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Explore the networking protocols and technologies used by the device to connect to Wi-Fi networks, Bluetooth devices, and cellular data services.

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macOS DNS Proxy system extension makes device stop processing MDM commands until reboot
Hi, I see an interaction issue between a DNS Proxy system extension and MDM on macOS: after some time the device stops processing MDM commands until reboot, while DNS filtering continues to work. Environment: macOS: 15.x / 26.x (reproduced on multiple minor versions) App: /Applications/MyMacProxy.app System extension: NEDNSProxyProvider as system extension Bundle id: com.company.agent.MyMacProxy.dnsProxy Deployment: MDM (SimpleMDM) DNS proxy config via com.apple.dnsProxy.managed Devices: supervised Macs Steps to reproduce: Enrol Mac into MDM. Install MyMacProxy app + DNS proxy system extension via pkg and apply com.apple.dnsProxy.managed profile. DNS proxy starts, DNS is filtered correctly, user network works normally. After some hours, try to manage the device from MDM: push a new configuration profile, remove an existing profile, or install / remove an app. 5.MDM server shows commands as pending / not completed. On the Mac, DNS is still filtered via our DNS proxy, and general network access (Safari etc.) continues to work. After reboot, pending MDM commands are processed and we can remove the app, profile and system extension normally. This is reproducible on our test machines. What I see on the Mac in the “stuck” state apsd is running: sudo launchctl print system/com.apple.apsd # job state = running com.apple.mdmclient.daemon exists as a job but is not running: sudo launchctl print system/com.apple.mdmclient.daemon Abbreviated output: system/com.apple.mdmclient.daemon = { ... state = not running job state = exited runs = 5 last exit code = 0 ... } So the MDM client daemon has exited cleanly (exit code 0) and is currently not running; its APS endpoints are configured. Our DNS proxy system extension is still processing flows: we see continuous logging from our NEDNSProxyProvider, and DNS filtering is clearly active (requests go through our upstream). systemextensionsctl list still shows our DNS proxy system extension as active. From the user’s perspective, everything works (with filtered DNS). From the MDM server’s perspective, commands stay pending until the next reboot. After reboot, MDM behaviour is normal again. Uninstall / cleanup (current approach, simplified) We currently use an MDM‑delivered shell script that: disables our DNS proxy configuration for the console user by editing ~/Library/Preferences/com.apple.networkextension.plist and setting Enabled = false for our DNSProxyConfigurations entries; flushes DNS cache and restarts mDNSResponder; unloads our LaunchDaemon / LaunchAgent for the host app; kills the system extension process using pgrep -f "com.company.agent.MyMacProxy.dnsProxy" | xargs kill -9; removes the extension binary from /Library/SystemExtensions/.../com.company.agent.MyMacProxy.dnsProxy.systemextension; removes /Applications/MyMacProxy.app and related support files. We currently do not call systemextensionsctl uninstall <TEAMID> com.company.agent.MyMacProxy.dnsProxy from MDM, mainly because of SIP and because we understand that fully silent system extension uninstall is constrained. The MDM responsiveness issue, however, can appear even if we don’t run this aggressive uninstall script and just let the extension run for some hours. Questions Is it expected that a DNS Proxy system extension (managed via com.apple.dnsProxy.managed) can leave a device in a state where: apsd is running, com.apple.mdmclient.daemon is not running (last exit code 0), DNS proxy continues to filter traffic, but MDM commands remain pending until reboot? Are there known best practices or pitfalls when combining: DNS Proxy system extensions (NEDNSProxyProvider), MDM‑distributed com.apple.dnsProxy.managed profiles, and MDM app / profile management on recent macOS versions? For uninstall in an MDM environment, what pattern do you recommend? For example, is it better to: disable / remove the DNS proxy profile, stop the NE configuration via NEDNSProxyManager from the app, avoid killing the system extension or removing files from /Library/SystemExtensions immediately, and instead require a reboot for full removal? I can provide a sysdiagnose and unified logs (including nesessionmanager, mdmclient and our logs) from an affected machine if that would be helpful.
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The network expansion process will become a zombie process and the network will be unusable.
Hi, I developed a network extension program on macOS. I tried to update the program by changing the version number. My update process was to first turn off network filtering via "NEFilterManager.sharedManager.enabled = NO", and then use "[OSSystemExtensionRequest activationRequestForExtension:bundleid queue:dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)];" to let the system replace the old network extension program. However, sometimes the old network extension process will become a zombie process like pid=86621 in the figure. As long as the zombie process exists, the network cannot be used. After about 10 minutes, it will be cleared and the network will be available. Restarting Wi-Fi can also clear the zombie process immediately. Why is this? How to avoid this problem?
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119
Jun ’25
Filing a Wi-Fi Bug Report
Every now and again I end up helping a developer with a Wi-Fi issue. These fall into two groups: User-level Wi-Fi issues Development Wi-Fi issues A user-level Wi-Fi issue is one where the developer hasn’t created any of the products involved. An example of this is when you’re developing an app for an accessory and iOS is having problems connecting to that accessory but you don’t control the accessory’s firmware. In general, I recommend that you escalate such issues to the accessory vendor. They can then run their own investigation and, if necessary, file their own bug report. A development Wi-Fi issue is one that directly affects one of your products. For example, you’re developing a Wi-Fi accessory and iOS is having problems connecting to it. In that case, the onus is on you [1] to investigate why things are failing. If your conclusion is that iOS is behaving incorrectly, file a bug about that. IMPORTANT If you do file a bug in the context of some forums thread, please post your bug number to the thread, just for the record. When filing this sort of bug report it’s important to provide: Solid evidence that the problem is on the Apple side of the fence Enough information for Apple’s engineers to investigate it effectively Let’s start with that second point. If you can reproduce the problem reliably, install the Wi-Fi debug profile on your device, reproduce the problem, noting down a rough timestamp, and include the resulting logs and that timestamp in your bug report. Also, consider attaching a packet trace. There are three options here: Record a packet trace from the perspective of the Apple device. On iOS, use an RVI packet trace for this. Record a packet trace from the perspective of your accessory. Record a Wi-Fi level packet trace. You can do this from your Mac (see Recording a Wi-Fi Packet Trace) but it might be easier to do this with the infrastructure you used during the bring up of your accessory. It’s fine to include all three (-: Also include any relevant context about the issue. For example: If the issue is tied to a specific device model (In that case, it’d be good to include the above information for both the successful and failing cases.) If the problem shows up when joining from Settings > Wi-Fi, or whether it’s tied to a specific API, like NEHotspotConfigurationManager Finally, make sure to include an explanation of why you think this is an Apple bug, referencing specific items in the logs and packet traces that you attached. Of course, it’s only possible to do all of this if you can reproduce the problem. Investigating an intermittent issue based on reports coming in from users is much harder. It’s OK to file a bug about such issues, but your bug might not be actionable. At a minimum you should aim to include a sysdiagnose log with your bug. IMPORTANT This log has to be taken shortly after reproducing the problem. Don’t just attach any old log. One option is to request such a log from your users. I talk more about this in Using a Sysdiagnose Log to Debug a Hard-to-Reproduce Problem. You can also ask your users to file their own bugs using the Feedback Assistant app. It should automatically capture and attach a sysdiagnose log. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" [1] Well, your organisation. It’s rare to find a team where the same engineer works on both the iOS app and the accessory firmware. But if that’s you, good job!
