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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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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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478
Jun ’25
App occassionally crashing while connecting to public wifi
We are using the [NEHotspotHelper supportedNetworkInterfaces] to get the Wi-Fi interface in our app, but it occasionally crashes on some devices with the following stack trace: 0 CaptiveNetwork 0x0000000221d87a4c ServerConnectionGetHandlerQueue + 0 (ServerConnection.c:509) 1 CaptiveNetwork 0x0000000221d8577c CNPluginCopySupportedInterfaces + 180 (CNPlugin.c:457) 2 NetworkExtension 0x00000001b0446618 +[NEHotspotHelper supportedNetworkInterfaces] + 32 (NEHotspotHelper.m:563) It seems like the crash is happening on apple's api of supportedNetworkInterfaces. We would like to understand the cause of the crash.
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104
May ’25
Background UDP receive for lighting control (Art-Net/sACN)
I'm developing a lighting control app for iOS that receives Art-Net (UDP port 6454) and sACN (UDP port 5568) packets from a lighting console and relays commands to BLE wristbands with LEDs. This is used in live event production — the participant locks their phone while in a show and expects lighting control to continue uninterrupted. The problem UDP receive stops reliably ~30 seconds after the screen locks. I understand this is by design - iOS suspends apps in the background. However, I'm trying to understand if any supported path exists for this use case. What I've already tried UIRequiresPersistentWiFi = true - helps with Wi-Fi association but doesn't prevent app suspension Silent AVAudioEngine loop with UIBackgroundModes: audio - keeps the app alive, works in testing, but risks App Store rejection and feels like an abuse of the audio background mode NWListener (Network framework) on the UDP port - same suspension behaviour Socket rebind on applicationWillEnterForeground - recovers after resume but doesn't prevent dropout What I'm asking Is there any supported background mode or entitlement for sustained UDP receive in a professional/enterprise context? (Similar to how VoIP apps get the voip background mode for sustained network activity.) Is the silent audio workaround considered acceptable for App Store distribution in a professional tools context, or will it be rejected? Is NEAppProxyProvider or another Network Extension a viable path, and if so does it require a special entitlement? Test project I have a minimal Xcode project (~130 lines) demonstrating the issue — NWListener on port 6454, packet counter, staleness timer, and silent audio toggle. I can share the test code. STEPS TO REPRODUCE In Xcode (one-time setup): Select the UDPBackgroundTest target → Signing & Capabilities → set your Team Plug in your iPhone → select it as the run destination Build & run — confirm packets appear on screen when you run 'send_test_udp.py' Lock the phone and observe the dropout Test: Open the app and run 'python3 send_test_udp.py 192.168.0.XXX' The app counts up the packages, they match the python output. 1 packet per second. lock screen & and wait 10 seconds unlock phone an see the numbers are 10 packets off
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88
Apr ’26
TLS for App Developers
Transport Layer Security (TLS) is the most important security protocol on the Internet today. Most notably, TLS puts the S into HTTPS, adding security to the otherwise insecure HTTP protocol. IMPORTANT TLS is the successor to the Secure Sockets Layer (SSL) protocol. SSL is no longer considered secure and it’s now rarely used in practice, although many folks still say SSL when they mean TLS. TLS is a complex protocol. Much of that complexity is hidden from app developers but there are places where it’s important to understand specific details of the protocol in order to meet your requirements. This post explains the fundamentals of TLS, concentrating on the issues that most often confuse app developers. Note The focus of this is TLS-PKI, where PKI stands for public key infrastructure. This is the standard TLS as deployed on the wider Internet. There’s another flavour of TLS, TLS-PSK, where PSK stands for pre-shared key. This has a variety of uses, but an Apple platforms we most commonly see it with local traffic, for example, to talk to a Wi-Fi based accessory. For more on how to use TLS, both TLS-PKI and TLS-PSK, in a local context, see TLS For Accessory Developers. Server Certificates For standard TLS to work the server must have a digital identity, that is, the combination of a certificate and the private key matching the public key embedded in that certificate. TLS Crypto Magic™ ensures that: The client gets a copy of the server’s certificate. The client knows that the server holds the private key matching the public key in that certificate. In a typical TLS handshake the server passes the client a list of certificates, where item 0 is the server’s certificate (the leaf certificate), item N is (optionally) the certificate of the certificate authority that ultimately issued that certificate (the root certificate), and items 1 through N-1 are any intermediate certificates required to build a cryptographic chain of trust from 0 to N. Note The cryptographic chain of trust is established by means of digital signatures. Certificate X in the chain is issued by certificate X+1. The owner of certificate X+1 uses their private key to digitally sign certificate X. The client verifies this signature using the public key embedded in certificate X+1. Eventually this chain terminates in a trusted anchor, that is, a certificate that the client trusts by default. Typically this anchor is a self-signed root certificate from a certificate authority. Note Item N is optional for reasons I’ll explain below. Also, the list of intermediate certificates may be empty (in the case where the root certificate directly issued the leaf certificate) but that’s uncommon for servers in the real world. Once the client gets the server’s certificate, it evaluates trust on that certificate to confirm that it’s talking to the right server. There are three levels of trust evaluation here: Basic X.509 trust evaluation checks that there’s a cryptographic chain of trust from the leaf through the intermediates to a trusted root certificate. The client has a set of trusted root certificates built in (these are from well-known certificate authorities, or CAs), and a site admin can add more via a configuration profile. This step also checks that none of the certificates have expired, and various other more technical criteria (like the Basic Constraints extension). Note This explains why the server does not have to include the root certificate in the list of certificates it passes to the client; the client has to have the root certificate installed if trust evaluation is to succeed. In addition, TLS trust evaluation (per RFC 2818) checks that the DNS name that you connected to matches the DNS name in the certificate. Specifically, the DNS name must be listed in the Subject Alternative Name extension. Note The Subject Alternative Name extension can also contain IP addresses, although that’s a much less well-trodden path. Also, historically it was common to accept DNS names in the Common Name element of the Subject but that is no longer the case on Apple platforms. App Transport Security (ATS) adds its own security checks. Basic X.509 and TLS trust evaluation are done for all TLS connections. ATS is only done on TLS connections made by URLSession and things layered on top URLSession (like WKWebView). In many situations you can override trust evaluation; for details, see Technote 2232 HTTPS Server Trust Evaluation). Such overrides can either tighten or loosen security. For example: You might tighten security by checking that the server certificate was issued by a specific CA. That way, if someone manages to convince a poorly-managed CA to issue them a certificate for your server, you can detect that and fail. You might loosen security by adding your own CA’s root certificate as a trusted anchor. IMPORTANT If you rely on loosened security you have to disable ATS. If you leave ATS enabled, it requires that the default server trust evaluation succeeds regardless of any customisations you do. Mutual TLS The previous section discusses server trust evaluation, which is required for all standard TLS connections. That process describes how the client decides whether to trust the server. Mutual TLS (mTLS) is the opposite of that, that is, it’s the process by which the server decides whether to trust the client. Note mTLS is commonly called client certificate authentication. I avoid that term because of the ongoing industry-wide confusion between certificates and digital identities. While it’s true that, in mTLS, the server authenticates the client certificate, to set this up on the client you need a digital identity, not a certificate. mTLS authentication is optional. The server must request a certificate from the client and the client may choose to supply one or not (although if the server requests a certificate and the client doesn’t supply one it’s likely that the server will then fail the connection). At the TLS protocol level this works much like it does with the server certificate. For the client to provide this certificate it must apply a digital identity, known as the client identity, to the connection. TLS Crypto Magic™ assures the server that, if it gets a certificate from the client, the client holds the private key associated with that certificate. Where things diverge is in trust evaluation. Trust evaluation of the client certificate is done on the server, and the server uses its own rules to decided whether to trust a specific client certificate. For example: Some servers do basic X.509 trust evaluation and then check that the chain of trust leads to one specific root certificate; that is, a client is trusted if it holds a digital identity whose certificate was issued by a specific CA. Some servers just check the certificate against a list of known trusted client certificates. When the client sends its certificate to the server it actually sends a list of certificates, much as I’ve described above for the server’s certificates. In many cases the client only needs to send item 0, that is, its leaf certificate. That’s because: The server already has the intermediate certificates required to build a chain of trust from that leaf to its root. There’s no point sending the root, as I discussed above in the context of server trust evaluation. However, there are no hard and fast rules here; the server does its client trust evaluation using its own internal logic, and it’s possible that this logic might require the client to present