General: Forums subtopic: App & System Services > Networking TN3151 Choosing the right networking API Networking Overview document — Despite the fact that this is in the archive, this is still really useful. TLS for App Developers forums post Choosing a Network Debugging Tool documentation WWDC 2019 Session 712 Advances in Networking, Part 1 — This explains the concept of constrained networking, which is Apple’s preferred solution to questions like How do I check whether I’m on Wi-Fi? TN3135 Low-level networking on watchOS TN3179 Understanding local network privacy Adapt to changing network conditions tech talk Understanding Also-Ran Connections forums post Extra-ordinary Networking forums post Foundation networking: Forums tags: Foundation, CFNetwork URL Loading System documentation — NSURLSession, or URLSession in Swift, is the recommended API for HTTP[S] on Apple platforms. Moving to Fewer, Larger Transfers forums post Testing Background Session Code forums post Network framework: Forums tag: Network Network framework documentation — Network framework is the recommended API for TCP, UDP, and QUIC on Apple platforms. Building a custom peer-to-peer protocol sample code (aka TicTacToe) Implementing netcat with Network Framework sample code (aka nwcat) Configuring a Wi-Fi accessory to join a network sample code Moving from Multipeer Connectivity to Network Framework forums post NWEndpoint History and Advice forums post Network Extension (including Wi-Fi on iOS): See Network Extension Resources Wi-Fi Fundamentals TN3111 iOS Wi-Fi API overview Wi-Fi Aware framework documentation Wi-Fi on macOS: Forums tag: Core WLAN Core WLAN framework documentation Wi-Fi Fundamentals Secure networking: Forums tags: Security Apple Platform Security support document Preventing Insecure Network Connections documentation — This is all about App Transport Security (ATS). WWDC 2017 Session 701 Your Apps and Evolving Network Security Standards [1] — This is generally interesting, but the section starting at 17:40 is, AFAIK, the best information from Apple about how certificate revocation works on modern systems. Available trusted root certificates for Apple operating systems support article Requirements for trusted certificates in iOS 13 and macOS 10.15 support article About upcoming limits on trusted certificates support article Apple’s Certificate Transparency policy support article What’s new for enterprise in iOS 18 support article — This discusses new key usage requirements. Technote 2232 HTTPS Server Trust Evaluation Technote 2326 Creating Certificates for TLS Testing QA1948 HTTPS and Test Servers Miscellaneous: More network-related forums tags: 5G, QUIC, Bonjour On FTP forums post Using the Multicast Networking Additional Capability forums post Investigating Network Latency Problems forums post WirelessInsights framework documentation iOS Network Signal Strength forums post Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" [1] This video is no longer available from Apple, but the URL should help you locate other sources of this info.

Hello, How long does it usually take for a URL Filter request to be reviewed? It's been 2.5 weeks since we submitted the request form but we haven't received any feedback yet. Just in case, the request ID is D3633USVZZ

Apology for repost. I needed to fix the tags for original thread. https://developer.apple.com/forums/thread/777159 On iOS 18.3, I noted that partition "HTTPCookiePropertyKey: StoragePartition" is not observed to be set for cookies returned from the wkwebview cookie store. Now on 18.4 beta 4 we are now seeing those same cookies are populated with a partition property. Is there documentation for this change? Is it intended to be suddenly populated in 18.4? Now that partition property is set, HTTPCookieStorage.shared.cookies(for: serverUri) doesn't seem to return the expected cookies correctly. For context, we are using the cookies extracted from wkwebview, setting them in HTTPCookieStorage.shared and using URLSession to make network calls outside the webivew. Works fine once I forcefully set partition on the cookie to nil. More details on what the cookie looks like here: https://feedbackassistant.apple.com/feedback/16906526 Hopefully this is on your radar?

