Looks like Apple audio bug to me. The first version uses older API and it works ok (in that it calls the callback): func startMic1(_ mic: AudioDeviceID) { var desc = AudioComponentDescription(componentType: kAudioUnitType_Output, componentSubType: kAudioUnitSubType_HALOutput, componentManufacturer: kAudioUnitManufacturer_Apple, componentFlags: 0, componentFlagsMask: 0) let comp = AudioComponentFindNext(nil, &desc) var unit: AudioUnit! AudioComponentInstanceNew(comp!, &unit) var enable: UInt32 = 1 AudioUnitSetProperty(unit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Input, 1, &enable, 4) var disable: UInt32 = 0 AudioUnitSetProperty(unit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Output, 0, &disable, 4) var device = mic AudioUnitSetProperty(unit, kAudioOutputUnitProperty_CurrentDevice, kAudioUnitScope_Global, 0, &device, 8) var cb = AURenderCallbackStruct(inputProc: { _, _, _, _, _, _ in fatalError("callback") }, inputProcRefCon: nil) AudioUnitSetProperty(unit, kAudioOutputUnitProperty_SetInputCallback, kAudioUnitScope_Global, 1, &cb, 16) AudioUnitInitialize(unit) AudioOutputUnitStart(unit) } The second version utilises a newer API and doesn't work (doesn't call the callback): func startMic2(_ mic: AudioDeviceID) { let desc = AudioComponentDescription(componentType: kAudioUnitType_Output, componentSubType: kAudioUnitSubType_HALOutput, componentManufacturer: kAudioUnitManufacturer_Apple, componentFlags: 0, componentFlagsMask: 0) let unit = try! AUAudioUnit(componentDescription: desc, options: []) unit.isInputEnabled = true unit.isOutputEnabled = false try! unit.setDeviceID(mic) unit.inputHandler = { _, _, _, _ in fatalError("callback") } try! unit.allocateRenderResources() try! unit.startHardware() } Error handling removed for brevity.

Same issue under iOS. Older API works (calls the callback): func startMic1() { let session = AVAudioSession.sharedInstance() try! session.setCategory(.playAndRecord, mode: .default) try! session.setPreferredSampleRate(44100) try! session.setPreferredInputNumberOfChannels(1) try! session.setPreferredIOBufferDuration(0.1) try! session.setActive(true) var desc = AudioComponentDescription(componentType: kAudioUnitType_Output, componentSubType: kAudioUnitSubType_RemoteIO, componentManufacturer: kAudioUnitManufacturer_Apple, componentFlags: 0, componentFlagsMask: 0) let comp = AudioComponentFindNext(nil, &desc) var unit: AudioUnit! var err = AudioComponentInstanceNew(comp!, &unit) precondition(err == noErr) var enable: UInt32 = 1 err = AudioUnitSetProperty(unit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Input, 1, &enable, 4) precondition(err == noErr) var disable: UInt32 = 0 err = AudioUnitSetProperty(unit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Output, 0, &disable, 4) precondition(err == noErr) var cb = AURenderCallbackStruct(inputProc: { _, _, _, _, _, _ in fatalError("callback") }, inputProcRefCon: nil) err = AudioUnitSetProperty(unit, kAudioOutputUnitProperty_SetInputCallback, kAudioUnitScope_Global, 1, &cb, 16) precondition(err == noErr) err = AudioUnitInitialize(unit) precondition(err == noErr) err = AudioOutputUnitStart(unit) precondition(err == noErr) // from now on the (UI) app continues its normal run loop } Newer API doesn't work (callback is not called): func startMic2() { let session = AVAudioSession.sharedInstance() try! session.setCategory(.playAndRecord, mode: .default) try! session.setPreferredSampleRate(44100) try! session.setPreferredInputNumberOfChannels(1) try! session.setPreferredIOBufferDuration(0.1) try! session.setActive(true) let compDesc = AudioComponentDescription(componentType: kAudioUnitType_Output, componentSubType: kAudioUnitSubType_RemoteIO, componentManufacturer: kAudioUnitManufacturer_Apple, componentFlags: 0, componentFlagsMask: 0) let unit = try! AUAudioUnit(componentDescription: compDesc, options: []) unit.isInputEnabled = true unit.isOutputEnabled = false precondition(unit.canPerformInput) unit.inputHandler = { flags, timeStamp, frameCount, bus in fatalError("never gets here") // now the weird part - this is never called! } try! unit.allocateRenderResources() try! unit.startHardware() // let's go! print("mic should be working now... why it doesn't?") // from now on the (UI) app continues its normal run loop }

Hahaha, found a stupid mistake above, closing the issue.

