[AltDaemon] Replaces local socket communication with XPC

Allows AltDaemon to be launched on demand + reject any connections not made from AltStore.

AltDaemon/XPCConnectionHandler.swift

@@ -0,0 +1,90 @@
+//
+//  XPCConnectionHandler.swift
+//  AltDaemon
+//
+//  Created by Riley Testut on 9/14/20.
+//  Copyright © 2020 Riley Testut. All rights reserved.
+//
+
+import Foundation
+import Security
+
+class XPCConnectionHandler: NSObject, ConnectionHandler
+{
+    var connectionHandler: ((Connection) -> Void)?
+    var disconnectionHandler: ((Connection) -> Void)?
+    
+    private let dispatchQueue = DispatchQueue(label: "io.altstore.XPCConnectionListener", qos: .utility)
+    private let listener = NSXPCListener.makeListener(machServiceName: XPCConnection.machServiceName)
+    
+    deinit
+    {
+        self.stopListening()
+    }
+        
+    func startListening()
+    {
+        self.listener.delegate = self
+        self.listener.resume()
+    }
+    
+    func stopListening()
+    {
+        self.listener.suspend()
+    }
+}
+
+private extension XPCConnectionHandler
+{
+    func disconnect(_ connection: Connection)
+    {
+        connection.disconnect()
+        
+        self.disconnectionHandler?(connection)
+    }
+}
+
+extension XPCConnectionHandler: NSXPCListenerDelegate
+{
+    func listener(_ listener: NSXPCListener, shouldAcceptNewConnection newConnection: NSXPCConnection) -> Bool
+    {
+        let maximumPathLength = 4 * UInt32(MAXPATHLEN)
+        
+        let pathBuffer = UnsafeMutablePointer<CChar>.allocate(capacity: Int(maximumPathLength))
+        defer { pathBuffer.deallocate() }
+        
+        proc_pidpath(newConnection.processIdentifier, pathBuffer, maximumPathLength)
+        
+        let path = String(cString: pathBuffer)
+        let fileURL = URL(fileURLWithPath: path)
+                
+        var code: UnsafeMutableRawPointer?
+        defer { code.map { Unmanaged<AnyObject>.fromOpaque($0).release() } }
+        
+        var status = SecStaticCodeCreateWithPath(fileURL as CFURL, 0, &code)
+        guard status == 0 else { return false }
+        
+        var signingInfo: CFDictionary?
+        defer { signingInfo.map { Unmanaged<AnyObject>.passUnretained($0).release() } }
+        
+        status = SecCodeCopySigningInformation(code, kSecCSInternalInformation | kSecCSSigningInformation, &signingInfo)
+        guard status == 0 else { return false }
+        
+        // Only accept connections from AltStore.
+        guard
+            let codeSigningInfo = signingInfo as? [String: Any],
+            let bundleIdentifier = codeSigningInfo["identifier"] as? String,
+            bundleIdentifier.contains("com.rileytestut.AltStore")
+        else { return false }
+        
+        let connection = XPCConnection(newConnection)
+        newConnection.invalidationHandler = { [weak self, weak connection] in
+            guard let self = self, let connection = connection else { return }
+            self.disconnect(connection)
+        }
+
+        self.connectionHandler?(connection)
+        
+        return true
+    }
+}