I want to add more cipher suites. I use NWConnection to make a connection. Before I use sec_protocol_options_append_tls_ciphersuite method to add more cipher suites, I found that Apple provided 20 cipher suites shown in the client hello packet. But after I added three more cipher suites, I found that nothing changed, and still original 20 cipher suites shown in the client hello packet when I made a new connection. The following is the code about connection. I want to add three more cipher suites: tls_ciphersuite_t.ECDHE_ECDSA_WITH_AES_128_CBC_SHA256, tls_ciphersuite_t.ECDHE_ECDSA_WITH_AES_256_CBC_SHA384, tls_ciphersuite_t.ECDHE_RSA_WITH_AES_256_CBC_SHA384 Can you give me some advice about how to add more cipher suites? Thanks. By the way, I working on a MacOS app. Xcode version: 16 MacOS version: 15.6

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.

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.

Our application uses NEFilterPacketProvider to filter network traffic and we sometimes get a wired crash when removing/updating the network extension. It only happens on MacOS 11-12 . The crashing thread is always this one and it shows up after I call the completionHandler from the stopFilter func Application Specific Information: BUG IN CLIENT OF LIBDISPATCH: Release of a suspended object Thread 6 Crashed:: Dispatch queue: com.apple.network.connections 0 libdispatch.dylib 0x00007fff2039cc35 _dispatch_queue_xref_dispose.cold.1 + 24 1 libdispatch.dylib 0x00007fff20373808 _dispatch_queue_xref_dispose + 50 2 libdispatch.dylib 0x00007fff2036e2eb -[OS_dispatch_source _xref_dispose] + 17 3 libnetwork.dylib 0x00007fff242b5999 __nw_queue_context_create_source_block_invoke + 41 4 libdispatch.dylib 0x00007fff2036d623 _dispatch_call_block_and_release + 12 5 libdispatch.dylib 0x00007fff2036e806 _dispatch_client_callout + 8 6 libdispatch.dylib 0x00007fff203711b0 _dispatch_continuation_pop + 423 7 libdispatch.dylib 0x00007fff203811f4 _dispatch_source_invoke + 1181 8 libdispatch.dylib 0x00007fff20376318 _dispatch_workloop_invoke + 1784 9 libdispatch.dylib 0x00007fff2037ec0d _dispatch_workloop_worker_thread + 811 10 libsystem_pthread.dylib 0x00007fff2051545d _pthread_wqthread + 314 11 libsystem_pthread.dylib 0x00007fff2051442f start_wqthread + 15 I do have a DispatchSourceTimer but I cancel it in the stop func. Any ideas on how to tackle this?

All of our uses of CFSockets have started causing crashes in iOS 16. They seem to be deprecated so we are trying to transition over to using the Network framework and NWConnection to try to fix the crashes. One of our uses of them is to ping a device on the local network to make sure it is there and online and provide a heartbeat status in logs as well as put the application into a disabled state if it is not available as it is critical to the functionality of the app. I know it is discouraged to disable any functionality based on the reachability of a resource but this is in an enterprise environment where the reachability of this device is mission critical. I've seen other people ask about the ability to ping with the Network framework and the answers I've found have said that this is not possible and pointed people to the SimplePing sample code but it turns out our existing ping code is already using this technique and it is crashing just like our other CFSocket usages, inside CFSocketInvalidate with the error BUG IN CLIENT OF LIBPLATFORM: Trying to recursively lock an os_unfair_lock. Is there any updated way to perform a ping without using the CFSocket APIs that now seem to be broken/unsupported on iOS 16?

This is just an FYI in case someone else runs into this problem. This afternoon (12 Dec 2025), I updated to macOS 26.2 and lost my network. The System Settings' Wi-Fi light was green and said it was connected, but traceroute showed "No route to host". I turned Wi-Fi on & off. I rebooted the Mac. I rebooted the eero network. I switched to tethering to my iPhone. I switched to physical ethernet cable. Nothing worked. Then I remembered I had a beta of an app with a network system extension that was distributed through TestFlight. I deleted the app, and networking came right back. I had this same problem ~2 years ago. Same story: app with network system extension + TestFlight + macOS update = lost network. (My TestFlight build might have expired, but I'm not certain) I don't know if anyone else has had this problem, but I thought I'd share this in case it helps.