This is old but let me fill the gap for the benefit of future readers with the same question. the other products definitely use usbmuxd, there's no other way. connecting iPhone to ethernet via a powered adaptor or two looks very odd and not ergonomic for end users. the cables themselves are not quite ergonomic either, if you can use wifi - go for it. cables still have their use, I wish Apple to introduce a supported API or enhance one of existing API's (e.g. Network framework) to support connectivity over USB.

Nice. And if you don't want using ssh from Mac for some reason (e.g. you are paranoid and think that it might work over ssh as part of Apple magic but that doesn't mean it will work with other protocols) you can do the same for the blower part and launch it on mac: class Model: ObservableObject { @Published var text: String = "" private var listenerQ: NWListener? private var browserQ: NWBrowser? func log(_ string: String) { print(string) text.append(string + "\n") } func startBrowser() -> NWBrowser { log("browser will start") let browser = NWBrowser(for: .bonjour(type: "_ssh._tcp", domain: nil), using: .tcp) browser.stateUpdateHandler = { newState in self.log("brower did change state, new: \(newState)") } browser.browseResultsChangedHandler = { results, changes in self.log("brower did change results, new: \(results) \(changes)") } browser.start(queue: .main) return browser } func stopBrowser(browser: NWBrowser) { log("browser will stop") browser.stateUpdateHandler = nil browser.cancel() } func startStopBrowser() { if let browser = browserQ { browserQ = nil stopBrowser(browser: browser) } else { browserQ = startBrowser() } } var isBrowserStarted: Bool { browserQ != nil } var isListenerStarted: Bool { listenerQ != nil } ... } Change the "_ssh._tcp" appropriately and don't forget to change the corresponding string in "Bonjour services" array in the plist of your iOS app. I also used log instead and in addition to bare print so iPhone app can be self contained and show the log without Xcode: struct ContentView: View { @StateObject private var model = Model() var body: some View { VStack(alignment: .leading) { Button(model.isListenerStarted ? "Stop Listener" : "Start Listener") { model.startStopListener() }.padding() Button(model.isBrowserStarted ? "Stop Browser" : "Start Browser") { model.startStopBrowser() }.padding() HStack { Text(model.text) .font(.caption2.monospaced()) Spacer() } Spacer() } .padding() } } IMPORTANT It’s possible that this only works because of developer bits (the Mac having Xcode installed or the iPhone being in Developer Mode). I don’t have time to test this with a non-developer configuration. I encourage you try that for yourself. This is very important indeed unless of course you want to make an app that works just for you or for people who wouldn't mind installing relevant components in case they are important. Just to check if it works in clean environment is somewhat a challenge, you'd either need to enable developer mode on the phone, install the app via Xcode and then disable developer mode, making sure it cleanly disabled all dev bits and pieces, or you'd need to make a TestFlight version of this tester app. Also make sure you do the actual test on the Mac that didn't have Xcode installed. The open questions at this point: does this work in "clean environment" (without developer bits on Mac and/or iPhone)? To be tested. assuming it does (or it is not important to have environment clean), does it still work over USB if I leave wifi / bluetooth enabled? (This feature might unwanted, e.g. for security reasons. Or, equally, it could be desired). assuming working over wifi/bluetooth is undesired for some reason (e.g. security), could we make it stop working when wifi/BT are enabled and I unplugged the USB cable? (in other words set an option to disable all wireless connectivity similar to how it is possible disabling cellular connectivity in URLSession).

Thank you! I guess if I want to drill into those manufacturer fields I'd have to hunt for those specs in many various places. Are you aware of a resource (a web page? json?, open database?) that attempts to summarise some frequently used manufacturerData fields in one place? If I were to do it, I'd probably use json, something like this: [ { "id": "0x0123", // company identifier "specification": "a url pointing to a particular specification", "version: 1.3", "fields": [ { "size": 1, "type": "int", "name": "flags", "description": "Various flags" }, // bytes 0 ..< 1 { "size": 1, "type": "byte", "name": "padding", "description": "-" }, // bytes 1 ..< 2 { "size": 3, "type": "int", "name": "batteryLevel", "description": "Battery level" }, // bytes 2 ..< 5 ] }, { "id": "0x0456", // company identifier ... ] Would I be the first one to do this or is something like this already exist?

Assuming signal propagating in "vacuum" approximation: FSPL = ((4*pi*d*f) / c)^2 // Free-space path loss rssi = txPowerLevel - FSPL rssi0 = txPowerLevel - FSPL0 = 12 - 40 = -28 // rssi at 1 meter distance // pi = 3.14, d = 1, f = 2.4E9, c = 3e8 Is this correct calculation? (given the approximate nature of it of course, plus I'd need to apply some high frequency filter to get rid of noise).

"The interpretation of any other octets within the data shall be defined by the manufacturer specified by the company identifier" Where could I find the spec of Apple's manufacturerData?