intermediates, or indeed present the root certificate even though it’s typically redundant. If you have problems with this, you’ll have to ask the folks running the server to explain its requirements. Note If you need to send additional certificates to the server, pass them to the certificates parameter of the method you use to create your URLCredential (typically init(identity:certificates:persistence:)). One thing that bears repeating is that trust evaluation of the client certificate is done on the server, not the client. The client doesn’t care whether the client certificate is trusted or not. Rather, it simply passes that certificate the server and it’s up to the server to make that decision. When a server requests a certificate from the client, it may supply a list of acceptable certificate authorities [1]. Safari uses this to filter the list of client identities it presents to the user. If you are building an HTTPS server and find that Safari doesn’t show the expected client identity, make sure you have this configured correctly. If you’re building an iOS app and want to implement a filter like Safari’s, get this list using: The distinguishedNames property, if you’re using URLSession The sec_protocol_metadata_access_distinguished_names routine, if you’re using Network framework [1] See the certificate_authorities field in Section 7.4.4 of RFC 5246, and equivalent features in other TLS versions. Self-Signed Certificates Self-signed certificates are an ongoing source of problems with TLS. There’s only one unequivocally correct place to use a self-signed certificate: the trusted anchor provided by a certificate authority. One place where a self-signed certificate might make sense is in a local environment, that is, securing a connection between peers without any centralised infrastructure. However, depending on the specific circumstances there may be a better option. TLS For Accessory Developers discusses this topic in detail. Finally, it’s common for folks to use self-signed certificates for testing. I’m not a fan of that approach. Rather, I recommend the approach described in QA1948 HTTPS and Test Servers. For advice on how to set that up using just your Mac, see TN2326 Creating Certificates for TLS Testing. TLS Standards RFC 6101 The Secure Sockets Layer (SSL) Protocol Version 3.0 (historic) RFC 2246 The TLS Protocol Version 1.0 RFC 4346 The Transport Layer Security (TLS) Protocol Version 1.1 RFC 5246 The Transport Layer Security (TLS) Protocol Version 1.2 RFC 8446 The Transport Layer Security (TLS) Protocol Version 1.3 RFC 4347 Datagram Transport Layer Security RFC 6347 Datagram Transport Layer Security Version 1.2 RFC 9147 The Datagram Transport Layer Security (DTLS) Protocol Version 1.3 Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" Revision History: 2025-11-21 Clearly defined the terms TLS-PKI and TLS-PSK. 2024-03-19 Adopted the term mutual TLS in preference to client certificate authentication throughout, because the latter feeds into the ongoing certificate versus digital identity confusion. Defined the term client identity. Added the Self-Signed Certificates section. Made other minor editorial changes. 2023-02-28 Added an explanation mTLS acceptable certificate authorities. 2022-12-02 Added links to the DTLS RFCs. 2022-08-24 Added links to the TLS RFCs. Made other minor editorial changes. 2022-06-03 Added a link to TLS For Accessory Developers. 2021-02-26 Fixed the formatting. Clarified that ATS only applies to URLSession. Minor editorial changes. 2020-04-17 Updated the discussion of Subject Alternative Name to account for changes in the 2019 OS releases. Minor editorial updates. 2018-10-29 Minor editorial updates. 2016-11-11 First posted.
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8.4k
Nov ’25
test NEAppProxyProvider without MDM?
This discussion is for iOS/iPadOS. I've written an NEAppProxyProvider network extension. I'd like to test it. I thought that using the "NETestAppMapping" dictionary was a way to get there, but when I try to instantiate an NEAppProxyProviderManager to try to install stuff, the console tells me "must be MDM managed" and I get nowhere. So can someone tell me, can I at least test the idea without needing to first get MDM going? I'd like to know if how I'm approaching the core problem even makes sense. My custom application needs to stream video, via the SRT protocol, to some place like youtube or castr. The problem is that in the environment we are in (big convention centers), our devices are on a LAN, but the connection from the LAN out to the rest of the world just sucks. Surprisingly, cellular has better performance. So I am trying to do the perverse thing of forcing traffix that is NOT local to go out over cellular. And traffic that is completely local (i.e. talking to a purely local server/other devices on the LAN) happens over ethernet. [To simplify things, wifi is not connected.] Is an app proxy the right tool for this? Is there any other tool? Unfortunately, I cannot rewrite the code to force everything through Apple's Network framework, which is the one place I know we can say "use cellular." [E.g. URLSession() has absolutely no way of forcing cellular, and even so, the low level streaming library I use is written with raw sockets, and its not feasible for me to rewrite it.] Any other suggestions of how to accomplish this "send non-local traffic to cellular, all local traffic out over ethernet" gratefully welcomed!
9
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171
Mar ’26
NEHotspotNetwork headaches
I'm trying to use NEHotspotNetwork to configure an IoT. I've read all the issues that have plagued other developers when using this framework, and I was under the impression that bugs were filed and fixed. Here are my issues in hopes that someone can catch my bug, or has finally figured this out and it's not a bug in the framework with no immediate fix on the horizon. If I use the following code: let config = NEHotspotConfiguration(ssid: ssid) config.joinOnce = true KiniStatusBanner.shared.show(text: "Connecting to Kini", in: presentingVC.view) NEHotspotConfigurationManager.shared.apply(config) { error in DispatchQueue.main.async { if let nsError = error as NSError?, nsError.domain == NEHotspotConfigurationErrorDomain, nsError.code == NEHotspotConfigurationError.alreadyAssociated.rawValue { print("Already connected to \(self.ssid)") KiniStatusBanner.shared.dismiss() self.presentCaptivePortal(from: presentingVC, activationCode: activationCode) } else if let error = error { // This doesn't happen print("❌ Failed to connect: \(error.localizedDescription)") KiniStatusBanner.shared.update(text: "Failed to Connect to Kini. Try again later.") KiniStatusBanner.shared.dismiss(after: 2.5) } else { // !!!! Most often, this is the path the code takes NEHotspotNetwork.fetchCurrent { current in if let ssid = current?.ssid, ssid == self.ssid { log("✅✅ 1st attempt: connected to \(self.ssid)") KiniStatusBanner.shared.dismiss() self.presentCaptivePortal(from: presentingVC, activationCode: activationCode) } else { // Dev forums talked about giving things a bit of time to settle and then try again DispatchQueue.main.asyncAfter(deadline: .now() + 2) { NEHotspotNetwork.fetchCurrent { current in if let ssid = current?.ssid, ssid == self.ssid { log("✅✅✅ 2nd attempt: connected to \(self.ssid)") KiniStatusBanner.shared.dismiss() self.presentCaptivePortal(from: presentingVC, activationCode: activationCode) } else { log("❌❌❌ 2nd attempt: Failed to connect: \(self.ssid)") KiniStatusBanner.shared.update(text: "Could not join Kini network. Try again.") KiniStatusBanner.shared.dismiss(after: 2.5) self.cleanupHotspot() DispatchQueue.main.asyncAfter(deadline: .now() + 2) { print("cleanup again") self.cleanupHotspot() } } } } log("❌❌ 1st attempt: Failed to connect: \(self.ssid)") KiniStatusBanner.shared.update(text: "Could not join Kini network. Try again.") KiniStatusBanner.shared.dismiss(after: 2.5) self.cleanupHotspot() } As you can see, one can't just use NEHotspotConfigurationManager.shared.apply and has to double-check to make sure that it actually succeeds, by checking to see if the SSID desired, matches the one that the device is using. Ok, but about 50% of the time, the call to NEHotspotNetwork.fetchCurrent gives me this error: NEHotspotNetwork nehelper sent invalid result code [1] for Wi-Fi information request Well, there is a workaround for that randomness too. At some point before calling this code, one can: let locationManager = CLLocationManager() locationManager.requestWhenInUseAuthorization() That eliminates the NEHotspotNetwork nehelper sent invalid result code [1] for Wi-Fi information request BUT... three issues. The user is presented with an authorization alert: Allow "Kini" to use your location? This app needs access to you Wi-Fi name to connect to your Kini device. Along with a map with a location pin on it. This gives my users a completely wrong impression, especially for a device/app where we promise users not to track their location. They actually see a map with their location pinned on it, implying something that would freak out anyone who was expecting no tracking. I understand why an authorization is normally required, but since all we are getting is our own IoT's SSID, there should be no need for an authorization for this, and no map associated with the request. Again, they are accessing my IoT's network, NOT their home/location Wi-Fi SSID. My app already knows and specifies that network, and all I am trying to do is to work around a bug that makes it look like I have a successful return from NEHotspotConfigurationManager.shared.apply() when in fact the network I was looking for wasn't even on. Not only do I get instances where the network doesn't connect, and result codes show no errors, but I also get instances where I get an alert that says that the network is unreachable, yet my IoT shows that the app is connected to its Wi-Fi. On the iOS device, I go to the Wi-Fi settings, and see that I am on the IoT's network. So basically, sometimes I connect, but the frameworks says that there is no connection, and sometimes it reports a connection when there is none. As you can see in the code, I call cleanupHotspot() to make the iOS device get off of my temp Wi-Fi SSID. This is the code: func cleanupHotspot() { NEHotspotConfigurationManager.shared.removeConfiguration(forSSID: ssid) } That code gets called by the above code when things aren't as I expect and need to cleanup. And I also call it when the user dismisses the viewcontroller that is attempting to make the connection. It doesn't always work. I get stuck on the tempo SSID, unless I go through this whole thing again: try to make the connection again, this time it succeeds quickly, and then I can disconnect. Any ideas? I'm on iOS18.5, and have tried this on multiple iPhones including 11, 13 and 16.