I am trying to activate an application which sends my serial number to a server. The send is being blocked. The app is signed but not sandboxed. I am running Sequoia on a recent iMac. My network firewall is off and I do not have any third party virus software. I have selected Allow Applications from App Store & Known Developers. My local network is wifi using the eero product. There is no firewall or virus scanning installed with this product. Under what circumstances will Mac OS block outgoing internet connections from a non-sandboxed app? How else could the outgoing connection be blocked?

Is Apple's Wi-Fi Aware certified by the Wi-Fi Alliance? Is there any non-compliance of Apple's Wi-Fi Aware with the Wi-Fi Alliance standards? Does Apple have a roadmap to switch AWDL to Wi-Fi Aware? Does Apple have plans to adopt Wi-Fi Aware in Mac computers?

We are currently working on a zero-configuration networking compliant device thru avahi-daemon. Our Device want to have multiple Instance name for different services. Example InstanceA._ipps._tcp.local. InstanceA._ipp._tcp.local. InstanceB._ipps._tcp.local. InstanceB._ipp._tcp.local. Will BCT confuse this as multiple device connected in the network and cause it to fail? Does Bonjour only allows only a Single Instance name with multiple services?

For important background information, read Extra-ordinary Networking before reading this. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" Broadcasts and Multicasts, Hints and Tips I regularly see folks struggle with broadcasts and multicasts on Apple platforms. This post is my attempt to clear up some of the confusion. This post covers both IPv4 and IPv6. There is, however, a key difference. In IPv4, broadcasts and multicasts are distinct concepts. In contrast, IPv6 doesn’t support broadcast as such; rather, it treats broadcasts as a special case of multicasts. IPv6 does have an all nodes multicast address, but it’s rarely used. Before reading this post, I suggest you familiarise yourself with IP addresses in general. A good place to start is The Fount of All Knowledge™. Service Discovery A lot of broadcast and multicast questions come from folks implementing their own service discovery protocol. I generally recommend against doing that, for the reasons outlined in the Service Discovery section of Don’t Try to Get the Device’s IP Address. There are, however, some good reasons to implement a custom service discovery protocol. For example, you might be working with an accessory that only supports this custom protocol [1]. If you must implement your own service discovery protocol, read this post and also read the advice in Don’t Try to Get the Device’s IP Address. IMPORTANT Sometimes I see folks implementing their own version of mDNS. This is almost always a mistake: If you’re using third-party tooling that includes its own mDNS implementation, it’s likely that this tooling allows you to disable that implementation and instead rely on the Bonjour support that’s built-in to all Apple platforms. If you’re doing some weird low-level thing with mDNS or DNS-SD, it’s likely that you can do that with the low-level DNS-SD API. [1] And whose firmware you can’t change! I talk more about this in Working with a Wi-Fi Accessory. API Choice Broadcasts and multicasts typically use UDP [1]. TN3151 Choosing the right networking API describes two recommended UDP APIs: Network framework BSD Sockets Our general advice is to prefer Network framework over BSD Sockets, but UDP broadcasts and multicasts are an exception to that rule. Network framework has very limited UDP broadcast support. And while it’s support for UDP multicasts is less limited, it’s still not sufficient for all UDP applications. In cases where Network framework is not sufficient, BSD Sockets is your only option. [1] It is possible to broadcast and multicast at the Ethernet level, but I almost never see questions about that. UDP Broadcasts in Network Framework Historically I’ve claimed that Network framework was useful for UDP broadcasts is very limited circumstances (for example, in the footnote on this post). I’ve since learnt that this isn’t the case. Or, more accurately, this support is so limited (r. 122924701) as to be useless in practice. For the moment, if you want to work with UDP broadcasts, your only option is BSD Sockets. UDP Multicasts in Network Framework Network framework supports UDP multicast using the NWConnectionGroup class with the NWMulticastGroup group descriptor. This support has limits. The most significant limit is that it doesn’t support broadcasts; it’s for multicasts only. Note This only relevant to IPv4. Remember that IPv6 doesn’t support broadcasts as a separate concept. There are other limitations, but I don’t have a good feel for them. I’ll update this post as I encounter issues. Local Network Privacy Some Apple platforms support local network privacy. This impacts broadcasts and multicasts in two