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NSURLSession’s Resume Rate Limiter
IMPORTANT The resume rate limiter is now covered by the official documentation. See Use background sessions efficiently within Downloading files in the background. So, the following is here purely for historical perspective. NSURLSession’s background session support on iOS includes a resume rate limiter. This limiter exists to prevent apps from abusing the background session support in order to run continuously in the background. It works as follows: nsurlsessiond (the daemon that does all the background session work) maintains a delay value for your app. It doubles that delay every time it resumes (or relaunches) your app. It resets that delay to 0 when the user brings your app to the front. It also resets the delay to 0 if the delay period elapses without it having resumed your app. When your app creates a new task while it is in the background, the task does not start until that delay has expired. To understand the impact of this, consider what happens when you download 10 resources. If you pass them to the background session all at once, you see something like this: Your app creates tasks 1 through 10 in the background session. nsurlsessiond starts working on the first few tasks. As tasks complete, nsurlsessiond starts working on subsequent ones. Eventually all the tasks complete and nsurlsessiond resumes your app. Now consider what happens if you only schedule one task at a time: Your app creates task 1. nsurlsessiond starts working on it. When it completes, nsurlsessiond resumes your app. Your app creates task 2. nsurlsessiond delays the start of task 2 a little bit. nsurlsessiond starts working on task 2. When it completes, nsurlsessiond resumes your app. Your app creates task 3. nsurlsessiond delays the start of task 3 by double the previous amount. nsurlsessiond starts working on task 3. When it completes, nsurlsessiond resumes your app. Steps 8 through 11 repeat, and each time the delay doubles. Eventually the delay gets so large that it looks like your app has stopped making progress. If you have a lot of tasks to run then you can mitigate this problem by starting tasks in batches. That is, rather than start just one task in step 1, you would start 100. This only helps up to a point. If you have thousands of tasks to run, you will eventually start seeing serious delays. In that case it’s much better to change your design to use fewer, larger transfers. Note All of the above applies to iOS 8 and later. Things worked differently in iOS 7. There’s a post on DevForums that explains the older approach. Finally, keep in mind that there may be other reasons for your task not starting. Specifically, if the task is flagged as discretionary (because you set the discretionary flag when creating the task’s session or because the task was started while your app was in the background), the task may be delayed for other reasons (low power, lack of Wi-Fi, and so on). Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" (r. 22323366)
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14k
Jul ’25
iOS Resumable Uploads Troubles
I am referencing: https://developer.apple.com/documentation/foundation/pausing-and-resuming-uploads Specifically: You can’t resume all uploads. The server must support the latest resumable upload protocol draft from the HTTP Working Group at the IETF. Also, uploads that use a background configuration handle resumption automatically, so manual resuming is only needed for non-background uploads. I have control over both the app and the server, and can't seem to get it to work automatically with a background url session. In other words, making multiple requests to get the offset then upload, easy but I am trying to leverage this background configuration resume OS magic. So anyone know what spec version does the server/client need to implement? The docs reference version 3, however the standard is now at like 11. Of course, I am trying out 3. Does anyone know how exactly this resume is implemented in iOS, and what exactly it takes care of? I assumed that I can just POST to a generic end point, say /files, then the OS receives a 104 Location, and saves that. If the upload is interrupted, when the OS resumes the upload, it has enough information to figure out how to resume from the exact offset, either by making a HEAD request to get the offset, or handle a 409. I am assuming it does this, as if it doesn't, the 'uploads that use a background configuration handle resumption automatically' is useless, if it just restarts from 0. Note, of course making individual POST/HEAD/PATCH requests manually works, but at that point I'm not really leveraging any OS auto-magic, and am just consuming an API that could really implement any spec. This won't work in the background, as the OS seems to disallow random HTTP requests when it wakes the app for URLSession background resumes. As of right now, I have it 'partially' working, insofar as the app does receive the 104 didReceiveInformationalResponse url delegate call, however it seems to then hang; it stops sending bytes, seemingly when the 104 is received. However, the request does not complete. In other words, it doesn't seem to receive a client timeout or otherwise indicate the request has finished. Right now, I am starting a single request, POSTing to a /files end point, i.e. I am not getting the location first, then PATCHing to that, as if I do that, the OS 'automatic' resuming fails with a 409, i.e. it doesn't seem to make a HEAD request and/or use the 409 offset correction then continue with the PATCH. Any idea what could be going on?
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129
Mar ’26
iOS UDP Multicast: Receiving works but sending silently fails
Hi everyone, I’m working with UDP Multicasting on iOS (iOS 15+) using Network.framework and facing a confusing issue. Setup: Multicast IP: 239.255.0.1 Port: 45454 Using NWConnectionGroup / NWMulticastGroup NSLocalNetworkUsageDescription is present in Info.plist Devices are on the same Wi-Fi network Problem: Receiving multicast packets works perfectly Sending multicast packets does NOT work No errors are thrown send() completion handler reports success stateUpdateHandler sometimes doesn’t transition to .ready No packets are actually transmitted on the network Observations: The app can receive data from other multicast senders Sending appears to be silently blocked Reinstalling the app fixes the issue This points to a Local Network permission problem If permission was denied once, iOS does not re-prompt Inbound multicast works, outbound multicast is blocked Questions: Is it expected on iOS that receiving multicast works even when sending is blocked? Is reinstalling the app the only way to recover if Local Network permission was denied? Is there any reliable runtime way to detect that outbound multicast is blocked? Is NWConnectionGroup the correct and only supported way to send multicast on iOS? Any clarification or official guidance would really help. Thanks in advance!
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138
Feb ’26
Reproducible EXC_BAD_ACCESS in NEDNSProxyProvider when using async/await variants of NEAppProxyUDPFlow
Description I am seeing a consistent crash in a NEDNSProxyProvider on iOS when migrating from completion handlers to the new Swift Concurrency async/await variants of readDatagrams() and writeDatagrams() on NEAppProxyUDPFlow. The crash occurs inside the Swift Concurrency runtime during task resumption. Specifically, it seems the Task attempts to return to the flow’s internal serial executor (NEFlow queue) after a suspension point, but fails if the flow was invalidated or deallocated by the kernel while the task was suspended. Error Signature Thread 4: EXC_BAD_ACCESS (code=1, address=0x28) Thread 4 Queue : NEFlow queue (serial) #0 0x000000018fe919cc in swift::AsyncTask::flagAsAndEnqueueOnExecutor () #9 0x00000001ee25c3b8 in _pthread_wqthread () Steps The crash is highly timing-dependent. To reproduce it reliably: Use an iOS device with Developer Settings enabled. Go to Developer > Network Link Conditioner -> High Latency DNS. Intercept a DNS query and perform a DoH (DNS-over-HTTPS) request using URLSession. The first few network requests should trigger the crash Minimum Working Example (MWE) class DNSProxyProvider: NEDNSProxyProvider { override func handleNewFlow(_ flow: NEAppProxyFlow) -> Bool { guard let udpFlow = flow as? NEAppProxyUDPFlow else { return false } Task(priority: .userInitiated) { await handleUDPFlow(udpFlow) } return true } func handleUDPFlow(_ flow: NEAppProxyUDPFlow) async { do { try await flow.open(withLocalFlowEndpoint: nil) while !Task.isCancelled { // Suspension point 1: Waiting for datagrams let (flowData, error) = await flow.readDatagrams() if let error { throw error } guard let flowData, !flowData.isEmpty else { return } var responses: [(Data, Network.NWEndpoint)] = [] for (data, endpoint) in flowData { // Suspension point 2: External DoH resolution let response = try await resolveViaDoH(data) responses.append((response, endpoint)) } // Suspension point 3: Writing back to the flow // Extension will crash here on task resumption try await flow.writeDatagrams(responses) } } catch { flow.closeReadWithError(error) flow.closeWriteWithError(error) } } private func handleFlowData(_ packet: Data, endpoint: Network.NWEndpoint, using parameters: NWParameters) async throws -> Data { let url = URL(string: "https://dns.google/dns-query")! var request = URLRequest(url: url) request.httpMethod = "POST" request.httpBody = packet request.setValue("application/dns-message", forHTTPHeaderField: "Content-Type") let (data, _) = try await URLSession.shared.data(for: request) return data } } Crash Details & Analysis The disassembly at the crash point indicates a null dereference of an internal executor pointer (Voucher context): ldr x20, [TPIDRRO_EL0 + 0x340] ldr x0, [x20, #0x28] // x20 is NULL/0x0 here, resulting in address 0x28 It appears that NEAppProxyUDPFlow’s async methods bind the Task to a specific internal executor. When the kernel reclaims the flow memory, the pointer in x20 becomes invalid. Because the Swift runtime is unaware that the NEFlow queue executor has vanished, it attempts to resume on non-existing flow and then crashes. Checking !Task.isCancelled does not prevent this, as the crash happens during the transition into the task body before the cancellation check can even run. Questions Is this a known issue of the NetworkExtension async bridge? Why does Task.isCancelled not reflect the deallocation of the underlying NEAppProxyFlow? Is the only safe workaround? Please feel free to correct me if I misunderstood anything here. I'll be happy to hear any insights or suggestions :) Thank you!