3
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220
Nov ’25
Matter OTA on TestNet: HomePod always replies "UpdateNotAvailable" (Device is already CSA Certified)
Hi Apple Team / Community, We are currently pulling our hair out over a TestNet OTA issue and could really use some help. Our Matter Door Lock (VID: 5424, PID: 513) has already obtained official CSA Certification, so we are 100% confident that our device firmware and OTA Requestor logic are completely solid. However, we simply cannot get Apple's TestNet to serve the update via HomePod. Here is exactly what is happening: Our device successfully sends a QueryImage command to the HomePod. The HomePod receives it, but immediately fires back a QueryImageResponse that essentially means "UpdateNotAvailable", forcing the device into an 86400-second sleep timeout. Here is what we have verified so far: Local OTA works perfectly: If we use Nordic's chip-ota-provider-app locally with the exact same .ota file, the BDX transfer triggers instantly and the device updates without a hitch. DCL details are 100% accurate: We published a brand new version (1.0.4 / 16778240) which is strictly higher than the device's current version (1.0.1 / 16777472). The otaFileSize (973839) and Base64 Checksum match the file perfectly. ZERO hits on our server: The OTA file is hosted on an AWS S3 direct link (SSL Grade A via SSL Labs, ATS compliant). We checked our server logs, and there hasn't been a single download attempt from any Apple IP addresses. Since our device is certified and local OTA works flawlessly, it strongly feels like Apple's TestNet backend either has a stuck/cached "invalid" state for our VID/PID (very similar to what was reported in CHIP GitHub Issue #29338), or the Apple backend crawler is failing to reach our URL for some internal reason. Could someone please check if there is a cached exception for VID: 5424 / PID: 513 on the TestNet backend? Any help or pointers would be hugely appreciated! Thanks in advance.
3
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176
Mar ’26
URL Filter Prefetch Interval guarantee
Hello, I have implemented a URL Filter using the sample provided here: Filtering Traffic by URL. I am also using an App Group to dynamically manage the Bloom filter and block list data. However, when I update my block list URLs and create a new Bloom filter plist in the App Group, the extension does not seem to use the updated Bloom filter even after the prefetch interval expires. Also for testing purpose can I keep this interval to 10 mins or below ?
3
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331
Mar ’26
Could not delete cookies on IOS18
Hello, I have encountered an issue with an iPhone 15PM with iOS 18.5. The NSHTTPCookieStorage failed to clear cookies, after clearing them, I was still able to retrieve them. However, on the same system NSHTTPCookie *cookie; NSHTTPCookieStorage *storage = [NSHTTPCookieStorage sharedHTTPCookieStorage]; for (cookie in [storage cookies]) { [storage deleteCookie:cookie]; } NSArray *cookies = [[NSHTTPCookieStorage sharedHTTPCookieStorage] cookiesForURL:[[self url] absoluteURL]]; // still able to get cookies,why???
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131
Jun ’25
AccessorySetupKit / Wi-Fi Aware example?
Greetings, According to Apple's Wi-Fi Aware documentation (https://developer.apple.com/documentation/wifiaware) the Wi-Fi Aware APIs can be used only with peer devices that have been paired. Pairing can be performed using AccessorySetupKit or DeviceDiscoveryUI. Unfortunately, the sample code for Wi-Fi Aware doesn't include either of these APIs. (https://developer.apple.com/documentation/wifiaware/building-peer-to-peer-apps) Looking at the sample code for AccessorySetupKit (https://developer.apple.com/documentation/accessorysetupkit/setting-up-and-authorizing-a-bluetooth-accessory) there is only an example using Bluetooth. And the AccessorySetupKit APIs don't yet document how Wi-Fi Aware is used or how one sets up the Info.plist with the appropriate keys. Can Apple update its example code to fill in these gaps or point me to documentation that can fill in these gaps? It is hard to develop an understanding of the capabilities of these APIs when they are so poorly documented. Thanks for any help, Smith
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261
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!
4
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379
Feb ’26
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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64
Mar ’26
Understanding NEHotspotConfigurationErrorInternal
Error 8 in the NEHotspotConfigurationError domain is .internal, aka NEHotspotConfigurationErrorInternal. This error typically indicates that something went wrong in some sort of expected way, but we decided not to surface the exact cause [1]. This has come up a bunch of times before on the forums, and I have various titbits to share. To start, I want to address some specific cases: You’ll see this error if your app isn’t signed with the com.apple.developer.networking.HotspotConfiguration entitlement. To fix this, use Xcode’s Signing & Capabilities editor to add the Hotspot capability to your app. Historically developers reported a situation where once they encountered the error it would show up consistently, but then it would go away on restarting the device. If you see behaviour like that, that’s definitely a bug and I encourage you to file it as such. I have more about filing such bugs in Filing a Wi-Fi Bug Report. Of course, you have to wait to reproduce the error again before you’ll be able to file that bug, because the act of restarting cleared the issue. I’ve seen reports where such problems only occur on a specific type of device, for example, on iPhone 16 but not on earlier or later iPhones. That’s definitely something that Apple should investigate, and I recommend that you file a bug about it. If the problem is being reported by your users but you can’t reproduce it yourself, consider the various suggestions in Using a Sysdiagnose Log to Debug a Hard-to-Reproduce Problem. Assuming you’re still here (-: the next step is to determine whether the problem is specific to NEHotspotConfigurationManager or not. Try joining the accessory’s network from Settings > Wi-Fi. Does that also have problems? If so, that’s not something we can help you with here on the forums. The focus of the Apple Developer Forums is primarily to help developers with the APIs in Apple’s various platform SDKs [2]. We’re not set up to help accessory developers with Wi-Fi issues. However, there are still things you can do, as I explain in Filing a Wi-Fi Bug Report. At this point you have an error that: Persists across restarts Happens with all Apple devices You can reproduce Only affects NEHotspotConfigurationManager If that’s correct then there are a couple of things you might look at: Coerce the error to an NSError and print that. Does it reveal anything interesting? Also check the underlying error property (NSUnderlyingErrorKey) for hints. When reproducing the error, monitor the system log for log entries in the com.apple.networkextension subsystem. Do those offer any clues? Note For lots of hints and tips about the system log, see Your Friend the System Log. And finally, if you have questions about this case, feel free to start a thread here on the forums and we’ll try to help you out. Put it in the App & System Services > Networking subtopic and tag it with Network Extension. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" [1] There’s also the .unknown error. See this post for a brief summary of the difference. [2] And with Apple tools and some developer-oriented services. Revision History 2026-03-18 Added a missing entitlement bullet to the specific case list. 2026-03-17 First posted.
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Mar ’26
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
WiFi 6 MIMO and spatial audio support for CarPlay
On "Accessory Interface Specification CarPlay Addendum R10", it says that it is recommended that the accessory uses a MIMO (2x2) hardware configuration, does this imply that WiFi 5 and SISO (1X1) will be phased out in the near future? When will WiFi 6 MIMO (2x2) become mandatory? On "Accessory Interface Specification CarPlay Addendum R10", it says that Spatial Audio is mandatory. However, for aftermarket in-vehicle infotainment (IVI) system due to the number of speakers are less than 6, is it allowed not to support spatial audio for this type of aftermarket IVI system?