ways: Broadcasts and multicasts require local network access, something that’s typically granted by the user. Broadcasts and multicasts are limited by a managed entitlement (except on macOS). TN3179 Understanding local network privacy has lots of additional info on this topic, including the list of platforms to which it applies. Send, Receive, and Interfaces When you broadcast or multicast, there’s a fundamental asymmetry between send and receive: You can reasonable receive datagrams on all broadcast-capable interfaces. But when you send a datagram, it has to target a specific interface. The sending behaviour is the source of many weird problems. Consider the IPv4 case. If you send a directed broadcast, you can reasonably assume it’ll be routed to the correct interface based on the network prefix. But folks commonly send an all-hosts broadcast (255.255.255.255), and it’s not obvious what happens in that case. Note If you’re unfamiliar with the terms directed broadcast and all-hosts broadcast, see IP address. The exact rules for this are complex, vary by platform, and can change over time. For that reason, it’s best to write your broadcast code to be interface specific. That is: Identify the interfaces on which you want to work. Create a socket per interface. Bind that socket to that interface. Note Use the IP_BOUND_IF (IPv4) or IPV6_BOUND_IF (IPv6) socket options rather than binding to the interface address, because the interface address can change over time. Extra-ordinary Networking has links to other posts which discuss these concepts and the specific APIs in more detail. Miscellaneous Gotchas A common cause of mysterious broadcast and multicast problems is folks who hard code BSD interface names, like en0. Doing that might work for the vast majority of users but then fail in some obscure scenarios. BSD interface names are not considered API and you must not hard code them. Extra-ordinary Networking has links to posts that describe how to enumerate the interface list and identify interfaces of a specific type. Don’t assume that there’ll be only one interface of a given type. This might seem obviously true, but it’s not. For example, our platforms support peer-to-peer Wi-Fi, so each device has multiple Wi-Fi interfaces. When sending a broadcast, don’t forget to enable the SO_BROADCAST socket option. If you’re building a sandboxed app on the Mac, working with UDP requires both the com.apple.security.network.client and com.apple.security.network.server entitlements. Some folks reach for broadcasts or multicasts because they’re sending the same content to multiple devices and they believe that it’ll be faster than unicasts. That’s not true in many cases, especially on Wi-Fi. For more on this, see the Broadcasts section of Wi-Fi Fundamentals. Snippets To send a UDP broadcast: func broadcast(message: Data, to interfaceName: String) throws { let fd = try FileDescriptor.socket(AF_INET, SOCK_DGRAM, 0) defer { try! fd.close() } try fd.setSocketOption(SOL_SOCKET, SO_BROADCAST, 1 as CInt) let interfaceIndex = if_nametoindex(interfaceName) guard interfaceIndex > 0 else { throw … } try fd.setSocketOption(IPPROTO_IP, IP_BOUND_IF, interfaceIndex) try fd.send(data: message, to: ("255.255.255.255", 2222)) } Note These snippet uses the helpers from Calling BSD Sockets from Swift. To receive UDP broadcasts: func receiveBroadcasts(from interfaceName: String) throws { let fd = try FileDescriptor.socket(AF_INET, SOCK_DGRAM, 0) defer { try! fd.close() } let interfaceIndex = if_nametoindex(interfaceName) guard interfaceIndex > 0 else { fatalError() } try fd.setSocketOption(IPPROTO_IP, IP_BOUND_IF, interfaceIndex) try fd.setSocketOption(SOL_SOCKET, SO_REUSEADDR, 1 as CInt) try fd.setSocketOption(SOL_SOCKET, SO_REUSEPORT, 1 as CInt) try fd.bind("0.0.0.0", 2222) while true { let (data, (sender, port)) = try fd.receiveFrom() … } } IMPORTANT This code runs synchronously, which is less than ideal. In a real app you’d run the receive asynchronously, for example, using a Dispatch read source. For an example of how to do that, see this post. If you need similar snippets for multicast, lemme know. I’ve got them lurking on my hard disk somewhere (-: Other Resources Apple’s official documentation for BSD Sockets is in the man pages. See Reading UNIX Manual Pages. Of particular interest are: setsockopt man page ip man page ip6 man page If you’re not familiar with BSD Sockets, I strongly recommend that you consult third-party documentation for it. BSD Sockets is one of those APIs that looks simple but, in reality, is ridiculously complicated. That’s especially true if you’re trying to write code that works on BSD-based platforms, like all of Apple’s platforms, and non-BSD-based platforms, like Linux. I specifically recommend UNIX Network Programming, by Stevens et al, but there are lots of good alternatives. https://unpbook.com Revision History 2025-09-01 Fixed a broken link. 2025-01-16 First posted.

