1[](https://cocoapods.org/pods/gRPC) 2# gRPC Objective-C with CFStream 3 4gRPC now provides the option to use Apple's CFStream API (rather than TCP 5sockets) for networking. Using CFStream resolves a bunch of network connectivity transition issues 6(see the [doc](https://github.com/grpc/grpc/blob/master/src/objective-c/NetworkTransitionBehavior.md) 7for more information). 8 9<s>CFStream integration is now in experimental state. You will need explicit opt-in to use it to get 10the benefits of resolving the issues above. We expect to make CFStream the default networking 11interface that gRPC uses when it is ready for production.</s> 12 13As of v1.21.0, CFStream integration is now the default networking stack being used by gRPC 14Objective-C on iOS layer. You get to use it automatically without special configuration needed. See 15below on how to disable CFStream in case of problem. 16 17As of v1.23.0, CFStream is enabled by default on iOS for all wrapped languages. See below on how to 18disable CFStream in case of a problem. 19 20## Usage 21If you use gRPC on iOS, CFStream is on automatically. If you use it on other 22platforms, you can turn it on with macro `GRPC_CFSTREAM=1` for the pod 'gRPC-Core' and 'gRPC'. In 23case of problem and you want to disable CFStream on iOS, you can set environment variable 24"grpc\_cfstream=0". 25 26## Caveats 27It is known to us that the CFStream API has some bug (FB6162039) which will cause gRPC's CFStream 28networking layer to stall occasionally. The issue mostly occur on MacOS systems (including iOS 29simulators on MacOS); iOS may be affected too but we have not seen issue there. gRPC provides a 30workaround to this problem with an alternative poller based on CFRunLoop. The poller can be enabled 31by setting environment variable `GRPC_CFSTREAM_RUN_LOOP=1`. Note that the poller is a client side 32only poller that does not support running a server on it. That means if an app opts in to the 33CFRunLoop-based poller, the app cannot host a gRPC server (gRPC Objective-C does not support running 34a server but other languages running on iOS do support it). 35 36## Notes 37 38- Currently we do not support platforms other than iOS, although it is likely that this integration 39 can run on MacOS targets with Apple's compiler. 40- Let us know if you meet any issue by filing issue and ping @stanleycheung. 41
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