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Jul ’25
NWEndpoint History and Advice
The path from Network Extension’s in-provider networking APIs to Network framework has been long and somewhat rocky. The most common cause of confusion is NWEndpoint, where the same name can refer to two completely different types. I’ve helped a bunch of folks with this over the years, and I’ve decided to create this post to collect together all of those titbits. If you have questions or comments, please put them in a new thread. Put it in the App & System Services > Networking subtopic and tag it with Network Extension. That way I’ll be sure to see it go by. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" NWEndpoint History and Advice A tale that spans three APIs, two languages, and ten years. The NWEndpoint type has a long and complex history, and if you’re not aware of that history you can bump into weird problems. The goal of this post is to explain the history and then offer advice on how to get around specific problems. IMPORTANT This post focuses on NWEndpoint, because that’s the type that causes the most problems, but there’s a similar situation with NWPath. The History In iOS 9 Apple introduced the Network Extension (NE) framework, which offers a convenient way for developers to create a custom VPN transport. Network Extension types all have the NE prefix. Note I’m gonna use iOS versions here, just to keep the text simple. If you’re targeting some other platform, use this handy conversion table: iOS | macOS | tvOS | watchOS | visionOS --- + ----- + ---- + ------- + -------- 9 | 10.11 | 9 | 2 | - 12 | 10.14 | 12 | 5 | - 18 | 15 | 18 | 11 | 2 At that time we also introduced in-provider networking APIs. The idea was that an NE provider could uses these Objective-C APIs to communicate with its VPN server, and thereby avoiding a bunch of ugly BSD Sockets code. The in-provider networking APIs were limited to NE providers. Specifically, the APIs to construct an in-provider connection were placed on types that were only usable within an NE provider. For example, a packet tunnel provider could create a NWTCPConnection object by calling -createTCPConnectionToEndpoint:enableTLS:TLSParameters:delegate:] and -createTCPConnectionThroughTunnelToEndpoint:enableTLS:TLSParameters:delegate:, which are both methods on NEPacketTunnelProvider. These in-provider networking APIs came with a number of ancillary types, including NWEndpoint and NWPath. At the time we thought that we might promote these in-provider networking APIs to general-purpose networking APIs. That’s why the APIs use the NW prefix. For example, it’s NWTCPConnection, not NETCPConnection. However, plans changed. In iOS 12 Apple shipped Network framework as our recommended general-purpose networking API. This actually includes two APIs: A Swift API that follows Swift conventions, for example, the connection type is called NWConnection A C API that follows C conventions, for example, the connection type is called nw_connection_t These APIs follow similar design patterns to the in-provider networking API, and thus have similar ancillary types. Specifically, there are an NWEndpoint and nw_endpoint_t types, both of which perform a similar role to the NWEndpoint type in the in-provider networking API. This was a source of some confusion in Swift, because the name NWEndpoint could refer to either the Network framework type or the Network Extension framework type, depending on what you’d included. Fortunately you could get around this by qualifying the type as either Network.NWEndpoint or NetworkExtension.NWEndpoint. The arrival of Network framework meant that it no longer made sense to promote the in-provider networking APIs to general-purposes networking APIs. The in-provider networking APIs were on the path to deprecation. However, deprecating these APIs was actually quite tricky. Network Extension framework uses these APIs in a number of interesting ways, and so deprecating them required adding replacements. In addition, we’d needed different replacements for Swift and Objective-C, because Network framework has separate APIs for Swift and C-based languages. In iOS 18 we tackled that problem head on. To continue the NWTCPConnection example above, we replaced: -createTCPConnectionToEndpoint:enableTLS:TLSParameters:delegate:] with nw_connection_t -createTCPConnectionThroughTunnelToEndpoint:enableTLS:TLSParameters:delegate: with nw_connection_t combined with a new virtualInterface property on NEPacketTunnelProvider Of course that’s the Objective-C side of things. In Swift, the replacement is NWConnection rather than nw_connection_t, and the type of the virtualInterface property is NWInterface rather than nw_interface_t. But that’s not the full story. For the two types that use the same name in both frameworks, NWEndpoint and NWPath, we decided to use this opportunity to sort out that confusion. To see how we did that, check out the <NetworkExtension/NetworkExtension.apinotes> file in the SDK. Focusing on NWEndpoint for the moment, you’ll find two entries: … - Name: NWEndpoint SwiftPrivate: true … SwiftVersions: - Version: 5.0 … - Name: NWEndpoint SwiftPrivate: false … The first entry applies when you’re building with the Swift 6 language mode. This marks the type as SwiftPrivate, which means that Swift imports it as __NWEndpoint. That frees up the NWEndpoint name to refer exclusively to the Network framework type. The second entry applies when you’re building with the Swift 5 language mode. It marks the type as not SwiftPrivate. This is a compatible measure to ensure that code written for Swift 5 continues to build. The Advice This sections discusses specific cases in this transition. NWEndpoint and NWPath In Swift 5 language mode, NWEndpoint and NWPath might refer to either framework, depending on what you’ve imported. Add a qualifier if there’s any ambiguity, for example, Network.NWEndpoint or NetworkExtension.NWEndpoint. In Swift 6 language mode, NWEndpoint and NWPath always refer to the Network framework type. Add a __ prefix to get to the Network Extension type. For example, use NWEndpoint for the Network framework type and __NWEndpoint for the Network Extension type. Direct and Through-Tunnel TCP Connections in Swift To create a connection directly, simply create an NWConnection. This support both TCP and UDP, with or without TLS. To create a connection through the tunnel, replace code like this: let c = self.createTCPConnectionThroughTunnel(…) with code like this: let params = NWParameters.tcp params.requiredInterface = self.virtualInterface let c = NWConnection(to: …, using: params) This is for TCP but the same basic process applies to UDP. UDP and App Proxies in Swift If you’re building an app proxy, transparent proxy, or DNS proxy in Swift and need to handle UDP flows using the new API, adopt the NEAppProxyUDPFlowHandling protocol. So, replace code like this: class AppProxyProvider: NEAppProxyProvider { … override func handleNewUDPFlow(_ flow: NEAppProxyUDPFlow, initialRemoteEndpoint remoteEndpoint: NWEndpoint) -> Bool { … } } with this: class AppProxyProvider: NEAppProxyProvider, NEAppProxyUDPFlowHandling { … func handleNewUDPFlow(_ flow: NEAppProxyUDPFlow, initialRemoteFlowEndpoint remoteEndpoint: NWEndpoint) -> Bool { … } } Creating a Network Rule To create an NWHostEndpoint, replace code like this: let ep = NWHostEndpoint(hostname: "1.2.3.4", port: "12345") let r = NENetworkRule(destinationHost: ep, protocol: .TCP) with this: let ep = NWEndpoint.hostPort(host: "1.2.3.4", port: 12345) let r = NENetworkRule(destinationHostEndpoint: ep, protocol: .TCP) Note how the first label of the initialiser has changed from destinationHost to destinationHostEndpoint.
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Jul ’25
Pair iOS Central with MacOS Peripheral for encrypted characteristic
Is this even possible? Instead of any pairing dialog appearing, my central code get the "Authentication is insufficient" error when reading the characteristic. My peripheral (in the macOS app) code uses the .notifyEncryptionRequired property and uses .readEncryptionRequired and .writeEncryptionRequired permissions. No descriptors are set, but I think they get added automatically since this characteristic notifies. 2900 and 2902 descriptors are set by the peripheral/CoreBluetooth. If the Mac and iPhone are using the same Apple ID does that affect pairing?
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Feb ’26
Consult about the "CNCopyCurrentNetworkInfo" interface
Hi In the "CaptiveNetwork.h", the "CNCopyCurrentNetworkInfo" is marked as "API_TO_BE_DEPRECATED" CFDictionaryRef __nullable CNCopyCurrentNetworkInfo (CFStringRef interfaceName) API_DEPRECATED_WITH_REPLACEMENT("[NEHotspotNetwork fetchCurrentWithCompletionHandler:]", ios(4.1, API_TO_BE_DEPRECATED), macCatalyst(14.0, API_TO_BE_DEPRECATED)) API_UNAVAILABLE(macos, tvos, watchos, visionos); But in developer documents, it is marked as "DEPRECATED": https://developer.apple.com/documentation/systemconfiguration/cncopycurrentnetworkinfo Before we use Xcode 16.2 to archive app, this interface still work on iOS 26 device. But after we changed to Xcode 26.2, this interface return nothing on iOS 26 and we need to use "NEHotspotNetwork" related interface. My question is: Why there are difference between the documents and framework sdk how we can know that a interface marked "API_TO_BE_DEPRECATED" or "DEPRECATED", when will they not work totally. Is there a accurate timeline or standard for them? Some interface marked deprecated after 12.0 is still working Now. After knowing the accurate timeline we can plan the interfaces migration.