Continuing with my investigations of several issues that we have been noticing in our testing of the JDK with macosx 15.x, I have now narrowed down at least 2 separate problems for which I need help. For a quick background, starting with macosx 15.x several networking related tests within the JDK have started failing in very odd and hard to debug ways in our internal lab. Reading through the macos docs and with help from others in these forums, I have come to understand that a lot of these failures are to do with the new restrictions that have been placed for "Local Network" operations. I have read through https://developer.apple.com/documentation/technotes/tn3179-understanding-local-network-privacy and I think I understand the necessary background about these restrictions. There's more than one issue in this area that I will need help with, so I'll split them out into separate topics in this forum. That above doc states: macOS 15.1 fixed a number of local network privacy bugs. If you encounter local network privacy problems on macOS 15.0, retest on macOS 15.1 or later. We did have (and continue to have) 15.0 and 15.1 macos instances within our lab which are impacted by these changes. They too show several networking related failures. However, I have decided not to look into those systems and instead focus only on 15.3.1. People might see unexpected behavior in System Settings > Privacy & Security if they have multiple versions of the same app installed (FB15568200). This feedback assistant issue and several others linked in these documentations are inaccessible (even when I login with my existing account). I think it would be good to have some facility in the feedback assistant tool/site to make such issues visible (even if read-only) to be able to watch for updates to those issues. So now coming to the issue. Several of the networking tests in the JDK do mulicasting testing (through BSD sockets API) in order to test the Java SE multicasting socket API implementations. One repeated failure we have been seeing in our labs is an exception with the message "No route to host". It shows up as: Process id: 58700 ... java.net.NoRouteToHostException: No route to host at java.base/sun.nio.ch.DatagramChannelImpl.send0(Native Method) at java.base/sun.nio.ch.DatagramChannelImpl.sendFromNativeBuffer(DatagramChannelImpl.java:914) at java.base/sun.nio.ch.DatagramChannelImpl.send(DatagramChannelImpl.java:871) at java.base/sun.nio.ch.DatagramChannelImpl.send(DatagramChannelImpl.java:798) at java.base/sun.nio.ch.DatagramChannelImpl.blockingSend(DatagramChannelImpl.java:857) at java.base/sun.nio.ch.DatagramSocketAdaptor.send(DatagramSocketAdaptor.java:178) at java.base/java.net.DatagramSocket.send(DatagramSocket.java:593) (this is just one example stacktrace from java program) That "send0" is implemented by the JDK by invoking the sendto() system call. In this case, the sendto() is returning a EHOSTUNREACH error which is what is then propagated to the application. The forum text editor doesn't allow me to post long text, so I'm going to post the rest of this investigation and logs as a reply.

