecting the request, so stale data should not be served.
    var shouldFallBackToCache: Bool {
        if let errorStatusCode {
            return errorStatusCode.isServerError
        } else {
            return true
        }
    }

    /// Whether this error is transient and therefore worth retrying: connection-level failures
    /// (no HTTP status code) and `5xx` server responses. `4xx` responses are terminal — the backend
    /// authoritatively rejected the request, so retrying won't yield a different result.
    var isTransient: Bool {
        switch self {
        case .decoding, .unableToCreateRequest, .signatureVerificationFailed:
            return false
        case .dnsError, .networkError, .unexpectedResponse:
            return true
        case let .errorResponse(_, statusCode, _):
            return statusCode.isServerError
        }
    }

    /// Whether this error was caused by the *device* lacking connectivity, as opposed to the host being
    /// unreachable.
    ///
    /// Only device-side `URLError` codes qualify. Host-side or ambiguous failures — `.cannotConnectToHost`,
    /// `.cannotFindHost`, `.dnsLookupFailed`, `.timedOut`, and DNS blocking (``NetworkError/dnsError``) — are
    /// not considered device connectivity errors, since a different host may still succeed.
    var isDeviceConnectivityError: Bool {
        switch self {
        case let .networkError(error, _):
            return error.domain == NSURLErrorDomain
                && Self.deviceConnectivityURLErrorCodes.contains(error.code)
        case .decoding,
             .dnsError,
             .unableToCreateRequest,
             .unexpectedResponse,
             .errorResponse,
             .signatureVerificationFailed:
            return false
        }
    }

    /// `URLError` codes that indicate the device has no working connection to any host.
    private static let deviceConnectivityURLErrorCodes: Set<Int> = [
        NSURLErrorNotConnectedToInternet,
        NSURLErrorNetworkConnectionLost,
        NSURLErrorInternationalRoamingOff,
        NSURLErrorCallIsActive,
        NSURLErrorDataNotAllowed
    ]

    /// A request may be retried against a fallback host only for transient failures (connection-level
    /// errors and 5xx) that point at the host rather than the device. A device-connectivity failure
    /// (see ``NetworkError/isDeviceConnectivityError``) can't be fixed by switching hosts, so it is
    /// excluded. See ``NetworkError/isTransient``.
    var isAllowedToRetryWithFallbackHost: Bool {
        return self.isTransient && !self.isDeviceConnectivityError
    }

}

extension NetworkError {

    typealias Source = ErrorSource

}