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2h
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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478
Activity
Jun ’25
App occassionally crashing while connecting to public wifi
We are using the [NEHotspotHelper supportedNetworkInterfaces] to get the Wi-Fi interface in our app, but it occasionally crashes on some devices with the following stack trace: 0 CaptiveNetwork 0x0000000221d87a4c ServerConnectionGetHandlerQueue + 0 (ServerConnection.c:509) 1 CaptiveNetwork 0x0000000221d8577c CNPluginCopySupportedInterfaces + 180 (CNPlugin.c:457) 2 NetworkExtension 0x00000001b0446618 +[NEHotspotHelper supportedNetworkInterfaces] + 32 (NEHotspotHelper.m:563) It seems like the crash is happening on apple's api of supportedNetworkInterfaces. We would like to understand the cause of the crash.
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104
Activity
May ’25
Background UDP receive for lighting control (Art-Net/sACN)
I'm developing a lighting control app for iOS that receives Art-Net (UDP port 6454) and sACN (UDP port 5568) packets from a lighting console and relays commands to BLE wristbands with LEDs. This is used in live event production — the participant locks their phone while in a show and expects lighting control to continue uninterrupted. The problem UDP receive stops reliably ~30 seconds after the screen locks. I understand this is by design - iOS suspends apps in the background. However, I'm trying to understand if any supported path exists for this use case. What I've already tried UIRequiresPersistentWiFi = true - helps with Wi-Fi association but doesn't prevent app suspension Silent AVAudioEngine loop with UIBackgroundModes: audio - keeps the app alive, works in testing, but risks App Store rejection and feels like an abuse of the audio background mode NWListener (Network framework) on the UDP port - same suspension behaviour Socket rebind on applicationWillEnterForeground - recovers after resume but doesn't prevent dropout What I'm asking Is there any supported background mode or entitlement for sustained UDP receive in a professional/enterprise context? (Similar to how VoIP apps get the voip background mode for sustained network activity.) Is the silent audio workaround considered acceptable for App Store distribution in a professional tools context, or will it be rejected? Is NEAppProxyProvider or another Network Extension a viable path, and if so does it require a special entitlement? Test project I have a minimal Xcode project (~130 lines) demonstrating the issue — NWListener on port 6454, packet counter, staleness timer, and silent audio toggle. I can share the test code. STEPS TO REPRODUCE In Xcode (one-time setup): Select the UDPBackgroundTest target → Signing & Capabilities → set your Team Plug in your iPhone → select it as the run destination Build & run — confirm packets appear on screen when you run 'send_test_udp.py' Lock the phone and observe the dropout Test: Open the app and run 'python3 send_test_udp.py 192.168.0.XXX' The app counts up the packages, they match the python output. 1 packet per second. lock screen & and wait 10 seconds unlock phone an see the numbers are 10 packets off
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88
Activity
Apr ’26
TLS for App Developers
Transport Layer Security (TLS) is the most important security protocol on the Internet today. Most notably, TLS puts the S into HTTPS, adding security to the otherwise insecure HTTP protocol. IMPORTANT TLS is the successor to the Secure Sockets Layer (SSL) protocol. SSL is no longer considered secure and it’s now rarely used in practice, although many folks still say SSL when they mean TLS. TLS is a complex protocol. Much of that complexity is hidden from app developers but there are places where it’s important to understand specific details of the protocol in order to meet your requirements. This post explains the fundamentals of TLS, concentrating on the issues that most often confuse app developers. Note The focus of this is TLS-PKI, where PKI stands for public key infrastructure. This is the standard TLS as deployed on the wider Internet. There’s another flavour of TLS, TLS-PSK, where PSK stands for pre-shared key. This has a variety of uses, but an Apple platforms we most commonly see it with local traffic, for example, to talk to a Wi-Fi based accessory. For more on how to use TLS, both TLS-PKI and TLS-PSK, in a local context, see TLS For Accessory Developers. Server Certificates For standard TLS to work the server must have a digital identity, that is, the combination of a certificate and the private key matching the public key embedded in that certificate. TLS Crypto Magic™ ensures that: The client gets a copy of the server’s certificate. The client knows that the server holds the private key matching the public key in that certificate. In a typical TLS handshake the server passes the client a list of certificates, where item 0 is the server’s certificate (the leaf certificate), item N is (optionally) the certificate of the certificate authority that ultimately issued that certificate (the root certificate), and items 1 through N-1 are any intermediate certificates required to build a cryptographic chain of trust from 0 to N. Note The cryptographic chain of trust is established by means of digital signatures. Certificate X in the chain is issued by certificate X+1. The owner of certificate X+1 uses their private key to digitally sign certificate X. The client verifies this signature using the public key embedded in certificate X+1. Eventually this chain terminates in a trusted anchor, that is, a certificate that the client trusts by default. Typically this anchor is a self-signed root certificate from a certificate authority. Note Item N is optional for reasons I’ll explain below. Also, the list of intermediate certificates may be empty (in the case where the root certificate directly issued the leaf certificate) but that’s uncommon for servers in the real world. Once the client gets the server’s certificate, it evaluates trust on that certificate to confirm that it’s talking to the right server. There are three levels of trust evaluation here: Basic X.509 trust evaluation checks that there’s a cryptographic chain of trust from the leaf through the intermediates to a trusted root certificate. The client has a set of trusted root certificates built in (these are from well-known certificate authorities, or CAs), and a site admin can add more via a configuration profile. This step also checks that none of the certificates have expired, and various other more technical criteria (like the Basic Constraints extension). Note This explains why the server does not have to include the root certificate in the list of certificates it passes to the client; the client has to have the root certificate installed if trust evaluation is to succeed. In addition, TLS trust evaluation (per RFC 2818) checks that the DNS name that you connected to matches the DNS name in the certificate. Specifically, the DNS name must be listed in the Subject Alternative Name extension. Note The Subject Alternative Name extension can also contain IP addresses, although that’s a much less well-trodden path. Also, historically it was common to accept DNS names in the Common Name element of the Subject but that is no longer the case on Apple platforms. App Transport Security (ATS) adds its own security checks. Basic X.509 and TLS trust evaluation are done for all TLS connections. ATS is only done on TLS connections made by URLSession and things layered on top URLSession (like WKWebView). In many situations you can override trust evaluation; for details, see Technote 2232 HTTPS Server Trust Evaluation). Such overrides can either tighten or loosen security. For example: You might tighten security by checking that the server certificate was issued by a specific CA. That way, if someone manages to convince a poorly-managed CA to issue them a certificate for your server, you can detect that and fail. You might loosen security by adding your own CA’s root certificate as a trusted anchor. IMPORTANT If you rely on loosened security you have to disable ATS. If you leave ATS enabled, it requires that the default server trust evaluation succeeds regardless of any customisations you do. Mutual TLS The previous section discusses server trust evaluation, which is required for all standard TLS connections. That process describes how the client decides whether to trust the server. Mutual TLS (mTLS) is the opposite of that, that is, it’s the process by which the server decides whether to trust the client. Note mTLS is commonly called client certificate authentication. I avoid that term because of the ongoing industry-wide confusion between certificates and digital identities. While it’s true that, in mTLS, the server authenticates the client certificate, to set this up on the client you need a digital identity, not a certificate. mTLS authentication is optional. The server must request a certificate from the client and the client may choose to supply one or not (although if the server requests a certificate and the client doesn’t supply one it’s likely that the server will then fail the connection). At the TLS protocol level this works much like it does with the server certificate. For the client to provide this certificate it must apply a digital identity, known as the client identity, to the connection. TLS Crypto Magic™ assures the server that, if it gets a certificate from the client, the client holds the private key associated with that certificate. Where things diverge is in trust evaluation. Trust evaluation of the client certificate is done on the server, and the server uses its own rules to decided whether to trust a specific client certificate. For example: Some servers do basic X.509 trust evaluation and then check that the chain of trust leads to one specific root certificate; that is, a client is trusted if it holds a digital identity whose certificate was issued by a specific CA. Some servers just check the certificate against a list of known trusted client certificates. When the client sends its certificate to the server it actually sends a list of certificates, much as I’ve described above for the server’s certificates. In many cases the client only needs to send item 0, that is, its leaf certificate. That’s because: The server already has the intermediate certificates required to build a chain of trust from that leaf to its root. There’s no point sending the root, as I discussed above in the context of server trust evaluation. However, there are no hard and fast rules here; the server does its client trust evaluation using its own internal logic, and it’s possible that this logic might require the client to present intermediates, or indeed present the root