safari: more cleanup and commenting

extension/safari/TabFS/TabFS Extension/SafariWebExtensionHandler.swift

@@ -18,23 +18,34 @@ class SafariWebExtensionHandler: NSObject, NSExtensionRequestHandling {
         guard message["op"] as! String == "safari_did_connect" else { return }
         
         // The XPC service is a subprocess that lives outside the macOS App Sandbox.
+        // (Safari extension native code, including this file, has to live in the sandbox.)
         // It can do forbidden things like spawn tabfs filesystem and set up WebSocket server.
         
+        // We only use one native message to bootstrap the XPC service, then do all communications
+        // to that service (which in turn talks to tabfs.c) over WebSocket instead.
+        // (Safari makes doing native messaging quite painful, so we try to avoid it.
+        // It forces the browser to pop to front if you message Safari in the obvious way,
+        // for instance: https://developer.apple.com/forums/thread/122232
+        // And with the WebSocket, the XPC service can talk straight to background.js, whereas
+        // native messaging would require us here to sit in the middle.)
+
         let connection = NSXPCConnection(serviceName: "com.rsnous.TabFSService")
         connection.remoteObjectInterface = NSXPCInterface(with: TabFSServiceProtocol.self)
         connection.resume()
         
         let service = connection.remoteObjectProxyWithErrorHandler { error in
-            os_log(.default, "Received error:  %{public}@", error as! CVarArg)
+            os_log(.default, "Received error:  %{public}@", error as CVarArg)
         } as? TabFSServiceProtocol
         
-        // need this one XPC call to actually initialize the service
-        service?.upperCaseString("hello XPC") { response in
-            os_log(.default, "Response from XPC service:  %{public}@", response)
+        // Need this one XPC call to actually initialize the service.
+        service?.start() {
+            os_log(.default, "Response from XPC service")
             
             // FIXME: report port back?
             let response = NSExtensionItem()
-            response.userInfo = [ "message": [ "aResponse to": "moop" ] ]
+            response.userInfo = [ "message": "alive" ]
+            // This response (over native messaging) prompts background.js to
+            // connect to the WebSocket server that the XPC service should now be running.
             context.completeRequest(returningItems: [response]) { (what) in
                 print(what)
             }

extension/safari/TabFS/TabFSService/TabFSService.swift

@@ -67,7 +67,7 @@ class TabFSService: NSObject, TabFSServiceProtocol {
                 let context = NWConnection.ContentContext(identifier: "context", metadata: [metaData])
                 conn.send(content: req, contentContext: context, completion: .contentProcessed({ err in
                     if err != nil {
-                        os_log(.default, "req %{public}@ error: %{public}@", String(data: req, encoding: .utf8) as! CVarArg, err!.debugDescription as CVarArg)
+                        os_log(.default, "req %{public}@ error: %{public}@", String(data: req, encoding: .utf8)!, err!.debugDescription as CVarArg)
                         // FIXME: ERROR
                     }
                 }))
@@ -81,6 +81,7 @@ class TabFSService: NSObject, TabFSServiceProtocol {
                         return
                     }
                     
+                    // Send the response back to tabfs.c.
                     self.fsInput.write(withUnsafeBytes(of: UInt32(resp.count)) { Data($0) })
                     self.fsInput.write(resp)
                     read()
@@ -89,15 +90,14 @@ class TabFSService: NSObject, TabFSServiceProtocol {
             read()
         }
         
-        // split new thread
         DispatchQueue.global(qos: .default).async {
             while true {
-                // read from them
+                // Blocking read from the tabfs process.
                 let length = self.fsOutput.readData(ofLength: 4).withUnsafeBytes { $0.load(as: UInt32.self) }
                 let req = self.fsOutput.readData(ofLength: Int(length))
                 
-                // send to other side of WEBSOCKET
                 if let handleRequest = handleRequest {
+                    // Send the request over the WebSocket connection to background.js in browser.
                     handleRequest(req)
                 } else {
                     // FIXME: ERROR
@@ -107,9 +107,9 @@ class TabFSService: NSObject, TabFSServiceProtocol {
         // FIXME: disable auto termination
     }
     
-    func upperCaseString(_ string: String, withReply reply: @escaping (String) -> Void) {
-        let response = string.uppercased()
-        reply(response)
+    func start(withReply reply: @escaping () -> Void) {
+        // This XPC call is enough to just force the XPC service to be started.
+        reply()
     }
 }
 

extension/safari/TabFS/TabFSService/TabFSServiceProtocols.swift

@@ -8,5 +8,5 @@
 import Foundation
 
 @objc public protocol TabFSServiceProtocol {
-    func upperCaseString(_ string: String, withReply reply: @escaping (String) -> Void)
+    func start(withReply reply: @escaping () -> Void)
 }