Summary

On iOS 18, after BasicNetworkManager::CreateNetworks() creates all interfaces, a bug in RTCNetworkMonitor::initWithObserver is causing only one interfaces to remain. As a results, any ICE candidates on these interfaces are excluded and the connection will fail.

This seems to be because the nw_path_enumerate_interfaces block is missing it's return value which impacts iOS 18.

📌 Note: The same code executed on iOS 17.5.1 and earlier seems continue to enumerate all interfaces. It's possible that iOS 18 has changed how this block continues by default.

nw_path_enumerate_interfaces_block_t requires you to Return true to continue enumerating, or false to stop enumerating.

To resolve this issue, add return true; inside the nw_path_enumerate_interfaces block:

...
- (instancetype) :(webrtc::NetworkMonitorObserver *)observer {
...
    std::map<std::string, rtc::AdapterType, rtc::AbslStringViewCmp> *map =
            new std::map<std::string, rtc::AdapterType, rtc::AbslStringViewCmp>();
        nw_path_enumerate_interfaces(
            path, (nw_path_enumerate_interfaces_block_t) ^ (nw_interface_t interface) {
              const char *name = nw_interface_get_name(interface);
              nw_interface_type_t interfaceType = nw_interface_get_type(interface);
              RTCLog(@"NW path monitor available interface --->: %s", name);
              rtc::AdapterType adapterType = AdapterTypeFromInterfaceType(interfaceType);
              map->insert(std::pair<std::string, rtc::AdapterType>(name, adapterType));
              return true;//<----- this is missing
            });
...

What steps will reproduce the problem?

Enable webrtc logging, build and deploy on iOS 18 beta
Monitor the logs for RTCNetworkMonitor
Notice the incorrect number of networks are monitored, as compared with basic_port_allocator.cc which will print out all networks on the device. For example:

(basic_port_allocator.cc:712): Count of networks: 9
(basic_port_allocator.cc:714): Net[utun6:fdd4:3d3c:0000:x:x:x:x:x/64:Unknown:id=7]
(basic_port_allocator.cc:714): Net[pdp_ip0:2600:0000:0000:x:x:x:x:x/64:Unknown:id=5]
(basic_port_allocator.cc:714): Net[pdp_ip1:2600:0000:0000:x:x:x:x:x/64:Unknown:id=6]
(basic_port_allocator.cc:714): Net[en0:192.168.1.x/24:Unknown:id=1]
(basic_port_allocator.cc:714): Net[pdp_ip0:100.75.0000.x/32:Unknown:id=4]
(basic_port_allocator.cc:714): Net[utun8:129.1xx.0.x/16:Unknown:id=8]
(basic_port_allocator.cc:714): Net[utun8:129.2xx.0.x/16:Unknown:id=9]
(basic_port_allocator.cc:714): Net[lo0:0:0:0:x:x:x:x:x/128:Loopback:id=3]
(basic_port_allocator.cc:714): Net[lo0:127.0.0.x/8:Loopback:id=2]

What is the expected result?

Interfaces, like utun and pdp are expected to be enumerated. For example:

(RTCNetworkMonitor.mm:72 -[RTCNetworkMonitor initWithObserver:]_block_invoke): NW path monitor: updated.
(RTCNetworkMonitor.mm:79 -[RTCNetworkMonitor initWithObserver:]_block_invoke): NW path monitor status: satisfied.
(RTCNetworkMonitor.mm:89 -[RTCNetworkMonitor initWithObserver:]_block_invoke_2): NW path monitor available interface: en0
(RTCNetworkMonitor.mm:89 -[RTCNetworkMonitor initWithObserver:]_block_invoke_2): NW path monitor available interface: pdp_ip0
(RTCNetworkMonitor.mm:89 -[RTCNetworkMonitor initWithObserver:]_block_invoke_2): NW path monitor available interface: utun8

What do you see instead?

On iOS 18 Beta (2-5), only one interface en0 is monitored

(RTCLogging.mm:33): (RTCNetworkMonitor.mm:65 -[RTCNetworkMonitor initWithObserver:]): NW path monitor created.
(RTCLogging.mm:33): (RTCNetworkMonitor.mm:72 -[RTCNetworkMonitor initWithObserver:]_block_invoke): NW path monitor: updated.
(RTCLogging.mm:33): (RTCNetworkMonitor.mm:79 -[RTCNetworkMonitor initWithObserver:]_block_invoke): NW path monitor status: satisfied.
(RTCLogging.mm:33): (RTCNetworkMonitor.mm:89 -[RTCNetworkMonitor initWithObserver:]_block_invoke_2): NW path monitor available interface: en0

Depending on timing, if ICE had started before the failed enumeration, you may also see:

(basic_port_allocator.cc:898): Prune 7 ports because their networks were gone
(p2p_transport_channel.cc:2151): Removed port: Port[161c2300:0:1:0:host:Net[en2:169.254.0.x/16:Unknown:id=2]] 7 remaining
(p2p_transport_channel.cc:2151): Removed port: Port[161c2800:0:1:0:host:Net[pdp_ip0:100.1xx.xx.x/32:Unknown:id=5]] 6 remaining
(p2p_transport_channel.cc:2151): Removed port: Port[161c2d00:0:1:0:host:Net[utun7:129.1xx.0.x/16:Unknown:id=9]] 5 remaining
(p2p_transport_channel.cc:2151): Removed port: Port[161c3700:0:1:0:host:Net[utun7:129.2xx.0.x/16:Unknown:id=10]] 4 remaining
(p2p_transport_channel.cc:2151): Removed port: Port[16002800:0:1:0:host:Net[utun4:fd61:000:0000:x:x:x:x:x/64:Unknown:id=8]] 3 remaining
(p2p_transport_channel.cc:2151): Removed port: Port[16002d00:0:1:0:host:Net[pdp_ip0:2600:1006:0000:x:x:x:x:x/64:Unknown:id=6]] 2 remaining
(p2p_transport_channel.cc:2151): Removed port: Port[161f8000:0:1:0:host:Net[pdp_ip2:2600:1006:0000:x:x:x:x:x/64:Unknown:id=7]] 1 remaining
(basic_port_allocator.cc:1265): Removed 7 candidates

What version of the product are you using?

WebRTC commit/Release: git master

On what operating system?

OS: iOS
Version: 18 beta (8/8/24)