certificate even though it’s typically redundant. If you have problems with this, you’ll have to ask the folks running the server to explain its requirements. Note If you need to send additional certificates to the server, pass them to the certificates parameter of the method you use to create your URLCredential (typically init(identity:certificates:persistence:)). One thing that bears repeating is that trust evaluation of the client certificate is done on the server, not the client. The client doesn’t care whether the client certificate is trusted or not. Rather, it simply passes that certificate the server and it’s up to the server to make that decision. When a server requests a certificate from the client, it may supply a list of acceptable certificate authorities [1]. Safari uses this to filter the list of client identities it presents to the user. If you are building an HTTPS server and find that Safari doesn’t show the expected client identity, make sure you have this configured correctly. If you’re building an iOS app and want to implement a filter like Safari’s, get this list using: The distinguishedNames property, if you’re using URLSession The sec_protocol_metadata_access_distinguished_names routine, if you’re using Network framework [1] See the certificate_authorities field in Section 7.4.4 of RFC 5246, and equivalent features in other TLS versions. Self-Signed Certificates Self-signed certificates are an ongoing source of problems with TLS. There’s only one unequivocally correct place to use a self-signed certificate: the trusted anchor provided by a certificate authority. One place where a self-signed certificate might make sense is in a local environment, that is, securing a connection between peers without any centralised infrastructure. However, depending on the specific circumstances there may be a better option. TLS For Accessory Developers discusses this topic in detail. Finally, it’s common for folks to use self-signed certificates for testing. I’m not a fan of that approach. Rather, I recommend the approach described in QA1948 HTTPS and Test Servers. For advice on how to set that up using just your Mac, see TN2326 Creating Certificates for TLS Testing. TLS Standards RFC 6101 The Secure Sockets Layer (SSL) Protocol Version 3.0 (historic) RFC 2246 The TLS Protocol Version 1.0 RFC 4346 The Transport Layer Security (TLS) Protocol Version 1.1 RFC 5246 The Transport Layer Security (TLS) Protocol Version 1.2 RFC 8446 The Transport Layer Security (TLS) Protocol Version 1.3 RFC 4347 Datagram Transport Layer Security RFC 6347 Datagram Transport Layer Security Version 1.2 RFC 9147 The Datagram Transport Layer Security (DTLS) Protocol Version 1.3 Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" Revision History: 2025-11-21 Clearly defined the terms TLS-PKI and TLS-PSK. 2024-03-19 Adopted the term mutual TLS in preference to client certificate authentication throughout, because the latter feeds into the ongoing certificate versus digital identity confusion. Defined the term client identity. Added the Self-Signed Certificates section. Made other minor editorial changes. 2023-02-28 Added an explanation mTLS acceptable certificate authorities. 2022-12-02 Added links to the DTLS RFCs. 2022-08-24 Added links to the TLS RFCs. Made other minor editorial changes. 2022-06-03 Added a link to TLS For Accessory Developers. 2021-02-26 Fixed the formatting. Clarified that ATS only applies to URLSession. Minor editorial changes. 2020-04-17 Updated the discussion of Subject Alternative Name to account for changes in the 2019 OS releases. Minor editorial updates. 2018-10-29 Minor editorial updates. 2016-11-11 First posted.
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Activity
Nov ’25
test NEAppProxyProvider without MDM?
This discussion is for iOS/iPadOS. I've written an NEAppProxyProvider network extension. I'd like to test it. I thought that using the "NETestAppMapping" dictionary was a way to get there, but when I try to instantiate an NEAppProxyProviderManager to try to install stuff, the console tells me "must be MDM managed" and I get nowhere. So can someone tell me, can I at least test the idea without needing to first get MDM going? I'd like to know if how I'm approaching the core problem even makes sense. My custom application needs to stream video, via the SRT protocol, to some place like youtube or castr. The problem is that in the environment we are in (big convention centers), our devices are on a LAN, but the connection from the LAN out to the rest of the world just sucks. Surprisingly, cellular has better performance. So I am trying to do the perverse thing of forcing traffix that is NOT local to go out over cellular. And traffic that is completely local (i.e. talking to a purely local server/other devices on the LAN) happens over ethernet. [To simplify things, wifi is not connected.] Is an app proxy the right tool for this? Is there any other tool? Unfortunately, I cannot rewrite the code to force everything through Apple's Network framework, which is the one place I know we can say "use cellular." [E.g. URLSession() has absolutely no way of forcing cellular, and even so, the low level streaming library I use is written with raw sockets, and its not feasible for me to rewrite it.] Any other suggestions of how to accomplish this "send non-local traffic to cellular, all local traffic out over ethernet" gratefully welcomed!
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171
Activity
Mar ’26
NEHotspotNetwork headaches
I'm trying to use NEHotspotNetwork to configure an IoT. I've read all the issues that have plagued other developers when using this framework, and I was under the impression that bugs were filed and fixed. Here are my issues in hopes that someone can catch my bug, or has finally figured this out and it's not a bug in the framework with no immediate fix on the horizon. If I use the following code: let config = NEHotspotConfiguration(ssid: ssid) config.joinOnce = true KiniStatusBanner.shared.show(text: "Connecting to Kini", in: presentingVC.view) NEHotspotConfigurationManager.shared.apply(config) { error in DispatchQueue.main.async { if let nsError = error as NSError?, nsError.domain == NEHotspotConfigurationErrorDomain, nsError.code == NEHotspotConfigurationError.alreadyAssociated.rawValue { print("Already connected to \(self.ssid)") KiniStatusBanner.shared.dismiss() self.presentCaptivePortal(from: presentingVC, activationCode: activationCode) } else if let error = error { // This doesn't happen print("❌ Failed to connect: \(error.localizedDescription)") KiniStatusBanner.shared.update(text: "Failed to Connect to Kini. Try again later.") KiniStatusBanner.shared.dismiss(after: 2.5) } else { // !!!! Most often, this is the path the code takes NEHotspotNetwork.fetchCurrent { current in if let ssid = current?.ssid, ssid == self.ssid { log("✅✅ 1st attempt: connected to \(self.ssid)") KiniStatusBanner.shared.dismiss() self.presentCaptivePortal(from: presentingVC, activationCode: activationCode) } else { // Dev forums talked about giving things a bit of time to settle and then try again DispatchQueue.main.asyncAfter(deadline: .now() + 2) { NEHotspotNetwork.fetchCurrent { current in if let ssid = current?.ssid, ssid == self.ssid { log("✅✅✅ 2nd attempt: connected to \(self.ssid)") KiniStatusBanner.shared.dismiss() self.presentCaptivePortal(from: presentingVC, activationCode: activationCode) } else { log("❌❌❌ 2nd attempt: Failed to connect: \(self.ssid)") KiniStatusBanner.shared.update(text: "Could not join Kini network. Try again.") KiniStatusBanner.shared.dismiss(after: 2.5) self.cleanupHotspot() DispatchQueue.main.asyncAfter(deadline: .now() + 2) { print("cleanup again") self.cleanupHotspot() } } } } log("❌❌ 1st attempt: Failed to connect: \(self.ssid)") KiniStatusBanner.shared.update(text: "Could not join Kini network. Try again.") KiniStatusBanner.shared.dismiss(after: 2.5) self.cleanupHotspot() } As you can see, one can't just use NEHotspotConfigurationManager.shared.apply and has to double-check to make sure that it actually succeeds, by checking to see if the SSID desired, matches the one that the device is using. Ok, but about 50% of the time, the call to NEHotspotNetwork.fetchCurrent gives me this error: NEHotspotNetwork nehelper sent invalid result code [1] for Wi-Fi information request Well, there is a workaround for that randomness too. At some point before calling this code, one can: let locationManager = CLLocationManager() locationManager.requestWhenInUseAuthorization() That eliminates the NEHotspotNetwork nehelper sent invalid result code [1] for Wi-Fi information request BUT... three issues. The user is presented with an authorization alert: Allow "Kini" to use your location? This app needs access to you Wi-Fi name to connect to your Kini device. Along with a map with a location pin on it. This gives my users a completely wrong impression, especially for a device/app where we promise users not to track their location. They actually see a map with their location pinned on it, implying something that would freak out anyone who was expecting no tracking. I understand why an authorization is normally required, but since all we are getting is our own IoT's SSID, there should be no need for an authorization for this, and no map associated with the request. Again, they are accessing my IoT's network, NOT their home/location Wi-Fi SSID. My app already knows and specifies that network, and all I am trying to do is to work around a bug that makes it look like I have a successful return from NEHotspotConfigurationManager.shared.apply() when in fact the network I was looking for wasn't even on. Not only do I get instances where the network doesn't connect, and result codes show no errors, but I also get instances where I get an alert that says that the network is unreachable, yet my IoT shows that the app is connected to its Wi-Fi. On the iOS device, I go to the Wi-Fi settings, and see that I am on the IoT's network. So basically, sometimes I connect, but the frameworks says that there is no connection, and sometimes it reports a connection when there is none. As you can see in the code, I call cleanupHotspot() to make the iOS device get off of my temp Wi-Fi SSID. This is the code: func cleanupHotspot() { NEHotspotConfigurationManager.shared.removeConfiguration(forSSID: ssid) } That code gets called by the above code when things aren't as I expect and need to cleanup. And I also call it when the user dismisses the viewcontroller that is attempting to make the connection. It doesn't always work. I get stuck on the tempo SSID, unless I go through this whole thing again: try to make the connection again, this time it succeeds quickly, and then I can disconnect. Any ideas? I'm on iOS18.5, and have tried this on multiple iPhones including 11, 13 and 16.