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359
Feb ’26
How to detect the SIM card status?
Before iOS16, we can use https://developer.apple.com/documentation/coretelephony/ctcarrier But after iOS this is deprecated and has no replacement. There are some discussions on it, eg. https://developer.apple.com/forums/thread/714876 https://developer.apple.com/forums/thread/770400 Now I asked AI, then it provided this solution, to check the serviceCurrentRadioAccessTechnology, so it this ok to check the SIM card status? var hasSIMCard = false let info = CTTelephonyNetworkInfo() if let rat = info.serviceCurrentRadioAccessTechnology, rat.values.contains(where: { !$0.isEmpty }) { hasSIMCard = true. // has RAT } BTW, I can see a lot of changes in the Core Telephony framework. https://developer.apple.com/documentation/coretelephony 1.isSIMInserted https://developer.apple.com/documentation/coretelephony/ctsubscriber/issiminserted A Boolean property that indicates whether a SIM is present. iOS 18.0+ iPadOS 18.0+ This value property is true if the system finds a SIM matching the Info.plist carrier information (MCC / MNC / GID1 / GID2). Is this ok to check SIM insert status, this seems must preconfig some info in the info.plist. 2.iOS26 provide CTCellularPlanStatus https://developer.apple.com/documentation/coretelephony/ctcellularplanstatus Can I use this to check SIM status?
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Jun ’25
On FTP
Questions about FTP crop up from time-to-time here on DevForums. In most cases I write a general “don’t use FTP” response, but I don’t have time to go into all the details. I’ve created this post as a place to collect all of those details, so I can reference them in other threads. IMPORTANT Apple’s official position on FTP is: All our FTP APIs have been deprecated, and you should avoid using deprecated APIs. Apple has been slowly removing FTP support from the user-facing parts of our system. The most recent example of this is that we removed the ftp command-line tool in macOS 10.13. You should avoid the FTP protocol and look to adopt more modern alternatives. The rest of this post is an informational explanation of the overall FTP picture. This post is locked so I can keep it focused. If you have questions or comments, please do create a new thread in the App & System Services > Networking subtopic and I’ll respond there. Don’t Use FTP FTP is a very old and very crufty protocol. Certain things that seem obvious to us now — like being able to create a GUI client that reliably shows a directory listing in a platform-independent manner — aren’t possible to do in FTP. However, by far the biggest problem with FTP is that it provides no security [1]. Specifically, the FTP protocol: Provides no on-the-wire privacy, so anyone can see the data you transfer Provides no client-authenticates-server authentication, so you have no idea whether you’re talking to the right server Provides no data integrity, allowing an attacker to munge your data in transit Transfers user names and passwords in the clear Using FTP for anonymous downloads may be acceptable (see the explanation below) but most other uses of FTP are completely inappropriate for the modern Internet. IMPORTANT You should only use FTP for anonymous downloads if you have an independent way to check the integrity of the data you’ve downloaded. For example, if you’re downloading a software update, you could use code signing to check its integrity. If you don’t check the integrity of the data you’ve downloaded, an attacker could substitute a malicious download instead. This would be especially bad in, say, the software update case. These fundamental problems with the FTP protocol mean that it’s not a priority for Apple. This is reflected in the available APIs, which is the subject of the next section. FTP APIs Apple provides two FTP APIs: All Apple platforms provide FTP downloads via URLSession. Most Apple platforms (everything except watchOS) support CFFTPStream, which allows for directory listings, downloads, uploads, and directory creation. All of these FTP APIs are now deprecated: URLSession was deprecated for the purposes of FTP in the 2022 SDKs (macOS 13, iOS 16, iPadOS 16, tvOS 16, watchOS 9) [2]. CFFTPStream was deprecated in the 2016 SDKs (macOS 10.11, iOS 9, iPadOS 9, tvOS 9). CFFTPStream still works about as well as it ever did, which is not particularly well. Specifically: There is at least one known crashing bug (r. 35745763), albeit one that occurs quite infrequently. There are clear implementation limitations — like the fact that CFFTPCreateParsedResourceListing assumes a MacRoman text encoding (r. 7420589) — that won’t be fixed. If you’re looking for an example of how to use these APIs, check out SimpleFTPSample. Note This sample hasn’t been updated since 2013 and is unlikely to ever be updated given Apple’s position on FTP. The FTP support in URLSession has significant limitations: It only supports FTP downloads; there’s no support for uploads or any other FTP operations. It doesn’t support resumable FTP downloads [3]. It doesn’t work in background sessions. That prevents it from running FTP downloads in the background on iOS. It’s only supported in classic loading mode. See the usesClassicLoadingMode property and the doc comments in <Foundation/NSURLSession.h>. If Apple’s FTP APIs are insufficient for your needs, you’ll need to write or acquire your own FTP library. Before you do that, however, consider switching to an alternative protocol. After all, if you’re going to go to the trouble of importing a large FTP library into your code base, you might as well import a library for a better protocol. The next section discusses some options in this space. Alternative Protocols There are numerous better alternatives to FTP: HTTPS is by far the best alternative to FTP, offering good security, good APIs on Apple platforms, good server support, and good network compatibility. Implementing traditional FTP operations over HTTPS can be a bit tricky. One possible way forward is to enable DAV extensions on the server. FTPS is FTP over TLS (aka SSL). While FTPS adds security to the protocol, which is very important, it still inherits many of FTP’s other problems. Personally I try to avoid this protocol. SFTP is a file transfer protocol that’s completely unrelated to FTP. It runs over SSH, making it a great alternative in many of the ad hoc setups that traditionally use FTP. Apple doesn’t have an API for either FTPS or SFTP, although on macOS you may be able to make some headway by invoking the sftp command-line tool. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" [1] In another thread someone asked me about FTP’s other problems, those not related to security, so let’s talk about that. One of FTP’s implicit design goals was to provide cross-platform support that exposes the target platform. You can think of FTP as being kinda like telnet. When you telnet from Unix to VMS, it doesn’t aim to abstract away VMS commands, so that you can type Unix commands at the VMS prompt. Rather, you’re expected to run VMS commands. FTP is (a bit) like that. This choice made sense back when the FTP protocol was invented. Folks were expecting to use FTP via a command-line client, so there was a human in the loop. If they ran a command and it produced VMS-like output, that was fine because they knew that they were FTPing into a VMS machine. However, most users today are using GUI clients, and this design choice makes it very hard to create a general GUI client for FTP. Let’s consider the simple problem of getting the contents of a directory. When you send an FTP LIST command, the server would historically run the platform native directory list command and pipe the results back to you. To create a GUI client you have to parse that data to extract the file names. Doing that is a serious challenge. Indeed, just the first step, working out the text encoding, is a challenge. Many FTP servers use UTF-8, but some use ISO-Latin-1, some use other standard encodings, some use Windows code pages, and so on. I say “historically” above because there have been various efforts to standardise this stuff, both in the RFCs and in individual server implementations. However, if you’re building a general client you can’t rely on these efforts. After all, the reason why folks continue to use FTP is because of it widespread support. [2] To quote the macOS 13 Ventura Release Notes: FTP is deprecated for URLSession and related APIs. Please adopt modern secure networking protocols such as HTTPS. (92623659) [3] Although you can implement resumable downloads using the lower-level CFFTPStream API, courtesy of the kCFStreamPropertyFTPFileTransferOffset property. Revision History 2025-10-06 Explained that URLSession only supports FTP in classic loading mode. Made other minor editorial changes. 2024-04-15 Added a footnote about FTP’s other problems. Made other minor editorial changes. 2022-08-09 Noted that the FTP support in URLSession is now deprecated. Made other minor editorial changes. 2021-04-06 Fixed the formatting. Fixed some links. 2018-02-23 First posted.