Can't you use google drive API directly from the QLExtension?

It's for macOS. In my experience the child process crashes if I enable sandbox in the main app. Minimal test: Test.m #include "Test.h" #import <Cocoa/Cocoa.h> #include <spawn.h> void launchWithFork(void) { pid_t pid = fork(); if (pid == -1) { printf("error %d\n", pid); } else if (pid == 0) { execv("/System/Applications/Preview.app/Contents/MacOS/Preview", nil); exit(0); } else { // parent } } void launchWithSpawn(void) { pid_t pid = 0; int result = posix_spawn(&pid, "/System/Applications/Preview.app/Contents/MacOS/Preview", nil, nil, nil, nil); printf("result: %d\n", result); } void launchWithTask(void) { NSURL* url = [NSURL fileURLWithPath:@"/System/Applications/Preview.app/Contents/MacOS/Preview"]; NSError* error = nil; NSTask* task = [NSTask launchedTaskWithExecutableURL:url arguments:@[] error:&error terminationHandler:nil]; NSLog(@"task %@, error: %@", task, error); } void launchWithWorkspace(void) { NSURL* url = [NSURL fileURLWithPath:@"/System/Applications/Preview.app/Contents/MacOS/Preview"]; NSError* error = nil; NSApplication* app = [NSWorkspace.sharedWorkspace launchApplicationAtURL:url options:0 configuration:@{} error:&error]; NSLog(@"task %@, error: %@", app, error); } Test.h void launchWithFork(void); void launchWithSpawn(void); void launchWithTask(void); void launchWithWorkspace(void); Bridging header #include "Test.h" main.swift launchWithFork() //launchWithSpawn() //launchWithTask() //launchWithWorkspace() RunLoop.current.run(until: .distantFuture) Without app sandbox enabled all launching methods work. With app sandbox enabled only the last method works. (I'm launching Preview.app for a test, in the actual app it will launch a different thing).

The crash in the launched app looks like this: Process: Preview [22445] Path: /System/Applications/Preview.app/Contents/MacOS/Preview ... System Integrity Protection: enabled Crashed Thread: 0 Dispatch queue: com.apple.main-thread Exception Type: EXC_BREAKPOINT (SIGTRAP) Exception Codes: 0x0000000000000001, 0x00000001a554d1c0 Termination Reason: Namespace SIGNAL, Code 5 Trace/BPT trap: 5 Terminating Process: exc handler [22445] Application Specific Signatures: SYSCALL_SET_PROFILE Thread 0 Crashed:: Dispatch queue: com.apple.main-thread 0 libsystem_secinit.dylib 0x1a554d1c0 _libsecinit_appsandbox.cold.5 + 92 1 libsystem_secinit.dylib 0x1a554c3d0 _libsecinit_appsandbox + 1688 2 libsystem_trace.dylib 0x19994d81c _os_activity_initiate_impl + 64 3 libsystem_secinit.dylib 0x1a554bce4 _libsecinit_initializer + 80 4 libSystem.B.dylib 0x1a5562654 libSystem_initializer + 272 5 dyld 0x1998901d8 invocation function for block in dyld4::Loader::findAndRunAllInitializers(dyld4::RuntimeState&) const::$_0::operator()() const + 168 6 dyld 0x1998d1e94 invocation function for block in dyld3::MachOAnalyzer::forEachInitializer(Diagnostics&, dyld3::MachOAnalyzer::VMAddrConverter const&, void (unsigned int) block_pointer, void const*) const + 340 7 dyld 0x1998c51a4 invocation function for block in dyld3::MachOFile::forEachSection(void (dyld3::MachOFile::SectionInfo const&, bool, bool&) block_pointer) const + 528 8 dyld 0x1998702d8 dyld3::MachOFile::forEachLoadCommand(Diagnostics&, void (load_command const*, bool&) block_pointer) const + 296 9 dyld 0x1998c41cc dyld3::MachOFile::forEachSection(void (dyld3::MachOFile::SectionInfo const&, bool, bool&) block_pointer) const + 192 10 dyld 0x1998d1958 dyld3::MachOAnalyzer::forEachInitializer(Diagnostics&, dyld3::MachOAnalyzer::VMAddrConverter const&, void (unsigned int) block_pointer, void const*) const + 516 11 dyld 0x19988c85c dyld4::Loader::findAndRunAllInitializers(dyld4::RuntimeState&) const + 448 12 dyld 0x199895f6c dyld4::PrebuiltLoader::runInitializers(dyld4::RuntimeState&) const + 44 13 dyld 0x1998b07fc dyld4::APIs::runAllInitializersForMain() + 76 14 dyld 0x1998752d0 dyld4::prepare(dyld4::APIs&, dyld3::MachOAnalyzer const*) + 3480 15 dyld 0x199873e18 start + 1964 ...