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Nov ’25
Matter OTA on TestNet: HomePod always replies "UpdateNotAvailable" (Device is already CSA Certified)
Hi Apple Team / Community, We are currently pulling our hair out over a TestNet OTA issue and could really use some help. Our Matter Door Lock (VID: 5424, PID: 513) has already obtained official CSA Certification, so we are 100% confident that our device firmware and OTA Requestor logic are completely solid. However, we simply cannot get Apple's TestNet to serve the update via HomePod. Here is exactly what is happening: Our device successfully sends a QueryImage command to the HomePod. The HomePod receives it, but immediately fires back a QueryImageResponse that essentially means "UpdateNotAvailable", forcing the device into an 86400-second sleep timeout. Here is what we have verified so far: Local OTA works perfectly: If we use Nordic's chip-ota-provider-app locally with the exact same .ota file, the BDX transfer triggers instantly and the device updates without a hitch. DCL details are 100% accurate: We published a brand new version (1.0.4 / 16778240) which is strictly higher than the device's current version (1.0.1 / 16777472). The otaFileSize (973839) and Base64 Checksum match the file perfectly. ZERO hits on our server: The OTA file is hosted on an AWS S3 direct link (SSL Grade A via SSL Labs, ATS compliant). We checked our server logs, and there hasn't been a single download attempt from any Apple IP addresses. Since our device is certified and local OTA works flawlessly, it strongly feels like Apple's TestNet backend either has a stuck/cached "invalid" state for our VID/PID (very similar to what was reported in CHIP GitHub Issue #29338), or the Apple backend crawler is failing to reach our URL for some internal reason. Could someone please check if there is a cached exception for VID: 5424 / PID: 513 on the TestNet backend? Any help or pointers would be hugely appreciated! Thanks in advance.
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Mar ’26
URL Filter Prefetch Interval guarantee
Hello, I have implemented a URL Filter using the sample provided here: Filtering Traffic by URL. I am also using an App Group to dynamically manage the Bloom filter and block list data. However, when I update my block list URLs and create a new Bloom filter plist in the App Group, the extension does not seem to use the updated Bloom filter even after the prefetch interval expires. Also for testing purpose can I keep this interval to 10 mins or below ?
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Mar ’26
Could not delete cookies on IOS18
Hello, I have encountered an issue with an iPhone 15PM with iOS 18.5. The NSHTTPCookieStorage failed to clear cookies, after clearing them, I was still able to retrieve them. However, on the same system NSHTTPCookie *cookie; NSHTTPCookieStorage *storage = [NSHTTPCookieStorage sharedHTTPCookieStorage]; for (cookie in [storage cookies]) { [storage deleteCookie:cookie]; } NSArray *cookies = [[NSHTTPCookieStorage sharedHTTPCookieStorage] cookiesForURL:[[self url] absoluteURL]]; // still able to get cookies,why???
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Jun ’25
AccessorySetupKit / Wi-Fi Aware example?
Greetings, According to Apple's Wi-Fi Aware documentation (https://developer.apple.com/documentation/wifiaware) the Wi-Fi Aware APIs can be used only with peer devices that have been paired. Pairing can be performed using AccessorySetupKit or DeviceDiscoveryUI. Unfortunately, the sample code for Wi-Fi Aware doesn't include either of these APIs. (https://developer.apple.com/documentation/wifiaware/building-peer-to-peer-apps) Looking at the sample code for AccessorySetupKit (https://developer.apple.com/documentation/accessorysetupkit/setting-up-and-authorizing-a-bluetooth-accessory) there is only an example using Bluetooth. And the AccessorySetupKit APIs don't yet document how Wi-Fi Aware is used or how one sets up the Info.plist with the appropriate keys. Can Apple update its example code to fill in these gaps or point me to documentation that can fill in these gaps? It is hard to develop an understanding of the capabilities of these APIs when they are so poorly documented. Thanks for any help, Smith
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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
URL Filter OHTTP Gateway
Hello team, We are using below example https://github.com/apple/pir-service-example as a starting point to setup PIR server for our backend, but I am not really understanding what else we need in this example to configure OHTTP gateway. Any help will be appreciated.
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Apr ’26
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.
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Feb ’26
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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Mar ’26
Understanding NEHotspotConfigurationErrorInternal
Error 8 in the NEHotspotConfigurationError domain is .internal, aka NEHotspotConfigurationErrorInternal. This error typically indicates that something went wrong in some sort of expected way, but we decided not to surface the exact cause [1]. This has come up a bunch of times before on the forums, and I have various titbits to share. To start, I want to address some specific cases: You’ll see this error if your app isn’t signed with the com.apple.developer.networking.HotspotConfiguration entitlement. To fix this, use Xcode’s Signing & Capabilities editor to add the Hotspot capability to your app. Historically developers reported a situation where once they encountered the error it would show up consistently, but then it would go away on restarting the device. If you see behaviour like that, that’s definitely a bug and I encourage you to file it as such. I have more about filing such bugs in Filing a Wi-Fi Bug Report. Of course, you have to wait to reproduce the error again before you’ll be able to file that bug, because the act of restarting cleared the issue. I’ve seen reports where such problems only occur on a specific type of device, for example, on iPhone 16 but not on earlier or later iPhones. That’s definitely something that Apple should investigate, and I recommend that you file a bug about it. If the problem is being reported by your users but you can’t reproduce it yourself, consider the various suggestions in Using a Sysdiagnose Log to Debug a Hard-to-Reproduce Problem. Assuming you’re still here (-: the next step is to determine whether the problem is specific to NEHotspotConfigurationManager or not. Try joining the accessory’s network from Settings > Wi-Fi. Does that also have problems? If so, that’s not something we can help you with here on the forums. The focus of the Apple Developer Forums is primarily to help developers with the APIs in Apple’s various platform SDKs [2]. We’re not set up to help accessory developers with Wi-Fi issues. However, there are still things you can do, as I explain in Filing a Wi-Fi Bug Report. At this point you have an error that: Persists across restarts Happens with all Apple devices You can reproduce Only affects NEHotspotConfigurationManager If that’s correct then there are a couple of things you might look at: Coerce the error to an NSError and print that. Does it reveal anything interesting? Also check the underlying error property (NSUnderlyingErrorKey) for hints. When reproducing the error, monitor the system log for log entries in the com.apple.networkextension subsystem. Do those offer any clues? Note For lots of hints and tips about the system log, see Your Friend the System Log. And finally, if you have questions about this case, feel free to start a thread here on the forums and we’ll try to help you out. Put it in the App & System Services > Networking subtopic and tag it with Network Extension. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" [1] There’s also the .unknown error. See this post for a brief summary of the difference. [2] And with Apple tools and some developer-oriented services. Revision History 2026-03-18 Added a missing entitlement bullet to the specific case list. 2026-03-17 First posted.
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Mar ’26
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
WiFi 6 MIMO and spatial audio support for CarPlay
On "Accessory Interface Specification CarPlay Addendum R10", it says that it is recommended that the accessory uses a MIMO (2x2) hardware configuration, does this imply that WiFi 5 and SISO (1X1) will be phased out in the near future? When will WiFi 6 MIMO (2x2) become mandatory? On "Accessory Interface Specification CarPlay Addendum R10", it says that Spatial Audio is mandatory. However, for aftermarket in-vehicle infotainment (IVI) system due to the number of speakers are less than 6, is it allowed not to support spatial audio for this type of aftermarket IVI system?