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5.8k
Oct ’25
Real-Time WatchConnectivity Sync Not Working Between iPhone and Apple Watch
Hi everyone, I'm building a health-focused iOS and watchOS app that uses WatchConnectivity to sync real-time heart rate and core body temperature data from iPhone to Apple Watch. While the HealthKit integration works correctly on the iPhone side, I'm facing persistent issues with WatchConnectivity — the data either doesn't arrive on the Watch, or session(_:didReceiveMessage:) never gets triggered. Here's the setup: On iPhone: Using WCSession.default.sendMessage(_:replyHandler:errorHandler:) to send real-time values every few seconds. On Apple Watch: Implemented WCSessionDelegate, and session(_:didReceiveMessage:) is supposed to update the UI. Both apps have WCSession.isSupported() checks, activate the session, and assign delegates correctly. The session state shows isPaired = true and isWatchAppInstalled = true. Bluetooth and Wi-Fi are on, both devices are unlocked and nearby. Despite all this, the Watch never receives messages in real-time. Sometimes, data comes through in bulk much later or not at all. I've double-checked Info.plist configurations and made sure background modes include "Uses Bluetooth LE accessories" and "Background fetch" where appropriate. I would really appreciate guidance on: Best practices for reliable, low-latency message delivery with WatchConnectivity. Debugging steps or sample code to validate message transmission and reception. Any pitfalls related to UI updates from the delegate method. Happy to share further details. Thanks in advance!
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370
Jun ’25
WiFi Aware connection cannot be established when both peers publish and subscribe
It works when one device is only a publisher and the other is only a subscriber. However, when both devices act as both publisher and subscriber simultaneously—which Apple’s documentation (https://developer.apple.com/documentation/wifiaware/adopting-wi-fi-aware#Declare-services) indicates is valid—the connection never establishes. After timing out, both NetworkListener and NetworkBrowser transition to the failed state. This appears to be a race condition in Network framework. Task.detached { try await NetworkListener( for: .wifiAware( .connecting( to: .myService, from: .allPairedDevices, datapath: .defaults ) ), using: .parameters { Coder( sending: ..., receiving: ..., using: NetworkJSONCoder() ) { TCP() } } ).run { connection in await self.add(connection: connection) } } Task.detached { try await NetworkBrowser( for: .wifiAware( .connecting( to: .allPairedDevices, from: .myService ) ), using: .tcp ).run { endpoints in for endpoint in endpoints { await self.connect(to: endpoint) } } }
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126
Jan ’26
Local network request blocked in Safari but working in Chrome
For Local network access, Chrome prompts the user to allow access and adds it to Settings --> Privacy & Security --> Local Network. However, for Safari, no prompt appears. How do I force Safari to authorise these local network access requests if it won't trigger the permission dialogue? Is there a specific WKWebView configuration or Safari-specific header required to satisfy this security check?
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507
Jan ’26
How to stop or disable Network Extension without removing
I develop a Network Extension with NEFilterDataProvider and want to understand how to stop or disable it on exit of the base app without deactivating NE from OS and leave ability to start it again without requiring a password from the user. It starts normally, but when I try to disable it: NEFilterManager.sharedManager.enabled = NO; [NEFilterManager.sharedManager saveToPreferencesWithCompletionHandler:^(NSError * _Nullable error) { // never called }]; the completion handler has never called. But stopFilterWithReason inside the NE code called by the framework where I only replay with required completionHandler();. Then NE process keeps alive. I also tried to call remove, which should disable NE: [NEFilterManager.sharedManager removeFromPreferencesWithCompletionHandler:^(NSError * _Nullable error) { // never called }]; with same result - I freeze forever on waiting completion handler. So what is the correct way to disable NE without explicit deactivation it by [OSSystemExtensionRequest deactivationRequestForExtension:...]?
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89
Nov ’25
DNS updates and Apple Private Relay - major issue
After dropping an A-record TTL to 60 secs (it was previously no higher than 600 secs for several weeks) and making an IP change for a small business website on Monday, I took down the old web service just over 24 hours later on Tuesday evening. We then had reports of some customers not being able to access the website on Wednesday morning. On investigation using my iPhone it would appear that Apple Private Relay is still directing clients to the old IP address. It's just as well I have iCloud+ as I would never have seen this issue otherwise and would have been none the wiser as to why some customers were having problems. Has anyone else seen this and/or have a fix other than waiting longer? Do you know how long it takes for Apple Private Relay to update? This isn't expected behaviour of DNS? I spoke to someone at Apple yesterday and there wasn't much they can do. I hope they're escalating internally as almost 3 days later it's still pointing users to the old IP address despite having ample time for proper DNS propagation.
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186
Nov ’25
NEAppPushProvider lifecycle guarantees for safety-critical local networking
We have an iOS companion app that talks to our IoT device over the device’s own Wi‑Fi network (often with no internet). The app performs bi-directional, safety-critical duties over that link. We use an NEAppPushProvider extension so the handset can keep exchanging data while the UI is backgrounded. During testing we noticed that if the user backgrounds the app (still connected to the device’s Wi‑Fi) and opens Safari, the extension’s stop is invoked with NEProviderStopReason.unrecoverableNetworkChange / noNetworkAvailable, and iOS tears the extension down. Until the system restarts the extension (e.g. the user foregrounds our app again), the app cannot send/receive its safety-critical data. Questions: Is there a supported way to stop a safety-critical NEAppPushProvider from being terminated in this “background app → open Safari” scenario when the device remains on the same Wi‑Fi network (possibly without internet)? If not, is NEAppPushProvider the correct extension type for an always-on local-network use case like this, or is there another API we should be using? For safety-critical applications, can Apple grant entitlements/exemptions so the system does not terminate the extension when the user switches apps but stays on the local Wi‑Fi? Any guidance on the expected lifecycle or alternative patterns for safety-critical local connectivity would be greatly appreciated.
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Nov ’25
DeviceDiscoveryUI's UIViewControllers are available for Wi-Fi Aware?
HI, I am currently developing an app that utilizes Wi-Fi Aware. According to the Wi-Fi Aware framework examples and the WWDC25 session on Wi-Fi Aware, discovery is handled using DevicePairingView and DevicePicker from the DeviceDiscoveryUI module. However, these SwiftUI views present their connection UI modally when tapped. My app's design requires the ability to control the presentation of this UI programmatically, rather than relying on a user tap. While inspecting the DeviceDiscoveryUI module, I found DDDevicePairingViewController and DDDevicePickerViewController, which appear to be the UIViewController counterparts to the SwiftUI views. The initializer for DDDevicePairingViewController accepts a ListenerProvider, so it seems I can pass the same ListenerProvider instance that is used with the DevicePairingView. However, the initializer for DDDevicePickerViewController requires an NWBrowser.Descriptor, which seems incompatible with the parameters used for the SwiftUI DevicePicker. I have two main questions: (1) Can DDDevicePairingViewController and DDDevicePickerViewController be officially used for Wi-Fi Aware pairing? (2) Are there any plans to provide more customization or programmatic control over the DevicePairingView and DevicePicker (for example, allowing us to trigger their modal presentation programmatically)? Thank you.