Very helpful information, thank you. I also found that when I enable App Sandbox there's another thread running. Without app sandbox there's just one thread. Could that affect fork? Crashing example that involves just fork with nothing else: import Cocoa class AppDelegate: NSObject, NSApplicationDelegate { var window: NSWindow? } func app() { let appDelegate = AppDelegate() let application = NSApplication.shared application.delegate = appDelegate print("launch app") let _ = NSApplicationMain(CommandLine.argc, CommandLine.unsafeArgv) print("never here") } // without App Sandbox there's one thread at this point // with App Sandbox there are two threads at this point let pid = forkme() if pid == -1 { fatalError("error") } else if pid == 0 { print("after fork in child") app() print("exiting child") } else { print("after fork in parent") usleep(10_000_000) print("exiting parent") } C helper: pid_t forkme(void) { return fork(); } Partial crash log: System Integrity Protection: enabled Crashed Thread: 0 Dispatch queue: com.apple.main-thread Exception Type: EXC_BREAKPOINT (SIGTRAP) Exception Codes: 0x0000000000000001, 0x000000019984afac Termination Reason: Namespace SIGNAL, Code 5 Trace/BPT trap: 5 Terminating Process: exc handler [47238] Application Specific Information: crashed on child side of fork pre-exec Thread 0 Crashed:: Dispatch queue: com.apple.main-thread 0 libobjc.A.dylib 0x19984afac objc_initializeAfterForkError + 0 1 libobjc.A.dylib 0x199832958 initializeNonMetaClass + 1064 2 libobjc.A.dylib 0x1998325bc initializeNonMetaClass + 140 3 libobjc.A.dylib 0x19984cf14 initializeAndMaybeRelock(objc_class*, objc_object*, locker_mixin<lockdebug::lock_mixin<objc_lock_base_t>>&, bool) + 156 4 libobjc.A.dylib 0x1998321c8 lookUpImpOrForward + 884 5 libobjc.A.dylib 0x199831b64 _objc_msgSend_uncached + 68 6 For 0x104a68b68 app() + 76 (main.swift:43) 7 For 0x104a68488 main + 480 (main.swift:57) 8 dyld 0x199873f28 start + 2236 There's also this debug message in the console: objc[47238]: +[NSResponder initialize] may have been in progress in another thread when fork() was called. exiting parent If I swap what's done in child and what's done in parent: } else if pid == 0 { print("after fork in child") usleep(10_000_000) print("exiting child") } else { print("after fork in parent") app() print("exiting parent") } then it works. So there's something I can and can't do in the child process? What are the rules? In one of the links above you mentioned that fork is fundamentally incompatible with "higher level frameworks"? Does that include, say, XPC? or URLSession? or Network framework? Basically I want to make the old style "treadless" app (understandably the threads created by OS or standard library are probably inevitable): create N sub processes, off-load work to them from the main process and communicate to those processes by some means (I'm considering between pipes, XPC, Network framework and URLSession but I am open to consider a better alternative!).

Your previous post was about the former, but now you’ve pivoted to the latter. That’s fine, but I want to highlight the change. Yep. I was under the impression that fork would be faster than "Process().run" or posix_spawn, and if you are going to run a copy of "itself" it sounded the more "direct" approach. Limit your language and API choice, as described above. From what you told here and in the linked thread it does sound that even when my app is written in C and uses threads it won't be safe using fork (without immediate exec) due to exactly same reasons: some mutexes would stay locked and never unlocked, malloc memory state could be partly damaged at the time of fork. I noticed that at the very beginning of the app written in Swift (in main.swift) I don't see threads created by the system or runtime. (Unless I enable App Sandbox – then I see another thread added, which is not doing much it seems) Do you think in that special case (at least without the sandbox where some secondary thread is created) it's fine using fork (without exec) in the swift app or are there still gotchas to look out for?

This is the current formula I'm using: let n = 2.0 let distance = pow(10, Double(txPowerLevel - 12 - 62 - rssi) / (10 * n)) Here 12 was the txPowerLevel reported from one test device of mine, and -62 was approximate averaged rssi level at 1 meter distance from that test device. Will give this a test in a field to see how well it goes.

No. I mean, it’ll probably work, but it’s relying on implementation details that could change. In a way it feels even safer to fork in pure Swift app's main.swift file so long as this is done as the very first thing. In C++ app globals' constructors could create threads, mutexes, call malloc and whatnot before (and during) the app hitting main(). I encourage you to run a performance test Indeed fork is not faster than posix_spawn, each took about 120 µs in a simple app. (I forked/spawned 1000 processes for accuracy).