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Jul ’25
NWEndpoint History and Advice
The path from Network Extension’s in-provider networking APIs to Network framework has been long and somewhat rocky. The most common cause of confusion is NWEndpoint, where the same name can refer to two completely different types. I’ve helped a bunch of folks with this over the years, and I’ve decided to create this post to collect together all of those titbits. If you have questions or comments, please put them in a new thread. Put it in the App & System Services > Networking subtopic and tag it with Network Extension. That way I’ll be sure to see it go by. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" NWEndpoint History and Advice A tale that spans three APIs, two languages, and ten years. The NWEndpoint type has a long and complex history, and if you’re not aware of that history you can bump into weird problems. The goal of this post is to explain the history and then offer advice on how to get around specific problems. IMPORTANT This post focuses on NWEndpoint, because that’s the type that causes the most problems, but there’s a similar situation with NWPath. The History In iOS 9 Apple introduced the Network Extension (NE) framework, which offers a convenient way for developers to create a custom VPN transport. Network Extension types all have the NE prefix. Note I’m gonna use iOS versions here, just to keep the text simple. If you’re targeting some other platform, use this handy conversion table: iOS | macOS | tvOS | watchOS | visionOS --- + ----- + ---- + ------- + -------- 9 | 10.11 | 9 | 2 | - 12 | 10.14 | 12 | 5 | - 18 | 15 | 18 | 11 | 2 At that time we also introduced in-provider networking APIs. The idea was that an NE provider could uses these Objective-C APIs to communicate with its VPN server, and thereby avoiding a bunch of ugly BSD Sockets code. The in-provider networking APIs were limited to NE providers. Specifically, the APIs to construct an in-provider connection were placed on types that were only usable within an NE provider. For example, a packet tunnel provider could create a NWTCPConnection object by calling -createTCPConnectionToEndpoint:enableTLS:TLSParameters:delegate:] and -createTCPConnectionThroughTunnelToEndpoint:enableTLS:TLSParameters:delegate:, which are both methods on NEPacketTunnelProvider. These in-provider networking APIs came with a number of ancillary types, including NWEndpoint and NWPath. At the time we thought that we might promote these in-provider networking APIs to general-purpose networking APIs. That’s why the APIs use the NW prefix. For example, it’s NWTCPConnection, not NETCPConnection. However, plans changed. In iOS 12 Apple shipped Network framework as our recommended general-purpose networking API. This actually includes two APIs: A Swift API that follows Swift conventions, for example, the connection type is called NWConnection A C API that follows C conventions, for example, the connection type is called nw_connection_t These APIs follow similar design patterns to the in-provider networking API, and thus have similar ancillary types. Specifically, there are an NWEndpoint and nw_endpoint_t types, both of which perform a similar role to the NWEndpoint type in the in-provider networking API. This was a source of some confusion in Swift, because the name NWEndpoint could refer to either the Network framework type or the Network Extension framework type, depending on what you’d included. Fortunately you could get around this by qualifying the type as either Network.NWEndpoint or NetworkExtension.NWEndpoint. The arrival of Network framework meant that it no longer made sense to promote the in-provider networking APIs to general-purposes networking APIs. The in-provider networking APIs were on the path to deprecation. However, deprecating these APIs was actually quite tricky. Network Extension framework uses these APIs in a number of interesting ways, and so deprecating them required adding replacements. In addition, we’d needed different replacements for Swift and Objective-C, because Network framework has separate APIs for Swift and C-based languages. In iOS 18 we tackled that problem head on. To continue the NWTCPConnection example above, we replaced: -createTCPConnectionToEndpoint:enableTLS:TLSParameters:delegate:] with nw_connection_t -createTCPConnectionThroughTunnelToEndpoint:enableTLS:TLSParameters:delegate: with nw_connection_t combined with a new virtualInterface property on NEPacketTunnelProvider Of course that’s the Objective-C side of things. In Swift, the replacement is NWConnection rather than nw_connection_t, and the type of the virtualInterface property is NWInterface rather than nw_interface_t. But that’s not the full story. For the two types that use the same name in both frameworks, NWEndpoint and NWPath, we decided to use this opportunity to sort out that confusion. To see how we did that, check out the <NetworkExtension/NetworkExtension.apinotes> file in the SDK. Focusing on NWEndpoint for the moment, you’ll find two entries: … - Name: NWEndpoint SwiftPrivate: true … SwiftVersions: - Version: 5.0 … - Name: NWEndpoint SwiftPrivate: false … The first entry applies when you’re building with the Swift 6 language mode. This marks the type as SwiftPrivate, which means that Swift imports it as __NWEndpoint. That frees up the NWEndpoint name to refer exclusively to the Network framework type. The second entry applies when you’re building with the Swift 5 language mode. It marks the type as not SwiftPrivate. This is a compatible measure to ensure that code written for Swift 5 continues to build. The Advice This sections discusses specific cases in this transition. NWEndpoint and NWPath In Swift 5 language mode, NWEndpoint and NWPath might refer to either framework, depending on what you’ve imported. Add a qualifier if there’s any ambiguity, for example, Network.NWEndpoint or NetworkExtension.NWEndpoint. In Swift 6 language mode, NWEndpoint and NWPath always refer to the Network framework type. Add a __ prefix to get to the Network Extension type. For example, use NWEndpoint for the Network framework type and __NWEndpoint for the Network Extension type. Direct and Through-Tunnel TCP Connections in Swift To create a connection directly, simply create an NWConnection. This support both TCP and UDP, with or without TLS. To create a connection through the tunnel, replace code like this: let c = self.createTCPConnectionThroughTunnel(…) with code like this: let params = NWParameters.tcp params.requiredInterface = self.virtualInterface let c = NWConnection(to: …, using: params) This is for TCP but the same basic process applies to UDP. UDP and App Proxies in Swift If you’re building an app proxy, transparent proxy, or DNS proxy in Swift and need to handle UDP flows using the new API, adopt the NEAppProxyUDPFlowHandling protocol. So, replace code like this: class AppProxyProvider: NEAppProxyProvider { … override func handleNewUDPFlow(_ flow: NEAppProxyUDPFlow, initialRemoteEndpoint remoteEndpoint: NWEndpoint) -> Bool { … } } with this: class AppProxyProvider: NEAppProxyProvider, NEAppProxyUDPFlowHandling { … func handleNewUDPFlow(_ flow: NEAppProxyUDPFlow, initialRemoteFlowEndpoint remoteEndpoint: NWEndpoint) -> Bool { … } } Creating a Network Rule To create an NWHostEndpoint, replace code like this: let ep = NWHostEndpoint(hostname: "1.2.3.4", port: "12345") let r = NENetworkRule(destinationHost: ep, protocol: .TCP) with this: let ep = NWEndpoint.hostPort(host: "1.2.3.4", port: 12345) let r = NENetworkRule(destinationHostEndpoint: ep, protocol: .TCP) Note how the first label of the initialiser has changed from destinationHost to destinationHostEndpoint.
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Jul ’25
Pair iOS Central with MacOS Peripheral for encrypted characteristic
Is this even possible? Instead of any pairing dialog appearing, my central code get the "Authentication is insufficient" error when reading the characteristic. My peripheral (in the macOS app) code uses the .notifyEncryptionRequired property and uses .readEncryptionRequired and .writeEncryptionRequired permissions. No descriptors are set, but I think they get added automatically since this characteristic notifies. 2900 and 2902 descriptors are set by the peripheral/CoreBluetooth. If the Mac and iPhone are using the same Apple ID does that affect pairing?
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Feb ’26
Consult about the "CNCopyCurrentNetworkInfo" interface
Hi In the "CaptiveNetwork.h", the "CNCopyCurrentNetworkInfo" is marked as "API_TO_BE_DEPRECATED" CFDictionaryRef __nullable CNCopyCurrentNetworkInfo (CFStringRef interfaceName) API_DEPRECATED_WITH_REPLACEMENT("[NEHotspotNetwork fetchCurrentWithCompletionHandler:]", ios(4.1, API_TO_BE_DEPRECATED), macCatalyst(14.0, API_TO_BE_DEPRECATED)) API_UNAVAILABLE(macos, tvos, watchos, visionos); But in developer documents, it is marked as "DEPRECATED": https://developer.apple.com/documentation/systemconfiguration/cncopycurrentnetworkinfo Before we use Xcode 16.2 to archive app, this interface still work on iOS 26 device. But after we changed to Xcode 26.2, this interface return nothing on iOS 26 and we need to use "NEHotspotNetwork" related interface. My question is: Why there are difference between the documents and framework sdk how we can know that a interface marked "API_TO_BE_DEPRECATED" or "DEPRECATED", when will they not work totally. Is there a accurate timeline or standard for them? Some interface marked deprecated after 12.0 is still working Now. After knowing the accurate timeline we can plan the interfaces migration.
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