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Nov ’25
URLSession.dataTask(with: URL) error: Type of expression is ambiguous without a type annotation
I'm a long-time developer, but pretty new to Swift. I'm trying to get information from a web service (and found code online that I adjusted to build the function below). (Note: AAA_Result -- referenced towards the end -- is another class in my project) Trouble is, I'm getting the subject error on the call to session.dataTask. Any help/suggestions/doc pointers will be greatly appreciated!!! var result: Bool = false var cancellable: AnyCancellable? self.name = name let params = "json={\"\"}}" // removed json details let base_url = URL(string: "https://aaa.yyy.com?params=\(params)&format=json")! // removed URL specifics do { let task = URLSession.shared.dataTask(with: base_url) { data, response, error in if let error = error { print("Error: \(error)") } guard let response = response as? HTTPURLResponse, (200...299).contains(response.statusCode) else { print("Error \(String(describing: response))") } do { let decoder = JSONDecoder() let ar = try decoder.decode(AAA_Result.self, from: response.value) // removed specific details... result = true } catch { print(error) } } task.resume() } catch { print(error) } return result }
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May ’25
macOS DNS Proxy system extension makes device stop processing MDM commands until reboot
Hi, I see an interaction issue between a DNS Proxy system extension and MDM on macOS: after some time the device stops processing MDM commands until reboot, while DNS filtering continues to work. Environment: macOS: 15.x / 26.x (reproduced on multiple minor versions) App: /Applications/MyMacProxy.app System extension: NEDNSProxyProvider as system extension Bundle id: com.company.agent.MyMacProxy.dnsProxy Deployment: MDM (SimpleMDM) DNS proxy config via com.apple.dnsProxy.managed Devices: supervised Macs Steps to reproduce: Enrol Mac into MDM. Install MyMacProxy app + DNS proxy system extension via pkg and apply com.apple.dnsProxy.managed profile. DNS proxy starts, DNS is filtered correctly, user network works normally. After some hours, try to manage the device from MDM: push a new configuration profile, remove an existing profile, or install / remove an app. 5.MDM server shows commands as pending / not completed. On the Mac, DNS is still filtered via our DNS proxy, and general network access (Safari etc.) continues to work. After reboot, pending MDM commands are processed and we can remove the app, profile and system extension normally. This is reproducible on our test machines. What I see on the Mac in the “stuck” state apsd is running: sudo launchctl print system/com.apple.apsd # job state = running com.apple.mdmclient.daemon exists as a job but is not running: sudo launchctl print system/com.apple.mdmclient.daemon Abbreviated output: system/com.apple.mdmclient.daemon = { ... state = not running job state = exited runs = 5 last exit code = 0 ... } So the MDM client daemon has exited cleanly (exit code 0) and is currently not running; its APS endpoints are configured. Our DNS proxy system extension is still processing flows: we see continuous logging from our NEDNSProxyProvider, and DNS filtering is clearly active (requests go through our upstream). systemextensionsctl list still shows our DNS proxy system extension as active. From the user’s perspective, everything works (with filtered DNS). From the MDM server’s perspective, commands stay pending until the next reboot. After reboot, MDM behaviour is normal again. Uninstall / cleanup (current approach, simplified) We currently use an MDM‑delivered shell script that: disables our DNS proxy configuration for the console user by editing ~/Library/Preferences/com.apple.networkextension.plist and setting Enabled = false for our DNSProxyConfigurations entries; flushes DNS cache and restarts mDNSResponder; unloads our LaunchDaemon / LaunchAgent for the host app; kills the system extension process using pgrep -f "com.company.agent.MyMacProxy.dnsProxy" | xargs kill -9; removes the extension binary from /Library/SystemExtensions/.../com.company.agent.MyMacProxy.dnsProxy.systemextension; removes /Applications/MyMacProxy.app and related support files. We currently do not call systemextensionsctl uninstall <TEAMID> com.company.agent.MyMacProxy.dnsProxy from MDM, mainly because of SIP and because we understand that fully silent system extension uninstall is constrained. The MDM responsiveness issue, however, can appear even if we don’t run this aggressive uninstall script and just let the extension run for some hours. Questions Is it expected that a DNS Proxy system extension (managed via com.apple.dnsProxy.managed) can leave a device in a state where: apsd is running, com.apple.mdmclient.daemon is not running (last exit code 0), DNS proxy continues to filter traffic, but MDM commands remain pending until reboot? Are there known best practices or pitfalls when combining: DNS Proxy system extensions (NEDNSProxyProvider), MDM‑distributed com.apple.dnsProxy.managed profiles, and MDM app / profile management on recent macOS versions? For uninstall in an MDM environment, what pattern do you recommend? For example, is it better to: disable / remove the DNS proxy profile, stop the NE configuration via NEDNSProxyManager from the app, avoid killing the system extension or removing files from /Library/SystemExtensions immediately, and instead require a reboot for full removal? I can provide a sysdiagnose and unified logs (including nesessionmanager, mdmclient and our logs) from an affected machine if that would be helpful.
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25m
The network expansion process will become a zombie process and the network will be unusable.
Hi, I developed a network extension program on macOS. I tried to update the program by changing the version number. My update process was to first turn off network filtering via "NEFilterManager.sharedManager.enabled = NO", and then use "[OSSystemExtensionRequest activationRequestForExtension:bundleid queue:dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)];" to let the system replace the old network extension program. However, sometimes the old network extension process will become a zombie process like pid=86621 in the figure. As long as the zombie process exists, the network cannot be used. After about 10 minutes, it will be cleared and the network will be available. Restarting Wi-Fi can also clear the zombie process immediately. Why is this? How to avoid this problem?
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Activity
Jun ’25
Filing a Wi-Fi Bug Report
Every now and again I end up helping a developer with a Wi-Fi issue. These fall into two groups: User-level Wi-Fi issues Development Wi-Fi issues A user-level Wi-Fi issue is one where the developer hasn’t created any of the products involved. An example of this is when you’re developing an app for an accessory and iOS is having problems connecting to that accessory but you don’t control the accessory’s firmware. In general, I recommend that you escalate such issues to the accessory vendor. They can then run their own investigation and, if necessary, file their own bug report. A development Wi-Fi issue is one that directly affects one of your products. For example, you’re developing a Wi-Fi accessory and iOS is having problems connecting to it. In that case, the onus is on you [1] to investigate why things are failing. If your conclusion is that iOS is behaving incorrectly, file a bug about that. IMPORTANT If you do file a bug in the context of some forums thread, please post your bug number to the thread, just for the record. When filing this sort of bug report it’s important to provide: Solid evidence that the problem is on the Apple side of the fence Enough information for Apple’s engineers to investigate it effectively Let’s start with that second point. If you can reproduce the problem reliably, install the Wi-Fi debug profile on your device, reproduce the problem, noting down a rough timestamp, and include the resulting logs and that timestamp in your bug report. Also, consider attaching a packet trace. There are three options here: Record a packet trace from the perspective of the Apple device. On iOS, use an RVI packet trace for this. Record a packet trace from the perspective of your accessory. Record a Wi-Fi level packet trace. You can do this from your Mac (see Recording a Wi-Fi Packet Trace) but it might be easier to do this with the infrastructure you used during the bring up of your accessory. It’s fine to include all three (-: Also include any relevant context about the issue. For example: If the issue is tied to a specific device model (In that case, it’d be good to include the above information for both the successful and failing cases.) If the problem shows up when joining from Settings > Wi-Fi, or whether it’s tied to a specific API, like NEHotspotConfigurationManager Finally, make sure to include an explanation of why you think this is an Apple bug, referencing specific items in the logs and packet traces that you attached. Of course, it’s only possible to do all of this if you can reproduce the problem. Investigating an intermittent issue based on reports coming in from users is much harder. It’s OK to file a bug about such issues, but your bug might not be actionable. At a minimum you should aim to include a sysdiagnose log with your bug. IMPORTANT This log has to be taken shortly after reproducing the problem. Don’t just attach any old log. One option is to request such a log from your users. I talk more about this in Using a Sysdiagnose Log to Debug a Hard-to-Reproduce Problem. You can also ask your users to file their own bugs using the Feedback Assistant app. It should automatically capture and attach a sysdiagnose log. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" [1] Well, your organisation. It’s rare to find a team where the same engineer works on both the iOS app and the accessory firmware. But if that’s you, good job!