multicast sockets fail to send/receive on macosx, errno 65 "no route to host". Wireshark and Terminal.app (which have root privileges) both show incoming multicast traffic just fine. Normal UDP broadcast sockets have no problems. Toggling the Security&Privacy -> Local Network setting may fix the problem for some Users. There is no pattern for when multicast socket fails. Sometimes, recreating the sockets fix the problem. Restart the app, sometimes multicast fails, sometimes success (intermittent, no pattern). Reboot machine (intermittent fail) Create a fresh new user on machine, install single version of app, give app permission. (intermittent fail, same as above). We have all the normal entitlements / notarized app. Similar posts here see FB16923535, Related to FB16512666 https://forum.xojo.com/t/udp-multicast-receive-on-mac-failing-intermittant/83221 see my post from 2012 "distinguishing between SENDING sockets and RECEIVING sockets" for source code example of how we bind multicast sockets. Our other socket code is standard "Stevens, et al." code. The bind() is the call that fails in this case. https://stackoverflow.com/questions/10692956/what-does-it-mean-to-bind-a-multicast-udp-socket . Note that this post from 2012 is still relevant, and that it is a workaround to a longstanding Apple bug that was never fixed. Namely, "Without this fix, multicast sending will intermittently get sendto() errno 'No route to host'. If anyone can shed light on why unplugging a DHCP gateway causes Mac OS X multicast SENDING sockets to get confused, I would love to hear it." This may be a hint as to the underlying bug that Apple really needs to fix, but if it's not, then please Apple, fix the Sequoia bug first. These are probably different bugs because in one case, sendto() fails when a socket becomes "unbound" after you unplug an unrelated network cable. In this case, bind() fails, so sendto() is never even called. Note, that we have also tried to use other implementations for network discovery, including Bonjour, CFNetwork, etc. Bonjour fails intermittently, and also suffers from both bugs mentioned above, amongst others.

It works when one device is only a publisher and the other is only a subscriber. However, when both devices act as both publisher and subscriber simultaneously—which Apple’s documentation (https://developer.apple.com/documentation/wifiaware/adopting-wi-fi-aware#Declare-services) indicates is valid—the connection never establishes. After timing out, both NetworkListener and NetworkBrowser transition to the failed state. This appears to be a race condition in Network framework. Task.detached { try await NetworkListener( for: .wifiAware( .connecting( to: .myService, from: .allPairedDevices, datapath: .defaults ) ), using: .parameters { Coder( sending: ..., receiving: ..., using: NetworkJSONCoder() ) { TCP() } } ).run { connection in await self.add(connection: connection) } } Task.detached { try await NetworkBrowser( for: .wifiAware( .connecting( to: .allPairedDevices, from: .myService ) ), using: .tcp ).run { endpoints in for endpoint in endpoints { await self.connect(to: endpoint) } } }

Every now and again folks notice that Network framework seems to create an unexpected number of connections on the wire. This post explains why that happens and what you should do about it. If you have questions or comments, put them in a new thread here on the forums. Use the App & System Services > Networking topic area and the Network tag. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" Understanding Also-Ran Connections Network framework implements the Happy Eyeballs algorithm. That might create more on-the-wire connections than you expect. There are two common places where folks notice this: When looking at a packet trace When implementing a listener Imagine that you’ve implemented a TCP server using NWListener and you connect to it from a client using NWConnection. In many situations there are multiple network paths between the client and the server. For example, on a local network there’s always at least two paths: the link-local IPv6 path and either an infrastructure IPv4 path or the link-local IPv4 path. When you start your NWConnection, Network framework’s Happy Eyeballs algorithm might [1] start a TCP connection for each of these paths. It then races those connections. The one that connects first is the ‘winner’, and Network framework uses that connection for your traffic. Once it has a winner, the other connections, the also-ran connections, are redundant, and Network framework just closes them. You can observe this behaviour on the client side by looking in the system log. Many Network framework log entries (subsystem com.apple.network) contain a connection identifier. For example C8 is the eighth connection started by this process. Each connection may have child connections (C8.1, C8.2, …) and grandchild connections (C8.1.1, C8.1.2, …), and so on. You’ll see state transitions for these child connections occurring in parallel. For example, the following log entries show that C8 is racing the connection of two grandchild connections, C8.1.1 and C8.1.2: type: debug time: 12:22:26.825331+0100 process: TestAlsoRanConnections subsystem: com.apple.network category: connection message: nw_socket_connect [C8.1.1:1] Calling connectx(…) type: debug time: 12:22:26.964150+0100 process: TestAlsoRanConnections subsystem: com.apple.network category: connection message: nw_socket_connect [C8.1.2:1] Calling connectx(…) Note For more information about accessing the system log, see Your Friend the System Log. You also see this on the server side, but in this case each connection is visible to your code. When you connect from the client, Network framework calls your listener’s new connection handler with multiple connections. One of those is the winning connection and you’ll receive traffic on it. The others are the also-ran connections, and they close promptly. IMPORTANT Depending on network conditions there may be no also-ran connections. Or there may be lots of them. If you want to test the also-ran connection case, use Network Link Conditioner to add a bunch of delay to your packets. You don’t need to write special code to handle also-ran connections. From the perspective of your listener, these are simply connections that open and then immediately close. There’s no difference between an also-ran connection and, say, a connection from a client that immediately crashes. Or a connection generated by someone doing a port scan. Your server must be resilient to such things. However, the presence of these also-ran connections can be confusing, especially if you’re just getting started with Network framework, and hence this post. [1] This is “might” because the exact behaviour depends on network conditions. More on that below.

