[Both] Adds support for installing apps over USB

AltServer/Connections/ClientConnection.swift

@@ -0,0 +1,231 @@
+//
+//  ClientConnection.swift
+//  AltServer
+//
+//  Created by Riley Testut on 1/9/20.
+//  Copyright © 2020 Riley Testut. All rights reserved.
+//
+
+import Foundation
+import Network
+
+import AltKit
+import AltSign
+
+extension ClientConnection
+{
+    enum Connection
+    {
+        case wireless(NWConnection)
+        case wired(WiredConnection)
+    }
+}
+
+class ClientConnection
+{
+    let connection: Connection
+    
+    init(connection: Connection)
+    {
+        self.connection = connection
+    }
+    
+    func disconnect()
+    {
+        switch self.connection
+        {
+        case .wireless(let connection):
+            switch connection.state
+            {
+            case .cancelled, .failed:
+                print("Disconnecting from \(connection.endpoint)...")
+                
+            default:
+                // State update handler might call this method again.
+                connection.cancel()
+            }
+            
+        case .wired(let connection):
+            connection.disconnect()
+        }
+    }
+    
+    func send<T: Encodable>(_ response: T, shouldDisconnect: Bool = false, completionHandler: @escaping (Result<Void, ALTServerError>) -> Void)
+    {
+        func finish(_ result: Result<Void, ALTServerError>)
+        {
+            completionHandler(result)
+            
+            if shouldDisconnect
+            {
+                // Add short delay to prevent us from dropping connection too quickly.
+                DispatchQueue.global().asyncAfter(deadline: .now() + 1.0) {
+                    self.disconnect()
+                }
+            }
+        }
+        
+        do
+        {
+            let data = try JSONEncoder().encode(response)
+            let responseSize = withUnsafeBytes(of: Int32(data.count)) { Data($0) }
+            
+            self.send(responseSize) { (result) in
+                switch result
+                {
+                case .failure: finish(.failure(.init(.lostConnection)))
+                case .success:
+                    
+                    self.send(data) { (result) in
+                        switch result
+                        {
+                        case .failure: finish(.failure(.init(.lostConnection)))
+                        case .success: finish(.success(()))
+                        }
+                    }
+                }
+            }
+        }
+        catch
+        {
+            finish(.failure(.init(.invalidResponse)))
+        }
+    }
+    
+    func receiveRequest(completionHandler: @escaping (Result<ServerRequest, ALTServerError>) -> Void)
+    {
+        let size = MemoryLayout<Int32>.size
+        
+        print("Receiving request size")
+        self.receiveData(expectedBytes: size) { (result) in
+            do
+            {
+                let data = try result.get()
+                
+                print("Receiving request...")
+                let expectedBytes = Int(data.withUnsafeBytes { $0.load(as: Int32.self) })
+                self.receiveData(expectedBytes: expectedBytes) { (result) in
+                    do
+                    {
+                        let data = try result.get()
+                        let request = try JSONDecoder().decode(ServerRequest.self, from: data)
+                        
+                        print("Received installation request:", request)
+                        completionHandler(.success(request))
+                    }
+                    catch
+                    {
+                        completionHandler(.failure(ALTServerError(error)))
+                    }
+                }
+            }
+            catch
+            {
+                completionHandler(.failure(ALTServerError(error)))
+            }
+        }
+    }
+    
+    func send(_ data: Data, completionHandler: @escaping (Result<Void, Error>) -> Void)
+    {
+        switch self.connection
+        {
+        case .wireless(let connection):
+            connection.send(content: data, completion: .contentProcessed { (error) in
+                if let error = error
+                {
+                    completionHandler(.failure(error))
+                }
+                else
+                {
+                    completionHandler(.success(()))
+                }
+            })
+            
+        case .wired(let connection):
+            connection.send(data) { (success, error) in
+                if !success
+                {
+                    completionHandler(.failure(ALTServerError(.lostConnection)))
+                }
+                else
+                {
+                    completionHandler(.success(()))
+                }
+            }
+        }
+    }
+    
+    func receiveData(expectedBytes: Int, completionHandler: @escaping (Result<Data, Error>) -> Void)
+    {
+        func finish(data: Data?, error: Error?)
+        {
+            do
+            {
+                let data = try self.process(data: data, error: error)
+                completionHandler(.success(data))
+            }
+            catch
+            {
+                completionHandler(.failure(ALTServerError(error)))
+            }
+        }
+        
+        switch self.connection
+        {
+        case .wireless(let connection):
+            connection.receive(minimumIncompleteLength: expectedBytes, maximumLength: expectedBytes) { (data, _, _, error) in
+                finish(data: data, error: error)
+            }
+            
+        case .wired(let connection):
+            connection.receiveData(withExpectedSize: expectedBytes) { (data, error) in
+                finish(data: data, error: error)
+            }
+        }
+    }
+}
+
+extension ClientConnection: CustomStringConvertible
+{
+    var description: String {
+        switch self.connection
+        {
+        case .wireless(let connection): return "\(connection.endpoint) (Wireless)"
+        case .wired(let connection): return "\(connection.device.name) (Wired)"
+        }
+    }
+}
+
+private extension ClientConnection
+{
+    func process(data: Data?, error: Error?) throws -> Data
+    {
+        do
+        {
+            do
+            {
+                guard let data = data else { throw error ?? ALTServerError(.unknown) }
+                return data
+            }
+            catch let error as NWError
+            {
+                print("Error receiving data from connection \(connection)", error)
+                
+                throw ALTServerError(.lostConnection)
+            }
+            catch
+            {
+                throw error
+            }
+        }
+        catch let error as ALTServerError
+        {
+            throw error
+        }
+        catch
+        {
+            preconditionFailure("A non-ALTServerError should never be thrown from this method.")
+        }
+    }
+}