[AltServer] Fetches anisette data without Mail plug-in

Works on all macOS versions supported by AltServer.

AltServer/Anisette Data/AnisetteError.swift

@@ -0,0 +1,51 @@
+//
+//  AnisetteError.swift
+//  AltServer
+//
+//  Created by Riley Testut on 9/13/23.
+//  Copyright © 2023 Riley Testut. All rights reserved.
+//
+
+import Foundation
+
+extension AnisetteError
+{
+    enum Code: Int, ALTErrorCode
+    {
+        typealias Error = AnisetteError
+        
+        case aosKitFailure
+        case missingValue
+    }
+    
+    static func aosKitFailure(file: String = #fileID, line: UInt = #line) -> AnisetteError {
+        AnisetteError(code: .aosKitFailure, sourceFile: file, sourceLine: line)
+    }
+    
+    static func missingValue(_ value: String?, file: String = #fileID, line: UInt = #line) -> AnisetteError {
+        AnisetteError(code: .missingValue, value: value, sourceFile: file, sourceLine: line)
+    }
+}
+
+struct AnisetteError: ALTLocalizedError
+{
+    var code: Code
+    var errorTitle: String?
+    var errorFailure: String?
+    
+    @UserInfoValue
+    var value: String?
+    
+    var sourceFile: String?
+    var sourceLine: UInt?
+    
+    var errorFailureReason: String {
+        switch self.code
+        {
+        case .aosKitFailure: return NSLocalizedString("AltServer could not retrieve anisette data from AOSKit.", comment: "")
+        case .missingValue:
+            let valueName = self.value.map { "anisette data value “\($0)”" } ?? NSLocalizedString("anisette data values.", comment: "")
+            return String(format: NSLocalizedString("AltServer could not retrieve %@.", comment: ""), valueName)
+        }
+    }
+}