Have you ever encountered the issue where the Wi-Fi MAC address information can no longer be retrieved after I updated to iOS 26?

I'm a long-time developer, but pretty new to Swift. I'm trying to get information from a web service (and found code online that I adjusted to build the function below). (Note: AAA_Result -- referenced towards the end -- is another class in my project) Trouble is, I'm getting the subject error on the call to session.dataTask. Any help/suggestions/doc pointers will be greatly appreciated!!! var result: Bool = false var cancellable: AnyCancellable? self.name = name let params = "json={\"\"}}" // removed json details let base_url = URL(string: "https://aaa.yyy.com?params=\(params)&format=json")! // removed URL specifics do { let task = URLSession.shared.dataTask(with: base_url) { data, response, error in if let error = error { print("Error: \(error)") } guard let response = response as? HTTPURLResponse, (200...299).contains(response.statusCode) else { print("Error \(String(describing: response))") } do { let decoder = JSONDecoder() let ar = try decoder.decode(AAA_Result.self, from: response.value) // removed specific details... result = true } catch { print(error) } } task.resume() } catch { print(error) } return result }

We are using Multipeer Connectivity (MCSession, MCNearbyServiceBrowser, MCNearbyServiceAdvertiser) for nearby peer discovery and communication. **Observed behaviour: ** When Wi-Fi is ON (Not connected to any network) and Mobile Data is also ON: Peer discovery (foundPeer) consistently succeeds Invitation is sent using invitePeer MCSession transitions to .connecting The session remains indefinitely in .connecting connected is never reached notConnected is also not reported When Mobile Data is turned OFF, the same flow reliably reaches .connected. Key details: Both devices have Wi-Fi and Bluetooth enabled Browsing and advertising are active on both devices Application-level timeouts and session resets are implemented The Issue is reproducible across multiple devices with iOS 26 versions. Expectation / Question: We understand that Multipeer Connectivity does not use cellular data for peer discovery or transport. However, when Wi-Fi is available and peers are discovered successfully, we would like clarification on the following: Is it expected behavior that enabling Mobile Data can cause the invitation/connection phase to remain indefinitely in .connecting without transitioning to .notConnected? Are there recommended best practices to avoid stalled invitation or transport negotiation in this scenario? Is there a supported way to detect or recover from a stalled .connecting state beyond application-level timeouts and session resets? Any guidance on expected behavior or recommended handling would be appreciated.

1、已经检查过手机的存储空间，还有一百多G的空间。app端进行网络接口情况的时候报错了，报错信息如下： Error : Error Domain=NSPOSIXErrorDomain Code=28 "No space left on device" UserInfo={_NSURLErrorFailingURLSessionTaskErrorKey=LocalDataTask <7DB1CBFD-B9BE-422D-9C9A-78D8FC04DC1B>.<76>, _kCFStreamErrorDomainKey=1, _kCFStreamErrorCodeKey=28, _NSURLErrorRelatedURLSessionTaskErrorKey=( "LocalDataTask <7DB1CBFD-B9BE-422D-9C9A-78D8FC04DC1B>.<76>" ), _NSURLErrorNWPathKey=satisfied (Path is satisfied), interface: pdp_ip0[lte], ipv4, ipv6, dns, expensive, estimated upload: 65536Bps, uses cell} 2、手机型号是iPhone 15 Plus，iOS 17.6.1