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3w
NSURLSession’s Resume Rate Limiter
IMPORTANT The resume rate limiter is now covered by the official documentation. See Use background sessions efficiently within Downloading files in the background. So, the following is here purely for historical perspective. NSURLSession’s background session support on iOS includes a resume rate limiter. This limiter exists to prevent apps from abusing the background session support in order to run continuously in the background. It works as follows: nsurlsessiond (the daemon that does all the background session work) maintains a delay value for your app. It doubles that delay every time it resumes (or relaunches) your app. It resets that delay to 0 when the user brings your app to the front. It also resets the delay to 0 if the delay period elapses without it having resumed your app. When your app creates a new task while it is in the background, the task does not start until that delay has expired. To understand the impact of this, consider what happens when you download 10 resources. If you pass them to the background session all at once, you see something like this: Your app creates tasks 1 through 10 in the background session. nsurlsessiond starts working on the first few tasks. As tasks complete, nsurlsessiond starts working on subsequent ones. Eventually all the tasks complete and nsurlsessiond resumes your app. Now consider what happens if you only schedule one task at a time: Your app creates task 1. nsurlsessiond starts working on it. When it completes, nsurlsessiond resumes your app. Your app creates task 2. nsurlsessiond delays the start of task 2 a little bit. nsurlsessiond starts working on task 2. When it completes, nsurlsessiond resumes your app. Your app creates task 3. nsurlsessiond delays the start of task 3 by double the previous amount. nsurlsessiond starts working on task 3. When it completes, nsurlsessiond resumes your app. Steps 8 through 11 repeat, and each time the delay doubles. Eventually the delay gets so large that it looks like your app has stopped making progress. If you have a lot of tasks to run then you can mitigate this problem by starting tasks in batches. That is, rather than start just one task in step 1, you would start 100. This only helps up to a point. If you have thousands of tasks to run, you will eventually start seeing serious delays. In that case it’s much better to change your design to use fewer, larger transfers. Note All of the above applies to iOS 8 and later. Things worked differently in iOS 7. There’s a post on DevForums that explains the older approach. Finally, keep in mind that there may be other reasons for your task not starting. Specifically, if the task is flagged as discretionary (because you set the discretionary flag when creating the task’s session or because the task was started while your app was in the background), the task may be delayed for other reasons (low power, lack of Wi-Fi, and so on). Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" (r. 22323366)
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Jul ’25
iOS Resumable Uploads Troubles
I am referencing: https://developer.apple.com/documentation/foundation/pausing-and-resuming-uploads Specifically: You can’t resume all uploads. The server must support the latest resumable upload protocol draft from the HTTP Working Group at the IETF. Also, uploads that use a background configuration handle resumption automatically, so manual resuming is only needed for non-background uploads. I have control over both the app and the server, and can't seem to get it to work automatically with a background url session. In other words, making multiple requests to get the offset then upload, easy but I am trying to leverage this background configuration resume OS magic. So anyone know what spec version does the server/client need to implement? The docs reference version 3, however the standard is now at like 11. Of course, I am trying out 3. Does anyone know how exactly this resume is implemented in iOS, and what exactly it takes care of? I assumed that I can just POST to a generic end point, say /files, then the OS receives a 104 Location, and saves that. If the upload is interrupted, when the OS resumes the upload, it has enough information to figure out how to resume from the exact offset, either by making a HEAD request to get the offset, or handle a 409. I am assuming it does this, as if it doesn't, the 'uploads that use a background configuration handle resumption automatically' is useless, if it just restarts from 0. Note, of course making individual POST/HEAD/PATCH requests manually works, but at that point I'm not really leveraging any OS auto-magic, and am just consuming an API that could really implement any spec. This won't work in the background, as the OS seems to disallow random HTTP requests when it wakes the app for URLSession background resumes. As of right now, I have it 'partially' working, insofar as the app does receive the 104 didReceiveInformationalResponse url delegate call, however it seems to then hang; it stops sending bytes, seemingly when the 104 is received. However, the request does not complete. In other words, it doesn't seem to receive a client timeout or otherwise indicate the request has finished. Right now, I am starting a single request, POSTing to a /files end point, i.e. I am not getting the location first, then PATCHing to that, as if I do that, the OS 'automatic' resuming fails with a 409, i.e. it doesn't seem to make a HEAD request and/or use the 409 offset correction then continue with the PATCH. Any idea what could be going on?
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Mar ’26
iOS UDP Multicast: Receiving works but sending silently fails
Hi everyone, I’m working with UDP Multicasting on iOS (iOS 15+) using Network.framework and facing a confusing issue. Setup: Multicast IP: 239.255.0.1 Port: 45454 Using NWConnectionGroup / NWMulticastGroup NSLocalNetworkUsageDescription is present in Info.plist Devices are on the same Wi-Fi network Problem: Receiving multicast packets works perfectly Sending multicast packets does NOT work No errors are thrown send() completion handler reports success stateUpdateHandler sometimes doesn’t transition to .ready No packets are actually transmitted on the network Observations: The app can receive data from other multicast senders Sending appears to be silently blocked Reinstalling the app fixes the issue This points to a Local Network permission problem If permission was denied once, iOS does not re-prompt Inbound multicast works, outbound multicast is blocked Questions: Is it expected on iOS that receiving multicast works even when sending is blocked? Is reinstalling the app the only way to recover if Local Network permission was denied? Is there any reliable runtime way to detect that outbound multicast is blocked? Is NWConnectionGroup the correct and only supported way to send multicast on iOS? Any clarification or official guidance would really help. Thanks in advance!
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Activity
Feb ’26
Reproducible EXC_BAD_ACCESS in NEDNSProxyProvider when using async/await variants of NEAppProxyUDPFlow
Description I am seeing a consistent crash in a NEDNSProxyProvider on iOS when migrating from completion handlers to the new Swift Concurrency async/await variants of readDatagrams() and writeDatagrams() on NEAppProxyUDPFlow. The crash occurs inside the Swift Concurrency runtime during task resumption. Specifically, it seems the Task attempts to return to the flow’s internal serial executor (NEFlow queue) after a suspension point, but fails if the flow was invalidated or deallocated by the kernel while the task was suspended. Error Signature Thread 4: EXC_BAD_ACCESS (code=1, address=0x28) Thread 4 Queue : NEFlow queue (serial) #0 0x000000018fe919cc in swift::AsyncTask::flagAsAndEnqueueOnExecutor () #9 0x00000001ee25c3b8 in _pthread_wqthread () Steps The crash is highly timing-dependent. To reproduce it reliably: Use an iOS device with Developer Settings enabled. Go to Developer > Network Link Conditioner -> High Latency DNS. Intercept a DNS query and perform a DoH (DNS-over-HTTPS) request using URLSession. The first few network requests should trigger the crash Minimum Working Example (MWE) class DNSProxyProvider: NEDNSProxyProvider { override func handleNewFlow(_ flow: NEAppProxyFlow) -> Bool { guard let udpFlow = flow as? NEAppProxyUDPFlow else { return false } Task(priority: .userInitiated) { await handleUDPFlow(udpFlow) } return true } func handleUDPFlow(_ flow: NEAppProxyUDPFlow) async { do { try await flow.open(withLocalFlowEndpoint: nil) while !Task.isCancelled { // Suspension point 1: Waiting for datagrams let (flowData, error) = await flow.readDatagrams() if let error { throw error } guard let flowData, !flowData.isEmpty else { return } var responses: [(Data, Network.NWEndpoint)] = [] for (data, endpoint) in flowData { // Suspension point 2: External DoH resolution let response = try await resolveViaDoH(data) responses.append((response, endpoint)) } // Suspension point 3: Writing back to the flow // Extension will crash here on task resumption try await flow.writeDatagrams(responses) } } catch { flow.closeReadWithError(error) flow.closeWriteWithError(error) } } private func handleFlowData(_ packet: Data, endpoint: Network.NWEndpoint, using parameters: NWParameters) async throws -> Data { let url = URL(string: "https://dns.google/dns-query")! var request = URLRequest(url: url) request.httpMethod = "POST" request.httpBody = packet request.setValue("application/dns-message", forHTTPHeaderField: "Content-Type") let (data, _) = try await URLSession.shared.data(for: request) return data } } Crash Details & Analysis The disassembly at the crash point indicates a null dereference of an internal executor pointer (Voucher context): ldr x20, [TPIDRRO_EL0 + 0x340] ldr x0, [x20, #0x28] // x20 is NULL/0x0 here, resulting in address 0x28 It appears that NEAppProxyUDPFlow’s async methods bind the Task to a specific internal executor. When the kernel reclaims the flow memory, the pointer in x20 becomes invalid. Because the Swift runtime is unaware that the NEFlow queue executor has vanished, it attempts to resume on non-existing flow and then crashes. Checking !Task.isCancelled does not prevent this, as the crash happens during the transition into the task body before the cancellation check can even run. Questions Is this a known issue of the NetworkExtension async bridge? Why does Task.isCancelled not reflect the deallocation of the underlying NEAppProxyFlow? Is the only safe workaround? Please feel free to correct me if I misunderstood anything here. I'll be happy to hear any insights or suggestions :) Thank you!
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Feb ’26
How to detect the SIM card status?
