Supports blocking third-party sources

Blocked sources cannot be added by new users, or updated for existing users.

AltStore/Operations/UpdateKnownSourcesOperation.swift

@@ -0,0 +1,79 @@
+//
+//  UpdateKnownSourcesOperation.swift
+//  AltStore
+//
+//  Created by Riley Testut on 4/13/22.
+//  Copyright © 2022 Riley Testut. All rights reserved.
+//
+
+import Foundation
+
+private extension URL
+{
+    #if STAGING
+    static let sources = URL(string: "https://f000.backblazeb2.com/file/altstore-staging/altstore/sources.json")!
+    #else
+    static let sources = URL(string: "https://cdn.altstore.io/file/altstore/altstore/sources.json")!
+    #endif
+}
+
+extension UpdateKnownSourcesOperation
+{
+    struct Source: Decodable
+    {
+        var identifier: String
+        var sourceURL: URL?
+    }
+    
+    private struct Response: Decodable
+    {
+        var version: Int
+        
+        var trusted: [Source]
+        var blocked: [Source]?
+    }
+}
+
+class UpdateKnownSourcesOperation: ResultOperation<([UpdateKnownSourcesOperation.Source], [UpdateKnownSourcesOperation.Source])>
+{
+    override func main()
+    {
+        super.main()
+        
+        let dataTask = URLSession.shared.dataTask(with: .sources) { (data, response, error) in
+            do
+            {
+                if let response = response as? HTTPURLResponse
+                {
+                    guard response.statusCode != 404 else {
+                        self.finish(.failure(URLError(.fileDoesNotExist, userInfo: [NSURLErrorKey: URL.sources])))
+                        return
+                    }
+                }
+                
+                guard let data = data else { throw error! }
+                
+                let response = try Foundation.JSONDecoder().decode(Response.self, from: data)
+                let sources = (trusted: response.trusted, blocked: response.blocked ?? [])
+                
+                // Cache trusted sources
+                let trustedSourceIDs = Set(sources.trusted.map { $0.identifier })
+                UserDefaults.shared.trustedSourceIDs = trustedSourceIDs
+                
+                // Cache blocked sources
+                let blockedSourceIDs = Set(sources.blocked.map { $0.identifier })
+                let blockedSourceURLs = Set(sources.blocked.compactMap { $0.sourceURL })
+                UserDefaults.shared.blockedSourceIDs = blockedSourceIDs
+                UserDefaults.shared.blockedSourceURLs = blockedSourceURLs
+                
+                self.finish(.success(sources))
+            }
+            catch
+            {
+                self.finish(.failure(error))
+            }
+        }
+        
+        dataTask.resume()
+    }
+}