Before iOS16, we can use https://developer.apple.com/documentation/coretelephony/ctcarrier But after iOS this is deprecated and has no replacement. There are some discussions on it, eg. https://developer.apple.com/forums/thread/714876 https://developer.apple.com/forums/thread/770400 Now I asked AI, then it provided this solution, to check the serviceCurrentRadioAccessTechnology, so it this ok to check the SIM card status? var hasSIMCard = false let info = CTTelephonyNetworkInfo() if let rat = info.serviceCurrentRadioAccessTechnology, rat.values.contains(where: { !$0.isEmpty }) { hasSIMCard = true. // has RAT } BTW, I can see a lot of changes in the Core Telephony framework. https://developer.apple.com/documentation/coretelephony 1.isSIMInserted https://developer.apple.com/documentation/coretelephony/ctsubscriber/issiminserted A Boolean property that indicates whether a SIM is present. iOS 18.0+ iPadOS 18.0+ This value property is true if the system finds a SIM matching the Info.plist carrier information (MCC / MNC / GID1 / GID2). Is this ok to check SIM insert status, this seems must preconfig some info in the info.plist. 2.iOS26 provide CTCellularPlanStatus https://developer.apple.com/documentation/coretelephony/ctcellularplanstatus Can I use this to check SIM status?
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Jun ’25
On FTP
Questions about FTP crop up from time-to-time here on DevForums. In most cases I write a general “don’t use FTP” response, but I don’t have time to go into all the details. I’ve created this post as a place to collect all of those details, so I can reference them in other threads. IMPORTANT Apple’s official position on FTP is: All our FTP APIs have been deprecated, and you should avoid using deprecated APIs. Apple has been slowly removing FTP support from the user-facing parts of our system. The most recent example of this is that we removed the ftp command-line tool in macOS 10.13. You should avoid the FTP protocol and look to adopt more modern alternatives. The rest of this post is an informational explanation of the overall FTP picture. This post is locked so I can keep it focused. If you have questions or comments, please do create a new thread in the App & System Services > Networking subtopic and I’ll respond there. Don’t Use FTP FTP is a very old and very crufty protocol. Certain things that seem obvious to us now — like being able to create a GUI client that reliably shows a directory listing in a platform-independent manner — aren’t possible to do in FTP. However, by far the biggest problem with FTP is that it provides no security [1]. Specifically, the FTP protocol: Provides no on-the-wire privacy, so anyone can see the data you transfer Provides no client-authenticates-server authentication, so you have no idea whether you’re talking to the right server Provides no data integrity, allowing an attacker to munge your data in transit Transfers user names and passwords in the clear Using FTP for anonymous downloads may be acceptable (see the explanation below) but most other uses of FTP are completely inappropriate for the modern Internet. IMPORTANT You should only use FTP for anonymous downloads if you have an independent way to check the integrity of the data you’ve downloaded. For example, if you’re downloading a software update, you could use code signing to check its integrity. If you don’t check the integrity of the data you’ve downloaded, an attacker could substitute a malicious download instead. This would be especially bad in, say, the software update case. These fundamental problems with the FTP protocol mean that it’s not a priority for Apple. This is reflected in the available APIs, which is the subject of the next section. FTP APIs Apple provides two FTP APIs: All Apple platforms provide FTP downloads via URLSession. Most Apple platforms (everything except watchOS) support CFFTPStream, which allows for directory listings, downloads, uploads, and directory creation. All of these FTP APIs are now deprecated: URLSession was deprecated for the purposes of FTP in the 2022 SDKs (macOS 13, iOS 16, iPadOS 16, tvOS 16, watchOS 9) [2]. CFFTPStream was deprecated in the 2016 SDKs (macOS 10.11, iOS 9, iPadOS 9, tvOS 9). CFFTPStream still works about as well as it ever did, which is not particularly well. Specifically: There is at least one known crashing bug (r. 35745763), albeit one that occurs quite infrequently. There are clear implementation limitations — like the fact that CFFTPCreateParsedResourceListing assumes a MacRoman text encoding (r. 7420589) — that won’t be fixed. If you’re looking for an example of how to use these APIs, check out SimpleFTPSample. Note This sample hasn’t been updated since 2013 and is unlikely to ever be updated given Apple’s position on FTP. The FTP support in URLSession has significant limitations: It only supports FTP downloads; there’s no support for uploads or any other FTP operations. It doesn’t support resumable FTP downloads [3]. It doesn’t work in background sessions. That prevents it from running FTP downloads in the background on iOS. It’s only supported in classic loading mode. See the usesClassicLoadingMode property and the doc comments in <Foundation/NSURLSession.h>. If Apple’s FTP APIs are insufficient for your needs, you’ll need to write or acquire your own FTP library. Before you do that, however, consider switching to an alternative protocol. After all, if you’re going to go to the trouble of importing a large FTP library into your code base, you might as well import a library for a better protocol. The next section discusses some options in this space. Alternative Protocols There are numerous better alternatives to FTP: HTTPS is by far the best alternative to FTP, offering good security, good APIs on Apple platforms, good server support, and good network compatibility. Implementing traditional FTP operations over HTTPS can be a bit tricky. One possible way forward is to enable DAV extensions on the server. FTPS is FTP over TLS (aka SSL). While FTPS adds security to the protocol, which is very important, it still inherits many of FTP’s other problems. Personally I try to avoid this protocol. SFTP is a file transfer protocol that’s completely unrelated to FTP. It runs over SSH, making it a great alternative in many of the ad hoc setups that traditionally use FTP. Apple doesn’t have an API for either FTPS or SFTP, although on macOS you may be able to make some headway by invoking the sftp command-line tool. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" [1] In another thread someone asked me about FTP’s other problems, those not related to security, so let’s talk about that. One of FTP’s implicit design goals was to provide cross-platform support that exposes the target platform. You can think of FTP as being kinda like telnet. When you telnet from Unix to VMS, it doesn’t aim to abstract away VMS commands, so that you can type Unix commands at the VMS prompt. Rather, you’re expected to run VMS commands. FTP is (a bit) like that. This choice made sense back when the FTP protocol was invented. Folks were expecting to use FTP via a command-line client, so there was a human in the loop. If they ran a command and it produced VMS-like output, that was fine because they knew that they were FTPing into a VMS machine. However, most users today are using GUI clients, and this design choice makes it very hard to create a general GUI client for FTP. Let’s consider the simple problem of getting the contents of a directory. When you send an FTP LIST command, the server would historically run the platform native directory list command and pipe the results back to you. To create a GUI client you have to parse that data to extract the file names. Doing that is a serious challenge. Indeed, just the first step, working out the text encoding, is a challenge. Many FTP servers use UTF-8, but some use ISO-Latin-1, some use other standard encodings, some use Windows code pages, and so on. I say “historically” above because there have been various efforts to standardise this stuff, both in the RFCs and in individual server implementations. However, if you’re building a general client you can’t rely on these efforts. After all, the reason why folks continue to use FTP is because of it widespread support. [2] To quote the macOS 13 Ventura Release Notes: FTP is deprecated for URLSession and related APIs. Please adopt modern secure networking protocols such as HTTPS. (92623659) [3] Although you can implement resumable downloads using the lower-level CFFTPStream API, courtesy of the kCFStreamPropertyFTPFileTransferOffset property. Revision History 2025-10-06 Explained that URLSession only supports FTP in classic loading mode. Made other minor editorial changes. 2024-04-15 Added a footnote about FTP’s other problems. Made other minor editorial changes. 2022-08-09 Noted that the FTP support in URLSession is now deprecated. Made other minor editorial changes. 2021-04-06 Fixed the formatting. Fixed some links. 2018-02-23 First posted.
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Oct ’25
Real-Time WatchConnectivity Sync Not Working Between iPhone and Apple Watch
Hi everyone, I'm building a health-focused iOS and watchOS app that uses WatchConnectivity to sync real-time heart rate and core body temperature data from iPhone to Apple Watch. While the HealthKit integration works correctly on the iPhone side, I'm facing persistent issues with WatchConnectivity — the data either doesn't arrive on the Watch, or session(_:didReceiveMessage:) never gets triggered. Here's the setup: On iPhone: Using WCSession.default.sendMessage(_:replyHandler:errorHandler:) to send real-time values every few seconds. On Apple Watch: Implemented WCSessionDelegate, and session(_:didReceiveMessage:) is supposed to update the UI. Both apps have WCSession.isSupported() checks, activate the session, and assign delegates correctly. The session state shows isPaired = true and isWatchAppInstalled = true. Bluetooth and Wi-Fi are on, both devices are unlocked and nearby. Despite all this, the Watch never receives messages in real-time. Sometimes, data comes through in bulk much later or not at all. I've double-checked Info.plist configurations and made sure background modes include "Uses Bluetooth LE accessories" and "Background fetch" where appropriate. I would really appreciate guidance on: Best practices for reliable, low-latency message delivery with WatchConnectivity. Debugging steps or sample code to validate message transmission and reception. Any pitfalls related to UI updates from the delegate method. Happy to share further details. Thanks in advance!
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1
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0
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370
Activity
Jun ’25
WiFi Aware connection cannot be established when both peers publish and subscribe
It works when one device is only a publisher and the other is only a subscriber. However, when both devices act as both publisher and subscriber simultaneously—which Apple’s documentation (https://developer.apple.com/documentation/wifiaware/adopting-wi-fi-aware#Declare-services) indicates is valid—the connection never establishes. After timing out, both NetworkListener and NetworkBrowser transition to the failed state. This appears to be a race condition in Network framework. Task.detached { try await NetworkListener( for: .wifiAware( .connecting( to: .myService, from: .allPairedDevices, datapath: .defaults ) ), using: .parameters { Coder( sending: ..., receiving: ..., using: NetworkJSONCoder() ) { TCP() } } ).run { connection in await self.add(connection: connection) } } Task.detached { try await NetworkBrowser( for: .wifiAware( .connecting( to: .allPairedDevices, from: .myService ) ), using: .tcp ).run { endpoints in for endpoint in endpoints { await self.connect(to: endpoint) } } }
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1
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0
Views
126
Activity
Jan ’26
How to detect if Wifi is being used for CarPlay
What is the best way to detect if the Wifi is being used for Wireless Carplay or is just a normal network interface?
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9
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0
Views
302
Activity
Jan ’26
Local network request blocked in Safari but working in Chrome
For Local network access, Chrome prompts the user to allow access and adds it to Settings --> Privacy & Security --> Local Network. However, for Safari, no prompt appears. How do I force Safari to authorise these local network access requests if it won't trigger the permission dialogue? Is there a specific WKWebView configuration or Safari-specific header required to satisfy this security check?
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1
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0
Views
507
Activity
Jan ’26
How to stop or disable Network Extension without removing
I develop a Network Extension with NEFilterDataProvider and want to understand how to stop or disable it on exit of the base app without deactivating NE from OS and leave ability to start it again without requiring a password from the user. It starts normally, but when I try to disable it: NEFilterManager.sharedManager.enabled = NO; [NEFilterManager.sharedManager saveToPreferencesWithCompletionHandler:^(NSError * _Nullable error) { // never called }]; the completion handler has never called. But stopFilterWithReason inside the NE code called by the framework where I only replay with required completionHandler();. Then NE process keeps alive. I also tried to call remove, which should disable NE: [NEFilterManager.sharedManager removeFromPreferencesWithCompletionHandler:^(NSError * _Nullable error) { // never called }]; with same result - I freeze forever on waiting completion handler. So what is the correct way to disable NE without explicit deactivation it by [OSSystemExtensionRequest deactivationRequestForExtension:...]?
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1
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0
Views
89
Activity
Nov ’25
DNS updates and Apple Private Relay - major issue
After dropping an A-record TTL to 60 secs (it was previously no higher than 600 secs for several weeks) and making an IP change for a small business website on Monday, I took down the old web service just over 24 hours later on Tuesday evening. We then had reports of some customers not being able to access the website on Wednesday morning. On investigation using my iPhone it would appear that Apple Private Relay is still directing clients to the old IP address. It's just as well I have iCloud+ as I would never have seen this issue otherwise and would have been none the wiser as to why some customers were having problems. Has anyone else seen this and/or have a fix other than waiting longer? Do you know how long it takes for Apple Private Relay to update? This isn't expected behaviour of DNS? I spoke to someone at Apple yesterday and there wasn't much they can do. I hope they're escalating internally as almost 3 days later it's still pointing users to the old IP address despite having ample time for proper DNS propagation.
Replies
2
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0
Views
186
Activity
Nov ’25
NEAppPushProvider lifecycle guarantees for safety-critical local networking
We have an iOS companion app that talks to our IoT device over the device’s own Wi‑Fi network (often with no internet). The app performs bi-directional, safety-critical duties over that link. We use an NEAppPushProvider extension so the handset can keep exchanging data while the UI is backgrounded. During testing we noticed that if the user backgrounds the app (still connected to the device’s Wi‑Fi) and opens Safari, the extension’s stop is invoked with NEProviderStopReason.unrecoverableNetworkChange / noNetworkAvailable, and iOS tears the extension down. Until the system restarts the extension (e.g. the user foregrounds our app again), the app cannot send/receive its safety-critical data. Questions: Is there a supported way to stop a safety-critical NEAppPushProvider from being terminated in this “background app → open Safari” scenario when the device remains on the same Wi‑Fi network (possibly without internet)? If not, is NEAppPushProvider the correct extension type for an always-on local-network use case like this, or is there another API we should be using? For safety-critical applications, can Apple grant entitlements/exemptions so the system does not terminate the extension when the user switches apps but stays on the local Wi‑Fi? Any guidance on the expected lifecycle or alternative patterns for safety-critical local connectivity would be greatly appreciated.
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1
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0
Views
71
Activity
Nov ’25
Labeling an eSIM during the installation wizard, not present on iOS 26
Hi there, How can I best understand the changes on the eSIM Installation wizard, i.e. on iOS 18 and later after an eSIM installation you used to get steps such as labeling the eSIM, deciding what to use for iMessage & FaceTime, what to use for mobile data, main voice line, etc. Whereas on iOS 26 you are not prompted for these steps.
Replies
4
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0
Views
223
Activity
Feb ’26
-10985 network error from urlSession
Getting -10985 error from urlSession while attempting to make a connection. Not sure why this is happening if anyone is aware please help
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1
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0
Views
214
Activity
Nov ’25
DeviceDiscoveryUI's UIViewControllers are available for Wi-Fi Aware?
HI, I am currently developing an app that utilizes Wi-Fi Aware. According to the Wi-Fi Aware framework examples and the WWDC25 session on Wi-Fi Aware, discovery is handled using DevicePairingView and DevicePicker from the DeviceDiscoveryUI module. However, these SwiftUI views present their connection UI modally when tapped. My app's design requires the ability to control the presentation of this UI programmatically, rather than relying on a user tap. While inspecting the DeviceDiscoveryUI module, I found DDDevicePairingViewController and DDDevicePickerViewController, which appear to be the UIViewController counterparts to the SwiftUI views. The initializer for DDDevicePairingViewController accepts a ListenerProvider, so it seems I can pass the same ListenerProvider instance that is used with the DevicePairingView. However, the initializer for DDDevicePickerViewController requires an NWBrowser.Descriptor, which seems incompatible with the parameters used for the SwiftUI DevicePicker. I have two main questions: (1) Can DDDevicePairingViewController and DDDevicePickerViewController be officially used for Wi-Fi Aware pairing? (2) Are there any plans to provide more customization or programmatic control over the DevicePairingView and DevicePicker (for example, allowing us to trigger their modal presentation programmatically)? Thank you.
Replies
0
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0
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53
Activity
Nov ’25
URLSession.dataTask(with: URL) error: Type of expression is ambiguous without a type annotation
I'm a long-time developer, but pretty new to Swift. I'm trying to get information from a web service (and found code online that I adjusted to build the function below). (Note: AAA_Result -- referenced towards the end -- is another class in my project) Trouble is, I'm getting the subject error on the call to session.dataTask. Any help/suggestions/doc pointers will be greatly appreciated!!! var result: Bool = false var cancellable: AnyCancellable? self.name = name let params = "json={\"\"}}" // removed json details let base_url = URL(string: "https://aaa.yyy.com?params=\(params)&format=json")! // removed URL specifics do { let task = URLSession.shared.dataTask(with: base_url) { data, response, error in if let error = error { print("Error: \(error)") } guard let response = response as? HTTPURLResponse, (200...299).contains(response.statusCode) else { print("Error \(String(describing: response))") } do { let decoder = JSONDecoder() let ar = try decoder.decode(AAA_Result.self, from: response.value) // removed specific details... result = true } catch { print(error) } } task.resume() } catch { print(error) } return result }
Replies
4
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0
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124
Activity
May ’25